Optimization Design And Stability Analysis Of Spray Anchor Bracing System For Deep Foundation Pit

Spray anchor bracing is a new technology used in slope supporting of deep foundation pit in recent years. A certain number of anchors were hit into the soil and interacted with the soil, then the strength and overall performance of soil were enhanced. The method is stable and reliable, with the characteristics of low cost, short construction period and a wide range of use. Therefore, it is very necessary to develop the research of design and stability of spray anchor bracing in deep foundation.This paper is derived from foundation pit support project of the block E, the engineering laboratory building in the school. The finite difference software, FLAC3 D, was used to analyze the impact of the structural parameters of spray anchor bracing on the stability of the foundation pit in the project. Besides, the influence of water content variations and vibration load generated from the work of concrete pumping on the deformation of foundation pit were also studied. The main contents are as following.1) According to the parameters of the actual conditions, the soil deformations during the stratified excavation of foundation pit were analyzed through the software FLAC3 D. The results showed that the horizontal displacement increases gradually with the excavations, while the increase rate decreased constantly. The deformation displacements of foundation pit were controlled effectively by the anchoring effects of the spray anchor bracing in the process of excavation.2) The influences of anchor length, vertical spacing and inclination on the deformation of foundation pit were analyzed through the software FLAC3 D. The results showed that the horizontal displacement and surface subsidence of foundation pit wall showed a decreasing tendency, with the increasing of anchor length, especially the length of anchorage segment length. The reduction of the vertical spacing of anchor and the increase of the inclination angle of anchor were able to limit the displacements of the excavation soil and raise the reinforcement ability of anchor, which enhanced the integrity of soil.3)The relation curve between water content changes and deformation of foundation pit was obtained through the simulation analysis of water content variations during the construction. The results showed that the deformation displacement becomes larger with the increase of water content at the same depth position; the deformation displacement becomes larger with the increase of excavation depth with the same water content.4)The vibration loads with different calculation periods were applied to the model. The changes of displacement of foundation pit under the dfferent calculation periods were analyzed. The displacements increased with the increasing of calculation periods, and the deformation was the biggest near the edge loads in the foundation pit, while it was almost unchanged in the middle. At the edges of foundation pit, the changes of displacements were more obvious in the 10 previous calculation periods, and the displacements were also increased in the 10 later calculation periods, while the increasing rate began to decrease, which means the deformation of foundation pit tended to smooth in the late.