Formation Mechanism And Control Measures Of The Pebbly Clay Landslide

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...