干湿循环作用下银川地区重塑粉质黏土强度劣化试验研究

Experimental Study on Strength Deterioration of Remolded Silty Clay in Yinchuan Area under Drying-wetting Cycles

地处黄河冲积、湖积平原的银川地区,粉质黏土分布广泛,为探讨干湿交替环境对粉质黏土强度劣化规律,选取银川地区典型粉质黏土,制作不同压实度和饱和度的重塑土样,进行了不同干湿循环次数和不同围压下的不固结不排水三轴试验。分析了应力应变曲线形式、峰值应力、抗剪强度指标的试验数据。结果表明:(1)干湿循环作用改变土体应力应变曲线形式,随干湿循环进程的发展,其形式由应变硬化型过渡为应变软化型,且3次干湿循环后,软化程度逐渐增大;(2)干湿循环前期、末期峰值应力在高饱和度下衰减较快,干湿循环中期峰值应力在低饱和度下衰减较快,并且认为干湿循环作用对不同压实度、不同饱和度及不同围压下土体具有归一特性;(3)干湿循环后,黏聚力与内摩擦角均发生劣化,但黏聚力劣化程度较内摩擦角更大;干湿循环前期黏聚力在高饱和度下劣化较大,干湿中期、末期在低饱和度下劣化较大,且黏聚力随干湿循环次数的劣化规律在低饱和度下符合线性回归,高饱和度下符合二次曲线回归,相关性较好。

The silty clay in the Yinchuan area, which is located in the Yellow River alluvial and lake plains, is widely distributed. In order to investigate the deterioration of the strength of silty clay in the drying-wetting alternate environment, the typical soil sample of silty clay in Yinchuan area is selected to reshape the samples under different compactnesses and saturations, and the unconsolidated undrained tri-axial test under different drying-wetting cycles and different confining pressures is conducted. The experimental data of the form of stress strain curve, the peak stress and the shear strength indicator are analyzed. The result shows that(1) The form of stress strain curve of soil changes due to the drying-wetting cycles. With the development of the cycles, it changes from strain hardening to strain softening. After 3 drying-wetting cycles, the softening degree gradually comes to obvious.(2) The peak stress at the early and final stages of the drying-wetting cycle decays rapidly at high saturation. In the middle of the drying-wetting cycle, the peak stress decays faster at low saturation, and it is considered that the drying-wetting cycle has a normalized property for the soil mass under different compactnesses, different saturations and different confining pressures.(3) After the drying-wetting cycles, the cohesion and the internal friction angle are degraded, but the degree of cohesion deterioration is much greater than that of internal friction angle.(4) The cohesion at the early stage of drying-wetting cycles deteriorates greatly under high saturation, it deteriorates highly under low saturation at the middle and the end stages of drying-wetting cycles. The deterioration of cohesive force with the number of drying-wetting cycles accorded with linear regression under low saturation, while it accorded with quadratic curve regression under high saturation, the correlation is good.