山西煤矿矿区井下地应力场分布特征研究

采用煤矿井下专用的小孔径水压致裂地应力测量装置，在山西省的晋城、潞安、汾西、华晋、阳泉、平朔、大同等矿区，完成了160个测点的地应力测量，测点地质条件涵盖了山西省煤矿大部分条件.基于实测数据，分析了地应力与测点埋深的关系，不同深度条件下煤矿矿区井下地应力状态；绘制出山西省煤矿矿区井下地应力分布图，并与震源机制解的分析结果进行了比较，得出山西省煤矿矿区井下地应力场分布特征与变化规律.煤矿井下水平应力总体上随着埋深增加而增大，但由于各矿区地质条件差异较大，导致地应力测试数据离散性也较大；埋深小于250 m的岩层应力状态主要为σH>σh>σV型，埋深处于250~500 m的岩层应力状态以σH>σV>σh型为主，埋深较大的矿区主要为σV>σH>σh型；最大水平主应力与垂直主应力的比值绝大部分集中在0.5~2.0之间，而且随着埋深增加，侧压比呈现减小的趋势，并向1附近集中；最大水平主应力与最小水平主应力的比值主要集中在1.5～2.0之间；平均水平主应力与垂直主应力的比值大多处于0.5～1.5，尤以0.5～1.0之间最多；山西省煤矿矿区从北到南，最大水平主应力方向发生了较大变化.北部最大水平主应力方向为NE，往南发生偏转到NNW；靠东部与西部偏向NW；靠东南部出现了多变的方向.井下实测数据与震源机制解相比在部分区域一致性较好，而在另一些区域存在明显的差异.特别是在受较大地质构造影响的区域，水平主应力方向往往发生明显的扭转和变化.

Study on characteristics of underground in-situ stress distribution in Shanxi coal mining fields

By means of the small borehole hydraulic fracturing measurement unit designed for underground coal mines, in-situ stress measurements at 160 sites were made in Jincheng, Lu′an, Fenxi, Huajin, Yangquan, Pingshuo and Datong coal mining fields in Shanxi province, which cover the most geological conditions of Shanxi coal mines. The relation between in-situ stresses and depths of measurement sites, and the in-situ stress status of different depths were analyzed based on measurement data. The underground in-situ stress distribution map of Shanxi coal mining fields was drawn and the characteristics and law of underground in-situ stress distribution was made by comparing the results with the focal mechanism solutions. It is shown that the horizontal stresses basically increase with the depths of measurement sites as a whole. A large scatter of the in-situ stress measurements is also found because of the different geological conditions in different coal mining fields. The in-situ stress patterns are σ_H>σ_h>σ_V when depth is below 250 m, σ_H>σ_V>σ_h when depth is between 250 m and 500 m, and σ_V>σ_H>σ_h when depth is above 500 m. The ratio between the maximum horizontal principal stresses and vertical principal stresses mostly concentrates in the interval of 0.5 to 2.0, and decreases and converges to 1 with the depth increasing; The ratio between the maximum horizontal principal stresses and minimum horizontal principal stresses is mainly in the interval of 1.5 to 2.0; The ratio between the mean horizontal principal stresses and vertical principal stresses mainly varies from 0.5 to 1.5 with most in the interval of 0.5 to 1.0. The orientations of the maximum horizontal principal stresses in Shanxi coal mining fields change considerably from north to south. The orientations are NE in northern part, deflect to NNW southwards, vary to NW in western and eastern parts, and changeable in southeast part. Comparing the results from underground in-situ measurements with the focal mechanism solutions, they show good agreement in some coal mining fields, but obvious divergence exists in other areas. Especially in the areas affected by local large geological structures, the orientations of the horizontal principal stresses frequently reverse and change obviously.