A Criterion of Hollow Core Disking Initiation.
A Criterion of Hollow Core Disking Initiation.
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DOI：
10.2473/shigentosozai.114.875
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Y. Obara;Seong-seung Kang;T. Seguchi;A. Sato
中科院分区：
文献类型：
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作者：
Y. Obara;Seong-seung Kang;T. Seguchi;A. Sato
大多数岩石应力测量的复盖方法使用大直径钻孔，即所谓的复盖，以减轻安装传感器的导孔周围的应力。当覆盖层在高岩石应力作用下进入坚硬岩石时，有时会观察到岩心盘片现象。由于回收的磁芯具有一定的厚度，其中心有一个像甜甜圈一样的孔，因此这种磁芯盘被称为空心磁芯盘。本文以轴对称弹性力学半解析边界元法在任意边界条件下的计算结果为基础，模拟了主应力轴线与钻孔轴线重合的三维初始应力状态下的覆岩过程，讨论了覆岩过程中产生的空心岩心盘。首先，在初始应力各主应力独立作用的情况下，分析了井眼切向和旋转方向的表面应力强度系数；结果表明，在覆盖层推进超过钻孔半径的范围内，系数不会发生变化。其次，利用表面应力强度系数，分析了三维初始应力状态下钻孔的表面应力，建立了覆盖层拉应力引起的裂缝起裂判据，该判据是覆盖层推进的函数。最后，对覆岩引起的井眼表面应力进行了分析，明确了初始应力状态对起裂位置、裂缝类型和盘面厚度的影响。
Most of the overcoring method for rock stress measurements use a large diameter drilling, what is called the overcoring, to relieve the stress around a pilot hole in which a transducer is installed. When the overcoring is advanced into hard rock subjected to high rock stress, a phenomenon of a core disking is sometimes observed. As the recovered cores which have a constant thickness have a center hole like a doughnut, this core disking is called a hollow core disking. In this paper, simulating the overcoring under three dimensional initial stress state in which the axis of a principal stress coincides with that of a borehole, the hollow core disking initiated during the overcoring is discussed, based on the results calculated by a semi-analytical boundary element process for axisymmetric elasticity with arbitrary boundary conditions. Firstly, the surface stress intensity coefficients in the tangential and rotational directions of the borehole are analyzed under the conditions in which each principal stress of initial stress is subjected independently. It is clarified that the coefficients is not changed beyond the advance of the overcoring more than the radius of the borehole. Secondly, using the surface stress intensity coefficients, the surface stresses of the borehole are analyzed under three dimensional initial stress state, then the fracture criterion which represents the fracture initiation due to the tensile stress induced by the overcoring is formulated as a function of the advance of the overcoring. Finally, analyzing the surface stress of the borehole induced by the overcoring, it is made clear that the location of the fracture initiation, the type of the fracture and the thickness of disk are dependent upon initial stress state.