Experimental Study Of Soil Conditioning For Earth Pressure Balance Shield In Argillaceous Siltstone Stratum And Its Application

Abstract:In the process of the excavation of Earth Pressure Balance(EPB) shield, in order to achieve the goal of excavating successfully, reducing disturbance, supporting the stability of tunnel face and potential problems, the condition of the soil that has excavated from tunnel face need to be improved. Based on the fifth bid EPB section of Metro Line1, the issue of soil conditioning that EPB shield excavates across two types of layers-argillaceous siltstone stratum and the layer that contain argillaceous siltstone and gravel--have discussed by means of site investigation, laboratory experiment, application verification and so on. The main contents of this thesis are:(1) Based on the geological and hydrological condition of this project, those problems of clogging and spewing and other problems relate to soil conditioning confirm to be happening through mineral composition analyzing, determination of liquid and plastic limits of argillaceous siltstone in this site, site investigation of the soil excavated, sieve analysis test of gravel layers and other tests.(2) In order to address the potential problems for soil conditioning, a test scheme has proposed so as to obtain soil conditioning parameters for EPB shield excavation. The foaming agent determines to be applied based on the mechanism of soil conditioning. Furthermore, two kinds of devices have been designed for identifying the performance of foaming agent. After all the parameters of four kinds of typical soil have defined, the slump test has been conducted to obtain the conditioning parameters. Meanwhile, the moisture content and optimal FIR for soil conditioning have determined.(3) Considering the problem of a relatively high range of FIR value for soil conditioning, the consumption of foaming agent has been optimized based on the result of laboratory test and the influencing factors for the condition of soil.(4) Based on the field condition, designing and construction factors of subway tunnel, a Calculation formula has been deduced when laboratory result applying for excavation. For verifying applicability of the new laboratory scheme, the soil from shield machine has been sampled and the soil conditioning parameters have also been statistical analyzed. Those practices have strongly proved that applying the new laboratory scheme for guiding field construction in terms of solving the problems of clogging in argillaceous siltstone stratum and spewing in ground of upper-soft and lower-hard. In addition, some methods and precautionary measures have been proposed in the process of soil conditioning practices.