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Friction characteristics of organic soil with construction materials
Soils and Foundations ]]]];](]):]]]–]]]
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The Japanese Geotechnical Society
Soils and Foundations www.sciencedirect.com journal homepage: www.elsevier.com/locate/sandf
Friction characteristics of organic soil with construction materials Hanifi Canakcia, Majid Hamedb, Fatih Celika,n, Waleed Sidikb, Fevzi Eviza a
Department of Civil Engineering, Gaziantep University, Gaziantep, Turkey b Department of Civil Engineering, Kerkuk University, Kerkuk, Iraq
Received 14 April 2015; received in revised form 19 April 2016; accepted 17 May 2016
Abstract Understanding the basic phenomena controlling the mobilization of friction at the soil-solid surface contact is essential for such traditional foundation structures such as piles, micropiles and anchors. In this study, the interface frictional characteristics of organic soil and a variety solid construction materials, including concrete, steel, and wood, were investigated. The interface friction angles of organic soil-solid surfaces were determined for different water content and granular soil content. In addition, the relationship between surface roughnesses and interface friction was investigated. All tests in this study were performed using a direct shear test device under different normal stresses. The test results showed that the frictional resistance between construction material and organic soil is affected by the water and granular soil content of the organic soil, the type of material, and the surface roughness. & 2016 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Organic soil; Construction materials; Interface friction angle; Surface roughness
1. Introduction Organic soil is a mixture of fragmented organic material formed in wetlands under appropriate climatic and topographic conditions, derived from vegetation that has been chemically changed and fossilized (Dhowian and Edil, 1980). This type of soil has low shear strength and high compressive deformation (Anggraini, 2006). Though there are a variety of improvement methods which can be adopeted, problems with bearing capacity and settlement are generally solved by using pile foundations. Friction piles tend to be the pile foundations of choice in this type of soil: they transfer the load to the soil through interface friction between soil and pile material. One n
Corresponding author. E-mail addresses: [email protected] (H. Canakci), [email protected] (M. Hamed), [email protected] (F. Celik), [email protected] (W. Sidik), [email protected] (F. Eviz). Peer review under responsibility of The Japanese Geotechnical Society.
of the important parameters for frictional resistance is the friction coefficient between the pile material and the soil. The majority of the design interface friction values are based on empirical correlations. They are related to soil shear strength parameters. In current geotechnical engineering practices, the soil–structure friction values recommended by the Naval Facilities Engineering Command (NAVFAC) Design Manual (DM) 7.02 (US Department of Navy, 1986) are widely adopted. An extensive series of investigations on this topic has already been performed by several authors both in laboratory and in situ (Potyondy, 1961; Coyle and Sulaiman, 1967; Kulhaway and Peterson, 1979; Evgin and Fakharian, 1996; Hryciw and Irsyam, 1993; Uesugi et al., 1988; Hu and Pu, 2004; Canakci et al., 2011; Celik and Canakci, 2014; Nasir and Fall, 2008). Potyondy (1961) measured the ratio of skin friction and adhesion with soil friction and cohesion, respectively. He performed direct shear tests on the interface of concrete, steel, and wood with sand, sandy silt, cohesive soil,
http://dx.doi.org/10.1016/j.sandf.2016.11.002 0038-0806/& 2016 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
H. Canakci et al. / Soils and Foundations ] (]]]]) ]]]–]]]
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rock flour, and clay. The tests were conducted for certain preset moisture contents as well as for dry specimens. The results showed that the frictional resistance of a soil depends on the amount of mixed sand it possesses. Coyle and Sulaiman (1967) investigated the frictional resistance between sand and the steel pile, and Kulhaway and Peterson (1979) measured the frictional resistance between sand and concrete. Several other researchers such as Evgin and Fakharian (1996), Hryciw and Irsyam (1993), Uesugi et al. (1988) and Hu and Pu (2004) conducted direct shear tests on the interface between steel or concrete and sand to measure the interface frictional resistance. As an alternative to the direct shear device, Paikowsky et al. (1995) developed a dual interface apparatus. In addition, Yoshimi and Kishida (1981) developed a ring shear device to measure interface frictional resistance for large deformations. The previous studies showed that several factors affect the value of the interface friction angle. These factors are their mineralogical composition, density, grain shape, grain size and gradation, as well as the roughness of the material surface (Uesugi and Kishid, 1986; Lambe and Whitman, 1979; Yoshimi and Kishida, 1981). A survey of existing literature showed that limited information is available for practicing engineers about interfacial friction between organic soil and various construction materials. In this study, an intensive investigation was carried out to determine interface friction values. For this purpose, concrete, smooth and rough steel, and wood were selected as structural materials. Tests were done at different water contents and different granular soil content in the organic soil. All tests were performed using the direct shear test device.
Fig. 1. Classification system for peat deposits (Wüst et al., 2003).
