A systematic engineering geological evaluation of diabase dikes exposed at the underground caverns of Dagangshan hydropower station, Southwest China

摘要

Dagangshan hydropower station is located in the middle of Dadu River, Southwest China. Many diabase dikes were exposed in the adamellite granite body during excavation of the underground caverns. The dikes are highly directional, have crushed interiors, exhibit strong alteration, and have poor contact relationships with surrounding rocks, all of which is inconsistent with the characteristics of typical diabase. This paper describes systematic research that focused on the dikes' spatial distribution, macroscopic characteristics, physical and mechanical properties, and common instability modes. Factors influencing their stability and their corresponding control measurements are discussed in the context of the site and its conditions. Results show that most of the dikes located in the underground caverns are the branches of the main dike beta 9, which produced from a strong basic magma extrusion-overflow event happened in between the Permian and Triassic. Due to multiple strong tectonic activities, the chlorite alignment of these dikes generally tended to be significant and leaded the physical and mechanical properties to be poor. Then, excavation and repetitive blasts resulted in strong disturbances to the original dikes and even caused rock unloading (collapse, rock block fall) and groundwater runoff system (water inflow) change. According to the common instability modes and reasons of diabase dikes, some specific control measures including solidified rubbles, reinforcement methods, pre-grouting, and small ducts are implemented in order to keep the surrounding of diabase safety, and the results show that the control methods perform a proper effect on these engineering problems.