Effects of Thermal Stress of Rock Masses Generated by Geothermal Gradient on Rockburst Prediction
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摘要:
为使在高地温环境下通过水压致裂获得的应力更加真实地预测岩爆，提出在岩爆预测过程中应考虑地温梯度孕育的岩体热应力. 结合弹性理论获得了在高地温环境下水压致裂的理论应力解；基于此理论应力解对圆形隧道进行了岩爆预测；应用岩体热应力公式对桑珠岭隧址区的岩爆进行了预测. 研究结果表明：在高地温环境下，恒定压力和水平主应力会增加约一倍的岩体热应力，裂隙重开压力会增加约两倍的岩体热应力，垂直应力不变；如果在高地温环境下直接采用水压致裂测得的应力进行岩爆预测，当水平原位地应力大于竖向原位地应力时，得到的岩爆等级偏高，当水平原位地应力在重力应力和竖向原位地应力之间时，得到的岩爆预测位置与实际不一致，当水平原位地应力小于重力应力时，得到的岩爆等级偏低；桑珠岭隧址区的岩体热应力约为重力应力的61%，若不考虑此热应力进行岩爆预测会导致严重的错误.
Abstract:To make the stress obtained by hydraulic fracturing in a high geo-temperature environment more truly predict rockbursts, it is proposed that the thermal stress of rock masses generated by geothermal gradients should be considered during the rockburst prediction. Combined with the theory of elasticity, the theoretical stress solution of hydraulic fracturing in a high geo-temperature environment was obtained firstly. Then the rockburst prediction of a circular tunnel was conducted based on this theoretical stress solution. Finally, according to the thermal stress formula of rock masses, the rockburst prediction for the Sangzhuling tunnel was applied. The results show that the instantaneous shut-in pressure and the horizontal principal stress are increased by about one time the thermal stress of rock masses, and the reopening pressure is increased by about two times the thermal stress of rock masses. In addition, vertical stresses do not change. If the stress measured by hydraulic fracturing in a high geo-temperature environment is directly used for rockburst prediction, the estimated grade of rockbursts is high when horizontal in-situses are greater than vertical in-situ stresses, and the predicted position of rockbursts is inconsistent with reality when horizontal in-situ stresses are between gravitational stresses and vertical in-situ stresses. In addition, the estimated grade of rockbursts is low when horizontal in-situ stresses are less than gravitational stresses. The thermal stress of rock masses for the Sangzhuling tunnel is about 61% of the gravitational stress of rock masses. The rockburst prediction can lead to serious errors if the thermal stress is not considered.
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Key words:
- high geo-temperature /
- rock burst /
- thermal stress /
- geothermal gradient /
- hydraulic fracturing
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图 1 水压致裂应力测量的力学模型
Figure 1. Mechanical model of hydraulic fracturing stress measurement
图 2 垂直应力不考虑岩体热应力的圆形隧道计算模型
Figure 2. Calculated model of a circular tunnel that vertical stresses do not add the thermal stress of rock masses
表 1 计算参数
Table 1. Calculation parameters
参数 数值 单位 弹性模量 36 GPa 泊松比 v 0.2 重度$\gamma $ 26 kN·m−3 黏聚力 15 MPa 内摩擦角 50 （°） 热膨胀系数$\beta $ 8 × 10−6 ℃−1 导热系数 3.69 W·（m·K）−1 比热容 630 J·（kg·℃）−1 
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