Triaxial And Creep Experiment Study On Mechanical Properties Of High Fill Coarse-Grained Soil In Water-Level Fluctuation Zone Of Baihetan Reservoir

After the Baihetan Dam reservoir area is filled with water,the high fill site with coarse-grained soil located in the fluctuation zone will experience long-term water level fluctuation,which is very disadvantageous to the deformation and stability of the site.In this paper,based on the research project on the stability of high fill site in the water-level-fluctuating zone of the Baihetan Dam reservoir area,a large number of particle experiments have been carried out under the condition that the physical state of indoor samples is as consistent as possible with that of on-site soil samples,large-scale triaxial shear tests and creep tests were carried out,and the stress-strain relationship,shear morphology,long-term strength and deformation law of coarse-grained soil under wet-dry cycles and saturated conditions were analyzed.The main contents and achievements of the thesis are as follows:（1）The conventional triaxial tests under the condition of wet-dry cycle show that:（1）The coarse-grained soil is strain-hardened when it is sheared,and has obvious plastic deformation characteristics when it is close to failure.（2）The peak deviating stress of coarse-grained soil increases exponentially with confining pressure（n≤2）or logarithm.The peak deviating stress of coarse-grained soil decreases logarithmically with the number of dry-wet cycles under high confining pressure,and is not obvious at low confining pressure.The higher the confining pressure is,the higher the strength of coarse-grained soil will be,but when the confining pressure is too high,the coarse-grained soil particles will be broken,which will lead to a decrease in the strength of coarse-grained soil.The more the wet-dry cycles,the more serious the particle breakage and the lower the strength.（3）For coarse-grained soil with dense skeleton,it may show the characteristics of secondary ultimate strength when there is obvious dilatancy deformation,and the peak value of partial stress should lag behind the volume strain inflexion.When n≤3,the coarse-grained soil samples shear shrinkage first and then dilatancy,and with the increase of dry-wet cycles,the maximum shear shrinkage deformation decreased gradually,the dilatancy deformation increased gradually,and the bulk strain inflection point was advanced.When n>3,the coarse-grained soil has only shear deformation,and with the increase of dry-wet cycles,the maximum shear deformation gradually increases,and the axial strain at the maximum strain point also increases.（4）The effect of confining pressure on the strain of coarse-grained soil is the restraint of force,while the effect of wetting-drying cycle is the deterioration of particle strength,pore size and skeleton structure.（5）The Duncan-Chang model works well,but when it comes to the problem of deformation,the parameters can not be completely applied.The change rule of cohesion is more complicated,and the internal friction angle decreases approximately s-shape with the increase of wet-dry cycle times.（5）The creep behavior of coarse-grained soil shows that the axial strain increases exponentially with the stress level and confining pressure,but becomes linear under high confining pressure due to particle breakage.The higher the stress level is,the greater the effect of confining pressure on the creep stability of coarse-grained soil is,and the two promote each other and act synergistically.（6）After shearing,the specimen presents a non-uniform drum shape,the deformation at both ends increases by 7.45%,the deformation at the waist increases by 27.66%,and the volume deformation of the specimen increases by 10.5%.The shear plane usually runs through the whole specimen at the middle and lower part（1/2～1/4 of the specimen）,and the shear plane intersectsσ₃at a small angle,usually at 20～30°.The shear surface is rough,and the shape is mainly determined by the content and size of coarse aggregate particles near the shear surface.（2）The triaxial creep tests under water saturation show that:（1）The long-term strength of the coarse-grained soil sample can reach more than 64%of that under shear failure,and the axial deformation is less than 7%,the creep is small,and the low confining pressure is not obvious.The long-term strength of the coarse-grained soil sample can reach more than 64%of that under shear failure,and the axial deformation is less than 7%.The long-term strength of coarse-grained soil is lower than the actual value by using isochronous curve,for the project is too conservative,will cause a certain degree of waste of resources.（2）The creep behavior of coarse-grained soil shows that the axial strain increases exponentially with the stress level and confining pressure,but becomes linear under high confining pressure due to particle breakage.The higher the stress level is,the greater the effect of confining pressure on the creep stability of coarse-grained soil is,and the two promote each other and act synergistically.（3）The creep morphology is consistent with shear,and the shape of drum is uneven.The failure surface is slightly different,uneven,but less ups and downs.The failure surface is located in the middle,middle and lower parts of the specimen and intersects withσ₃horizontally or at a minimum angle.The characteristics of failure surface are mainly related to the content and size of coarse aggregate.