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Treated Soil Tested with Uniaxial and Biaxial Flexural Tests
Available online at www.sciencedirect.com
ScienceDirect Transportation Research Procedia 14 (2016) 1923 – 1929
6th Transport Research Arena April 18-21, 2016
Mechanical fatigue of a stabilized/treated soil tested with uniaxial and biaxial flexural tests Mathieu Preteseille a, Thomas Lenoir a,* a
LUNAM Université, IFSTTAR, GERS, GMG, F-44340 Bouguenais, France
Abstract During Civil Engineering works, it is a common practice to upgrade mechanical performances of in situ soils by adding few percent of hydraulic binders such as lime and/or cement. But the specificity of stress state in railways structures (biaxial tension) and the lack of knowledge about the fatigue mechanical performances of treated/stabilized natural soils under this stress state have led to the non-use of treated soils in HSR layers. To enable the use of treated soils in railways infrastructures a specific test was developed to induce biaxial tension. This biaxial test, dedicated to railways structures and a uniaxial test from pavement design are applied to a treated soil. Results are compared; it appears that the treated soil has better performances under biaxial tension. ©©2016 The Authors. Published by Elsevier B.V. B.V.. This is an open access article under the CC BY-NC-ND license 2016The Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Road and Bridge Research Institute (IBDiM). Peer-review under responsibility of Road and Bridge Research Institute (IBDiM) Keywords: High Speed Rails infrastructures; mechanical fatigue; biaxial flexural test; stabilized/cement-treated soils; High Speed Rails design
1. Introduction The in-situ soils present in the right-of-way of civil engineering projects have generally mechanical characteristics inconsistent with stress rates generated by the infrastructure they have to support. To upgrade these
* Corresponding author. Tel.: +33 240845785; fax: +33 240845997. E-mail address: [email protected]
2352-1465 © 2016 The Authors. Published 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/). Peer-review under responsibility of Road and Bridge Research Institute (IBDiM) doi:10.1016/j.trpro.2016.05.159
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Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
materials by using them in subgrade layers, it is common to mix them with a few percent of hydraulic binders to improve their mechanical performances (Bell 1996, Chew, Kamruzzaman et al. 2004, Kolias, Kasselouri-Rigopoulou et al. 2005). Besides, this process has the advantage to minimize the environmental impact and to reduce the economic cost of the infrastructures (Nunes, Bridges et al. 1996, Salem, AbouRizk et al. 2003, Ferber, Jatteau et al. 2010, Patrick and Arampamoorthy 2010, Pratico, Saride et al. 2011, Jullien, Proust et al. 2012). This approach is widely used in numerous civil engineering applications such as road construction, embankments, foundations, slabs and piles (Al-Rawas, Hago et al. 2005, Al-Amoudi, Khan et al. 2010, El Euch Khay, Neji et al. 2010). For transport structures, fatigue is one of the main failure modes (Di Benedetto, de La Roche et al. 2004, Lav, Lav et al. 2006). In the pavement sector, the fatigue behavior is studied with flexural cyclic test. More specifically, in France, the two-point bending test (2PBT) is performed (Preteseille and Lenoir 2015a). In the railway sector, the loadings and the structure is different. Consequently, the lack of knowledge about stresses in high speed rail (HSR) structures has purely and solely led to the non-use of treated soils and at the present time, in classic HSR projects, the in-situ materials that don’t have sufficient characteristics are stripped, landfilled and substituted by materials from quarries. Therefore, to enable the use of treated soils in railways infrastructures, the structure was modeled and the stress state was determined (Preteseille, Lenoir et al. 2013). The treated layer works in a biaxial tension. A specific test was developed to reproduce this stress state (Preteseille, Lenoir et al. 2014, Preteseille and Lenoir 2015b). This test is the Biaxial Flexure Test (BFT). Both methods (2PBT and BFT) are applied to a treated soil and results are compared. The aim of this paper is to give a first trend on the mechanical fatigue behavior of stabilized/treated soils under biaxial tension. 2. Materials and methods 2.1. Fatigue tests For the design of land transport infrastructures, the sizing criterion of layers made with hydraulically bound materials is the maximal tensile stress Vmax resulting of the loading on the whole structure (SETRA-LCPC 1994). The position of this worst tensile stress is located at the bottom of the stabilized layers (Dac Chi 1981, Sobhan and Mashnad 2003, Preteseille, Lenoir et al. 2013). To be suitable, the material must have a fatigue strength defined as its cyclic tensile stress that can be withstood for N loadingsVN superior to Vmax (Larson and Nussbaum 1967, Raad, Monismith et al. 1977, Dac Chi and Mulders 1984, Matthews, Monismith et al. 1993, SETRA-LCPC 1994, SETRA-LCPC 2000, Xuan, Houben et al. 2012). The number of loadings N is determined in relation with the expected traffic and the service life of the structure, The uniaxial test used is the French standardized test, the “two-point bending” test (AFNOR 1994, AFNOR 1994). It is a two-steps procedure applied on pseudo-trapezoidal specimens clamped at their base (Figure 1). First, the monotonic flexural test consists in applying a steadily increasing load to the top surface of the specimen to measure the maximum bending stress Vf 2PBT (Equation 1). Then, a sinusoidal cyclic load Vlog10(Nfail.) with a constant amplitude and a zero mean value at 30 Hz is applied to the top surface to measure the number N fail. of cycles before the failure.
