Stability Analysis Of High-rise Structure On Natural Foundation Of Pebble Layer

In the context of the increasing use of high-rise buildings,how to choose the appropriate foundation form is of great practical significance.At present,most of the actual projects use pile foundations,which have high bearing capacity and wide application conditions.However,blind selection of pile foundations may cause uneconomic conditions.Under certain good site conditions,the direct use of natural gravel or fine sand as the supporting layer of high-rise buildings can fully meet the engineering requirements and save a lot of cost.Therefore,it is necessary to study the bearing properties of natural foundations.This paper combines the natural foundation design of a 32-story shear wall structure in a certain area of Xi'an.Firstly,the indoor large-scale direct shear test is carried out to study the shear characteristics of the bottom surface of the pebble soil and the raft foundation.Then the ABAQUS software is used to establish the upper soil-foundationstructure interaction model and verify the feasibility of using natural foundations for highrise buildings with pebble layer as the main bearing layer from two aspects of static and dynamic.The main results are as follows:(1)The shear stress of the pebble soil under the action of four vertical pressures shows a good linear relationship,which basically conforms to the Mohr-Coulomb strength theory.When the vertical pressure is small,the soil samples of each group have obvious shear stress peaks.With the increase of vertical pressure,the shear stress increases slowly,there is no obvious peak point.(2)The cohesion of pebble soil is smaller than that of fine-grained soil.When the unevenness coefficient and the curvature coefficient are constant,the larger the maximum particle size of the pebble soil,the larger the internal friction angle and the smaller the cohesive force.When the maximum particle size of the soil is the same and the curvature coefficient is constant,the soil sample with smaller unevenness coefficient has larger cohesive force and smaller internal friction angle.As the maximum height of the concrete bottom profile increases,the cohesive force of the contact surface decreases while the internal friction angle increases.(3)The analysis results of the interaction model show that with the increase of floor load,the rate of subsoil's subsidence increases.The vertical stress of the raft foundation along the long edge is the largest,while the center point is only half the size.The grading of the good pebble soil has less internal force and settlement than the poor graded soil.In the case where the unevenness coefficient and the curvature coefficient are constant,the larger the maximum particle size,the larger the average stress and settlement of the pebble soil.(4)The self-vibration form of the superstructure is dominated by low frequency vibration,and the natural vibration period decreases with the increase of the mode order.The foundation soil has amplifying and filtering effect on the propagation of seismic waves,and the waves reaching the surface are mainly close to the component of the natural vibration period of the site.Under the action of earthquake,the horizontal acceleration,velocity,displacement and maximum interlayer displacement angle of the superstructure increase with the number of layers.The reaction values of the basement layer are smaller than the dynamic response of the soil on the surface of the upper structure and the surface of the pebble layer,indicating that the basement of the high-rise building has a good effect of earthquake absorption and isolation.(5)The maximum settlement and overall inclination of the soil-foundationsuperstructure interaction system under static load are less than the specification limit,the interlayer displacement angle of the structure under 8° frequent and 8° rare earthquakes also satisfies the design requirements,so the natural foundation scheme of the project is feasible.