Method And Device Of Gradient Static Stress Loading For Rock Specimen

Due to dead weight stress and excavation and unloading in engineering practice,rock masses often bear linear and nonlinear gradient in-situ stress.When studying the physical and mechanical characteristics of rock mass under relevant working conditions in laboratory tests,the corresponding stress environment cannot be simulated.In view of the inadequacy of the rock mechanics laboratory test device and test system that can not accurately simulate the static static stress of the test piece,this paper proposes a method to simulate the actual stress environment of the rock mass,and develops a corresponding test device.The device can apply linear and non-linear gradient static stress to long rock specimens.The stress wave propagation test of red sandstone specimens under the linear gradient static stress is carried out,which verifies the advantages of the test device in rock dynamics.The main research contents and conclusions of this article are as follows:(a)The test device is composed of "flexible material-test piece-flexible material",and the normal load is applied to the test piece through the bolt.The determination of the bolt preload in the test device in this paper,the number and sequence of loading of the bolt preload,and the influence of the friction force between rubber and rock on the test results are analyzed.A set of standard test operation methods are proposed..The test results show that the test device for applying gradient static stress to the rock specimen can apply a computable and accurate axial gradient static stress to the rock specimen,and the error between the calculated value and the measured value is small.By tightening the bolts,uniform or non-uniform normal pressure can be applied to the upper and lower sides of the test piece,thereby achieving the purpose of applying a uniform or non-uniform gradient static stress to the test piece.The uniform tightening torque corresponds to the linear gradient static stress,and the non-uniform tightening torque corresponds to the nonlinear gradient static stress;the gradient value of the static stress change can be realized by adjusting the variation form of the tightening torque.The size of the static friction factor between rubber-stainless steel and rubber-red sandstone is not a fixed value.As the normal pressure increases,both static friction factors show a gradual decrease.(b)Based on the test device,the mechanical properties of the red sandstone specimen under linear gradient static stress and nonlinear gradient static stress were tested.Based on the strain data of the specimen under different working conditions,the effect of static stress gradient on the mechanical properties of the red sandstone specimen was revealed,and the feasibility of the test device was verified.The test results show that the greater the value of the uniform bolt torque applied to the stainless steel specimen as an elastic material,the greater the linear gradient value of the normal stress value on the cross-section of the specimen;The greater the increasing gradient of,the greater the gradient of the nonlinear variation of the normal stress on the cross-section.For a red sandstone specimen,when uniform bolt tightening torque is applied,the axial strain at different cross-sections changes in a non-linear form,but as the value of uniform tightening torque increases,the curvature of the compressive strain evolution curve becomes smaller and smaller;When a non-uniform bolt tightening torque is applied,the axial strain at different cross-sections also changes in a nonlinear form.As the non-uniform gradient value of the bolt tightening torque increases,the nonlinear gradient value of the axial compressive strain also increases The bigger.(c)Based on the test system,the feasibility of the stress wave propagation test of the red sandstone specimen under the linear gradient static stress was verified,and the stress wave propagation test of the red sandstone specimen under the linear gradient static stress was performed.The time attenuation coefficient in the stress wave propagation test is discussed.On the basis of carrying out a large number of stress wave propagation tests,the stress wave propagation test data of red sandstone specimens without gradient static stress is compared,revealing the dynamics of static stress gradient on red sandstone Influence of mechanical properties.Compared with the existing research results at home and abroad,this article mainly achieved the following innovative results:(a)A test device for applying gradient static stress to long specimens has been developed,which provides a new idea for studying the deformation characteristics of rocks under deep gradient static stress;(b)Accurately simulate the actual working conditions of linear and non-linear gradient in-situ stresses caused by dead weight stress and excavation unloading;(c)The device can carry out stress wave propagation tests under linear gradient stress conditions and nonlinear gradient stress conditions.