EPB Shield Research Articles

Surface settlement induced by frictional force of epb shield tunneling in sandy gravels.

The excavation of Earth Pressure Balance (EPB) shield can be divided into two distinct stages, i.e. advancing and lining installation. The frictional force applied on surrounding soils reverses at these two stages, which is harmful to the settlement control. Based on Mindlin's method, a new model of surface settlement is derived to involve the reversed friction. A closed form formula is then obtained for the major type of metro tunnels. Main operational parameters are also used as input of the formula. Numerous operational data and measured settlements are collected from EPB tunnels of Chengdu Metro, Line 7. The proposed formula is validated against these field data in sandy gravels. It is shown that the new formula gives reasonable prediction of surface settlement along the tunnel sections. The accuracy of new formula is significantly higher than that of Peck's formula. This study provides a new vision in settlement control of EPB shield tunneling. The increase of chamber pressure will induce higher negative friction during the lining installation. Therefore, surface settlement of EPB tunneling cannot be controlled by just increasing chamber pressure. A balanced relationship between the chamber pressure and the thrust should be maintained instead.

Active learning-based research of foaming agent for EPB shield soil conditioning in gravel stratum

Injecting soil conditioner into the soil during EPB shield construction is crucial for soil enhancement. Foam agent consumption is common but developing their composition and qualities is time-consuming. Hence, there is an urgent need for a novel approach to material design. This study presents the development of an active learning-based model for foam agents to enhance soil conditioning in gravel strata during EPB shield operations. Foaming volume and half-lift time were forecasted using six machine learning algorithms. The Extra Tree Regression (ETR) model was the most effective for volume prediction, while CatBoost Integration (CB) model performed best for time prediction. The new foam has a half-life of 945 s and the Foam Expansion Ratio (FER) of 21, suitable for EPB shield soil conditioning. The results of slump value and shear strength experiments show a positive correlation between soil slump value, shear strength, and an increase in Foam Inject Ratio (FIR).

Predicting Maximum Settlement Induced by EPB Shield Tunneling Through Image Processing and an Intelligent Approach

Predicting Maximum Settlement Induced by EPB Shield Tunneling Through Image Processing and an Intelligent Approach

Reliability Analysis of Hinged Hydraulic System of Remanufactured EPB Shield Machine

Abstract To verify the reliability of the Earth Pressure Balance (EPB shield machine) hinged system, firstly, this paper analyses the reliability of the remanufactured EPB shield machine hinged system and then aims at the problem of the high failure rate of the hinged system in EPB shield machine. A fault tree model was established, and the qualitative and quantitative analysis of the fault tree was carried out. Finally, it is determined that the main cause of the oil cylinder malfunction in the hinged system is the insufficient pressure caused by the malfunction of the solenoid valve’s directional switching.

Research on Prediction of EPB Shield Tunneling Parameters Based on LGBM

At present, the determination of tunnel parameters mainly rely on engineering experience and human judgment, which leads to the subjective decision of parameters and an increased construction risk. Machine learning algorithms could provide an objective theoretical basis for tunnel parameter decision making. However, due to the limitations of a machine learning model’s performance and parameter selection methods, the prediction model had poor prediction results and low reliability for parameter research. To solve the above problems, based on a large number of construction parameters of a composite section subway in Shenzhen, this paper combined dimensionality reduction data with service analysis to optimize the selection process of shield tunneling parameters, and determined the total propulsion force, cutter head torque, cutter head speed, and advance rate as key tunneling parameters. Based on an LGBM algorithm and Bayesian optimization, the prediction model of key tunneling parameters of an earth pressure balance shield was established. The results showed that the average error of the LGBM model on the test set was 8.18%, the average error of the cutter head torque was 13.93%, the average error of the cutter head speed was 3.16%, and the average error of advance rate was 13.35%. Compared with the RF model, the prediction effect and the generalization on the test set were better. Therefore, an LGBM algorithm could be used as an effective prediction method for tunneling parameters in tunnel construction and provide guidance for the setting of tunneling parameters.

A method for real-time identification of muck flow state inside EPB shield chambers in fine-grained soils

This study aims to evaluate the effectiveness of the newly developed shield test device (VMS) by Tongji University in Shanghai for determining the muck state inside EPB shield chambers in fine-grained soils. Muck blockage inside shield chambers frequently results in significant stratum deformation and excessive damage to these machines. The engineering community requires real-time and effective monitoring technology to assess the muck flow state inside EPB shield chambers. Three motion modes of the muck composed of fine-grained soil near the partition have been identified: flow around the central axis, overall static and local adhesion. These modes correspond to the three characteristics of shear plate torque near the shield partition: the periodic fluctuation, the three-stage change of ‘rise-fall-stability’, and a noticeable amplitude difference at the top and lower sides of the chamber. Finally, a preliminarily validated wireless signalling-type shear plate device that can be assembled on the field shield and an actual measurement method was further developed to determine the muck state inside the shield chamber in real-time.

