非饱和原状黄土强度特性试验研究

为了探究非饱和原状黄土在快速施工条件下,不同含水率、剪切速率和围压对其强度特性的影响,进行了UU三轴剪切试验。试验结果表明:试样的体积含水率在脱湿和吸湿过程中均随着基质吸力的增大而减小。当剪切速率达到1.5 mm/min时,3种含水率试样的黏聚力分别达到各自的峰值43.2 kPa、40.6 kPa和38.7 kPa,当剪切速率小于此值时黏聚力随着剪切速率的增大而增大。剪切速率达到3 mm/min时,黏聚力分别降为31.8 kPa、21.2 kPa和19.6 kPa;在剪切速率仅为0.5 mm/min时,3种含水率下试样的内摩擦角分别为27.5°、27.3°和27.6°。而后,随着剪切速率的增大内摩擦角逐渐减小,降幅分别为1.6°、1.3°、1.8°;试样的黏聚力随着剪切速率的增大表现为先增大后减小,而内摩擦角随着剪切速率的增大逐渐减小。随着含水率的增大,试样的黏聚力明显减小,但含水率对内摩擦角影响甚微。原状黄土的应力-应变曲线、抗剪强度与剪切速率之间是二次函数关系,存在临界剪切速率;与含水率之间呈负相关性,含水率的增大对土体强度具有软化作用;与围压之间呈单向递增函数关系,围压的增大对土体强度具有强化作用。

Experimental study on strength characteristics of unsaturated and undisturbed loess

In order to explore the impacts from different water contents，shearing rates and confining pressures on the strength of unsaturated and undisturbed loess under the condition of rapid construction，a UU triaxial shear test is performed． The result shows that the volumetric water contents of the sample during both the dewetting and moisture absorption processes are decreased along with the increase of the matrix suction． When the shearing rate reaches 1. 5 mm/min，the cohesions of the soil samples with three water contents reach to their peak values respectively，i． e． 43. 2 kPa、40. 6 kPa and 38. 7 kPa，while the cohesion is increased along with the increase of the shearing rate when the shearing rate is less than this value． When the shearing rate reaches 3 mm/min，the cohesions are decreased by 31. 8 kPa、21. 2 kPa and 19. 6 kPa respectively，while the internal friction angles of the samples with three water contents are 27. 5°，27. 3°，and 27. 6° respectively when the shearing rate is only 0. 5 mm/min． Afterwards，the internal friction angles are gradually decreased with the decreasing amplitudes of 1. 6°，1. 3°，1. 8° along with the increase of the shearing rate，while the cohesions of the samples present as increasing at first and then decreasing，but the internal friction angles are gradually decreased along with the increase of the shearing rate． following with the increase of the water content，the cohesion of the sample is obviously decreased，but the impact from the water content on the internal friction angle is very little． For the stress-strain curve and shearing strength of the undisturbed loess，they have a quadratic function relationship with the shearing rate，for which a critical shear rate is there，and exhibit a negative correlation with the water content，for which the increase of the water content has a softening effect on the strength of the soil mass，moreover，present a one-way increasing function relationship with the confining pressure as well．