昭通巧家烂泥箐滑坡滑带土特征及滑坡发生机制研究

Study on the characteristics of sliding zone soil and occurrence mechanism of Qiaojia Lanniqing landslide in Zhaotong

滑带土是滑坡发展过程的产物,对滑坡的孕育和演化过程具有良好的记录作用。以昭通巧家小河镇烂泥箐滑坡为研究对象,用野外地质调查及室内试验的方法,详细阐述了该滑坡滑带土的物理-水理-力学特征,同时结合XRD衍射分析矿物成分和SEM微结构观察的手段,从多角度分析了烂泥箐滑坡滑带土的特征,揭示了烂泥箐滑坡的形成演变过程及驱动机制。结果表明:烂泥箐滑坡滑带土含有较多黏土矿物,具有黏粒含量多、质地细的特点,呈现出明显的黏性土特性。烂泥箐滑坡滑带土的细粒含量明显比受滑动扰动小的滑床土多,表明在滑坡孕育过程中滑带内发生了多次滑移剪切错动。不同含水率条件下滑带土快剪试验表明,滑带土具有明显的应变硬化特征,随着含水率增加,抗剪强度逐渐降低,特别是含水率为40%时,滑带土强度损失很大,软化明显;低含水率时,黏聚力和内摩擦角均较高,随着含水率增加,黏聚力和内摩擦角均逐渐减小。试验结果表明降雨条件下滑带土随着含水率增加表现出明显“软黏土”特征。由于斜坡受后缘Y093乡道的改扩建、后缘行车荷载的长期作用及斜坡中部烂泥箐村庄小路的改扩建工程的长期扰动,坡体内部逐渐发生变形,发展孕育了潜在滑面及该滑动面上的多期蠕动变形,多次的剪切滑动使滑带土内黏粒含量增多,质地更细。而受其黏性土材料特性的影响,低渗透率的滑动带在降雨作用下易形成隔水屏障。加之降雨条件下滑带土强度快速软化降低,剪切带内形成的静水压力和局部隔水屏障形成的超孔隙水压力直接触发了烂泥箐滑坡的发生。利用烂泥箐滑坡的发生机制可以探讨其孕育-激发过程的3个阶段:滑带区初步形成阶段、滑带演化阶段、滑带土软化以及滞水层-滑坡形成阶段。研究成果可为山区降雨型滑坡的系统研究提供一定的借鉴价值。

Sliding zone soil is the product of the landslide development process and provides a good record of the gestation-evolution of landslides.Taking Lanniqing landslide in Xiaohe Town,Qiaojia County,Zhaotong City as an example,by using the methods of field geological survey and tests,the physical and mechanical characteristics of Lanniqing landslide sliding zone was elaborated.At the same time,using XRD diffraction analysis to analyze the mineral composition of soil and SEM to observe the microstructure of soils,the characteristics of Lanniqing landslide sliding zone soil were described from different perspectives.On this basis,the formation,evolution process and driving mechanism of Lanniqing landslide were revealed.The results show that:Lanniqing landslide sliding zone soil is characterized by abundant clay minerals,high clay content and fine texture.It has distinct clay characteristics.In addition,it contains significantly more fine particles than the sliding bed soil,indicating that there were many shear dislocations in the sliding zone during the landslide preparation process.Fast shear tests on sliding zone soils at different moisture contents show that sliding zone soils have significant strain hardening properties.The shear strength gradually decreases as the moisture content increases.In particular,the sliding zone soil lose much of their strength at a moisture content of 40%and become very soft.The cohesion and angle of internal friction are high at low water contents and decrease with increasing water content.The test results show that under rainfall conditions the soils exhibit distinct soft clay characteristics as the water content increases.The widening of the Lanniqing Village road in the middle of the slope,the Y093 road at its rear edge,and the long-term effects of traffic loads all contributed to the gradual internal deformation of slope,which in turn produced the development of a potential sliding surface and multi-period creep deformation on this sliding surface.The soil in the slip zone becomes more textured and has a higher clay content as a result of repeated shear sliding.Furthermore,the low permeability sliding zone is more likely to create a water barrier during rainfall because of the characteristics of clayey soil materials.In addition,the strength of the soil is gradually decreasing and the soil is rapidly softening under the condition of rainfall.The hydrostatic pressure generated in the shear zone and the excess pore water pressure caused by the local water barrier of the sliding zone directly lead to the occurrence of the Lanniqing landslide.Therefore,the process of incubation and excitation of Lanniqing landslide can be divided into three stages based on its occurrence mechanism:the preliminary formation stage of the slip zone area,the slip zone development stage,and the formation stage of the stagnant water layer in the slip zone and the landslide.The research results can provide references for the systematic study of rainfall-type landslides in mountainous areas.