Earth Pressure Balance Shield Research Articles

Coupled DEM-FDM numerical model for EPB shield tunnelling simulation with foam conditioning

It is widely recognized that an appropriate application of soil conditioning significantly improves the tunnelling performance of earth pressure balance (EPB) shield tunnel boring machines (TBMs). This study presents a numerical approach that simulates an EPB shield tunnelling, considering the injection of foam into the soil. To enhance computational efficiency and reduce the number of particles simulated in the ground formation, the numerical study coupled the discrete element method (DEM) and the finite difference method (FDM). The properties of in-situ soil and foam-conditioned soil were incorporated into the DEM domain by determining the contact parameters of particles using two calibration models: the triaxial compression test and the pressurized vane shear test models. With the established model, tunnelling analyses were conducted under specific TBM operation conditions, such as the penetration rate, and rotational speed of the cutter head and the screw conveyor. The effect of foam injection on EPB shield TBM operation was evaluated by adjusting the contact parameters of DEM elements. The numerical simulations revealed that foam conditioning reduced the torque, thrust force, and forces on cutting tools. These simulations provided valuable insights into the applicability of the numerical approach in assessing foam conditioning for EPB shield TBMs.

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.

In situ resource reutilization of earth pressure balance (EPB) shield muck for the generation of novel synchronous grouting materials

The utilization of large quantities of shield muck resources is a pressing issue that requires immediate attention and resolution. In this paper, an innovative approach that fully utilizes shield muck as an aggregate for synchronous grouting is introduced to realize the in situ resource utilization of this material. The newly formulated synchronous grouting grouts comprise shield muck and a solid waste-based cementitious material. The influences of components and compositions on the macroscopic performance of new grouts are investigated, and the formulation is optimized with a single-factor test and response surface methodology (RSM) analysis. The optimal formulation with a slurry specific gravity (SG) of 1.383 g/cm³ and a cementitious material (CM) content of 21.456% is determined. The microscopic characteristics of the grouts are revealed by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Two main hydration products, namely AFt and C-S-H gel, are observed, exhibiting a crisscross growth pattern that contributes to the formation of a robust micronetwork structure. A full set of shield muck in situ pulping equipment is independently developed, thereby establishing an integrated grout production process. Considering the Suzhou Metro Line 6 as an engineering case, a field industrialization experiment is conducted, and the results demonstrate that the pulping system operates smoothly and can stably produce grouts. Compared with conventional cement-based finished grout, the newly developed synchronous grouting material with an optimal formulation exhibits significant superiorities in terms of surface deformation control (average reduction of 30∼40%), segment attitude control, and anti-seepage effect. The proposed approach effectively realizes in-situ resource utilization and source reduction of shield muck and can significantly reduce the cost of synchronous grouting. Aligned with the dual carbon strategy, the prospects for widespread adoption of this approach are promising, and the results of this study are highly significant.

Rheological characterization of the conditioned sandy soil under gas-loading pressure for earth pressure balance shield tunnelling

Soil conditioning technology is usually required to modify the excavated soil to a fluid plastic state during the construction with earth pressure balance (EPB) shield. The steady pressure distribution in the excavation face is linked to soil fluidity. Compared with the slump test, the rheological behavior of the conditioned soil can better reflect the dynamic flow characteristics. A gas-loading rotational rheometer is developed to test the rheological properties of the conditioning agents and the conditioned sandy soil, which can overcome the disadvantage of uneven mechanical loading and create gas-loading conditions. The rheological properties of sandy soil conditioned by different agents under atmospheric and gas-loading pressure conditions were studied, and the influences of foam injection ratio (FIR), bentonite slurry injection ratio (SIR), and polymer injection ratio (PIR) on soil viscosity were analyzed. The test results show that the ambient air pressure only greatly influences the experimental group with foam. Under the same gas-loading pressure, the foam’s apparent viscosity decreases with the foam expansion ratio (FER) increasing. The rheological behavior of the conditioned sandy soil conforms to the Bingham model under atmospheric pressure and conforms to the Power Law model when PIR ≤ 5 % under gas-loading pressure of 3 bar. The Weissenberg effect accounts for the differences. When PIR > 10 %, the rheological curve of three agents conditioned sand conforms to the Herschel Bulkley model. The higher content polymer reacts with bentonite to increase the soil viscosity, and blocks the foam seepage channel, making it difficult for the foam to re-enter the soil under gas-loading pressure. Investigating the rheological behavior of different conditioned sandy soil provides optimization strategies for EPB performance.

