The characteristics of measured in-situ stress field in a tunnel site in Central Tianshan Mountains and its significance to regional crustal stability
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摘要: 新疆中天山地质及构造条件复杂，某隧址埋深最大接近
1336 m，探明隧址区地应力场特征和断层摩擦系数对隧址区稳定性评价具有重要工程及理论价值。本文基于隧址区内9个钻孔获得的37条实测地应力数据，通过统计及拟合数据，引入断层摩擦系数μ、地壳应力积累指标μm，并结合区域地震分布和震源机制等分析。研究表明，中天山隧址区最大水平主应力优势方向为N37°E，与区域构造应力场NNE方向相符；浅部地壳以水平构造应力为主，最大、最小水平主应力随深度线性增长梯度分别为0.024和0.017，应力状态以逆冲型为主，局部兼有走滑型。隧址区内断层摩擦系数μ分析揭示，其主要分布范围为0.15～0.3，表明大部分断层处于低强度状态，而F6断裂μ值达到0.39明显高于其他断层，同时区内地壳应力积累指标μm近80%应力积累不高，未达到临界滑动值0.5，但F6断裂处应力积累程度均高于0.5，说明F6断裂相较其它断层的应力积累更大，更具有活动性。结合NWW向断层附近地震频发及近年小震震源机制解特征，表明隧址区断层更易沿北西西向形成滑动。Abstract: The geological and tectonic conditions in the central Tianshan Mountains of Xinjiang are complex. A tunnel site in this region has a large burial depth, reaching a maximum of nearly 1,336 meters. Investigating the characteristics of the in-situ stress field and fault friction coefficient in the tunnel site area is of significant engineering and theoretical value for evaluating the stability of the tunnel site. Based on 37 measured in-situ stress data obtained from nine boreholes within the tunnel site area, this paper conducts statistical and fitting analyses, introduces fault friction coefficient μ and crustal stress accumulation index μm, and combines these with the analysis of regional seismic distribution and focal mechanism. The research shows that the dominant direction of the maximum horizontal principal stress in the tunnel site area of the central Tianshan Mountains is N37°E, which is consistent with the NNE direction of the regional tectonic stress field. Horizontal tectonic stress dominates in the shallow crust, with the maximum and minimum horizontal principal stresses increasing linearly with depth at gradients of 0.024 and 0.017, respectively. The stress state is primarily thrust-type, with some local strike-slip-type characteristics. The analysis of the fault friction coefficient μ in the tunnel site area reveals that its main distribution range is 0.15 to 0.3, indicating that most faults are in a low-intensity state. However, the μ value of the F6 fault reaches 0.39, which is significantly higher than other faults. Meanwhile, nearly 80% of the crustal stress accumulation index μm in the region is not high, failing to reach the critical sliding value of 0.5. However, the stress accumulation degree at the F6 fault is higher than 0.5, indicating that the F6 fault has greater stress accumulation and is more active compared to other faults. Combined with the frequent occurrence of earthquakes near the NWW-oriented faults and the focal mechanism solutions, it is indicated that the faults in the tunnel site area are more prone to sliding along the NWW direction. -
图 1 区域M≥2.0地震震中分布及区域构造图
Figure 1. The epicenter distribution and regional tectonic map of M≥2.0 earthquakes in the region
图 2 最大、最小水平主应力随深度变化
Figure 2. The maximum and minimum horizontal principal stresses vary with depth.