Table 1 Engineering properties of the organic soil. Properties of organic soil Organic content (%) pH Natural water content (%) Liquid limit (%) Plasticity index (%) Specific gravity
70 5.0 256 125 None plastic 1.97
2. Materials and methods 2.1. Organic soil The organic soil used in this study was obtained from the Sakarya region of Turkey. This peat was bought from a commercial firm as packed peat. Once the peat was delivered to the laboratory, all of it was dried in an oven. Its moisture content was determined before testing. Since it is quite difficult to prepare organic soil samples with high water content for the tests proposed, peat of four different moisture contents as selected for this work. The properties of peat soils, including their natural water content, acidity, degree of humification, fiber content, shear strength, and compressibility, are affected by the formation of peat deposit (Ajlouni, 2000). This indicates that in terms of content, fibrous peat is different from one location to another (Berry and Poskitt, 1972; Ajlouni, 2000; Robinson, 2003). Sakarya peat (natural soil) has herbaceous characteristics, and can absorb 3–4 times its weight of water with respect to its decomposition rate. Its initial density ranges from 0,121 to 0,217 g/ cm3. Remoulded soil has a dry density of 6,44 kN/m3 and an optimum moisture content of 58%. The fibrous peat used for all tests was passed through a 2 mm sieve size and retained on a 100 (0.15 mm) sieve. Organic soil is classified as
Fig. 2. Construction materials used in the test; (a) smooth steel (b) rough steel (c) concrete and (d) wood.
peat by both the Unified Soil Classification System (USCS) and the Wüst et al. (2003) classification chart shown in Fig. 1. It is also classified as fibric according ASTM D 1997, high ash according to ASTM D 2974, and moderately acidic according to ASTM D 2976. Organic soil can also be classified according to its decomposition rate. According to the Von Post (1922) scale, the decomposition rate changes from H1 to H10. In this
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
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Fig. 3. Soil testing method used in this study; (a) lower and upper box of the direct shear device used for this study and (b) lower shear box, filled with the structural material.
2.3. Structural materials
Table 2 Mix proportions of the soils used in the tests. Material type Sand content (%) (CS-RS)a
W/O (%)
Sand (g)
Organic soil Water (g) (g)
Wood Concrete Smooth steel Rough steel
0,75
0 4,29 8,57 30 25,71 Water (g)
42,86 32,14 38,57 34,28 12,85 17,14 Organic soil Sand (g) (g) 55 20 49,5 44 38,5 33
a
0 10 20 30 40 Water content (%) (CS-RS)a 0 8 17 28 41,5
S/O (%) 40
0 5,5 11 16,5 22
To evaluate the interface frictional resistance between organic soil and solid structural materials, four plates of commonly used construction materials were prepared; concrete, rough and smooth steel, and wood. The steels plates used in this study were prepared in the laboratory from metal sheets. The concrete plate was prepared in the laboratory using aggregates and cements, and cast in food frame, while the wood plate used in this study was cut from a pine tree. The construction materials used in the study are shown in Fig. 2. The dimeansions of all types of structural materials were 60 60 10 mm, exactly the same size as the lower box under the direct shear device.
CS: crushed sand; RS: rounded sand.
2.4. Testing method rating system, rather than the water content itself being the main parameter, the main parameter is the color of water obtained after squeezing the original peat. Therefore, peat from different regions may have the same decomposition rate but a different water content. The decomposition rate of the organic soil used in this study was in the range of H1–H4. The organic content was estimated after firing the soil at 440 1C in an oven for 4 h, according to ASTM D 2974. According to this process, the ash content of the soil was 30% and its organic content was 70%. According to Hartlen and Wolski (1996), fibrous peat with a fiber content of more than 60% usually falls into a decomposition rate ranging between H1 and H4. The liquid limit of the organic soil was estimated by the fall cone test according to ASTM D 4318 and found to be 119%. The engineering properties of the organic soil are listed in Table 1.
2.2. Sand Two types of sand, rounded and angular, were used in this study. Both of them were poorly graded, passing through the 2 mm sieve size and then retained on the 0.425 mm sieve. These types of sandy soil were used to test the effect of particle shape on interface friction.
A fully automated direct shear device was used in this study. The dimensions of the upper part of the shear box filled with organic soil were 60 60 15 mm (Fig. 3a). To perform the interface tests between organic soil and solid materials, the lower box of the direct shear device was completely blocked by the solid plates (Fig. 3b). The internal friction angle of the original soil was 431 and the cohesion was 5.8 kPa. The peat was bought from a commercial firm in the form of packed peat, and was then oven-dried. Then, the peat was separated according to its moisture content. The samples were consolidated under different vertical loads (30, 60, 120 kPa) before testing. Organic soil samples with different water content and sand-organic content were prepared. The temperature during the test was at room temperature (24 1C) and all of the tests were consolidated and drained (CD). To investigate the effect of the sand content in the organic soil on the interface friction angle, 10%, 20%, 30%, and 40% sand by weight was mixed with the organic soil. For this series of tests, the water content was kept constant (w¼ 0.75). In the second series of tests, the effect of the water content on the interface friction angle was investigated. Various water contents were used, 8%, 17%, 28%, and 41,5%, respectively, and the granular soil content was considered to be 40%. The density of the soil was kept
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
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Fig. 4. Surface waves with respect to surface length; (a) concrete (b) wood (c) rough steel and (d) smooth steel.
