Study On Evolution Of Bearing Capacity Of Layered Foundation Under Rainfall Infiltration

The bearing capacity of the foundation is a primary concern in the field of foundation engineering.The self weight of the structure and the applied loads are transferred to the soil safety and economically.The load at which the shear failure occurs is called ultimate bearing capacity of foundation.Most of the work has been carried out on single layer foundation e.g.,sand or clay layer only.Very few studies are available on a double layer soil system.Understanding the bearing capacity response on layered soils under rainfall infiltration has always been a challenge for researchers.Rainwater infiltration is the main cause of bearing capacity decrease.At present,study on evolution of bearing capacity for layered foundation under rainfall conditions often requires complex numerical simulation methods or experimental methods,which takes a long time and costs.Due to limitations of numerical simulation methods and experimental methods,it had been difficult to understand the true bearing behavior.Some researchers have tried solving this problem by analytical methods and have found some success.In this thesis,a numerical model of matric suction for layered foundation under uniform,front-peak,post-peak and medium-peak rainfall patterns is developed,using the finite element software Geo-Studio,"SEEP/W" program.Then based on this,the evolution law of matric suction and ultimate bearing capacity for layered foundation under different rainfall patterns is studied and the effects of rainfall pattern,rainfall intensity and rainfall duration on bearing capacity for layered foundation are analyzed.The main contents and conclusions:(1)The parameters of layered foundation and rainfall intensity are determined;The finite element software Geo-Studio,"SEEP/W" program is used to establish the numerical simulation of layered foundation and determine the transient distribution of matric suction in the process of rainfall infiltration;The average matric suction of layered foundation during rainfall infiltration process is calculated;Hansen ultimate bearing capacity formula is used to calculate the ultimate bearing capacity of layered foundation in the process of rainfall infiltration.(2)The evolution law of matric suction and bearing capacity of layered foundation under different rainfall duration and rainfall intensity is revealed.Based on the numerical solution of matric suction and the expression of ultimate bearing capacity,the evolution law of matric suction and ultimate bearing capacity for layered foundation is studied during rainfall duration of 10 days and the rainfall intensity in the range of 0cm/h to 0.75cm/h.The results show that:under no rainfall in the early stage of foundation,the ultimate bearing capacity of the initial unsaturated foundation reaches 1.5 times of the ultimate bearing capacity of the saturated foundation;The average matric suction decreases with the increase of time.Its decreases firstly fast and then slow and shows a linear with the increase of rainfall intensity.(3)Evolution law of matric suction and ultimate bearing capacity for foundation under different rainfall patterns are explored.Based on the numerical solution of matric suction and analytical expression of ultimate bearing capacity under uniform,front-peak,post-peak and medium-peak rainfall patterns,the evolution law of matric suction and ultimate bearing capacity is analyzed.The results show that:for the uniform rainfall pattern,more the rainfall duration increases more the matric suction and ultimate bearing capacity decreases;For the front-peak rainfall pattern,the matric suction firstly decreases due to the rainfall duration and secondly,more the rainfall duration increases more the matric suction increases.The ultimate bearing capacity of foundation decrease with the increase of rainfall intensity;For the post-peak rainfall pattern,more the rainfall intensity increases more the matric suction decreases.With the increase of rainfall intensity,the average matric suction decreases,therefore the ultimate bearing capacity of foundation also decrease;For the medium-peak rainfall pattern,the matric suction firstly decreases and finally increases due to the rainfall duration.With the increase of rainfall intensity,the average matric suction decreases,therefore the ultimate bearing capacity of foundation also decrease.