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A THEORETICAL AND EXPERIMENTAL STUDY FOR ESTIMATING THREE-DIMENSIONAL IN-SITU STRESSES FROM CORE DISCING

估算岩心切割三维原位应力的理论和实验研究

基本信息

批准号：
08405066
负责人：
MATSUKI Koji
金额：
$ 9.66万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1998
项目状态：
已结题

项目摘要

The direction and the magnitude of tensile principal stresses within and below a long HQ core stub were analyzed with a finite element method for 77 in-situ stress conditions. 26 stress conditions were identified to be those under which core discing is likely to occur. A criterion for core discing was then proposed by evaluating the maximum tensile principal stress which is necessary for the contour plane to be formed throughout a cross-section of the core. A detail analysis on the distributions of the direction of tensile principal stresses showed that almost planar surfaces might be formed in the central part of the end surfaces of a dics and that large difference between the maximum and intermediate principal stresses might produce a so-called saddle shaped periphery. Summarizing the results obtained by the analysis, a procedure for determining principal in-situ stress directions from the geometry of a disc was proposed, based upon the symmetry of the end surfaces, the normal direction in the central part of the end surfaces and the direction of the concave or the convex axes in the end surfaces.To verify the methods for estimating three-dimensional in-situ stresses from core discing, described above, experiments on core discing were carried out for Shirakawa welded tuff and Kimachi sandstone by loading a block containing a long core with a triaxial loading system. The criterion for core discing proposed in this study approximately estimated the stresses at which core discing initiated for Shirakawa welded tuff. However, the stresses predicted by the criterion did not coincide with the experimental results for Kimachi sandstone, for which the core discing was accompanied by compressive failure at the borehole bottom. A saddle shaped dicing was not observed for these rocks even if two horizontal stresses were different.

用有限元法分析了77种地应力条件下HQ长芯桩内部和下部的主拉应力方向和大小。26种应力条件被确定为可能发生堆芯盘裂的条件。然后，提出了一个标准的核心discking通过评估的最大拉伸主应力，这是必要的轮廓平面形成整个芯的横截面。对拉伸主应力方向分布的详细分析表明，在模具端面的中心部分可能形成几乎平坦的表面，最大主应力与中间主应力之间的较大差异可能产生所谓的鞍形周边。根据分析结果，提出了一种从圆盘几何形状确定主地应力方向的方法，该方法是根据圆盘端面的对称性、端面中心部分的法线方向和端面中凹轴或凸轴的方向来确定主地应力方向的。用三轴加载系统对白川熔结凝灰岩和木町砂岩进行了长岩心块体加载的岩心圆盘实验。在这项研究中提出的核心盘的标准近似估计的应力，核心盘开始白川焊接凝灰岩。然而，该标准预测的应力与Kimachi砂岩的实验结果并不一致，对于Kimachi砂岩，岩心盘裂伴随着钻孔底部的压缩破坏。鞍形切割没有观察到这些岩石，即使两个水平应力不同。