Study On The Mechanism Of Deformation Disintegration Failure And The Stability Of Debris Landslide

In order to summarize the general regular development pattern of debris landslide, analyze its stability, and reveal its mechanism of deformation, disintegration and failure, and the main reviving and failure mechanism of ancient debris landslide and their main induced factors, through the collection, arrangement and analysis of related datum, the site investigation and exploration of engineering geology, site test and monitoring, indoor and outdoor physical mechanics test, adopting the analytic means of mathematic statistics, unbalanced-thrust method, large deformation elastic-plastic FEM algorithm, elastic-plastic FEM contact algorithm, nonlinear science cusp-catastrophe theory, and the theory of groundwater pipe network drainage system, some studies were completed as follows: First, the general regular development pattern of debris landslide was researched systematically. Second, the relationship between slop-mass slide displacement and precipitation and the one among the landslide stability coefficient, the saturation-area ratio of slip-mass, and the shear-strength parameters of rock and soil of sliding surface were analyzed. Third, the general statistical model of slope-mass displacement and precipitation for debris landslide and the cusp-catastrophic model of shallow landslide under intensive rainfall were established. Fourth, the influence of rainfall on the stability of debris landslide was analyzed. Fifth, the mechanism of deformation, disintegration and failure of debris landslide, the main reviving and failure mechanism of ancient debris landslide, and their main induced factors were revealed. Furthermore, the new methods of the stability analysis of debris landslide were raised. Through these studies, some main results below are obtained.In the first place, the pipe network system of groundwater discharge in natural debris landslide is often developed. Furthermore, groundwater seepage has great inhomogeneity and characteristic of concentrating seepage. The deformation and failure of debris landslide is a slow-developing process. Rainfall, especially, intensive rainfall is the main induced factor of debris landslide.Secondly, by the nonlinear regression analysis and comparison of exponent model and power function one to the slope-mass slide displacement and precipitation of typical shallow and medium layer loose soil landslide separately, the distribution law of power function generally followed by the relationship between slope-mass slide displacement and precipitation is derived, which may provide the scientific basis for the study on themechanism of deformation, disintegration and failure, the stability, and the forecast and prediction of this kind of loose soil landslide under rainfall. The linear distribution law followed by the relationship between the saturation-area ratio of debris landslide slip-mass and its stability coefficient is derived also. Furthermore, its stability coefficient decreases as the saturation-area ratio of slip-mass increases.Through the sensitivity analysis of main factors to influence on the stability of debris landslide, its order is internal friction angle of sliding surface, topographic grade, saturation-area ratio of slip-mass and cohesion of sliding surface by descending order of their sensitivity coefficients.Thirdly, the new method that is used to analyze the stability and compute the stability coefficient of bedding landslide by the non-separation contact elastic-plastic FEM strength reduction method is provided, furthermore, connected with the concrete engineering example, it is shown that to analyze the stability of bedding landslide may more clearly reflect actual state of landslide deformation, disintegration and failure.Fourthly, the sliding surface of debris landslide is determined by the method of limit plastic strain analysis of large deformation elastic-plastic FEM. The sections of different utilization degrees of shear strength are determined on the basis of plastic strain value under the limiting state of landslide. The unbalanced-thrust method comprehensively thinking over different utilization degrees of shear strength of rock and soil on sliding plane is provided, and it is shown by the analysis of concrete engineering example that it may be very well used to analyze the stability of debris landslide and calculate its stability coefficient by this new method, which can more really reflect actual locating state of debris landslide.Fifthly, three dimensional contact elastic-plastic FEM strength reduction method is used to compute the integral stability coefficient of debris landslide and analyze its stability and process of the deformation, disintegration and failure, which the mechanism of deformation, disintegration and failure is revealed. Furthermore, the research result shows that adopting the new method may think over the spatial effect of landslide mass and better reflect the actual locating state and sliding process of debris landslide. In addition, the new method to compute the stability coefficient by the contact elastic-plastic FEM algorithm is led on the basis of physical meaning of landslide stability coefficient, that is, the method to compute the two dimensional section stability coefficient of debris landslide by extracting the friction stress on sliding surface on the basis of the compute result by the three dimensional contact elastic-plastic FEM algorithm. Furthermore, that this new method is fitter to analyze the stability of debris landslide is derived from the comparison among it, the unbalanced-thrust method and the strength reduction method of two dimensional contact elastic-plastic FEM used to compute the stability coefficient of debris landslide.Sixthly, connected with concrete engineering practice, through site exploration and test and indoor physical-mechanics experiment of rock and soil, the process ofdeformation, disintegration and failure of debris landslide under rainfall is analyzed by the analytic means of mathematic statistics, the unbalanced-thrust method, two dimensional non-separation contact elastic-plastic FEM algorithm and three dimensional one, and the theory of debris slope groundwater pipe network drainage system, based on the characteristic analysis of debris general physical-mechanics and seepage. Furthermore, the main mechanism and general mechanics mechanism of deformation, disintegration and failure of debris landslide under rainfall are revealed. Meanwhile, the research result is shown that intensive rainfall and long time proper strength steady rain or intensive rainfall are separately the main induced factors of shallow debris landslide and medium and deep one taking place instability. Additionally, the rainfall influence on the stability of debris landslide is modeled and analyzed by coupling the unbalanced-thrust method adopting equivalent shear strength with the saturation-area ratio of slip-mass with two dimensional non-separation contact elastic-plastic FEM algorithm and three dimensional one.Seventhly, through site exploration and test, and indoor physical-mechanics experiment of rock and soil, adopting the analytic means of mathematic statistics, unbalanced-thrust method, three dimensional large deformation elastic-plastic FEM contact algorithm, and the theory of groundwater pipe network drainage system, the reviving and failure process of ancient debris landslide and its stability are analyzed. Furthermore, not only the main reviving and failure mechanism of ancient debris landslide under rainfall is revealed, but it is revealed also that long time proper strength steady rain or intensive rainfall is the main induced factor of its reviving instability and failure. Meanwhile, the research result is shown that adopting the three dimensional large deformation elastic-plastic FEM contact algorithm to analyze the stability of ancient debris landslide may think over the spatial effect of landslide mass, which makes compute result still more accurate.Eighthly, based on the correlation data of slope-mass sliding displacement and precipitation reported by documents and connected by engineering concrete example, one cusp-catastrophic model of shallow landslide is established by the analytic means of mathematic statistics, the unbalanced-thrust method and the means of nonlinear science cusp-catastrophe theory. Meanwhile, according to this model, the failure mechanism of sudden instability of shallow landslide under intensive rainfall is revealed. Furthermore, it is revealed also that intensive rainfall is the most decisive triggering factor of shallow landslide and the external main reason that influences the stability coefficient value of shallow landslide and its stability. In addition, the reason that few of shallow landslides sometimes come down after intensive rainfall taking place is revealed through the established cusp-catastrophic model of shallow landslide.