岩滩扩建工程石英脉侵入带对厂房顶拱围岩稳定性影响分析

Analysis on Influence of Quartz Veins Invasion Zone to Stability of Surrounding Rock at Underground Powerhouse Crown in Expansion Project of Yantan Hydropower Station

在岩滩水电站扩建工程中,由白色石英脉岩和浅色蚀变辉绿岩组成的石英脉侵入带,低于水库蓄水位,与地下厂房左端墙的顶拱临空面最近距离为十余米,属Ⅲ类围岩,其总体性状比Ⅱ类新鲜辉绿岩为差。因其仍属于力学强度较高坚硬岩体,未发现软弱层带,透水性很弱,离厂顶临空面较远,厂房洞挖应力松弛影响范围、厂顶随机块体最大影响深度和锚索压缩应力均达不到该处,文中分析,施工中若能及时做好顶拱和边墙的关键块体的加固处理,厂顶以上围岩整体稳定性较好,即石英脉对厂房稳定基本无影响,可不作长锚索处理。但需在石英脉侵入带内预埋监测仪器,做好施工期的应力—应变监测。

Quartz veins invasion zone, which is composed of white quartz veins rock and light color erosion diabase, is below the impounded level of the reservoir, and is near lOm to the closet left wall away from free face of underground powerhouse roof. Quartz veins invasion zone, which is called ＂white cap＂, belongs to surrounding rock of grade Ⅲ, and its general properties are worse than fresh diabase. Because the quartz veins invasion zone is calculous rock body with rather big mechanical strength, weak formation is not found in the zone, and its hydraulic permeability is very weak. The zone is rather far away from the free face of powerhouse roof. Influence of stress relaxation during cave-digging of the powerhouse, maximal effecting depth of stochastic block of powerhouse roof and compression stress of anchor cable cannot reach the ＂white cap＂. As the surrounding rock above powerhouse enjoys favorable stability, the quartz veins basically do not affect the stability of the powerhouse provided that reinforcing treatment measures are taken for key blocks of umbrella arch and side wall during construction. So long anchor cable may not be made. But monitoring instruments shall be pre-buried in quartz veins invasion zone and monitoring of stress-strain shall be made during construction.