Study On Deformation Of High-speed Rail Soft Soil Foundation Under Intermittent Drainage

The soft soil settlement caused by train load will seriously threaten the safety of high-speed railway.Previous studies mainly focus on the material of subgrade,while soft soil foundation is often ignored.Due to the development of transportation industry,a large number of traffic facilities are built on soft soil foundation,and the additional settlement during operation will become a huge potential safety hazard.At present,the research on the settlement of soft soil foundation under traffic load mostly stays on the long-term cyclic load,but in fact,there are intermittent periods between train operation and non operation period,during which consolidation and drainage can still produce part of settlement,which can not be ignored.Therefore,considering the cumulative stress of natural drainage in intermittent period,the study is close to the reality and provides reference and basis for the design of high-speed railway subgrade.In this paper,the fourth layer of undisturbed saturated soft clay in Shanghai is taken as the research object.By means of numerical simulation and indoor dynamic triaxial test,the dynamic strain and dynamic pore pressure of undisturbed saturated soft clay under traffic load and intermittent drainage are studied,Finally,the cumulative plastic strain prediction model of undisturbed saturated soft clay under traffic load is obtained considering the intermittent natural drainage and other conditions.The main research achievements of this paper include the following aspects.(1)Through the derivation and simplification of the boundary model,a threedimensional dynamic triaxial test model of small samples is constructed.It is found that different model parameters have different research results on dynamic strain and dynamic pore pressure,and there are obvious differences in the degree of influence on the results.N has a greater influence on the axial strain,and presents a certain regularity for the size of the results.(2)The results of orthogonal test on the amplitude,vibration number and inclination of stress path show that the influence degree of the results is as follows:dynamic stress amplitude > vibration times > stress path inclination.(3)The consolidation strain of partial drainage in interval will accumulate a part,and it will decrease gradually in the form of inverse proportional function.By keeping the amplitude and frequency of the dynamic stress of soil constant,the average principal stress of soil can be changed,and the dynamic strain of soil can be related to the average principal stress.With the increase of the average principal stress,the ability of soil to resist deformation increases.(4)Based on the test data obtained after 1000 cycles loading,the accumulated strain under the larger cycle times is calculated.The parameters required by the formula have a simple fitting relationship with CSR.It can be used to predict the cumulative strain of soil under different CSR and different cycles.Therefore,the method has a wider application range,But the prediction accuracy is determined by the correlation coefficient of the fitting formula between CSR and dynamic strain obtained in the previous test.Combined with the drainage conditions of intermittent period set up in laboratory test,a strain prediction formula including cumulative plastic strain produced by consolidation drainage in intermittent period is proposed.This thesis has 95 figures,9 tables and 127 references.