压磁套芯三维原地应力测量研究

压磁套芯解除法是20世纪50年代开始发展起来的原地应力测试技术。为了实现在单一钻孔中进行三维地应力测量研制了单孔全应力计。在简单介绍压磁全应力计结构和计算原理的基础上，通过现场测试，对在锦屏二级水电站地下厂房洞群区压磁套心解除3孔交汇法三维地应力测量和单孔三维地应力测量及水压致裂地应力测量进行了比较分析研究。测量结果表明，在探洞浅部，受局部地形影响，测点的应力分布主要受自重和地形地貌控制，形成特有的“V”型河谷岸坡内的局部应力状态，最大主应力为11 MPa左右，作用方向NNW基本近水平；在探洞深部地应力应力值较高，最大主应力为40 MPa左右，作用方向近直立；随水平埋深的增大最大主应力由近水平状态转变为近直立状态，说明在洞深部自重应力起主导作用。通过三种方法测量结果的对比分析，说明压磁套心解除单孔三维地应力测试技术与压磁套心解除3孔交汇法和水压致裂地应力测试技术具有相同测试精度。

Study on 3-D in-situ stress measurement by piezomagnetic overcoring method

The piezomagnetic overcoring method is an in-situ stress measurement technique that developed since 1950 s. In order to implement three dimensional stresses measurement in a single borehole, the total stresses sensor has been developed. The structure and calculating theory of piezomagnetic total stresses sensor are introduced. The comparing study of in-situ stress measured has been carried among the piezomagnetic overcoring method using several inclined boreholes which are oriented in different directions, piezomagnetic method in single borehole and hydraulic fracturing at Jinping Ⅱ Hydropower Station. The measurement result indicate: in-situ stress at shallow depth of tunnel is controlled by deadweight, topography and region formation, formed typical stresses distribution of V-shaped river valley; the maximum stress is about 11 MPa and the direction is about NNW. The in-situ stress at deep depth of tunnel is higher, the maximum stress is about 40 MPa, and the direction is about vertical. The direction of maximum stress changes from level state to vertical state along with increasing of level burying; and it indicates that the deadweight stress is dominant effect. After comparison of in-situ stresses measured, it is shown that they are consistent fundamentally. We consider the piezomagnetic overcoring three dimensional stresses measurement method in a single borehole can provide reasonable in-situ stress information as same with the piezomagnetic overcoring method and hydraulic fracturing using several inclined boreholes which are oriented in different directions.