V f 2PBT
F ( h e z )v ( z ) I y ( z)
(1)
where: F – applied load (N); h – height of the specimen (m); e – gap following the z-axis between the top of the specimen and the point of the load application (m); Iy – moment of inertia (m4); v – distance from neutral axis (m). The second test induces biaxial flexure and is called BFT. The BFT, spread in the domain of ceramics and glasses (ASTM 2009), was recently proposed for concrete (Zi, Oh et al. 2008, Ekincioglu 2010, Kim, Kim et al. 2013) and adapted for treated soils (Preteseille, Lenoir et al. 2013, Preteseille, Lenoir et al. 2014).
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Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
The method consists in laying a circular plate with a thickness t and a diameter D on a support ring and to apply a load with a ring (Figure 1) with respectively a diameter equal to DS and DL. The test generates a homogeneous bending moment inside the loading ring. The formula for the radial (Vr) and tangential (Vt) stresses in the area under the loading ring is given by the Equation 2 (ASTM 2009) and is based on theory of plates (Timoshenko and Woinowsky-Krieger 1959, Vitman and Pukh 1963, Ritter, Jakus et al. 1980). This equation is valid considering three assumptions: x There is no friction between rings and the plate. x The thickness of the plate has to be thin compared with its diameter. x The plate has weak deflection. To minimize friction between rings and the plate three different layers are set, one layer of silicone between two layers of Teflon (Kim, Kim et al. 2013). The dimensions of the plate (Figure 1) were determined in agreement with the aggregate size present in natural soils and were validated with a numerical modeling (Preteseille, Lenoir et al. 2014). The procedure is similar. First, the monotonic flexural test consists in applying a steadily increasing load to the loading ring to measure the maximum bending stress Vf BFT. Then, a sinusoidal cyclic load Vlog10(Nfail.) with a constant amplitude at 30 Hz with a minimal load equal to 10% of the maximal load is applied to the loading ring to measure the number Nfail. of cycles before the failure.
V rr
V TT
Vf
BFT
DS2 DL2 D º 3F ª 1 1 Q ln s » Q 2 « 2 DL ¼ 2S t ¬ 2 DS
(2)
where: t – thickness of the specimen (m); DS – diameter of the support ring (m); DL – diameter of the loading ring (m); D – diameter of the specimen (m); Q – Poisson’s ratio. Both tests results are presented in a Wohler’s diagram and fitted with a straight line following the Equation 3 (Dac Chi and Mulders 1984, SETRA-LCPC 1994, El Euch Khay, Neji et al. 2010).
S
V log10( N Vf
fail . )
1 E log10 ( N fail . )
(3)
where: S – stress ratio; Vlog10(Nfail.) – applied stress (Pa); Vf – flexural strength (Pa); E – slope of the fatigue curve; Nfail. – number of cycle leading to failure.
Fig. 1. Schemes of the 2PBT and the BFT.
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Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
2.2. Treated soil 2.2.1. Soil The soil (called ASE) was sampled from the right of way of the French HSR project Bretagne Pays de la Loire. This line will connect Le Mans and Rennes’ cities, 160 km away (Figure 2). The sample was taken with an excavator equipped with a ditch bucket at a depth between 1.5 m and 3 m. x Geological background According to geological data (BRGM 2013), these materials were sampled on a sedimentary substrate consisting in indurated clayey silts. It dates from the Brioverian epoch (-670 to -540 million years). The alteration of this substratum has led to the formation of a sandy clayey regolith.
Fig. 2. Sketching of the HSR project Bretagne – Pays de la Loire. Black dot ASE points out sampling area.
x Geotechnical identification As previously, the maximal diameter of larger elements in this material is less than 50 mm and it can be classified as fine grained soil. Through a sieve of 2 mm, the cumulated undersize is equal to 67%. The cumulated undersize less than 80 Pm is equal to 36%. This result means that its mechanical behavior is controlled both by its fine fraction and by its stone skeleton, interestingly mineralogical identification of this skeleton show, in addition of quartz, a large occurrence of micas. It is also made up of 16% of silts and 12 % of clays (Figure 3). Mineral identification shows that the clay fraction is composed by quartz, phyllosilicates with kaolinite layers, and a large occurrence of phyllosilicates with mica sheets, and iron oxides. All these considerations show that this soil is at the edge between sandy and coarse-grained material. The Liquid limit WL is equal to 41% and Plastic limit WP to 22%. It appears that the plasticity index I P is equal to 19. The methylene blue value is equal to 0.9 g/100gdry matter. These results show the importance of the grains in the whole matrix.
