Research On Suitability Of Large-Diametre Slurry Shield In Sand And Gravel Formations Of Beijing

In this paper, the adaptability of large-diameter slurry shield to Beijing sand and gravel soils was studied systematically and exhaustively through DEM simulation, theoretical analysis, laboratory test and field measurement. Based on this project, features and influenc factors of tunnel face instability, parameters determination of mud fluid properties, influences of shield tunnelling on neighboring environment, and adaptability of cutterhead were systematically studied, respectively. The main results are as follows:(1)The relationships between micro-parameters of PFC2D and macro-parameters c and ? of sand and gravel soils were obtained by means of PFC2D biaxial numerical tests and soil tri-axial tests indoor. Then the PFC numerical simulations (DEM) were conducted to obtain progressivity variation features of slide and failure in tunnel face and surrounding soils. The evolution laws of displacement field and dynamic relationships between friction coefficient of soils and ground deformation were also obtained. And on this basis, the fundamental principles of stability of tunnel face were stated systematically.(2) Forming fine filter cake on the excavation face is significantly important to maintain stability of the shield tunnel face. Thickness and adhesive strength of the filter cake are the most important factors. Filter cake with certain thickness and adhesive strength on the excavation face is vital to ensure stability of the excavation face. Through numerous slurry tests, based on action principle, the characteristic parameter which is applicable to large-diameter slurry shield to Beijing sand and gravel soils were proposed such as relative density and viscosity. In this paper, the effect and adaptability of3types of slurry were analyzed and evaluated from4aspects, including penetration distance, limit seepage flow, pore-water pressure and mud film impermeability.(3) According to field data, the slurry shield was of fine adaptability to Beijing sand and gravel soils, on the conditions of scientific configuration of cutter head, appropriate slurry parametersand reasonable tunneling parameters. Ground deformation caused by shield tunnelling can meet the safety and control requirements of environmental impact. Based on the field data and theoretical analysis, the relationship between the shield tunneling parameters and ground deformation were established. Moreover, the safety of change tools under compressed air condition and the impact on the surrounding environment were demonstrated.(4) In order to make large-diameter slurry shield has better adaptability to Beijing sand and gravel soils, the configuration of cutter head and cutter tool was designed specially. And a scheme in which disc cutters, ripper, scrape and other tools of different size were configurated rationally and three-dimensionally was put forward. Based on the field data, a comparative analysis about average wear coefficient between single-edged disc cutter and double-edged disc cutter was made, and then the principles of tool replacement during tunneling process for sand and gravel soils were put forward, which contain check inside the chamber under compressed air condition once every100?120m and replace badly worn tools; set a reinforced stop point every230?300m to change cutting tools.