Vertical Bearing Capacity Of Expansive Concrete Pile In Coral Sand

The South China sea is located in the Pacific Ocean also the guard of the Malacca strait.The sea area is vast and rich in products.At the same time,it has important military strategic significance.Coral sand is a special kind of marine sediments with high calcium carbonate content and widely distributed in the South China sea.The existing practice and research showed that the traditional theories and experience of pile foundation in coral sand are not suitable due to the properties of grain crushing,high internal porosity and cementation action.With the development of the "marine power" strategy,it will inevitably encounter coral sand engineering geological problems.A new kind of pile i.e.expansive concrete pile,has gained its popularity recently in civil engineering by adding expansion agent in the concrete to make the pile expand.The volume expansion of the pile will provide additional pressure to increase the bearing capacity and decrease the influence of virtual soil under the pile.In this paper,the study on vertical bearing capacity of expansive concrete pile in coral sand is researched by model test and numerical simulation.Meanwhile,a finite element model is established through the PLAXIS 3D software to discuss the influencing factors of bearing capacity.The main contents and conclusions are as follows:(1)The physical and mechanical parameters of the test materials are obtained by the basic physical and mechanical properties test.Specific experimental scheme including the test conditions,model layout,instrument,process and loading scheme is designed.(2)The vertical compression model test of single pile under 10 working conditions is carried out.The load-settlement curves,shaft axial force,skin friction,lateral soil pressure and load-sharing between end-bearing capacity and skin resistance are measured and analyzed.The vertical bearing characteristics of expansive concrete piles under coral sand foundation is revealed.The ultimate bearing capacity of 71 mm pile adding 25%HCSA and UEA expansion agent is increased by 16.02% and 18.91% respectively.The ultimate bearing capacity of 41 mm pile is increased by 42.42% when the 25% UEA expansive is added.(3)The effects of expansion agent,expansion agent amount and diameter on the bearing capacity of expansive concrete pile under coral sand foundation are obtained by the model test.Under different pile diameters,the expansion agent has less influence on the ultimate bearing capacity.Furthermore,the pile with smaller diameter has the greater effect of increasing the ultimate bearing capacity.(4)A finite element model is also established through the PLAXIS 3D software.The linear expansion rate of the solid element is set to simulate the expansion of the pile.The numerical simulations are well matched with experiments,which proves the rationality of the established model.(5)The effects of linear expansion,diameter and soil properties on the bearing capacity are calculated by numerical simulation.The results show that increasing the linear expansion ratio of the pile is an effective method to improve bearing capacities of the pile.The linear expansion rate of the pile body is more economical between 1.0% and1.2%.Increasing pile diameter has limited effect on improving ultimate bearing capacity.The influence of soil properties is studied,and it is concluded that the elastic modulus has a greater influence on the bearing characteristics.The bearing performance of the pile is less affected by the internal friction angle within the common internal friction angle range of coral sand.