Multi-approach analysis of maximum riverbed scour depth above subway tunnel

When subway tunnels are routed underneath rivers, riverbed scour may expose the structure, with potentially severe consequences. Thus, it is important to identify the maximum scour depth to ensure that the designed buried depth is adequate. There are a range of methods that may be applied to this problem, including the fluvial process analysis method, geological structure analysis method, scour formula method, scour model experiment method, and numerical simulation method. However, the application ranges and forecasting precision of these methods vary considerably. In order to quantitatively analyze the characteristics of the different methods, a subway tunnel passing underneath a river was selected, and the aforementioned five methods were used to forecast the maximum scour depth. The fluvial process analysis method was used to characterize the river regime and evolution trend, which were the baseline for examination of the scour depth of the riverbed. The results obtained from the scour model experiment and the numerical simulation methods are reliable; these two methods are suitable for application to tunnel projects passing underneath rivers. The scour formula method was less accurate than the scour model experiment method; it is suitable for application to lower risk projects such as pipelines. The results of the geological structure analysis had low precision; the method is suitable for use as a secondary method to assist other research methods. To forecast the maximum scour depth of the riverbed above the subway tunnel, a combination of methods is suggested, and the appropriate analysis method should be chosen with respect to the local conditions.

Simulation Experimental Study on Hydrodynamics Process of Erosion and Sediment by Runoff in Grassland

[Objective]The aim was to study the simulation test of hydrodynamics process of erosion.[Method]Through the runoff scouring experiment,the property of soil erosion in Damaoqi grassland in Inner Mongolia was studied.The process and mechanism of soil erosion were studied.[Result]The results of runoff scouring experiment on inner Damaoqi steppe showed that the mean flow velocity of change slope increased with the discharge of flow and slope gradient.The mean silt content rate,the mean sediment transport rate and the mean sheer stress all increased when the discharge of flow increased,which changed in parabolic form with the increase of slope gradient and the critical gradient is 25°.The relationship between the mean sediment transport rate and the mean sheer stress was linear.[Conclusion]The study provided theoretic basis for the report of soil erosion in grassland in China.