反复干湿循环对重塑非饱和黄土力学特性影响

Experimental Research on the Effect of Repeated Drying-wetting Cycles on the Mechanical Properties of Remolded Unsaturated Loess

研究目的:降雨和蒸发反复交替循环作用下,浅层土体内的水气状态处于动态变化中,该过程会对土体力学特性产生不可逆转的影响。本文对不同干湿循环次数的重塑非饱和黄土进行SWCC曲线试验及三轴试验,研究干湿循环作用对非饱和黄土持水特性、强度及变形特性的影响。研究结论:(1)非饱和黄土的土水特征曲线具有明显的滞回效应,随着干湿循环次数的增大,该效应逐渐减弱;(2)VG模型对重塑非饱和黄土具有更好的适用性,继而建立了不同干湿循环次数下SWCC曲线的预测模型;(3)干湿循环使得其应力-应变曲线由应变硬化型转化为应变软化型,经干湿循环的试样初始剪切刚度较初始试样大,但破坏应力较小;(4)随着干湿循环次数的增加,黄土抗剪强度参数c′、φ′及φ^(b)均逐渐下降,相比之下,c′受干湿循环的影响最大,φ^(b)次之,φ′的影响最小;(5)本研究成果可为黄土地区边坡工程设计及加固中强度参数取值提供参考。

Research purposes:Under the action of the repeated cycles of rainfall and evaporation,the water and gas state in shallow layers are in dynamic variation,which will have an irreversible effect on the mechanical properties of soil.In this paper,the SWCC curve test and triaxial test of remolded unsaturated loess after different times of dry-wet cycle were carried out.The effects of dry-wet cycle on water-holding capacity,strength and deformation characteristics of unsaturated loess were studied.Research conclusions:(1)There is an obvious hysteretic phenomenon for the soil-water characteristic curve of unsaturated loess,which is gradually diminished with the increase of the times of dry-wet cycle.(2)The more suitable SWCC empirical model for unsaturated loess is VG model,and then the SWCC prediction models for loess under different dry-wet cycle times are established based on the VG model.(3)The stress-strain curve profiles are transformed from the strain hardening type to the strain softening type due to wet-dry cycle,the initial shear stiffness after wet-dry cycle is larger than that of the initial specimens,nevertheless,the failure strength is smaller.(4)With the increase of dry-wet cycle times,the effective cohesion c′,effective friction angleφ′and the suction friction angleφ^(b)of unsaturated loess are all decreased gradually.By comparison,the dry-wet cycle has the most effect on the effective cohesion,followed by effective friction angle,and the suction angle is affected least.(5)The research results can provide a reference for the selection of strength parameters in slope engineering design and reinforcement in loess area.