Studies on Loosened zone of surrounding rock underground powerhouse cavities for Jinping I Hydropower Station in construction

This paper introduces the test results of loosened zone of surrounding rock underground powerhouse cavities for Jinping I Hydropower Station in construction and the results are analyzed and studied. Loosened zone of surrounding rock scale and distribution are influenced by geological conditions and excavation, Loosened zone of surrounding rock in upstream and downstream sidewall obvious asymmetry. Downstream side upper and upstream side mid-lower of main powerhouse is bigger; upstream side-wall bottom and downstream side-wall mid-upper of main transformer chamber is large. Loosened zone of surrounding rock and wave velocity change has obvious time- related feature, loosened zone development and rock wave decrease is faster excavation early; after excavation, it is stopped gradually, but, finish this process needs six months. Wave velocity decrease degree of surrounding rock rapid decline reduced with depth increase, superficial wave velocity of surrounding rock attenuation is obvious. Loosened zone of surrounding rock and wave velocity change are influenced by extra geostress, low rock mass strength, lithology, structure surface, geological conditions and construction excavation unloading.