Experimental Research On The Stress-strain Property Of Bio-Enzyme-Treated Silty Clay

Silty clay soil is a special kind of cohesive soil,and it is characterized by its strong structure,porosity and water sensitivity.Silty clay is often used as a foundation and subgrade filling.Silty clay has obvious capillarity,strong water absorption ability,and can retain water for a long time.As a result,when the climate and environment changes such as rainfall and frost,the structural connection between silty clay particles was weakened,the physical and mechanical properties of the soil was changed,and the bearing capacity of roadbed and foundation is easy to decrease.Therefore,it is very important to improve the strength of silty clay through appropriate curing agent.And it can avoid engineering accidents and disasters to meet the requirements of relevant engineering specifications.Based on Central South University of Forestry and Technology(Grant No.2013ZDXK006)and Hunan Engineering Laboratory for Manufacturing and Application Technology of Modern Timber Structural Engineering Materials(Grant No.HELFMTS1707).The structural influence of water content on silty clay was studied though the consolidation tests of undisturbed and remolded silty clay.The effects of bio-enzyme on the physical and mechanical properties of silty clay were studied through the experiments of improving the physical and mechanical properties of silty clay by bio-enzyme.Based on the triaxial shear test of bio-enzyme-treated silty clay,the stress-strain relationship of bio-enzyme-treated silty clay was obtained.The stress ratio parameter model was esta'blished to predict the test datas.Besides,the modified Duncan-Chang model based on the disturbed state theory was established to predict the stress-strain relationship of bio-enzyme-treated silty clay.The contents and results are as follow:1.Based on the consolidation test,the undisturbed soil and remolded soil compression curve and compressibility index were analyzed.The structural yield pressure,pre-consolidation pressure and structural strength of undisturbed soil are calculated by using the cubic polynomial model and the reduction curve model,and the effect of water content on the structure of undisturbed soil was analyzed.It provides theoretical analysis basis for foundation and subgrade engineering application.2.Based on the atterberg limits test,compaction test,free swelling ratio test,direct shear test by bio-enzyme,lime and cement,the influences of bio-enzyme contents,lime contents and cement contents on the physical and mechanical indexes of silty clay were analyzed.The experimental datas show that the improvement effect of three curing agents is from better to worse:bio-enzyme,lime and cement.3.Based on the consolidated drained triaxial test of bio-enyme-treated silty clay,the stress ratio parameter was defined according to the strength enhancement law of bio-enzyme-treated silty clay.The change law of stress ratio parameters of silty clay with different confining pressures and enzyme contents is obtained.According to the change law of stress ratio parameters of bio-enzyme-treated silty clay,and considering the factors of spherical stress,deviator stress,shear stress,confining pressure,the constitutive model of strength increasing parameter of stress ratio of bio-enzyme-treated silty clay was established.It can predict the strength increasing parameter of stress ratio of silty clay under different confining pressures and bio-enzyme contents.It is proved that the prediction effect is good.4.Based on the consolidated drained triaxial test of bio-enzyme-treated silty clay,combined with the Duncan-Chang model,the influences of enzyme content on the cohesion and internal friction angle,the initial tangent modulus,the peak strength,the principal stress limit value,the parameters K,n,Kl and nl in the Duncan-Chang model were obtained.Combining with the disturbance state theory,a modified Duncan-Chang model for bio-enzyme-treated silty clay was established.It can better predict the stress-strain relationship of silty clay affected by the disturbance of different bio-enzyme content.