Search Results (150)

The management of waste bentonite slurry (WBS) produced during slurry shield TBM excavation involves environmental and operational challenges from the perspective of developing a more sustainable tunnelling construction process. In this study, the potential reuse of WBS as a complete replacement for bentonite in two-component grout formulations used for TBM backfilling is explored. A comprehensive laboratory testing program is conducted, in which the effects of WBS on the properties of two-component grout (unit weight, viscosity, bleeding, gel time, and mechanical strength) are assessed after various curing times, and the outcomes are compared with standard values commonly given in technical specifications. WBS produced from two different commercial bentonites is investigated. The results show that while the first formulation exhibits rapid setting and irregular gelation, the mix derived from the second bentonite demonstrates superior mechanical performance, increasing compressive strength by up to 40%. This enhancement is primarily governed by a physical filler effect, where fine soil particles optimize packing density and refine the microstructure. Consequently, the incorporation of selected types of WBS into a two-component grout could be a practicable approach, since it offers benefits in terms of mechanical performance, although careful mix design would be required to manage workability. This study shows how tunnelling can become more sustainable by reusing excavation waste and transforming it into a useful by-product. Full article

Karst pile foundation cavity treatment requires grouting materials with suitable flowability, stability, strength, and cost-effectiveness, while large quantities of waste mudstone generated by tunnel excavation in Guangxi, China, also require sustainable valorization. In this study, tunnel-excavated mudstone from a tunnel project in Guangxi, China, was used as the primary raw material to develop a solidified grouting material for karst pile foundation cavity treatment. Uniform experimental design, stepwise nonlinear regression, response surface analysis, and multi-objective optimization were employed to evaluate the effects of key mix parameters and determine the optimal formulation. The results showed that the optimal slurry was obtained at a cementitious material-to-mudstone ratio of 0.16, an admixture-to-cementitious material ratio of 0.06, a water-to-solid ratio of 0.63, and the slag powder content-to-cementitious materials ratio of 0.34. In addition, the anti-dispersion performance improved by 87.78%, and compared with conventional cement-soil, C25 concrete, and C30 concrete, the CO₂ emissions were reduced by 37%, 67.4%, and 68.6%, respectively, with the material cost being 73.8% lower than that of traditional cement mortar. These results indicate that the proposed material has promising engineering applicability and demonstrates significant economic and environmental benefits, as well as the valorization potential of tunnel-excavated mudstone. Full article

Large deformations in deep soft rock roadways primarily stem from low rock strength under high in situ stress and intense mining disturbance. This renders stability control a critical challenge in tunneling support engineering. Utilizing Xinhe Coal Mine’s deep soft rock tunnel as a representative case, this study integrates field monitoring, laboratory experimentation, and numerical simulation to investigate how excavation and grouted rock bolting influence surrounding rock stability. Building upon field-observed deformation mechanisms and support failure patterns, constitutive models for FLAC^3D’s embedded cable and beam elements were modified to achieve high-fidelity simulation of grouted support systems. Numerical models simulating diverse support schemes were established to analyze roadway displacement fields, plastic failure development, and structural behavior of support components, ultimately identifying the optimal rehabilitation solution. The research results indicate that the numerical simulation outcomes of the original support scheme exhibit good agreement with field observations in terms of roadway deformation patterns, deformation magnitudes, and occurrences of bolt/cable fractures. This demonstrates that the adopted refined numerical simulation methodology and parameters are reasonable and exhibit high reliability. Considering both surrounding rock stability and cost control, Roadway Rehabilitation Scheme S1 was identified as the optimal support solution. Its specific parameters are pre-grouting + full-section rock bolts (diameter 22 mm, length 2.4 m, spacing 0.8 m, row spacing 1.6 m) + full-section grouted cables (diameter 22 mm, length 6.2 m, spacing 1.0 m, row spacing 1.6 m). Full article

During the construction of underwater shield tunnels (excavated using a slurry pressure balance shield machine), whether seawater (Sw) can be used to replace freshwater (Fw) in the preparation of cement–sodium silicate grout (CSG) has become a major concern in the engineering community. CSG is formed by mixing components A and B, where component A is a liquid prepared by mixing bentonite, cement, and water, and component B is a sodium silicate solution. In this paper, the CSG was prepared using Sw instead of part of Fw. The properties, including bleeding rate, initial and final setting time, gel time, compressive strength, and microscopic characteristics, were tested to investigate the influence of Sw on the performance of CSG and explore its impact mechanism. The results showed that when expanding bentonite with Sw, the bleeding rate of Component A exceeded 50%, failing to meet the engineering requirement of 10%. However, expanding bentonite with Fw, the seawater replacement ratio has almost no effect on Component A, with all values remaining below 10%. As the seawater replacement ratio increases, the setting time of CSG is significantly shortened. Although the inclusion of seawater results in a marginally lower 1-day strength for CSG, it notably boosts the strength at later ages. Specifically, at a 45% seawater replacement ratio, the 28-day strength showed a marked increase of 52% relative to the CSG without seawater. In the later stage of hydration, the positive effect of Cl⁻ in seawater, promoting the hydrolysis of C₃S and C₂S on strength, is significantly higher than the negative effect of sulfate ion erosion in seawater on strength. Therefore, seawater significantly increases the 28-day compressive strength of CSG. This study can provide reference and guidance for the application of seawater in the preparation of two-component grout for submarine shield tunnels. Full article

