Research On The Treatment Scheme And Information Construction Of Large Karst Cavern Under The Foundation Of Wudu Reservoir Dam

There are large karst caves under the foundation of Wudu reservoir dam. In particular, the K111 karst cave that is beneath the dam foundation has shallow depth and large volume, this causes great theat to the safety of the RCC dam. In the cave treatment, the weak structural plane, high sidewall and blasting are extremely unfavorable to the stability of surrounding rock. The author established the three-dimensional numerical model of the karst cave and dam foundation, has studied the influence to the foundation of dam on some karst cave treatments and the influence to the stability of surrounding rock on the excavation methods and the reinforcement patterns. In the cave treatment, author has carried on the safe monitor and has studied the information construction of the karst cave. The findings can be obtained as follows:(1) The numerical simulation analysis founds that the large cave at the bottom of the foundation worsens the stress condition. The foundation of the dam on the karst cave will have a stress concentration when the dam complets and is in operational phase, and will have a great tensile stress region in the surrounding rock of the karst cave. This cause great theat to the safety of the dam and foundation and the anti-seepage curtain. Therefore, it is necessary to treat the cave in the stress influence area.(2) In the cave treatment, the backfills of different intensity concretes affect the stress and displacement of the dam and foundation. The research indicats that the C15 concretes are more reasonable. The treatment scope is at least to 16m from the dam axis.(3) In the cave treatment, it is suitable to chose the treatment scheme of less affection of surrounding rock. Excavating section by section and backfill effectively reduces the disturbance to the surrounding rock, and significantly reduces the plastic zone in the surrounding rock. It is necessary to reinforce surrounding rock in bolt, the system bolt of the spacing of 2 m, a length of not less than 7 m can effectively reduce stress and the development of plastic zone, can basically eliminate the layer face effects of high sidewall, can ensure the stability of surrounding rock.(4) In the design of safety monitoring of karst cave treatment, it is important to set reasonable monitoring equipment on the basis of geology and numerical simulation, and timely grasp and feedback the the overall stability of surrounding rock to provide safety and security for construction unit.(5) On the base of the analysis of monitoring data and numerical simulation achievement, it is realise that the deposit in the cave has a small force to surrounding rock, the surrounding rock displacement has basically released. So, when the safety warning indicators are determined in the surrounding rock stability evaluation, it should focus on the rate of displacement and supporting force.(6) It is important of the partial stability problem in the karst cave treatment. Because the deposit in the cave has covered the joint of surrounding rock, this increases the judgment difficulty and the risk of excavation. The efficient way to guarantee excavation security is that correct analysis of geological data, strengthen geological inspections and timely support.