Liquefaction-induced Lateral Spreading Of Soil Layer Under Two Mechanisms

With appearance of the concept of performance-based design, evaluation of soil deformation gradually becomes the dominant criterion in anti-seismic design of geotechnical engineering. Research on liquefaction-induced lateral spreading of ground has become more and more important for the anti-seismic design and security of foundation and geotechnical structures.In this paper, the outcomes from case studies on large ground displacement during the past earthquakes are reviewed firstly. Then liquefaction-induced lateral spreading is divided into two types based on the different characteristics. The first type of large lateral ground displacement is sliding of the sloping soil layers along failure plane under the action of seismic motion. This type of displacement is calculated by using the previous works. Another type of large ground displacement is the overall lateral spreading of soil layers near river or sea band due to liquefaction in the earthquake.The main achievements obtained in the paper are shown as follows:(1) The damages caused by liquefaction-induced lateral spreading during past earthquakes are summarized. The large lateral ground displacement is divided into two types based on the scene and mechanism. Numerical methods and shaking table tests relating to the lateral ground deformation are reviewed.(2) The mechanism of lateral ground deformation of sloping ground is discussed. The conclusion is that the liquefied layers and the overlaying layer move downhill together along the sliding surface in sometime of the whole duration of earthquake. The principle of Newmark's rigid sliding block model and the process of Newmark's rigid sliding block model are elaborated respectively. The procedure is given for calculating this type of lateral spreading. The accelerogram can automatically be turned into a series of sinusoidal waves and as a result, the time histories such as acceleration in sliding surface, yield acceleration, excess pore water pressure, modulus reduction, velocity and displacement of surface can be got easily.(3) The mechanism of liquefaction-induced lateral spreading nearriver or sea band is analyzed through the past earthquake investigation, shaking table tests and cyclic triaxial tests. The deformation is thought not as relative sliding between two parts of soil layers, but as overall permanent deformation of the whole ground. When sand liquefied, the shear modulus decreases rapidly with an increase of excess pore water pressure. The skeleton of soil is softened and the deviatoric strain of soil increases rapidly.(4) An analytical method for the liquefaction-induced lateral spreading near river or sea band is presented by using modulus soften model. The method includes dynamic FEM, static FEM and liquefaction estimation and modulus attenuation. The method here is compared with the results during the 1995 Kobe earthquake and the calculated displacements are roughly equal to the actual results.(5) Simulation of moving of sea wall and ground is accomplished through calculating, drawing of the picture and making animation.(6) The effect of various parameters on the lateral spreading near river or sea band is studied. First is soil property. The displacement of sea wall is quite small and doesn't change a lot with the increasing of input peak acceleration when there are no liquefied areas in the ground. On the contrary, the displacement of sea wall is large and increases with the increasing of input peak acceleration when there are liquefied areas in the ground. Second factor is different input accelerogram. As demonstrated in numerical calculation, both the degree of liquefaction of the ground and the displacement of the wall are quite different when the input acceleration time histories are different although the peak acceleration and duration of the accelerogram are the same. Third factor is the influence of vertical seismic motion. A comparison is made between the results when only horizontal acceleration is inputted and horizontal and vertical accelerations are inputted at same time. The results show...