岩石电阻率变化各向异性与微裂隙扩展方位实验研究
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摘要
将不同规格的长方体花岗岩标本 ,按事先设计的图案布设多个电极 ,并用抽真空的方法将标本进行水饱和 .然后将标本电极面和相邻面的一小部分 (包括棱 )用防水绝缘胶密封 .用多电极组合法 ,将己布电极组合成不同方向、不同极距的电阻率各向异性测线和电测剖面、电测深测线 .使标本在装有水的承压水箱中 ,沿标本长轴方向受压 ,观测标本电阻率随压力的变化 .在实验中 ,一些标本被压坏 ,出现宏观裂隙 ;一些标本没有被压坏 ,没有被压坏的标本通常压到电阻率出现明显破裂前兆为止 .然后 ,将未压坏的标本测量面显微照相 ,从照片上寻找裂隙的优势方向 ,和被压坏标本的宏观裂隙一起 ,与电阻率各向异性计算结果进行对比 ,实验结果表明 :1裂隙和破碎带通过区域的测点 ,视电阻率变化各向异性结果好 ,4种组合求得的 4个各向异性主轴方向趋于一致 ,且与破碎带方向基本吻合 ;裂隙和破碎带不经过区域的测点 ,或者 4个视电阻率变化各向异性主轴方向不一致 ,或者根本求不出各向异性解 .这后一种情况 ,在裂隙面平行测量面时 ,表现最为明显 ;2显微照相显示的微观裂隙或破碎带的优势方向与电阻率变化最大的各向异性主轴方向基本一致 ;3电测剖面的结果 ,能较好地反映裂隙的位置和区域
Multiple electrodes are arranged on the surfaces of cubic granite samples of different sizes according to pre designed patterns. Samples are fully saturated with water in vacuum. Waterproof insulation glue is coated on the measuring surface and a small parts (including two arrises ) of the adjacent surfaces of the saturated sample to ensure that the electric current flows only within the sample through the connection between the electrodes. The multiple electrodes are combined form arrays of different direction and spacing with symmetrical four electrode method according to need of measuring of resistivity changing anisotropy, electric profiling and electric sounding. The samples are placed into container filled with water. The samples are uniaxially compressed along the direction parallel to the longest dimension of the cubic, and the variation of resistivity during the whole loading process is observed. In the experiments, some samples are loaded to rupture with macro fractures, some are only loaded to the stage, which shows obvious precursors in variation of resistivity associated with the indication of forthcoming rupture. Finally a quantitative comparison between the dominant orientation of pre existing cracks in photo micrography of unruptured samples and those macro fractures in ruptured sample is made, together with their respective resistivity changing anisotropy behaviors. The experimental results are as follows: ① For measuring points in areas that are passed by cracks or rupture bands, the directions of principal anisotropy axes deduced from four kinds of combinatorial equation sets are essentially identical with each other, and accord with the orientation of cracks or main rupture bands approximately. For measuring points in areas without crack or rupture band passing through, either the directions of calculated principal anisotropy axes by different combinatorial arrays are inconsistent with each other, or the principal anisotropy axis cannot be determined, especially in the cases where the crack plane is parallel to the measuring surface. ② The dominant orientation of microfractures or rupture bands shown from micrographs is close to the direction of principal anisotropy axis along which the variation in resistivity is the greatest. ③ The results of e lectric profiling can be used for detecting the localization of cracks.
Multiple electrodes are arranged on the surfaces of cubic granite samples of different sizes according to pre designed patterns. Samples are fully saturated with water in vacuum. Waterproof insulation glue is coated on the measuring surface and a small parts (including two arrises ) of the adjacent surfaces of the saturated sample to ensure that the electric current flows only within the sample through the connection between the electrodes. The multiple electrodes are combined form arrays of different direction and spacing with symmetrical four electrode method according to need of measuring of resistivity changing anisotropy, electric profiling and electric sounding. The samples are placed into container filled with water. The samples are uniaxially compressed along the direction parallel to the longest dimension of the cubic, and the variation of resistivity during the whole loading process is observed. In the experiments, some samples are loaded to rupture with macro fractures, some are only loaded to the stage, which shows obvious precursors in variation of resistivity associated with the indication of forthcoming rupture. Finally a quantitative comparison between the dominant orientation of pre existing cracks in photo micrography of unruptured samples and those macro fractures in ruptured sample is made, together with their respective resistivity changing anisotropy behaviors. The experimental results are as follows: ① For measuring points in areas that are passed by cracks or rupture bands, the directions of principal anisotropy axes deduced from four kinds of combinatorial equation sets are essentially identical with each other, and accord with the orientation of cracks or main rupture bands approximately. For measuring points in areas without crack or rupture band passing through, either the directions of calculated principal anisotropy axes by different combinatorial arrays are inconsistent with each other, or the principal anisotropy axis cannot be determined, especially in the cases where the crack plane is parallel to the measuring surface. ② The dominant orientation of microfractures or rupture bands shown from micrographs is close to the direction of principal anisotropy axis along which the variation in resistivity is the greatest. ③ The results of e lectric profiling can be used for detecting the localization of cracks.
引文
陈大元 ,陈峰 ,王丽华 .1 983 .单轴压力下岩石电阻率的研究电阻率的各向异性 [J].地球物理学报 ,2 6(增刊 ) :784～ 792
陈峰 ,修济刚 ,安金珍 ,等 .2 0 0 0 .用动态岩石电阻率变化各向异性探测岩石破裂前兆和确定主破裂扩展方向 [J].地震学报 ,2 2 ( 2 ) :2 1 0～ 2 1 3
钱家栋 ,曹爱民 .1 998.1 976年唐山 7.8级地震地电阻率和地下水前兆综合物理机制研究 [J].地震 ,1 8(增刊 ) :1～ 9
王妙月 ,底青云 ,张美根 ,等 .1 999.地震孕育、发生、发展动态过程的三维有限元数值模拟 [J].地球物理学报 ,4 2 :2 1 8～ 2 2 7
陈峰 ,修济刚 ,安金珍 ,等 .2 0 0 0 .用动态岩石电阻率变化各向异性探测岩石破裂前兆和确定主破裂扩展方向 [J].地震学报 ,2 2 ( 2 ) :2 1 0～ 2 1 3
钱家栋 ,曹爱民 .1 998.1 976年唐山 7.8级地震地电阻率和地下水前兆综合物理机制研究 [J].地震 ,1 8(增刊 ) :1～ 9
王妙月 ,底青云 ,张美根 ,等 .1 999.地震孕育、发生、发展动态过程的三维有限元数值模拟 [J].地球物理学报 ,4 2 :2 1 8～ 2 2 7
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