- Email: [email protected]
Material properties of solidified soil grains produced from dredged marine clay
Available online at www.sciencedirect.com
HOSTED BY
ScienceDirect Soils and Foundations xxx (2018) xxx–xxx www.elsevier.com/locate/sandf
Material properties of solidified soil grains produced from dredged marine clay Hiroshi Shinsha ⇑, Takahiro Kumagai Institute of Technology, Penta-Ocean Construction Co., Ltd., 1534-1, Yonkucho, Nasushiobara-shi, Tochigi 329-2746, Japan Received 20 September 2017; received in revised form 19 January 2018; accepted 22 February 2018
Abstract Solidified soil grains are produced by crushing a solidified soil mass which is made of dredged soil mixed with cement. It would be beneficial if these solidified soil grains could be used as fill material instead of sand/gravel. However, the strength property of solidified soil grains has not yet been thoroughly studied. In addition, as it is well known that solidified soil tends to deteriorate in seawater due to the leaching of calcium, it is necessary to make a complete study of the deterioration properties of solidified soil grains. In the current study, the material properties of solidified soil grains have been investigated. The test results revealed that (1) the strength of normal single solidified soil grains is smaller than that of natural rock grains, (2) the internal friction angle of solidified soil grains is greater than 30°, and (3) the internal friction angle of solidified soil grains tends to decrease along with the progress of deterioration; however, deterioration will not be experienced by solidified soil grains which have unconfined compressive strength larger than approximately 14 MN/m2. Ó 2018 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.
Keywords: Solidified soil grains; Dredged marine clay; Deterioration; Seawater; Internal friction angle
1. Introduction To maintain the required water depth of fairways and basins etc., about 20 million m3 of sediment soil are dredged every year in Japan despite the low availability of dumping areas. The way with which this dredged soft soil should be dealt has become a serious problem that must be resolved. In order to utilize the dredged soil effectively, a lot of solidification methods (Coastal Institute, 2002; Kitazume, 2017; Tsuchida et al., 2004) for mixing dredged soil with cement have already been developed. The required shear strength can be achieved in a short period by these methods. In fact, a very soft dredged soil with
Peer review under responsibility of The Japanese Geotechnical Society. ⇑ Corresponding author. E-mail addresses: [email protected] (H. Shinsha), [email protected] (T. Kumagai).
negligible strength can be changed to a stiff soil with an unconfined compressive strength of 100–500 kN/m2 by the application of the above solidification methods. As the volume of dredged soil is huge, there is always a demand for the development of more effective solutions for dredged soil. In addition, from the viewpoint of the protection of the natural environment, it is strongly advised here in Japan that stones be acquired from excavations in mountains and that sand/gravel be acquired from the dredging of rivers. There is a chronic deficiency of these materials in construction work. Therefore, to simultaneously resolve the problem of the disposal of dredged soil and to counteract the shortage of sand/gravel, the use of solidified soil grains as an alternative material to sand/gravel is proposed. Solidified soil grains are produced by crushing a solidified soil mass which is made of dredged soil mixed with cement (Shinsha and Tsutsumi, 2016a). On the other hand,
https://doi.org/10.1016/j.sandf.2018.03.003 0038-0806/Ó 2018 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
2
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
84.3%, the fine fraction content is 82% and the ignition loss is 9.3%. The mix proportions of the solidified soil are summarized in Table 2. Portland blast-furnace slag cement B was used. The cement, in a slurry condition with the mass ratio of 1:1 of cement and water, was mixed with 1 m3 of clay, as seen in Table 2. The water content of the marine clay was 101% and the cement content was in the range of 100–400 kg/m3. After curing the sample for 28 days, the results showed that the unconfined compressive strength (UCS) of the sample was from 1.205 MN/m2 to 7.400 MN/m2 (Table 2). The solidified soil grains were produced according to the following simple steps: (1) The cement was mixed with the marine clay. (2) The mixture was poured into a plastic bag with a diameter of 5 cm and a length of 40 cm. (3) The mixture was cured in a homeothermal room, at a temperature of 20 °C and humidity of 60%, for 28 days and, as a result, the solidified soil mass was produced. (4) The solidified soil mass was crushed into coarse grains less than 50 mm in size, and then the grains were further crushed into smaller ones less than 10 mm in size. (5) The grains were then filtered through sieves having several different mesh sizes. Finally, grains with the size of 0.85 mm to 2 mm (Grain-A), 2 mm to 4.75 mm (Grain-B) and 4.75 mm to 9.5 mm (Grain-C) were prepared for the soil tests.
solidified soil grains can also be produced by mixing together dredged soil, cement and a polymer using a special mixing device (Dong et al., 2011; Hayano et al., 2014). The addition of a polymer is advantageous in that the polymer can absorb the superfluous pore water contained in clay that has a very high water content so that solidified soil grains can be easily produced. However, there are also disadvantages to this method, namely, that the production costs tend to increase with the addition of a polymer and that large volumes of solidified soil grains cannot be produced in a short period due to the small mixing device. On the other hand, the method whereby solidified soil grains are produced by crushing a solidified soil mass is advantageous in that large volumes of solidified soil grains can be produced in a short period using such mixing methods as the premixing method, the pneumatic flow mixing method etc. It is desirable for solidified soil grains to possess the following features: (1) (2) (3) (4)
The general strength is similar to that of sand/gravel. The permeability is higher than 1 105 m/s. The internal friction angle is higher than 30°. The unit weight is less than that of normal soil for reducing the earth pressure. (5) The material properties continue to be stable for a long period.
3. Material properties of single solidified soil grains In order to examine the material properties for the above items (1) to (4) for solidified soil grains, two kinds of strength tests were carried out. One is the compression test for single grains and the other is the consolidated-drained tri-axial compression test for aggregated grains. In addition, in order to examine the properties for item (5), two kinds of strength tests for solidified soil exposed to seawater were carried out. One is the needle penetration test for the solidified soil mass and the other is the consolidateddrained tri-axial compression test for the grains. Based on the results of these tests, the performances of the proposed solidified soil grains are clarified. In particular, with the desirable features for permeability, the internal friction angle and the unit weight for items (2) to (4), the applicability of the proposed material as quasi-alternative material for natural sand/gravel is revealed in this study.
3.1. Densities of solidified soil The densities of the solidified soil are shown in Table 2. When the solidified soil mass is crushed, the density of the grains does not change from that of the solidified soil mass, and the densities fall in the range of 1.471 g/cm3 to 1.510 g/cm3. Therefore, the density of the solidified soil mass is considerably less than that of the dredged soil particles, namely, 2.668 g/cm3. This is because the solidified soil grains of the solidified soil contain a great deal of water and the water contains liquid water and a hydrate compound, which is transformed from liquid water by a chemical reaction. The theoretical amount of water transformed for the complete hydration of the cement is 42.4 ml per 100 g of cement (Fujii, 1986; Japan Cement Association, 2012) (see Fig. 6).
2. Production of solidified soil grains 3.2. Strength of single solidified soil grains Marine clay dredged from Nagoya Port in Japan was used in this study. The physical properties of the marine clay are summarized in Table 1. The liquid limit is
Strength tests on single solidified soil grains were carried out, as seen below: (1) 30 grains (Grain-C) were used. It is
Table 1 Physical properties of marine clay. Specific gravity qs (g/cm3) 2.668
Clay
Grain size distribution (%) Silt
Sand
Liquid limit wL (%)
Plastic limit wP (%)
Ignition loss Li (%)
38
44
18
84.3
24.4
9.3
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
3
Table 2 Mix proportions and strength of solidified soil. Total
Density (g/cm3)
qu28 (MN/m2)
Grain strength rcm (MN/m2)
70 70
1621 1103
1.471
1.205
0.369
200 66
140 140
1791 1205
1.486
3.540
0.872
729 729
300 99
210 210
1961 1308
1.499
5.853
1.274
729 729
400 132
280 280
2131 1411
1.510
7.400
1.480
Case
Clay
Cement slurry
Soil particle
Water
Cement
Water
Case-100
722 271
729 729
100 33
Case-200
722 271
729 729
Case-300
722 271
Case-400
722 271
Upper row is mass (kg) and lower row is volume (l)
also the number of tests required for the normal distribution of strength to be assumed. The reason why 30 samples were chosen can be explained using statistics by the assumption of an infinitely large parent population. The true population rate is estimated from the observed samples using Eq. (1). sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Pð1 PÞ P 6 P Z ða=2Þ ð1Þ n where P is the true population rate, P is the observed population rate in the sample data, n is the number of samples and Z ða=2Þ is the variable in the standard normal distribution corresponding to the degree of reliability (1 a) to be supposed. In the above equation, the range in errors between the true population rate and that obtained from the sample data is the second term on the right-hand side. Therefore, once the range in errors is supposed, the required number of samples can be calculated by Eq. (2). nP
Pð1 PÞ ðe=Zða=2Þ Þ2
ð2Þ
where e is the range in errors to be supposed. In Eq. (2), the required number of samples is maximized for the case in which P is set at 0.5. When the degree of reliability is supposed to be 95%, Z ða=2Þ corresponds to 1.96. Moreover, by setting the range in error e at 20%, the number of required samples is calculated as n > 24. Therefore, 30 samples more than this calculated number of 24 were tested in this study. The dimensions in three-directions, x, y and z, of a single grain were measured so that the load could be converted into stress. (2) Each grain was put in its most stable state. (3) The grain was loaded in the loading apparatus at a load rate of 0.25 mm/min (Fig. 1). Fig. 2 shows the relation between the load and the displacement obtained from the strength tests for single grains. Although the load gradually increased with the increase in displacement, it was seen that small peaks of load appeared several times due to the partial crushing of
Load cell Displacement pick-up Loading Defense cylinder Solidified soil grain
Fig. 1. Strength test apparatus for single solidified soil grains.
