Study On Rupture Process Of Overlaying Soil Due To Fault Bedrock Dislocation Of Earthquake Fault And Its Effects On Buried Pipelines

Damage reason of buried pipelines is primarily resulted from the overlaying soil rupture due to the earthquake fault dislocation. The form and state of overlaying soil rupture depend on the types of the fault and its dip-slip angle and size of dislocation, and the thickness of overlaying soil and its distribution. The cases of bedrock fault, including the types of fault and its dip-slip angle, size of dislocation, is related with the properties of the faults and the intensity of earthquake, which can be evaluated based on geological data. The aim of this paper is to reveal the rupture process of overlaying soil and its effects on buried pipelines crossing the fault. The paper consists of two parts: the first part is about simulation of the rupture process of the overlaying soil on bedrock, including single homogeneous soil layer and soil layer with soft/hard interlayer, due to bedrock fault dislocation. The second part is about analysis of its effects on buried pipelines. In the first part, we use plain strain finite element method, to establish a nonlinear model of overlaying soil on bedrock, and study the rupture process of overlaying soil and its failure states. In order to know well the failure states on the different conditions, we simulated the cases not only of the single homogeneous soil but also the soil with soft/hard interlayer. The main research achievements are:a) Establishing a new FEM model, in which we modified the boundary constrained conditions of the soil and made use of nonlinear constitutive model as well as property of soil crack-slip, simulated the process of the overlaying soil.b) The earthquake damage phenomena are simulated, that is the rupture failure of the earth's surface doesn't mean a rupture overlaying soil.c) Influences of soft/hard interlayer in the overlaying soil is discussed on soil rupture process. Results show: the overlaying soil with a soft interlayer can obstruct the rupture failure from bedrock up to earth's surface, however, a soft interlayer deeply buried will bring about a wider range of the earth's surface rupture failure; Otherwise, Thickness of the soft interlayer may effect the rupture course of the overlaying soil. There is a smaller influence on the rupture failure of the overlaying soil with hard interlayer.In the second part, we establish a 3D FEM model to study the overlaying soil rupture effects on buried pipeline crossing fault. Some conclusions are obtained:a) Overlaying soil can consume some energy from fault bedrock rupture, and decrease pipeline damage. Thickness of the overlaying soil has influence on the plastic deformation length of the buried pipelines. The point of intersection that the rupture trace of the overlaying soil intersects at the buried pipelines is the position that the pipeline is apt to failure.b) At the two sides of the rupture trace, the pipeline's relative vertical displacement doesn't change with the change of overlayer's thickness. Thus, size of the fault dislocation is a key factor inducing pipeline failure.c) Different kinds of overlaying soils have apparent influence on deformation position and value of the pipeline.In the first part of this paper, on the basis of former researches, we have an elaborate division of this job and get some new conclusions. In the second part we just did some preliminary research work for the engineering application.