Fig. 5. Shear stress–horizontal displacement curves for 120 kPa normal load (a) 40% crushed sand content and (b) 40% rounded sand content.
Fig. 6. Vertical displacement–horizontal displacement curve for 120 kPa normal load (a) crushed sand 40% sand content, and (b) rounded sand 40% sand content.
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Fig. 8. Shear envelopes for the organic soil–construction materials interfaces for 40% granular soil (a) dry and (b) 40% water content.
Fig. 7. Shear envelopes for the organic soil–construction materials interfaces for (a) 0% crushed sand content (b) 40% crushed sand content (c) 0% rounded sand content. (d) 40% rounded sand content.
constant at 1.39 g/cm3 for all mixtures. The testing program and mix proportions are presented in Table 2. During the shearing test, the rate of shearing displacement was kept equal to 1 mm/min for all tests. Three different normal stresses (30, 60, and 120 kPa, respectively) were used and the shear stress at 10% horizontal displacement of the box was considered the maximum shear stress. The roughness index of the material surface is also an important parameter which influences the interface friction angle. The roughness index is a function of the smoothness of the structural materials (Sayers, 1995). Rough surfaces usually have higher friction coefficients than smooth surfaces. The surface roughness is quantified by the vertical deviations of the real surface from its ideal form. If these deviations are large, the surface is considered to be rough; if they are small, the surface is smooth (Kwang et al., 1992). The roughness coefficients of the structural materials were estimated by using an electronic dial guage. This dial guage was moved on surface of the structural materials and the readings were taken by a data logger and recorded. For each of the plates, measurement were taken at different points along the centerline from the edges of the plates. Fig. 4 shows the surface waves for each of
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
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Fig. 10. Effect of water content on interface friction angle.
Fig. 9. Changes in interface friction angle with respect to shape of sand (w ¼75%) (a) crushed sand, and (b) rounded sand.
the construction materials. These figures were used to calculate the Roughness index as described by Kwang et al. (1992). 3. Results and discussion Typical direct shear test results for different organic soilconstruction material interfaces are presented and discussed in this section. Generally, shear test results are presented in three types of graphs: (1) the shear stress–horizontal displacement curves, (2) the horizontal shear displacement–vertical deformation curves, and (3) the shear strength envelopes, which give the interface shear strength parameters (cohesion or adhesion, c; friction angle, φ). The typical shear stress versus horizontal displacement performed on the organic soil containing 40% angular and rounded sand under 120 kPa normal stress is shown in Fig. 5a and b. These figures show a relatively similar trend and shape. In addition, it can be seen from the figures that the interface shear stress increases gradually with horizontal displacement until a certain amount of deformation takes place, beyond which it becomes relatively constant. The curves showed a slight strain softening behavior. Since the maximum horizontal
deformation reached for all the tests was 10% shear deformation, the residual shear condition could not be achieved in the tests. Similar behavior was observed for the same soils under different normal stresses for all the construction materials tested. In all tests, the maximum shear stress values were obtained at the interface between the organic soil and concrete, while the minimum values were observed at the interface between the organic soil and smooth steel. Fig. 6a and b shows the typical results of horizontal shear displacement versus vertical displacement of the interface between organic soil containing 40% crushed and rounded sand and construction materials under 120 kPa normal stress. A larger amount of vertical displacement was observed for specimens under an applied normal stress of 120 kPa due to the higher reduction of local voids associated with higher applied normal stress for all the interface surfaces (Plesha, 1987; Kamari and Stead, 2008). This behavior may be attributed to the degradation of the organic soil due to relatively high applied normal stresses. The effect of granular content in the organic soil has very little effect on the amount of vertical displacement during shearing on the construction material interface. This may be due to the sand particles embedded in the soft organic soil at the interface. Figs. 7a and d and 8a and b show typical interface shear strength envelopes for construction material and organic soil mixed with rounded and angular sand. These envelopes were drawn by using three normal stresses and corresponding shear stresses for each test. A linear regression line was fitted through the set of interface shear stress versus normal stresses data. The strength values of all the tests were taken at 10% shear deformation: they provide an excellent straight line fit with R2 values around 0.99. For each regression line, values of interface friction angles and adhesions were obtained from linear curves shown in Figs. 7a and d and 8a and b. The results are consistent with expected trends in behavior where the shear strength increases with increasing normal stress. It can be seen from Fig. 7a and d, that regardless of the type of construction material, the strength data can be well described by a Mohr–Coulomb failure criterion. It can also be seen from this figure that organic soil mixed with two types of sand showed
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
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Fig. 11. Friction parameters of the construction materials (a) coefficient of friction and (b) surface roughness.
