Earth Pressure Balance Shield Tunneling Research Articles

Assessment of ground surface displacements induced by an earth pressure balance shield tunneling using partial least squares regression

This paper presents a methodology to link the ground surface displacements to a tunnel boring machine (TBM) operation parameters. The approach consists at first in the exploration and description of the TBM operation parameters, recorded during the construction of the Toulouse (France) subway line B tunnel, using principal component analysis and agglomerative hierarchical clustering (AHC). Then, partial least squares (PLS) regression models were developed for the prediction of the displacements for the two groups of observations, identified by the AHC (pure settlements and heave at the center), as a function of the ten selected TBM operation parameters and the geometry parameter (X 2/H 2). The developed models take into account the nonlinear relationship between displacements and the operation parameters and the collinearity that exists in the parameters. In addition, the PLS regression allows identifying the parameters that affect the displacement of each group. The comparison of the predicted displacements with the measurements for the validation samples of the two groups shows good agreement.

Research on Chamber Earth Pressure of EPB Shield Considering Soil Arching Effect

Chamber earth pressure is one of the significant parameters during the Earth Pressure Balance (EPB) shield construction processing. The soil arching effect is existence when the tunnel depth is enough. It is significant to consider the influence of arching effect to analyze the pressure in soil chamber in shield tunneling. In this paper, the influence of arching effect is considered to calculate the chamber earth pressure. Firstly, the soil is supposed as loose media, and the necessary buried depth of producing arching affects is deduced according to the loose media theory. Then, based on the characteristic of proper arching axis, the equation and the height of proper arch are obtained. At last, the calculation formula of minimum chamber earth pressure of EPB shield tunnel is deduced which can consider the effect of arching effect.

Environmental Effect and Control of Large Diameter EPB Shield Tunneling below an Operating Airport

AbstractIn this paper, a super-large diameter earth pressure balance (EPB) shield tunnel crossing below an operating airport in a soft soil region is introduced to investigate the environmental effect of EPB shield tunneling. The new tunnel with a length of 1,862.7 m was constructed using the EPB shield machine with a diameter of 14.27 m. Field tests of 100 tunnel segments tunneling were conducted prior to the construction of the airport area. The distribution of pore water pressure and soil pressure on the excavation surface of the super-large diameter EPB shield and its relationship with the construction parameters are studied. In addition, the influence of the shield construction parameters on the ground movements is investigated by monitoring the surface settlement. The construction control criteria of EPB shield tunneling under the airport is then recommended, including the chamber earth pressure setting, synchronous grouting, advance speed, and stopping excavation. Application and practice show that...

Soil conditioning for EPB shield tunnelling

The use of conditioning agents that change the mechanical and hydraulic behavior of a cohesionless soil into an impervious and plastic paste is the key point for the correct management of EPB (Earth Pressure Balance) shield tunneling. The design of soil conditioning sets and the choice of the best products to be used require special laboratory tests. These tests should be carried out already at the design stage to allow to check if the needed results can be achieved in the soil to be excavated. In the paper an overview of the different type of laboratory tests that can be used on cohesionless soils are presented and the most important results that can be obtained are discussed.

Earth pressure balance tunnelling in rock masses: Laboratory feasibility study of the conditioning process

Earth pressure balance (EPB) shield tunnelling is considered to be an effective tunnelling method when surface settlements must be avoided by controlling face stability and underground water inflow. EPB technology is applied increasingly to the conditioning of rock masses in which the presence of polluting material is foreseen and must be controlled, or when explosive gases from the rock mass must be prevented from entering in the machine. The use of an EPB machine in ‘closed mode’ can prevent the dispersion of dangerous materials in the underground environment. This study was performed to evaluate the feasibility of using EPB technology in rock masses and the effectiveness of this tunnelling process in terms of soil conditioning, conditioned soil permeability, pressure transmission on the tunnel face, and the ability to extract the material with a screw conveyor. The research was developed with a set of laboratory tests carried out on three different types of rock masses where tunnelling with EPB machines are planned to be constructed in Italy but the results can be easily applied to similar rock mass types. The tests have been carried out both with slump tests and with a specially constructed screw conveyor extraction device. In the paper the most important results are presented and discussed.

