Aiming at the phenomenon of partial cracking and deformation of surrounding rock mass developing continuously at arch crown in the underground powerhouse,based on geology,monitoring data and construction process,qualitative analysis and quantitative analysis are made respectively combining with information of macroscopic deformation character and results of safety monitoring. The phenomena of collapse and crack occurred during the excavation of underground caverns is mainly formed by small unstable blocks because of stress distribution and blasting effect. Among the causes of its formation,the structure surface of fault and rock cracks is the main geological factor,and supporting lag is the main factor of construction. So considering the discontinuous characteristics of rock masses,it is important to take timely and effective support measures to ensure that surrounding rock mass of arch crown is in situation of stability. Parallel construction can speed up the construction progress in a certain extent,but it could have an effect on the displacement of surrounding rock. In the situation of parallel construction,although construction work has been far from arch crown,due to high construction intensity and frequent blasting,the displacement development of surrounding rock mass is still controlled obviously by construction schedule. So under the condition of complex geology,it is very necessary to avoid the parallel construction during construction process.%针对水电站地下厂房开挖过程中顶拱出现局部坍塌和变形持续发展的现象，结合地质资料、监测成果和施工过程，对变形产生的原因从表面宏观变形表现和深部位移特征2个角度作定性和定量的分析。分析结果表明，在地下洞室开挖过程中产生的坍塌和垮塌现象，主要是受开挖后应力重分布，以及爆破作业的影响，形成的小型不稳定块体，断层及裂隙结构面的存在是主要地质因素，支护滞后是造成局部坍塌的主要施工因素。因此，考虑岩体的非连续性，施工期采取有力的支护措施对确保顶拱围岩稳定十分重要。平行施工在一定程度上可以加快施工进度，但对围岩位移会造成一定影响。对于顶拱围岩而言虽然施工作业面已远离，但由于施工强度大、爆破频繁，对顶拱部位围岩位移发展仍具有一定的控制作用，因此在复杂地质条件下施工过程中应尽量避免平行施工。
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