Test And Modeling On Behavior Of The Pre-bored Grouting Planted Nodular Pile

The pre-bored grouting planted nodular pile is a type of composite pile foundation that consists of a precast pile and the surrounding cemented soil. The pre-bored grouting planted nodular pile has been used in some actual projects in Shanghai and Ningbo, China, however, little study on the load transfer mechanism of this composite pile foundation has been conducted and the theoretical study of this composite pile is far behind its practical application. A series of field tests, model tests, and numerical simulation were used to investigate the bearing capacity of the pre-bore grouting planted nodular pile under compression and tension, and the main research work and the conclusions are listed below:(1) The frictional capacity of the concrete-cemented soil interface and the cemented soil-sandy soil interface was investigated through a series of interface shearing tests, moreover, the influence of cemented soil properties on the interface frictional capacity was also studied by changing the ratios of the cemented soil.The test results showed that:the frictional capacity of the cemented soil-sandy soil interface is mainly controlled by the properties of the sandy soil, while the frictional capacity of the concrete-cemented soil interface is controlled by the cemented soil properties. The ultimate friction of the concrete-cemented soil interface is much larger than the ultimate friction of the cemented soil-sandy soil interface, which proves that the precast pile and the cemented soil of the pre-bored grouting planted nodular pile can act as a whole during the load transfer process.(2) A group of field tests of the pre-bored grouting planted nodular piles and the bored piles were carried out to investigate the compressive bearing capacity of the pre-bored grouting planted nodular pile, and the test results showed that the compressive bearing capacity of the pre-bored grouting planted nodular pile is better than the compressive bearing capacity of the bored pile.A field test was carried out to investigate the load transfer mechanism of the pre-bored grouting planted nodular pile. It was found that the frictional capacity of the cemented soil-soil interface of the pre-bored grouting planted nodular pile is better than the frictional capacity of the pile-soil interface of the bored pile.A model test was conducted to investigate the load transfer mechanism and the function of the cemented soil around the precast pile during the load transfer process, the test results showed that the function of the cemented soil along the shaft is different from the function of the cemented soil at the enlarged base. Specifically, the stress in the cemented soil along the shaft is relatively small, and it acts as a transition layer in the load transfer process, while the enlarged cemented soil base shares part of the tip resistance.The tip bearing capacity of the pre-bored grouting planted nodular pile was analyzed by conducting a group of field tests and model tests. It was found that the enlarged cemented base can help promote the tip bearing capacity of the pile foundation, moreover, the ultimate tip bearing capcity achieves the maximum value when the nodular pile base is located at the middle of the enlarged cemented soil base.(3) A group of destructive field tests were carried out to investigate the behavior of the pre-bored grouting planted nodular pile under tension. It was found that the load-displacement curve of the pre-bored grouting planted nodular pile under tension tends to be flat.A group of field tests were conducted to investigate the fictional capacity and the function of the enlarged pile base of the pre-bored grouting planted nodular pile under tension. The test results showed that the frictional capacity of the pre-bored grouting planted nodular pile under tension is better than the frictional capacity of the bored pile. It was also found that the enlarged cemented soil base is effective in promoting the uplift bearing capacity of the pre-bored grouting planted nodular pile.(4) The finite element software ABAQUS was used to build three-dimensional models to analyze the influencing factors of the compressive and uplift bearing capacity of the pre-bored grouting planted nodular pile, after verifying the reliability of the built models.The influence of the distance of the adjacent nodes along the nodular pile shaft, the parameters of the cemented soil (cohesion, internal frictional angle and elastic modulus), the frictional coefficient of the cemented soil-soil interface, the diameter of the pile shaft, the elastic modulus of the cemented soil at the enlarged base and the diameter of the enlarged pile base on the compressive bearing capacity of the pre-bored grouting planted nodular pile were analyzed based on the simulation results.The simulation results also showed that the enlarged cemented soil base shares a considerable part of the uplift load, which is effective in promoting the uplift bearing capacity of the pre-bored grouting planted nodular pile; moreover, the influence of the elastic modulus of the cemented soil at the enlarged base, the height of the enlarged base, the diameter of the enlarged pile base and the diameter of the pile shaft on the uplift bearing capacity of the pre-bored grouting planted nodular pile were also analyzed by referring to the simulation results.