| With the development of the national economy, the quality of the highway becomes higher and higher, and the deep cut-covering is inescapable. As a transient flow, the unsaturated seepage of the rainfall can change the pore pressure field of highway slopes and reduce the stability of the slope. As a result, many collapses of high slopes are occurred after the rainstorm, which causes quantities of economic losses and casualties. So, in order to get the stress-strain state and the correct evaluation of the slopes on stability during the rainfall, it is necessary to study the unsaturated seepage for slopes.The paper briefly introduces the seepage theory for porous medium, and the mathematical expression and its simplified form of the water-soil characteristic curve and osmosis function, and controlling equation of aqueous phase unsaturated seepage flow. The paper also introduced the basic controlling equation, numerical computation formula and the stress-coupling formula of the Two-phase flow in FLAC~2D.Presently, for the calculation on the unsaturated seepage of slopes during the rainfall, that about gas-flow and simplified calculation of stress coupling is not considered. To meet this problem, the paper introduced two-phase flow-stress coupling into the rainfall analysis of Xianglin Yunnan highway slope. According to the engineering geological characteristic, FLAC~2D is applied to setup the model to finish the two-phase flow calculations. And strength reduction method is used to calculate the slide surface and safety coefficient. Many tests are done to the parameters, such as the rainfall intensity, rainfall durative time and ratio of the slope. The main achievements are as follow:(1) At the beginning of the rainfall, the aqueous phase osmosis of soil is not good, and its saturation increases slowly even the rainfall intensity is very great. It is with the increment of the rainfall durative time that becomes heaver. During this period, gas moves to the soil of the slope surface as the seepage of the rain, and with the increment of the saturation, some of the gas moves out of the slope, while some is pressed into it.(2) The negative pore water pressure of surface soil increases to 0 and the saturation increases to 1 due to the rainfall. When the immersional wetting appears, the pore water pressure increases quickly. But after the immersional peak, theincrement of moisture content is not obvious. And the unsaturated zone exiting in the slope gets less and less during the action of the rainfall.(3) One part of the rainwater is absorbed by the unsaturated surface soil, which increases the moisture content and saturation. And the other part flows to the slope toe, which heads up the slope toe and induces slope toe failure.(4) With the increment of the rainfall intensity and the passage of time, the depths of infiltrating into the embankment becomes larger, the suction and the slope stability safety factor becomes less. The influence degree during rainfall infiltration of slope whose ratio is 1:1 is as nearly the same as that of 1:0.75. |
