Causes and Control Measures of Mixed Free-Surface-Pressure Flow in Steep-slope Tunnel

The mixed free-surface-pressure flow which is easily formed in steep-slope tunnels results in cavitation erosion,vibration and impact damage.On the basis of model test data of steep-slope tunnels,the influencing factors and the control measures of mixed free-surface-pressure flow in steep-slope tunnel is researched.It’s found that the main influencing factors include relative submerge depth H / a,tunnel shape(bottom slope,inlet top shape,tunnel height,tunnel length,bending section,gate shaft),inlet approach channel configuration and the consequent air suction swirl and air intake in the gate shaft.According to the terrain condition,geological condition,project function,operation safety and economic factor,measures as follows can be adopted to control the mixed free-surfacepressure flow in steep-slope tunnel: vortex suppression,air intake suppression in gate shaft,and optimization of inlet top shape,tunnel height and tunnel length.