1. Project Overview

 

　　This project is the reconstruction and expansion of Shanghai First People's Hospital. According to the design by Tongji University Architectural Design and Research Institute Co., Ltd., the supplementary pile foundation for this project is located at the current site of No. 86 Wujin Road, Hongkou District, Shanghai, adjacent to Jiulong Road to the east, a fire station to the west, Wujin Road to the south, and Harbin Road to the north. The reconstruction project involves a 4-story teaching building from the 1920s, which is preserved and renovated for reinforcement. A total of 387 anchor static pressure piles are constructed for compressive sinking, with steel pipe piles of diameter Ф245mm, wall thickness 10mm, steel material Q235B, pile length 33m, pile top elevation approximately 0.400-0.650m, and the bearing stratum is 5-3 gray silty clay with clayey silt. The design value of single pile compressive bearing capacity is RD=500KN. The standard value of single pile vertical compressive ultimate bearing capacity is QUK=1000KN.

 

 

　　2.1 Reaction force problem of anchor pile construction in this project

 

　　Due to the age of the building, the existing foundation slab cannot meet the requirements of pile sinking pressure. It is necessary to construct new reinforced concrete pile caps, which increases construction difficulty and brings some uncertainty to the pile sinking schedule.

 

　　2.2 Impact of anchor static pressure pile construction on existing buildings

 

　　2.3 Each new pile has a reaction force of 100 tons during pressing, which greatly affects the existing building structure. The handling of any abnormal situation is directly related to the protection of existing buildings. The constant monitoring and measurement by relevant units during construction are crucial.

 

　　3.1 Construction Preparation

 

　　① Before pile pressing, set out the pile positions at the predetermined locations, drill holes of diameter 370 using a drilling machine with a row-hole method, and remove obstacles such as concrete cushion and wooden piles in the holes. Especially, it is necessary to detect whether there are wooden piles underground. If there are foreign objects such as wooden piles, they must be cleaned up in time to ensure that no foreign objects affect pile pressing.

 

　　② Subsequently, construct new concrete reaction pile caps and embed pile pressing anchor stems. After the concrete of the pile cap reaches the required curing strength, mark the cross lines of pile positions at the reserved pile holes. Excavate and remove any remaining wooden forms, concrete debris, and other obstacles in the reserved pile holes. Clean the area within 5 meters around the pile holes and pile caps, and drain accumulated water.

 

　　③ Before formal pile pressing, check whether the connections of various pile pressing equipment parts are firm, whether the hydraulic system component joints and oil pipes are loose or damaged, and whether there are oil leaks at connections.

 

　　④ Check whether the oil tank has sufficient hydraulic oil. The oil tank outlet valve must be opened, and the nut must be tightened.

 

　　⑤ The processing and delivery of steel pipe piles should be coordinated with the construction sequence and progress, and delivered in a timely manner. Determine the quantity of each length specification based on floor height and pile length.

 

　　⑥ The storage site for steel pipe piles should be level. The stacking height should not be too high (no more than 3 layers) to prevent deformation under pressure. Wedge the sides of steel pipe piles to prevent sliding.

 

　　⑦ Based on the site conditions of floor slabs and beams, the steel pipe piles are initially set to be divided into 22 sections, each 1.5 meters long. Adjustments can be made according to actual site conditions.

 

　　3.2 Pile Pressing Construction

 

　　3.2.1 Preparation Work

 

　　① The pile pressing frame shall be processed, assembled, and accepted according to the design pile pressing force. Check that all components meet the pile pressing requirements and are suitable for pile pressing conditions. Check whether the hydraulic system component joints and oil pipes are loose, damaged, or leaking.

 

　　② Calibrate and test the pressure gauge instruments of the high-pressure oil pump for pile pressing to ensure they meet requirements, and check whether the oil tank of the oil pump has sufficient hydraulic oil.

 

　　③ Arrange construction power supply according to standards, check the insulation condition of power lines, and ensure power lines are connected to leakage protection switches.

 

　　④ After all components are connected, a trial pressure test and safety inspection must be conducted. Only after passing the inspection can normal operation proceed. The following figure shows the detailed drawing of the pile pressing reaction frame for this project.

