AN EXPERIMENTAL RESEARCH INTO DETERMINATION OF HIGHEST PALEOTECTONIC STRESS STATE EXPERIENCED BY ROCK THROUGH GEOLOGICAL AGES
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摘要: 当前国内外尚无测定三维古构造应力场的理想方法.提出了一种新方法: 从待测地点取大岩心或新鲜石块, 从6个以上方向取岩石试样, 每方向至少10个试样, 以声发射的广义抹录不净现象, 测定岩石经历的各主要构造运动期的最大主应力值.而后, 统计出岩石记忆的最高古应力状态的最大主应力值σmt.由于岩石对最高古应力状态在各取样方向的正应力σmn尚有记忆, 只不过隐藏于各期较低古应力状态的最大主应力值之间, 不易区分, 故以σmt为目标, 通过“AE反演搜索法”, 则可将隐藏的各σmn搜索出来, 从而计算出岩石经历的最高古应力状态.以准平面应力状态模拟实验检验了该新方法的可行性.Abstract: Until now there has been no perfect method for the determination of three-dimensional paleotectonic stress field. In this paper, a new method for this determination is shown in the following steps: Firstly, rock specimens are drilled in six or more different directions out of the large rock cores or fresh rock blocks in the testing site. For each direction, ten or more specimens should be obtained. Secondly, the maximum principal stresses of the main tectonic movements experienced by the rock specimens to be measured are determined by means of the "Acoustic Emission Incomplete Erase Phenomenon in the General Sense". Thirdly, the maximum principal stress value (σmt) of the highest paleotectonic stress state left in the rock specimens is obtained via statistical analysis. It has been found that the rock specimens still contain the normal stresses (σmn) induced by the highest paleotectonic stress state in different sampling directions. However, these normal stresses are hidden between the maximum main stress values induced by the relatively low paleotectonic stress states in different phases, so that they are not easy to differentiate from each other. In this paper, these hidden normal stresses σmn can be located by means of the "AE inversion searching method" with σmt as a target. Therefore, the highest paleotectonic stress state experienced by the rock specimens can be calculated. The feasibility of this new method has been confirmed by a simulation experiment in the pseudo-plane stress state.
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Key words:
- acoustic emission /
- paleotectonic stress /
- paleotectonic stress field /
- geostress
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图 1 砂石大试样(No.1)单轴加载至破坏的全过程AE累积数与外加压应力响应曲线
Fig. 1. Response curve of total AE counts versus applied stress for sandstone specimen (No.1) during loading till failure
图 2 小试样(Mn30) 的复压响应曲线
Fig. 2. Response curve of total AE counts versus applied stress for small specimen (Mn30) during reloading
图 3 前三组最大主应力方向出现率直方图
Fig. 3. Histogram of occurrence frequency of the first three groups for direction of maximum principal stress
图 4 第4组最大主应力方向出现率直方图
Fig. 4. Histogram of occurrence frequency of the fourth group for direction of maximum principal stress
图 5 最小主应力出现率直方图
Fig. 5. Histogram of occurrence frequency for the minimum principal stress
表 1 各向小试样的记忆应力
Table 1. Memorized stresses of the differently directional small specimens
表 2 三个不同方向的试样组成的平面应力状态计算组
Table 2. Calculating groups of stress state consist of specimens cored from three different directions
表 3 各取样方向正应力理论值
Table 3. Theoretical values of normal stresses for specimens cored in different directions
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