Stability Of Retaining Structure And Water Sandy Pebble Stratum Permeability Analysis

One of the prominent problems in the construction of the subway is the pit design and construction which has become the technical difficulties of underground engineering and research focus. The rational design of foundation pit support and construction programs not only guarantee the pit itself security and stability but also control the movement of the pit formation effectively in order to protect the surrounding environment. Therefore, it has become an important research topic of geotechnical engineering field. Based on Changsha City Metro Line provincial government station engineering, this paper systematically studied and summarize the characteristics of the envelope structure security and stability during excavation. The main research contents:(1) Based on the thinkness of provincial government station pit’s sand and cobble layer byond the underground continuous wall can be inserted, therefore the excavation of foundation pit need sleeved injection tube grouting block. Reasonable grouting parameters which obtained through field trials, make use of cement-silicate two-liquid slurry, to form the slurry into a closed waterproof curtain, to reduce the coefficient of permeability of the sand and gravel formations, cement and fill the voids of the soil play a confining effect to achieve impermeability during excavation and reinforcement of the formation, so that the base strength and bearing capacity to improve.(2) According to the subway across the Quaternary loose sand and gravel stratum, underground water make a significance influence to station design and construction of the retaining structure. This paper focus on the influence which pit excavation brings to support structure and military-beam strength, stiffness and stability, anti-floating ability of every bid-section, the northern end of station grouting section anti-permeability ability.(3) Aiming at the large span pit, complex geological condition and the hole of continuous wall easy to collapse’s feature in sand and gravel layer, adopt site Monitoring Measurement means to research the land subsidence of surrounding buildings and pit around, the top level of envelope displacement, vertical displacement and lateral deformation characteristics and laws with the changes in the foundation construction process. Through the feedback which based on monitoring results to achieve on-site construction safety guidance.Practical experience and achievements of this project provide a reference for similar projects, and providing insight into the characteristics of pit excavation under the conditions of the water-rich sand and gravel strata can draw experience.