relatively similar adhesion values, both of which were very small. As it is clearly seen from Fig. 7a and d, the highest shear strength values were observed between organic soil and concrete at all normal stresses. On the other hand, the smallest one was obtained when smooth steel was used. This can be explained by surface roughness of the construction materials used in the study. These results indicate that the values of shear stress are directly related to surface roughness. This finding concurs with the findings reported in the existing literature (Potyondy, 1961; Gireesha and Muthukkumaran, 2011). Fig. 8a and b, clearly shows that the increase of water content decreases the interface shear strength between the soil– concrete and soil–wood. On the other hand, water has very limited effect on the interface shear strength between soil–steel. This can be explained by the increase in the slipperiness of the surface of construction materials due to the addition of water in organic soil, and the resultant reduction in shear stress at the interface. The comparison of the results of interface shear tests presented above suggest that the sand and water content of organic soil have a significant impact on the mechanical behavior at the interface between organic soil–sand mixtures and construction materials (Fig. 9a and b). The results also an increase in the interface friction angle of organic soil with granular particles tends the interface of construction materials as the sand content increases. This can be attributed to the frictional resistance between the construction materials and individual sand particles. The highest interface friction angles at different sand contents were observed in the concrete interface. On the other hand, the smallest ones were observed for smooth steel at same condition (Tiwari and Al-Adhadh, 2014). Moreover, as it is clearly seen from Fig. 9a and b, the shape of the sand particles in the organic soil (crushed or rounded) does not have much effect on the interface friction angle. Fig. 10 shows the effect of the water content on the interface friction angle between organic soil and construction materials. As can be seen from the graph, concrete and wood were
affected by the water content. An increase in water content of the organic soil resulted in a reduction in the interface friction for these two materials. On the other hand, water was shown to have a very limited effect on the interface friction angle in the case of steel. The coefficient of friction and surface roughness values (Ra) for construction materials are shown in Fig. 11a and b. As can be seen from the figures, the highest coefficient of friction (0.67) and surface roughness (330 mm) values among all the constructon materials were obtained for the concrete. On the other hand, the smallest coefficient of friction (0.39) and surface roughness (35 mm) values were measured for smooth steel. The results showed that the coefficient of friction value was directly related to surface roughness (Ra) for organic soil. The internal friction angle of organic soil used in this study (431) and other organic soil reported in the literature (40–601; Mesri and Ajlouni, 2007) are high compared to the measured interface friction angle. It indicates that all the failures which occurred were between the soil samples and construction material but not inside the soil samples themselves.
4. Conclusion In this study, the interface shear behavior of organic soil and construction material was evaluated using a direct shear test apparatus. The following conclusions were drawn. Test results showed that the highest interface friction angle was obtained between the organic soil and the concrete, and that this was higher than that of other construction materials regardless of the shape of the soil particles. On the other hand, the lowest interface friction angle was observed in the case of smooth steel. It was also found that the shape of the sand particles had no affect on the interface friction for any of the construction materials with added content. An increase in the water content of organic soil decreased the interface friction angle for both concrete and the wood. The study also showed a strong correlation between the surface roughness (Ra) of the
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
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construction material and coefficient of the interface friction angle for organic soil. References Ajlouni, M.A., 2000. Geotechnical Properties of Peat and Related Engineering Problems (Ph.D. thesis). University of Illinois, Urbana-Champaign. Anggraini, V., 2006. Shear Strength Improvement of Peat Soil due to Consolidation. (The Degree of Master of Engineering thesis). Berry, P.L., Poskitt, T.J., 1972. The consolidation of peat. Geotechnique 22 (l), 27–52. Canakci, H., Yavuz, H.E., Celik, F., Güllü, H., 2011. Interface friction between organic soil and construction materials. In: Proceedings of the International Balkans Conference on Challenges of Civil Engineering. BCCCE, 19–21 May 2011, EPOKA University, Tirana, Albania. Celik, F., Canakci, H., 2014. An investigation of the effect of sand content on geotechnical properties of fibrous peat. Arab. J. Sci. Eng. 39, 6943–6948. http://dx.doi.org/10.1007/s13369-014-1298-x. Coyle, H.M., Sulaiman, I., 1967. Skin friction for steel piles in sand. J. Soil Mech. Found. Div. 97 (12), 1657–1673. Dhowian, A.W., Edil, T.B., 1980. Consolidation behavior of peats. Geotech. Test. J. 3 (3), 105–114. Evgin, E., Fakharian, K., 1996. Effect of stress paths on the behavior of sand– steel interfaces. Can. Geotech. J. 33 (6), 485–493. Hryciw, R.D., Irsyam, M., 1993. Behavior of sand particles around rigid inclusion during shear. Soils Found. J. 33 (3), 1–13. Hu, L., Pu, J., 2004. Testing and modeling of soil-structure interface. J. Geotech. Geoenviron. Eng. 130 (8), 851–860. Gireesha, T., Muthukkumaran, K., 2011. Study on soil-structure interface strength properties. Int. J. Earth Sci. Eng. 4 (6), 89–93. Kamari, A., Stead, D., 2008. Asperity degradation and damage in the direct shear test: a hybrid FEMDEM approach. Rock Mech. Rock Eng. J. 41 (2), 229–266. Kulhaway, F.H., Peterson, M.S.,1979. Behavior of sand and concrete interfaces. In: Proceedings of the 6th Pan American Conference on Soil Mechanics and Foundation Engineering. Brazil, 2, pp. 225–230.
