黄河上游某坝址平硐开挖后岩体变异时间效应规律分析

ANALYSIS OF THE TIME EFFECT ON THE PROPERTIES OF THE ROCKMASS AFTER EXCAVATION AT A DAMSITE ON THE YELLOW RIVER

工程岩体开挖后改变了原来的赋存条件与环境，沿硐壁岩体表面卸荷，由于应力的重新调整，表现在波速上的下降，即岩体性状发生变异。随着时间的增加，变异程度加大，而变异的速率却逐年下降。文章根据黄河上游某水电工程坝址平硐硐壁不同时间（几个同点位）弹性波速测定结果，拟合了波速年下降率Ｄ（％）与开挖一测定时间间隔Ｎ（ａ）的函数关系。并根据这种关系进行岩体波速的反算，求得开挖时岩体的波速值，反映其本来的性状。对于反算结果的检验，应用了地震穿透法，结果二者波速值吻合。

The initial stress state of a rockmass is changed after excavation. The properties of the rockmass vary at the same time due to rebouncing and unloading.This effect will last with the time going on, but the changing rate will decrease. It is impossible to measure the real properties of the changed rockmass directily. Thus the time-effect should be corrected． In this paper a function of D（the annual de-crease rate of Vp）with N（time interval between excavation and measurement ）is set up based on the Vp during different time of the rockmass in the adits of one damsite on the upper Yellow river. The funcion is applied to calculate the excavated rockmass，The theoritic results are close to the long distance Vp measured through micro-seismic wave.The time-effect on the properties of excavated rockmass is proved.