Bearing Performance And Computational Method Of Piles In Hydraulic-Reclamation Area

With the rapid development of economy in coastal area, the land resources become increasingly nervous, which leads to more and more land reclamation project. The geological conditions of hydraulic-reclamation area are characterized by unconsolidated filled layer above the underlying soft seabed sediments. Therefore, the influence of negative friction on pile act an important impact on the infrastructure project, and the negative friction were caused by both the consolidation of upper filled layer and the settlement in the substratum under reclamation loads. By studying the mechanical characteristics of pile in new land reclamation site, the mechanism of negative friction on pile with the effect of combined factors can be investigated to evaluate the negative friction development process. Then the corresponding calculation and analysis method can be presented, which can provide theoretical and technical support for engineering construction in rapid development of reclamation area.This paper research the bearing performance of piles in large land reclamation area by the field test and numerical simulation. Furthermore, the distribution model and simplified calculation method of negative friction on piles in the reclamation area are summarized. Conclusions can be obtained as follows.(1)A long term in-situ test for pile in the large area land reclamation is taken to analyze the emergence and development of negative friction pile. The law that side friction resistance and axial stress of pile changes are obtained by the long-term monitoring on two test pile body adopting sliding micrometer. The field results indicate that pile is gradually affected by the negative friction after construction completed. Meanwhile, the axial force of pile and the neutral point depth increases with time, which is still not stable after pile-sinking completed one year later. The negative friction effects obviously on the upside of pile, among which negative friction increases in reclamation soil layer and decreases in undisturbed substratum with the increase of depth.(2)Based on the Biot’s consolidation theory that considered saturated soil fluid-soil coupling, the long-term mechanical characteristics of pile in the reclamation area is analyzed by numerical simulation. According to the result of test static load test, confirm the parameters for the numerical calculation of the soil layer and compare with the results of geological survey report and the field test. Then, take the verified parameters to evaluate long-term development of the characters about the fraction on the two test pile. The calculating results showed that pile’s axial force and the depth of neutral poin can achieve basic stability after pile-sinking for 3 years, when the negative friction distribution is still characterized that it increases in reclamation soil layer and decreases in undisturbed substratum with the increase of depth.(3) Considering the various working conditions of pile while in design and in use, above-mentioned numerical simulation is used for the parameters analysis of mechanical property on the pile. The influence of conditions that heap load and length of pile have in negative friction is analyzed on account of the combined action of load on the top of pile and heap load around the pile. According to the characteristics of the reclaimed site, the impact of thickness of dredger fill layer and measures to eliminate negative friction on the pile is researched by analysis of parameters. And compare the difference of negative friction on pile under the effect of dredger fill layer with heap load, which is beneficial to verify the development and distribution of negative friction.(4) A simplified calculation method is raised for negative friction on pile in the reclamation area when taking field test and numerical analysis into account. The method currently used in calculating the neutral point and maximum negative friction makes some undetectable deviations so that a method that simplify the distribution patterns of negative friction on the pile is put forward, which is modified by the results of in-situ test and numerical analysis. In this model, negative friction increases in reclamation soil layer and decreases in undisturbed substratum with the increase of depth, and then a formula to calculate the neutral point and axial force of pile is deduced. The validity of the model is verified by compared with the results calculated in criterion and predicted by numerical simulation. Therefore, this method can confirm the mechanical behavior of pile in reclamation area simply and accurately, and it provides the reference value for the engineering design.