Abstract: Borehole strain monitoring is an important geodetic means with a wide range of use in geodynamics research. One of the main reasons for the slow development of this kind of observation is that the establishment of a borehole strain monitoring site is costly and the success rate is not very high. Some sites fail due to the unfavorable borehole conditions,that is,rocks at the depth where the sensor is embedded are not intact but fractured. Sometimes even if the rocks were found not as good as required,the instrument had to be installed because of the expansive cost in drilling the hole. To solve the problem,it is necessary to prospect the rock condition of the site before drilling. Fractured rocks usually contain ground water in the fractures,which lower the rocks' resistivity. Resistivity imaging survey can be applied to the investigation of underground condition and give local distribution of resistivity with relatively high resolution. Three experiments have been carried out in Shanxi Province,in which single profiling is done at Shanghuangzhuang,cross profilings at Dongmafang and at Jiaokou,respectively. Three boreholes at Shanghuangzhuang and one at Dongmafang and at Jiaokou each were drilled for comparison of different types of instruments. Results of rocks strength experiments and instrument installations for the five boreholes agree well with results of the surveys. It suggests that resistivity imaging survey is an effective method to predict the underground condition of rocks. Instrument installation should avoid low-resistivity zones indicated by the profiling to prevent putting the sensor into fractured rocks.

Key words: borehole strainmeter, resistivity imaging survey, rock condition, low resistivity zone

摘要： 钻孔应变观测是一种重要的地球动力学研究手段，具有广泛的用途。但是，建立钻孔应变观测点的费用比较高，而成功率又不够高，限制了这种观测的普遍推广。一些观测点的失败，其主要原因是钻孔条件不理想，即仪器安装深度岩石破碎。因为钻孔费用高，所以即使钻孔后发现岩石条件没有达到要求，往往也只能勉强安装仪器。要解决这个问题，就要事先对场地岩石条件进行预判。岩石裂隙通常都含有裂隙水，会降低其电阻率。高密度电法勘探对地下岩石的电阻率有比较高的分辨率，用这种方法在山西的上皇庄、东马坊和交口3个观测点建设中进行了实验。其中，在上皇庄拉了1条测线，东马坊和交口分别拉了2条互相垂直的测线。在上皇庄打了3个钻孔，其他2个点分别只有1个。5个钻孔和取心的岩石强度实验结果以及仪器安装情况，都与勘探结果相符，这表明高密度电法是一个有效的预判岩石完整性的手段。要防止钻孔打在破碎带上，就要避开电法勘探显示的低阻区。

关键词: 钻孔应变仪, 高密度电法勘探, 岩石完整性, 低阻区