Study On Surrounding Rock Failure Modes Classification And Support Optimization Of Shallow-buried Underground Powerhouse During Construction Period

China’s hydropower resources are mainly distributed in the high mountain valley area in the southwest basin,and it is usually necessary to build a large number of large underground powerhouses when developing hydropower projects,among which shallow-buried underground powerhouses are very common in the construction of underground projects.Under the influence of geological structure and other factors,in the construction of the project is faced with complex geological conditions,diverse lithology,a large number of large faults or structural surfaces,the development of joints and fissures and other types of geological problems,resulting in underground powerhouse safety construction is difficult,during the construction of the surrounding rock failure phenomenon is common.Therefore,it is of great significance to classify the failure modes of surrounding rock during the construction of shallow-buried underground powerhouse and to optimize the anchorage support of the corresponding failure modes of surrounding rock.Aiming at the engineering characteristics of shallow-buried underground powerhouse,this thesis considers the important factor of stress adjustment of surrounding rock during layered excavation during construction,and classifies the failure modes of surrounding rock of shallow-buried underground powerhouse in detail.According to the classification,the anchoring support optimization experiment and numerical simulation analysis are carried out on the common failure modes of surrounding rock in shallow-buried underground engineering,and the anchoring support optimization suggestions under the corresponding failure modes are put forward.Finally,the proposed classification of surrounding rock failure modes and optimization suggestions of anchoring support are verified in the main powerhouse of Tuoba Hydropower Station.Based on the research content,the main research work carried out is as follows:(1)Through extensive investigation of large-scale hydropower engineering examples,the definition of shallow-buried is given by analyzing the main engineering information.Based on this,the characteristics of stress adjustment of surrounding rock in layered excavation of shallowburied underground powerhouse are analyzed.According to the stress distribution law of surrounding rock in different excavation stages,the layered excavation of main powerhouse is simplified into two stages: the excavation completion stage above the rock-anchored beam and above the side wall.The stress state of surrounding rock in different parts of each stage is described macroscopically.(2)Fully absorbing the research results of surrounding rock failure modes of underground engineering,the failure modes of surrounding rock are summarized according to the level of ground stress.On this basis,the failure characteristics of surrounding rock of shallow-buried underground engineering are analyzed.From the perspective of stress adjustment of surrounding rock during construction,the classification of potential or apparent failure modes of surrounding rock of shallow-buried underground powerhouse considering excavation stage,typical parts and basic quality of rock mass(BQ)is proposed,and the failure phenomenon and mechanism of surrounding rock under various conditions are elaborated in detail.(3)According to the classification of surrounding rock failure modes,the common failure mode of surrounding rock in the construction period of shallow-underground powerhouse are selected as the optimization objectives of support,and the sliding instability of rock mass along the structural plane in the side wall of block instability failure is taken as the main research object.The anchoring mechanism of different structural plane angles and different anchoring modes is analyzed by experiment and numerical simulation.According to the experimental and simulation results,the anchoring support optimization suggestions for this kind of surrounding rock failure mode are put forward.(4)The classification of surrounding rock failure modes during the construction period of shallow-underground powerhouse and the optimization suggestions of anchorage support proposed in this thesis are applied to the main powerhouse of Tuoba Hydropower Station.Through the analysis of surrounding rock failure phenomena during the construction period,the accuracy of the classification of surrounding rock failure modes considering stress adjustment during the construction period is reflected.Combined with numerical simulation calculation,the rationality of anchorage support optimization suggestions for rock mass sliding instability along structural plane in block instability failure is verified.