Study On Mechanical Properties And Scale Effect Analysis Of Coarse-grained Material For Dam Construction

Coarse-grained materials have a series of excellent engineering characteristics such as strong water permeability,high shear strength,good compaction performance,and small settlement deformation,and have become the first choice for dam filling materials.However,the strength and deformation characteristics of coarse-grained materials are affected by various factors such as coarse particle content,parent rock,stress level,water content,etc.,which will produce great differences.As the main filling material of the dam body,the mechanical properties and deformation performance of coarse granules play a decisive role in the safety of the dam body.This paper takes the coarse-grained materials-rockfill and sand-gravel materials of a high concrete face gravel dam as the research object.Through large-scale indoor triaxial tests,it reveals the strength,deformation characteristics,and model parameters of the coarse-grained materials under different conditions.The law of change;and with the help of discrete element software,a simple understanding of the scale effect of two kinds of coarse-grained materials at different scale levels and confining pressures.The following is the specific research content and conclusions:1.Under different confining pressure and gradation conditions,the three axial shear tests were carried out for two kinds of coarse granules.The test results showed that: Under the same conditions,the two kinds of coarse-grained materials show basically the same change rule,and the confining pressure of the sample,grading(coarse particle content)and other factors have a certain influence on the peak stress of the coarse-grained materials.According to the experimental data,the axial peak force of the two kinds of coarse granules increases with the increase of confining pressure.The higher the content of coarse particles is,the greater the corresponding peak force is when the grading of coarse particles is from the upper to the lower cladding.The volumetric and axial strain curves of two kinds of coarse granules were drawn.It was found that the volumetric variation rule of coarse granules in triaxial shear process could be summarized as low expansion and high contraction,first contraction and then expansion.Under low confining pressure,the dilatancy of the two kinds of coarse granules is easy to occur.With the increase of confining pressure,the dilatancy of the coarse granules is gradually weakened,and the volume deformation of the coarse granules is transformed from dilatancy to dilatancy.When the confining pressure is higher,the volume shrinkage of the coarse granules is larger.Under low confining pressure,during the shearing process of coarse-grained materials,the volume change is as follows: the sample undergoes shear shrinkage first,and then shear dilatancy.The sample grading from the upper envelope to the lower envelope,with the increase of the content of coarse particles,the more significant the dilatancy of the sample,the smaller the shrinkage value.2.According to different confining pressures and gradations,the model parameters are displayed: As the content of coarse particles increases,the model parameters φ0 and Δφbecome larger,the value of K becomes larger,the value of n decreases,the value of Rf decreases,and Kb As it becomes larger,m decreases,Rd decreases,nd increases,and cd decreases.With the increase of confining pressure,φ0 and Δφ decrease,K increases,n decreases,Rf decreases,Kb decreases,m increases,Rd increases,and nd decreases.3.According to the data,most of the stress-strain curves under each cladding(gradation)of rockfill and gravel are in the state of strain hardening on the whole.When the confining pressure is 3000 k Pa,the stress-strain curves of the cladding under rockfill show weak strain softening.By analyzing the particle breakage rate of rockfill,it is found that when the content of coarse particles is too high and the confining pressure is too large,the particle will be broken violently,and the strength reduction caused by particle breakage is greater than the increase of the confining pressure on the strength of coarse particles,which leads to the decrease of the strength of coarse particles after reaching the peak value,thus showing softening.4.This paper selects the rockfill materials and sand gravel materials under the average envelope as the simulation objects,and uses the PFC2 D software to perform numerical triaxial simulation analysis on the two coarse-grained materials.After several simulations and calculations,the simulation results were compared with the indoor large-scale triaxial test data,and the corresponding meso-parameters of the two coarse-grained materials under different confining pressures were calibrated.The simulated curve and the stress-strain curve obtained in the indoor test.The change trend is similar and the coincidence is high,which proves the rationality of using PFC2 D to simulate the mechanical properties of rockfill and sand gravel.5.Based on the results of numerical triaxial simulation and calibration,the mechanical properties of two kinds of coarse-grained materials under different scale levels and different confining pressures are analyzed by numerical triaxial.The simulation data shows that the two kinds of coarse-grained materials have more Similar change law,with the increase of the scale level(that is,the increase in the scale ratio,the smaller the largest particle size after the scale),the lower the strength of the coarse-grained material;with the increase of the confining pressure,the same size The greater the axial stress value corresponding to the same axial strain of the sample,the higher the axial peak force,which is consistent with the change law of the indoor physical test.