This article is based on the measured date of the underground power house of the three Gorges and doing research for the deformation of main power house side wall-excavation. Finally come to the conclusion that the wall deformation area is mainly below rock anchorage beams. Also this article has done research about how does the excavation height、different blasting excavation type (the bench blasting, the backing wayside blasting, pref splitting blasting) influence the deformation of surrounding rock and has summarized some useful conclusions, which has offered reference for related underground power house-building project.
The Three Gorges underground main power house is with long-span excavation、high side wall、thin arch covering and its periphery is affected by the excavation of channel water hole、bus tunnel、access tunnel、tail race tunnel. It is a very major problem to ensure high crown and the sidewall rock stability during the project construction. Currently, there are many large underground powerhouses being in the construction, such as the Three Gorges Project, Xiluodu, Xi anglia Dam. The geological conditions are ever-changing during the construction process. It is a problem to know how to ensure underground construction's safety、efficiency、fast in underground large group cavern's construction.
Three Gorges Right Bank Underground Power Station is a large underground group caverns which is composed by the main plant, diversion tunnel, tail race tunnel, being located in micro-new rock. The rock is hard and with good integrity. The general thickness of the coated mountain on the main plant is 34m~98m. From the surface of the earth to the cavern, the white pointed rock layer are completed rock mass weathering, strong rock mass weathering, weak rock mass weathering and micro-new rock respectively. The rock layer thickness of completed rock mass weathering is larger comparatively. The surrounding rocks of the caverns mostly are in weak rock mass weathering and micro-new rocks. The original horizontal stress of powerhouse is 7~12Map; The intersection angle between the land stress direction and the vertical line of the main plant is 78.5°. The main plant is a large underground cavern, of which the embedded depth is not deep and some of the surrounding rocks are thin. In the process of construction, the blasting must be strictly controlled in order to prevent the damage of surrounding rocks.
The cavern in main plant is arched straight wall with max height of 87.3m and side wall height of 49~79.5m. The span over the rock anchor crane beam is 32.6m and below it is 31m. The segment size of single generators is 31m×38.3m.
According to underground geological conditions, structure and construction features and the existing security technical problems, selecting the 27 # and 30 # generator as an important monitoring section, fully disposing and setting monitoring facilities on all sections with a total of 9 sets of monitoring section.