Kwang, H.J.; Morosiuk, G., Emby, J.,1992. Assessment of skid resistance and macro texture of bituminous road surface in Malaysia. In: Proceedings of the Seventh REAA Conference. Singapore, pp. 443–449. Lambe, T.W., Whitman, R.V., 1979. Soil Mechanics, SI version. John Wiley & Sons, Inc., New York. Mesri, G., Ajlouni, M., 2007. Engineering properties of fibrous peat. J. Geotech. Geoenviron. Eng. ASCE 133 (7). Nasir, O., Fall, M., 2008. Shear behaviour of cemented pastefill-rock interfaces. Eng. Geol. 101, 146–153. Paikowsky, S.G., Player, C.M., Connor, P.J., 1995. A dual interface apparatus for testing unrestricted friction of soil along solid surfaces. Geotech. Test. J. 18 (2), 168–193. Plesha, M., 1987. Constitutive models for rock discontinuities with dilatancy and surface degradation. Int. J. Numer. Anal. Methods Geomech. 11, 345–362. Potyondy, J.G., 1961. Skin friction between various soils and construction materials. Geotechnique 11 (4), 339–353. Robinson, R.G., 2003. A study on the beginning of secondary compression of soils. J. Test. Eval. 31 (5), 1–10. Sayers, M.W., 1995. Profiles of Roughness. Transport Research Board (TRB), Washington D.C., no.1260. Tiwari, B., Al-Adhadh, A.R., 2014. Influence of relative density on static soil– structure frictional resistance of dry and saturated sand. Geotech. Geol. Eng. 32, 411–427. US Department of Navy, 1986. NAVFAC Engineering Manual, EM 7.02/. Uesugi, M., Kishida, H., Tsubakihara, Y., 1988. Behavior of sand particles in sand–steel friction. Soils Found. 28 (1), 107–118. Uesugi, M., Kishida, H., 1986. Influential factors of friction between steel and dry sands. Soil Found. 26 (2), 33–46. Von Post, L., 1922. Sveriges Geologiska Undersoknings torvinventering och nagre av dess hittills vunna resultat. Sr. Mosskulturfor. Tidskr. 1, 1–27. Wüst, R., Bustin, R.M., Lavkulich, L.M., 2003. New classification systems for tropical organic-rich deposits based on studies of the Tasek Bera Basin, Malaysia. Catena 53, 133–163. Yoshimi, Y., Kishida, T., 1981. A ring torsional apparatus for evaluation of friction between soil and metal surface. Geotech. Test. J. 4 (4), 145–152.
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
HOSTED BY
The Japanese Geotechnical Society
Soils and Foundations www.sciencedirect.com journal homepage: www.elsevier.com/locate/sandf
Friction characteristics of organic soil with construction materials Hanifi Canakcia, Majid Hamedb, Fatih Celika,n, Waleed Sidikb, Fevzi Eviza a
Department of Civil Engineering, Gaziantep University, Gaziantep, Turkey b Department of Civil Engineering, Kerkuk University, Kerkuk, Iraq
Received 14 April 2015; received in revised form 19 April 2016; accepted 17 May 2016
Abstract Understanding the basic phenomena controlling the mobilization of friction at the soil-solid surface contact is essential for such traditional foundation structures such as piles, micropiles and anchors. In this study, the interface frictional characteristics of organic soil and a variety solid construction materials, including concrete, steel, and wood, were investigated. The interface friction angles of organic soil-solid surfaces were determined for different water content and granular soil content. In addition, the relationship between surface roughnesses and interface friction was investigated. All tests in this study were performed using a direct shear test device under different normal stresses. The test results showed that the frictional resistance between construction material and organic soil is affected by the water and granular soil content of the organic soil, the type of material, and the surface roughness. & 2016 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Organic soil; Construction materials; Interface friction angle; Surface roughness
1. Introduction Organic soil is a mixture of fragmented organic material formed in wetlands under appropriate climatic and topographic conditions, derived from vegetation that has been chemically changed and fossilized (Dhowian and Edil, 1980). This type of soil has low shear strength and high compressive deformation (Anggraini, 2006). Though there are a variety of improvement methods which can be adopeted, problems with bearing capacity and settlement are generally solved by using pile foundations. Friction piles tend to be the pile foundations of choice in this type of soil: they transfer the load to the soil through interface friction between soil and pile material. One n
Corresponding author. E-mail addresses: [email protected] (H. Canakci), [email protected] (M. Hamed), [email protected] (F. Celik), [email protected] (W. Sidik), [email protected] (F. Eviz). Peer review under responsibility of The Japanese Geotechnical Society.
