Research On Deformation Characteristics And Application Of Large Diameter Cement Soil Stabilization Piles

In the soft soil foundation pit support project of Guangdong,after the engineer's summary practice,the cemented soil mixing pile is improved and innovated,and a large-diameter cement-spinning jet mixing pile has been produced.Compared with ordinary cement soil mixing pile,the large diameter cement-spinning jet mixing pile has many characteristics include large diameter,high strength,good impermeability and strong ability to cut soil.A new foundation pit supporting structure is formed by pouring a certain length of the reinforced concrete pile in the large diameter cement soil rotary spray mixing pile and combining with the broad pressure roof.The combined support structure has great rigidity and obvious control effect on foundation pit deformation,It can also reduce the use of internal supports and increase the spacing between internal support,at the same time,it has good economic performance.It has been applied in deep foundation pit support in soft soil area of Guangdong,and it has wide application prospects and popularization value.This paper based on the existing research about cement soil composite retaining wall,the composite supporting structure of concrete cast-in-place pile with large diameter cement soil rotary jet mixing pile was studied.The main work carried out the following aspects:(1)According to the characteristics of this composite supporting structure,the difference between the gravity cement soil retaining wall,the mechanism of SMW method and the calculation method are analyzed,and the design and calculation method of this composite supporting system is summarized and discussed.(2)This paper uses the numerical simulation method to analyze the composite retaining structure in foundation pit excavation work under the conditions of the characters.Analysing large diameter soil cement jet mixing piles with different length and strength of core concrete piles with different length and diameter,and large diameter soil cement jet mixing piles relative position of influence factors on the deformation about foundation pit,which bases on the three dimensional "stratigraphic structure" model.The results show that the contribution of the stiffness about the cement-spinning jet mixing pile depends on the core-containing rate of the stiffening pile in the composite pile,when the soil cement jet mixing piles achieve the embedded effect,the effect of increasing the inner core concrete filling pile on controlling the horizontal deformation of the foundation pit is not obvious,It can be done within the appropriate core concrete grouting pile length,and in order to save cost.(3)With reference to the existing crown beam research methods,,the three-dimensional numerical model is established to simulate the excavation of the foundation pit in cantilever support.To investigate the capping plate width,thickness,span change effect on deformation of foundation pit,and analyze the deformation characteristics of the capping plate.The results show that the capping plate can significantly reduce the horizontal displacement of foundation pit,increase the width of foundation pit capping plate displacement control significantly;because deformation of capping plate is more complex,it should increase the amount of reinforcement in the middle of the excavation side and combined pile connections.(4)The above numerical simulation results and calculation methods are applied to the design of the actual foundation pit support engineering.Compared with the original traditional support plan,verifying the superiority of this combined support structure,and calculated by the integral finite element model.The analysis and comparison with the actual engineering monitoring data verify the superiority of the support structure and the rationality of the analysis.