the grains. When a single grain generates shear resistance, based on the internal friction angle, it is thought that the first peak load, shown in Fig. 2, is related to the crush load of the grain. The strength of a single solidified soil grain (rc) is evaluated using Eq. (3). rc ¼
4Fc pd 20
ð3Þ
where Fc is a first peak load. d0 is the average length in the three directions of the grain. The cross-section area of the grain is assumed to be circular with a diameter of average length. In addition, s, shown in Fig. 2, is the standard deviation. Fig. 3 shows the relation between the cement content (C) and the average strength of a single grain (rcm), as well as the unconfined compressive strength (UCS, qu28) using the specimen (u5 cm H10 cm) from the solidified soil mass after 28 days of curing. From Fig. 3, Eqs. (4) and (5) are obtained. qu28 ¼ 0:0209 C 0:725
ð4Þ
rcm ¼ 0:0037 C þ 0:065
ð5Þ
Fig. 4 shows the relation between the cement content and the strength ratio (b), which is defined as rcm/qu28. As shown in Fig. 1, the single grain specimen is loaded normally in the strength test apparatus at the periphery of the grain. Therefore, the tensile stress perpendicular to
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
4
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 50
100
40
30
20
40
20
10
0 0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 0.0
1.8
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
1.4
1.6
1.8
Displacement(mm)
Displacement (mm) 160
100
Case-300 28 days of curing σcm=1.274 MN/m2 s=0.348 MN/m2
Case-400 28 days of curing σcm=1.480 MN/m2 s=0.659 MN/m2
140
1st peak load
120
Load (N)
80
Load (N)
1st peak load
60
1st peak load
Load (N)
Load (N)
Case-200 28 days of curing 80 σcm=0.872 MN/m2 s=0.352 MN/m2
Case-100 28 days of curing σcm=0.369 MN/m2 s=0.108 MN/m2
60
40
100
1st peak load
80 60 40
20 20
0 0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0 0.0
0.2
0.4
Displacement (mm)
0.6
0.8
1.0
1.2
Displacement (mm)
Fig. 2. Relation between load and displacement of single grains.
0.5
q u28= 0.0209C- 0.725
8
6 4
σc m= 0.0037C + 0.065
2
Strength ratio β=σcm/qu28
Strength (MN/m2 )
10
0.3 0.2 0.1 0.0
0 0
100
200
Cement content
300
400
500
C(kg/m3 )
Fig. 3. Relation between cement content and strength of solidified soil.
the loading axis is generated inside the grain, and the grain is considered to be crushed dominantly by the tension stress at the failure state. Therefore, the strength of a single grain measured in this study is equal to the tension strength. It is well known that the ratio between the tension strength and the UCS, obtained from the specimen with the same size of 5 cm in diameter 10 cm in height, lies in the range of 0.15–0.20 (Kitazume et al., 2003). However, the ratio between the strength test results (=tension strength) of a single solidified soil grain with the size of 4.75–9.5 mm and the UCS, obtained from the specimen of 5 cm in diameter 10 cm in height, lies in the range of 0.2–0.3. The strength ratios are different because the size of the specimens for the strength tests is different.
β= -0.0003C+ 0.3293
0.4
0
100
200
300
400
500
Cement content C (kg/m3 ) Fig. 4. Relation between cement content and strength ratio.
3.3. Strength of single rock grains Strength tests for single natural rock grains were carried out using the sample with the same size as the solidified soil grain. Two kinds of rock grains were selected, namely, basalt grains and granite grains. Fig. 5 shows the strength test results for both rock grains. Although the maximum strength of the solidified soil grains in this study was 1.48 MN/m2 (Table 2), the strength of the basalt grains and the granite grains was 3.761 MN/m2 and 6.878 KN/m2, respectively. Therefore, the strength ratios of the solidified soil grains to the rock grains become 39% for the basalt grains and 22% for the granite grains. This reveals that the strength of the solidified soil grains is less than that
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 1,000
800
Basalt σcm=3.761 MN/m2 s=3.351 MN/m2
600
Granite σcm=6.878MN/m2 s=4.725 MN/m2
1st peak load
600
Load (N)
Load (N)
800
5
1st peak load 400
200
200
0 0.0
400
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0 0.0
0.2
Displacement (mm)
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Displacement (mm)
Fig. 5. Relation between load and displacement of single rock grains.
Table 3 Maximum and minimum densities of solidified soil grains. Solidified soil
qmax g/cm3
qmin g/cm3
Specimen q g/cm3
Dr %
Grain-A
A-100 A-200 A-300 A-400
0.849 0.877 0.862 0.877
0.616 0.617 0.663 0.665
0.817 0.828 0.817 0.829
89.6 86.0 81.6 81.7
Grain-B
B-100 B-200 B-300 B-400
0.897 0.903 0.909 0.927
0.712 0.744 0.764 0.766
0.860 0.869 0.880 0.889
83.4 81.7 82.6 79.8
of the natural rock grains for the conditions of cement quantity applied in this study. 4. Material properties of aggregated solidified soil grains 4.1. Maximum and minimum densities of grains Maximum and minimum density tests were carried out for the samples of aggregated solidified soil grains. The test results are shown in Table 3. The maximum density of the sample from Grain-A falls in the range of 0.849– 0.877 g/cm3 compared to 0.897–0.927 g/cm3 of the sample from Grain-B. On the other hand, the minimum density
Water between grains
Solidified soil grain
0.41 m3, 0.43 t
Water
0.42m3, 0.43 t
Soil particle
0.13m3 , 0.31 t
Cement ρsat
1.31g/cm 3,
0.04m3 , 0.14 t ρ`=0.28g/cm3
Fig. 6. Composition of water, soil particles and cement in specimen of solidified soil grains (B-300).
of the sample from Grain-A falls in the range of 0.616– 0.665 g/cm3 compared to 0.712–0.766 g/cm3 of the sample from Grain-B. The maximum and minimum densities of the solidified soil grains tend to increase with the size of the grains. This is because as the size of the grains increases, the proportion of the grain volume occupying the space increases with large voids filled with nonuniform shapes of grains in long and short axes. 4.2. Density of specimen for tri-axial tests The relative density of the specimen for the tri-axial compression tests was around 85% (Table 3). The relative density of 85% was determined by taking into consideration not only the ease with which the specimen could be compacted, but also the importance of not crushing the grains as much as possible. The measured relative density was in the range of 79.8–89.6% due to the influence of the upper surface shaping of the specimen. Fig. 6 shows the composition of the soil particles, the water and the cement in the specimen with a relative density of 85%. From this figure, it is clear that the volume of 83% of the specimen consists of water, and the submerged density becomes 0.28 g/cm3, whereas the density of water is 1.03 g/cm3. Therefore, it is clear that specimens produced from solidified soil grains have lightness compared to those produced from normal sand with a submerged density of 1.0 g/cm3.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
6
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
4.3. Permeability
k ¼ ck ð0:7 þ 0:03T Þ D210
The permeability of the specimen produced from solidified soil grains was obtained from the consolidation process in the tri-axial tests. The consolidation process for the three-axis compression tests and the onedimensional consolidation phenomenon are different in deformation behavior, but since the application of the one-dimensional consolidation theory is considerably easy, Terzaghi’s consolidation theory was applied here to the consolidation process of the specimen in the three-axis compression tests, and the consolidation properties were obtained. The volume compressibility coefficient, mv, was obtained based on Eq. (6), the consolidation coefficient, cv, was obtained based on Eq. (7) and the permeability coefficient, k, was obtained based on Eq. (8). evf mv ¼ ð6Þ Dp
Here, Ck is 150 for uniform particles. T is the temperature which is equal to 20 °C. The unit of k in Eq. (9) is cm/s. Based on Eq. (9), the permeability coefficient of Grain-A is calculated as 1.42 102 m/s and that of Grain-B is 7.80 102 m/s. It is revealed that the test results are 0.1 to 0.4 times lower than the values estimated by Eq. (9).
T vH 2 t k ¼ m v c v cw
ð7Þ
cv ¼
ð8Þ
Here, Dp is the consolidation pressure and Tv is the time factor. When the average consolidation degree is 90%, the time factor value is 0.848. H is equal to 5 cm in drainage distance. t is the consolidation time with the average consolidation degree of 90%. evf is the volume strain at the end of the primary consolidation. cw is the unit weight of the pore water. In the range of consolidation pressure of 50 kN/m2 to 150 kN/m2, the value of the volume compressibility coefficient of the samples from Grain-A and Grain-B was in the range of 3.5 103 m2/kN to 4.5 104 m2/kN. The permeability coefficient of the sample from Grain-A was in the range of 1.17 m/s to 2.46 103 m/s and that from Grain-B was in the range of 1.35 m/s to 2.75 103 m/s. Therefore, it is clear that the permeability coefficients of both grains are considerably higher than that of normal sand at 1 105 m/s (Japanese Geotechnical Society, 2009). In addition, the permeability coefficient of granular materials can be obtained by Hazen’s formula, given in Eq. (9), using a particle diameter of 10%, D10 (cm).
