Surrounding Rock Stability Analysis And Support Design Study For Xiangjiaba Underground Powerhouse

The right underground powerhouse of Xiangjiaba Hydropower Station is installed with four units of installed capacity 750MW each; the excavated span of the machine hall reaches 31.40m/33.40m (up and down the rock anchored crane beam), which is the largest one among the completed, under construction and planned projects. The surround rock of the underground chambers is of slight dip angle and contains coal layers that had been mined in the history, in which the grade II weak structures develops and hydrological geology condition is complex. The stable of surround rock and supporting design of underground chambers is one of key technologies concerned of the design of Xiangjiaba Hydropower Station; it may affect the safety and investment of the project. So it is necessary to conduct calculation and analyses on the surround rock of the underground chambers, to analyses the stress and deformation characteristics of surround rock is to provide proofs for the supporting design to realize design optimization. This thesis focuses on the studying methods of the supporting design and analyses on the surround rock.Firstly it is to demonstrated that adopting the supporting of anchoring and shotcrete is feasible by adopting methods of codes, specifications, Q system, similar projects and other projects experiences, then to put forward adopting strengthening supporting measures such as pre-stressed anchorage ropes for the arch top of machine hall and main transformer chamber and the side walls through determining the supporting parameters and analyzing the engineering geology characters of main chambers as well as considering the analyses results of rock block stable, at last the supporting types and parameters of main underground chambers are suggested after the parameter comparison has been completed by the methods of plan and three-dimension finite element.In order to conduct a general reasoning on the stable of underground surround chamber, the results of geological structure and site crust stress in the powerhouse area have been analyzed and counter analyses on the primary crust stress field has also been conducted; excavation process has been studied according to the arrangement character of underground chambers; then the stable analyses of surround rock has been done by adopting three-dimension elastic plastic damnification finite element with consideration of the affection of seepage field to surround rock stable, finally the stable condition of underground chambers has synthetically been appraised.The stable analyses results for the surround rock of underground chambers indicate that the whole stability of surround rock of underground powerhouse is relatively good.