Study On The Regularity Of Surface Settlement Caused By Shield Tunneling In Chengdu Sandy Pebble Stratum

With the rapid development of Chengdu subway construction, the surface settlement caused by shield tunneling has aroused extensive attention in engineering application. The sandy pebble stratum of Chengdu is widely distributed, which has a distinct regional characteristic. Based on spatial distribution regularities and engineering properties of sandy pebble stratum in Chengdu, the research of regularity is carried out in the view of surface settlement lead by the tunneling disturbances of sandy pebble stratum, the results has strong practical implications. This paper based on lots of monitoring data and geological survey data in the west extension of Line 4, analyzed the characteristics of surface settlement caused by shield tunneling. The major work may be summarized as the follows:1. On the basis of collecting and collating many borehole data and investigation data of the west extension of Line 4, and according to the GOCAD tool, this paper built the 3-dimensin geological model for the west extension. At the same time, combined with the investigation about the characteristic of particle size and shape in a typical pit, it carried out comprehensive analysis of spatial distribution regularities of sandy pebble stratum along the subway line;2. Combined with the engineering properties of sandy pebble stratum, tunneling effects and groundwater dynamic balance, it analyzed the settlement mechanism caused by shield tunneling in water-rich sandy pebble stratum;3. According to the water storage capacity and moisture medium characteristics along the subway line (material composition, structure, thickness and spatial distribution, permeability), combined with distribution characteristics of groundwater table and the feature of flow direction, this paper would make the division of geological units along the subway line;4. In this paper, FLAC3D is adopted to simulate the influence of single and double hole tunneling to the lateral and longitudinal settlement, and comparative analyzed the magnitude and range caused by groundwater in the equilibrium state, drainage condition and supplying condition, and got the settlement regularity of sandy pebble stratum under the seepage effect;5. Based on plenty of settlement monitoring statistics of excavation sections in Chengdu subway, making use of the least squared method to regression analyze, coming out the range of width coefficient of settlement troughs K value and volume loss ratio η value in Peck formula, and combined with the real-time monitoring data of Chengdu subway lines, analyze and amend the reliability of the Peck formula’s parameter identification. Meanwhile introduce the weighted settlement model and weighted internal friction angle to normalize the stratum character, then study the influence of stratum character on K and η. Finally, compared the surface settlement rule of double tunnels excavation.