Modeling and analysis of thrust force for EPB shield tunneling machine

Abstract Thrust force is an important parameter for the design and operation of earth pressure balance (EPB) shield tunneling machine. The analysis of in-situ data indicates that the conventional thrust force estimation model based on an empirical equation gives rather rough result. In order to reduce uncertainties, composition analysis and corresponding calculation of thrust force are proposed. Laboratory test with a Φ1.8 m EPB shield tunneling machine and calculation result of the new model have been compared. The new model has been improved step by step based on experimental result as well as the further analysis of the working principle of shield excavation. The relative error between the experimental thrust force and the calculation result with the final model is reduced to 3% at the smooth stage and 4% at the trembling stage. The influences of cutting ratio, hatch ratio and equivalent earth pressure on the total thrust force have been investigated.

A new calculation model of cutterhead torque and investigation of its influencing factors

Cutterhead torque is a crucial parameter for the design and operation of earth pressure balance (EPB) shield tunneling machine. However, the traditional calculation models of cutterhead torque are too rough or exist gross errors under variable geological conditions. In order to improve the precision of the calculation model of cutterhead torque, dynamic operation parameters are considered and a new model is proposed. Experiment is carried out on a Φ1.8 m shield machine test rig and the calculating result with the new model is compared with the experimental data to verify the validity of the new model. The relative error of the new model is as low as 4% at smooth stage and is reduced to 5% at the end of trembling stage. Based on the results of the new model and the test data obtained from the Φ1.8 m test rig and the construction site, the inner relationships between several operation parameters and cutterhead torque are investigated and some quantitative conclusions are obtained.

Online Fault Prediction for EPB Shield Tunneling Based on Neural Network

For the complex earth conditions and uncertain factors, the earth pressure balance (EPB) shield tunneling is a complicated and high-risk process. There would cause some faults, such as earth caking, soil occluding in the capsule, water spewing, surface settlement. To avoid them, this paper applies artificial neural network (ANN) to predict the common shielding faults. The neural network is trained by several samples about the tunnel boring machine’s (TBM) parameters, and then it will have self-learning to identify the fault. With the parallel computing ability, the network could detect and predict abnormal behaviors online. This paper includes three parts, firstly, the introduction of EPB, and four usual blockings; and then the principle of BP neural network is present, for the defect of BP algorithm, two kinds of improved BP algorithms are applied in the network; finally, an simulation is given to illustrate the prediction.

Online Fault Prediction for EPB Shield Tunneling Based on Neural Network

For the complex earth conditions and uncertain factors, the earth pressure balance (EPB) shield tunneling is a complicated and high-risk process. There would cause some faults, such as earth caking, soil occluding in the capsule, water spewing, surface settlement. To avoid them, this paper applies artificial neural network (ANN) to predict the common shielding faults. The neural network is trained by several samples about the tunnel boring machine’s (TBM) parameters, and then it will have self-learning to identify the fault. With the parallel computing ability, the network could detect and predict abnormal behaviors online. This paper includes three parts, firstly, the introduction of EPB, and four usual blockings; and then the principle of BP neural network is present, for the defect of BP algorithm, two kinds of improved BP algorithms are applied in the network; finally, an simulation is given to illustrate the prediction.

Tunnel face stability analysis based on pressure field surface's normal vector for earth pressure balanced shield

Under extremely unpredictable geological and hydrogeological conditions the tunnel face instability would occur during the earth-pressure-balance (EPB) shield working. It is thus significant to judge the face stability online based on the pressure sensors set inside the shield chamber. In this paper, a new numerical method based on the geometrical characteristics of the pressure field surface in work chamber for analysing the tunnel face stability of the EPB shield, is presented. The normal vector of the pressure field surface is derived by the discrete derivatives calculated from the signals sampled through the pressure sensors, by which real-time analysis can be made on the change situation of active and passive earth pressures for the ground in front of the tunnel face. This mechanism provides the basis for ensuring the tunnelling safety and automatic controlling of the EPB shield tunnel process. Finally, a simulation is given to demonstrate feasibility of the proposed method.

