地下厂房岩锚梁纵向裂缝成因分析及发展趋势

 地下厂房第六层开挖结束后，岩锚梁混凝土上表面出现纵向裂缝，测缝计监测结果显示岩锚梁裂缝部位两处的下部开合度数据大于上部值，不符合一般规律。结合现场地质条件、监测数据、施工因素和数值计算，对岩锚梁纵向裂缝的成因进行详细的分析。研究结果表明，岩锚梁距离母线洞洞顶距离只有5.2 m，3条夹层斜穿岩锚梁部位围岩和母线洞，施工开挖造成围岩应力调整，局部应力集中现象明显，导致岩锚梁部位岩体产生不均匀变形。数值计算结果表明，夹层JC2–2及下部小夹层形成的锥形块体随地下厂房的开挖有向外“挤出”的趋势，当变形体位于岩锚梁下部时，即形成下部的开合度值大于上部的开合度值这样一种看似不合理的现象，且CZ0+87断面开度值大于CZ0+127断面的，计算结论与监测结果吻合良好。最后，预测不同部位的岩锚梁现有裂缝发展趋势及可能出现裂缝的部位，并给出几点支护处理措施的建议。

CAUSE ANALYSIS OF LONGITUDINAL CRACKS OF ROCK-ANCHORED BEAM AND ITS DEVELOPMENTAL TREND IN UNDERGROUND POWERHOUSES

After the completion of excavation of the 6th layer of the underground powerhouse，the longitudinal cracks appeared in the concrete upper surface of the rock-anchored beam. Monitoring data indicate that the width of the cracks in lower part between the concrete and the rock mass is larger than the upper one，which is an unusual phenomenon. Detailed cause analysis of these cracks was made based on the in-situ geological environment，monitoring data，constructional procedure and the numerical simulation. The analysis results indicate that the distance between the top of the bus gallery and the rock-anchored beam is only 5.2 m，and rock mass is cut by 3 weak interlayers. Due to the construction of the main machine hall，the ground stress was readjusted，and the obviously concentrated stress phenomenon appeared at the rock mass，which resulted in the non-uniform deformation of the rock mass. Numerical calculating results indicate that as the excavation goes on，the rock mass between the interlayer JC2–2 and the lower one has the trend to be squeezed out of the palisades，while this deformable body lies in the lower part of the rock-anchored beam，the widths of the cracks in lower part are larger than ones in the upper part，which explains the unusual phenomenon of the monitoring results. Simulation results also indicate that this value in cross section CZ0+87 is larger than that in cross section CZ0+127，which agrees well with the monitoring data. Finally，forecasting is made on the displacement development trend of cracks in the rock- anchored beam；and several advices are given.