Study Of Moisture Transfer Characteristics Of The Mountain Highway Subgrade Under Rainfall Infiltration

Roadbed as the basis of the road, is an important part of the road structure, its engineering characteristics to some extent determines the project impact and performance of the road. Among the many factors that affect the engineering properties of embankment, the water content more prominent role, many of roadbed diseases are caused by water, such as a roadbed instability, subsidence and so on. This is because that when the water content is large, th structural strength of the subgrade would be substantially reduced; at the same time, when the subgrade moisture changes, the seepage would produce scouring action on the internal subgrade soil, and affecting the stability of the soil structure. Rainfall is the main source of subgrade moisture: on the one hand, the rain would infiltrate into the roadbed through pavement cracks and slope, etc., and change the water content and distribution of subgrade; on the other hand,since mountainous excavation subgrade close to or even below the groundwater table,the rainfall would recharge groundwater, and infiltrate into the roadbed by capillary action. Studying the motion characteristics of subgrade moisture in the conditions of rainfall,which would help to understand the law of embankment seepage and its moisture changce and distribution,and provide a reference for roadbed engineering and its drainage system design.Firstly,This article begins with unsaturated soil theory, depth analysis of the mechanical properties of unsaturated soils, soil- water characteristic curve and unsaturated soil subgrade problems. By using darcy’s law and combining with soil water potential theory, saturated-unsaturated seepage theory and differential equations, boundary conditions, etc., it deeply analyzes the saturated subgrade- unsaturated seepage problem; Secondly, with infiltration, infiltration rate and permeability coefficient and other parameters,it describes the mechanism and process of roadbed rainfall infiltraton in detail,and introduces several models of rainfall infiltration and border infiltration; Finally, it conducts a comprehensive analysis of Numerical simulation of roadbed rainfall infiltration and field test of water monitoring,and summarizes the law of subgrade moisture changes and distribution in the conditions of rainfall.This research,which in the engineering background of Guangzhou City, North Second Ring Expressway,focuses on the long-term monitoring of subgrade moisture content and pore water pressure by burying a large amount of soil moisture meter and pore water pressure gauge in the subgrade(excavation,fill)of the test section. And with professional seepage analysis software used,finite element model is established and numerical simulation experiments of rainfall infiltration are achieved,then through comparative analysis of field test and simulation data, summarized the migration law of roadbed water; Finally, combined with the actual situation of the project, the test section of the drainage system was optimized.