4.4. Volumetric strain Fig. 7 shows the volumetric strains of the solidified soil grains due to the consolidation process and the shearing process under various confining pressure conditions, as well as the two natural rock grains of basalt and granite. The size of the rock grains is the same as that of the solidified soil grains (Grain-B). The volumetric strains of solidified soil grains in both the consolidation process and the shearing process are larger than that of the natural rock grains. In particular, the volumetric strain of the solidified soil grains tends to decrease with the compressive strength of the single grains. In addition, when shear stress was imposed on the specimen after consolidation, the volumetric strain of the specimen from the solidified soil grains increased with the shear strain. However, the volumetric strain of the specimen from the natural rock grains increased first with the shear strain and then decreased with the shear strain due to dilatancy. 4.5. Internal friction angle The Mohr’s stress circles of the specimen from the solidified soil grains obtained from the tri-axial compression tests are shown in Fig. 8. The rupture envelope line can be drawn starting from the zero point (Fig. 8), and the slope of the envelope line tended to decrease with an increase in confining pressure. Therefore, the shear strength can be considered as a secondary function of the confining pressure. Thus, the internal friction angle (ud) can be obtained from Eq. (10). ud ¼ tan1 ðDs=Dr0 Þ
15
10
5
50
100
150
Confining pressure
(kN/m 2 )
200
250
B-100 B-200 B-300 B-400 Basalt Granaite
Shearing process Volumetric strain(%)
B-100 B-200 B-300 B-400 Basalt Granite
Consolidation process Volumetric strain(%)
ð10Þ
20
20
0 0
ð9Þ
15 10 5 0 -5 0
50
100
150
200
250
Confining pressure (kN/m 2 )
Fig. 7. Relation between confining pressure and volumetric strain. Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
Shear strength τ (kN/m 2 )
Shear strength τ (kN/m2)
250
A-200 200 150 100 50
7
250
B-200 200 150 100 50 0
0 0
100
200
300
400
0
500
100
200
300
400
500
Confining stress σ' (kN/m 2 )
Confining stress σ' (kN/m2) Fig. 8. Mohr’s stress circle from tri-axial tests.
50
Grain-A
Internal friction angle ( )
Internal friction angle ( )
50
40
30
A-100 A-200
20
A-300 A-400 10
0
50
100
150
200
250
300
Confining pressure (kN/m2)
40
30
B-100 B-200 B-300 B-400 Basalt Granite
20
Grain-B
10 0
50
100
150
200
250
300
Confining pressure (kN/m 2 )
Fig. 9. Relation between confining stress and internal friction angle.
Internal friction angle ( )
55
single granite grains is considerably higher than that of solidified soil grains, as shown in Fig. 10. The reason why the internal friction angles of granite grains are smaller than those of basalt grains is thought to be because the granite grains have been weathered so that the sharp corners of the particles have disappeared and become round.
50 45 40 B-100
35 30
B-200 d=10.1
B-300
ln(σcm +40.8
B-400
25 20 0
Basalt Granite
1
2
3
4
5
Strength of single grain (MN/m2 )
6
7
Fig. 10. Relation between strength of single grain and internal friction angle.
where, s = E r0 2 + F r0 , and E and F are constants. Fig. 9 shows the relation between the confining pressure and the internal friction angle of both Grain-A and Grain-B. From this figure, it is revealed that the internal friction angle changes with the size of the grains, the cement content and the confining pressure, and that the internal friction angle lies in the range of 30° to 45°. The internal friction angles of the specimens from the natural rock grains are also shown in Fig. 9. The internal friction angles of the basalt grains are higher than those of the solidified soil grains. On the other hand, the internal friction angles of the granite grains are similar to those of the solidified soil grains, but their internal friction angles do not decrease with the increase in confining pressure. This is because the strength of
5. Deterioration property of solidified soil exposed to seawater 5.1. Introduction In order to use solidified soil grains as fill material instead of sand/gravel, it is necessary to investigate the deterioration property of solidified soil. Since it is well known that once a solidified soil is exposed to seawater, a deteriorated layer forms on the outer surface due to the leaching of the calcium that is inside the soil into the seawater, which will reduce the strength of the deterioration layer to nearly zero (Watabe et al., 2016) . For the case of solidified soil grains, the deterioration might be even worse due to the increased contact area between the solidified soil grains and the seawater. Since the deterioration process might significantly reduce the internal friction angles of the solidified soil grains, tests were carried out to investigate the effects of the deterioration on the material properties of the solidified soil mass and the grains.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
8
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
Penetration force (N)
500
Deterioration amount
400 300
(56 days from production)
200
F-55
S-28
100 0
200F-55 200S-28
no-exposure 0
2
4
200-0
6
8
10
Penetration amount (mm) Fig. 11. Needle penetration test results at two curing conditions.
Penetration force (N)
500 400 300 200
200F-34 200F-55 200F-87 200F-177
F-177 F-87 F-55
F-34
no-exposure 100 0 0
2
4
6
8
10
Penetration amount (mm) Fig. 12. Needle penetration test results at some exposure times.
5.2. Deterioration property of solidified soil mass Needle Penetration Tests (NPTs) were conducted using the samples exposed to seawater after 1 day of curing (sub-script: F) and 28 days of curing (sub-script: S). In these tests, a circular pillar, 4 mm in diameter with a flat edge, was penetrated into the test sample at a loading rate of 2 mm/min. The penetration force was measured together with the penetration depth. NPTs are suitable for accurately measuring the distribution of strength of the surface layer portion of deteriorated solidified soil. By comparing the distribution of strength of deteriorated and nondeteriorated samples, the amount of deterioration of the samples can be obtained. If the strength of the solidified soil is too high, the sample will crack when penetrating the needle, making it impossible to obtain the deterioration amount.
Deterioration amount (mm)
12
F-34 F-55 F-87 F-177 S-7 S-28 S-60 S-150
10 8 6 4 2
0 50 100 150 200 250 300 350 400 450 500 550 600
Cement content (kg/m3) Fig. 13. Deterioration amount from needle penetration tests.
Fig. 11 shows the test results for the samples exposed to seawater after 1 day of curing and 28 days of curing. Fig. 12 shows the test results for the samples at some exposure times. The amount of deterioration under the condition of exposure was larger than that under the noexposure condition, and the amount of deterioration increased with the increase in exposure time in the seawater. In order to determine the deterioration amount of a solidified soil, the test results for both the exposure and the no-exposure conditions were studied. As shown in Fig. 11, it was found that the penetration force measured for the samples in the no-exposure condition increased rapidly from zero. However, the penetration force measured for the samples in the exposure condition increased gradually from zero. Thus, the amount of deterioration (D) is defined as follows: (1) As presented in Figs. 11 and 12, the line showing the relationship between the penetration amount (d) and the penetration force (P) in the noexposure condition shifted parallel to fit the line showing the relation in the exposure condition along the axis for the penetration amount. (2) The deterioration amount was defined as the amount of penetration with the penetration force of 0 (P = 0) at the point where both lines coincide well. Fig. 13 shows the relation between the cement content and the amount of deterioration. The deterioration amount grew smaller with an increase in the cement content. Ikegami et al. (2004) proposed Eq. (11) to predict the deteriorated amount (D). However, when Eq. (11) was applied to the test results, it was seen that the prediction did not agree very well with the test results. Therefore, an improved Eq. (12) (Shinsha and Tsutsumi, 2016b) is used in this paper. The results predicted using Eq. (12) are shown in Fig. 14. It can be seen from this figure that the predicted results agree quite well with the test results. Eq. (12) is an empirical equation. However, as the value of B is very small, even if the amount of degradation after several years with B in Eq. (12) as 0 is estimated, the revealed error will be small, where t is the time (year), A is a material fixed coefficient that shows the amount of deterioration after 1 year and B is a material fixed number. D ¼ A t0:5
ð11Þ
D ¼ A ðt0:5 BÞ
ð12Þ
In the prediction of the deterioration amount, the cement content (C) and the unconfined compressive strength (UCS) are the two key factors. Since both the cement content and the UCS are related to the total volume of Ca2+, the deterioration is caused by the loss of Ca2+. The relation between the UCS after 28 days of curing and the cement content has already been shown in Eq. (4). Based on Eq. (4) and Fig. 14, the relationship between the UCS and a material fixed coefficient of A is obtained as shown by Eq. (13). A ¼ 6:038 lnðqu28 Þ þ 15:834
ð13Þ
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 12
100F 200F 300F 400F
10 8
Deterioration amount (mm)
12
Deterioration amount (mm)
9
D= 17.86(t 0.5 - 0.0770)
6
D = 11.72(t 0.5- 0.0903)
4
D = 6.640(t 0.5 - 0.0840) D= 0.991(t 0.5- 0.2374)
2 0 0.2
0.4
0.6
0.8
Exposure time
1.0
10 8
100S 200S 300S
D = 13.54(
6
D = 7.999(
0.5-
0.0861)
0.5-
0.0930)
4 2 0 0.0
D= 4.626(t 0.5 - 0.0833) 0.2
0.4
0.6
0.8
1.0
Exposure time t 0.5
t 0.5
Fig. 14. Relation between exposed time and deterioration amount.
Material fixed number A
30
A =-6.038
ln(qu ) +15.834 F : after 1 day of curing
Membrane
Man-made seawater
S : after 28 days of curing
20
Hara(2013)
Rubber band
SGM3)
Test piece
Container of half-sawing φ5cm H10cm
PFM 2)
10
CDM4) 0 0.1
1
2 sticks
Concrete 0.5 0.8 10
Porous stone
100
Unconfined compressive strength q u28 (MN/m2)
Water tank
Fig. 15. Relation between qu28 and A.
Fig. 17. Installation of specimen in seawater.
Material fixed number B
0.3 F : 1 day of curing S : 28 days of curing
0.2
B=0.0856
0.1
0.0
0.1
1
10
100
the seawater, it is possible to use the solidified soil grains with the UCS higher than the NDS as an alternative material to sand/gravel. The value for B, set at approximately 0.0856, is presented in Fig. 16. With regard to the leaching of calcium from the surface of solidified soil into the seawater, the reference of Hara et al. (2013) is helpful. They have observed that the calcium ion in solidified soil is leached by the salt in the seawater that contains magnesium ions.
Unconfined compressive strength q u28 (MN/m2) Fig. 16. Relation between qu28 and B.
