Research On Foundation Treatment Of Site Formation Engineering Under Complex Environment

With the vigorous development of urbanization,it is facing the pressure of the concentrated release of demand for construction land.In order to increase the supply of construction land,China has carried out large-scale various forms of "Site Formation" activities,and these projects often encounter foundation treatment problems under complex environmental conditions.In this paper,based on the combination of theoretical analysis,numerical simulation and engineering practice,combined with the Site Formation Project of Pukou Development Zone in Nanjing,the concept,types and characteristics of "Site Formation" under complex environmental conditions,the control indexes and standard,the selection and application of foundation treatment methods,as well as the design calculation and engineering practice of riprap combined with dynamic compaction,which is the main treatment method in site formation projects,are analyzed and studied in five aspects.The main research results are as follows:(1)Based on the analysis of a large number of engineering examples,the concept of "Site Formation" is defined.The site formation engineering is divided into three types: sea reclamation engineering,large area undesirable foundation reconstruction and land reclamation by cutting mountains,and their characteristics are summarized.It is proposed that the site elevation,foundation bearing capacity and settlement are the control indexes for "Site Formation",and the way to determine them is defined.The characteristics of foundation treatment in site formation engineering are analyzed and summarized,and the determinant process of foundation treatment method is worked out.The implementation process of site formation engineering is put forward to guide engineering practice.(2)For riprap combined with dynamic compaction,which is the main treatment method in site formation projects,through the theoretical analysis,the mechanism of reinforcement,the effective extrusion depth,the shape of the reinforced section and the design calculation are studied.The main reinforcement mechanism is the replacement of riprap,dynamic displacement and compaction.The height correction formula and the total backfill height formula of riprap combined with dynamic compaction are put forward.It is presumed that the shape of the filling section under the action of riprap combined with dynamic compaction.(3)For riprap combined with dynamic compaction in site formation projects,the finite element numerical simulation method is used to analyze the deformation,stress and strain relation,the shape of reinforced section,the effective extrusion depth and the development of the plastic zone.It is concluded that the bottom of the filling body will form a "flat pan bottom" shape.The maximum depth of the filling body into the silt is 1.622 m,and the maximum height of the silt is 0.671 m.The settlement of the center point on the top of the filling body is 1.003 m,which forms a ramming pit similar to the "dynamic compaction replacement".It also verifies the rationality of the formula proposed in this paper for the relationship between the height of filling and the depth of subsidence.(4)Combined with the Site Formation Project of Pukou Development Zone in Nanjing,the application of site formation concept in engineering practice is analyzed.According to the site conditions,the design of riprap combined with dynamic compaction is carried out.