Study On The Mechanical Performance Of Large Diameter Steel-tube-concrete Rock-socketed Piles In The Frame Wharf

According to the national science and technology support plan, the shipping construction key technology of permanent backwater region in the Three Gorges reservoir(code:2011BAB09B01), the 4th project "the bearing performance and design technology of rock-socketed pile foundation for deep water wharf", and relying on second phase expansion project working in the Guoyuan working area of Chongqing port, the mechanical performance of large diameter steel-tube-concrete rock-socketed piles and the steel tube concrete interface characteristics have been studied respectively in this paper, through the single pile comparison test in indoor physical model, the series of numerical simulation analysis for steel-tube-concrete rock-socketed piles of frame wharf and verification with the help of the corresponding physical model test results. The main research results are as follows:(1) According to the large and small scale contrast test results, the characteristics of single steel-tube-concrete rock-socketed pile was similar to the general rock-socketed pile under vertical load.The failure mode of steel-tube-concrete rock-socketed pile was not same the general rock-socketed pile under horizontal load. The failure surface of general rock-socketed pile was tilt and near ground surface, but that of steel-tube-concrete rock-socketed pile was level and across the bottom of the tube.(2) Under horizontal load, steel-tube and concrete interface was bonding in the pressure side, but the interface slip occurred in the tensile side.The tensile stress was significantly larger than the compressive stress. That shows poor structure stress.(3) Due to the lateral friction resistance increases of the large diameter steel-tube rock-socketed pile, the vertical bearing capacity was increased,but pile rock-socketed depth increase, the bearing capacity raise few. The reasonable economic embedded depth of steel-tube rock-socketed is about(1 ~ 2) D(for pile diameter D).Steel-tube can increase the horizontal bearing capability, reduce the displacement, the tensile stress and tensile stress area of pile body. The flexural capacity of steel tube section increased significantly, but has a mutation in the bottom of the steel-tube.(4) All of steel-tube rock-socketed piles of the bent in frame wharf were showing the largest displacement in pile top and was zero in rock surface. The displacement of the piles was basically the same, much smaller than no steel-tube. Maximum negative bending moment was at the top of the pile, the most-positive bending moment in the rock surface. The moment above rock surface was bigger than that of no steel-tube, rock-socketed segment changed little.The maximum bending moment appeared in the back row pile.The shear had mutations in the cross arm, reverse in rock-socketed segment, the maximum shear also appeared in the rear pile.The axial force was small in both ends and great in middle, the maximum axial force located in the front row pile.(5) The greater elastic modulus of rock mass, the smaller displacement of steel-tube rock-socketed pile. The cohesive force and internal friction angle change, there was little influence on pile body displacement and bending moment.(6) Construction order of framework wharf bent pile foundation and bank filling way had significant effect on the working performance of steel-tube rock-socketed piles.embankment bank slope(bank-slope stability) before piles construction could greatly reduce the pile’s displacement and internal force. Layered filling was better than filling in full, high slope andsteep bank slope should be first filled and then piled.(7) The work soaked and water level raised, the displacement,bending moment and shear force were increased in steel-tube rock-socketed piles of frame wharf bent.Water level drop and slow change were affected greatly the displacement and axial force in rear two column piles and the lateral force in the former pile.(8) Based on the above test and numerical analysis, considering the socketed depth, rock modulus, pile diameter, horizontal load location and structural important factor, it has been put forward of the simplified calculation formula for socketed depth on the large diameter steel-tube rock-socketed piles. It was good agreement through compared with the actual project.It can be reference for design and calculation horizontal capacity to large diameter steel-tube rock-socketed piles in soft rock.