Soil Conditioning for EPB Shield Tunneling in Coastal Silty Clay Strata: Laboratory Research and Field Application

Soil Conditioning for EPB Shield Tunneling in Coastal Silty Clay Strata: Laboratory Research and Field Application

Mechanism analysis of foam penetration in EPB shield tunnelling with a focus on FER and soil particle size

Parameters of foam penetration in earth pressure balance (EPB) shield tunnelling, such as permeability coefficients and penetration distances, significantly impact tunnel face stability. However, existing studies have faced inaccuracies in analysing these parameters due to imitations in experimental methods. This study addresses this issue by employing enhanced methods for a more precise analysis of foam penetration. Experiments involving three distinct sand types (coarse, medium, and fine) and three foam expansion ratios (FER) (10, 15, and 20) are conducted using a modified model test setup. Benefiting from a novel computer vision-based method, the model test outcomes unveil two distinct foam penetration paths: liquid migration (Lw) and bubble migration (Lf). Three penetration phases — namely, injection, blockage & drainage, and breakage — are identified based on Lw and Lf variations. The initial “injection” phase conforms to Darcy's law and is amenable to mathematical description. The foam with FER of 15 has the maximum viscosity and, hence the Lf and permeability in the penetration tests with FER of 15 are the lowest in the same sand. The bubble size distribution of foam with different FER shows minor differences. Nevertheless, the characteristics of foam penetration vary due to the distinct particle size distribution (PSD) of different sands. Foam penetration creates low-permeability layers in both medium and fine sands due to the larger bubble size of the foam compared to the estimated pore sizes of medium and fine sands. While the coarse sand results in a different situation due to its large pore size. The distinctive characteristics of foam penetration in different sand strata are notably shaped by FER, PSD, and pore size distributions. These insights shed light on the complex interactions during foam penetration at the tunnel face, contributing valuable knowledge to EPB shield tunnelling practices.

Study on Numerical Simulation of Surrounding Rock Structure Safety of Urban Underwater Shield Tunnel: A Case in Chongqing

Based on the engineering background of shield construction of a subway section in Chongqing, which needs to pass through a park and there is a lake inside this park, this paper adopts theoretical analysis methods and numerical simulation calculation methods to explore the distribution law of the seepage field and the characteristics of water pressure in lining segments during shield tunneling. The results show that, during the whole excavation of a double-track tunnel with EPB shield, the maximum vertical effective stress is about 4.24 MPa, which is located at the arch foot of the tunnel. The maximum effective stress in the horizontal direction is about 3.61 MPa, which is located on both side walls of the tunnel in the horizontal direction; after the left and right tunnels are excavated in sequence, a “double precipitation funnel-shaped” pore pressure distribution is formed around the tunnel; during the construction of the shield tunnel, the vertical displacement and horizontal displacement of the surrounding rock show an increasing trend and gradually tend to be stable values of 24.09 mm and 25.28 mm; the segment vault has settlement, the maximum settlement is 21.8 mm, the arch bottom has uplift, and the maximum uplift is 24.4 mm. The maximum horizontal displacement of the segment appears on both sides of the arch waist, and the maximum horizontal displacement decreases with the increase of excavation steps; the positive bending moment of the lining segment is mainly distributed on both sides of the arch crown, and the negative bending moment is mainly distributed on both sides of the arch bottom. The axial force of the lining segment is compressive stress, and the maximum axial force is mainly distributed on both sides of the arch waist. The maximum normal shear stress occurs on both sides of the segment arch bottom. The study conclusions provide theoretical foundation and a new guidance for long-term safety evaluation of underwater tunnel structures.

Online real-time prediction of propulsion speed for EPB shield machine by SSA-GRU

Online real-time prediction of propulsion speed for EPB shield machine by SSA-GRU

Online real-time prediction of propulsion speed for EPB shield machine by SSA-GRU

Online real-time prediction of propulsion speed for EPB shield machine by SSA-GRU

Experimental Verification of Torque Calculation Method for Shield Screw Conveyor

The normal function of the shield spiral dumper has an important impact on the safe and efficient tunnelling of EPB shield, and the driving torque is the key decisive parameter that determines whether the spiral dumper can function normally. On the self-designed and commissioned manufacturing model test platform, the indoor reproduction test of EPB shield screw conveyor slag simulation was carried out. The theoretical calculated values were highly consistent with the test results, and the average relative error of the three tests was 8.65% to 9.18% at 6 rpm. The average relative error after entering the steady state was 4.6%, and the maximum relative error was 8.9% at 15 rpm. Through the shield model screw conveyor laboratory test, the correctness and validity of the proposed shield screw driving torque calculation model were verified and the proposed theoretical calculation method has good practical application. It is obvious that this calculation method has sufficient validity in the design of shield screw device.

