Study On The Reasonable Overburden Depth For Subaqueous Rock Tunnel

The reasonable overburden depth plays an important role in the construction of subaqueous rock tunnel. It must take safety factors and economy factors into consideration during its construction and usage period. How to determine reasonable overburden depth is still an intractable research subject. The thesis studied these problems mentioned above based on ChangJiang tunnel of DongGanZui in LuZhou.①On the basis of data collection of subaqueous rock tunnel at home and aboard, the key factors of the reasonable overburden depth of subaqueous rock tunnel as well as empirical research methods are generalized as follows: Norwegian empirical methods of subaqueous rock tunnel construction, Japanese empirical methods of minimum discharge, domestic empirical formula for underwater coal mining. Take the water depth, geological conditions and construction methods of ChangJiang tunnel into account by importing the three methods mentioned above, the range of the reasonable overburden depth is determined as 29.5 to 38 meters.②FLAC3D is applied to the permeation analysis of ChangJiang tunnel under eight different rock overburden depths. The results show that it presents parabolie relation of minimum discharge versus overburden depths under the conditions of fixed coefficient of permeability and water depth, accompanied by increase of overburden depths, discharge decreases to a minimum numerical value then increases. Discharge is a minimum when overburden depths is determined as 30 meters. On the premise of fixed water depth., overburden depth corresponding minimum leakage is only and can be regarded as reaseable overburden depth.By taking above empirical research methods into account, the reasonable overburden depth of ChangJiang tunnel is ascertained as 30 to 38 meters.③FLAC3D is applied to the the elastic-plastic simulating analysis of ChangJiang tunnel under eight different rock overburden depths. By takeing into consideration of stress effect range, all overburden depths of ChangJiang tunnel meet the requirements. By taking displacement convergence of surrounding rock into account, it is reasonable that overburden depth of ChangJiang tunnel is ascertained as 30 meters.④On the basis of the 30 meters overburden depth which is ascertained by research methods, empirical leakage analysis and elastic-plastic simulation, this paper is further researched through hydromechanical coupling analysis. It indicates that the affection of seepage flow on displacement and stress of rock in the tunnel is local. the overburden depth of 30 meters will ensure the safety of tunnel construction.⑤During of the permeation and stress analysis, furthermore, blasting is simulated by lowering strength and increasing coefficient of permeability. There is constract between considering blast and not, results show that blasting enlarges displacement, stress of rock and seepage discharge, but the value increase little . Finally the reasonable overburden depth of ChangJiang tunnel is determined as30 meters.