含碎石粘性土滑坡的成因机理

边坡是山地丘陵区工程建设的基本地质环境，确保边坡安全是人类生活与工程活动的基本要求。但由于大量工程建设地处复杂的地质环境条件区，边坡失稳时有发生，滑坡灾害成为山地丘陵区工程建设所面临的主要问题之一。在我国南方地区，含碎石粘性土滑坡是最主要的滑坡类型，如浙江省1991~2000年间调查过的979处滑坡中有80％就是此类滑坡。本论文基于大量滑坡实例的调查分析和监测试验，围绕含碎石粘性土滑坡的成因机理与防治对策展开系统的研究工作。 本文以大量含碎石粘性土滑坡的现场调查和变形破坏过程监测为基础，分别对坡面堆载诱发型滑坡、坡脚开挖诱发型滑坡和自然斜坡型滑坡的成因机制、影响因素和变形破坏特征进行了系统研究。在此基础上，通过数值模拟和物理模拟，对滑坡形成和发展过程中的力学作用机制进行了深入分析，并对滑坡治理工程的作用方式和效果进行了全面评价。 通过深入的现场调查和室内模型试验，揭示了含碎石粘性土边坡中的地下水渗流管道系统。我国南方地区雨水充沛，在地下水渗流的长期作用下，含碎石粘性土边坡中往往形成管道状地下水排泄系统。通过对含碎石粘性土滑坡的地质调查、地下水位监测和抽水试验，揭示了松散堆积土边坡中地下水管道系统的发育特征，并在此基础上通过室内模型试验再现了地下水渗流管道系统的形成过程。 通过对大量含碎石粘性土滑坡的深入研究，揭示工程活动引起的边坡水文地质条件的改变是此类滑坡发生的主要原因。边坡坡面堆载一方面直接使边坡沿潜在滑面的下滑力增大，另一方面又使路基土产生压缩变形而破坏松散土中的地下水排泄系统，使坡体中的地下水位提高，从而进一步增大下滑力。坡脚开挖不仅减小滑坡的抗滑力，而且开挖面附近的局部坍塌破坏还会导致地下水渗流管道的破坏而引起地下水位的抬升，使边坡的整体稳定性进一步降低。而自然斜坡的失稳，主要是斜坡区水文地质条件的改变和长时间的持续降雨，地表水的大量入渗导致地下水入渗量超过了坡体中原有排泄系统的排泄能力，从而使坡体中的地下水位上升、斜坡稳定性降低。 采用弹塑性接触模型非线性有限元分析方法，模拟了滑坡变形破坏的力学过程，揭示了滑动面上法向应力和摩擦力的分布规律及与滑面强度参数的关系，分析了滑面摩擦阻力发挥与滑动变形的关系，为滑坡稳定性评价提供了新的方法；揭示了滑体沿滑面的滑动位移具有差异性滑动的变形非协调现象，为分析地表变形和滑坡解体过程奠定了新的理论基础。 对含碎石粘性土滑坡的不同治理措施进行了系统研究。分析计算了地表和地下排水对提高滑坡稳定性的效果;采用数值方法模拟了抗滑桩的力学作用，用物理模型模拟了锚固边坡在地下水渗流作用下的变形破坏过程。通过对含碎石粘性土滑坡的成因机理分析和不同治理措施的研究，提出此类滑坡的治理应以治水为主，即防止此类滑坡发生的经济有效的治理措施就是降低滑坡体中的地下水位，在此基础上再结合滑坡的具体情况，辅以其它如砍头压脚和抗滑工程等措施，从而达到经济有效地防治滑坡的目的。关键词:岩土工程，滑坡，含碎石粘性土边坡，地下水管道排泄系统，渗流场， 物理模拟，数值模拟，弹塑性接触模型，治理措施
工业羊毛毡
For safety of the human life and engineering activities, it is essential to ensure the slope stability, which consists of the basic geological environment for the engineering construction in hilly country. However, the landslide is the one of main problems for construction in complex geological environment as it usually gives rise to the probability of slope failure. In South China, the pebbly clay landslide is the main type of landslide. For example, 80% of 979 landslides from 1991 to 2000 in Zhejiang province are pebbly clay landslides. Basing on a great deal of field investigation and monitoring tests, systematic research is carried out in the thesis to investigate the formation mechanism and control measures of pebbly clay landslide.Through the landslide in situ survey and deformation monitoring, systematic study is conducted to find out the deformation mechanism, influential factors, and deformation characteristic of the landslide induced by the surface loading, slope toe excavation and the nature slope. Based on the above research, numerical simulation and physical model simulation are implemented to analyze the landslide genetic mechanism as well as the effects of various treatment measures.Through in situ survey and model tests, it’s found that there exists groundwater piper seepage system in pebbly clay slope. In South China, groundwater piper drainage system often develops at the seepage of the groundwater carried by the profuse rainfall. The development characteristics of the piper drainage system are found in pebbly clay slope through geological survey, groundwater monitoring and pumping tests. By physical model simulation, the formation process of the piper seepage system is witnessed.Detailed research on various pebbly clay landslides indicates that the change of hydrogeology condition due to human construction activities or natural causes is the prime factor for occurrence of this kind of landslide. Loading on slope surface can influence the slope stability through two ways. In one hand, surface loading can increase the sliding force; in the other hand, surface loading may lead to slope deformation and destroy the groundwater piper seepage system, which will also increase the sliding force by elevating the groundwater table. Excavation at slope toe has the similar influence on slope stability. Such excavation will not only decrease the anti-slide force, but also endanger the slope stability by increasing the groundwater table when it destroys the groundwater piper seepage system. The main reason of nature slope failure is the elevation of groundwater table, which can be caused by the change of hydrogeology condition, consistent rainfall or surface water seepage into slope mass,which bring so much water to the slope mass cannot discharge in time.By nonlinear finite element analysis of elastic-plastic contact model, the landslide deformation process is simulated. The relationship between normal stress and friction force distribution and strength parameters of sliding plane, as well as the relationship between friction force magnitude and landslide sliding displacement, are both obtained by the finite element analysis, which provides new method for estimation of landslide stability. It’s also discovery that there is displacement discrepancy in the slide mass along the slip surface, which sets new theoretical base for ground surface deformation analysis and slope failure process.Systematic study has been carried out on treatment measures for pebbly clay slope, including influence of discharge of surface water and groundwater on slope stability, numerical simulation on anti-slide pile mechanism and failure process of anchored slope due to the ground water seepage through model test. On the basis of the aforesaid research it’s suggested that the most effective and economical treatment measures for pebbly clay landslide is to control the groundwater level arising. Then other reinforcing measures such as anti-slide projects, loading on the slope toe or unloading on posterior margin of the slope are assisted co