Machine learning–informed soil conditioning for mechanized shield tunneling

AbstractEffective soil conditioning is critical for mechanized shield tunneling, yet the selection of conditioning parameters remains experience‐oriented. This study presents a machine learning–informed soil conditioning strategy, aiming at enabling automatic decision‐making for soil conditioning during tunneling. The proposed procedure includes feature engineering to process raw data, the selection of an optimal model, and a committee‐based uncertainty quantification strategy to evaluate the reliability of models. High‐dimensional data visualization techniques are leveraged to examine the influence of data distribution on the model's performance. Results demonstrate that feature engineering and the selection of models lay a foundation for machine learning–enabled automatic soil conditioning, while historical soil conditioning parameters should be incorporated in models to account for time‐dependent features during tunneling. The committee‐based uncertainty quantification strategy can effectively identify the reliability of both interpolated and extrapolated predictions. The proposed data‐driven soil conditioning framework can promote the application of machine learning toward automating earth pressure balance (EPB) shield tunneling.

On recycling earth pressure balance shield muck with residual foaming agent: defoaming and antifoaming investigations.

Earth pressure balance (EPB) shield is increasingly employed in metro tunnel construction, and causes a series of environmental, safety, and resource waste problems due to the disposal of a considerable amount of muck. In situ recycling of EPB shield muck is an effective solution, whereas the foam is generated by residual foaming agents used as the muck conditioning material during tunnelling, which often adsorbs clay particles and overflows the flocculation tank. To achieve defoaming and antifoaming during the reuse of muck, this study prepared novel eco-friendly silicone oil-polyether defoamers by condensation, compounding, and shear emulsification. Defoaming and antifoaming performances of different defoamers were tested using a modified Ross-Miles method and a scale model of field flocculation systems. The results indicated that a high efficiency in defoam and antifoam was characterized by chemical grafting of nano-SiO2 from silicone oils, uniform distribution and large size of grains, low viscosity, and surface tension. The defoamer dosage of 0.002-0.004 wt% near critical micelle concentration (CMC) for each defoamer is reasonable. Overall, the prepared hydroxyl silicone oil-glycerol polyoxypropylene ether (H-G) defoamer compared with other silicone oil-polyether defoamers and commercial defoamers presents the highest defoaming and antifoaming efficiency. Considering the effects of EPB shield muck, the H-G defoamer is least affected by the compound materials and increasing concentration of the commercial foaming agent. Nevertheless, the stability of the H-G emulsion system is weaker than that of the dimethyl silicone oil-glycerol polyoxypropylene ether (D-G) emulsion system after 1 month of sealed storage.

Analysis of the Drive Torque for the Spiral Pipe Section of an Earth Pressure Balanced Shield Tunnel Screw Conveyor

The driving torque of the shield machine is intricately linked to the soil silo muck load and the mechanical properties of both the muck and the spiral structure. Considering the shield screw conveyor’s mechanical structure and operational conditions, based on the momentum moment balance conditions, the separate calculation method was used to derive the spiral driving torque in the helical casing, the friction torque in the bearing and the friction torque of the sealing ring through mechanical analysis, and finally a torque calculation expression for the spiral pipe section was established. The research results provide technical guidance for the design and manufacture of shield screw conveyors and safe tunneling during construction.