 

　　3.2.2 Construction Process Flow:

 

　　① When installing the pile pressing frame, it must be kept vertical both in and out of plane, and the base must be firmly fixed to prevent the pile frame from shaking. Check and adjust at any time during pile sinking.

 

　　② Use a hoist to lift the pile section into position and straighten it. Fit the main pile cap so that the jack and the pile section axis are on the same vertical line. Only after confirming the pile position is correct and the verticality meets specifications and design requirements can pile pressing begin. Apply initial pre-pressure gently to ensure pile verticality. If tilting occurs, correct it promptly or pull out and reposition. Repeat pile pressing and pile splicing.

 

　　③ Pile splicing: The lower pile section should protrude 250mm to 300mm above the ground floor as working height. Install the inner lining steel pipe sleeve, weld evenly and symmetrically with full weld seams, welding grade 2. Use Φ1.2 CO2 gas shielded welding wire. After welding, wait 1 minute for cooling before pile pressing.

 

　　④ Pile pressing: Construction should be uniform and continuous, with one penetration per 20cm. Strictly control the verticality of pile pressing, control the penetration depth, and press correctly to the design elevation of the pile (based on elevation control).

 

　　⑤ Record actual measurement data for each pile, keeping records at all times according to progress. Upon completion of each pile, promptly request supervision witness and sign-off.

 

 

　　① Anchor bolts shall be embedded in correct relative positions, vertically, and the corresponding base surface around the anchor bolts shall be level. During embedding, observe whether the surrounding environment and height are favorable for pile frame positioning and pile pressing.

 

　　② Control the manufacturing quality of steel pipe piles, including outer diameter, length, camber, pipe end flatness, and inclination between pipe end plane and pipe center. Re-measure using steel tape and calipers, with allowable deviations meeting design requirements and specifications. Pre-configure inner lining steel pipe sleeves for welded steel pipes. The inner lining steel pipe welded inside the pipe should be placed on supports.

 

　　③ During handling and transportation of pipe piles, prevent impact on the pipe body to avoid bending deformation and damage.

 

　　④ The storage site for pipe piles shall be level. Wedge the sides of steel pipe piles with wooden wedges, and mark the pipe ends to prevent damage from collision with other objects. Stacking height shall not exceed 3 layers.

 

　　⑤ The pile pressing frame shall be positioned vertically both in and out of plane, with a firmly fixed base. Check and adjust at any time during construction.

 

　　⑥ Pile sections must be positioned vertically, and verticality shall be re-measured with a plumb bob. The jack and pile section axis shall be on the same vertical line. Construction can proceed only after acceptance.

 

　　⑦ During pile splicing, the lower pile top shall be controlled at an effective splicing height above the ground floor to ensure welding quality.

 

　　⑧ Check whether the pipe pile is deformed. If deformed, repair immediately and remove oil stains, rust, water marks, and other attachments on the pile top that are detrimental to welding.

 

　　⑨ Steel pipe pile welding shall use CO2 gas shielded welding, and dry welding rods matching the steel pipe material must be used. According to the grade 2 weld inspection standard, on-site construction must cooperate with the testing unit for ultrasonic flaw detection of welds.

 

　　⑩ Select appropriate welding current, voltage, speed, and welding gun angle. Welding quality shall meet design and specification requirements, and construction can proceed only after acceptance by the supervisor. The lower end of the upper pile section shall have a 400±50 groove weld. Welding must be symmetrical and uniform to prevent deformation of the steel pipe after cooling, which would affect verticality. After welding, wait 1 minute for cooling, and only after passing inspection can pile pressing proceed. During pile pressing, the jack and pile section axis must be on the same vertical line, and eccentric pressing is not allowed. Two plumb bobs shall be set in two-dimensional directions to check the verticality of the pile body, ensuring the verticality of the pile section is controlled within 1%.

 

　　Pile pressing for each pile shall not be interrupted midway and should be completed in one go. If interruption is necessary, the pile tip should remain in the soft soil layer, and the interruption time should not exceed 24 hours.

 

 

　　Although this project was difficult, the above methods achieved good results, and the renovation and reinforcement project was successfully completed (specific effects can be added). Facts have proven that as long as existing technical specifications, measures, and relevant regulations are strictly implemented during application, construction is strictly carried out, and the level of technical application is continuously improved, various problems in construction can be well addressed, and the construction quality of static pressure prestressed pipe piles can be controlled.