Experimental Study On The Expansive Force In The Expansive Soil In Ningming County Of Guangxi

Expansive soil generally swells and softens when the water is adsorbed into the soils,while asit will be shrinkage when the pore water is loss.Furthermore,the engineering behavior of expansive soil is very complex and difficult to characterize.Numerous geotechnical disasters often occur in the area of expansive soils.Degrees of expansion will vary in a expansive soil,both in a saturated and unsaturated environments,,in which different expansion forces is shown.Hence,the disasters on the engineering construction will be caused in the expansive soil area.Although there is a certain understanding of the swelling characteristics of saturated soils,there is a lack of research on the expansion characteristics of soils in unsaturated environments,especially in the relative humidity control environment.In this paper,the ultimate swelling force and natural swelling force were measured in Ningxia expansive soil under unsaturated water environment and controlled humidity.The expansion mechanism was analyzed.The main contents of this paper are as follows: the test of the ultimate swelling force of the expansive soil in the saturated environment and the swelling test of the expansive soil in the unsaturated environment.The main results are as follows:(1)At present,the main soil swelling force measuring include swelling-consolidation method,pressure swelling method,balance pressure method,constant volume method.Based on the constant volume method of measuring soil swelling force,the use of TST-55-type permeameter,high-precision pressure sensors and data acquisition system to improves measuring method of soil swelling force,and study the expansion characteristics of expansive soil.Test results showed that the initial water content and dry density of soil sample has a significant influence to limit swelling force,and established the equation between they and limit swelling forces;at lower initial water content,when soil sample's limit swelling force of different dry density reaches a peak,it has a different rate decreases,the value along with increasing of the dry density come decreased.A linear relationship exists in the double logarithmic coordinate axis about the reduction value of limit swelling force and the dry density.at higher initial water content,when soil sample's limit swelling force of different dry density reaches a peak,it will remain stable trend.There is a good linear relationship between the logarithm of limit swelling force and initial water content.There is a both good linear relationship between the logarithm of water absorption of soil sample and initial water content or dry density.(2)In order to study the swelling force of expansive soil under unsaturated environment,combined with the constant volume method for measuring the expansion force and the steam balance method for control the suction(control the relative humidity),a device for measuring the expansion force of expansive soil in unsaturated environment is designed,and expansion characteristics of expansive soil in Ningming is studied.The test results show that the natural swelling force of expansive soil increases with the increase of relative humidity in the environment.By axis translation method and steam balance method,found that moisture curve and desorption curves of Ningming expansive soil are not consistent,they constitute a hysteresis loop.Natural expansion force will be slightly reduced after reaching a peak,and finally reaches a stable value,that is the residue swelling force.The equilibrium time between the natural swelling force and the residual swelling force are related to the relative humidity.The similar formulas of Fredlund-Xing model can be used to describe the relationship between the swelling force and the suction,and obtain the swelling force formula of an initial state expansive soil under unsaturated environment to saturated environment(including saturated environment).