In order to make clear the testing method and judging standard of testing the void under cement concrete pavement slab by falling weight deflectometer(FWD),based on the formation mechanism of the void of cement con-crete pavement slab bottom,the basic principle of the testing technology,testing point arrangement requirements,void judging method and standard of FWD are studied and analyzed in this paper.During the test by FWD on site,the testing point should be cleaned,a constant load applied and small temperature difference should be selected.According to the engineering application case and FWD verification test,when the deflection ratio of midpoint of edge and midpoint of the slab is greater than 2 or the deflection ratio of corner and midpoint of the slab is greater than 3,it should be judged comprehensively that there is void under cement concrete plate slab.
Overlong and overweight prefabricated bent have made higher requirements on transportation and lifting equipment and hindered the technical development and engineering promotion of fully assembled bridges,which has become a key problem to be solved urgently.The development of lightweight and high performance prefabricated bent caps with reasonable structure is an alternative solution to the above problems,which is worth paying attention to.In this paper,the key technologies and typical engineering applications of light weight bent caps are systemati-cally reviewed;Secondly,the research progress of the mechanical properties is discussed in detail.The future re-search direction is expounded as well;Finally,the calculation method and flow of flexural and shear capacity are summarized.The results show that when the prefabricated mold shell and the core concrete bonding strength is higher,the mechanical properties and failure mode of the prefabricated shell cover beam are similar to the destruction mode.UHPC hollow thin-bent cap has strong shear and crack resistance.However,the promotion of lightweight bent caps engineering still faces the problems such as the internal mold fixation and demolition,design and construction tech-nology standard formulation,lightweight pier node reliability connection and its seismic performance,which ur-gently need the improvement and breakthrough.
Taking a tunnel in weak surrounding rocks as an example,the influence of different advanced support re-inforcement forms on the tunnel structure and excavation face stability were analyzed by numerical simulation.The different reinforcement forms were compared and analyzed.The analysis results indicate that when the distance be-tween the surface grouting reinforcement and the tunnel arch is close to 1.2 m,the control effect on the settlement of the tunnel arch is significantly improved;The thicker the pipe shed support reinforcement area,the better the con-trol effect on tunnel arch settlement;Under the surface grouting reinforcement,pipe shed support reinforcement and combined support,the extrusion deformation trend of the excavation face is basically the same,with the maximum extrusion deformation value in the middle;Under the combined support,the vertical extrusion deformation value in the middle of the excavation face is the smallest,which is reduced by about 38.5％,27.3％,and 9.1％compared with unsupported,surface grouting reinforcement and pipe shed reinforcement respectively;On the same horizontal line,the lateral extrusion deformation value of the excavation face is basically the same.At the place 3 m from the tunnel excavation section to the tunnel face,the length of the lateral extrusion stable deformation value in the middle of the face is longer.While at the place 6 m,the length is shorter.The relevant research results can provide reference for the support of tunnels in weak surrounding rocks.
The main bridge of Hongzhou Bridge of Nanchang City in Jiangxi Province is a self-anchored suspension bridge with steel-concrete composite beams and double towers with double cable plane.The main pier is set with two independent cofferdams.The cofferdams are made of circular cofferdams supported by lock-gate steel pipe piles and piers.The pier structure is reasonable.During the construction,the inner support of the pier is first installed on the drilling platform.And then,guided by the ring beam the lock steel pipe pile is driven by the combination of DZ-90 vibration hammer and YC-5 hydraulic impact hammer after the total lowering.At the same time,the vertical degree,rock depth and plane position of the lock steel pipe pile are controlled to optimize the closing process.Finally,the pier construction is quickly completed.The relevant research can provide reference for similar projects.
The urban rail transit has been rapidly developed in Beijing.With the continuous construction and opera-tion of new lines and the network continues to be encrypted,the demand for multi-line interchange increases.In order to meet the requirements of the passengers travelling,some earlier constructed stations without reserved trans-fer conditions need interchange renovation under non-stop operation.Taking the public zone renovation of Sanyuan-qiao Station of the existing Beijing subway line 10 under non-stop operation as an example,the renovation content and operation demand of the existing station are analyzed,the impact of the non-stop renovation is summarized,and specific response strategies such as step-by-step renovation are put forward.At the same time,passenger flow organization of the scheme is verified and optimized by analogue simulation.The relevant conclusions can provide a reference for the non-stop renovation of the public area of similar stations.
