Study On Surrounding Rock’s Deformation Failure Modes Of Underground Engineering In High Crustal-stress Area

Knowledge of high crustal-stress is very significant for many problems in designing andconstruction of underground engineering as well as in assessment of surrounding-rock’sstability. From the standpoint of mechanics, tunnels’ stability is effected by not onlyenvironmental stress but also rock properties itself. That’s to say, environmental stress can beknown as acting force, and surrounding-rock can be known as a carrier to react against thehigh crustal-stress, both of them are in equilibrium which can ensure the security ofunderground engineering. Despite the connection between high crustal-stress andunderground engineering, based on numerous actual projects and measured data of the in situstress, this thesis is intended to discuss the manifestation features of high crustal-stress inunderground engineering, analyze the deformation characteristics of cave excavation, deducethe mechanism between soft and hard rock, summarize the geological modes of highcrustal-stress in cave excavation. Some views of manifestation features and geological modesfor high crustal-stress are demonstrated to compare with the actual projects.Various thoughts about high crustal-stress need abundant scientific research andmeticulous experiments. To begin with, plentiful engineering cases at home and abroad aregathered in coverage of water resources and hydropower engineering, railway engineering,highway engineering, mining engineering and so on. Manifestation features of highcrustal-stress are gained in view of lithologic characters, excavation and investigation process,stress-strain relation as well as physical and mechanical indexes. In the second place,according to the study of differences and similarities of typical engineering cases domesticand overseas, three kinds of lithology are chose. By numerical simulation ofthree-dimensional mode, the stress distribution and displacement variation in gravity stressand high crustal-stress are produced. Considering three situations that intersection betweenchamber axis and maximal principal stress of surrounding rock contains parallel, vertical andcrossing, characteristics of stress and displacement can be known well with deliberation onpractical cases. Once again, take the point of elastic-plastic mechanics and fluid mechanics,deduce the mechanisms of surrounding rock during excavation, and connect the results of numerical simulation, geological modes of soft and hard rocks in excavation affected by highcrustal-stress can be summarized. In the end, take Xiaowan hydropower station as theresearch object, build an analytical mode, and study deformation characteristics ofunderground powerhouse crossing faults during excavation, the calculated stress are in accordwith actual measured stress. Lastly, use the given conclusions to check the geological modesof all other large underground excavations.The main subjects drawn from the paper are as follows：(1) Manifestation features ofhigh crustal-stress in underground engineering can be generalized that rock burst occurs inhard rock, but severe plastic deformation mainly happens in soft rocks.(2) Geological modesof surrounding rock in high crustal-stress consist of seven kinds: opening and cracking, archup and heave down, splitting and collapse, rock burst, loose and flexure, plastic extrusion anddilation.(3) Based on mechanics theory, soft and hard rock’s mechanism in high crustal-stressduring excavation are deduced. Apply all conclusions to Xiaowan hydropower station and theother12large underground engineering objects, the gained results are in accord to the actualconditions, which demonstrates that the research on this thesis has theoretical importance andpractice value to certain extents.