Research On Calculation Of Wave Forces On The Elevated Cap-Pile Group Foundation For Sea-Crossing Bridges

In this dissertation,the wave forces on the cap and piles have been studied by using model test and numerical simulation for the cap-pile group foundations which are commonly used for sea-crossing bridges.The laboratory experiments of the cap-pile group foundation model under nonlinear shallow water waves have been carried out first.Due to the disturbance of the cap on wave field and the surface elevations at the rear of the cap are not considered in the Mc Pherson empirical method,the calculated value shows significant difference compared with the experimental results.The wave forces on pile group have been calculated with the Morison equation by using the second order solitary wave theory and cnoidal wave theory.The calculated wave forces show good agreement with the experimental results.The calculation method for the wave forces on cap under solitary wave has been studied.The analysis of simulation results for the square cap under solitary waves shows that hydrostatic force significantly overestimated the horizontal wave force on the cap,and the hydrodynamic force caused by the vertical acceleration of the water particles on the front surface significantly reduced the horizontal wave force.Corresponding calculation method is proposed using three determined influencing parameters,namely,the surface elevations in front and rear of the cap and the vertical acceleration of the surface elevation in front of the cap.Both experimental and simulation results show that the vertical wave force and horizontal wave force on the circular cap are proportional to the square cap of the same dimension under the same shallow water waves(solitary wave and cnoidal wave).Then the calculation method for the wave forces on cap under nonlinear periodic waves has been investigated.Due to the large cap dimension and the specific location near the near the still water level,the effects of the nonlinear surface elevation on the wave forces on the cap have been analyzed and a calculation method for the horizontal wave force on cap has been proposed.The comparison with the experimental results shows that the proposed method is also suitable for the calculation of horizontal force on the cap under wave and current.Last,the calculation of the wave forces on piles under cap effects has been investigated.The cap effect coefficient has been defined as the ratio of the wave force on pile under cap and the wave force on isolated single pile.The effects of influencing parameters,such as wave length,wave height,pile location,cap dimension and submerged depth on the cap effect coefficient have been systematically investigated,and the non-dimensional parameter /has been determined as the key parameter.An analytical method combined with the twodimensional solution of potential theory and the Morison equation has been presented to calculate the wave forces on piles under cap.The accuracy of the analytical method has been validated by comparing with the simulation results.