The coefficient of A to be estimated by Eq. (13) is drawn in Fig. 15 and compared with the test results for other types of solidified soils in previous studies, such as the lightweight treated soil referred to as Super Geo-Material (Tsuchida et al., 2004), pneumatic flow mixing soil (Kitazume, 2017) and cement deep-mixing soil (Ikegami et al., 2002). It is found that Eq. (13) can be applied to other types of solidified soil materials as well as to the soil proposed in this study. Based on Eq. (13), deterioration coefficient A becomes almost zero under the condition whereby the UCS exceeds approximately 14 MN/m2. Here, this 14 MN/m2 can be referred to as the non-deterioration strength (NDS) of the solidified soil. It is thought that since the solidified soil grains with the UCS higher than the NDS will hardly be deteriorated by the leaching of calcium into
5.3. Deterioration property of solidified soil grains The deterioration property of the solidified soil grains was also examined through tri-axial compression tests. The tri-axial compression tests were carried out for the test samples under the exposure times of 0 day, 60 days and 150 days, respectively. The installation procedure for a specimen is described below and is shown in Fig. 17: (1) The bottom of a halfsawing container, 5 cm in diameter and 10 cm in height, was removed first and 2 points at the top and the bottom of the container were fixed by rubber bands. (2) A rubber membrane, 0.25 mm in thickness, was set inside the container, and a porous stone, 5 mm in thickness, was put at the bottom of the container. (3) Solidified soil grains with a relative density of 85% were placed inside the container. (4) Tri-axial compression tests were carried out with cell pressures of 50 kN/m2, 100 kN/m2 and 150 kN/m2, respectively.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
10
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 20
σr '=100 kN/m2
Consolidation process
20
B-100 B-200 B-300 B-400
10
0
0
50
100
150
200
Volumetric strain εv2 (%)
Volumetric strain εv1 (%)
30
σr '=100 kN/m2
Shearing process 10
B-100 B-200 B-300 B-400 0
250
0
50
100
150
200
250
Exposure time (day)
Exposure time (day) Fig. 18. Volumetric strain from tri-axial tests.
Shear strength (kN/m 2 )
300
considerably larger than that of the samples under the exposure time of 0 day without any deterioration. The volumetric strain (ev2) from the shearing process after consolidation, obtained at 15% of axial strain, is also shown in Fig. 18. According to the test results under the exposure time of 0 day without any deterioration, the volumetric strain of the samples clearly decreased as the grain strength increased, due to the comparison of the results of the test cases of B-100 and B-400. On the other hand, the volumetric strain of the samples under the exposure times of 60 and 150 days are similar in all test cases of B-100 to B-400. This is thought to be the influence of the deteriorating surface of the grains and the layer with weak strength forming on the samples in all test cases.
B-300-0 B-300-60 B-300-150
250 200 150 100 50 0 0
100
200
300
400
500
600
Confining stress (kN/m 2 ) Fig. 19. Mohr’s stress circle from tri-axial compression tests.
(1) Volumetric strain The volumetric strain obtained from the tri-axial compression tests is shown in Fig. 18. The volumetric strain (ev1) from the consolidation process will become larger if the cement content is less. It is thought that for the case without any deterioration, volumetric strain (ev1) will only be caused by the re-arrangement and the crushing of the grains. On the other hand, for the case with deterioration, the additional volumetric strain due to the consolidation of the deteriorated soil forming on the outer surface of the grains and the movement of the deteriorated soil into the voids between the grains will be added to that of the case without any deterioration. It can be seen from the test results, shown in Fig. 18, that the volumetric strain (ev1) of the samples under the exposure time of 60 days is
100S-0 100S-60 100S-150 200S-0 200S-60 200S-150
40
Internal friction angle ( )
Internal friction angle ( )
The Mohr’s stress circles from the tri-axial compression tests are shown in Fig. 19. After the comparison of the Mohr’s stress circles of the samples under the exposure times of 0 day, 60 days and 150 days, it can be concluded that the Mohr’s stress circles become smaller with the increase in exposure time. The results from Fig. 20 show that for the case of no-deterioration, the internal friction angle becomes larger with the increase in cement content. Meanwhile, for the case of deterioration, the internal friction angle is smaller compared to that without any deterioration. 50
50
30
20
(2) Internal friction angle
40
20
0
50
100
150
Confining pressure (kN/m 2)
200
300S-0 300S-60 300S-150 400S-0 400S-60 400S-150
30
0
50
100
150
200
Confining pressure (kN/m2)
Fig. 20. Relation between confining pressure and internal friction angle. Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
6. Conclusions Solidified soil grains are produced by crushing a solidified soil mass made of dredged soil mixed with cement. The main conclusions obtained from the tests on solidified soil grains are as follows: (1) The strength of single solidified soil grains produced by the maximum addition of 400 kg/m3 of cement in this study is 1.48 MN/m2. This strength is smaller compared to 3.77 MN/m2 of natural basalt grains and 6.88 MN/m2 of natural granite grains. In order to achieve desirable strength as large as that of natural gravel, additional measures should be considered in future research works. (2) The aggregated solidified soil grains have the desirable feature of permeability with the permeability coefficient in the range of 1.17–2.75 103 m/s, which is considerably higher than that of normal sand, namely, 1 105 m/s. (3) The aggregated solidified soil grains have the desirable feature of unit weight with the saturated density of the aggregated solidified soil grains underwater with the relative density of 85% of 1.28 g/cm3, which is smaller than that of normal sand, namely, 2.0 g/cm3. (4) The internal friction angle of the aggregated solidified soil grains changes with the size of the grains, the cement content and the confining pressure ranging from 30 to 45°. The desirable feature of the shear strength is confirmed for the aggregated solidified soil grains. (5) The solidified soil grains tend to deteriorate in seawater; however, the deterioration rate decreases with the increase in strength. It is confirmed that the amount of deterioration D is proportional to the square root of the time passed, and an improved equation for estimating D is proposed, as shown in Eq. (12). At this point, the material fixed coefficient of A to be used in Eq. (12), which governs the deterioration rate, is formulated by a correlation with the strength of the soil, as shown in Eq. (13). The validity of the proposed formula is verified by a comparison with the test results of the previous studies. (6) Based on Fig. 15, where the unconfined compressive strength (USC) reaches approximately 14 MN/m2, the progress of the deterioration becomes negligible. Therefore, it is thought that the solidified soil grains produced by crushing the mass with the USC higher than 14 MN/m2 will hardly be deteriorated by the leaching of calcium. (7) At the site where the loading conditions do not exceed the threshold to cause the crushing failure of the grains, the solidified soil grains are expected to
11
be applicable on land as quasi-alternative material to sand/gravel with the desirable features of permeability, internal friction angle and unit weight considering less strength compared with natural rocks. Moreover, in cases where the mass of the solidified soil has unconfined compression strength (USC) over 14 MN/m2, the solidified soil grains to be produced by crushing are hardly deteriorated for a long period, and they can be similarly applied even under seawater conditions.
References Coastal Development Institute of Technology, 2002. The Deep Mixing Method, A BALKEMA BOOK, 123p. Dong, P., Hayano, K., Kikuchi, Y., Takahashi, H., Morikawa, Y., 2011. Deformation and crushing of particles of cement treat granulate soil. Soils Found. 51 (4), 611–624. Fujii, K., 1986. Condition and properties of bound water. Cem.-Concr. 469, 2–9 (in Japanese). Hara, H., Suetsugu, D., Hayashi, S., Matsuda, H., 2013. Deterioration mechanism of cement-treated soil under seawater. J. Civil Eng. 69 (4), 469–479 (in Japanese). Hayano, K., Yamauchi, H., Sasaki, K., Fujishima, K., 2014. Fundamental study on a new granulation method with the process of crumbling partially-cemented liquid muds. J. JSCE, Div. C 70 (4), 424–432 (in Japanese). Ikegami, M., Masuda, K., Ichiba, T., Tsuruya, K., Satou, S., Terashi, M., Oishi, K., 2002. Soundness of submarine clay improved by the cement deep mixing method after 20 years. In: The 57th Annual Meeting Lecture Collection of JSCE, pp. 121–122 (in Japanese). Ikegami, M., Satou, S., Ichiba, T., Osoku, N., Nishida, T., Terashi, M., 2004. Simple prediction method on degradation progression of cement stabilized soil, in: The 59th Annual Meeting Lecture Collection of JSCE, pp. 1073–1074 (in Japanese). Japan Cement Association, 2012. Ground Improvement Manual by Cementitious Solidification Material, fourth ed., Gihodo Publication, pp. 29–32 (in Japanese). Japanese Geotechnical Society, 2009. Japanese Geotechnical Society Standards- Laboratory Testing Standards of Geomaterials, vol. 1, 262p. Kitazume, M., 2017. The Pneumatic Flow Mixing Method, A BALKEMA BOOK, 233p. Kitazume, M., Hayano, K., Hashizume, H., 2003. Seismic stability of cement treated ground by tilting and dynamic shaking table tests. Soils Found. 43 (6), 25–140. Shinsha, H., Tsutsumi, A., 2016a. Strength characteristics of crushed cement-mixed soil as granular geomaterials. J. JSCE, Div. C 72 (2), 74– 85 (in Japanese). Shinsha, H., Tsutsumi, A., 2016b. Experimental study on deterioration of cement-mixed soil and crushed particles in seawater. J. JSCE, Div. C 72 (3), 265–276 (in Japanese). Tsuchida, T., Egashira, K., 2004. The Lightweight Treated Soil Method, A BALKEMA BOOK, 120p. Watabe, Y., Kikuchi, Y., Shinsha, H., 2016. Long-Term Properties of AirFoam Treated Lightweight Soil Cured in Seawater, 19SEAGC & 2AGSSEA, Kuala Lumpur, 31 May–3 June.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
HOSTED BY
ScienceDirect Soils and Foundations xxx (2018) xxx–xxx www.elsevier.com/locate/sandf
Material properties of solidified soil grains produced from dredged marine clay Hiroshi Shinsha ⇑, Takahiro Kumagai Institute of Technology, Penta-Ocean Construction Co., Ltd., 1534-1, Yonkucho, Nasushiobara-shi, Tochigi 329-2746, Japan Received 20 September 2017; received in revised form 19 January 2018; accepted 22 February 2018
Abstract Solidified soil grains are produced by crushing a solidified soil mass which is made of dredged soil mixed with cement. It would be beneficial if these solidified soil grains could be used as fill material instead of sand/gravel. However, the strength property of solidified soil grains has not yet been thoroughly studied. In addition, as it is well known that solidified soil tends to deteriorate in seawater due to the leaching of calcium, it is necessary to make a complete study of the deterioration properties of solidified soil grains. In the current study, the material properties of solidified soil grains have been investigated. The test results revealed that (1) the strength of normal single solidified soil grains is smaller than that of natural rock grains, (2) the internal friction angle of solidified soil grains is greater than 30°, and (3) the internal friction angle of solidified soil grains tends to decrease along with the progress of deterioration; however, deterioration will not be experienced by solidified soil grains which have unconfined compressive strength larger than approximately 14 MN/m2. Ó 2018 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.
