Abstract:Earthquakes can result in huge losses of human life and property.According to extensive field surveys,a significant number of foundation failure cases are due to sand settlement,as foundation upsetting and cracking can be caused by large deformations or differential settlements. Seismic waves are a type of random and irregular dynamic pulse and have a great influence on the seismic settlement of sand.By setting the boundary value in a time history curve to 60% of the maximum peak acceleration,various seismic waves can be divided into two types:vibration-type waves,which have more than two wave crests within the boundary value,and impact-type waves.Different types of seismic waves have different effects on the liquefaction and compression of sand,possibly due to the problem of energy release.However,traditional methods for calculating the seismic settlement of sand neglect the different types of waves;they merely consider the maximum acceleration amplitude to simplify this complex problem by using an equivalent sinusoidal quantity.This simplification may cause larger errors during practical applications.In this paper,the nonlinear finite element software ABAQUS,which is a frequently used commercial software for numeric calculations,is used to develop a bounding surface hypoplaticity model for sand that includes a UMAT subroutine.The formulation of this constitutive model is based on the bounding surface plasticity theory,which a large number of laboratory experiments have proven to be effective in describing the cyclic behavior of sand.The dynamic simple shear test has a few advantages in assessing the seismic behavior of soil.Primarily,since it applies cyclic shear stresses onto horizontal planes and permits the continuous rotation of principal stress axes,this test replicates field loading conditions much more accurately than the cyclic triaxial test.By simulating the dynamic simple shear test using sand with different relative densities under different types of seismic wave loading,this paper studies the influence of wave type on the process of seismic settlement and the final settlement value,as well as the deformation of sand under earthquake loading.Finally,a series of time-history curves comparing shear strain versus vertical strain were be obtained from this series of numerical experiments,and were compared with laboratory results. The main conclusions are as follows.The wave band prior to the maximum peak acceleration governs the controlling effect on seismic settlement;however,the left wave band also has an obvious influence when the peak value attains 80% of the maximum value under vibration-type seismic loading.An analogous experiment yielded similar compression results;under the same conditions but under the influence of different types of seismic waves,the compression results were disparate,as vertical strains caused by vibration-type seismic waves were greater than those caused by impact-type waves.By taking into account the wave type,this method is much more practical for the simulation of sand seismic settlement at actual sites.As the model parameters related to the dilatancy effect are constant,there is a certain amount of bias between the simulated and experiment results.Further research into these parameters is needed.
