Discrete element model for performance analysis of cutterhead excavation system of EPB machine

doi:10.1016/j.tust.2013.03.003

Tunnelling and Underground Space Technology

Volume 37, August 2013, Pages 37-44

https://doi.org/10.1016/j.tust.2013.03.003 Get rights and content

Highlights

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The discrete element model of cutterhead system tunneling is presented.
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The performance indicator of the cutterhead system is defined and measured in the DEM model.
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The model can be used to forecast the system performance and optimize the system structure.

Abstract

With the aim of probing for design theory of cutterhead excavation system of earth pressure balance (EPB) machine, the parameters representing the system performance are concluded firstly. Then a 3D model for cutterhead excavation system of EPB machine is presented with the discrete element method (DEM) software PFC^3D, which is capable of simulating the tunneling ground in site, the machine structure and the excavation operation. The performance parameters indicating stability of excavation face, soil discharging rate, cutterhead system torque and cutter wear are measured by running the DEM code. The results obtained with the DEM model are accord with situ data. It indicates that the DEM model is a promising method replacing the field experiment to analyze the influences of the structural parameters on system performances, which are essential for structure optimization design of the cutterhead system of EPB machine.

Introduction

The full face tunnel boring machine (TBM) includes the soft ground TBM and the rock TBM. The soft ground TBM includes the EPB machine and the slurry machine according to different supporting ways of excavation face. Performance prediction of the rock TBM has already been studied. Rostami and Ozdemir, 1993, Burger, 2006, Karlheinz, 2009, Peter, 2009, Abdolreza and Siamak, 2012 and Bilgin et al. (2012) are among the researchers who realized the pioneering works with respect to rock TBM performance. Contrary to rock TBMs, the soft ground TBM performance forecasting is a new science. It is rather difficult in capturing the complex interaction between the pressurized shield drive and the ground. Since the early 20th century, the soft ground TBM cutterhead design has historically been driven by iterative designs based on empirical data, observations over various projects and industry rules of thumb (Glenn and Mustafa, 2011). Nishitake (1987) in Mitsubishi Heavy Industries Ltd., described several types of EPB shields which can cope with large size boulders, and the existing machine is modified to deal with the problem. Dowden and Cass (1991) in Robbins Corp. reviewed the current designs of shielded type machines and their application, and discussed new developments which blended hard and soft ground tunneling technology. Burger (2007) in German Herrenknecht Corp. described the technical points of the cutterhead design of the slurry shield and the EPB shield machine.

Nowadays a lot of scholars try to find out the relations between the tunneling parameters, the soil parameters and the structure parameters of cutterhead system. Wang and Fu (2006) formulated mathematical models with respect to the total thrust, the soil pressure in chamber, the rotation speed of screw conveyor and the advance speed by theoretical analysis, and the formula is validated by in situ measured data. Zhang et al. (2005) proposed mathematical models of the advance speed and the torque of EPB cutterhead respectively. Yang et al. (2006) analyzed the thrust force, the torque of cutterhead and soil pressure in chamber in two different cutterhead opening rates of 30% and 70% by model tests. Shi et al. (2011) introduced an improved torque calculation formula taking account of cutterhead structures and cutting principle of tools. Lambrughi et al. (2012) developed a three-dimensional FEM numerical model of EPB machines simulating the overall process of excavation and construction of a tunnel. The influence on calculated ground displacements is investigated by means of a series of operation parameters analyzes. Manuel and Luis (2005) established a DEM model to study the problem of soil stability at the tunnel face, the thrust and the torque needed to excavate the tunnel. The research works described above give the factors affecting the cutterhead torque, the thrust and ground stability. However, the performance index of the cutterhead excavation system is not definitely proposed from the view of system design.

Recently, Ulrich and Marc (2011) pointed out the key performance indicators for estimating the performance of EPB tunneling based on the evaluation of data from a great number of projects. Glenn and Mustafa (2011) examined how discrete element analysis can be applied to cutterhead performance optimization. This paper establishes a DEM model of the cutterhead excavation system, taking an EPB machine tunneling in Beijing metro construction as prototype. The performance parameters representing the stability of excavation face, the soil discharge rate, the system torque and the cutterhead wear are shown by running the DEM model. Parameters of EPB tunneling are measured in situ to validate the model. The DEM model is an effective tool for performance prediction and design of cutterhead system.