Keywords: Solidified soil grains; Dredged marine clay; Deterioration; Seawater; Internal friction angle
1. Introduction To maintain the required water depth of fairways and basins etc., about 20 million m3 of sediment soil are dredged every year in Japan despite the low availability of dumping areas. The way with which this dredged soft soil should be dealt has become a serious problem that must be resolved. In order to utilize the dredged soil effectively, a lot of solidification methods (Coastal Institute, 2002; Kitazume, 2017; Tsuchida et al., 2004) for mixing dredged soil with cement have already been developed. The required shear strength can be achieved in a short period by these methods. In fact, a very soft dredged soil with
Peer review under responsibility of The Japanese Geotechnical Society. ⇑ Corresponding author. E-mail addresses: [email protected] (H. Shinsha), [email protected] (T. Kumagai).
negligible strength can be changed to a stiff soil with an unconfined compressive strength of 100–500 kN/m2 by the application of the above solidification methods. As the volume of dredged soil is huge, there is always a demand for the development of more effective solutions for dredged soil. In addition, from the viewpoint of the protection of the natural environment, it is strongly advised here in Japan that stones be acquired from excavations in mountains and that sand/gravel be acquired from the dredging of rivers. There is a chronic deficiency of these materials in construction work. Therefore, to simultaneously resolve the problem of the disposal of dredged soil and to counteract the shortage of sand/gravel, the use of solidified soil grains as an alternative material to sand/gravel is proposed. Solidified soil grains are produced by crushing a solidified soil mass which is made of dredged soil mixed with cement (Shinsha and Tsutsumi, 2016a). On the other hand,
https://doi.org/10.1016/j.sandf.2018.03.003 0038-0806/Ó 2018 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
2
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
84.3%, the fine fraction content is 82% and the ignition loss is 9.3%. The mix proportions of the solidified soil are summarized in Table 2. Portland blast-furnace slag cement B was used. The cement, in a slurry condition with the mass ratio of 1:1 of cement and water, was mixed with 1 m3 of clay, as seen in Table 2. The water content of the marine clay was 101% and the cement content was in the range of 100–400 kg/m3. After curing the sample for 28 days, the results showed that the unconfined compressive strength (UCS) of the sample was from 1.205 MN/m2 to 7.400 MN/m2 (Table 2). The solidified soil grains were produced according to the following simple steps: (1) The cement was mixed with the marine clay. (2) The mixture was poured into a plastic bag with a diameter of 5 cm and a length of 40 cm. (3) The mixture was cured in a homeothermal room, at a temperature of 20 °C and humidity of 60%, for 28 days and, as a result, the solidified soil mass was produced. (4) The solidified soil mass was crushed into coarse grains less than 50 mm in size, and then the grains were further crushed into smaller ones less than 10 mm in size. (5) The grains were then filtered through sieves having several different mesh sizes. Finally, grains with the size of 0.85 mm to 2 mm (Grain-A), 2 mm to 4.75 mm (Grain-B) and 4.75 mm to 9.5 mm (Grain-C) were prepared for the soil tests.
solidified soil grains can also be produced by mixing together dredged soil, cement and a polymer using a special mixing device (Dong et al., 2011; Hayano et al., 2014). The addition of a polymer is advantageous in that the polymer can absorb the superfluous pore water contained in clay that has a very high water content so that solidified soil grains can be easily produced. However, there are also disadvantages to this method, namely, that the production costs tend to increase with the addition of a polymer and that large volumes of solidified soil grains cannot be produced in a short period due to the small mixing device. On the other hand, the method whereby solidified soil grains are produced by crushing a solidified soil mass is advantageous in that large volumes of solidified soil grains can be produced in a short period using such mixing methods as the premixing method, the pneumatic flow mixing method etc. It is desirable for solidified soil grains to possess the following features: (1) (2) (3) (4)
The general strength is similar to that of sand/gravel. The permeability is higher than 1 105 m/s. The internal friction angle is higher than 30°. The unit weight is less than that of normal soil for reducing the earth pressure. (5) The material properties continue to be stable for a long period.
3. Material properties of single solidified soil grains In order to examine the material properties for the above items (1) to (4) for solidified soil grains, two kinds of strength tests were carried out. One is the compression test for single grains and the other is the consolidated-drained tri-axial compression test for aggregated grains. In addition, in order to examine the properties for item (5), two kinds of strength tests for solidified soil exposed to seawater were carried out. One is the needle penetration test for the solidified soil mass and the other is the consolidateddrained tri-axial compression test for the grains. Based on the results of these tests, the performances of the proposed solidified soil grains are clarified. In particular, with the desirable features for permeability, the internal friction angle and the unit weight for items (2) to (4), the applicability of the proposed material as quasi-alternative material for natural sand/gravel is revealed in this study.
3.1. Densities of solidified soil The densities of the solidified soil are shown in Table 2. When the solidified soil mass is crushed, the density of the grains does not change from that of the solidified soil mass, and the densities fall in the range of 1.471 g/cm3 to 1.510 g/cm3. Therefore, the density of the solidified soil mass is considerably less than that of the dredged soil particles, namely, 2.668 g/cm3. This is because the solidified soil grains of the solidified soil contain a great deal of water and the water contains liquid water and a hydrate compound, which is transformed from liquid water by a chemical reaction. The theoretical amount of water transformed for the complete hydration of the cement is 42.4 ml per 100 g of cement (Fujii, 1986; Japan Cement Association, 2012) (see Fig. 6).
2. Production of solidified soil grains 3.2. Strength of single solidified soil grains Marine clay dredged from Nagoya Port in Japan was used in this study. The physical properties of the marine clay are summarized in Table 1. The liquid limit is
Strength tests on single solidified soil grains were carried out, as seen below: (1) 30 grains (Grain-C) were used. It is
Table 1 Physical properties of marine clay. Specific gravity qs (g/cm3) 2.668
Clay
Grain size distribution (%) Silt
Sand
Liquid limit wL (%)
Plastic limit wP (%)
Ignition loss Li (%)
38
44
18
84.3
24.4
9.3
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
3
Table 2 Mix proportions and strength of solidified soil. Total
Density (g/cm3)
qu28 (MN/m2)
Grain strength rcm (MN/m2)
70 70
1621 1103
1.471
1.205
0.369
200 66
140 140
1791 1205
1.486
3.540
0.872
729 729
300 99
210 210
1961 1308
1.499
5.853
1.274
729 729
400 132
280 280
2131 1411
1.510
7.400
1.480
Case
Clay
Cement slurry
Soil particle
Water
Cement
Water
Case-100
722 271
729 729
100 33
Case-200
722 271
729 729
Case-300
722 271
Case-400
722 271
Upper row is mass (kg) and lower row is volume (l)
also the number of tests required for the normal distribution of strength to be assumed. The reason why 30 samples were chosen can be explained using statistics by the assumption of an infinitely large parent population. The true population rate is estimated from the observed samples using Eq. (1). sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Pð1 PÞ P 6 P Z ða=2Þ ð1Þ n where P is the true population rate, P is the observed population rate in the sample data, n is the number of samples and Z ða=2Þ is the variable in the standard normal distribution corresponding to the degree of reliability (1 a) to be supposed. In the above equation, the range in errors between the true population rate and that obtained from the sample data is the second term on the right-hand side. Therefore, once the range in errors is supposed, the required number of samples can be calculated by Eq. (2). nP
Pð1 PÞ ðe=Zða=2Þ Þ2
ð2Þ
where e is the range in errors to be supposed. In Eq. (2), the required number of samples is maximized for the case in which P is set at 0.5. When the degree of reliability is supposed to be 95%, Z ða=2Þ corresponds to 1.96. Moreover, by setting the range in error e at 20%, the number of required samples is calculated as n > 24. Therefore, 30 samples more than this calculated number of 24 were tested in this study. The dimensions in three-directions, x, y and z, of a single grain were measured so that the load could be converted into stress. (2) Each grain was put in its most stable state. (3) The grain was loaded in the loading apparatus at a load rate of 0.25 mm/min (Fig. 1). Fig. 2 shows the relation between the load and the displacement obtained from the strength tests for single grains. Although the load gradually increased with the increase in displacement, it was seen that small peaks of load appeared several times due to the partial crushing of
Load cell Displacement pick-up Loading Defense cylinder Solidified soil grain
Fig. 1. Strength test apparatus for single solidified soil grains.
