复杂节理岩体对榆佳高速公路某隧道的初喷支护作用机理研究

Study on Support Mechanism of Initial Spray in a Tunnel of Yujia Highway Affected by Rock Mass with Complicated Joint

节理的产状和隧道轴线夹角的不同会极大地影响隧道的稳定性。以榆佳高速公路某隧道为研究对象,利用UDEC离散元软件,建立了0°、85°、120°和150°单层层状节理模型,以及由3组层状节理切割的复杂模型;设计了0.2、0.4、0.6、0.8、1.0MPa初喷混凝土接触面黏聚力计算工况,5、8、10cm初喷厚度计算工况。经计算,对比不同工况的塑性区、应力和监测点位移值,发现:单层节理条件下,节理倾角β对隧道稳定影响不大,0°时塑性区最大,最大位移5.6cm,围岩没有掉块,围岩自稳,无需支护;其余倾角隧道均能自稳,位移不大于1cm。黏聚力大于0.6 MPa为临界值,大于其隧道围岩自稳,洞顶位移值小于1cm,否则会出现掉块。初喷厚度8cm为临界值,大于其隧道围岩自稳,洞顶位移值小于1cm,否则会出现掉块。上述特征值均在单因素变化、其余参数参照基准值条件下获取,这些可以作为隧道设计的极限参考值。

Intersection angle between joint occurrence and tunnel axis will greatly affect stability of tunnel. A tunnel in Yujia Highway is selected as objective in the paper. One layer models with 0°, 85°, 120°and 150°joint occurrence, model with three groups of complicated joint are set up using UDEC. Com- puting schemes with 0.2, 0. 4, 0. 6, 0. 8 and 1.0 MPa contact surface cohesion of initial spray concrete and schemes with 5, 8 and 10 cm thickness of initial spray concrete are designed. Plastic zone, stress and dis- placement at different monitoring points under different computing conditions are compared with each oth- er. Found that dip angle of joint is not sensitive to tunnel stability under one layer joint condition. When the angle being 0°, its plastic zone is the largest with the, maximum displacement being 5.6 cm, without rock falling, surrounding rock being stable, which does not need support. Tunnel under other dip angles of joint all can self-stabilize, with displacement less than 1 cm. If cohesion larger than 0.6 MPa, the tunnel can self-stabilize, whose displacement less than 1 cm, otherwise rock falling will happen. If concrete thick- ness of initial spray larger than 8 cm, the tunnel can self-stabilize, whose displacement less than lcm, otherwise rock falling will happen. All these limit value obtained under no change of other factors can be used as reference value of tunnel design.