Study On Hydrodynamic Characteristics Of Stilling Basin With Wide Tail Pier And Numerical Simulation Of Hydraulic Fracturing Of Bottom Plate

Underflow stilling basin is widely used in water conservancy projects with low and medium water head,but the flow pattern is complex,which is prone to instability of bottom plate.The difference of surface hole opening mode will lead to the working condition which is not conducive to the stability.Compared with the flat tail pier stilling basin,the wide tail pier stilling basin has large differences in hydrodynamic characteristics.In the process of construction,the hydraulic concrete structure will inevitably have cracks,and the bottom plate will be destroyed.In this paper,the hydrodynamic characteristics and regulation response characteristics of the underflow stilling basin are studied by the combination of physical model test and numerical simulation.At the same time,numerical simulation is carried out to study the hydraulic fracturing in the bottom plate.The main research findings and conclusions are as follows:(1)The regulation response characteristics with wide tail pier are studied.When the opening mode is changed from symmetrical interval opening to symmetrical adjacent opening,it will weaken the maximum value of fluctuating pressure in the center line of the stilling basin.when the opening mode is changed from interval opening to adjacent opening,it will weaken the maximum value of fluctuating pressure in the center line of the stilling basin(when the 5#surface hole is open),the maximum value of fluctuating pressure in the center line of the pier between 6#and 7#surface hole(when the 6#or 7#surface hole open).(2)Comparison of hydrodynamic characteristics with wide tail pier and flat tail pier.At the front end of the anti-arc section,the time-averaged pressure of the wide tail pier is smaller than that of the flat tail pier,the fluctuating pressure is stronger,and opposite in stilling basin.According to the calculation formula for anti-floating stability,structural instability damage is more likely to occur under the condition of wide tail pier in the anti-arc section compared with flat tail pier.(3)The hydrodynamic characteristics of the anti-arc section are studied.Five surface holes fully open,the fluctuating pressure in the anti-arc section is almost normal distribution,and the kurtosis coefficient decreases gradually along the anti-arc section,and the fluctuating pressure has certain periodicity.When the 5#surface hole opens separately,the fluctuating pressure is relatively stable,close to the normal distribution.When the 4#5#6#surface holes and 3#5#7#surface holes open,the skewness coefficients and kurtosis coefficients of the last two measuring points increase.When the 3#4#6#7#surface holes and 4#6#surface holes open,the instantaneous spatial correlation coefficients and spatial integration scales gradually decrease.(4)The numerical simulation of the hydrodynamic characteristics and hydraulic fracturing of the bottom plate is carried out.According to the numerical simulation results and empirical formula,the lifting force on the bottom plate is 0～30.0× 10~4Pa.The equivalent stress of the center line of the bottom plate increases suddenly near the front edge of the crack,which is easy to cause damage.The bottom plate has only slight bending deformation during load application.(5)Study on the factors influencing the hydraulic fracturing of the bottom plate.The decrease of crack length greatly increases the bearing capacity of the bottom plate,and the initial crack will crack before the damage;the anchor bar can improve the bearing capacity,the maximum Z-direction displacement without anchorage is slightly larger than that of the anchorage under the same lifting force;the increase of the thickness of the upper bottom plate is conducive to the maximum bearing capacity.