Field performance of underground structures during shield tunnel construction

This paper presents a case history of an earth pressure balance (EPB) shield tunneling constructed in a close distance near constructed underground structures in soft deposit of Shanghai. In order to protect existing underground structures, field observation was carried out, including reinforcement stress of interior structure and lateral displacement of the diaphragm wall. Throughout the shield tunneling construction, various countermeasures were adopted based on field observation feedback to minimize adverse environmental influences. The maximum cumulative lateral displacement of the diaphragm wall is about 11mm. The maximum stress of reinforcement is 18.6MPa, much less than the design value of steel tensile strength. These results and countermeasures are useful for engineers and technicians to select serviceable machine operation parameters and reduce environmental impacts during shield tunneling construction.

Study on Soil Improvement Technology of EPBS Tunnel

The tunnel construction often encounters the problem of adaptability of sand-gravel formation and earth pressure balance shield (EPBS) construction, which has brought new technical problems and challenges to those who are participating in the construction project. In order to ensure the normal operation of shield construction, the soil must have ideal plasticity and liquidity, and low permeability to intercept groundwater. Therefore, we must adopt the soil improvement techniques ,namely, to inject the modified materials (mud, foam, polymer, etc.) into excavation face and earth pressure tank(if necessary, to the screw conveyor) to ensure the stability of excavation face, achieve EPBS driving, and help to reduce mechanical load, reduce land subsidence, and increase driving speed at the same time. The ground improvement technique is an important part of the EPBS method. The quality of the application of soil improvement technology is very important to maintain the stability of excavation face and the screw dump device’s dumping smoothly. It also has a significant impact on the shield machine’s functioning safely,economically and efficiently.

3D Finite Element Simulation on During Shield Tunneling

Based on the comprehensive analysis on the primary components of ground movement associated with earth pressure balance (EPB) shield tunneling, a three-dimensional nonlinear finite element model for simulating EPB shield tunneling is proposed. The proposed modeling techniques are applied to simulate a tunneling project. The distributions of soil displacement on the ground surface associated with the advance-ment process of shield tunnel are analyzed. According to the comparisons of numerical results with field measurements, the proposed numerical procedure is found to be an effective approach for predicting the deformation dun to shield tunneling. The further analysis shows that the computed results of the small-strain constitutive model are more reasonable, and the small-strain mechanical behaviors of soils should be taken into account

Determination of the cutterhead torque for EPB shield tunneling machine

Cutterhead torque is an important parameter for the design and operation of earth pressure balance (EPB) shields. Based on the analysis of several completed project cases from job sites, the conventional torque determination model based on experimentation proves rough enough to be improved. Composition and corresponding calculation method of cutterhead torque are presented, taking into account of cutterhead structure, cutting principle and the interaction between cutterhead and soil. Considering a Φ1.8 m EPB test machine in the lab, theoretical calculation following the improved model and test are carried out with three typical types of soils. Calculation and test results indicate that the cutterhead torque varies with geological conditions apparently, and the opening ratio of the cutterhead as well as earth pressure turns out to be the two most important factors in determining the cutterhead torque. The test results also show that the torque calculation formula for EPB shield tunneling can reasonably predict the excavation torque required by the cutterhead in clay soil tunneling, but for cohesionless tunneling, soil conditioning reduces the amount of torque necessary.

Force transmission characteristics for the non-equidistant arrangement thrust systems of shield tunneling machines

Earth Pressure Balance shield tunneling has been successfully adopted for urban tunneling and has resulted in increases in working speed, savings of man-hours and improved safety. Based on the ellipse eccentricity, the ellipse matrix equation for non-equidistant systems has been constructed. Through the analysis of the matrix, the characteristics of force ellipse eccentricity were investigated in detail. The distinction from the equidistant system was studied by applying the force ellipse to the thrust systems of shield machines in engineering applications. It provides a new arrangement for the thrust system hydraulic cylinders, under large change-of-direction forces or uneven geological bodies, which may prevent the segments from cracking due to an over-offset load.

