Comprehensive Observation Experiment Of Unloading Relaxation And Stability Study At The Columnar Joints Basalt Tunnel

As global warming intensifies and China’s energy structure adjustment, hydroelectric energy,as a low-carbon, renewable and clean energy, gets more and more attention and favor by the society. So a large number of long tunnel, large cavern, high slope and other important geotechnical engineering are build, the unloading destruction of geotechnical engineering will inevitably result in the relaxation of the surrounding rock, and thus have an impact on the overall stability of the project. As a special geological body, columnar jointed basalt has its own unique mechanical properties, so engineering in columnar jointed basalt should pay attention to the stability problem. In order to ensure the safety of the works, and provide a reference for the next step of construction, in the construction process of columnar jointed basalt area the integrated observing trials and stability analysis is necessary.Relying on Baihetan hydropower station diversion tunnel, on the analysis of the basis of geological materials and on-site survey, we select the test area and summarize unloading and relaxation variation of columnar jointed basalt tunnel by a long period of continuous monitoring, then we can further studied the stability of the tunnel by numerical methods, the main research work:(1) The unloading relaxation mechanism and determination method are analyzed by collecting the excavation unloading rock mass relaxation and the mechanical properties of columnar joints basalt related information, then we have a preliminary understanding and cognition of The mechanical properties of basalt columnar joints.(2) Collecting engineering geological data and surveying at local, we determine the monitoring area and the layout of the monitoring plan, then continue to monitor.(3) The paper summarizes basalt columnar joints relaxation change rule after tunnel excavation unloading by analyzing the field test data.(4) Establishing the Basalt columnar joints tunnel model, the displacement of surrounding rock and the stress distribution after excavation release are obtained by numerical calculation. Establishing the Basalt columnar joints tunnel model, the displacement of surrounding rock and the stress distribution after excavation release are obtained by numerical calculation.(5) The study verifies the credibility of numerical simulation method by comparing the field test data and numerical results. On this basis, the unloading relaxation rule of columnar joints basalt tunnel was concluded to analyze the stability of it. At last, several reasonable suggestions were given to improve the stability of the tunnel.