三峡库区侏罗系顺层滑坡滑带土的剪切蠕变特性

滑带土的蠕变行为对滑坡的预测预报和长期稳定性分析具有重要作用。选取三峡库区侏罗系典型顺层滑坡-万州兴福寺滑坡为研究实例,针对滑带土重塑样,先进行三轴压缩试验测定其峰值及残余抗剪强度指标,然后开展不同法向应力和不同含水率下滑带土试样的剪切蠕变试验。试验结果表明:①兴福寺滑坡滑带土在初始破坏之前经历瞬时蠕变和衰减蠕变阶段,并最终稳定在低速率的等速蠕变阶段。②法向应力越大,滑带土剪切蠕变速率和变形量越小,各级法向应力下蠕变破坏时的剪应变均小于5%。③含水率对滑带土剪切蠕变速率的影响不甚明显。含水率低于塑限时滑带土剪切蠕变模量最大。随着剪切蠕变的进行,低含水率和饱和试样的剪切蠕变模量均在短时间内急剧降低并分别稳定在某一稳定值,而含水率略高于塑限的试样则呈缓慢降低趋势。与此相反的是含水率接近液限的试样呈缓慢增大趋势。④滑带土长期黏聚力为峰值和残余黏聚力的70%和15.0倍,长期内摩擦角为峰值和残余内摩擦角的69%,70%,各强度指标均受滑带土细颗粒含量的影响。

Shear creep behaviors of sliding-zone soil of bedding landslide in Jurassic stratum in Three Gorges Reservoir area

The creep behaviors of sliding-zone soil play an important role in landslide prediction and long-term stability analysis. The Xingfusi landslide, which is the typical bedding landslide occurring in Jurassic stratum in Wanzhou area, is selected as the study case. The peak and residual shear strength indexes are determined by the triaxial compression tests on the remolding samples firstly, and then the shear creep behaviors of the sliding-zone soil samples are explored by the shear creep tests under different normal stresses and water contents. The results show that: (1) The sliding-zone soil of Xingfusi landslide exhibits the transition from instantaneous creep to attenuation one, and finally keeps a constant creep with a low strain rate before the initial failure. (2) The normal stress shows a negative effect on the strain rate and creep deformation. The shear creep strain at each normal stress is less than 5% before the initial failure. (3) The influence of water content on the strain rate of sliding-zone soil in shear creep is not obvious. The sliding-zone soil has the greatest shear creep modulus when the water content is lower than the plastic limit. As the shear creep proceeds, the shear creep modulis of the samples with low water content or saturated water content have a sharp decrease in short time and then keep a stable value, while the shear creep modulus of the sample with the water content slightly higher than the plastic limit decreases slowly. On the contrary, the shear creep modulus of the sample with water content close to the liquid limit showes a trend of slow increase. (4) The long-term cohesion of sliding-zone soil is 0.70 and 15.0 times the peak and residual cohesions, respectively, and the long-term internal friction angle is 69% and 70% of the peak and residual internal friction angles, respectively. All of the shear strength indexes are affected by the content of fine particles.