Fig. 3. Grading curve of the studied soil (AFNOR 1992, AFNOR 1996).
Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
2.2.2. Treatment and sample preparation The soil ASE has been treated with 5% of cement CEM II (AFNOR 2012). Specimens for fatigue tests have been compacted in a double static mode at 98.5% of the optimum Proctor density (1.88 g/cm3 at a water content of 14.3%). Treated soils are stored in a room at a constant temperature of 20 °C and protected with thin plastic layers to keep constant water content. Specimens for 2PBT were stored during 120 days before the test and 270 days for the BFT. A monotonic test has been performed at 120 days for the BFT to enable the comparison of the flexural strength. 3. Results For the 2PBT, flexural strength is Vf 2PBT = 1.13 (0.05) MPa. Results of fatigue expressed in a Wohler’s diagram (Figure 4) lead to a slope E = -1/14.2. For a given number of cycles Nfail. = 106, the endurance e, which is defined as the ratio Vf/V6 is equal to e = 0.58, V6 = 0.66 MPa and the measurement uncertainties are 'log10(Nfail.) = 0.69 and 'V = 0.05 MPa. For the BFT, flexural strength is Vf BFT = 0.99 MPa for 120 days and Vf BFT = 1.25 (0.17) MPa for 270 days. In the Wohler’s diagram (270 days), the slope is equal to -1/24.8. This data leads for one million of cycles to an endurance e = 0.76, V6 = 0.95 MPa and the measurement uncertainties are 'log10(Nfail.) = 0.54 and 'V = 0.02 MPa.
Fig. 4. Results of fatigue tests expressed in a Wohler’s diagram of the 2PBT (120 days) and BFT (270 days) for the treated soil ASE.
4. Discussions 4.1. Uniaxial and biaxial flexural strength Results from literature show that the strength is higher of 10–15% under biaxial stress than uniaxial (Ban and under biaxial stress (BFT) is weaker of 12%. This weaker strength is probably due to the nature of the soil ASE. Indeed, ASE is composed of schist plates. During the soil compaction, schist plates are mainly positioned perpendicularly to the compaction direction (Figure 5a). Due to the different test method, schist plates are not solicited in the same plane (Figure 5b). Consequently, the moment of inertia in the 2PBT configuration in higher, leading to a better strength. 4.2. Comparison of fatigue performances Although the number of day for the cure is different, the comparison of the endurance is possible because the cure has no influence on this parameter (Dac Chi and Mulders 1984). Few studies are available on the fatigue behavior under uniaxial and biaxial tension for hydraulically bound materials. The only study found by the authors in the literature was performed on concrete (Kim, Yi et al. 2013). The fatigue tests carried out in this paper are the four-point bending test (Preteseille, Lenoir et al. 2014) and the BFT. Results show that the uniaxial endurance is
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higher than the biaxial one. Once more, results on the soil ASE are different, the uniaxial endurance is weaker. This observation highlights the importance to induce stresses as close as possible of the stress state in the structure to have a better prediction of the fatigue life. Moreover, sizing studies of treated layer are based on the fatigue strength, a better assessment of the fatigue life leads to layers with an optimized thickness and structures more economic. These results have to be confirmed on different treated soils
Fig. 5. (a) Picture of the oriented schist plates; (b) Comparison of schist plates orientation against solicitation plane of both tests.
