Influence of moisture content on shearing strength of unsaturated undisturbed quaternary system middle pleistocene

Abstract

The unsaturated undisturbed quaternary system middle pleistocene loess, a typical unsaturated soil, often occurs in the implementation of western development strategy. To obtain the shearing strength characteristics of this unsaturated undisturbed loess, based on the analysis of mineral composition, the triaxial shear test of undisturbed quaternary system middle pleistocene loess under different moisture contents is conducted with the specialized triaxial instrument for unsaturated soil. The test results show that the mainly mineral composition of undisturbed quaternary system middle pleistocene loess is quartz and albite. Under the same confining pressure, the matric suction increases with the decrease of moisture content. The smaller the moisture content, the larger the matric suction; the higher the moisture content, the lower the matric suction. Under the same moisture content, the matric suction increases with the confining pressure and reaches a maximum when the confining pressure is 100 kPa, and then decreases with the increase of confining pressure. This phenomenon is closely related to the grain contact tightness of soil mass under high confining pressure. According to the triaxial test of loess, the sample of loess experiences 4 stages from loading to failure: 1) compaction stage; 2) compression stage; 3) microcrack developing stage; 4) shear failure stage. The test sample is of brittle failure (weak softening) under low moisture content and confining pressure. With the decrease of matric suction and the increase of consolidated confining pressure, the stress-strain curve changes from softening type to ideal plastic type. In the shearing strength parameters of unsaturated undisturbed loess, the influence of moisture content on internal friction angle is small, but that on cohesive force is obvious. Therefore, the shearing strength of unsaturated undisturbed loess is higher than that of saturated undisturbed loess and varies with the moisture content.

Keywords

unsaturated undisturbed loess / matric suction / test / shearing strength

References

[1] Munoz-CastelblancoJ A, PereiraJ M, DelageP, CuiY. The water retention properties of a natural unsaturated loess from northern France [J]. Geotechnique, 2012, 62(2): 95-106

[2] ChenJ-y, HaiYing. Determination of the shear strength of unsaturated loess based on the fractal model theory of unsaturated soils [C]. 2nd International Conference on Civil Engineering Clausthal-zellerfeld, 2012GermaryTrans Tech Publication, CEABM25-28

[3] PereiraJ M, TaA N, CuiY J, KaramJ R, ChaiH Y. A damage model for unsaturated natural loess submitted to cyclic loading [C]. Unsaturated Soils: Advances in Geo-Engineering, 2008Durham, EnglandCRC Press-Taylor & Francis Group647-652

[4] ZhongZ-l, LiuX-rong. Mechanical characteristics of intact middle pleistocene epoch loess in northwestern China [J]. Journal of Central South University, 2012, 19(4): 1163-1168

[5] ChenZ-han. Deformation, strength, yield and moisture change of a remolded unsaturated loess [J]. Chinese Journal of Geotechnical Engineering, 1999, 21(1): 82-90

[6] ZhangY-f, ZhangZ-q, ZhaoJ-hai. Investigation on mechanical properties and constitutive model of lime-fly ash loess [C]. International Symposium on Geomechanics and Geotechnics: From Micro to Macro, 2011NetherlandsCRC Press145-150

[7] GaoL-x, LuanM-t, YangQing. Experimental studies on microstructure and collapsibility behavior of unsaturated loess [C]. International Symposium on Geomechanics and Geotechnics: From Micro to Macro, 2010NetherlandsCRC Press157-162

[8] MalyshevM V, PustogachevV A. Some experimental stress-strain relationships for loess collapsing soils [J]. Acta Tech (Budapest), 1985, 98(1/2): 97-103

[9] YingJ, LiaoH-j, YinJ-hua. An experimental study on the shear strength of undisturbed loess [J]. Geotechnical Special Publication, 2006, 148: 127-135

[10] LiY-l, ZhangH-f, ShiX-g, HouJ-k, YangL-le. Experimental study of triaxial test of undisturbed unsaturated loess [J]. Rock and Soil Mechanics, 2008, 29(10): 2859-2863

[11] HuS-x, ZhouY-d, ChenZ-han. Test study on strength character of unsaturated and undisturbed loess [J]. Rock and Soil Mechanics, 2005, 26(4): 660-664

[12] HuZ-q, ShenZ-j, XieD-yi. Deformation properties of structural loess [J]. Chinese Journal of Rock Mechanics and Engineering, 2004, 23(24): 4142-4146

[13] FengZ-y, QiuB-s, XieD-yi. Experimental study of triaxial test of loess [J]. Journal of Xi’an University of Architecture & Technology, 2010, 42(6): 803-808

[14] HardcastleJ H, SharmaS. Shear modulus and damping of unsaturated loess [J]. Geotechnical Special Publication, 1998, 1: 178-188

[15] YanY-j, WenB-p, JiB-xun. Contribution of matric suction to shear strength of unsaturated remoulded loess soils [J]. Journal of Engineering Geology, 2011, 19(6): 865-874

[16] HanB, LiaoH-j, LiH-z, XiaoZ-hua. Experimental study on shear strength characteristics and stress-strain relationship of loess [J]. Key Engineering Materials, 2013, 535/536: 574-577

[17] FangX-w, ChenZ-h, ShenC-n, WangH-w, LiuH-jian. Triaxial shear properties of undisturbed loess Q2 [J]. Chinese Journal of Rock Mechanics and Engineering, 2008, 27(2): 384-389

[18] ZhongZ-l, LiuX-r, LiuY-xue. Research on elastoplastic damage constitutive model of intact Q2l loess in northwestern of China [J]. Environmental Earth Sciences, 2013, 69(1): 85-92

[19] GB/T50123-1999 [S]. Geotechnical engineering test method and criterion 1999. (in Chinese)

[20] FredlundD G. Comparison of soil suction and one-dimensional consolidation characteristics of a highly plastic clay [R]. Ottawa, 1964