Discrete element simulation of mechanical characteristic of conditioned sands in earth pressure balance shield tunneling

Abstract

The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sands were reproduced and the slump test and the direct shear test of the conditioned sands were implemented. A DEM equivalent model that can simulate the macro mechanical characteristic of the conditioned sands was proposed, and the corresponding numerical models of the slump test and the shear test were established. By selecting proper DEM model parameters, the errors of the slump values between the simulation results and the test results are in the range of 10.3%−14.3%, and the error of the curves between the shear displacement and the shear stress calculated with the DEM simulation is 4.68%−16.5% compared with that of the laboratory direct shear test. This illustrates that the proposed DEM equivalent model can approximately simulate the mechanical characteristics of the conditioned sands, which provides the basis for further simulation of the interaction between the conditioned soil and the chamber pressure system of the EPB machine.

Notice of Retraction: Discrete element model of conditioned soil for EPB tunneling

“…At this time the slump value is recorded 811 by measuring the distance between the highest particle position of the assembly and the initial height of the assembly. The detailed simulation process sees in literature [7]. The model parameters are listed in Tab.…”

Influence of Shield Attitude Change on Shield–Soil Interaction

“…Due to the uncertainty of load and stratum during the excavation process, the shield cannot always be consistent with the theoretical design axis [1][2][3][4]. The automatic control system used to control the shield attitude is based on existing engineering experience and not supported by appropriate theories [5]. Therefore, how to properly control the advance load is one of the main concerns in the construction of shield tunnels.…”

Experimental investigation on viscoplastic parameters of conditioned sands in earth pressure balance shield tunneling

“…However, natural soils do not usually have ideal properties (e.g., low inner friction, good plastic flow characteristics, low penetrability, and compressibility [1,2]) when excavated, especially, under unfavorable geological conditions, (e.g., sand ground). To improve the operation of EPB shield machines by modifying the properties of the excavated soils, conditioning agents such as foams, bentonite slurry, and polymers should be injected ahead of the cutterhead, into the working chamber, and along the screw conveyor, to mix with the original soil during the excavating process [3].…”

“…Most previously reported studies on the plastic flow characteristics of conditioned soil are based on the slump tests [1,[12][13][14][15][16][17] or the scale models for EPB excavation systems [2,15,[20][21][22][23][24].…”

“…Furthermore, a laboratory device that simulates the extraction of the conditioned soil from a pressurized tank with a screw conveyor has been used by several authors to study the plastic flow characteristics of the conditioned soil (Merritt and Mair [2], Vinai et al [15], Bezuijen and Schaminee [20,21], Yoshikawa [22], Mair et al [23], Peila et al [24]). This method is able to check the ability of soil to control the pressure both in the bulk chamber and along the screw conveyor.…”