二滩坝址岩心裂饼现象及其断裂破坏机制

岩心裂饼是钻探过程中特有的岩石力学现象。1958年哈斯特首先报道过岩心裂饼现象,且发现岩饼的厚度与其直径的比值随初始应力的增加而减少,其后,库克则利用钻孔岩心饼化的程度评价岩体中的初始应力状态。

DISCING PHENOMENON OF THE DRILLHOLE CORE AT ERTAN DAM SITE AND ANALYSIS OF ITS FRACTURE MECHANISM

In the exploration drillhole of riverbed the core universally suffers from discing failure. In this paper discing phenomenon of the core in riverbed drillhole and its characteristics are summarized; virgin stresses condition of the rock masses at the dam site and the microfissure in the core of syenite and its distribution characteristics are investigated; stress condition of the core during drilling is analysed; and analysis of fracture mechanism is made for the discing failure of the core using the theory of fracture mechanics. The analysis results show that the fracture spread of the core discing originates from the are microfissure on the surface or the microfissure near the surface of the core. Under the circumstances of the virgin stresses of Ertan riverbed, the critical dimension of the fracture microfissure is 0.22-0.27 mm or so, only about 1/5 of the corresponding centric microfissure which results in fracture spreading. According to the fracture mechanism of the core discing and the stress condition in the rock masses und ermentioned problems can be explained. These problems mainly are: the thickness of the core disc is directly proportional to the diameter of the core disc; the larger the virgin stresses in the rock mass are, the thinner the core discs; the number of core disc gradually decrease with the increasing depth of the drillhole; because the riverbed has most evident concentrated stresses, the cores of the drillhole in the riverbed tend to be fractured into discs.