of the important parameters for frictional resistance is the friction coefficient between the pile material and the soil. The majority of the design interface friction values are based on empirical correlations. They are related to soil shear strength parameters. In current geotechnical engineering practices, the soil–structure friction values recommended by the Naval Facilities Engineering Command (NAVFAC) Design Manual (DM) 7.02 (US Department of Navy, 1986) are widely adopted. An extensive series of investigations on this topic has already been performed by several authors both in laboratory and in situ (Potyondy, 1961; Coyle and Sulaiman, 1967; Kulhaway and Peterson, 1979; Evgin and Fakharian, 1996; Hryciw and Irsyam, 1993; Uesugi et al., 1988; Hu and Pu, 2004; Canakci et al., 2011; Celik and Canakci, 2014; Nasir and Fall, 2008). Potyondy (1961) measured the ratio of skin friction and adhesion with soil friction and cohesion, respectively. He performed direct shear tests on the interface of concrete, steel, and wood with sand, sandy silt, cohesive soil,
http://dx.doi.org/10.1016/j.sandf.2016.11.002 0038-0806/& 2016 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
H. Canakci et al. / Soils and Foundations ] (]]]]) ]]]–]]]
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rock flour, and clay. The tests were conducted for certain preset moisture contents as well as for dry specimens. The results showed that the frictional resistance of a soil depends on the amount of mixed sand it possesses. Coyle and Sulaiman (1967) investigated the frictional resistance between sand and the steel pile, and Kulhaway and Peterson (1979) measured the frictional resistance between sand and concrete. Several other researchers such as Evgin and Fakharian (1996), Hryciw and Irsyam (1993), Uesugi et al. (1988) and Hu and Pu (2004) conducted direct shear tests on the interface between steel or concrete and sand to measure the interface frictional resistance. As an alternative to the direct shear device, Paikowsky et al. (1995) developed a dual interface apparatus. In addition, Yoshimi and Kishida (1981) developed a ring shear device to measure interface frictional resistance for large deformations. The previous studies showed that several factors affect the value of the interface friction angle. These factors are their mineralogical composition, density, grain shape, grain size and gradation, as well as the roughness of the material surface (Uesugi and Kishid, 1986; Lambe and Whitman, 1979; Yoshimi and Kishida, 1981). A survey of existing literature showed that limited information is available for practicing engineers about interfacial friction between organic soil and various construction materials. In this study, an intensive investigation was carried out to determine interface friction values. For this purpose, concrete, smooth and rough steel, and wood were selected as structural materials. Tests were done at different water contents and different granular soil content in the organic soil. All tests were performed using the direct shear test device.
Fig. 1. Classification system for peat deposits (Wüst et al., 2003).
Table 1 Engineering properties of the organic soil. Properties of organic soil Organic content (%) pH Natural water content (%) Liquid limit (%) Plasticity index (%) Specific gravity
70 5.0 256 125 None plastic 1.97
2. Materials and methods 2.1. Organic soil The organic soil used in this study was obtained from the Sakarya region of Turkey. This peat was bought from a commercial firm as packed peat. Once the peat was delivered to the laboratory, all of it was dried in an oven. Its moisture content was determined before testing. Since it is quite difficult to prepare organic soil samples with high water content for the tests proposed, peat of four different moisture contents as selected for this work. The properties of peat soils, including their natural water content, acidity, degree of humification, fiber content, shear strength, and compressibility, are affected by the formation of peat deposit (Ajlouni, 2000). This indicates that in terms of content, fibrous peat is different from one location to another (Berry and Poskitt, 1972; Ajlouni, 2000; Robinson, 2003). Sakarya peat (natural soil) has herbaceous characteristics, and can absorb 3–4 times its weight of water with respect to its decomposition rate. Its initial density ranges from 0,121 to 0,217 g/ cm3. Remoulded soil has a dry density of 6,44 kN/m3 and an optimum moisture content of 58%. The fibrous peat used for all tests was passed through a 2 mm sieve size and retained on a 100 (0.15 mm) sieve. Organic soil is classified as
Fig. 2. Construction materials used in the test; (a) smooth steel (b) rough steel (c) concrete and (d) wood.
peat by both the Unified Soil Classification System (USCS) and the Wüst et al. (2003) classification chart shown in Fig. 1. It is also classified as fibric according ASTM D 1997, high ash according to ASTM D 2974, and moderately acidic according to ASTM D 2976. Organic soil can also be classified according to its decomposition rate. According to the Von Post (1922) scale, the decomposition rate changes from H1 to H10. In this
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Fig. 3. Soil testing method used in this study; (a) lower and upper box of the direct shear device used for this study and (b) lower shear box, filled with the structural material.
2.3. Structural materials
Table 2 Mix proportions of the soils used in the tests. Material type Sand content (%) (CS-RS)a
W/O (%)
Sand (g)
Organic soil Water (g) (g)
Wood Concrete Smooth steel Rough steel
0,75
0 4,29 8,57 30 25,71 Water (g)
42,86 32,14 38,57 34,28 12,85 17,14 Organic soil Sand (g) (g) 55 20 49,5 44 38,5 33
a
0 10 20 30 40 Water content (%) (CS-RS)a 0 8 17 28 41,5
S/O (%) 40
0 5,5 11 16,5 22
To evaluate the interface frictional resistance between organic soil and solid structural materials, four plates of commonly used construction materials were prepared; concrete, rough and smooth steel, and wood. The steels plates used in this study were prepared in the laboratory from metal sheets. The concrete plate was prepared in the laboratory using aggregates and cements, and cast in food frame, while the wood plate used in this study was cut from a pine tree. The construction materials used in the study are shown in Fig. 2. The dimeansions of all types of structural materials were 60 60 10 mm, exactly the same size as the lower box under the direct shear device.
