| The fundamental purpose of roadway coal mine support is to ensure that excessive displacements of roadway surrounding rock can be controlled. The interaction principle of the surrounding rock and support is the theoretical basis of controlling surrounding rock of roadway. At present, the conclusion that has been accepted wildly in this field is that the displacement and supporting force of roadway surrounding rock are in a reverse relation before its peak strength. The post-peak characteristics refer to the mechanical behavior at the stage of residual phase after peak intensity of the rock. Many roadways will be influenced by multiple production processes such as tunnelling and mining during their service period. In many situations, the deformation of the surrounding rock will undergo the following changes:elastoplasticity-rupture-crush-loose. Many roadway surrounding rocks are in the situation of large deformation of post-peak only when tunnelling begins. Therefore, it is a complex process that the control of surrounding rock in roadway. Obviously, the theory of the supporting force and displacement in inverse relation has been unable to guide the controlling of large deformation surrounding rock of roadway after peak strength. Based on that, the whole process of the post peak stage of roadway surrounding rock and support interaction is studied by comprehensive methods of field test, physical simulation, numerical simulation and theoretical analysis, characteristics and mechanism of surrounding rock and supporting of roadway in the condition of continuous and non-continuum medium are revealed by analysis of change characteristics of stress, displacement and structure of surrounding rock along with the increase of surface displacement. The corresponding stability control principle is proposed and applied to decision-making for a certain supporting design scheme. The result of In-situ application is reasonable. In sum, the main work and conclusions including:1. According to the triaxial compression test data of rock with different confining pressure, characteristic of post-peak strength and deformation of rock as well as their correlation are analyzed, which reveals the post-peak rock characteristics:with the increase of the confining pressure, rockmass converts from brittle to lithology; the relationship between the peak strength and confining pressure is a linear increasing function, which is the same for post-peak residual compressive strength and confining pressure; the value of peak compressive strength minus post-peak residual compressive strength and confining pressure has a linear relashionship.2. At present, the elastoplastic constitutive model is inconsistent with practice of roadway surrounding rock in terms of describing rupture, crush, loose etc., in the numerical simulation. Contraposing this actual problem from the macro prospective, the following ideas are proposed based on the characteristics of rock after peak:at the stage of post peak deformation of rock, its strength curve rotates around the fixed point in the coordinate system of maximum and minimum principal stress; the corresponding yield surface contracts and expands in principal stress space. The method and formula of describing characteristics of rock mass is established by using9physical quantities (E,v,v,σcp1,σcr1,σw1,σcp2,σcr2,σw2,εr) obtained by two sets of triaxial compression tests. The method of describing to rupture, failure and fragmentation flow of rock macroscopic deformation after peak are obtained. On that basis, FRMF constitutive model of post-peak rock mass is founded and successfully applied to numerical simulation in geotechnical engineering.3. A new roadway support that is dedicated to the test of physical similar simulation is developed, and the supporting force and deformation quantity of the roadway support are adjustable. The maximum adjustable range of deformation amount is50%of the model’s section, and the range of simulated actual range of support strength is0-30MPa if the ratio of similitude of the stress is1:20. The goal of observing strength of roadway support in the condition of limiting deformation of roadway surrounding rock is achieved. Thus the reference for other similar simulation tests can be provided.4. Volume-weight and compressive strength characteristics of the similar material that made by stone, sand and gypsum of different formulations are studied. The results show that the impact ratio of stone and sand on volume-weight of the similar material is9:5, and on peak compressive strength is3:2. Therefore, the similar material density and strength in different proportions is obtained. The simulation of the irregular internal fissures of rock is studied, of which the result provides the reference for the analog simulation test in similar conditions.5. The relation between required supporting strength and surrounding rock displacement of roadway in the condition of different surrounding rock intensity are studied by field test, physical simulation and numerical simulation. Thus, the equilibrium principles and stability characteristics of roadway surrounding rock in elastic, plastic, crash, broken as well as dispersion are obtained, mainly in six categories, respectively:linear reduction, negative exponential, fluctuant reduction, fluctuant advance, fluctuant increase, and nearly level constant type.6. The interaction mechanism of the surrounding rock and support is systematically studied by analyzing the evolution characteristics of stress, displacement and structure of surrounding rock at the stage of different deformation, the curve of relation between surrounding rock and support respectively:fluctuant reduction at the stage of post-peak crash extension, fluctuant increase at the stage of structure fracture, and nearly level constant at the stage of granular rock.7. Based on the analysis of the relation between anchor bolt force (or axial force) and free end displacement of the end-anchored bolt, the following conclusions are obtained:anchor force distribution of the anchorage section reduces from the interface of anchorage section and free section to free end in axial direction; the maximum effective anchor length depends on the rigidity of bolt, strength of anchoring agent and the stiffness of anchorage rock mass in conditions of end anchorage; influence distribution of anchorage section to anchorage body is in the form of "pull bubble", and "pull bubble" spheroid with its macroaxis is effective anchorage section of bolt.8. By analyzing the supporting effect of bolt pretightening force on roadway fractured roof, the following viewpoints are presented:the bolt pretightening force can improve compressive strength and shear strength of the roadway roof, making the fractured roof is in compression, preventing the stress of surrounding rock from damaging roof, and weakening destruction of surrounding rock and bed separation of rock stratum; with the increase of the bolt pretightening force fissure extending upward, fissure width decreases. Once the pretightening force is large enough, fracture zone distribution reduce gradually. High pretightening force can make the rock broken zone like the whole structure and improve the bearing capacity of the wall rock at high stress state as well as the mechanical properties of rock.9. The control of large deformation roadway roof stability is mainly to prevent the shear sliding layers of roof roadway in the layered structure, avoid the instability of arch foot sliding in three hinged arch structure, and utilize the pretightening force to make fracture zone of roof to become a load bearing structure in broken roof. Furthermore, the least support strength formula of maintaining stability is given respectively. The different failure modes and mechanism of roadway sides are obtained, besides the formulas of supporting strength calculation and damage depth. At last, the forenamed support theories and methods are successfully applied in actual roadway. Corresponding results prove that it is feasible. |
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