Study on Simplified Calculation Method for Critical Water Depth of Standard Arched Section Tunnels

Calculation of the critical water depth in the standard horseshoe tunnels requires applying transcendental equation.Furthermore,the calculation function is in two ranges due to the special section.So,the critical water depth cannot be calculated directly.The conventional graphics,trial method and approximation method all are with the calculation formula in section and complicated expression.In this paper,the minimum standard residual difference is taken as the target function based on the optimized fitting theory.Within the applicable range of the engineering parameters,one approximate formula featuring expression of one normal calculation formula,simple,direct,convenient for practice and calculation precision satisfying design requirement(error,0.489% at maximum) is concluded through the approaching fitting calculation.This formula is worth of developing in practice.