A parameter design model for EPB shield soil conditioning in gravel stratum based on machine learning

The utilization of soil conditioners plays a vital role in preserving excavation safety during the construction of an earth pressure balanced (EPB) shield, as they enhance the reliability of the cutting chamber. The kinds and amounts of soil conditioner that ought to be pumped into the EPB system, however, lack theoretical direction. This study aims to develop predictive and design models to investigate the reciprocal relationship between soil conditioners and soil characteristics. The soil conditioner parameters were designed with the targeted characteristics of the soil using the intelligent hybrid design model, which combined the prediction model and the design model. The study's conclusions showed that the Gradient Boosting Regression (GBR) model, which was developed, had improved generalization and accuracy abilities when used to forecast the properties of upgraded soils. The current Artificial Neural Network (ANN) design model provided a variety of available options, but its accuracy was poor, and it could not be used directly. A hybrid GBR-ANN model created by the researchers showed a difference between the goal value and the experimental value acquired from laboratory soil testing of less than 10%. A solution that was required was the model's time-consuming explosion of the marginal value design. As a result, it is determined that using the Hybrid GBR-ANN model is adequate for figuring out the necessary amount and composition of soil conditioner, making it a workable method for soil property-oriented design.

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.

Effect of water pressure on permeability of foam-conditioned sands for EPB shield tunneling

Foam conditioning is a widely adopted technique in earth pressure balance (EPB) shield tunneling for the purpose of reducing sand permeability and preventing water spewing. The permeability of foam-conditioned sands differs from that of natural sands due to the presence of foam bubbles. This study investigated the effect of water pressure on the permeability of foam-conditioned sands using novel laboratory permeability tests. The water pressure, for the first time, is decoupled with the hydraulic gradient, owing to a newly developed permeameter with the controllable downstream hydraulic pressure in the laboratory. The results show that the permeability is significantly affected by the water pressure, and the effect is also predominantly dependent upon the foam injection ratio. The initial hydraulic conductivity increases with the increasing water pressure, while the initial stable period duration decreases. The water-plugging structure formed by foam bubbles and sand particles is prone to be damaged under high water pressure due to the shrinkage of foam bubbles. This means that the existing permeability tests with low water pressure underestimate the permeability of foam-conditioned sands. The underlying mechanism of water pressure in modifying the permeability of foam-conditioned sands is also examined from a particle-scale perspective.

Face failure of EPB shield tunnels in dry dense sand: a model test and DEM study

This paper aims at addressing the face failure of earth pressure balance (EPB) shield tunnels in dry dense sand by model tests and discrete element method (DEM) models. The model tests incorporated a miniature EPB shield which could fully reproduce the real tunnel construction of excavation and support. DEM models simulating the model tests were developed to capture the underlying face failure mechanism. Results show that both the limit support pressure obtained at chamber board and tunnel face increase with increasing C/D (C is tunnel buried depth, D is tunnel diameter). The ratio of the former to the latter approximates 0.60 due to the soil retaining of cutterhead panel, and it is independent of C/D. The local face failure initializes around tunnel face and develops directly to the global failure outcropping the ground surface in one phase with C/D≤1.0, while the local failure develops to the global failure in three phases with C/D=2.0 due to the soil arching evolution. The soil arching gets weaker when it propagates upward, and the horizontal stress concentration in the longitudinal direction is stronger than the transverse direction due to the difference of arch foot.

Structural damage assessment and failure mode analysis for cross-fault submarine tunnels

Fault fracture zones represent unfavorable geological conditions that are often encountered in cross-sea tunnels. When such a tunnel crosses a fault, the sliding action of the fault easily results in significant tensile, compressive, and shear failure of the lining, thereby causing local buckling and even fractures. Therefore, in this study, a series of sophisticated 3D discontinuous contact numerical models were established; these models account for the underground rock stratum, hydrostatic pressure, and nonlinear behavior of materials. The developed models realistically reproduced the construction process for earth pressure balance shield tunnels, such as the jack force, grouting pressure, and grout hardening over time. The simulation results suggest that the relative spatial location and morphology of the fault fracture zone strongly influence the failure mode of the tunnel. The tunnel structure exhibits three typical failure modes: face bulge, local sliding failure, and overall sliding collapse. The dip angle and crossing angle of the fault will lead to the readjustment of shear forces and bending moments in the tunnel, leading to uneven displacement and localized torsional deformation of the adjacent lining. Additionally, increasing the ratio of diameter to thickness will decrease the overall rigidity and torsional resistance of the tunnel.