5. Conclusion In conclusion, the treated soil ASE has a weaker strength under biaxial strength due to the orientation of the schist plates. On the contrary, ASE has a better endurance with the BFT configuration. These findings highlight the importance to use the BFT to characterize the fatigue behavior for treated layers of HSR. A better assessment of the fatigue life leads to layers with an optimized thickness and structures more economic. Acknowledgements The authors would like to thank Réseau Ferré de France (RFF) for their interest and support of this work. References AFNOR (1992). Soils: investigation and testing. Granulometric analysis. Hydrometer method., AFNOR. NF P94-057. AFNOR (1994). Tests relating to pavements. Determination of fatigue resistance on material bound with hydraulic binders. Part 1: flexural fatigue test with constant stress AFNOR. NF-P98-233-1. AFNOR (1994). Tests relating to pavements. Determination of the mechanical characteristics on material bound with hydraulic binders. Part 4: flexural test AFNOR. NF-P-98-232-4. AFNOR (1996). Soils: investigation and testing. Granulometric analysis. Dry sieving method after washing., AFNOR. NF P94-056. AFNOR (2012). Cement – Part 1: composition, specifications and conformity criteria for common cements – Ciment, AFNOR. NF EN-197-1. Al-Amoudi, O.S.B., Khan, K. and Al-Kahtani, N.S. (2010). “Stabilization of a Saudi calcareous marl soil.” Construction and Building Materials 24(10): 1848–1854. Al-Rawas, A.A., Hago, A.W. and Al-Sarmi, H. (2005). “Effect of lime, cement and Sarooj (artificial pozzolan) on the swelling potential of an expansive soil from Oman.” Building and Environment 40(5): 681–687. ASTM (2009). C1499-09 – Standard test method for monotonic equibiaxial flexural strength of advanced ceramics at ambient temperature, ASTM International, West Conshohocken, PA. C1499-09. Ban, S. and Anusavice, K.J. (1990). “Influence of test method on failure stress of brittle dental materials.” Journal of Dental Research 69(12): 1791–1799. Bell, F.G. (1996). “Lime stabilization of clay minerals and soils.” Engineering Geology 42(4): 223–237. BRGM (2013). Geological map Vitré n°318, Bureau de Recherches Géologiques et Minières Editions. Chew, S.H., Kamruzzaman, A.H.M. and Lee, F.H. (2004). “Physicochemical and engineering behavior of cement treated clays.” Journal of Geotechnical and Geoenvironmental Engineering 130(7): 696–706.
Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
Dac Chi, N. (1981). “Etude du comportement en fatigue des matériaux traités aux liants hydrauliques pour assises de chaussées.” Bulletin de liaison des Laboratoires des Ponts et Chaussées 115: 33–48. Dac Chi, N. and Mulders, J. (1984). “Comportement en fatigue des sols fins traités à la chaux et au ciment. ” Bulletin de liaison des Laboratoires des Ponts et Chaussées. Di Benedetto, H., de La Roche, C., Baaj, H., Pronk, A. and Lundstrom, R. (2004). “Fatigue of bituminous mixtures.” Materials and Structures 37(267): 202–216. Ekincioglu, O. (2010). “A discussion of paper ‘A novel indirect tensile test method to measure the biaxial tensile strength of concretes and other quasibrittle materials’ by G. Zi, H. Oh, SK Park.” Cement and Concrete Research 40(12): 1769–1770. El Euch Khay, S., Neji, J. and Loulizi, A. (2010). “Compacted Sand Concrete in Pavement Construction: An Economical and Environmental Solution.” ACI Materials Journal 107(2). Ferber, V., Jatteau, C., Landes B., and Brossellier, E. (2010). “Evaluation ‘développement durable’ des travaux de terrassements.” Revue Générale des Routes 884. Jullien, A., Proust, C., Martaud, T., Rayssac, E. and Ropert, C. (2012). “Variability in the environmental impacts of aggregate production.” Resources Conservation and Recycling 62: 1–13. Kim, J., Kim, D.J. and Zi, G. (2013). “Improvement of the biaxial flexure test method for concrete.” Cement and Concrete Composites 37: 154–160. Kim, J., Yi, C., Lee, S.J. and Zi, G. (2013). “Flexural fatigue behaviour of concrete under uniaxial and biaxial stress.” Magazine of Concrete Research 65(12): 757–764. Kolias, S., Kasselouri-Rigopoulou, V. and Karahalios, A. (2005). “Stabilisation of clayey soils with high calcium fly ash and cement.” Cement & Concrete Composites 27(2): 301–313. Larson, T.J. and Nussbaum, P.J. (1967). “Fatigue of soil-cement.” Journal of The PCA Research and Development Laboratories 9: 37–59. Lav, A.H., Lav, M.A. and Goktepe, A.B. (2006). “Analysis and design of a stabilized fly ash as pavement base material.” Fuel 85(16): 2359–2370. Lee, S.K., Song, Y.C. and Han, S.H. (2004). “Biaxial behavior of plain concrete of nuclear containment building.” Nuclear Engineering and Design 227(2): 143–153. Matthews, J.M., Monismith, C.L. and