Experimental Methods to Assess the Effectiveness of Soil Conditioning with Foam in Fully Weathered Granite

Abstract

The application range of the earth pressure balance (EPB) shield has been expanded due to advances in optimization methods, one of which is the application of foam conditioning. This method is widely used in EPB tunnelling owing to its strong applicability in different hydrological and geological conditions. When applying the foam conditioning method under different circumstances, it is necessary to optimize the conditioning parameters. Therefore, it is necessary to propose a test procedure for evaluating foam properties and the conditioning effect. This paper proposes a procedure to assess foaming agents by the mixing test and microscopic observation of the foam and a procedure that combines the slump test, compression test, and shear test to assess the foam-conditioned soil and determine the optimal parameters of conditioning. The test method is introduced and performed on fully weathered granite from Guangzhou Metro Line 21. The test results demonstrate that the foam injection ratio and pressure and type of the foaming agent all influence the performance of the conditioned soil. Moreover, the suggested conditioning scheme is proposed, and the application of the scheme can improve the tunnelling efficiency.

Application Ranges of EPB Shield TBM in Weathered Granite Soil: A Laboratory Scale Study

“…Budach [3] proposed a compressibility value of 1.9%/0.5 bar or above for conditioned soil so that the face support pressure will be applied uniformly to the tunnel face in the working chamber and excavated materials will be efficiently extracted from the chamber through screw conveyors. In addition, many other studies were conducted recently, either to find optimal soil conditioning parameters or to assess the effectiveness of soil conditioning and/or EPB TBM performance [7][8][9].…”

Soil conditioning in EPB shield tunnelling – An overview of laboratory tests

“…The optimal FIR value has to be determined through specific laboratory tests [1]. Information on the properties of the foam (mainly the bubble size and its stability in time) can be found in [2] [3] [4] [5]. Mooney et al [2] [3], following previous researches of Bezuijen et al [6], took into account the effect of the pressure in the chamber, showing that an increase of the pressure reduces both FER and FIR.…”