Experimental Study On The Effect Of Disturbance Degree On Thixotropy Of Structural Clay In Zhanjiang Formation

With the continuous advancement of "One Belt And One Road" in our country,some key industrial projects have settled down in the coastal area of Beibu Gulf.The structural clay of Zhanjiang Formation,which is widely distributed in this area,is the main carrier of various engineering activities.Due to its strong structure,the strength of structural clay in Zhanjiang Formation decreases rapidly after being disturbed by engineering activities,and its thixotropic strength continues to recover after standing.The thixotropy of structural clay in Zhanjiang Formation is affected by disturbance,and the recovery of thixotropy strength varies with the degree of disturbance.In order to explore the influence of disturbance degree on thixotropy of structural clay in Zhanjiang Formation,a laboratory model test was carried out.Based on the in-situ cross plate shear test,a model device was designed.The disturbance process of soil samples was simulated by indoor vibration test.The micro-cross plate shear test was carried out on three kinds of soil samples under different disturbance degrees(0,33%,66%,100%)and different standing time(0 d,7 d,28 d,56 d,91 d).Under the same disturbance degree(66%)and different standing time(0 d,7 d,28 d,56 d,91 d),the unconfined compressive strength tests of the three soil samples were carried out.The undrained shear strength and unconfined compressive strength of the micro-cross plate at each standing time were tested respectively.The influence law of disturbance degree on thixotropic recovery strength of soil is analyzed.The main research results of this paper are as follows:(1)The three structural clays of Zhanjiang Formation have poor physical properties such as high water content,high liquid limit,high plasticity index and large porosity ratio,as well as high mechanical strength.According to the sensitivity of soil samples 1,2 and 3,they can be divided into high sensitivity soil,medium sensitivity soil and low sensitivity soil respectively.(2)The disturbance time required for structural clay of Zhanjiang Formation increases with the increase of disturbance degree,and the higher the sensitivity,the longer the disturbance time needed to reach the same disturbance degree.(3)Under the same disturbance degree,the undrained shear strength and strength recovery degree of the three kinds of structural clay undisturbed soil in Zhanjiang Formation did not change significantly with the increase of standing time.Disturbance degree 33%,66%and 100%,the three groups of structural clay in zhanjiang micro cross board undrained shear strength,strength recovery degree and thixotropic regain strength than that increases with the increase of incubation time,thixotropic sensitivity gradually decreased with the increase of incubation time,the stronger the soil structure,micro cross board undrained shear strength,strength recovery degree and the thixotropic regain strength than over time increases with the increase of amplitude and rate,the greater the thixotropic lower amplitude and rate,the greater the sensitivity.The power function relations of strength recovery degree and thixotropic recovery strength ratio and standing time under the same disturbance degree are obtained by fitting.(4)The strength recovery degree and thixotropic recovery strength ratio of the three structural clays in Zhanjiang Formation did not change with the increase of disturbance degree when the standing time was 0 d.Let stand for 7 d,28 d,56 d,91 d,the strength of the three groups of structural clay in zhanjiang recovery degree increases along with the disturbance degree,a linear relationship,thixotropic regain strength than all decreased with the increase of disturbance degree,assumes the inverse proportion,and three kinds of soil sample is obtained by fitting in the incubation time under the strength recovery degree,thixotropic regain strength ratio and the relation between the degree of disturbance;Under the same standing time,the stronger the soil structure is,the greater the rate and range of strength recovery will be with the increase of disturbance degree.