Study On Dynamic Mechanical Properties Of Cemented Sand Like Material Under Confining Pressure

In recent decades,the geomechanical model test has been playing a more and more important role in the underground engineering such as water and electricity,transportation,energy and mining engineering because of its image,intuitive and real characteristics.Local geomechanical model test with conventional model test mainly different,from the constitutive relation,the first is to consider the elastoplastic properties,followed by weight as far as possible to simulate the prototype model itself using density.In the final analysis,the main difference lies in the different materials of the model,so the key to the success of the geomechanical model test is the choice of the material and the mechanical properties of the material.Study on similar material test and physical model of the existing literature mainly focused on the static mechanical properties,while the research on the dynamic characteristics of similar materials are less,especially in research on dynamic mechanical properties under the condition of similar material is untraceable.Based on the physical similarity of cemented sand is often used to simulate sandstone model test of similar materials as the research object,because it belongs to the cementing material,and has the characteristics of low strength,low deformation modulus,and the material fast drying material,low cost,convenient processing,stable performance,preparation of flexible,non-toxic and harmless etc.it has been widely used.Selection of quartz sand,gypsum powder,cement and water as raw materials to make standard specimen,and test the basic physical and mechanical parameters;according to the sand:cement:Gypsum:water =1:0.095:0.05:0.10 ratio growth ratio is 0.5 of the specimen,with the help of SHPB test device for dynamic compression test and dynamic splitting test.The main research contents and results are as follows:(1)the similar physical and mechanical parameters such as bulk density,compressional wave velocity,uniaxial compressive strength and tensile strength were measured.According to the similarity coefficient and the strength of the original rock,the strength of the similar material is deduced,so that the mix ratio of the similar material is 1:0.095:0.05:0.10(sand:cement,gypsum,water).(2)analysis of the basic principle,split SHPB experimental device in the rod strain test and the experiment data processing method,and discusses the design principle of the sample,finally obtains the specimen with aspect ratio of 0.5 is the most suitable.This paper introduces in detail the SHPB test equipment system of the impact Laboratory of Anhui University Of Science And Technology,and gives the detailed operation steps and the matters needing attention in the test process.(3)using the split Hopkinson pressure bar experimental device of cemented sand specimens under uniaxial impact compression experiments with different strain rate(SHPB experiment),are analyzed using the simplified three wave method,get the similar material of cemented sand dynamic stress strain curve and the related kinetic parameters.The experimental results show that the cemented sand belongs to ductile failure types under impact load,the deformation process can be divided into initial stage,nonlinear yield stage and plastic deformation stage and unloading stage four stages of cemented sand damage;dynamic strength,peak strain and a significant correlation with strain rate,exhibit strain hardening and strain rate strengthening dynamic characteristics is significant.(4)using passive confining pressure device(sleeve)for three axis impact and confining pressure device of cemented sand specimen compression test according to the test results obtained under confining pressures of cemented sand and similar material dynamic stress-strain curve and the related kinetic parameters.Research shows that the cement sand specimens compared in compression test the dynamic compressive strength of three axial impact on Uniaxial Impact increased 1.5-3 times,dynamic strength,peak strain and strain rate still has significant correlation;the failure mode under the condition of confining pressure is changed from compression shear failure to tensile failure;the effect of active confining pressure also changes the properties of similar materials,from ductile to brittle to ductile transition.(5)the dynamic tensile stress and strain rate of rock specimens were tested by using the five different impact pressures.Through the analysis of the test data,it is found that the tensile strength of cemented sand specimen under high strain rate has strain rate effect.In the three,similar to the stress load of similar material model test,will indirectly enhance the compressive strength and tensile strength,especially on model materials by blasting,blasting load effect,the dynamic compressive strength and tensile strength of the material will be doubled,and the blasting damage model is different from the no stress loading situation.The research results can provide a practical reference for the parameter design of the similar model test of deep rock mass blasting,and provide a theoretical basis for the analysis of the law of blasting model test.