Craus, J. (1993). “Investigation of Laboratory Fatigue Testing Procedures for Asphalt Aggregate Mixtures.” Journal of Transportation Engineering-Asce 119(4): 634–654. Nunes, M.C.M., Bridges, M.G. and Dawson, A.R. (1996). “Assessment of secondary materials for pavement construction: Technical and environmental aspects.” Waste Management 16(1–3): 87–96. Patrick, J. and Arampamoorthy, H. (2010). Quantifying the benefits of waste minimisation, NZ Transport Agency: 58. Pratico, F., Saride, S. and Puppala, A.J. (2011). “Comprehensive Life-Cycle Cost Analysis for Selection of Stabilization Alternatives for Better Performance of Low-Volume Roads.” Transportation Research Record (2204): 120–129. Preteseille, M. and Lenoir, T. (2015a). “Mechanical fatigue behavior in treated/stabilized soils subjected to a uniaxial flexural test.” International Journal of Fatigue 77: 41–49. Preteseille, M. and Lenoir, T. (2015b). “Structural test at the laboratory scale for the utilization of stabilized fine-grained soils in the subgrades of High Speed Rail infrastructures: Experimental aspects.” International Journal of Fatigue, in press, doi:10.1016/j.ijfatigue.2015.09.005 Preteseille, M., Lenoir, T., Gennesseaux, E. and Hornych, P. (2014). “Structural test at the laboratory scale for the utilization of stabilized fine-grained soils in the subgrades of High Speed Rail infrastructures: Analytical and numerical aspects.” Construction and Building Materials 61: 164–171. Preteseille, M., Lenoir, T. and Hornych, P. (2013). “Sustainable upgrading of fine-grained soils present in the right-of-way of High Speed Rail projects.” Construction and Building Materials 44: 48–53. Raad, L., Monismith, L. and Mitchell, J.K. (1977). “Fatigue Behavior of Cement-Treated Materials.” Transportation Research Board 641. Ritter, J.E., Jr, Jakus, K., Batakis, A. and Bandyopadhyay, N. (1980). “Appraisal of biaxial strength testing.” Journal of Non-Crystalline Solids 38–39: 419–424. Salem, O., AbouRizk, S. and Ariaratnam, S. (2003). “Risk-Based Life-Cycle Costing of Infrastructure Rehabilitation and Construction Alternatives.” Journal of Infrastructure Systems 9(1): 6–15. SETRA-LCPC (1994). Conception et dimensionnement des structures de chaussée, SETRA-LCPC. SETRA-LCPC (2000). Traitement des sols à la chaux et/ou aux liants hydrauliques – Application à la réalisation des remblais et des couches de forme- Guide technique, SETRA-LCPC. Sobhan, K. and Mashnad, M. (2003). “Fatigue behavior of a pavement foundation with recycled aggregate and waste HDPE strips.” Journal of Geotechnical and Geoenvironmental Engineering 129(7): 630–638. Timoshenko, S. and Woinowsky-Krieger, S. (1959). Theory of Plates and Shells. New York. Vitman, F.F. and Pukh, V.P. (1963). “A method of determining sheet glass strength.” Zavodskava Laboratoriya 29(7): 863–867. Xuan, D.X., Houben, L.J.M., Molenaar, A.A.A. and Shui, Z.H. (2012). “Mechanical properties of cement-treated aggregate material – A review.” Materials & Design 33: 496–502. Zi, G., Oh, H. and Park, S.K. (2008). “A novel indirect tensile test method to measure the biaxial tensile strength of concretes and other quasibrittle materials.” Cement and Concrete Research 38(6): 751–756.
1929
ScienceDirect Transportation Research Procedia 14 (2016) 1923 – 1929
6th Transport Research Arena April 18-21, 2016
Mechanical fatigue of a stabilized/treated soil tested with uniaxial and biaxial flexural tests Mathieu Preteseille a, Thomas Lenoir a,* a
LUNAM Université, IFSTTAR, GERS, GMG, F-44340 Bouguenais, France
Abstract During Civil Engineering works, it is a common practice to upgrade mechanical performances of in situ soils by adding few percent of hydraulic binders such as lime and/or cement. But the specificity of stress state in railways structures (biaxial tension) and the lack of knowledge about the fatigue mechanical performances of treated/stabilized natural soils under this stress state have led to the non-use of treated soils in HSR layers. To enable the use of treated soils in railways infrastructures a specific test was developed to induce biaxial tension. This biaxial test, dedicated to railways structures and a uniaxial test from pavement design are applied to a treated soil. Results are compared; it appears that the treated soil has better performances under biaxial tension. ©©2016 The Authors. Published by Elsevier B.V. B.V.. This is an open access article under the CC BY-NC-ND license 2016The Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Road and Bridge Research Institute (IBDiM). Peer-review under responsibility of Road and Bridge Research Institute (IBDiM) Keywords: High Speed Rails infrastructures; mechanical fatigue; biaxial flexural test; stabilized/cement-treated soils; High Speed Rails design