CS: crushed sand; RS: rounded sand.
2.4. Testing method rating system, rather than the water content itself being the main parameter, the main parameter is the color of water obtained after squeezing the original peat. Therefore, peat from different regions may have the same decomposition rate but a different water content. The decomposition rate of the organic soil used in this study was in the range of H1–H4. The organic content was estimated after firing the soil at 440 1C in an oven for 4 h, according to ASTM D 2974. According to this process, the ash content of the soil was 30% and its organic content was 70%. According to Hartlen and Wolski (1996), fibrous peat with a fiber content of more than 60% usually falls into a decomposition rate ranging between H1 and H4. The liquid limit of the organic soil was estimated by the fall cone test according to ASTM D 4318 and found to be 119%. The engineering properties of the organic soil are listed in Table 1.
2.2. Sand Two types of sand, rounded and angular, were used in this study. Both of them were poorly graded, passing through the 2 mm sieve size and then retained on the 0.425 mm sieve. These types of sandy soil were used to test the effect of particle shape on interface friction.
A fully automated direct shear device was used in this study. The dimensions of the upper part of the shear box filled with organic soil were 60 60 15 mm (Fig. 3a). To perform the interface tests between organic soil and solid materials, the lower box of the direct shear device was completely blocked by the solid plates (Fig. 3b). The internal friction angle of the original soil was 431 and the cohesion was 5.8 kPa. The peat was bought from a commercial firm in the form of packed peat, and was then oven-dried. Then, the peat was separated according to its moisture content. The samples were consolidated under different vertical loads (30, 60, 120 kPa) before testing. Organic soil samples with different water content and sand-organic content were prepared. The temperature during the test was at room temperature (24 1C) and all of the tests were consolidated and drained (CD). To investigate the effect of the sand content in the organic soil on the interface friction angle, 10%, 20%, 30%, and 40% sand by weight was mixed with the organic soil. For this series of tests, the water content was kept constant (w¼ 0.75). In the second series of tests, the effect of the water content on the interface friction angle was investigated. Various water contents were used, 8%, 17%, 28%, and 41,5%, respectively, and the granular soil content was considered to be 40%. The density of the soil was kept
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
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Fig. 4. Surface waves with respect to surface length; (a) concrete (b) wood (c) rough steel and (d) smooth steel.
Fig. 5. Shear stress–horizontal displacement curves for 120 kPa normal load (a) 40% crushed sand content and (b) 40% rounded sand content.
Fig. 6. Vertical displacement–horizontal displacement curve for 120 kPa normal load (a) crushed sand 40% sand content, and (b) rounded sand 40% sand content.
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Fig. 8. Shear envelopes for the organic soil–construction materials interfaces for 40% granular soil (a) dry and (b) 40% water content.
Fig. 7. Shear envelopes for the organic soil–construction materials interfaces for (a) 0% crushed sand content (b) 40% crushed sand content (c) 0% rounded sand content. (d) 40% rounded sand content.
constant at 1.39 g/cm3 for all mixtures. The testing program and mix proportions are presented in Table 2. During the shearing test, the rate of shearing displacement was kept equal to 1 mm/min for all tests. Three different normal stresses (30, 60, and 120 kPa, respectively) were used and the shear stress at 10% horizontal displacement of the box was considered the maximum shear stress. The roughness index of the material surface is also an important parameter which influences the interface friction angle. The roughness index is a function of the smoothness of the structural materials (Sayers, 1995). Rough surfaces usually have higher friction coefficients than smooth surfaces. The surface roughness is quantified by the vertical deviations of the real surface from its ideal form. If these deviations are large, the surface is considered to be rough; if they are small, the surface is smooth (Kwang et al., 1992). The roughness coefficients of the structural materials were estimated by using an electronic dial guage. This dial guage was moved on surface of the structural materials and the readings were taken by a data logger and recorded. For each of the plates, measurement were taken at different points along the centerline from the edges of the plates. Fig. 4 shows the surface waves for each of
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Fig. 10. Effect of water content on interface friction angle.
Fig. 9. Changes in interface friction angle with respect to shape of sand (w ¼75%) (a) crushed sand, and (b) rounded sand.
