基于HI应变计的首次断裂带岩体地应力监测

采用空心包体(HI)应变计进行了首次断裂带岩体应力监测试验。在深埋隧洞施工开挖期,选择合适部位进行了大直径钻孔,利用对中装置、采用水泥净浆灌浆方式将HI应变计埋设在钻孔孔深24 m部位,建立了基于惠斯通电桥半桥测量的云监测系统。确定了只采用水泥净浆和HI材料弹性参数进行修正系数计算,通过分析监测数据规律确定应变计算初始时间后进行了三维应力增量计算。结果显示:以2021年9月16日为初始计算日期、在时段4和时段5期间的应力增量计算结果的第一主应力(σ₁)的范围为10.3~15.0 MPa,方向为缓倾角W向;第二主应力(σ₂)的范围为3.1~4.6 MPa,方向为陡倾角NEE至SEE向;第三主应力(σ₃)的变动范围为0.2~1.8 MPa,方向为缓倾角近S向;最大水平主应力(σ_H)和最小水平主应力(σ_h)分量的变动范围分别为10.1~13.9 MPa和0.2~1.8 MPa,最大水平主应力方向(α_H)为近EW向。结果讨论显示:通过监测数据规律分析确定的计算初始时间更具合理性;HI应变计应力监测受多因素影响,包括开挖应力扰动影响和一次监测洞段的应力和变形调整影响;本试验所得最大水平主应力量级及其方向与已有地应力试验结果接近,监测结果反映龙蟠-乔后断裂带的应力场特征。

Monitoring the Geostress of Rock Mass in Fault Zone Using Hollow-Inclusion Strain Gauge

The hollow-inclusion(HI) strain gauge is used for the first time to monitor the geostress of rock mass in fault zone. A cloud monitoring system based on half-bridge measurement circuit of Wheatstone bridge was established with the hollow-inclusion strain gauge buried at the depth of 24 m in the large-diameter borehole drilled at appropriate position by using centering device and cement paste grouting method during tunnel excavation. Only the elastic parameters of cement paste and hollow inclusion material were considered to calculate the correction coefficient. The three-dimensional stress increment was calculated after the initial time of strain calculation was determined by analyzing the law of monitoring data. Results showed that, with September 16, 2021 as the initial calculation date, the range of the first principal stress (σ₁) in the fourth and fifth period was 10.3~15.0 MPa with a gentle dip W direction; the second principal stress (σ₂) ranged between 3.1 MPa and 4.6 MPa, with a steep dip angle from NEE direction to SEE direction; the third principal stress (σ₃) varied between 0.2 MPa and 1.8 MPa, and the direction is gentle dip angle near S direction. The components of maximum horizontal principal stress (σ_H) and minimum horizontal principal stress (σ_h) varied from 10.1 MPa to 13.9 MPa, and 0.2 MPa to 1.8 MPa, respectively. The direction of maximum horizontal principal stress (α_H) was nearly EW. The results demonstrate that the initial calculation time determined by analyzing monitoring data is more rational. The stress monitoring of hollow inclusion strain gauge is affected by multiple factors including excavation-caused stress disturbance and one-time stress and deformation adjustment of the monitored segment. The obtained σ_H and α_H are close to in-situ stress test results, and the monitoring result reflects the stress field characteristics of the Longpan-Qiaohou fault zone.