1. Introduction The in-situ soils present in the right-of-way of civil engineering projects have generally mechanical characteristics inconsistent with stress rates generated by the infrastructure they have to support. To upgrade these
* Corresponding author. Tel.: +33 240845785; fax: +33 240845997. E-mail address: [email protected]
2352-1465 © 2016 The Authors. Published 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/). Peer-review under responsibility of Road and Bridge Research Institute (IBDiM) doi:10.1016/j.trpro.2016.05.159
1924
Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
materials by using them in subgrade layers, it is common to mix them with a few percent of hydraulic binders to improve their mechanical performances (Bell 1996, Chew, Kamruzzaman et al. 2004, Kolias, Kasselouri-Rigopoulou et al. 2005). Besides, this process has the advantage to minimize the environmental impact and to reduce the economic cost of the infrastructures (Nunes, Bridges et al. 1996, Salem, AbouRizk et al. 2003, Ferber, Jatteau et al. 2010, Patrick and Arampamoorthy 2010, Pratico, Saride et al. 2011, Jullien, Proust et al. 2012). This approach is widely used in numerous civil engineering applications such as road construction, embankments, foundations, slabs and piles (Al-Rawas, Hago et al. 2005, Al-Amoudi, Khan et al. 2010, El Euch Khay, Neji et al. 2010). For transport structures, fatigue is one of the main failure modes (Di Benedetto, de La Roche et al. 2004, Lav, Lav et al. 2006). In the pavement sector, the fatigue behavior is studied with flexural cyclic test. More specifically, in France, the two-point bending test (2PBT) is performed (Preteseille and Lenoir 2015a). In the railway sector, the loadings and the structure is different. Consequently, the lack of knowledge about stresses in high speed rail (HSR) structures has purely and solely led to the non-use of treated soils and at the present time, in classic HSR projects, the in-situ materials that don’t have sufficient characteristics are stripped, landfilled and substituted by materials from quarries. Therefore, to enable the use of treated soils in railways infrastructures, the structure was modeled and the stress state was determined (Preteseille, Lenoir et al. 2013). The treated layer works in a biaxial tension. A specific test was developed to reproduce this stress state (Preteseille, Lenoir et al. 2014, Preteseille and Lenoir 2015b). This test is the Biaxial Flexure Test (BFT). Both methods (2PBT and BFT) are applied to a treated soil and results are compared. The aim of this paper is to give a first trend on the mechanical fatigue behavior of stabilized/treated soils under biaxial tension. 2. Materials and methods 2.1. Fatigue tests For the design of land transport infrastructures, the sizing criterion of layers made with hydraulically bound materials is the maximal tensile stress Vmax resulting of the loading on the whole structure (SETRA-LCPC 1994). The position of this worst tensile stress is located at the bottom of the stabilized layers (Dac Chi 1981, Sobhan and Mashnad 2003, Preteseille, Lenoir et al. 2013). To be suitable, the material must have a fatigue strength defined as its cyclic tensile stress that can be withstood for N loadingsVN superior to Vmax (Larson and Nussbaum 1967, Raad, Monismith et al. 1977, Dac Chi and Mulders 1984, Matthews, Monismith et al. 1993, SETRA-LCPC 1994, SETRA-LCPC 2000, Xuan, Houben et al. 2012). The number of loadings N is determined in relation with the expected traffic and the service life of the structure, The uniaxial test used is the French standardized test, the “two-point bending” test (AFNOR 1994, AFNOR 1994). It is a two-steps procedure applied on pseudo-trapezoidal specimens clamped at their base (Figure 1). First, the monotonic flexural test consists in applying a steadily increasing load to the top surface of the specimen to measure the maximum bending stress Vf 2PBT (Equation 1). Then, a sinusoidal cyclic load Vlog10(Nfail.) with a constant amplitude and a zero mean value at 30 Hz is applied to the top surface to measure the number N fail. of cycles before the failure.
V f 2PBT
F ( h e z )v ( z ) I y ( z)
(1)
where: F – applied load (N); h – height of the specimen (m); e – gap following the z-axis between the top of the specimen and the point of the load application (m); Iy – moment of inertia (m4); v – distance from neutral axis (m). The second test induces biaxial flexure and is called BFT. The BFT, spread in the domain of ceramics and glasses (ASTM 2009), was recently proposed for concrete (Zi, Oh et al. 2008, Ekincioglu 2010, Kim, Kim et al. 2013) and adapted for treated soils (Preteseille, Lenoir et al. 2013, Preteseille, Lenoir et al. 2014).