Dynamic collapse characteristics of the tunnel face induced by the shutdown of earth pressure balance shields (EPB): A 3D material point method study

The collapse of the tunnel face is a prevalent geological disaster in tunnelling. This study employs a three-dimensional (3D) material point method (MPM) to simulate the dynamic collapse process and post-failure mechanisms of the tunnel face. The specific focus is on the scenario where the auxiliary air pressure balanced shield with a partially filled chamber is shut down. To assess the suitability of the 3D MPM, numerical solutions are compared with the results from small-scale experimental tests. Subsequently, a series of large-scale numerical simulations is conducted to explore the dynamic collapse characteristics of the tunnel face induced by the shutdown of the EPB shield under various support air pressures and cutter head conditions. The temporal evolution of the accumulated soil masses in the soil chamber and ground responses under different support air pressures, cutter head types and opening ratios are discussed. In particular, the associated surface subsidence due to the tunnel face collapse is determined and compared with empirical solutions. Numerical results confirm the applicability of the 3D MPM for simulating the large-scale tunnel face collapse scenarios, spanning from small to large deformation analysis.

Ground movements induced by shield tunnelling in sand layers, Ho Chi Minh City mass rapid transit Line 1

AbstractThe EPB shield tunnelling for mass rapid transit (MRT) Line 1 of Ho Chi Minh City (HCMC) is the first tunnel excavation in Vietnam to use a tunnel boring machine (TBM). A comprehensive instrumentation programme was developed for safety control and to obtain a better understanding of the characteristics of induced ground movement and the forecasts. The observed ground surface settlement is summarized and interpreted with respect to the tunnelling operation parameters. The settlement trough is compared with the forecast data by applying the empirical Gaussian function and numerical 2D finite‐element analysis (FEA). The trough width parameter in the city's sandy subsoil is determined. The relation between the volume loss of the ground surface and that of the tunnel (contraction ratio) is identified. The result of the investigation is useful for future shield tunnel projects in HCMC and elsewhere in Vietnam.

Estimating Maximum Surface Settlement Caused by EPB Shield Tunneling Utilizing an Intelligent Approach

To control tunneling risk, the prediction of the surface settlement rate induced by shield tunneling using earth pressure balance plays a crucial role. To achieve this, ten independent variables were identified that can affect the amount of settlement. The nonlinear relationship between maximum ground surface settlements and ten influential independent variables was considered in artificial neural network (ANN) models. A total of 150 genuine datasets derived from the Southern Development Section of the Tehran Metro Line 6 project were used to train, validate, and test ANN techniques. Hence, the ground surface settlements of the mentioned project were predicted by the most accurate back propagation ANN technique. Ultimately, the importance level of different influential parameters on ground settlement at tunneling is relatively determined based on the results of the optimal neural network. The results used in this paper to evaluate the relative importance of each variable involved in the rate of ground surface settlement demonstrate that the parameters of grout injection and permeability equivalent to the proportions of approximately 16.91% and 5.07% have the highest and lowest impact, successively.

Correction: Hussaine, S.M.; Mu, L. Intelligent Prediction of Maximum Ground Settlement Induced by EPB Shield Tunneling Using Automated Machine Learning Techniques. Mathematics 2022, 10, 4637

The authors wish to make the following corrections to this paper [...]

Experimental Study on the Effects of New Foam on the Improvement of Sandy Soil for Earth Pressure Balance Shield

In this paper, starting from the foaming amount, half-life and other indicators, the surfactant with excellent performance is optimized, and the optimal compound ratio and appropriate foam stabilizer, viscosity enhancer, and additives are studied. A new type of foam agent formula for the EPB shield is developed. The performance of the new foam agent is compared with that of domestic foam and imported foam from the aspects of foaming rate, stability, micromorphology and temperature resistance, which verifies that it meets the parameter requirements and advantages of a foam agent for shield tunneling. Then, by means of laboratory tests, such as the mixing test, friction coefficient test, adhesion resistance test, slump test and direct shear test, the improvement effect of the new foam agent is compared with existing foam agent products at home and abroad, and the improvement effect of the new foam agent on soil is evaluated. The formulation of the new foam agent is as follows: 1.6% sodium dodecyl sulfate (SDS) + 8% dodecyl dimethyl betaine (BS-12) + 7% dodecanol + 0.06% guar gum + 0.6% ammonium chloride. The foaming rate, stability, microstructure and temperature resistance of new foam meet the requirements of shield construction. New foam, imported foam and domestic foam have advantages in sand and soil improvement experiments, but from an economic point of view, the new type of bubble is better than the other two. A new type of shield foam agent is prepared to meet the needs of construction. There is a big advantage in terms of price.

