| The coastal roadbed is affected by tidal changes,which makes its structural design and destabilisation mechanism different from that of ordinary roadbeds,presenting certain special features and requiring emphasis on the effects of wave loads,dynamic water pressure and traffic loads.Based on the tide level data,the thesis explores the distribution law of wave loads and optimises the structural form of the roadbed from the perspective of energy dissipation;a threedimensional roadbed model is established through numerical simulation,and the stability of the roadbed under the joint action of multiple tide levels and traffic loads is analysed and predicted by using Abaqus software.The content and results are as follows.(1)Explore the distribution pattern of wave loads on slopes.Based on the measured data from Haimen Tidal Station and extended to forty-eight different conditions,the distribution formula of wave loads on the slope was fitted using MATLAB software.The results show that the wave pressure distribution has the characteristic of local concentration,and the strongest part is concentrated within 1/4 to 1/2 of the wave height range on both sides of the maximum wave pressure point,and the range of action is generally below the design tidal level.In addition,wave loads are greatly influenced by wave height and wavelength,increasing as the wave height and wavelength increase,and decreasing as the slope becomes gentler.(2)To analyse the instability mechanism of coastal roadbeds under the action of coupled hydrodynamic forces.Using the Abaqus fluid-structure coupling module and developing the Dload subroutine,the changes of seepage field,displacement field and plastic zone of the roadbed under the joint action of 1～10 times of tidal level rise and fall and traffic load were analysed,and the stability evaluation and prediction were carried out by the strength reduction method.The coefficient of safety starts to decrease during high tide,rises during low tide and drops to the lowest during low tide,and gradually decreases with the increase of the number of rising and falling tides.The slip surface of the roadbed destabilisation during high and low tide occurs on the leeward side,while the slip surface during low tide occurs on the seaward side.The effect of traffic load on the stability of the roadbed is mainly reflected after the roadbed is unstable,which shows that the sudden change in displacement of the foot of the slope is faster and the safety factor is relatively lower when the iterations do not converge,indicating that the traffic load accelerates the deformation of the roadbed after instability.(3)Optimize the structure form of coastal roadbed.The design elevation of coastal roadbed is composed of three parts: design tide level,wave climbing height and safety height.Through the comparison of the calculation of wave climbing height in the three standards of 《Design Code for Embankment Engineering 》、《 Design Code for Seawall Engineering 》 and《Engineering Technology Provisions for Sea Ponds in Zhejiang Province》,it is found that the calculation result of 《Design Code for Seawall Engineering》 is more reliable and can meet the requirements of safety and wave crossing volume.When determining the design elevation of the coastal roadbed,the wave creep height can be calculated by referring to the Code for the Design of Seawall Engineering and using the guidelines for controlling the amount of overtopping;in addition,the wave creep height can be reduced and the wave energy weakened by setting up a wave elimination platform,adjusting the slope rate of the upper and lower slopes,and reasonably selecting the surface protection blocks,and it is recommended that a combined section be used and a wave elimination platform be set up on the seaward side.The location of the platform can be set within 0.5 times the wave height above and below the design tide level,and the width should be greater than 5m. |
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