| Along with our country urbanization accelerating,more and more underground projects construct intensively.With advantages of construction safety,good adaptability to formations and less impact on the environment,the pipe jacking roof method become one of the key technology for large underground structures construction.The curved pipe jacking roof applied in Gongbei Tunnel represents the advanced technology in pipe jacking roof.It adopts innovatively to combine curved pipe jacking technology and ground freezing method and is the largest curved pipe roof project in the world,which is made up of 36 steel pipes with a diameter of 1620 mm and length of 255 m.The construction environment is belong to typical coastal high water pressure and multiple soft soil.Additionally,it underneath pass the Gongbei Port and the surrounding buildings are numerous.Therefore,the construction will face with high technical difficulties and huge risks.Prior to this project,all pipe jacking roof project were in the form of straight lines with short distances.There is no similar project practice to reference for large curved pipe jacking roof construction in coastal high water pressure and multiple soft soil.In addition,there is no mature design specification for curved steel pipe jacking as a composed unit.Hence,the existing construction technology and basic theories are difficult to meet the design and construction requirements of large curved pipe jacking roof.Therefore,this dissertation takes the super large curved pipe jacking roof in Gongbei tunnel as research object.It solves the technical difficulties of pipe jacking equipment selection in rich water and multiple soft soil,the precision control of the combined curved pipe jacking roof and preparation of pipe jacking mud in coastal environment.Steel reception casing device and technical solutions under high water pressure conditions are developed.The sealing performance of the starting device,pipe joints and reception device used in the construction are verified by pipe jacking sealing test in laboratory.Additionally,the sealing rubber ring structure of pipe joint is optimized.The variation law of monitored jacking parameters,pipe-soil pressure and pipe stress of curved pipe jacking in different conditions are demonstrated,and the calculation models to calculate jacking force considering pipe-soil and pipe-mud of frictional resistance,pipe-soil pressure and pipe stress are established.The mechanical model of the supporting pipe based on Pasternak elastic foundation beam theory is established as well to provide the basis for pipe diameter optimization.With analysis of soil disturbance during curved pipe jacking construction and multiple jacking of pipe roof,the pipe jacking order is optimized and reduces the formation deformation caused by construction.All research results provide technical support for the successful construction of curved pipe jacking roof in Gongbei Tunnel and the research works are show as following in detail:According to the pipe jacking equipment selection in condition of rich water and multiple soft soil,the slurry pipe jacking machines with mixed cutterhead is the optimization used in construction.The precision control technology of the composite curve with small spacing is summarized and meets the control requirements of ±50mm,including starting with straight line,UNS automatic guiding and Artificial measurement checking and three-line control reception.By analysis the mechanism of pipe jacking mud,the mud performance requirements and reasonable slurry and lubrication mud formula for coastal multiple formations are put forward,which has realized efficient excavation in multiple formations and the friction reduce to 1kpa.The numerical simulations of different types pipe joint rubber rings and joints under different deflection angles are carried out by ABAQUS software.Additionally,the sealing test of pipe jacking is execute in laboratory.The results show that the structure of rubber ring is more reasonable after optimization.The opening sealing device and pipe joint satisfy the sealing requirements of 0.3MPa on-site.But the sealing of reception casing needs to be strengthened.With successful application of innovative steel reception casing technology in the actual construction,which has realized the safe reception of pipe jacking under high water pressure soft soil layer and loose stratum.With summarizing the commonly jacking force calculation formulas of curved pipe jacking,a new curved jacking force model is deduced by using Persson contact theory to analyze the pipe-soil contact mechanical properties and considering the thixotropy of the lubrication mud.The results show that the calculated values of cutterhead resistance is larger than the measured values generally.The cutterhead resistance calculated by mud pressure is the closest to the actual value,and it is also convenient to use in field.The measured frictional resistance is basically located between the calculated values of Persson model,which is indicated that it can be more accurate to predicate frictional resistance.Through the on-site monitoring test of pipe-soil pressure and pipe stress,the mechanical characteristic of curved steel pipe jacking are indicated under four construction conditions,such as jacking process,jacking stoppage,jacking completed and jacking of adjacent pipe.The results show that pipe-soil pressure and pipe stress are significantly asymmetric during jacking process.Generally,the values of pipe-soil pressure at crown and bottom are relatively close,and the crown pressure is slightly larger than that at the bottom.The horizontal pressure inside of pipe is less than the outside.The pipe axial stress is mainly affected by jacking force,and hoop stress mainly depends on ring load out of pipe.The stress concentration is located inside of pipe jacking curve.Under a large buried depth condition,the pipe axial stress will change from full sectional compression to local compression.Based on the commonly soil pressure calculation models used in pipe jacking and shield standards,the soil pressure calculation model of curved steel pipe jacking is proposed in different construction conditions.In this model,the additional pressure caused by the horizontal deformation of the steel pipe is taken into account,and the Terzaghi model considering the height of the soil arch shear zone is applied to calculate the vertical soil stress.Then,based on the Castigliano theorem,the pipe stress formula under any loads is solved.The calculated results of pipe-soil pressure and pipe stress show that the calculated values are close to the measured values at the site,which proves the applicability of the theoretical model established.By selected the most unfavorable bottom supporting pipe as the research object in large section pipe roof,the supporting pipe mechanical model is established by using the Pasternak elastic foundation beam theory.The displacement and internal force equations are deduced.With analysis of the maximum strain of supporting pipe under different conditions of excavation footage,pipe diameter and spacing,the results show that the supporting pipe maximum strain decrease quickly with pipe diameter increases.When pipe diameter increases to a certain value,the supporting effect of pipe roof do not improve observably by increasing the pipe diameter simply.Based on the soil disturbance field test,the variations of surface subsidence,deep soil subsidence,the horizontal displacement of deep soil and soil and water pressure induced by curved pipe jacking construction are analyzed.The result indicates that the induced ground settlement is not symmetry about tunnel axis and the maximum settlement point may appear on outside or inside of jacking path curve.The soil loss caused by relative position of curved pipe jacking and tunnel is the main reason for the ground settlement offset.The calculated result of modified Peck formula is accordance with measured values,which can respond offset effect of ground settlement curve and the maximum settlement during curved pipe jacking construction in sand and mucky soil.It can be used to predicate the surface deformation caused by curved pipe jacking.By using ABAQUS numerical simulation method,the influence of stratum deformation,stratum stress,maximum pipe stress and deformation are analyzed with different jacking procedure schemes.The results show that the vertical ground deformation curve induced by pipe roof jacking is a bimodal curve.A symmetrical jacking procedure causes symmetrical distribution of vertical ground deformation,and an asymmetric deformation curve is occurring during asymmetric jacking procedure.The ground deformation caused by symmetrical jacking is smaller than asymmetric condition.Compared to other jacking schemes,the C1 scheme jacked from the bottom up,is optimal and has an advantage in reducing pipe stress and deformation.The rapid development of surface deformation caused by pipe roof construction is occurred in the main jacking stage with a large number of pipe jacking construction.In the final stage and end of the main jacking stage,the settlement value is not increased obviously due to the supporting and reinforcement of the constructed pipes. |
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