Remodeling Weak Expansive Soil Soil-water Characteristic Curve And Research On Unsaturated Permeability Characteristics

Expansive soil is widespread in China.The expansion and contraction deformation of expansive soil in the process of absorbing and losing water threaten to destory the safety of artificial structures and various engineering buildings.The changes in moisture in the environment is an important factor to induce the swelling and shrinkage deformation of soil.By blocking the flow of water in soil,the continuous expansion and deformation of soil can be effectively controlled.The changes of water content or suction will also lead to the great change of its hydraulic and mechanical properties in unsaturated expansive soil.Therefore,it is of great significance to study the soil-water characteristics of expansive soil and the migration law for predicting and preventing the deformation of expansive soil.This paper takes remolded weakly expansive soil for example – studying the expansion characteristics and microstructure characteristics of weakly expansive soil.The calibration curve of domestic double-circle No.203 filter paper and the soil-water characteristic curve of remolded weakly expansive soil were measured.The soil-water characteristic curve was applied to the instantaneous profile test in order to studying the water migration law and unsaturated permeability characteristics of weakly expansive remolded soil.The main work and research results of this paper are as follows:(1)According to the results of montmorillonite content,free expansion rate and cation exchange capacity,the test soil sample was determined as weakly expansive soil.The results suggest that the swelling characteristics of remodeled weakly expansive soils are closely related to the initial state and the overburden load.According to mercury injection test results,there are two kinds of pore modes in remolded weakly expansive soil: inter-aggregates and intra-aggregates.The macroscopic compression deformation of expansive soil under load is to change the inter-aggregates pore content of soil mainly,while the pore structure in intar-aggregates is hardly affected by strong cementation.(2)With different concentrations of Na Cl solution as the suction source,the vapor balance method was used to measure the total suction calibration curve of the filter paper;at the same time,use the pressure plate instrument to determine the matrix suction calibration curve.According to the calibration curve,the soil-water characteristic curve of remolded weakly expansive soil was measured by combining filter paper method and pressure plate instrument.The results indicate that the soil-water characteristic curve of the remolded weakly expansive soil shows a bimodal distribution-because of a bimodal distribution of the micro-pore structure of the remolded weakly expansive soil.And there are two kinds of pores in the expansive soil: intra-and inter-aggregates.(3)Through self-made test equipment,the instantaneous profile test in the laboratory was used to study the water migration and unsaturated permeability characteristics in the soil column.The results show that the changes of volumetric moisture content of each section of the soil column keep the same trend.The volumetric moisture content increases firstly and decreases subsequently until its tends is stable.The growth rate of the volumetric moisture content of the section in the water injection stage is significantly higher than that in the free seepage stage.The most swelling deformation of the soil column occurs in the free seepage stage.For the lateral confinement,the unsaturated permeability coefficient curve of remolded weakly expansive soil does not change in a single way.It decreases firstly and increases subsequently with the decrease of suction.And the permeability coefficient reaches the minimum value when the suction is about 2500 k Pa.In the free seepage stage,the unsaturated permeability coefficient is uniformly distributed with suction.The distribution of permeability coefficient is concentrated at the water supply stage,and some of the permeability coefficients are greater than that in the free seepage stage.