Experimental Study On The Mechanical Performance Of Assembly Integrated Precast Utility Concrete Tunnel

The assembly integrated precast utility concrete tunnel is a kind of underground building that can accommodate many kinds of urban public pipelines,and it is one of the important infrastructure of modern urban development,which is generally constructed with concrete structure.According to the construction technology,the utility concrete tunnel structure can be divided into three forms:integral cast-in-place,prefabricated and assembly integrated precast.The integral cast-in-place utility tunnel is constructed by the process of on-site formwork pouring,with good structural integrity and convenient waterproof treatment,but with large amount of on-site wet work and long construction period;the prefabricated utility tunnel is constructed by the process of segmental whole or block prefabrication and assembly,which is easy to guarantee the prefabrication quality and short on-site construction period,but limited by the hoisting size and weight,the longitudinal length of the prefabricated segment Small,resulting in a large number of joints,joint waterproof treatment tends to be difficult;prefabrication and assembly of integral utility tunnel is to use some prefabricated and partially cast-in-place composite components for each panel of the utility tunnel,which is composed of sandwich wall limb,laminated roof and laminated floor,combined with the advantages of integral cast-in-place and prefabricated assembly structures,which not only reduces the wet operation on site,but also shortens the construction period,and reduce the number of seam and seam waterproof easy to achieve,has a better application prospects.At present,the cast-in-place and prefabricated utility tunnel structures are mainly used in the project,and the relevant design and construction specifications are also mainly oriented to these two types of structures.The design theory and engineering application research of the prefabricated integral utility tunnel structure are few,and the mechanical deformation performance of the structure needs to be verified,which makes the experimental research on the mechanical performance of the prefabricated integrated utility tunnel structure,especially the experimental research based on the full-scale model very valuable.Therefore,based on the actual project,this paper makes an experimental study on the mechanical and deformation performance of prefabricated integrated concrete utility tunnel structure,in order to provide a certain basis for the design and construction of prefabricated integrated utility tunnel structure.The main contents of this paper are as follows:(1)Introduced the background of the topic,the category and development of utility tunnel,and summarized the research status of utility tunnel and prefabricated integrated structure.(2)The full-scale segmental model test were conducted on the assembly integrated precast utility concrete tunnel with double warehouses.The results show that:the failure mode for the large warehouse roof was shear failure after the yielding longitudinal reinforcement,while the shear failure was observed in the small warehouse roof before reaching its bending bearing capacity.The shear bearing capacity of the roof with larger thickness for the tunnel is more likely to be the control factor in the design;the working performance of the bonding interface can be guaranteed,provided that the anchorage of the truss reinforcing bars across the bonding interface was reliable;the lap structure between u-shaped steel bar reserved in the precast part of the wall and the steel bar extending into the cast-in-place layer of the roof,can meet the stress requirement of the joint;the structural design of the existing tunnel has sufficient safety reserve and good normal operation performance.(3)Based on the finite element software ABAQUS,a finite element analysis model of the assembly integrated precast utility concrete tunnel structure with double-warehouses with truss reinforced was established.The calculated load-displacement curve,failure shape and crack distribution were consistent with the test results.The influence of parameters,such as the configuration and ratio of web bars in the truss-type reinforcement in the concrete plates of utility tunnel structure,longitudinal reinforcement configuration,concrete strength grade,on the mechanical performance of utility tunnel structure was analyzed on the base of the nonlinear finite element model established.The results showed that:in the case of analysis,the contribution of web bars in the truss-type reinforcement to the shear capacity of utility tunnel structure roof plate was similar to that of rectangular stirrup with the same stirrup ratio,and the shear resistance of web bars in the truss-type reinforcement could be approximately considered as vertical stirrup;the angle of web bars in the truss-type reinforcement increased from 67~o to 113~o,the shear capacity increased by 17.5%;the reinforcement ratio of truss web member increased from 0.30%to 1.53%,the shear bearing capacity increased by 22%,and the maximum reinforcement ratio of the web bars was about1.5%;in order to ensure that the reinforcement at the most unfavorable position of the roof and the negative bending moment area near the middle node of the utility tunnel structure does not yield prematurely,when the total number of longitudinal bars of the roof plate was unchanged,more longitudinal bars could be appropriately arranged for the soil facing side of the utility slab;the concrete strength grade was increased from C35 to C55,and the shear bearing capacity increased by 20%.