Research On The Application Of Internal Bracing Pile-anchor Supporting Structure In Deep Foundation Pit Engineering

Under construction,due to the large excavation depth of foundation pit and the close distance between foundation pit boundary line and adjacent existing buildings,the excavation deformation of foundation pit should be strictly limited.A single support form is often difficult to meet the design requirements,and the support structure formed by the combination of two or more support forms is often the best choice.Nowadays,Combination of pile,anchor and brace has been used in a lot of deep foundation pit supporting engineering in practice successfully,For this kind of complex combined foundation pit support,there are many influencing factors,now is the lack of a mature design theory,lead to the deformation of supporting structure theoretical calculated values and measured values tend to have larger error,theoretical research is far cannot satisfy the requirement of engineering practiceThe numerical method can consider various factors in the model,which provides a powerful means to solve such engineering problems.Besides,the principle of minimum potential energy does not consider the intermediate process,but only the change of initial energy,which can simplify many secondary factors.Therefore,based on the numerical analysis and the principle of minimum potential energy,combined with the field monitoring data,this paper studies the supporting structure of supporting piles and anchors.First of all,this paper summarizes the research status of the supporting structure of pile-anchor,and analyzes the merits of this kind of supporting structure contrasts the structure with pile-anchor and pile-brace.Secondly,Second,the shandong chiping 2#car dumper foundation pit monitoring data collection and analysis,using FLAC~3DD numerical model is established,simulated the whole process of excavation and supporting,explored the pile spacing,the support and the first bolt spacing,anchor cable Angle,just support level spacing,the influence of the coefficient of embedded depth of foundation pit deformation,and analyzes the sensitivity of the parameters by orthogonal experiment.Finally,based on the principle of minimum potential energy,the analytical solution of the maximum displacement of the pile roof of the support structure is given,and the main parameters are analyzed,considering the factors such as internal,crown beam and enclosing purlin.The main conclusions are as follows:(1)Through the comparative analysis of the characteristics of the three types of support structures,namely pile-anchor,pile-support and inner-support,it can be seen that the stress of the structure is more reasonable,the construction is convenient and the scope of application is wider.(2)The results of on-site monitoring and numerical simulation show that the horizontal displacement curve of the pile body is in a"Parabola"shape,and the pile maximum displacement appear in the middle and lower position of foundation pit excavation depth.(3)In general,the lateral displacement distribution of the crown beam along the periphery of the foundation pit is uniform,the maximum value of the crown beam no more than the limit value,and the horizontal displacement of the inner support to the crown beam plays an effective constraint role.In addition,the internal support is arranged so that the internal force distribution of the crown beam tends to be uniform,and the mechanical property of the material is fully exerted.(4)In the inner bracing pile-anchor support structure,the main design parameters are listed in order of sensitivity:pile spacing,spacing between internal support and the first bolt,anchor cable inclination,horizontal spacing between internal support,and embedding depth coefficient.(5)The stress mechanism of pile-and-anchor combined support structure is complex and there are many influencing factors.At present,there is no mature and reliable method to determine the maximum horizontal displacement of pile top of this kind of retaining structure.The theoretical calculation method presented in this paper can be used for reference in similar engineering design.