Research On The Composite Mechanism And Bearing Capacity Of Solidified Soil And Pipe Pile

The composite pile with solidified soil and pipe pile is a kind of technology,using rotation tool into holes on the pile location.The soil was cut by the stirring blade or the high pressure slurry,and pile soil and solidifying agent slurry were mixed,which stirred to form a plastic solidified soil.Then high strength prestressed pipe piles adopted auxiliary equipment before the initial solidification of solidified soil were implanted into the plastic solidified soil.After the hardening of solidified soil around tubular pile,the tubular pile and the solidified soil were formed into a whole.The composite pile can give full play to the strength of foundation soil and pile,having the characteristics of a convenient pile,no squeezing soil,no emission,clean environmental protection,high quality and so on.Through uniaxial compression test of solidified soil,ANSYS finite element simulation,the composite mechanism of solidified soil and tubular pile,and the vertical and horizontal static load test of composite pile,the composite mechanism and bearing capacity of solidified soil and pipe pile were studied,and the design method of vertical and horizontal bearing capacity of composite pile was obtained.The main conclusions are as follows:(1)Based on the enhanced hardening mechanism of soft soil,soft soil solidifying agent is preferred.The main factors influencing forsoft soil solidifying agent enhancingand hardeningsilt soil with high water contentare determined by indoor uniaxial compressive strength test and field core strength test.It is concluded that the strength of the solidified soil increases with the increase of the content of the softening agent,and the increasing rate of strength decreases somewhat with the increase of dosage,but the increasing rate of 28d strength is still greater than that of cement.The difference of early strength decreases with the increase of water-cement ratio.When the water-cement ratio is 2.0,the 7d strength of soft soil solidifying agent is slightly lower than that of cement soil.The 28d strength of the solidified soil of the soft soil solidifying agent is 1.52-2.24 times of that of the cement soil.The core strength is 1.56-1.94 times of the cement soil,and it has better solidifying effect for the silty clay with high water content of 41%-51%.(2)The finite element model is established,and the influence of the cross section area of the solidified soil,the thickness ratio of the pipe pile and the length diameter ratio on the vertical and horizontal bearing capacity of the composite pile is analyzed,then the optimal design of the composite pile is realized.It is concluded that the vertical bearing capacity of composite piles can be greatly improved by increasing the cross section area of the solidified soil and the length diameter ratio of the pipe pile.Because the bond strength between the solidified soil and the pipe pile is higher,when the strength of the pipe pile meets the requirements of the ultimate bearing capacity of the composite pile,the vertical bearing capacity of the composite pile is not significant by changing the thickness ratio of the pipe pile.When the length-diameter ratio of the pipe pile is larger than 12,the increase of the length-diameter ratio of the pipe pile will have little effect on the horizontal bearing capacity of the composite pile.Increasing the cross-sectional area of the pipe pile will significantly improve the horizontal bearing capacity of the composite pile,and it is beneficial to the deformation control of composite pile.The thickness of the pipe pile is the same,and reducing the thickness ratio of pipe pile can directly improve the stiffness of composite pile,which increases the ability of the composite pile to resist horizontal load and deformation.When the diameter of pipe pile is definite,and the thickness ratio of pipe pile increases from 0.167 to 0.25,the horizontal bearing capacity of composite pile has little change,but it can reduce the maximum horizontal displacement of pile head properly.(3)The composite mechanism of composite pile under horizontal load is analyzed,and the stiffness of composite pile under different stress conditions is deduced.It is concluded that the contribution of solidified soil to the stiffness of composite piles should be taken into account whether or not the composite piles are in a state of stress.Increasing the pipe pile diameter of the solidified soil and the calculated width between the composite pile and the soil are favorable to the diffusion of the stress,which can significantly improve the horizontal bearing capacity of the composite pile.(4)The composite mechanism,failure type and ultimate bearing capacity of composite pile under vertical load are analyzed.The structural requirements of composite pile are put forward,and the design method of vertical bearing capacity of composite pile is summarized and established.Through vertical static loading test,the vertical bearing capacity of traditional composite pile and conjoined composite pile is tested,and the design method of bearing capacity of composite pile is preliminarily verified.It is concluded that composite piles can replace the same bearing capacity of the cast-in-place pile,thus saving the cost and duration of the pile foundation.(5)The calculation method of the horizontal bearing capacity of the composite pile under the composite stiffness is established.The theoretical calculation results show that the characteristic value of the horizontal bearing capacity of the composite pile is close to the horizontal static load test result,which is 1.77 times of the calculated value of the pile.Comparison test of horizontal bearing capacity between pipe pile and composite pile,the characteristic values and ultimate values of the horizontal bearing capacity of the composite pile are 1.81-2.62 and 2.00-2.25 times of the pipe pile,which further verifies the feasibility of the design theory of the horizontal bearing capacity of composite pile.(6)Through the contrast test of the horizontal bearing capacity between the pipe pile and the composite pile,it is concluded that there are two inflection points in the H-Δ Y0/ΔH curves of composite piles and pipe piles.The slope of the H-ΔY0/ΔH curve of the composite pile before the first inflection point is only about 1/6 of the pipe pile.The slope of the curve between the first inflection point and the second inflection point of the H-Δ Y0/Δ H curve of the pipe pile increases with the increase of the horizontal load,and that composite pile increases first and then decreases with the increase of horizontal load,and the verification law of the stiffness of composite pile under horizontal load is further verified.