Numerical study on the muck flow behavior in the screw conveyor during EPB shield tunneling

The muck flow behavior in the screw conveyor determines the pressure in the excavation chamber. The pressure in the chamber should be reduced to the atmospheric pressure at the outlet of the screw conveyor. Otherwise, the soil and water mixture would spew out form the screw conveyor, resulting in the pressure loss and face failure. In this study, three-dimensional numerical analyses of the muck transport performance of screw conveyor were performed using Computational Fluid Dynamics (CFD). The muck was assumed to behave as a Herschel-Bulkley (H-B) plastic fluid. A new model coupling rheological and wall slip models was developed and validated by a laboratory test. The error of the pressure transfer and the flow rate between simulation and test is around 3.8%. Through parametric analysis, the influence of the rheological parameters of muck and the working parameters of the screw conveyor on the muck flow behavior is further explored, and a spewing failure surface is given for the control of rheological parameters of the conditioned soil. The results in this study could provide some suggestions for soil conditioning and the optimization of screw conveyor performance.

Prediction method of shield tunneling parameters in pebble stratum formed by weathered granite and quartzite

The pebble formation formed by weathered quartzite and granite is usually of high strength, strong permeability and poor self stability, which brings great difficulties to shield tunneling. It is necessary to adjust the tunneling parameters at any time to prevent the consequences of instability of the tunnel face, loss of stratum and surface settlement caused by the imbalance of the soil bin pressure. GA algorithm is embedded into PSO algorithm for parameter optimization, and grey theory is combined to establish the prediction model of soil chamber pressure based on grey least square support vector machine, which can solve the problem of difficult control of tunneling parameters in pebble stratum formed by weathered quartzite and granite. Research indicates: GA-PSO-GLSSVM chamber Earth pressure prediction model enhances the EPB chamber Earth pressure forecast accuracy in complicated strata by integrating the global search capability of the GA algorithm, the quick convergence of the PSO algorithm, and the anti-disturbance capability of the GM model. The GA-PSO-GLSSVM model has high goodness-of-fit and accuracy compared with other prediction models. This model can successfully prevent the a series of undesirable consequences such as destabilization of the palm surface, missing strata and settlement due to ground surface due to pressure imbalance in the soil chamber pressure. The research results can provide reference for EPB shield tunneling parameter control in Grade V surrounding rock.

Research and Experimental Application of New Slurry Proportioning for Slag Improvement of EPB Shield Crossing Sand and Gravel Layer

Based on the construction practice of the Beijing Metro Line 10 shield tunneling project, this paper describes research on soil improvement technology for Beijing stratum characteristics (sandy gravel stratum) and covers similar engineering conditions. It also describes the development of a new type of mud improver. Based on the laboratory tests with bentonite as the base mud and different additives, the effects of guar gum, CMC, xanthan gum, and clay medium particles on mud performance are analyzed. Then, two kinds of mud were used to conduct indoor simulated muck improvement tests (mixing test, slump test, sliding plate test, and adhesion resistance test), and the improvement effects of new mud and ordinary mud applied in pebble/round gravel and sandy soil layers were compared. The results show that xanthan gum is the best material to improve the performance of slurry, using the contrast test of bentonite-based slurry and different additives. The optimum slurry preparation scheme is 4% bentonite, 0.2% xanthan gum, 0.04% soda ash, and 1% clay particles. Using indoor simulated muck improvement tests (mixing test, slump test, slide plate test, and adhesion resistance test), the improvement effects of applying new mud and ordinary mud in pebble/round gravel and sandy soil layers are compared, and the advantages of the new mud in the application of the above two formations are verified. Among them, the new slurry has great advantages for improving the two parameters of the soil adhesion resistance coefficient and slump during shield tunneling. When the improved soil mass reaches the flowing plastic state, the proportion of new mud added to different soil mass is different. The proportion of new mud added to improved pebble/pebble soil is 28%, and that of sand and clay is 32%. It can be seen that new mud is more suitable for improving pebble/pebble soil.