THE INITIAL CRACK SPACE OF PRESSURE TUNNEL CONCRETE LININGS IN NON-HOMOGENEOUS ROCK MASS

It is generally found that the spaces between initial cracks in the concrete linings of pressure tunnels are not the same in non-homogeneous rock mass, and the positions of these cracks can be distributed in a random manner. A numerical method is presented which is capable of determining the locations of the initial cracks under critical inner water pressure, the feasibility of which is verified through a comparison analysis of a prototype test. The Influence of typical geological conditions upon the location of the first crack has been analyzed. Parametric analyses have been conducted to investigate the characteristics of the space between initial cracks in the linings of pressure tunnel taking into account the influence of cracking induced stress release. It is found that under same rock mass conditions, the number of initial cracks in linings decreases as the tunnel diameter grows larger, while the tunnel diameter remains the same, the number of initial cracks in linings would be relatively small in the situation of non-homogeneous rock mass in comparison with the case under a homogeneous rock mass condition. Also it is found that the number of initial cracks in concrete linings for all the conditions considered in this paper ranges from 1 to 4, which is relatively small and can be attributed to the low value of average tangential stress between the lining and surrounding rock, about 0.05MPa, as well as the effect of a large stress release region induced by the cracking within the lining.