| The rock mass is not uniform and contains a large number of structural planes.The instability and destruction of the engineering rock mass are usually caused by the opening,closing and expansion of the internal structural surface of the rock mass.The non-penetrating structural plane rock mass consists of joints and rock bridges.The destruction of joints and the destruction of rock bridges together constitute the destruction of non-through structural plane rock masses.What are the effects of joints and rock bridges on the deformation and strength characteristics of non-penetrating structural rock masses,what are the rules of rock joint damage and development,and how the rock bridge affects the strength of shear failure surfaces? Not solved well.In the project,the Jennings weighted average intensity criterion is generally used as the peak shear strength of the non-penetrating structural plane.In fact,the measured peak shear strength is often smaller than the Jennings weighted average intensity criterion.This is because the predicted value of Jennings is based on the fact that the rock bridge is not damaged.Actually,when the peak shear strength of the non-penetrating structural plane reaches the peak,the rock bridge has been damaged.What impact does the rock bridge have on the overall shear strength of the nonpenetrating structural plane? The study is not very thorough.Therefore,in-depth study of non-penetrating structural plane penetration failure mechanism and establishment of comprehensive shear strength model is of great significance in theoretical research and practical application.In this paper,the indoor model test is used as the carrier to study the deformation and strength characteristics of non-through structure planes of interconnected and non-penetrating structures,and to study the failure mechanism and failure modes of non-penetrating structural planes.The mechanical properties of rock bridges are weakened and established.Comprehensive shear strength model.The main work and research results of this paper are as follows:(1)Considering the selection principle of similar materials synthetically,the 32.5R composite slag Portland cement is used as the cementing material,and the continuously grading medium coarse sand is used as the aggregate,and the water reducing agent and the composite early strength agent are used as additives.Rock-like material.(2)According to the concept of line connectivity and area connectivity,the nonthrough structure planes are divided into two types: line-connected non-penetrating structures and surface-connected non-penetrating structures,and four kinds of line connectivity with different connectivity rates are designed.Type and surface connection type non-through structure surface.(3)Summarize the method of making non-through-structure model specimens,analyze the advantages and disadvantages of various methods,and finally choose to use cement mortar to make a combination of small blocks,and then combine the combination of small blocks after the outside of the second Pouring cement mortar this method to make model specimens.(4)The deformation and strength characteristics of the whole shearing process of the non-penetrating structural specimen were studied.According to the normal deformation curve,the joints in the specimen will be fully densified under normal stress,and joints and rock bridges will bear the shear force.Further analysis of the tangential deformation curve reveals that as the tangential displacement increases,the tangential stress increases almost linearly in the initial stage,and when the shear stress approaches the peak,the curve slows down slightly until the peak shear stress is reached.The entire sample was broken,and the shear stress rapidly decreased to a certain value and it basically stabilized,and fluctuate only within a small range.The tangential deformation curve can be divided into four stages: the linear elastic stage,the peak stage,the post-peak stage,and the residual strength stage.When the shear stress reaches the peak shear strength,the shear stress decreases rapidly,which indicates that the model specimen has obvious brittle failure characteristics.(5)Mechanical analysis of non-penetrating structural planes to study the failure mechanism of rock bridges,dividing failure modes of rock bridges into tensile failures and shear failures,correcting the tensile failure theory of lajtai rock bridges,and the new rock bridges.Tensile failure theory can better explain the initial cracking of rock bridges and the extension of tensile cracks.(6)Combining the two failure modes of rock bridge microelements,according to the location of the cracks and the nature of the cracks during the shearing process of the model specimens,the failure modes of the non-penetrating structural planes are divided into a pull-shear composite type and a direct shear type.The influencing factors of failure modes of non-penetrating structural planes were analyzed and it was found that the joint connectivity ratio had a great influence on the failure modes of the specimens.As the connectivity rate decreases,the failure mode of the specimen changes from direct shear to tensile-shear composite.(7)Compare the measured shear strength parameters with Jennings weighted averages and find that the weighted value of Jennings is larger than the measured value,which confirms the concept of rock bridge mechanical properties weakening.It is found that the equivalent weakening degree of cohesion is greater,and the degree of weakening of the equivalent internal friction angle is smaller.With the decrease of connectivity,the weakening degree of the equivalent cohesion of the sample rock bridge increases.(8)A certain reduction in the cohesion of the rock bridge was obtained,and a new comprehensive shear strength model for the non-penetrating structural plane was obtained.After verifying the modified strength model,it was found that the average error between the formula prediction value and the experimental data was 5.2%,the maximum error was 9.4%,and the agreement was good. |
PDF Full Text Request