Deformation And Stability Analysis And Engineering Application Of Micro Steel Tube Pile Supporting Structure For Deep Foundation Pit

With the rapid expansion of city,the available space of land is becoming increasingly tight.Foundation pit is getting deeper,harder and larger.Traditional support structures,such as pile anchors,soil nail walls and composite soil nail walls,can no longer meet the complex environment requirements of foundation pit.As a new supporting technology,micro steel tube pile have attracted extensive attention due to their convenient construction,simple process and flexible layout,and their applications in foundation pit engineering increases yearly.However,because the late development of micro steel piles,people have not yet deeply understood its working mechanism and failure modes,and there is relatively little theoretical research.Aiming at the micro steel tube pile supporting structure,this article is based on previous studies: Firstly,the mechanical characteristics at work was explained,and a deformation calculation method considering the prestress of anchors is proposed.Then,a three-dimensional finite element model was established to analyze the deformation,internal force and the soil displacement inside and outside the pit,and compared with the ordinary row pile supporting structures.Finally,explore and consider the influence of foundation piles and jet grouting pile in the pit on the deformation,internal force and stability of the foundation pit.Specific research contents and conclusions are as follows:(1)The working mechanism and mechanical characteristics of the micro steel tube pile supporting structure are explained.Then a double stiffness calculation model considering the prestress of anchor is established.Based on the double stiffness model,a deformation calculation method of micro steel tube pile supporting structure is deduced.The stiffness of anchor,obtained by the calculation method of this paper,is less than that obtained by the current norms,so the size of the designed supporting structure is increased and the actual engineering is more secure.(2)The full-scale three-dimensional model of a practical project establish by using the geotechnical finite element calculation software PLAXIS 3D.On the basis of verifying the rationality of the model through on-site measured data,the internal force,deformation and soil displacement inside and outside the pit under the same excavation conditions of supporting structure with micro steel tube pile and the supporting structures with bored concrete piles were compared and studied The results show that the deformation,internal force and soil displacement inside and outside the pit of micro steel tube pile supporting structure are smaller than the supporting structures with bored concrete piles,which can better save the construction space,speed up the construction period and save the cost under the same conditions.(3)The interaction between foundation pile at the bottom of the pit and supporting structure(micro steel tube pile and ordinary piles)of foundation pit during excavation is analyzed.On the one hand,the foundation pile can improve the overall stability of the foundation pit and reduce the heave of pit bottom,on the other hand,it increases the deformation and internal force of the supporting structures.Excavation of foundation pit will increase the deformation of pile top and axial force of pile.(4)The reinforcement effect of grouting pile in saturated soil on foundation pit supporting structures(micro steel tube pile and ordinary piles)was explored.It is effective to reduce the deformation and internal force of the supporting structures to reinforce the soil between piles and the soil inside the pit by using jet grouting piles in saturated soil area.Increasing the length of the jet grouting piles has little effect on limiting the deformation of the supporting structure,but the effect of increasing the width is obvious.