Study On Creep Characteristics And Constitutive Model Of Non-persistent Rigid Structural Surface

There was a very obvious rheological phenomenon in the rock?rock mass?by a large number of rock mechanics experiments and practical engineering.The rock mass in nature is not homogeneous,but consists of a heterogeneous anisotropic and discontinuous composite structure composed of many joints,weak interlayers and faults.The structural surface generally controls the boundary of rock slope instability boundary,and the study of non-persistent structural surface is very important to reveal the mechanism and stability of slope start-up failure.At present,the research on the rheological mechanics of rocks was mainly limited to the rheological mechanics of intact rocks and rock masses with continuous structural surface.It is difficult to sample with non-persistent structural surface.There were few studies on rheological mechanics of rock masses with non-persistent structural surface.The rheological mechanical characteristics of rock masses with non-persistent structural surface are more complicated than those of intact rocks.Therefore,the study of the rheological mechanical characteristics of non-persistent structural surface has important value and significance in theory and engineering.In this paper,the non-persistent rigid structural surface was taken as the research object.Based on the geological prototype of Dagangshan hydropower station right bank dam site slope,the generalized model was refined,and the sample of non-persistent rigid structural surface was made for laboratory test.The uniaxial compressive strength,triaxial compressive strength and deformation characteristics of non-persistent structural surface samples were studied,and the deformation process was numerically simulated by RFPA2D to analyze the stress-strain and acoustic emission?AE?characteristics of the model.On the basis of the above test,the triaxial compression creep test was carried out on the specimens with non-persistent structural surface,and the stress-strain-time characteristics,creep rate and long-term strength parameters during creep were analyzed.At the same time,in this paper,the stress-strain-time characteristics and AE during the creep numerical test of RFPA2D-creep were analyzed.Based on the indoor creep test,two constitutive models were established to reflect the creep test and a creep model which was more suitable to describe the creep characteristics of the non-persistent rigid structural surface is obtained.The main research results of this article are as follows:?1?The uniaxial compression test of the non-persistent rigid structural surface specimens showed that the upper structural surface lengths a=0 cm and a=1 cm had a small difference in sample strength,and the sample strength would be a sudden drop when a=1 cm to a=3 cm.There were five stages of deformation process in the test.According to the deformation characteristics after the peak,it could be divided into ductile brittle failure and sudden brittle failure.Using RFPA2D software to perform uniaxial compression numerical tests on a=0 cm and a=3 cm numerical samples,it was found that the failure of the laboratory test samples was within the range of the maximum shear stress and AE concentration location of the numerical test.Combining the AE characteristics of the AE position and the failure mode of the laboratory test specimens,was is shown that the deformation and failure of the laboratory test specimens were both shear failure and tensile failure.?2?From the conventional triaxial compression test of the non-persistent rigid structural surface samples,it could be seen that a 5-stage deformation process occured during the test,and the triaxial compressive strength as a whole increases with the increase of the confining pressure and reduced with the length of the structural surface large.Using RFPA2D software,a=0 cm,?₃=2 MPa and a=3 cm,?₃=2 MPa numerical samples were tested under triaxial compression and the results showed that the failure of the specimens in the laboratory was in the range of the maximum shear stress and the location of AE.According to the AE characteristics of the AE position in the numerical test,under the condition of a=0 cm,?₃=2 MPa,the deformation failure of the samples was mainly shear failure and local tensile failure;under the condition of a=3cm,?₃=2 MPa,the deformation failure mode of the specimen was the coexistence of shear failure and tensile failure.?3?The characteristics of AE counts and AE energy in the numerical tests of uniaxial compression test and triaxial compression test showed that they have great similarity.When the load did not reach the failure strength of the sample,the AE counts and AE energy showed a stable development trend.When the load reached the failure strength of the sample,the AE showed a state of sudden and high-density events and energy release.?4?A complete creep test process was showed by the triaxial creep test process of the non-persistent rigid structural surface samples.Except for the instantaneous strain of the first stress level,with the increase of the stress level,the instantaneous strain of the specimen overall presented a trend of increasing.With the increase of stress level,the creep increment also showed an increasing trend.Under low and medium stress,there was a certain creep rate in the sample of non-persistent rigid structural surface.With the increase of stress level,the creep rate increased as a whole.The test curve showed that there was a steady-state creep rate mutation before the accelerated creep.In this study,long term strength is calculated by isochronous stress-strain curve method,and to compare the instantaneous strength and the long-term strength.The ratio of the long-term strength to the instantaneous strength was as low as 29.01%,as high as59.70%.In some cases,the long-term strength value under low stress was slightly higher than or slightly equal to the long-term strength value under high stress.After analysis,on the one hand,it was caused by the difference between the test accuracy and sample,on the other hand,it was mainly caused by the loading speed.?5?The creep test process of a=0 cm?₃=2 MPa specimens was simulated by RFPA2Dcreep.The results showed that the failure of the specimen starts from the top of the reverse inclined side of the lower structure surface,and gradually extended to the lower structure surface until it passed through.Combined with the laboratory test and numerical test,it was considered that the test specimens of the two test specimens were damaged under the combined action of shear failure and tensile failure.With the help of creep numerical tests,it could be inferred that when micro cracks or cracks appeared on the trailing edge of practical engineering?landslides?,it would be judged that the landslide had entered the accelerated creep time or accelerated creep stage.The stress-strain-time relationship was analyzed,and a similar understanding was obtained with the mechanical test,that was,as the stress level increases,the instantaneous strain increment and creep increment of the rock would increase accordingly.AE characteristics showed that as the stress level increases,the acoustic emission count and acoustic emission energy also increased.The cumulative count of AE and the cumulative energy of AE had the same trend as the stress-strain-time curve during creep.?6?Based on the results of laboratory creep tests,two different constitutive models were constructed,namely the nonlinear viscoelastic-viscoelastic plastic damage creep constitutive model based on the combination of traditional components and the rigid structural plane creep constitutive model based on fractional calculus,and the creep equations under one dimensional and three dimensional stress states were derived.The parameters of the creep equation under the three-dimensional stress state were identified by the laboratory test data.The two models could better reflect the whole creep process of the non-persistent rigid structural surface samples.The results showed that the creep constitutive model based on fractional calculus rigid structural surface was better than the traditional damage creep constitutive model for identifying the creep process of non-persistent rigid structural surface specimens.