Investigation On Collaborative Bearing Properties Of Bolted Rock-concrete Combination After High-temperature Treatment

In underground construction,the "geological body"(geotechnical structure)and the "engineering body"(supporting system)are coupled to bear the crustal stress.The thermal hazards including conflagration and coal spontaneous combustion have been evidenced to cause thermal damage to both the geological and engineering bodies.Because of the highly non-linear nature of mechanical properties of composite elements,the bearing characteristics of surrounding rock and support structure are further complicated by the coupling of high temperature and crustal stress.Therefore,it is of great scientific importance to clarify the nonlinear coupling channel and deterioration properties of the "geological body-engineering body" to reveal the destabilization mechanism of underground construction after high-temperature thermal hazards.In this thesis,the mechanical properties,deformation evolution,and rupture failure mechanism of the combined "rock-support" structure under high temperatures were focused.The main research contents and results are as follows:(1)Sandstone,concrete,and anchor stocks with certain universality and representativeness were selected as the composition materials,in which the sandstone-concrete combinations with non-anchorage,ending anchorage,and full-length anchorage were prepared according to the geometrically similar ratio of1:3 reduction.The basic mechanical properties of the three constituent materials were obtained by tensile tests for the anchor stocks,and uniaxial compression tests on sandstone and concrete subjected to different temperature respectively.The characteristics of loading deformation and compression mechanical parameters of sandstone and concrete materials with different heating temperature were compared laterally.(2)Uniaxial compression tests were conducted on the thermally-damaged sandstone-concrete combinations using the MTS816 mechanics testing machine.The influences of temperature effects and anchoring methods on loading characteristics,nominal compressive strength,peak strain and elastic modulus were investigated.The results manifest that the compressive mechanical response of the sandstone-concrete composite specimens has obvious temperature dependence: compressive strength and elastic modulus decrease monotonically,in which the adjustment magnitude is basically identical under different anchorage methods,while the temperature effect on the peak strain of the composite is not prominent.(3)By combining the non-contact optical strain measurement,acoustic emission monitoring system and through-axis anchoring force measurement,the external strain field,acoustic emission activity information and anchoring force characteristics of sandstone-concrete combinations with different heating temperatures and anchoring methods were obtained.The structural damage characteristics of the composite induced by high temperature and the path of crack stopping action were revealed from the stage of progressive rupture evolution of rock-concrete composite specimens during the loading process.(4)The anchor stock is simplified as a continuous material and the geotechnical medium as discrete particle units with cohesive properties,in which the numerical analysis model of sandstone-concrete anchoring combination is constructed by the continuous-discrete coupling numerical method which can reflect the material characteristics.Simplify the anchor rod as a continuous material and treat the geotechnical medium as a discrete particle element with cohesive properties.Construct a numerical analysis model of sandstone concrete anchor solid that can reflect structural characteristics through the continuous discrete coupling numerical method.Due to the differences in thermal parameters between sandstone and concrete materials,there is an asymmetric distribution of temperature field with the sandstone-concrete bonding interface as the boundary.The full-length anchorage transfers the continuous distribution characteristics of anchoring stress under end-anchor condition,in which the evolution process of anchoring load at both ends is related to the failure process of sandstone and concrete materials;The intermediate principal stress not only enhances the mechanical parameters of the composite specimens but also endows it with a "bimodal" loading response.This dissertation includes 81 diagrams,9 tables,and 143 references.