Study On Modulus Of Coarse-grained Soil Under Different Stress Paths

The stress and deformation of the water retaining structure are the key problems in the design of earth and rockfill dams.Taking the concrete-faced dam as an example,the stress state of its face depends mainly on the deformation of the dam body under it.The stress and deformation characteristics of coarse-grained soil in dam construction are closely related to the stress path it experiences.At present,the parameters of constitutive models generally used in FEM calculation are basically obtained through conventional triaxial tests.However,a large number of studies have shown that the stress path of dam during filling and water storage is complex,which is quite different from the conventional triaxial path.In addition,some pumped storage power stations have been newly built in our country in recent years.Considering that the annual circulation times of the upper reservoir water level of the pumped storage power station will be more than 300,it is very necessary to study the deformation characteristics of the dam body under the face slab under the condition of slow water level circulation.For this reason,this paper firstly uses the generalized plastic model to carry out finite element analysis on an actual face-slab dam,obtains the stress path of the dam body under the face-slab during filling,water storage and reciprocating water storage,and based on this,carries out the stress path experimental research of dam gravel materials.At the same time,in order to consider the difference of gradation and compaction characteristics caused by scale reduction and other reasons,several groups of tests were carried out with different scale reduction methods and initial void ratio.The research contents and main conclusions of this paper are as follows:?1?Duncan Chang E-B model is used to fit the stress and deformation curves of the samples in each stage.The fitting results show that the parameter K_ur in the filling and initial water storage stages is 1.6².2 times of the K.As the amplitude of cyclic deviatoric stress is only 1/3 of the total deviatoric stress,K_ur in the reciprocating water storage stage is greatly increased compared with that in the filling and water storage stages,which is about 6¹0times of the K during filling and 3⁵ times of K_ur during initial water storage.The initial void ratio has a significant effect on the deformation of dam filling and initial water storage,but it will not affect the proportion of initial water storage in the total deformation of the two stages,which is mainly affected by the grading structure.?2?Cyclic loading tests of constant?₃?constant P and constant?₁ paths were carried out at the same stress level of reciprocating water storage,and the axial deformation modulus of different path cycles and stress increment direction?were fitted with exponential function.The fitting parameters were related to the gradation structure and initial void ratio of the sample.The lower the initial void ratio and the smaller the non-uniformity coefficient,the greater the difference in deformation modulus of different paths.Due to the anisotropy of sample preparation,the difference of elastic modulus of samples on constant?₃ and constant?₁ paths increases with the increase of initial void ratio.Because the spherical stress and the deviatoric stress of the reciprocating water storage path increase and decrease synchronously,the elastic modulus of the reciprocating water storage path in each group of tests is slightly higher than that of the constant?₃ path,and Poisson's ratio is lower than that of the constant?₃ path.The elastic modulus of the recharge path is1%³%higher than that of the conventional path,and Poisson's ratio is only 0.4⁰.65 of the conventional path.The Poisson's ratio difference during water level reciprocating cycle cannot be ignored.?3?A series of dynamic cyclic tests with different dynamic stress amplitudes are continuously carried out at the same stress level.The results show that the slow cyclic elastic modulus under the constant?₃ path is slightly higher than the dynamic elastic modulus under the same strain amplitude.The difference between the slow cyclic Poisson's ratio and the dynamic Poisson's ratio is obvious.The dynamic Poisson's ratio is always larger than the slow cyclic Poisson's ratio,which may be due to the fact that the sample does not have time to drain water due to too fast load frequency.Dynamic cyclic tests were carried out on a rockfill under conventional and constant P paths with different confining pressures and different consolidation ratios.The results show that the dynamic elastic modulus of the two paths are relatively close,and the constant P path is slightly higher than the conventional path under the same dynamic strain amplitude.The smaller the dynamic stress,the higher the confining pressure and the larger the consolidation ratio,the more obvious the difference between the two paths is.