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Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
The method consists in laying a circular plate with a thickness t and a diameter D on a support ring and to apply a load with a ring (Figure 1) with respectively a diameter equal to DS and DL. The test generates a homogeneous bending moment inside the loading ring. The formula for the radial (Vr) and tangential (Vt) stresses in the area under the loading ring is given by the Equation 2 (ASTM 2009) and is based on theory of plates (Timoshenko and Woinowsky-Krieger 1959, Vitman and Pukh 1963, Ritter, Jakus et al. 1980). This equation is valid considering three assumptions: x There is no friction between rings and the plate. x The thickness of the plate has to be thin compared with its diameter. x The plate has weak deflection. To minimize friction between rings and the plate three different layers are set, one layer of silicone between two layers of Teflon (Kim, Kim et al. 2013). The dimensions of the plate (Figure 1) were determined in agreement with the aggregate size present in natural soils and were validated with a numerical modeling (Preteseille, Lenoir et al. 2014). The procedure is similar. First, the monotonic flexural test consists in applying a steadily increasing load to the loading ring to measure the maximum bending stress Vf BFT. Then, a sinusoidal cyclic load Vlog10(Nfail.) with a constant amplitude at 30 Hz with a minimal load equal to 10% of the maximal load is applied to the loading ring to measure the number Nfail. of cycles before the failure.
V rr
V TT
Vf
BFT
DS2 DL2 D º 3F ª 1 1 Q ln s » Q 2 « 2 DL ¼ 2S t ¬ 2 DS
(2)
where: t – thickness of the specimen (m); DS – diameter of the support ring (m); DL – diameter of the loading ring (m); D – diameter of the specimen (m); Q – Poisson’s ratio. Both tests results are presented in a Wohler’s diagram and fitted with a straight line following the Equation 3 (Dac Chi and Mulders 1984, SETRA-LCPC 1994, El Euch Khay, Neji et al. 2010).
S
V log10( N Vf
fail . )
1 E log10 ( N fail . )
(3)
where: S – stress ratio; Vlog10(Nfail.) – applied stress (Pa); Vf – flexural strength (Pa); E – slope of the fatigue curve; Nfail. – number of cycle leading to failure.
Fig. 1. Schemes of the 2PBT and the BFT.
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2.2. Treated soil 2.2.1. Soil The soil (called ASE) was sampled from the right of way of the French HSR project Bretagne Pays de la Loire. This line will connect Le Mans and Rennes’ cities, 160 km away (Figure 2). The sample was taken with an excavator equipped with a ditch bucket at a depth between 1.5 m and 3 m. x Geological background According to geological data (BRGM 2013), these materials were sampled on a sedimentary substrate consisting in indurated clayey silts. It dates from the Brioverian epoch (-670 to -540 million years). The alteration of this substratum has led to the formation of a sandy clayey regolith.
Fig. 2. Sketching of the HSR project Bretagne – Pays de la Loire. Black dot ASE points out sampling area.
x Geotechnical identification As previously, the maximal diameter of larger elements in this material is less than 50 mm and it can be classified as fine grained soil. Through a sieve of 2 mm, the cumulated undersize is equal to 67%. The cumulated undersize less than 80 Pm is equal to 36%. This result means that its mechanical behavior is controlled both by its fine fraction and by its stone skeleton, interestingly mineralogical identification of this skeleton show, in addition of quartz, a large occurrence of micas. It is also made up of 16% of silts and 12 % of clays (Figure 3). Mineral identification shows that the clay fraction is composed by quartz, phyllosilicates with kaolinite layers, and a large occurrence of phyllosilicates with mica sheets, and iron oxides. All these considerations show that this soil is at the edge between sandy and coarse-grained material. The Liquid limit WL is equal to 41% and Plastic limit WP to 22%. It appears that the plasticity index I P is equal to 19. The methylene blue value is equal to 0.9 g/100gdry matter. These results show the importance of the grains in the whole matrix.
Fig. 3. Grading curve of the studied soil (AFNOR 1992, AFNOR 1996).
Mathieu Preteseille and Thomas Lenoir / Transportation Research Procedia 14 (2016) 1923 – 1929
2.2.2. Treatment and sample preparation The soil ASE has been treated with 5% of cement CEM II (AFNOR 2012). Specimens for fatigue tests have been compacted in a double static mode at 98.5% of the optimum Proctor density (1.88 g/cm3 at a water content of 14.3%). Treated soils are stored in a room at a constant temperature of 20 °C and protected with thin plastic layers to keep constant water content. Specimens for 2PBT were stored during 120 days before the test and 270 days for the BFT. A monotonic test has been performed at 120 days for the BFT to enable the comparison of the flexural strength. 3. Results For the 2PBT, flexural strength is Vf 2PBT = 1.13 (0.05) MPa. Results of fatigue expressed in a Wohler’s diagram (Figure 4) lead to a slope E = -1/14.2. For a given number of cycles Nfail. = 106, the endurance e, which is defined as the ratio Vf/V6 is equal to e = 0.58, V6 = 0.66 MPa and the measurement uncertainties are 'log10(Nfail.) = 0.69 and 'V = 0.05 MPa. For the BFT, flexural strength is Vf BFT = 0.99 MPa for 120 days and Vf BFT = 1.25 (0.17) MPa for 270 days. In the Wohler’s diagram (270 days), the slope is equal to -1/24.8. This data leads for one million of cycles to an endurance e = 0.76, V6 = 0.95 MPa and the measurement uncertainties are 'log10(Nfail.) = 0.54 and 'V = 0.02 MPa.
