Experimental Study On Permeability Of The Clay Core For The Embankment Dams During Coupled Compression And Shear

Clay is the most commonly used impervious material of the embankment dams and the rockfill dams.Due to the large difference in the deformation modulus of the clay core wall,the dam shell and the bedrock slope,large shear deformation and even the shear crack will occur inside the impervious body and its contact parts with the dam shell and the bedrock slope;especially the large shear deformation zones of the clay core wall and the bank slope are parallel to the seepage direction,the concentrated seepage or contact erosion is easily occurred in this area and affect the dam safety.In view of this,a series of seepage tests under coupled compression and shear were performed on a typical clay by a newly-invented hollow cylinder permeability testing apparatus.The permeability characteristics of the clay before,during and after large shear deformation were studied comparably on the basis of the experimental and theoretical analysis.The main work and achievements of this paper are as follows:(1)The research background of the topic of this paper was introduced.The research status of permeability and seepage stability of the clay at home and abroad was summarized and the significance of the research was pointed out.(2)A hollow cylinder permeability testing apparatus is machined,reformed and verified,which can meet the test requirements of this paper.(3)The basic physical parameters of the test soil were determined.Based on the characteristics of the newly-invented hollow cylinder permeability testing apparatus,the vertical one-dimensional consolidation tests,the radial flow seepage test under the vertical compression and the radial flow seepage test under the coupling effect of vertical compression and torsion radial shearing were designed.Further,the data processing formula and the corresponding derivation process are given.(4)According to the test results,when the seepage direction was parallel to the shear plane,the effects of vertical stress,large shear deformation and hydraulic gradient on permeability coefficient and permeability stability were deeply analyzed.It was found that:The effects of the consolidation pressure and hydraulic gradient on the permeability coefficient of the test clay by the conventional radial permeability test are consistent with the general rules.The magnitude of current vertical stress controls the changing of the permeability coefficient and seepage stability of the clay during shearing.When the exerted vertical stress is greater than the preconsolidation stress of the specimen,the shear plane is compacted during shearing,no concentrated leakage is found in the specimen,and the overall permeability coefficient decreases slightly after shearing.In contrast,when the exerted stress is less than the preconsolidation stress of the specimen,the shear plane dilates and opens gradually during shearing,and then becomes a channel of concentrated leaking.Although the open shear plane can heal itself during steady seepage,its permeability coefficient after healing increases remarkably.For the normal consolidated specimen,the seepage stability have no significant change.For overconsolidated specimen,the seepage stability decreases significantly,and the pattern of seepage failure is hydraulic fracture and crack scouring when raising the water head rapidly.The newly-invented hollow cylinder permeability testing apparatus can be applied to the study of permeability test of cohesive soil samples,and it is feasible to study the permeability of clay by using hollow cylindrical samples.(5)In order to carry out the follow-up experimental study better,a new hollow cylinder permeability testing apparatus was designed and invented,which achieved a certain degree of digitization,automation and improved the accuracy of the test data acquisition and test accuracy.