Research On Safety Of Deepwater Pile Foundation Construction Platform In Reservoir Area

After the three Gorges Rsesrvoir was built and impounded,the navigation conditions of the reservoir area were greatly improved,but it also brought new challenges to the construction of the high pile wharf,bridge pile foundation,water revetment protection and other projects in the reservoir area.The research on the construction platform of deepwater pile foundation was carried out in this paper based on the construction scheme of using the bored piles and steel casing as the foundation to erect the deepwater construction platform proposed in the second phase project of Changbin road bank protection retaining wall and reinforcement in Yuzhong District,Chongqing.The mechanical properties of underwater concrete at early age has been studied based on the characteristics of early bearing of bored piles.Combined with the test results,using ANSYS finite element software,the stress characteristics and cracking of bored piles concrete were simulated under the condition of maintenance for 3,5 and 7 days,and safety risk assessment for deepwater pile foundation construction.Main research contents and conclusions are as follows:(1)According to the design,construction principle and construction process of the new deepwater pile foundation construction platform,the paper compares and analyzes the construction platform of traditional steel pipe pile.The result shows that the novel method can effectively solve the construction problems of the Three Gorges Reservoir area after the impoundment of the water depth and water level changes,and the difficulties of underwater foundation construction and the high cost,so it has broad application prospects.(2)Experimental study on mechanical properties of C30 underwater concrete at early age.In the early stage of conservation,the mechanical properties of underwater concrete increase rapidly.With the increase of age,the growth rate is getting slower and slower.At the end,it tends to be gentle.The first seven days is an important period for the increase of concrete strength.According to the test data,the calculation method of “three strengh and one modulus” of underwater concrete is obtained.On the basis of the test,the uniaxial compression constitutive relation of C30 underwater concrete and the relationship of the interface bond stress-relative slip curve of the concrete filled steel tube is proposed.(3)Combined with the test of underwater concrete stress-strain curve,the integral model of reinforced concrete is established,and the deformation and stress characteristics of the construction platform and the cracking of the bored piles are analyzed.The results show that drilling operation for 5 days of concrete maintenance and hoisting construction of crawler hoisting for 7 days of concrete maintenance have little influence on the integrity and later bearing capacity of bored piles.(4)Based on the analytic hierarchy process and the grey fuzzy theory,the safety risk grade of the construction of the bored piles in the second phase of the Changbin road bank protection retaining wall in Yuzhong district was “medium”.Popularization and application of new deepwater pile foundation construction platform,and the risk grade applied in Wanzhou Xintian operation area was “bigger”.