Similar Material Experiment Study On Dynamic Mechanical Properties Of Jointed Rock

The rock joints cause discontinuity and nonuniformity of the rock mass structure, then significantly affect the mechanical properties of rocks and vibration, seepage and heat transfer performance, etc. When the impact loading caused by stress wave propagates through rock joints, the rock mass structure plane such as rock joints, intercalation, etc, will seriously change wave propagate law, which leading to amplitude attenuation, high frequency filtering, signal delay and wave propagation speed slowing down. Meanwhile, it will block the spread of stress wave and increase energy attenuation. Joint rock mass are the most important medium in the slope and cavern engineering of mining, highway, water conservancy, hydropower and oil projects, the dynamic loading and dynamic response characteristics will directly affect the engineering safety and quality, a lot of practical engineering accidents are due to incorrect understanding or ignore the influence of the discontinue structure plane in the rock mass. So the research of joints characteristics and its influence on the rock dynamic mechanical play an important guiding role of stability analysis under dynamic loading in the rock engineering, the explosive energy utilization rate enhancement, and improvement of blasting effect and shock proof design, meanwhile, it is of great significance to national defense construction and national economy.The paper focus on the discontinuous surface structure such as rock joints and crack, on the basis of In-depth analysis of relevant information both at home and abroad, firstly, the basis equation of stress wave propagation is derived with the method of mathematics and mechanics. Secondly, transmission and reflection propagation process of the elastic wave in the finite length rod, including the transmission and reflection coefficient calculation formula of wave propagation through different media interface. Based on the front research, the theory of wave propagation through the single joints at a certain angle is derived. Then we obtain the transmission and reflection coefficient expressions of the stress wave propagation in the joint surface according to the theory, the calculation formula of incident energy, reflective energy, transmission energy, and dissipation energy are obtained too; Thirdly, according to the similar theory and geometric characteristics, different structure styles of joint rock specimens are made of mortar and plaster material, then the impact experiment was carried out on the jointed rock specimen with the help of SHPB test apparatus. Rock dynamic mechanics properties with impact loadings are acquired, which are affected with joint angle, joint filling material and thickness, and the degree of joint spacing, strain rate and loading speed. Finally, we get a series of research results which are inductived in three parts as follows:(1) Artificial joint rock specimen formed by different angles dynamic impacting compression experiment was carried out, then analyze wave propagation properties in rock mass which are influenced with joint angle from the perspective of energy transfer, the dynamic strength and failure pattern. Dynamic characteristics of rock specimen with a single joint are explored, which are influenced with different loading strain rate. The experimental conclusions are as follows:a) First of all, complete rock specimens on the same size are carried out on impact experiments with different loading rates, which are used to determine the impact speed range for energy analysis. Under the condition of the same incident energy, compared with complete specimen, the reflected energy ratio, transmission energy ratio and dissipation energy ratio of 0 ° angle jointed specimen are basically equal to the complete specimen,it is consistent with the results of rock weak plane influencing its strength in the statics experiment. When the joint angle increased from 15 ° to 60 °, reflective energy ratio increases gradually while transmission energy ratio is falling. When the angle is 60 °, reflection energy ratio is 1.56 times bigger than complete specimen, transmission energy ratio is only 11.04% of the complete specimen. When the joint angle is 90 °, reflection energy ratio falls, while transmission energy ratio rises instead, it is 40.46% of the complete specimen. Energy dissipation ratio changes in fluctuations with joint angle, energy consumption than the maximum,it is about 2 times than intact rock when joint angle is 30 °, basically equal to intact rock when joint angle is 60 °.b) Joint angle changes in the range of 0° to 30°, reflection energy ratio increases slowly, from 50.14% to 55.13%, when the range changes from 30° to 60°, reflection energy ratio increases quickly, from 55.13% to 76.58%, when the angle is 90°, the ratio reduces to 58.29%. With the increase of angle, transmission energy ratio gradually reduced in the range of 0° to 60°, from 32.43% to 3.58%, however, when the angle is 90°, energy transmission ratio increases to 13.12%. Joint angle change in the range 0° to 30°, the energy dissipation ratio increases from 18.51% to 36.58%, when the joint angle increased from 30° to 60°, energy dissipation ratio begin to decline, from 36.58% to 19.86%, When the joint angle is 90°, the energy dissipation ratio increase to 28.6%.c) Under the condition of impact loading, when the specimen joint angle is less than 60°, its peak strength decreases with the increasing of joint angle. When the joint angle is equal to its damage angle, dynamic breaking strength of the jointed specimens is minimal. If the angle is between 60°and 90°, the peak stress is gradually increased. The dynamic elastic modulus of intact specimens are significantly greater than other ones, the failure pattern of intact specimens and specimens with 60° and 90° joint angle is brittle failure, other specimens show the tension failure and shear failure.d) Incident energy, reflective energy, transmission energy and dissipation energy of intact specimens and specimens with 15° and 30° angle joint are basically weak power function relationship or linear relationship with strain rate. Although the joint angle affect the rock's energy and the rate of change, it did not change the variation tendency of energy. The dynamic elastic modulus and failure pattern of intact and different angle join rock specimen have the very strong strain rate. crack defects of intact rock extend along the direction paralleled the compressive stress, cutters reduce the dynamic peak stress of specimens, shearing action along the joint surface affect the rock failure pattern, but it is not obvious when the joint angle is less than 30° along with the strain rate increase to a certain extent.