Performance Study On Members Of Precast Monolithic Concrete Municipal Tunnel

The municipal tunnel,an intensive tunnel,sets up in the city's underground to accommodate public utilities such as communications,electricity,water supply drainage,and gas.The tunnel structure generally adopts integral cast-in-place,segment prefabrication and on-site splicing.The cast-in-place monolithic structure has good waterproof performance,but the disadvantages of long construction period and large environmental impact.The segmented precast municipal tunnel can be formed at one time in full section,but it provides many seams lead to be difficult to waterproof.The basic members of the precast monolithic concrete municipal tunnel are constructed by using partial factory prefabrication and partial site pouring.The precast monolithic concrete municipal tunnel has all advantages of both types described above.This paper based on a precast monolithic concrete municipal tunnel project researched the mechanical properties of the superimposed roof,composite wall,composite wall-top plate joint,and composite wall-underground joint.Some suggestions were proposed for the design and construction of municipal tunnel.The main contents of this paper are as follows:(1)An experimental research was taken on two composite slab specimens fabricated by steel truss and concrete.The top chords of the truss bars of the precast slab are subjected to compressive stress under the action of the construction load.Test results shown that some transverse cracks at the bottom of the slab and the width of the cracks were greater than the limit.Thus,the unsupported construction measures for the superposed slabs are proposed due to above reasons.By checking the bearing capacity,the limit of bending capacity of the composite slab is similar to that of cast-in-place slabs.By comparing domestic and foreign code,the china code is better to calculate the shear strength of overlapped surface.Based on the bond-slip characteristics of the laminated surface,the formula for calculating the deflection of the composite slab is derived.Compared with the predicted results by code,the calculated values have good agreement with the experimental value.(2)A test consisted of two composite wall specimens fabricated by steel truss and concrete was proposed.Test results presented that the specimens meet the mechanical performance requirements of the normal use limit state and the bearing capacity limit state while have different failure modes under the action of the compressive bending load.The reason for this phenomenal may be the difference in construction and manufacturing.Therefore,more stringent requirements have been put forward for the construction of the monolithic components.Based on the bond-slip characteristics of the overlapped surfaces,the formula for calculating the deflection of the wall was deduced.Compared with the standard calculation results,the calculated values are more consistent with the tested values.(3)An experimental was taken on the key joints of the precast monolithic concrete municipal tunnel fabricated by steel truss and concrete.A total of eight specimens divided to four groups were designed to investigate the effect of longitudinal reinforcement on the mechanical behavior of the structure.The experimental results show that the key joints meet the design requirements of "strong weak joints".Moreover,the longitudinal reinforcement at the joint location showed a little of effect on the bearing capacity of the joints,while a great difference on the shear performance of the overlapped joints was shown.