Study On Selection Criteria For Lining Structure Type Of Hydropower Plant Tunnels

Aimed at the current lack of reliable selection criteria for the lining structure type of diversion tunnels, a series of calculations of inner water exosmosis of diversion tunnels were conducted based on the seepage-stress-cracking coupled analysis model and program of diversion tunnels. Comprehensive water permeability under different conditions and different inner water pressure inside the tunnel were obtained. Relationships between inner water pressure and comprehensive permeability index were built up by using the comprehensive water permeability as the seepage failure standard of diversion tunnels. The relationship curves between inner water pressure according to allowed Lugeon values and comprehensive permeability index were fitted out. The curves could be taken as the boundaries among shotcrete-bolt, reinforced concrete and steel lining. The results can provide the theoretical basis for the lining selection of diversion tunnels. The main contents are as follows:(1) The design reality and specification of diversion tunnels are not perfect, structure and seepage computation is lack of reliable method and the allowed Lugeon values is still under research at present. Aimed at the above mentioned current situations, the research status and deficiency in design criteria, structure and seepage computation and allowed Lugeon values were summed up. The subjects need to be further studied are proposed based on the summary.(2)A series of surrounding rock permeability coefficient and deformation modulus, initial geo-stress, lining type, thickness were combined, and inner water exosmosis calculations were carried out by using the seepage-stress-cracking coupled numerical model. Using permeability rate, lining crack width and ultimate hydraulic pressure as the seepage stability index, effect of surrounding rock permeability and deformation modulus, initial geo-stress and lateral pressure coefficient, lining type and thickness were analyzed based on the calculation results.(3) Inner water exosmosis analysis of diversion tunnels under a series of cases were conducted by use of the seepage-stress-cracking coupled numerical model. Comprehensive water permeability of diversion tunnel under different cases and different inner water pressure were obtained. Relationships between inner water pressure and comprehensive permeability index were built up by using the comprehensive water permeability as the seepage failure standard of pressure tunnel. The relationship curves between inner water pressure according to allowed Lugeon values and comprehensive permeability index were fitted out. The curves could be taken as the boundaries among shotcrete-bolt, reinforced concrete and steel lining.(4) The statistical analysis results of actual project data were used to verify and refine the lining structure type selection guidelines. The results presented herein can provide the theoretical basis and guidelines for the pressure tunnels' lining selection.