Development of Downward Compact Conical-ended Borehole Overcoring Method for In-situ Stress Measurement at Great Depth.

深部地应力的认识对于地热能的开采和核废料的地下处置具有根本的重要性。为了高精度地估算深部地应力，开发了一种应力解除方法--下向紧凑锥头钻孔套芯法。DCCBO方法适用于泥浆充水的垂直/近垂直井眼。本研究的主要结果总结如下：1）选择了一种适用于垂直或近垂直充水钻孔底部的粘接剂; 2）研制了适用于500 m深充水钻孔的潜水钟型粘接装置; 3）研制了含氮气筒的16单元DCCBO锥形应变传感器; 4）通过对带钻孔立方体试件的加卸载试验，验证了所研制的16单元DCCBO锥形应变传感器在各向同性岩石中的实用性; 5）通过实验验证了16单元锥形应变传感器尖端充氮气系统的有效性; 6）在充水条件下成功地进行了16单元锥形应变传感器与岩石试件的粘接实验; 7）提出了DCCBO多通道数据记录仪的技术指标。

Knowledge of in-situ stress at great depth is of fundamental importance for geothermal energy extraction and underground disposal of nuclear waste. In order to estimate In-situ stress at great depth with a high accuracy, Downward Compact Conical-ended Borehole Overcoring Method(DCCBO), which is one of stress relief method was developed. DCCBO method is applicable to a mud water-filled vertical/sub-vertical borehole.Main results obtained in this study are summarized as follows :1) An adhesive which is applicable lo a water-filled vertical/sub-vertical borehole bottom was selected.2) Diving-bell type bonding device which is applicable to a water-filled borehole at a depth of 500m was developed.3) 16-elements conical strain cell for DCCBO which contained nitrogen gas cylinder was developed.4) The usefulness of the developed 16-elements conical strain cell in the isotropic rock is verified by loading and unloading tests to the cubic specimen with a borehole.5) The usefulness of the gushing system of nitrogen gas from the tip of 16-elements conical strain cell is verified by laboratory test using a borehole model made of acrylic.6) Bonding test of 16-elements conical strain cell to a rock specimen under water-filled condition was successful.7) Specification of a multi-channel data logger for DCCBO was proposed.