Experimental Research On Earth Pressure Of Unsaturated Intact Loess Slope And Permeability Rule Of Water In The Slope

To study the distribution characteristics and formation mechanism of earth pressure of unsaturated intact loess slope and the seepage properties of water in the unsaturated intact loess slope,a series of experiments were done,such as slope cutting and water immersion text at slope top.At first,the test scheme of measuring earth pressure of unsaturated intact loess slope was developed,in which one end of a tie bar was anchored in a pile that is at the stable region of a slope and the other end was anchored in the free force of the slope by steel pate and screw.The height of the vertical cut slope is 14.5 meters.Slope cutting is performed as segmentation from top to bottom of the undisturbed slope.We measured the tension of the tie bar so as to calculate the earth pressure on the steel plate which released when the intact slope was cutting through conversion.The test method in this experiment which can measure the earth pressure of unsaturated intact loess slope directly is different with the traditional way to measure the earth pressure which use retaining wall and earth pressure cell.This measured method is an attempt to measure the earth pressure of intact soil.Water immersion test is done when cutting slope was completed,observe variation conditions of earth pressure in the process of water immersion test and discuss permeability rule of water in unsaturated intact loess slope.Secondly,in the process of cutting slope,we could measure earth pressure on the bolting steel plate because of stress releasing of soil,and then we could get the curve of distribution characteristics of earth pressure of unsaturated intact loess slope.Analyze the variation characteristics of the curve and the causes,the results showed that the earth pressure of each point of measurement is nonlinear relation of increasing as depth of cutting slope is increasing;the height of independent stability with the soil index of this experiment is 9 to 10 meters;distribution curve of earth pressure strength is analogous to parabola distribution;calculate the earth pressure strength of experimental slope by classical Rankine earth pressure theory which is 22 times of earth pressure strength of measurement.Thirdly,analyze the variation regularities of earth pressure in the process of water immersion test.Discuss the real causes of earth pressure through specific position of slip plane and the height of shear opening of vertical slope which were got by actual measurement.The results showed that limit value of horizontal displacement of air face as for the unsaturated vertical loess slope is 1cm.If the displacement value is more than 1cm, the slope probably gets landslide.Earth pressure strength increased rapidly when water immersion was done on the top of slope,the maximum of earth pressure strength is 4 times of earth pressure strength without water immersion.The writer thinks that the earth pressure of air face can be considered as two pasts—sliding soil and stable soil.At last,analyze the variation regularities of daily moisture content of soil with the of 2～3m beneath the immersion test pit to discuss the formation and the migration process of transient saturated zone,thus analyze formation mechanism of permeability regions of water in unsaturated intact loess slope,and summarize migration rules of water in unsaturated intact loess slope.The results show that the process of water seepage in the unsaturated loess slope is the process of constant enlargement of transient saturated zone; permeability zones and wetting angle are not fixed value;permeability zone in the unsaturated loess would be closed region of approximate oval forever.