Expansive Behaviours Of Ningming Expansive Soil Under Controlled Humidity Environment

Expansive soil is widely distributed all over the world as a building material.Due to its own water-absorptivity,expansive soil causes problems such as uneven settlement of buildings,instability of slopes,and road tumbling.These varying degrees of engineering disasters bring huge losses to the country's property security,resulting in unnecessary economic and financial waste.What is more,it may endanger the lives of the general public and cause unnecessary casualties.It is necessary to concentrate on the study of the unsaturated expansive behaviours of expansive soil under different relative humidity in order to seek advantages and avoid hazards,and to better play the advantages of expansive soil.In this paper,Ningming expansive soil is selected as the main test soil,and Wyoming Bentonite is used as the reference soil.The saturated salt solution method is used to provide different relative humidity environments for the samples,and the constant volume method is used to measure the swelling deformation and swelling force under the relative humidity environments of unsaturated soil.The specific research content of this paper is as follows:1)Using saturated salt solution method to measure the swelling deformation of the two kinds of soils,and draw the two soils'swelling rate curves at each relative humidity.In the curves of the swelling rate under the relative humidity,the test results show that:From the shape of them,the laws of the swelling rate curves are similar,and the swelling rate values increase with time.Finally,it approaches a stable value.The swelling rate curves of the two expansive soils include three stages of change:(1)rapid expansion stage;(2)deceleration expansion stage;(3)slow expansion stage.2)The saturated salt solution method and the constant volume method are used to measure the swelling force of the two soils,and draw some curves of the two soils such as overall swelling force and time curves(P_s-t),swelling force and time curves(P_s-t)at each relative humidity,relative humidity and swelling force curves(RH-P_s),suction and swelling force curves(s-P_s).In the tests of the swelling force of the soil under the unsaturated conditions,from the perspective of time-consuming to reach stability,overall,Ningming is shorter.From the aspect of swelling force,the Ningming is significantly weaker than that of Wyoming Bentonite.In the curves of relative humidity and swelling force(RH-P_s),as the relative humidity increase,the swelling force of both soils increase,and the curves are roughly linear in the early stage.But in the curves of suction and swelling force(s-P_s),the rule is exactly opposite of the RH-P_s curves.The experimental results are similar to those of swelling curve,but the swelling force and time curves(P_s-t)of Ningming expansive soil decrease slightly after reaching the peak value,forming"residual swelling force".In addition,the cause of"residual swelling force"in Ningming expansive soil is analyzed,and the expansion mechanism of expansive soil in unsaturated condition is also explained.Because of the wet and rainy conditions in Guangxi,this kind of wet environment or varying degrees of rainfall often leads to slope instability,road slurry and other geological disasters.Therefore,taking Ningming expansive soil as a representative,the expansive behaviours of it under different relative humidity conditions are studied,which provide an important reference value for solving this kind of engineering problems.