P-WAVE VELOCITY PROPERTIES AND DENOTATION ON ROCK MASS QUALITY FOR TUNNELLING AT SANHEKOU DAM SITE

This paper investigates the P-wave velocity, the engineering quality and the basic quality of rock mass of 10 tunnels at the Sanhekou dam site on Ziwu River. The results show that the high wave speed occupies a large area(more than 70%).The velocity distribution has partition shapes. This shape was particularly obvious in the medium height of the left bank and the high medium of the right bank. The velocity increases as the tunnel depths increase.the low velocity length increases as the tunnel elevation increases. The rock mass quality has the similar variation characteristics to those of the velocity. The high quality value increases as the tunnel depth increases and the tunnel depth showing high quality value increases as the tunnel elevation increase. In local areas similar characteristics can be found in both medium high and high elevations. The P-wave velocity can reflect the engineering quality of rock mass especially for the rock mass having the low value(2000m s-1) and the high value(4000m s-1) of the P-wave velocity. The rock mass having the value between 2000m s-1 to 4000m s-1should combine other index. The correlation between the P-wave velocity and the basic quality of rock mass can illustrate the denotation on the basic quality of rock mass. Preliminary evaluation of the rock mass can be carried out with the correlation between the P-wave velocity and the rock mass and test selectivity to raise reconnaissance efficiency.