Study Of Creep Characteristic For Reinforced Red Clay Under Load And Unload Stress Path

Red clay is widely distributed in Yunnan-Guizhou Plateau,Eastern Sichuan,Hubei,Hunan,Guangdong and Guangxi Provinces in China.It is a kind of regional special soil.The red clay is easy to soften and creep when exposed to water,therefore,methods as increasing soil density or reinforcement are often used to reinforce the soil in engineering.In addition,the stress paths of the soil in different projects are also different.Therefore,it is of great engineering significance to study the influence of soil compactness,number of reinforced layers,and stress path on the creep characteristics of red clay.In order to reveal the creep law of red clay impacted by these factors,and to provide a reliable theoretical basis for the stability evaluation of existing red clay slopes,the design of new slopes,and the treatment of red clay roadbeds,a series of triaxial creep tests of red clay have been carried out in this paper.The main research work and results are as follows:(1)A series of indoor tests were carried out on the red clay,where the basic physical and mechanical properties indices of the red clay,i.e.,the natural weight,specific gravity of soil particles,liquid limit,plastic limit,particle grading curve,optimal moisture content,maximum dry density and shear strength indices were obtained.(2)The triaxial creep test of the red clay under drainage was carried out by using the self-designed triaxial creep tester,and the triaxial creep test curves of red clay under different dry densities were obtained.The physical meanings of the Burgers creep model parameters were analyzed.The model parameters were identified based on part of the creep test curves,and a modified Burgers creep model considering the influence of dry density was established.The Burgers creep model considering the influence of dry density was used to predict the creep test curves used for verification.The results show that the established model has a good predictive effect.(3)In this paper,32 groups of triaxial creep test of the reinforced red clay under loading(where the confining pressure remains unchanged and the axial pressure is applied)and unloading(where the axial pressure remains unchanged and the confining pressure is removed)stress paths were carried out by using the SR-6 triple triaxial creep tester.Based on the creep test results of B03,B13,B23,and B33 samples(where the numbers of reinforcement layers take 0,1,2 and 3,and the stress paths are all unloading stress paths),the modified Merchant creep model with creep damage was used to fit the creep test curve,and the creep model under unloading stress path of red clay considering the influence of the number of reinforced layers was established.The model was used to predict the creep test curve of B03,B13,B23,and B33 samples,and the results show that the model has a good predictive effect.(4)The modified Merchant creep model was used to fit the creep test curves of A03,A13,A23,A33 samples(where the numbers of reinforcement layers take 0,1,2 and 3,and the stress paths are all loading stress paths),and the creep model under loading stress path of red clay was established.Combining with the previously established creep model under unloading stress path of red clay,the change law of creep model parameters under the two stress path was compared and analyzed.Results show that:under the same deviatoric stress condition,the instantaneous elastic strain,creep strain,creep deformation rate,and creep damage degree of red clay under unloading and loading stress paths increase in sequence.Under the same initial confining pressure and axial pressure,the creep failure of red clay is more likely to occur under the unloading stress path than under the loading stress path.