The Mechanics Analysis And Optimized About The Enclosure Structures Of Working Well In Rectangular Pipe Jacking

In recent years, with the continuous development of social economy and theaccelerating urbanization levels, the available land resources are limited. So the utilizationof urban underground space is increasing year by year. The underground space such assubways, underground shopping malls has been great development. The development ofunderground space has been driving the optimization and improvement of foundation pitengineering. The design concept of foundation pit has been gradually by the strengthcontrol into deformation control. In this paper, based on the underpass project of InnerMongolia University of Science and Technology, through theoretical analysis, fieldmonitoring, numerical simulation, and other research methods, the stability anddeformation of the foundation pit, demolition of a part structure are studied.At the sametime, a part the enclosure structure had been optimization design. The main research resultsare as follows:(1) The status at domestic and international research of the foundation were reviewedand summarized. The analysis of monitoring data of retaining structure in practicalengineering, mainly considering the horizontal displacement and vertical displacement ofretaining piles, axial forces of reinforced concrete and steel pipe. It is pointed out that theadvantages of using steel pipe pile in practical engineering.(2) The analysis of excavation process by uing the FLAC3D numerical simulationsoftware set up a76m×86m×36m model of the foundation pit, using the Mohr Coulombmodel in the process of the excavation construction to find the displacement change. Thecontrast of the simulation values and horizontal displacement measured values offoundation pit retaining structure show that the simulated values and measured values areconsistent. And according to the simulate of FLAC3D numerical model, discussed thebreak sequence of retaining piles at foundation pit of pipe jacking construction, theconclusion is the order of a small amount of pile breaking has little influence on stability ofstructure. Meanwhile considering the demolition time of the north and the south side of retaining structure, through the numerical simulation of pipe jacking construction found theinfluence is limited in scope to the north and south. So the removal of retaining piles havelittle impact on the foundation pit. The appropriate time can be chose to dismantling theretaining pile in order to save construction period which can bring economic benefits.(3) It is difficult and takes a long time to remove the portal part of the originalretaining structure of reinforced concrete in the foundation pit. In this paper, optimizeddesign with steel pipe piles to replace part of the retaining structure at the portal. At thesame time we need to design bolts-flanges to connect the demolition and not demolitionpart of the steel pipe piles. So the design of steel pipe pile is a new pile retaining structuretype. This paper describes the steel pipe pile and bolts-flanges connection components,and gives the items that need to pay attention on the steel pipe pile in construction and theconstruction of possible problems about steel pipe pile and simple treatment methods. Atthe same time, the comparison analysis of construction period,cost and other things of thenew type pile and the original piles, it is concluded that the cost of steel pipe piles isslightly higher than that of bored piles but it has advantages in improving thecomprehensive economic benefits.