掌子面推进过程围岩应力及裂隙发育规律

Tunnel face advancing on development of stress and microfracture around excavation

利用数值分析软件,借鉴Griffith裂隙优势发育角度理论,对锦屏二级水电站施工排水洞SK11+000桩号段掌子面推进围岩应力量值、方向及裂隙优势发育规律动态变化过程进行研究。研究结果表明:开挖至监测面一倍洞径(D)距离时,最大主应力及主应力差值开始增加;穿过监测面时,中主应力及最小主应力突然降低,表现明显卸荷特征;穿过监测面后,洞壁不同部位围岩最大主应力分别表现增加与减小不同变化,2倍洞径距离(2D)后主应力量值基本趋于弹性力学解析解。掌子面推进过程中侧壁最大主应力倾角变化不大,一般保持90°左右,仅在0.25D范围内发生较小变化,到达监测面附近时倾向发生较大变化,穿过监测面后则逐渐发展至水平垂直洞轴方向;洞顶最大主应力倾向与倾角主要在掌子面接近监测面0.25D距离时开始变化,穿过监测面0.25D距离后,则基本保持竖直垂直洞轴方向。微裂隙优势发育角β随主应力大小变化而变化,侧壁围岩β一般减小,洞顶不同部位岩体β存在减小及增大不同变化;研究结果可为工程区围岩裂隙化问题的研究及支护工程设计提供参考。

Based on the theory of the angle（β） more favorable to break in the Griffith fracture theory and elastic geology material hypothesis, using numerical simulation technology, the variation of the magnitude and orientation of surrounding rock stress, the change of the angle β were researched of drainage tunnel in Jinping Ⅱ hydropower station SK11＋000 segment. The results show that during the progressive advancement of the tunnel faee（TF）, with the distance of the TF to the monitoring face（MF） less than one tunnel diameter D, the maximum principal stress σ1 and differential stresses increase simultaneously; the magnitude of the medium and minimum principal stress is reduced suddenly and immediately while TF passes through MF; after passing through, the σ1 of different position displays different change. The magnitude of principal stress tends to the analytical solution of the elastic mechanic with distance of TF to MF greater than 2D. The dip of the σ1 in the tunnel sidewall rockmass is always 90° in TF advancing progress, with only minor changes within 0.25D distance range. The trend of the σ1 change obviously when the TF is near the MF, and horizontally perpendicular to the hole-axis gradually. The dip and trend of the σ1 in the tunnel roof rock mass often changes within 0.25D distance range by TF to MF, and σ1 perpendicular to the hole-axis basically with the distance of theTF and MF greater than 0.25D after TF passes through the MF. The fl changes with principal stress variety, which decreases generally in the sidewall and decrease/increase of different position in the tunnel roof. The investigation can provide an effective way for the study of the fracture of the tunnel wall and support design optimization.