Study On Structural Response Of Asphalt Pavement Of Utility Tunnel

It is the main disease form in the transition section of asphalt pavement under the utility tunnel that the phenomenon of "bridge jump" occurring near the structure and roadbed cracking at the junction of filling and excavation.In the design and construction,we should pay attention to the difference of pavement settlement and the overall stability of backfilled subgrade.As the road-tunnel-soil structure in transition section is not uniform in all directions,it is easy to suffer many diseases such as pavement cracking and settlement under the repeated action of vehicle load.Therefore,the asphalt pavement structural response research is carried out on the road containing utility tunnel structure in the subgrade.Aiming at finding the position prone to diseases in the transition section,It was studied that the influence of subgrade pavement modulus,uneven settlement of subgrade and traffic load on the stress and strain of asphalt pavement.Because of different road grade utility tunnel design buried depth is not the same,coupled with the impact of the road surrounding environment,different construction methods will be adopted in engineering practice.Based on "Shanghai Songjiang South Railway Station large-scale Residential Community Utility Tunnel Phase II Project",and ABAQUS finite element model was established for full excavation and half excavation conditions respectively.The structural response of asphalt pavement under static load,the influence of uneven settlement of backfill on additional stress of asphalt pavement,and the mechanical response of asphalt pavement under moving load are studied.The main research work and conclusions are as follows:(1)On the basis of fully understanding the properties of road-pipe-soil in the middle of transition section,combined with theoretical analysis and numerical simulation,ABAQUS is used as a modeling and calculation tool.The distribution law of stress and strain in the transition section is analyzed by applying loads at different positions in the driving direction of asphalt pavement.According to the stress-strain distribution law,the transition section is divided to find the stress-strain sensitive region.(2)The control variable method was used to calculate the mechanical response indexes of the maximum load under two working conditions.The influences of the modulus of surface layer,base layer,sub-base layer and backfill soil on the stress and strain of asphalt pavement transition section under utility tunnel are obtained by calculation.It is used to guide the selection of material parameters and construction technology in engineering practice.(3)After the utility tunnel structure is completed,the layered backfilling process of subgrade soil is simulated by finite element method.The backfill compresses and deforms under its own gravity and the gravity of the upper pavement.Subgrade and pavement structure have coordinated deformation.In full excavation condition,the settlement of asphalt pavement mainly occurs within 0m～6m distance from the edge of utility tunnel structure.The maximum surface stress is located at the edge of utility tunnel structure.The maximum stress at the base layer is 3m away from the edge of the utility tunnel structure.In semi-excavation condition,the maximum settlement position of asphalt pavement is 8m away from the center line of utility tunnel structure.The maximum surface stress is located at the center line of utility tunnel structure.The maximum stress at the bottom of the base layer is 8m away from the center line of the utility tunnel structure.(4)An external Dload user subroutine is used to simulate the moving load.The influence of load velocity on subgrade settlement and stress response of the transition section under the utility tunnel was investigated by changing the load velocity.It is studied that the variation of surface tensile stress and base tensile stress at different positions of pavement with moving load.The results show that this type of step transition roadbed design can make the vehicle pass smoothly and safely.At the junction of transition subgrade and original subgrade,the asphalt pavement surface is more prone to crack diseases.The closer the asphalt pavement is to the utility tunnel structure,the more likely reflection cracks will occur.