图 3 最大水平主应力方向及断裂走向
Figure 3. Direction of maximum horizontal principal stress and fracture trend
图 4 侧压力系数k随深度变化拟合曲线
Figure 4. Fitting curve of the lateral pressure coefficient k versus depth
图 5 有效应力莫尔圆与断层摩擦系数分析
Figure 5. Analysis of the effective stress Mohr circle and fault friction coefficient
图 6 μm随深度变化及主应力间的关系
Figure 6. μm with depth and the relationship between principal stresses
图 7 隧址区附近历史地震震源机制解分布
Figure 7. Distribution of focal mechanism solutions of historical earthquakes near the tunnel site
表 1 隧址区内其余断层性质
Table 1. Properties of other faults in tunnel site area
断裂编号 产状 断裂性质 走向/(°) 倾向/(°) 倾角/(°) Fw-1 117 207 76 逆断层 Fw-2 108 18 40～80 右行平移断层 Fw-3 128 38 73 - Fw-4 81 351 60～80 - Fw-5 94 4 61 逆断层 Fw-6 114 204 86 逆断层 Fw-7 121 211 68 逆断层 Fw-8 42 312 86 正断层 Fw-9 105 - - - Fw-10 113 23 78 正断层 Fw-11 113 205 80 - Fw-12 115 203 80 - Fw-13 90 190 81 逆断层 Fw-14 100 190 83 逆断层 
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表 2 隧址区实测地应力数据
Table 2. In-situ stress data measured in tunnel site area
编号 测号段 深度/m 钻孔岩性 应力值/MPa 地应力累计指数μm 线性相关系数R σH σh σv ZK1 1 195.1 花岗闪长岩 16.8 9.3 4.9 0.63 0.63 2 278.3 花岗闪长岩 22.6 13.2 7.0 0.62 0.60 3 306.1 炭质板岩 23.3 14.7 7.7 0.60 0.55 4 333.7 炭质板岩 22.2 13.5 8.3 0.56 0.63 5 361.5 炭质板岩 25.7 15.4 9.0 0.58 0.62 6 383.1 炭质板岩 25.0 16.8 9.6 0.55 0.53 ZK2 1 119.8 片麻状花岗闪长岩 12.1 7.4 3.2 0.65 0.53 2 210.8 片麻状花岗闪长岩 15.1 9.8 5.7 0.54 0.56 3 301.8 片麻状花岗闪长岩 18.2 11.2 8.1 0.48 0.69 4 365.5 片麻状花岗闪长岩 20.3 12.5 9.9 0.44 0.75 5 447.4 片麻状花岗闪长岩 22.2 14.4 12.1 0.39 0.77 6 492.9 片麻状花岗闪长岩 21.8 15.5 13.3 0.33 0.74 7 547.5 片麻状花岗闪长岩 26.3 17.2 14.8 0.37 0.79 8 583.9 片麻状花岗闪长岩 28.1 18.5 15.8 0.37 0.78
ZK31 111.0 大理岩 7.1 5.2 3.0 0.46 0.46 2 156.5 大理岩 8.0 5.3 4.2 0.38 0.71 3 192.9 大理岩 9.5 6.5 5.2 0.36 0.70 4 220.2 大理岩 11.8 8.3 5.9 0.41 0.59 5 256.6 大理岩 14.5 9.9 6.9 0.44 0.61 6 302.1 大理岩 17.3 11.2 8.2 0.44 0.67 7 347.6 大理岩 18.5 11.1 9.4 0.42 0.81 8 429.5 大理岩 20.7 12.8 11.6 0.37 0.87 9 456.8 大理岩 21.4 14.3 12.3 0.36 0.78 10 484.1 大理岩 22.1 14.8 13.1 0.34 0.81 11 511.4 大理岩 23.0 14.3 13.8 0.33 0.95 ZK4 1 243.5 花岗闪长岩 9.9 6.8 5.9 0.35 0.77 2 511.2 石英片岩 16.3 11.4 12.3 0.26 0.83 ZK5 1 229.5 石英片岩 9.8 6.2 5.5 0.37 0.84 2 585.8 片麻岩 16.9 12.9 14.1 0.21 0.72 ZK6 1 350.0 花岗岩 11.5 8.7 8.6 0.21 0.98 2 776.0 花岗闪长岩 21.8 15.7 19.0 0.27 0.46 ZK7 1 231.8 片麻状闪长岩 8.4 5.7 5.6 0.27 0.94 2 761.8 片麻状闪长岩 20.2 12.7 18.3 0.41 0.26 ZK8 1 208.5 砂质板岩 9.5 6.1 5.0 0.41 0.75 2 352.8 大理岩 12.3 8.5 8.5 0.26 0.98 ZK9 1 235.4 砂质板岩 10.8 7.5 5.7 0.41 0.65 2 371.9 大理岩 13.6 9.6 8.9 0.28 0.87
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表 3 ZK9钻孔k值的拟合值与实测值误差分析
Table 3. ZK9 borehole k value fitting value and the measured value error analysis
深度/m 拟合kH max，kh min 实测kH max，kh min 误差/% 235.4 1.94 1.91 1 1.29 1.32 2 371.9 1.83 1.54 18 1.18 1.07 10
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表 4 400 m深度处钻孔的k、μ值
Table 4. k and μ values of boreholes at the depth of 400 m
钻孔 kH max kh min σ'/MPa τ μ ZK1 2.69 1.72 18.34 7.11 0.39 ZK2 1.95 1.26 14.65 4.50 0.31 ZK3 1.82 1.17 13.50 3.87 0.29 ZK4 1.75 0.95 9.05 1.82 0.20 ZK5 1.83 1.19 8.70 1.59 0.18 ZK6 1.84 1.20 8.28 1.34 0.16 ZK7 1.79 1.18 7.74 1.18 0.15 ZK8 1.76 1.22 8.64 1.55 0.18 ZK9 1.78 1.16 9.23 1.89 0.21
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