the grains. When a single grain generates shear resistance, based on the internal friction angle, it is thought that the first peak load, shown in Fig. 2, is related to the crush load of the grain. The strength of a single solidified soil grain (rc) is evaluated using Eq. (3). rc ¼
4Fc pd 20
ð3Þ
where Fc is a first peak load. d0 is the average length in the three directions of the grain. The cross-section area of the grain is assumed to be circular with a diameter of average length. In addition, s, shown in Fig. 2, is the standard deviation. Fig. 3 shows the relation between the cement content (C) and the average strength of a single grain (rcm), as well as the unconfined compressive strength (UCS, qu28) using the specimen (u5 cm H10 cm) from the solidified soil mass after 28 days of curing. From Fig. 3, Eqs. (4) and (5) are obtained. qu28 ¼ 0:0209 C 0:725
ð4Þ
rcm ¼ 0:0037 C þ 0:065
ð5Þ
Fig. 4 shows the relation between the cement content and the strength ratio (b), which is defined as rcm/qu28. As shown in Fig. 1, the single grain specimen is loaded normally in the strength test apparatus at the periphery of the grain. Therefore, the tensile stress perpendicular to
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
4
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 50
100
40
30
20
40
20
10
0 0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 0.0
1.8
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
1.4
1.6
1.8
Displacement(mm)
Displacement (mm) 160
100
Case-300 28 days of curing σcm=1.274 MN/m2 s=0.348 MN/m2
Case-400 28 days of curing σcm=1.480 MN/m2 s=0.659 MN/m2
140
1st peak load
120
Load (N)
80
Load (N)
1st peak load
60
1st peak load
Load (N)
Load (N)
Case-200 28 days of curing 80 σcm=0.872 MN/m2 s=0.352 MN/m2
Case-100 28 days of curing σcm=0.369 MN/m2 s=0.108 MN/m2
60
40
100
1st peak load
80 60 40
20 20
0 0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0 0.0
0.2
0.4
Displacement (mm)
0.6
0.8
1.0
1.2
Displacement (mm)
Fig. 2. Relation between load and displacement of single grains.
0.5
q u28= 0.0209C- 0.725
8
6 4
σc m= 0.0037C + 0.065
2
Strength ratio β=σcm/qu28
Strength (MN/m2 )
10
0.3 0.2 0.1 0.0
0 0
100
200
Cement content
300
400
500
C(kg/m3 )
Fig. 3. Relation between cement content and strength of solidified soil.
the loading axis is generated inside the grain, and the grain is considered to be crushed dominantly by the tension stress at the failure state. Therefore, the strength of a single grain measured in this study is equal to the tension strength. It is well known that the ratio between the tension strength and the UCS, obtained from the specimen with the same size of 5 cm in diameter 10 cm in height, lies in the range of 0.15–0.20 (Kitazume et al., 2003). However, the ratio between the strength test results (=tension strength) of a single solidified soil grain with the size of 4.75–9.5 mm and the UCS, obtained from the specimen of 5 cm in diameter 10 cm in height, lies in the range of 0.2–0.3. The strength ratios are different because the size of the specimens for the strength tests is different.
β= -0.0003C+ 0.3293
0.4
0
100
200
300
400
500
Cement content C (kg/m3 ) Fig. 4. Relation between cement content and strength ratio.
3.3. Strength of single rock grains Strength tests for single natural rock grains were carried out using the sample with the same size as the solidified soil grain. Two kinds of rock grains were selected, namely, basalt grains and granite grains. Fig. 5 shows the strength test results for both rock grains. Although the maximum strength of the solidified soil grains in this study was 1.48 MN/m2 (Table 2), the strength of the basalt grains and the granite grains was 3.761 MN/m2 and 6.878 KN/m2, respectively. Therefore, the strength ratios of the solidified soil grains to the rock grains become 39% for the basalt grains and 22% for the granite grains. This reveals that the strength of the solidified soil grains is less than that
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 1,000
800
Basalt σcm=3.761 MN/m2 s=3.351 MN/m2
600
Granite σcm=6.878MN/m2 s=4.725 MN/m2
1st peak load
600
Load (N)
Load (N)
800
5
1st peak load 400
200
200
0 0.0
400
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0 0.0
0.2
Displacement (mm)
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Displacement (mm)
Fig. 5. Relation between load and displacement of single rock grains.
Table 3 Maximum and minimum densities of solidified soil grains. Solidified soil
qmax g/cm3
qmin g/cm3
Specimen q g/cm3
Dr %
Grain-A
A-100 A-200 A-300 A-400
0.849 0.877 0.862 0.877
0.616 0.617 0.663 0.665
0.817 0.828 0.817 0.829
89.6 86.0 81.6 81.7
Grain-B
B-100 B-200 B-300 B-400
0.897 0.903 0.909 0.927
0.712 0.744 0.764 0.766
0.860 0.869 0.880 0.889
83.4 81.7 82.6 79.8
of the natural rock grains for the conditions of cement quantity applied in this study. 4. Material properties of aggregated solidified soil grains 4.1. Maximum and minimum densities of grains Maximum and minimum density tests were carried out for the samples of aggregated solidified soil grains. The test results are shown in Table 3. The maximum density of the sample from Grain-A falls in the range of 0.849– 0.877 g/cm3 compared to 0.897–0.927 g/cm3 of the sample from Grain-B. On the other hand, the minimum density
Water between grains
Solidified soil grain
0.41 m3, 0.43 t
Water
0.42m3, 0.43 t
Soil particle
0.13m3 , 0.31 t
Cement ρsat
1.31g/cm 3,
0.04m3 , 0.14 t ρ`=0.28g/cm3
Fig. 6. Composition of water, soil particles and cement in specimen of solidified soil grains (B-300).
of the sample from Grain-A falls in the range of 0.616– 0.665 g/cm3 compared to 0.712–0.766 g/cm3 of the sample from Grain-B. The maximum and minimum densities of the solidified soil grains tend to increase with the size of the grains. This is because as the size of the grains increases, the proportion of the grain volume occupying the space increases with large voids filled with nonuniform shapes of grains in long and short axes. 4.2. Density of specimen for tri-axial tests The relative density of the specimen for the tri-axial compression tests was around 85% (Table 3). The relative density of 85% was determined by taking into consideration not only the ease with which the specimen could be compacted, but also the importance of not crushing the grains as much as possible. The measured relative density was in the range of 79.8–89.6% due to the influence of the upper surface shaping of the specimen. Fig. 6 shows the composition of the soil particles, the water and the cement in the specimen with a relative density of 85%. From this figure, it is clear that the volume of 83% of the specimen consists of water, and the submerged density becomes 0.28 g/cm3, whereas the density of water is 1.03 g/cm3. Therefore, it is clear that specimens produced from solidified soil grains have lightness compared to those produced from normal sand with a submerged density of 1.0 g/cm3.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
6
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
4.3. Permeability
k ¼ ck ð0:7 þ 0:03T Þ D210
The permeability of the specimen produced from solidified soil grains was obtained from the consolidation process in the tri-axial tests. The consolidation process for the three-axis compression tests and the onedimensional consolidation phenomenon are different in deformation behavior, but since the application of the one-dimensional consolidation theory is considerably easy, Terzaghi’s consolidation theory was applied here to the consolidation process of the specimen in the three-axis compression tests, and the consolidation properties were obtained. The volume compressibility coefficient, mv, was obtained based on Eq. (6), the consolidation coefficient, cv, was obtained based on Eq. (7) and the permeability coefficient, k, was obtained based on Eq. (8). evf mv ¼ ð6Þ Dp
Here, Ck is 150 for uniform particles. T is the temperature which is equal to 20 °C. The unit of k in Eq. (9) is cm/s. Based on Eq. (9), the permeability coefficient of Grain-A is calculated as 1.42 102 m/s and that of Grain-B is 7.80 102 m/s. It is revealed that the test results are 0.1 to 0.4 times lower than the values estimated by Eq. (9).
T vH 2 t k ¼ m v c v cw
ð7Þ
cv ¼
ð8Þ
Here, Dp is the consolidation pressure and Tv is the time factor. When the average consolidation degree is 90%, the time factor value is 0.848. H is equal to 5 cm in drainage distance. t is the consolidation time with the average consolidation degree of 90%. evf is the volume strain at the end of the primary consolidation. cw is the unit weight of the pore water. In the range of consolidation pressure of 50 kN/m2 to 150 kN/m2, the value of the volume compressibility coefficient of the samples from Grain-A and Grain-B was in the range of 3.5 103 m2/kN to 4.5 104 m2/kN. The permeability coefficient of the sample from Grain-A was in the range of 1.17 m/s to 2.46 103 m/s and that from Grain-B was in the range of 1.35 m/s to 2.75 103 m/s. Therefore, it is clear that the permeability coefficients of both grains are considerably higher than that of normal sand at 1 105 m/s (Japanese Geotechnical Society, 2009). In addition, the permeability coefficient of granular materials can be obtained by Hazen’s formula, given in Eq. (9), using a particle diameter of 10%, D10 (cm).