the construction materials. These figures were used to calculate the Roughness index as described by Kwang et al. (1992). 3. Results and discussion Typical direct shear test results for different organic soilconstruction material interfaces are presented and discussed in this section. Generally, shear test results are presented in three types of graphs: (1) the shear stress–horizontal displacement curves, (2) the horizontal shear displacement–vertical deformation curves, and (3) the shear strength envelopes, which give the interface shear strength parameters (cohesion or adhesion, c; friction angle, φ). The typical shear stress versus horizontal displacement performed on the organic soil containing 40% angular and rounded sand under 120 kPa normal stress is shown in Fig. 5a and b. These figures show a relatively similar trend and shape. In addition, it can be seen from the figures that the interface shear stress increases gradually with horizontal displacement until a certain amount of deformation takes place, beyond which it becomes relatively constant. The curves showed a slight strain softening behavior. Since the maximum horizontal
deformation reached for all the tests was 10% shear deformation, the residual shear condition could not be achieved in the tests. Similar behavior was observed for the same soils under different normal stresses for all the construction materials tested. In all tests, the maximum shear stress values were obtained at the interface between the organic soil and concrete, while the minimum values were observed at the interface between the organic soil and smooth steel. Fig. 6a and b shows the typical results of horizontal shear displacement versus vertical displacement of the interface between organic soil containing 40% crushed and rounded sand and construction materials under 120 kPa normal stress. A larger amount of vertical displacement was observed for specimens under an applied normal stress of 120 kPa due to the higher reduction of local voids associated with higher applied normal stress for all the interface surfaces (Plesha, 1987; Kamari and Stead, 2008). This behavior may be attributed to the degradation of the organic soil due to relatively high applied normal stresses. The effect of granular content in the organic soil has very little effect on the amount of vertical displacement during shearing on the construction material interface. This may be due to the sand particles embedded in the soft organic soil at the interface. Figs. 7a and d and 8a and b show typical interface shear strength envelopes for construction material and organic soil mixed with rounded and angular sand. These envelopes were drawn by using three normal stresses and corresponding shear stresses for each test. A linear regression line was fitted through the set of interface shear stress versus normal stresses data. The strength values of all the tests were taken at 10% shear deformation: they provide an excellent straight line fit with R2 values around 0.99. For each regression line, values of interface friction angles and adhesions were obtained from linear curves shown in Figs. 7a and d and 8a and b. The results are consistent with expected trends in behavior where the shear strength increases with increasing normal stress. It can be seen from Fig. 7a and d, that regardless of the type of construction material, the strength data can be well described by a Mohr–Coulomb failure criterion. It can also be seen from this figure that organic soil mixed with two types of sand showed
Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002
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Fig. 11. Friction parameters of the construction materials (a) coefficient of friction and (b) surface roughness.
relatively similar adhesion values, both of which were very small. As it is clearly seen from Fig. 7a and d, the highest shear strength values were observed between organic soil and concrete at all normal stresses. On the other hand, the smallest one was obtained when smooth steel was used. This can be explained by surface roughness of the construction materials used in the study. These results indicate that the values of shear stress are directly related to surface roughness. This finding concurs with the findings reported in the existing literature (Potyondy, 1961; Gireesha and Muthukkumaran, 2011). Fig. 8a and b, clearly shows that the increase of water content decreases the interface shear strength between the soil– concrete and soil–wood. On the other hand, water has very limited effect on the interface shear strength between soil–steel. This can be explained by the increase in the slipperiness of the surface of construction materials due to the addition of water in organic soil, and the resultant reduction in shear stress at the interface. The comparison of the results of interface shear tests presented above suggest that the sand and water content of organic soil have a significant impact on the mechanical behavior at the interface between organic soil–sand mixtures and construction materials (Fig. 9a and b). The results also an increase in the interface friction angle of organic soil with granular particles tends the interface of construction materials as the sand content increases. This can be attributed to the frictional resistance between the construction materials and individual sand particles. The highest interface friction angles at different sand contents were observed in the concrete interface. On the other hand, the smallest ones were observed for smooth steel at same condition (Tiwari and Al-Adhadh, 2014). Moreover, as it is clearly seen from Fig. 9a and b, the shape of the sand particles in the organic soil (crushed or rounded) does not have much effect on the interface friction angle. Fig. 10 shows the effect of the water content on the interface friction angle between organic soil and construction materials. As can be seen from the graph, concrete and wood were
affected by the water content. An increase in water content of the organic soil resulted in a reduction in the interface friction for these two materials. On the other hand, water was shown to have a very limited effect on the interface friction angle in the case of steel. The coefficient of friction and surface roughness values (Ra) for construction materials are shown in Fig. 11a and b. As can be seen from the figures, the highest coefficient of friction (0.67) and surface roughness (330 mm) values among all the constructon materials were obtained for the concrete. On the other hand, the smallest coefficient of friction (0.39) and surface roughness (35 mm) values were measured for smooth steel. The results showed that the coefficient of friction value was directly related to surface roughness (Ra) for organic soil. The internal friction angle of organic soil used in this study (431) and other organic soil reported in the literature (40–601; Mesri and Ajlouni, 2007) are high compared to the measured interface friction angle. It indicates that all the failures which occurred were between the soil samples and construction material but not inside the soil samples themselves.
4. Conclusion In this study, the interface shear behavior of organic soil and construction material was evaluated using a direct shear test apparatus. The following conclusions were drawn. Test results showed that the highest interface friction angle was obtained between the organic soil and the concrete, and that this was higher than that of other construction materials regardless of the shape of the soil particles. On the other hand, the lowest interface friction angle was observed in the case of smooth steel. It was also found that the shape of the sand particles had no affect on the interface friction for any of the construction materials with added content. An increase in the water content of organic soil decreased the interface friction angle for both concrete and the wood. The study also showed a strong correlation between the surface roughness (Ra) of the
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Please cite this article as: Canakci, H., et al., Friction characteristics of organic soil with construction materials. Soils and Foundations (2016), http://dx.doi.org/ 10.1016/j.sandf.2016.11.002