Study On Shield Cutting Large Diameter Reinforced Concrete Piles Directly

ABSTRACT:While encountering pile obstacles during shield tunneling, the method of cutting pile directly has the advantage of small impact on surrounding environment, low cost and short construction period compared to traditional methods, as a result, its social and economic benefit is remarkable. However, the theory research and implementation technology of cutting piles are far from mature in the international scope currently, especially for cutting large-diameter reinforced concrete piles. Based on the construction of shield cutting14Φ1000～1200mm diameter bridge piles in Suzhou subway, the related mechanism, theory and technology of shield cutting reinforced concrete piles are studied by using investigation, theoretical analysis, finite element simulation, field test as well as construction measuring. The major contents and achievements of the study are as follows:(1) Considering material nonlinearity, geometric nonlinearity and contact nonlinearity, the whole process, interaction and mesoscopic mechanism of blade cutting steel, concrete were studied with the analysis platform of international famous nonlinear explicit dynamic software.(2) The shell cutter of negative front angle with double-side blade is fit for cutting piles. The influence laws of front angle, blade angle and blade width on cutting steel, concrete were obtained through finite element simulation. In order to adapt the continuous cutting of large-diameter reinforced concrete piles, a new type of cutting pile tool was invented. By establishing three-dimensional thermodynamic coupling model of cutting steel and three-dimensional whole-process model of cutting concrete, the dynamic cutting process and cutting performance of the new cutting tool were revealed. According to the simulation results, the wear mechanism of tool alloy when cutting steel, concrete was considered as hard point abrasive wear by comparing various wear types.(3) The cutting tools configuration was studied theoretically:Cutter layout can adopt the method of concentric circles, adjacent cutters should be positioned with equal phase angle, the determination of cutter spacing should cover the entire cutting plane of pile concrete. An integrated configuration scheme including obverse shell tools, edge shell tools, center small shell tools, overbeaking shell tools as well as claw tools was proposed in order to meet the multi-function requirements of cutting piles. (4) The mathematical model of cutterheand cutting pile was set up and the corresponding force calculation program was created, then the change characteristics and influence laws of thrust, torque and unbalanced force were obtained. The active cutting parameter setting suggestions were given for cutting piles of different size and offset distance. With the help of international mechanical design software, the cutterhead and tools models were drew, then the cutterhead stiffness was checked and reinforcement measures were put forward for the most unfavorable cutting conditions.(5)The field test of shield cutting reinforced concrete pile directly was carried out for the first time both at home and abroad, the cutting effect, tool damage law and cutting parameters characteristics were analyzed, meanwhile, the rationality of preliminary scheme of the tool configuration and cutting parameters settings was checked. The layout scheme of advancing shell tool and the concept of cutting rebar with different times were presented according to the experiment results, which was then confirmed by simulation, and was successfully applied in engineering practice eventually.(6) Taking Suzhou subway shield cutting large-diameter bridge piles as project background, the security performances of upper structure and segment lining under the condition of cutting piles were discussed, a comprehensive shield strengthening scheme was put forward, including cutter tools, screw conveyor, small flow pump and outside pipes. Slow advancing speed, medium rotation speed, stabile soil pressure, inert slurry and strict shield attitude were suggested to control the construction of cutting large-diameter piles.