Optimal earth pressure balance control for shield tunneling based on LS-SVM and PSO

To avoid ground deformation in the process of earth pressure balance (EPB) shield tunneling, it is necessary to keep the earth pressure balance on excavation face. However, at present the earth pressure control depends mainly on operation experiences which is hysteretic and could result in slow response to the change of earth pressure. To solve these problem, a predictive control strategy for earth pressure balance during excavation is proposed in this paper, where an earth pressure prediction model taking advance speed and screw conveyor speed as the control parameters is established by means of least squares support vector machine (LS-SVM). Further, by minimizing the difference between the predicted earth pressure and the desired one, an optimization model of the control parameters is established, and solved by the particle swarm optimization (PSO) algorithm. Therefore, an optimal EPB control scheme for shield tunneling automatically is presented here. The simulation results demonstrate that the method presented in this paper is very effective to control earth pressure balance.

Laboratory model tests and field investigations of EPB shield machine tunnelling in soft ground in Shanghai

In the last decades, many studies have been presented by different scholars on the environmental problems induced by the shield tunnelling in soft ground. But it mainly concentrated on ground surface settlement, tunnel surface stability and the influence to existing structures. Among them, little attention was paid to soil disturbance caused by the mismatch of machine’s operation parameters. In order to reveal this inherent relation, a series of laboratory model tests were carried out in the 1/16 scale for a field tunnel in practice where the tunnel had 6.4 m diameter. The tests to simulate earth pressure balance (EPB) shield tunnelling in soft ground were conducted with a microshield machine (0.4 m diameter). Measurements were carried out simultaneously in each test for total jack thrust force, cutting torque, chamber pressure, mucking ratio, ground surface displacement, and earth pressure. Based on the analysis of test results under different overburden ratio, cutterhead aperture ratio and screw rotation speed, the relationships between machine’s operation parameters themselves and its influence on disturbance to surrounding soil mass were discovered. Such discoveries were also verified by the field investigations. These results are useful for engineers and technicians to select suitable and serviceable machine operation parameters and reduce environmental influence at all stages of tunnel construction.

A procedure of parameter inversion for a nonlinear constitutive model of soils with shield tunneling

The identification of the parameters of a nonlinear constitutive model of soil mass is based on an inverse analysis procedure, which consists of minimizing the objective function representing the difference between the experimental data and the calculated data of the mechanical model. A gradient-based optimization algorithm is developed for estimating model parameters of soils in earth pressure balance (EPB) shield tunneling. The parameter values of the nonlinear constitutive model are searched for by using the Levenberg–Marquardt approximation which can provide fast convergence. The parameter identification results illustrate that the proposed parameter inversion procedure has not only higher computing efficiency but also better identification accuracy. The results from the model are compared with simulated observations. The models are found to have good predictive ability and are expected to be very useful for estimating model parameters for soils in EPB shield tunneling.

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

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.

A 3D finite element simulation of a shield tunnel in weathered Singapore Bukit Timah Granite

Both two- and three-dimensional finite element analyses of an Earth Pressure Balance (EPB) shield tunnel are carried out. For the back-analyses the contract T-06 (Queensway Tunnel) of the Deep Tunnel Sewerage System, in Singapore is considered. Soil parameters from laboratory tests are used and the results are compared to measurements from site. For the two-dimensional analyses a tunnel contraction approach is applied and for the three-dimensional analyses a step-by-step contraction procedure for shield tunnels is proposed in this paper. To obtain good results of numerical analyses it is important to understand the material behaviour of the soil, which implies to choose an appropriate material model. In this paper the non-linear behaviour of weathered Bukit Timah Granite is modelled realistically using an advanced soil model. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.