Research On The Mechanical Behavior Of Lightweight Utility Tunnel

In recent years,with the advancement of urbanization,the development and utilization of urban underground space has received more and more attention,and the scale of utility tunnels' construction has become larger and larger.Prefabricated Utility Tunnel has the characteristics of short construction period,labor saving,low pollution,and convenient management,is widely used in utility tunnels' construction.However,at this stage,the prefabricated utility tunnel segment has a high weight,which requires high requirements for lifting,transportation,site splicing and foundation treatment,so it is difficult to fully exert full advantages.Lightweight of prefabricated utility tunnels is necessary to expand its range of applications and to increase economic efficiency.To improve the status quo,the hollow concrete and high-strength lightweight concrete methods are studied.According to the results of experiments and simulations,the effects of two lightweight methods on the mechanical behavior of the utility tunnel are compared,advices also be given on its application in practice.In order to study the influence of opening on the overall mechanical behavior of the utility tunnel,monotonic static loading experiments on a common utility tunnel segment and a full-scale utility tunnel segment are did under the background of actual engineering.The deflection of the corridor,the distribution and development of the crack are also observed,the load-deflection curve and the load-strain curve of the subject were obtained.The results show that the opening will reduce the stiffness and cracking load,change the stress distribution and crack distribution characteristics of the utility tunnel;and the effect of the opening on the top plate subject to bending is greater than that of the main wall under pressure.The ABAQUS finite element analysis software is used to simulate the mechanical behavior of utility tunnel joints with different opening patterns and different opening ratios.Simulation results are well fitted to the experimental results and well present the experimental phenomena.The results show that after using lightweight concrete,the weight loss rate exceeds 20%,the stiffness and stress performance,as well as the cracking load of the utility tunnels are decreased.The deflections of the roof and sidewall are increased under the same load,and the internal force distribution changes.After using hollow concrete,the weight loss rate reduces to less than 20%.Research on different opening modes shows that mechanical behavior of unopened is the highest,next come round shaped holes,which is higher than hexagonal holes,and the last two one are elliptical and square holes.Moreover,as the opening ratio increases,the rigidity of the utility tunnel decreases,while the deformation and the stress of the steel bar increase.The research results show that both two ways to reduce weight have their own advantages and disadvantages.Lightweight has a higher weight loss rate of more than 20%,which brings a good weight loss effect,as well as better mechanical behavior;but it has complex compound process,high cost,poor crack resistance and poor impermeability.By comparison,the reasonable weight reduction rate of opening is about 15%,and the weight reduction effect is lower than that of lightweight,but it is cheaper,more convenient and experienced in application.