Fig. 4. Results of fatigue tests expressed in a Wohler’s diagram of the 2PBT (120 days) and BFT (270 days) for the treated soil ASE.
4. Discussions 4.1. Uniaxial and biaxial flexural strength Results from literature show that the strength is higher of 10–15% under biaxial stress than uniaxial (Ban and under biaxial stress (BFT) is weaker of 12%. This weaker strength is probably due to the nature of the soil ASE. Indeed, ASE is composed of schist plates. During the soil compaction, schist plates are mainly positioned perpendicularly to the compaction direction (Figure 5a). Due to the different test method, schist plates are not solicited in the same plane (Figure 5b). Consequently, the moment of inertia in the 2PBT configuration in higher, leading to a better strength. 4.2. Comparison of fatigue performances Although the number of day for the cure is different, the comparison of the endurance is possible because the cure has no influence on this parameter (Dac Chi and Mulders 1984). Few studies are available on the fatigue behavior under uniaxial and biaxial tension for hydraulically bound materials. The only study found by the authors in the literature was performed on concrete (Kim, Yi et al. 2013). The fatigue tests carried out in this paper are the four-point bending test (Preteseille, Lenoir et al. 2014) and the BFT. Results show that the uniaxial endurance is
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higher than the biaxial one. Once more, results on the soil ASE are different, the uniaxial endurance is weaker. This observation highlights the importance to induce stresses as close as possible of the stress state in the structure to have a better prediction of the fatigue life. Moreover, sizing studies of treated layer are based on the fatigue strength, a better assessment of the fatigue life leads to layers with an optimized thickness and structures more economic. These results have to be confirmed on different treated soils
Fig. 5. (a) Picture of the oriented schist plates; (b) Comparison of schist plates orientation against solicitation plane of both tests.
5. Conclusion In conclusion, the treated soil ASE has a weaker strength under biaxial strength due to the orientation of the schist plates. On the contrary, ASE has a better endurance with the BFT configuration. These findings highlight the importance to use the BFT to characterize the fatigue behavior for treated layers of HSR. A better assessment of the fatigue life leads to layers with an optimized thickness and structures more economic. Acknowledgements The authors would like to thank Réseau Ferré de France (RFF) for their interest and support of this work. References AFNOR (1992). Soils: investigation and testing. Granulometric analysis. Hydrometer method., AFNOR. NF P94-057. AFNOR (1994). Tests relating to pavements. Determination of fatigue resistance on material bound with hydraulic binders. Part 1: flexural fatigue test with constant stress AFNOR. NF-P98-233-1. AFNOR (1994). Tests relating to pavements. Determination of the mechanical characteristics on material bound with hydraulic binders. Part 4: flexural test AFNOR. NF-P-98-232-4. AFNOR (1996). Soils: investigation and testing. Granulometric analysis. Dry sieving method after washing., AFNOR. NF P94-056. AFNOR (2012). Cement – Part 1: composition, specifications and conformity criteria for common cements – Ciment, AFNOR. NF EN-197-1. Al-Amoudi, O.S.B., Khan, K. and Al-Kahtani, N.S. (2010). “Stabilization of a Saudi calcareous marl soil.” Construction and Building Materials 24(10): 1848–1854. Al-Rawas, A.A., Hago, A.W. and Al-Sarmi, H. (2005). “Effect of lime, cement and Sarooj (artificial pozzolan) on the swelling potential of an expansive soil from Oman.” Building and Environment 40(5): 681–687. ASTM (2009). C1499-09 – Standard test method for monotonic equibiaxial flexural strength of advanced ceramics at ambient temperature, ASTM International, West Conshohocken, PA. C1499-09. Ban, S. and Anusavice, K.J. (1990). “Influence of test method on failure stress of brittle dental materials.” Journal of Dental Research 69(12): 1791–1799. Bell, F.G. (1996). “Lime stabilization of clay minerals and soils.” Engineering Geology 42(4): 223–237. BRGM (2013). Geological map Vitré n°318, Bureau de Recherches Géologiques et Minières Editions. Chew, S.H., Kamruzzaman, A.H.M. and Lee, F.H. (2004). “Physicochemical and engineering behavior of cement treated clays.” Journal of Geotechnical and Geoenvironmental Engineering 130(7): 696–706.
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