4.4. Volumetric strain Fig. 7 shows the volumetric strains of the solidified soil grains due to the consolidation process and the shearing process under various confining pressure conditions, as well as the two natural rock grains of basalt and granite. The size of the rock grains is the same as that of the solidified soil grains (Grain-B). The volumetric strains of solidified soil grains in both the consolidation process and the shearing process are larger than that of the natural rock grains. In particular, the volumetric strain of the solidified soil grains tends to decrease with the compressive strength of the single grains. In addition, when shear stress was imposed on the specimen after consolidation, the volumetric strain of the specimen from the solidified soil grains increased with the shear strain. However, the volumetric strain of the specimen from the natural rock grains increased first with the shear strain and then decreased with the shear strain due to dilatancy. 4.5. Internal friction angle The Mohr’s stress circles of the specimen from the solidified soil grains obtained from the tri-axial compression tests are shown in Fig. 8. The rupture envelope line can be drawn starting from the zero point (Fig. 8), and the slope of the envelope line tended to decrease with an increase in confining pressure. Therefore, the shear strength can be considered as a secondary function of the confining pressure. Thus, the internal friction angle (ud) can be obtained from Eq. (10). ud ¼ tan1 ðDs=Dr0 Þ
15
10
5
50
100
150
Confining pressure
(kN/m 2 )
200
250
B-100 B-200 B-300 B-400 Basalt Granaite
Shearing process Volumetric strain(%)
B-100 B-200 B-300 B-400 Basalt Granite
Consolidation process Volumetric strain(%)
ð10Þ
20
20
0 0
ð9Þ
15 10 5 0 -5 0
50
100
150
200
250
Confining pressure (kN/m 2 )
Fig. 7. Relation between confining pressure and volumetric strain. Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
Shear strength τ (kN/m 2 )
Shear strength τ (kN/m2)
250
A-200 200 150 100 50
7
250
B-200 200 150 100 50 0
0 0
100
200
300
400
0
500
100
200
300
400
500
Confining stress σ' (kN/m 2 )
Confining stress σ' (kN/m2) Fig. 8. Mohr’s stress circle from tri-axial tests.
50
Grain-A
Internal friction angle ( )
Internal friction angle ( )
50
40
30
A-100 A-200
20
A-300 A-400 10
0
50
100
150
200
250
300
Confining pressure (kN/m2)
40
30
B-100 B-200 B-300 B-400 Basalt Granite
20
Grain-B
10 0
50
100
150
200
250
300
Confining pressure (kN/m 2 )
Fig. 9. Relation between confining stress and internal friction angle.
Internal friction angle ( )
55
single granite grains is considerably higher than that of solidified soil grains, as shown in Fig. 10. The reason why the internal friction angles of granite grains are smaller than those of basalt grains is thought to be because the granite grains have been weathered so that the sharp corners of the particles have disappeared and become round.
50 45 40 B-100
35 30
B-200 d=10.1
B-300
ln(σcm +40.8
B-400
25 20 0
Basalt Granite
1
2
3
4
5
Strength of single grain (MN/m2 )
6
7
Fig. 10. Relation between strength of single grain and internal friction angle.
where, s = E r0 2 + F r0 , and E and F are constants. Fig. 9 shows the relation between the confining pressure and the internal friction angle of both Grain-A and Grain-B. From this figure, it is revealed that the internal friction angle changes with the size of the grains, the cement content and the confining pressure, and that the internal friction angle lies in the range of 30° to 45°. The internal friction angles of the specimens from the natural rock grains are also shown in Fig. 9. The internal friction angles of the basalt grains are higher than those of the solidified soil grains. On the other hand, the internal friction angles of the granite grains are similar to those of the solidified soil grains, but their internal friction angles do not decrease with the increase in confining pressure. This is because the strength of
5. Deterioration property of solidified soil exposed to seawater 5.1. Introduction In order to use solidified soil grains as fill material instead of sand/gravel, it is necessary to investigate the deterioration property of solidified soil. Since it is well known that once a solidified soil is exposed to seawater, a deteriorated layer forms on the outer surface due to the leaching of the calcium that is inside the soil into the seawater, which will reduce the strength of the deterioration layer to nearly zero (Watabe et al., 2016) . For the case of solidified soil grains, the deterioration might be even worse due to the increased contact area between the solidified soil grains and the seawater. Since the deterioration process might significantly reduce the internal friction angles of the solidified soil grains, tests were carried out to investigate the effects of the deterioration on the material properties of the solidified soil mass and the grains.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
8
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
Penetration force (N)
500
Deterioration amount
400 300
(56 days from production)
200
F-55
S-28
100 0
200F-55 200S-28
no-exposure 0
2
4
200-0
6
8
10
Penetration amount (mm) Fig. 11. Needle penetration test results at two curing conditions.
Penetration force (N)
500 400 300 200
200F-34 200F-55 200F-87 200F-177
F-177 F-87 F-55
F-34
no-exposure 100 0 0
2
4
6
8
10
Penetration amount (mm) Fig. 12. Needle penetration test results at some exposure times.
5.2. Deterioration property of solidified soil mass Needle Penetration Tests (NPTs) were conducted using the samples exposed to seawater after 1 day of curing (sub-script: F) and 28 days of curing (sub-script: S). In these tests, a circular pillar, 4 mm in diameter with a flat edge, was penetrated into the test sample at a loading rate of 2 mm/min. The penetration force was measured together with the penetration depth. NPTs are suitable for accurately measuring the distribution of strength of the surface layer portion of deteriorated solidified soil. By comparing the distribution of strength of deteriorated and nondeteriorated samples, the amount of deterioration of the samples can be obtained. If the strength of the solidified soil is too high, the sample will crack when penetrating the needle, making it impossible to obtain the deterioration amount.
Deterioration amount (mm)
12
F-34 F-55 F-87 F-177 S-7 S-28 S-60 S-150
10 8 6 4 2
0 50 100 150 200 250 300 350 400 450 500 550 600
Cement content (kg/m3) Fig. 13. Deterioration amount from needle penetration tests.
Fig. 11 shows the test results for the samples exposed to seawater after 1 day of curing and 28 days of curing. Fig. 12 shows the test results for the samples at some exposure times. The amount of deterioration under the condition of exposure was larger than that under the noexposure condition, and the amount of deterioration increased with the increase in exposure time in the seawater. In order to determine the deterioration amount of a solidified soil, the test results for both the exposure and the no-exposure conditions were studied. As shown in Fig. 11, it was found that the penetration force measured for the samples in the no-exposure condition increased rapidly from zero. However, the penetration force measured for the samples in the exposure condition increased gradually from zero. Thus, the amount of deterioration (D) is defined as follows: (1) As presented in Figs. 11 and 12, the line showing the relationship between the penetration amount (d) and the penetration force (P) in the noexposure condition shifted parallel to fit the line showing the relation in the exposure condition along the axis for the penetration amount. (2) The deterioration amount was defined as the amount of penetration with the penetration force of 0 (P = 0) at the point where both lines coincide well. Fig. 13 shows the relation between the cement content and the amount of deterioration. The deterioration amount grew smaller with an increase in the cement content. Ikegami et al. (2004) proposed Eq. (11) to predict the deteriorated amount (D). However, when Eq. (11) was applied to the test results, it was seen that the prediction did not agree very well with the test results. Therefore, an improved Eq. (12) (Shinsha and Tsutsumi, 2016b) is used in this paper. The results predicted using Eq. (12) are shown in Fig. 14. It can be seen from this figure that the predicted results agree quite well with the test results. Eq. (12) is an empirical equation. However, as the value of B is very small, even if the amount of degradation after several years with B in Eq. (12) as 0 is estimated, the revealed error will be small, where t is the time (year), A is a material fixed coefficient that shows the amount of deterioration after 1 year and B is a material fixed number. D ¼ A t0:5
ð11Þ
D ¼ A ðt0:5 BÞ
ð12Þ
In the prediction of the deterioration amount, the cement content (C) and the unconfined compressive strength (UCS) are the two key factors. Since both the cement content and the UCS are related to the total volume of Ca2+, the deterioration is caused by the loss of Ca2+. The relation between the UCS after 28 days of curing and the cement content has already been shown in Eq. (4). Based on Eq. (4) and Fig. 14, the relationship between the UCS and a material fixed coefficient of A is obtained as shown by Eq. (13). A ¼ 6:038 lnðqu28 Þ þ 15:834
ð13Þ
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 12
100F 200F 300F 400F
10 8
Deterioration amount (mm)
12
Deterioration amount (mm)
9
D= 17.86(t 0.5 - 0.0770)
6
D = 11.72(t 0.5- 0.0903)
4
D = 6.640(t 0.5 - 0.0840) D= 0.991(t 0.5- 0.2374)
2 0 0.2
0.4
0.6
0.8
Exposure time
1.0
10 8
100S 200S 300S
D = 13.54(
6
D = 7.999(
0.5-
0.0861)
0.5-
0.0930)
4 2 0 0.0
D= 4.626(t 0.5 - 0.0833) 0.2
0.4
0.6
0.8
1.0
Exposure time t 0.5
t 0.5
Fig. 14. Relation between exposed time and deterioration amount.
Material fixed number A
30
A =-6.038
ln(qu ) +15.834 F : after 1 day of curing
Membrane
Man-made seawater
S : after 28 days of curing
20
Hara(2013)
Rubber band
SGM3)
Test piece
Container of half-sawing φ5cm H10cm
PFM 2)
10
CDM4) 0 0.1
1
2 sticks
Concrete 0.5 0.8 10
Porous stone
100
Unconfined compressive strength q u28 (MN/m2)
Water tank
Fig. 15. Relation between qu28 and A.
Fig. 17. Installation of specimen in seawater.
Material fixed number B
0.3 F : 1 day of curing S : 28 days of curing
0.2
B=0.0856
0.1
0.0
0.1
1
10
100
the seawater, it is possible to use the solidified soil grains with the UCS higher than the NDS as an alternative material to sand/gravel. The value for B, set at approximately 0.0856, is presented in Fig. 16. With regard to the leaching of calcium from the surface of solidified soil into the seawater, the reference of Hara et al. (2013) is helpful. They have observed that the calcium ion in solidified soil is leached by the salt in the seawater that contains magnesium ions.
Unconfined compressive strength q u28 (MN/m2) Fig. 16. Relation between qu28 and B.
