庆阳非饱和原状黄土固结快剪强度研究

Consolidated Undrained Shear Tests of Qingyang Unsaturated Undisturbed Loess Soil Samples

对庆阳原状黄土,在不同的净竖向压力及基质吸力组合下进行了固结快剪直剪试验。通过对这些试验结果的整理分析得出:(1)基质吸力s与净竖向压力p的增大均提高了原状黄土的抗剪强度和初始剪切模量。(2)吸力的增加主要引起了表观黏聚力c″=c′+(u_(α)-u_(ω))tanφ″的增加,吸力在s=0~100 kPa范围内对原状黄土的表观黏聚力c″影响显著,吸力s>100 kPa对原状黄土表观黏聚力c″的影响显著性逐步降低。这说明与基质吸力对应的摩擦角φ″不是常数,φ″随基质吸力的增大非线性减少。(3)有效内摩擦角φ′随吸力的增大而逐渐增大,这主要是由于吸力使黄土的粒团变大,导致粒团间的剪切互锁效应增强的结果。(4)在吸力s=0的饱和状态下庆阳原状黄土的表观黏聚力c″=2 kPa、趋近于零,说明在连续降雨条件下庆阳表层黄土饱和吸力接近丧失,极易诱发水土流失现象。

A series of consolidated undrained triaxial shear tests were conducted on Qingyang undisturbed loess samples with different confining pressure and matrix suction combinations.The test results reveal that 1)with increasing in suction or confining pressure,the shear strength and initial shear modulus are both increased for the undisturbed loess samples.2)increasing in the matric suction will cause the increase of apparent cohesion c″=c′+(u_(α)-u_(ω))tanφ″,the matric suction in the range of s=0~100 kPa will lead to an obvious increase in the apparent cohesion,whereas s>100 kPa will lead to a slow increase in the apparent cohesion in the undisturbed loess samples.This also shows that internal frictional angleφ″induced by the matrix suction is not a constant and it decreases nonlinearly as the matrix suction increases.3)the shear interlocking effect among particles increases with the increase of matric suction.This will induce an increase of the effective friction angle.4)the apparent cohesion c″=2 kPa of undisturbed loess in saturated state with suction s=0,this shows that runoff in the field occurs frequently for Qingyang loess being saturated and gradually lost the matrix suction under the continuous rainfall conditions.