Study On Evolution Of Bearing Capacity For Unsaturated Soil Foundation Under Rainfall Conditions

Bearing capacity of an unsaturated soil foundation is the focus of study in geotechnical engineering.Rainwater infiltration is the main cause of bearing capacity decrease.At present,bearing capacity evolution for foundation under rainfall conditions is usually studied with complicated numerical simulation methods or experimental methods,which cost much time and money.Therefore,it is of great practical significance to establish a convenient method for analyzing the bearing capacity of foundation under rainwater infiltration,to reveal the evolution of bearing capacity during rainy season quickly and to prevent foundation failure with the suitable measurements.Analytical solutions of matrix suction and ultimate bearing capacity for foundation under rainfall infiltration with the uniform,advanced-peak and delayed-peak rain patterns are derived and verified.With the derived analytical solutions,the evolution laws of matrix suction and ultimate bearing capacity for foundation under different rainfall patterns are studied.Based on the established BP-Olden significant analysis method,the significance of the influence of rainfall characteristic parameters on the bearing performance for foundation is determined.The main contents and conclusions are as follows:(1)Derivation and verification on analytical solutions of matrix suction and ultimate bearing capacity for foundation under rainfall conditions.Based on the unsaturated seepage control equation,analytical solutions of matrix suction for foundation under the uniform,advanced-peak and delayed-peak rain patterns infiltration are obtained by the Laplace transform,and are verified by the numerical simulation results.Based on the analytical solutions of matrix suction and the calculation theory of ultimate bearing capacity for unsaturated soil foundation,the analytical solution of ultimate bearing capacity for unsaturated soi1 foundation under rainfall condition is derived and verified by the existing experimental data.(2)Bearing capacity evolution for foundation under uniform rain intensity infiltration.Based on the analytical solution of matrix suction and ultimate bearing capacity under uniform rain pattern,under the initial state of foundation with or without rainfall,the evolution of matrix suction and ultimate bearing capacity for foundation is studied during the rainfall duration of 10days and the rainfall intensity in the range from 0cm/h to 0.75cm/h.The results show that:l)In the early stage of foundation without rainfall,the ultimate bearing capacity of the initial unsaturated foundation reaches 1.5 times of the ultimate bearing capacity of the saturated foundation.2)The average matrix suction of the basement decreases with the increase of time,which decreases firstly fast and then slow,and shows a linear decrease with the increase of rainfall intensity.3)After rainfall in the early stage of foundation,the average matrix suction and ultimate bearing capacity are less than the previous period without rainfall.(3)Bearing capacity evolution for foundation under linear rain patterns infiltration.Based on the analytical solution of matrix suction and ultimate bearing capacity under advanced-peak and delayed-peak rain patterns,the evolution of matrix suction and ultimate bearing capacity under the same amount of rainfall but different initial rain intensity and rain intensity coefficient,the same initial rain intensity and different rain intensity coefficient,different initial rain intensity and the same rain intensity coefficient are explored.The results show that:1)For advanced-peak rain pattern:under the same amount of rainfall,the small rain intensity coefficient and the great the initial rain intensity,the evolution law of average matrix suction and ultimate bearing eapacity firstly decreases and then increases.When rain intensity coefficient or initial rain intensity increases,the average matrix suction and ultimate bearing capacity decrease at the same time and the magnitude of the decreases with time.2)For delayed-peak rain pattern:under the same amount of rainfall,the greater rain intensity coefficient and the smaller the initial rain intensity,the average matrix suction decreases with the increase of time,its decreasing rate changes from firstly fast then slow to firstly slow then fast.The ultimate bearing capacity decreases with the increase of time,its decreasing rate changes from near linear to firstly slow then fast.When rain intensity coefficient or initial rain intensity increases,the average matrix suction and ultimate bearing capacity decrease at the same time and the magnitude of the decreases with time.(4)Sigrnificance analysis of the influence of rainfall characteristic parameters on the bearing capacity for foundation.Based on the BP-Olden method,a significant analysis method between the ultimate bearing capacity for the foundation and the rainfall characteristic parameters,such as the previous rain intensity qA and the rain type characteristic parameters(such as rainfall duration t,initial rain intensity q0,rain intensity variation coefficient a),is established.The significant size of each influencing factor is explored.The results show that:the order of significant effects for rainfall factors is as follows:t,b,a,qA The rain pattern characteristic parameter has a greater influence than the previous rain intensity.