The coefficient of A to be estimated by Eq. (13) is drawn in Fig. 15 and compared with the test results for other types of solidified soils in previous studies, such as the lightweight treated soil referred to as Super Geo-Material (Tsuchida et al., 2004), pneumatic flow mixing soil (Kitazume, 2017) and cement deep-mixing soil (Ikegami et al., 2002). It is found that Eq. (13) can be applied to other types of solidified soil materials as well as to the soil proposed in this study. Based on Eq. (13), deterioration coefficient A becomes almost zero under the condition whereby the UCS exceeds approximately 14 MN/m2. Here, this 14 MN/m2 can be referred to as the non-deterioration strength (NDS) of the solidified soil. It is thought that since the solidified soil grains with the UCS higher than the NDS will hardly be deteriorated by the leaching of calcium into
5.3. Deterioration property of solidified soil grains The deterioration property of the solidified soil grains was also examined through tri-axial compression tests. The tri-axial compression tests were carried out for the test samples under the exposure times of 0 day, 60 days and 150 days, respectively. The installation procedure for a specimen is described below and is shown in Fig. 17: (1) The bottom of a halfsawing container, 5 cm in diameter and 10 cm in height, was removed first and 2 points at the top and the bottom of the container were fixed by rubber bands. (2) A rubber membrane, 0.25 mm in thickness, was set inside the container, and a porous stone, 5 mm in thickness, was put at the bottom of the container. (3) Solidified soil grains with a relative density of 85% were placed inside the container. (4) Tri-axial compression tests were carried out with cell pressures of 50 kN/m2, 100 kN/m2 and 150 kN/m2, respectively.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
10
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx 20
σr '=100 kN/m2
Consolidation process
20
B-100 B-200 B-300 B-400
10
0
0
50
100
150
200
Volumetric strain εv2 (%)
Volumetric strain εv1 (%)
30
σr '=100 kN/m2
Shearing process 10
B-100 B-200 B-300 B-400 0
250
0
50
100
150
200
250
Exposure time (day)
Exposure time (day) Fig. 18. Volumetric strain from tri-axial tests.
Shear strength (kN/m 2 )
300
considerably larger than that of the samples under the exposure time of 0 day without any deterioration. The volumetric strain (ev2) from the shearing process after consolidation, obtained at 15% of axial strain, is also shown in Fig. 18. According to the test results under the exposure time of 0 day without any deterioration, the volumetric strain of the samples clearly decreased as the grain strength increased, due to the comparison of the results of the test cases of B-100 and B-400. On the other hand, the volumetric strain of the samples under the exposure times of 60 and 150 days are similar in all test cases of B-100 to B-400. This is thought to be the influence of the deteriorating surface of the grains and the layer with weak strength forming on the samples in all test cases.
B-300-0 B-300-60 B-300-150
250 200 150 100 50 0 0
100
200
300
400
500
600
Confining stress (kN/m 2 ) Fig. 19. Mohr’s stress circle from tri-axial compression tests.
(1) Volumetric strain The volumetric strain obtained from the tri-axial compression tests is shown in Fig. 18. The volumetric strain (ev1) from the consolidation process will become larger if the cement content is less. It is thought that for the case without any deterioration, volumetric strain (ev1) will only be caused by the re-arrangement and the crushing of the grains. On the other hand, for the case with deterioration, the additional volumetric strain due to the consolidation of the deteriorated soil forming on the outer surface of the grains and the movement of the deteriorated soil into the voids between the grains will be added to that of the case without any deterioration. It can be seen from the test results, shown in Fig. 18, that the volumetric strain (ev1) of the samples under the exposure time of 60 days is
100S-0 100S-60 100S-150 200S-0 200S-60 200S-150
40
Internal friction angle ( )
Internal friction angle ( )
The Mohr’s stress circles from the tri-axial compression tests are shown in Fig. 19. After the comparison of the Mohr’s stress circles of the samples under the exposure times of 0 day, 60 days and 150 days, it can be concluded that the Mohr’s stress circles become smaller with the increase in exposure time. The results from Fig. 20 show that for the case of no-deterioration, the internal friction angle becomes larger with the increase in cement content. Meanwhile, for the case of deterioration, the internal friction angle is smaller compared to that without any deterioration. 50
50
30
20
(2) Internal friction angle
40
20
0
50
100
150
Confining pressure (kN/m 2)
200
300S-0 300S-60 300S-150 400S-0 400S-60 400S-150
30
0
50
100
150
200
Confining pressure (kN/m2)
Fig. 20. Relation between confining pressure and internal friction angle. Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003
H. Shinsha, T. Kumagai / Soils and Foundations xxx (2018) xxx–xxx
6. Conclusions Solidified soil grains are produced by crushing a solidified soil mass made of dredged soil mixed with cement. The main conclusions obtained from the tests on solidified soil grains are as follows: (1) The strength of single solidified soil grains produced by the maximum addition of 400 kg/m3 of cement in this study is 1.48 MN/m2. This strength is smaller compared to 3.77 MN/m2 of natural basalt grains and 6.88 MN/m2 of natural granite grains. In order to achieve desirable strength as large as that of natural gravel, additional measures should be considered in future research works. (2) The aggregated solidified soil grains have the desirable feature of permeability with the permeability coefficient in the range of 1.17–2.75 103 m/s, which is considerably higher than that of normal sand, namely, 1 105 m/s. (3) The aggregated solidified soil grains have the desirable feature of unit weight with the saturated density of the aggregated solidified soil grains underwater with the relative density of 85% of 1.28 g/cm3, which is smaller than that of normal sand, namely, 2.0 g/cm3. (4) The internal friction angle of the aggregated solidified soil grains changes with the size of the grains, the cement content and the confining pressure ranging from 30 to 45°. The desirable feature of the shear strength is confirmed for the aggregated solidified soil grains. (5) The solidified soil grains tend to deteriorate in seawater; however, the deterioration rate decreases with the increase in strength. It is confirmed that the amount of deterioration D is proportional to the square root of the time passed, and an improved equation for estimating D is proposed, as shown in Eq. (12). At this point, the material fixed coefficient of A to be used in Eq. (12), which governs the deterioration rate, is formulated by a correlation with the strength of the soil, as shown in Eq. (13). The validity of the proposed formula is verified by a comparison with the test results of the previous studies. (6) Based on Fig. 15, where the unconfined compressive strength (USC) reaches approximately 14 MN/m2, the progress of the deterioration becomes negligible. Therefore, it is thought that the solidified soil grains produced by crushing the mass with the USC higher than 14 MN/m2 will hardly be deteriorated by the leaching of calcium. (7) At the site where the loading conditions do not exceed the threshold to cause the crushing failure of the grains, the solidified soil grains are expected to
11
be applicable on land as quasi-alternative material to sand/gravel with the desirable features of permeability, internal friction angle and unit weight considering less strength compared with natural rocks. Moreover, in cases where the mass of the solidified soil has unconfined compression strength (USC) over 14 MN/m2, the solidified soil grains to be produced by crushing are hardly deteriorated for a long period, and they can be similarly applied even under seawater conditions.
References Coastal Development Institute of Technology, 2002. The Deep Mixing Method, A BALKEMA BOOK, 123p. Dong, P., Hayano, K., Kikuchi, Y., Takahashi, H., Morikawa, Y., 2011. Deformation and crushing of particles of cement treat granulate soil. Soils Found. 51 (4), 611–624. Fujii, K., 1986. Condition and properties of bound water. Cem.-Concr. 469, 2–9 (in Japanese). Hara, H., Suetsugu, D., Hayashi, S., Matsuda, H., 2013. Deterioration mechanism of cement-treated soil under seawater. J. Civil Eng. 69 (4), 469–479 (in Japanese). Hayano, K., Yamauchi, H., Sasaki, K., Fujishima, K., 2014. Fundamental study on a new granulation method with the process of crumbling partially-cemented liquid muds. J. JSCE, Div. C 70 (4), 424–432 (in Japanese). Ikegami, M., Masuda, K., Ichiba, T., Tsuruya, K., Satou, S., Terashi, M., Oishi, K., 2002. Soundness of submarine clay improved by the cement deep mixing method after 20 years. In: The 57th Annual Meeting Lecture Collection of JSCE, pp. 121–122 (in Japanese). Ikegami, M., Satou, S., Ichiba, T., Osoku, N., Nishida, T., Terashi, M., 2004. Simple prediction method on degradation progression of cement stabilized soil, in: The 59th Annual Meeting Lecture Collection of JSCE, pp. 1073–1074 (in Japanese). Japan Cement Association, 2012. Ground Improvement Manual by Cementitious Solidification Material, fourth ed., Gihodo Publication, pp. 29–32 (in Japanese). Japanese Geotechnical Society, 2009. Japanese Geotechnical Society Standards- Laboratory Testing Standards of Geomaterials, vol. 1, 262p. Kitazume, M., 2017. The Pneumatic Flow Mixing Method, A BALKEMA BOOK, 233p. Kitazume, M., Hayano, K., Hashizume, H., 2003. Seismic stability of cement treated ground by tilting and dynamic shaking table tests. Soils Found. 43 (6), 25–140. Shinsha, H., Tsutsumi, A., 2016a. Strength characteristics of crushed cement-mixed soil as granular geomaterials. J. JSCE, Div. C 72 (2), 74– 85 (in Japanese). Shinsha, H., Tsutsumi, A., 2016b. Experimental study on deterioration of cement-mixed soil and crushed particles in seawater. J. JSCE, Div. C 72 (3), 265–276 (in Japanese). Tsuchida, T., Egashira, K., 2004. The Lightweight Treated Soil Method, A BALKEMA BOOK, 120p. Watabe, Y., Kikuchi, Y., Shinsha, H., 2016. Long-Term Properties of AirFoam Treated Lightweight Soil Cured in Seawater, 19SEAGC & 2AGSSEA, Kuala Lumpur, 31 May–3 June.
Please cite this article in press as: Shinsha, H., Kumagai, T., Material properties of solidified soil grains produced from dredged marine clay, Soils Found. (2018), https://doi.org/10.1016/j.sandf.2018.03.003