大型滑坡堆积体稳定性的三维数值分析

Three-dimensional numerical analysis of stability of large-scale landslide accumulation body

古水水电站争岗特大型滑坡堆积体方量高达4 750×104 m3,存在多处厚度超过50 m的超深层滑坡。稳定性直接关系到大坝的建设与运营。工程地质勘测、2008年降雨产生的变形资料表明,该滑坡体是一个多期次复合型滑坡,主要由基岩、滑带土和松散堆积物组成,地表已出现大量拉张和剪切裂缝,天然工况下整体处于沿贯通底滑面发生蠕滑变形的状态,各种工况下均存在滑塌的可能性,必须进行开挖加固治理。针对二维平面方法无法考虑计算断面的侧向约束和底滑面在空间上的曲率效应,运用三维极限平衡方法和大变形拉格朗日有限差分法,根据实际地质信息建立了多个三维计算模型,通过对治理前后滑坡体应力、变形、塑性区和安全系数变化对比分析,定性、定量对其稳定性进行了评价,并引入有限元点和面安全系数法对加固后稳定性进行了校核。结果真实反映了滑坡体的稳定性现状与规律,与现场勘查成果相吻合。开挖加固后,滑坡体局部和整体稳定性均有显著提高,结合排水措施,将更有利于保持其稳定性。研究成果可为类似工程问题提供有意义的参考。

The volume of Zhenggang large landslide accumulation body in Gushui hydropower station is up to more than 47,500,000 m3.There are many ultra-deep landslide places with the thickness over 50 m;its stability is directly related to dam construction and operation.However,Field engineering geological investigation and data of deformation caused by rainfall in 2008 show that the landslide is multi-period and complex,mainly composed of bedrock,slip soil and unconsolidated accumulation.There are so many tensile and shear cracks on the surface that the accumulation body is prone to produce creep deformation under the normal condition and slump under any condition,so the treatment such as excavation and reinforcement is needed.Due to lateral restraint of computation cross-sections and bottom sliding surface curvature effects in space not considered by two dimensional method,3D limit equilibrium method and large deformable Lagrange finite difference method are applied to build some 3D computational model according to actual geological information.By comparative analysis of changes of stress,deformation,plastic zone and safety factor before and after the treatment,the stability is evaluated qualitatively and quantitatively;and furthermore the stability after the reinforcement is checked by the finite element point and surface safety factor method.The results truly reflect the situations and laws of stability of the landslide,which are consistent with the field exploration results.The local and whole stability obviously increased after excavation and reinforcement;if combined with drainage measures will be more conducive to maintaining.The research results can provide meaningful references to the similar projects.