Section snippets

Performance indicators

The cutterhead system of EPB machine is mainly composed of the cutterhead, the soil chamber and the screw conveyor, the function of which is cutting ground, supporting excavation face and discharging soils (Fig. 1). The performance is related to the structure parameters, the operation parameters and the soil parameters. The design of cutterhead system is concerned of the cutterhead structure style, the opening location and size, the tool selection and layout, the arrangement of muddlers in the

DEM model for performance analysis

The DEM model of cutterhead excavation system tried to reproduce the tunneling ground (Fig. 2) from the north station of Jiaomen and the south station in the line 4 of Beijing metro. The ground is composed of rounded pebbles cemented by sand and gravel. The diameters of most pebbles are between 20 mm and 60 mm. The maximum diameter is 180 mm. The content of particles whose diameter is larger than 20 mm is more than 55%. The EPB machine (Fig. 3) constructed by Mitsubishi from Japan was used in the

Performance analysis results and discussion

The DEM model of cutterhead system excavating is shown in Fig. 4. With the advancement of system and the rotation of cutterhead, the soil particles flew into the chamber constantly through the opening in the cutterhead. When the calculation time reached 1200 s, the screw conveyor began to rotate. The chamber and the screw were filled with particles when the calculation time was 1320 s. Then the rotation speed screw conveyor was adjusted to 4 rpm, and the tunneling speed was turned to 30 mm/min. The

Conclusions

Taking an EPB machine tunneling in the 4 line of Beijing metro as prototype, the DEM model of EPB machine excavation was established in PFC^3D software. The model reproduced the excavation ground, the structure and the operation process of the cutterhead system. The performance indicators of the cutterhead system, which were the excavation face stability, the system torque, the cutterhead wear and the soil discharging rate were defined in the DEM model of the chamber system.

In DEM model, the

Acknowledgements

The authors are grateful to the support of the National Natural Science Foundation of China (Study on Dynamic Interaction between Cutterhead of Shield Tunneling Machine and Soils and Design Theory of Cutterhead System, Award No. 51105048).

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Citation Excerpt :
Based on the theory of discrete mechanics, DEM has great advantages in the analysis of problems with large deformations. Recently, DEM has been proven to be a promising tool for analyzing the tunneling process associated with the EPB shield tunneling [20–22,24,26]. The current simulation of the EPB tunneling based on the DEM can be generally divided into two categories based on the model complexity.
This paper presents laboratory tests and high-fidelity numerical simulations to examine the ground failure induced by Earth Pressure Balance (EPB) Shield Tunneling in granular soils. Specifically, we designed and conducted laboratory tests using a reduced-scale EPB Shield Tunnel machine, and built corresponding three-dimensional (3D) discrete-element method (DEM) models to simulate the dynamic excavation process and to gain further understandings of the mechanisms of the ground movement. The study is particularly focused on the combined influences of the cutterhead open ratio and the relative tunnel depth on the ground motions and stress perturbations during the EPB tunneling, which remain understudied in existing studies. The results show that the open ratio of the cutterhead has significant effects on the ground failure in granular soils, especially in cases of relatively shallow tunnels. The larger the open ratio of the cutterhead, the wider the surface and subsurface settlement trough and the greater the soil pressure in the chamber. The pressure distribution in the soil chamber with a larger cutterhead open ratio is significantly more non-linear than that of the case with a smaller cutterhead open ratio. For a given cover-to-diameter ratio (C/D) of the tunnel, the width parameter (k) is generally constant regardless of the depth for the case with a large cutterhead open ratio, especially in the relatively shallow tunnels, while it increases non-linearly with the depth for the case with a small cutterhead open ratio, especially in relatively deep tunnels. Furthermore, soil arching mechanisms are analyzed qualitatively with respect to different cutterhead open ratios and C/Ds. The study demonstrates quantitatively the response of ground surface to the cutterhead open ratios and C/Ds as well as the associated ground failure mechanisms through a combination of laboratory experiments and 3D DEM simulations, providing further insights into the ground behaviors during the dynamic EPB tunneling process.

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Discrete element model for performance analysis of cutterhead excavation system of EPB machine

Highlights

Abstract

Introduction

Section snippets

Performance indicators

DEM model for performance analysis

Performance analysis results and discussion

Conclusions

Acknowledgements

Tunn. Undergr. Space Technol.

Comput. Geotech.

Autom. Constr.

Tunnel Boring Machine (TBM) selection using fuzzy multicriteria decision making methods

Tunn. Undergr. Space Technol.

Shield Construction Technique

The influence of TBM design and machine features on performance and tool wear in rock

Geomech. Tunnelbau