(2) Mading artificial rock specimens according to the design scheme, which contain artificial through joint, then make different interlayer material in similar way which is carried out using model experiments, including cast, the filling joint specimens. Dynamic impact compression experiment is carried out on the Joint specimens containing different interlayer with the help of SHPB apparatus, then analyzed energy dissipation, strength characteristic and failure pattern when stress wave cross through specimens which contain different thickens or have different wave impedances. The following conclusions are obtained:a) Under the condition of same incident energy, the greater the joint filling thickness is, the smaller transmission capacity of stress wave is, while the energy dissipation ratio is bigger. The dynamic elastic modulus of the thick filling joint specimens is greater than the thin one, but less than the intact ones. The peak strength attenuation in a form of index with the increase of filling thicknesss. The failure pattern of different filling thickness specimens are mainly tensile damage and the crack break along the principal stress direction.b) Under the condition of same incident energy, the reflection energy ratio is arise and transmission energy ratio is gradually decline with the reduceing of the filling material's strength, Energy dissipation ratio is decided by the properties of the joint filling material. Dynamic elastic modulus of joint specimen with different filling material improve with the increase of filling material strength, dynamic compressive strength show a index form pattern attenuation along with strength decreasing of filling material. Specimens filling with soft material present the plastic failure pattern, the whole damage pattern of specimens are closely related with filling material characteristic.c) The incident and reflection energy of filling joint rock specimen show a increasing trend with the velocity growth. Transmission energy can reach maximum with a certain velocity. When the impact velocity range from 3.872m/s to 5.538m/s, damage variable have a weak power function relation with the impact velocity, meeting the function 2d =1.31 v -0.11 v -3.01, damage value d is 0.458 when the specimens failure. Stress-strain relationship curve and failure pattern are strongly correlated with the impact velocity, the dynamic elastic modulus grows with the increase of impact velocity, the relationship between stress peak and impact velocity meets the function0.177max1.1 55.89vse-= - +.(3) This paper also investigate the dynamic mechanics characteristic of rock with different number of joints, joint spacing and loading speeds by impact experiment, and get some more conclusions:a) Under the condition of same incident energy, the reflected energy ratio, transmission energy ratio and dissipation energy ratio of a single horizontal joint specimen are basically equal to the complete specimen. The more joints are, the less transmission energy is, the damage of the rock stress and strain is less also, peak intensity is approximate linear. Under the same impact velocity, the more joints are, the more serious damage of the specimen.b) When the same material specimens which contains two open joint without filling material are impacted by same incident energy, if the joint spacing change from 5mm to 42 mm, reflection energy ratio slowly decline with the increase of joint spacing, transmission energy ratio changes little but less than a complete specimen, dissipation energy ratio improves gradually. Although the specimen deformation under the condition of compression increases with the joint spacing increase, the dynamic elastic modulus and stress change process is similar, and the failure pattern remain the same.c) With the impact velocity increase, the incident energy and reflection energy of specimens which have the two parallel joints show a increase trend, transmission energy will reach maximum at a certain impact velocity. With a certain speed range, dissipation energy ratio show a trend of growth with the impact velocity increase, beyond the range, dissipation energy ratio decreases inversely. When the velocity range from 3.263m/s to 5.326m/s, the relationship between damage variation and impact velocity meets the function 0.3210014.08 0.83 vd e-= - +, the damage value d is 0.751 when the specimen is destroyed.Summarizing the experimental results listed above, the following innovative results are obtained:(1) using simulation experiment method, specimens of different joint angles, joint numbers, joint spacings, joint thickness and joint filling material, are artificial prefabricated. It is founded in the impact experiment that reflection, transmission and dissipation energy is strongly correlated with joint angle, the dynamic fracture strength of specimen is minimum when joint angle is equal to its damage angle.(2) Soft packing material has significant effects on the transmission of stress wave. Under the condition of same incident energy, the reflection capacity is arise and transmission capacity is gradually decline with the increase of the filling thickness, the dynamic compressive strength attenuation in exponential form.(3) Change the loading condition, it is obtained that the different wave energy in specimens is basically showing weak power function relationship or linear relationship with impact velocity.