A particle-scale insight into the face stability of shallow EPB shield tunnels in dry cobble-rich soil

The aim of this paper is to provide a particle-scale insight into the face stability of shallow (C/D = 1.0; C = tunnel buried depth and D = tunnel diameter) earth pressure balanced (EPB) shield tunnels in cobble-rich soil, considering both the dynamic excavation process and particle size gradation. The work was performed by three dimensional discrete element method (DEM). Results show that particle size greatly influences the movement of cobble particles. The coarse particles serve as the skeleton of the ground and provide the stability. The erosion of fine particles has little influence on tunnel face stability, while the erosion of middle particles weakens tunnel face stability. The limit support pressure pf increases with increasing cutterhead rotating speed, and the normalized limit support pressure pf/γD (γ = soil unit weight, D = tunnel diameter) obtained in this paper is larger than existing researches. The abrupt increase of middle particles in the muck composition can be recognized as the forewarning information against face failure.

Real-time laser scanning for conditioned coarse-grained soil monitoring on conveyor belt in earth pressure balance shield

To address the hysteresis in assessing the workability of conditioned soils and the inefficiency in estimating the soil volume flow rate in tunnelling practice, a novel real-time assessment and monitoring approach was proposed. Based on laser scanning technology and point cloud data analysis, the approach can monitor the workability and the volume flow rate of conditioned soils on the horizontal conveyor belt of an earth pressure balance (EPB) shield in real-time. Firstly, the accuracy of laser scanning measurements was verified by comparing manually measured slump and spread values with laser scanning results. Then, a series of model tests for scanning the coarse-grained soils with different conditioning parameters and belt speeds on the horizontal conveyor belt were performed. The appropriate ranges of secant angle and unevenness of soil cross-sectional profile were obtained for assessing the workability of conditioned soils. The volume flow rate was calculated by integrating the cross-sectional areas of conditioned soils. Finally, the proposed approach was successfully applied in identifying the workability of conditioned soil and its discharge rate in the EPB shield tunnelling project. This study contributes to the real-time monitoring of conditioned soils on the horizontal conveyor belt and provides practical insights for the optimal management of EPB shield tunnelling.

Soil disturbance induced by shield tunnelling in sensitive clay: In situ test and analyses

Shield tunnelling in sensitive soil causes disturbance to the surrounding soil, damages the soil structure, and results in soil strength reduction. It has a significant impact on the strength and deformation of the soil during shield tunnelling, and further affects the long-term post-construction settlement of the tunnel structure. This paper firstly obtained the soil disturbance and its distribution especially under the tunnel by the in-situ measurement, and the effect of tunneling advancing speed on soil disturbance degree was analyzed. In this paper, in situ tests were performed on an earth pressure balanced (EPB) shield tunnelling site of a subway in deep soft soil layers in Ningbo. Before and after the shield tunnelling, the cone penetration tests (CPTs) were carried out along the axis and profile of the tunnel, and the cross-hole shear wave velocity tests were conducted. Displacement of the surrounding soil and excess pore water pressure (EPWP) were also monitored during shield tunnelling. The results showed that after shield tunnelling the cone penetration resistance (CPR) and shear wave velocity of the surrounding soil decreased remarkably, further confirming that shield tunnelling caused disturbance to the sensitive soft soil. The soil disturbance degree (SDD) is defined based on the CPR, and the soil disturbance boundary caused by shield tunnelling is determined based on distributions of SDD and EPWP. Horizontally, the disturbance boundary of the surrounding soil is located about 0.8D (D represents the tunnel diameter) outside the tunnel, and vertically, the bottom and top of the disturbance boundary are located about 1.29D below and 0.58D above the tunnel. The maximum SDD at the bottom and top of the tunnel reached 80% and 90% respectively, and the average SDD of the disturbance range below the tunnel is about 60%. The testing results indicated that a higher advancing speed causes a greater disturbance to the surrounding soil, and all the analysis results provide helpful guidance for optimizing the EPB shield tunnelling and reducing soil disturbance.

