The Research On Earth Pressure And Reinforced Mechanism In The Active Area Behind Propped Flexible Retaining Walls

Rapid urban developments have resulted in many deep excavations for constructions of high buildings and subways. During the deep excavation, changes in the state of stress in the ground mass around the excavation and subsequent ground losses inevitably induced the deformation of retaining structures, especially in the case of flexible walls. These changes eventually affect the magnitude and distribution of earth pressure behind the walls greatly, which can increase the difficulty and complexity of the design and construction of deep excavations. Therefore, the investigation of earth pressure on retaining walls has become a focus in Geotechnical Engineering.On the last decades, there have been a large number of studies on the subject of earth pressure associated with deep excavation. Hereinto, many researches has investigated the distribution of active earth pressure on the flexible walls using experiments, in-situ tests and numerical simulations, respectively, and drawn a conclusion that the earth pressure has an R-shape distribution. However, these studies haven't been carried on further.In recently years, many new types of wall and support systems have been adopted in deep excavation projects. Though these retaining systems are only the integrations of the old ones, their mechanism hasn't been known exactly. Moreover, there are only two methods to reinforce the constructing retaining structures, the active area reinforcement and the passive area reinforcement. However, the reinforcing mechanism of the former is still unknown, and need more investigations.In order to study the aforementioned problems, the magnitude and distribution of active earth pressure and the reinforcing mechanism in active area behind retaining structures are investigated in detail.Firstly, retaining structures are classified according to their mechanism characteristics. Then pile-anchor, strut retaining and up-down construction are classified into the propped flexible retaining, which are investigated in detail in the paper on their mechanism and deformation.Secondly, the stress field and the displacement field are numerically simulated by using FLAC, and an arching effect coefficient is introduced to evaluate effects of the parameters on the distribution of active earth pressure, which include the soil modulus, the width of walls, the preload of the strut, the soil strength parameter and the inter-friction. Moreover, a general formula to determine the earth pressure behind the retaining walls is obtained by fitting method. And an analytic earth pressure formula for elastoplasticity is also obtained. Further, some advises is put forward to solve the nonlinear earth pressure and the decreasing of bending moment in design.Thirdly, the property of the vertical soil arch behind the retaining wall is also studied in detail, and a rational arch axial equation, which is a part of an ellipse, is put forward too. These studies can provide a determining criterion to ascertain the boundary between the stable area and the relaxed area.Finally, the mechanical characteristic and the deformation of soil and retaining structure for horizontal reinforcement and vertical reinforcement are investigated, respectively. Moreover, an actual project is simulated to confirm the efficiency of the horizontal reinforcement after settling the soil-nail behind the wall.The conclusion in the paper can provide reference for improving the design of excavation, which can save the cost of construction.