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甘肃北山预选区是我国高放废物地质处置库首选预选区。为掌握区域岩体地应力大小、方向及其分布规律,在预选区新场岩体内进行4个钻孔的水压致裂地应力测量。基于钻孔岩芯编录和钻孔电视成像结果,在0~700 m范围内共开展81段压裂试验,并在19个测试段内进行印模定向试验,成功获得地应力量值和最大水平应力方向数据。根据压力–时间关系曲线,采用3种不同方法判读瞬时关闭压力参数,保证水平主应力测量结果的精度与可靠性。测量结果表明,新场岩体地应力随着深度的增加而增大,在测量深度范围内,最大水平主应力小于25 MPa,且最大水平主应力普遍高于垂直应力,揭示新场岩体应力场以构造应力为主导的特点。最大水平主应力与垂直应力比率随深度的变化规律表明,构造应力的作用随着深度的增加逐渐减弱,垂直应力作用加强。此外,最大水平主应力的优势方向为NEE,与区域构造应力场方向基本一致,从而证实应力测量结果的准确性。研究成果可为高放废物处置工程的开挖设计及稳定性评价提供科学指导,并为我国西北地区应力场分布规律研究提供重要参考资料。
Gansu Beishan Preselected Area is China’s first choice of high-level radioactive geological repository pre-selected area. In order to grasp the size, direction and distribution of geo-stress of regional rock mass, hydrofracturing geostress of 4 boreholes was measured in the new field rock mass of preselected area. Based on the borehole core cataloging and borehole television imaging results, a total of 81 fracturing tests were carried out in the range of 0 ~ 700 m and the stamp orientation test was conducted in 19 test sections, and the value of the geostress and the maximum level of stress Stress direction data. According to the pressure-time curve, three different methods are used to interpret the instantaneous closing pressure parameters to ensure the accuracy and reliability of the horizontal principal stress measurement results. The measurement results show that the stress of the new field rock mass increases with the increase of depth. The maximum horizontal principal stress is less than 25 MPa within the measured depth range, and the maximum horizontal principal stress is generally higher than the vertical stress, revealing the stress of new field rock mass The field is dominated by tectonic stress. The variation of the maximum horizontal principal stress and vertical stress ratio with depth shows that the role of tectonic stress is weakened with the increase of depth and the vertical stress is strengthened. In addition, the dominant direction of the maximum horizontal principal stress is NEE, which is basically consistent with the direction of the regional tectonic stress field, thus confirming the accuracy of stress measurement results. The research results can provide scientific guidance for excavation design and stability evaluation of high level radioactive waste disposal projects and provide important reference materials for the study of stress field distribution in Northwest China.