Experimental study on the stratum applicability and mechanisms of bubble-slurry for earth pressure balance shields

Experimental study on the stratum applicability and mechanisms of bubble-slurry for earth pressure balance shields

Experimental study on workability and permeability of sandy soils conditioned with thickened foam

Water spewing and muck plugging often occur during earth pressure balance (EPB) shield machines tunnelling in water-rich sandy strata, even though the conventional foam has been employed to condition sandy soils. In this study, a novel thickened foaming agent suitable for EPB shield tunnelling in water-rich sandy strata is developed. In contrast to conventional foam-conditioned sands, the thickened foam-conditioned sand has a low permeability due to the consistent filling of soil pores with the thickened foam, and the initial permeability coefficient decreases by approximately two orders of magnitude. It also exhibits a suitable workability, which is attributed to the enhanced capability of the thickened foam to condition sandy soils. In addition, the effect of concentration on the stability of the foam is explained by the Gibbs-Marangoni effect, and conditioning mechanisms for the thickened foam on sands are discussed from the evolution of foam bubbles.

Quantitative evaluation of influence of the soil transportation mode on the excavation efficiency for a shield tunnel based on the Markov chain

The earth pressure balance (EPB) shield tunneling efficiency is greatly affected by the choice of soil transport mode. In this study, the influence of two soil transport modes, such as the continuous belt conveyor and rail train, on the efficiency of shield excavation was analyzed using the Markov chain model. A method was proposed to define the ideal and non-ideal excavation states and quantitatively evaluate the excavation efficiency of the two soil transportation modes of the EPB shield. Based on this model framework, a profitable Markov chain model was established to predict the expected profits of the two soil transportation modes. The Beijing Metro New Airport Line first-phase project was used as a case study to verify the model established. The results show that under the same conditions, the continuous belt conveyor soil transport mode can have a higher excavation efficiency and expected profit. This advantage gradually increases over time.

A study on soil conditioning for cohesive soils with high content of clay minerals: Microscopic simulation and laboratory experiment

An earth pressure balance shield machine (EPB) is prone to blockage when tunneling in strata with high clay mineral content. Engineers often improve soil fluidity and reduce soil adhesion through soil conditioning to ensure the safe and efficient tunneling of shields. This paper selected montmorillonite, kaolinite, and illite as research objects and used molecular dynamics simulation and laboratory experiments. The interfacial mechanical behavior between anionic surfactant (sodium dodecyl benzene sulfonate, SDBS) solution and clay minerals was simulated at the microscopic scale and the improvement mechanism of SDBS solution on clay minerals was revealed. Then, the zeta potential of clay minerals and the stirring torque of the soil under different foam injection ratios (FIR) were tested. Accordingly, the conditioning effect of the SDBS solution at the macroscopic scale can be evaluated. The results show that the electrostatic adsorption and repulsion of ions occur on the surface of clay minerals, which makes it difficult for clay particles to aggregate into clusters. The SO3H- groups of the SDBS surfactant are the key factor to change the hydrophilicity of clay minerals. When different soil samples are improved to the same state, montmorillonite requires the largest FIR due to its microstructure.

Recycling the discharged soil from EPBS tunnels as a soil conditioner and its rheological behaviors

Earth pressure balance shield (EPBS) has become the mainstream construction method for metro tunnels in China, which inevitably generates a large amount of discharged soil, putting enormous pressure on the environment and the cost. In order to realize the resource utilization of shield dregs, this paper explored the feasibility of recycling the waste silty clay as a soil conditioner in EPBS tunnel construction. Mixtures of bentonite, wasted silty clay, carboxymethyl cellulose (CMC), and tap water in different ratios were prepared. Defining the substituted ratio as the mass ratio of silty clay to (bentonite + silty clay), the effect of the substituted ratio on the apparent viscosity, flow curve, rheological model and physical stability of bentonite-silty clay composite slurry were investigated. Furthermore, the relationship between slurry microstructures and macroscopic rheological properties was revealed by scanning electron microscopy (SEM). The results show that the constitutive relationship of bentonite slurry (0% substituted ratio) can be well described by Herschel-Bulkley model. The silty clay has a deteriorating effect on the rheological behavior and physical stability, and changes the flow pattern of the composite slurry. Microscopically, CMC makes the clay particles in slurries form agglomerates with larger particle sizes, and can absorb excess free water from the slurry, thus significantly increasing the yield stress and apparent viscosity. The recycling scheme proposed in this study can not only greatly reduce the procurement cost of raw materials, but also eliminate the transportation and disposal costs of discharged soil, which has significant environmental benefits and promising application prospects.