Conventional synchronous grouting materials often exhibit low early strength, delayed setting, and insufficient utilization of excavated soil, hindering the green and efficient advancement of metro shield tunneling technology. To overcome these challenges, this study developed a high-performance grouting material by utilizing shield muck—primarily composed of quartz (71.47%) and calcite (15.3%)—as the main raw material, with sodium trimethylsilanolate (TMS-Na) introduced as a performance enhancer. Through orthogonal experiments and range analysis, the influences of cement content, slag content, and TMS-Na dosage on the workability and mechanical properties of synchronous grouting materials were systematically evaluated. Microstructural evolution was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TG) analysis, and mercury intrusion porosimetry (MIP) to elucidate the mechanism by which TMS-Na modifies the grout microstructure. The results demonstrate that incorporating 8% slag and 0.2% TMS-Na increases the utilization rate of shield muck to 60.8%. Compared with conventional grouts, the novel material exhibits approximately 97.4% and 93.3% enhancements in 3-day and 28-day compressive strength, respectively, alongside an impermeability grade reaching P10. The addition of slag improves the apparent density and early strength of the grout, although its contribution diminishes at later ages. TMS-Na effectively activates the hydration reactivity of slag, accelerates early hydration, reduces the setting time, and participates in a secondary hydration reaction with argillaceous siltstone present in the excavated soil, promoting the formation of additional calcium silicate hydrate (C-S-H). This process densifies the hardened grout matrix, refines the pore structure, and significantly enhances both mechanical performance and impermeability. Field application in a trial tunnel section confirms that the proposed grouting material achieves complete cavity filling, eliminates water leakage, controls ground deformation effectively, and offers favorable economic viability, demonstrating strong potential for large-scale engineering application. Full article

With the increasing density of urban underground space development, the soil disturbance induced by large-section rectangular pipe jacking poses a significant threat to the safety of underlying subway tunnels. Taking the Lihe Road utility tunnel project in Wuhan, which crosses over Metro Line 4, as the engineering background, a three-dimensional finite element (FE) model was established using Midas GTS NX to simulate the entire pipe jacking process. Field monitoring data from caisson excavation, ground improvement, pipe jacking, and backfill grouting were introduced for validation, enabling a systematic investigation of the influence mechanism of pipe jacking on existing tunnels. In the numerical simulation, the modified Mohr–Coulomb constitutive model was adopted for the soil, and a “portal-type” reinforcement system was introduced. The pipe jacking process was simulated equivalently with a 1.2 m advance per cycle. The results indicate that the ground settlement induced by pipe jacking exhibits a stage-wise accumulation pattern and eventually develops into a stable settlement trough. The vertical settlement of the tunnel follows an evolutionary law of “early occurrence in the near field, delayed response in the far field, and final convergence,” with peak settlements of 2.44 mm and 2.53 mm for the left and right lines, respectively. Ground improvement significantly mitigates soil deformation, reducing the maximum surface settlement from 45.5 mm to 11.1 mm, decreasing the tunnel’s peak vertical settlement by 37%, and reducing horizontal displacement by 64%, thereby effectively suppressing lateral soil extrusion. The proposed closed-loop analysis method of “numerical simulation–monitoring validation–measure evaluation” reveals the spatiotemporal evolution law of soil–tunnel interaction during pipe jacking construction and provides valuable reference for risk control in similar engineering projects. Full article

To investigate the stability of surrounding rock and support structures during tunnel excavation through karst cave groups, this study adopts an integrated methodology of laboratory tests and numerical simulations. The influence of cave groups with different spatial orientations relative to the tunnel (α = 90°, 45°, 0°, −45°, −90°) is systematically evaluated in terms of surrounding rock deformation, plastic zone development, and support structure loading. Results indicate that spatial orientation significantly affects rock mass stability. The cave groups positioned horizontally to the tunnel (α = 0°) induce the most extensive plastic zone penetration, representing the highest risk scenario. For this critical case, a safety distance threshold of L = 1.8D is proposed. When cavities intrude into the tunnel profile, localized deformation effects become pronounced. Remedial grouting with C25 concrete proves effective, reducing crown uplift, crown settlement, and horizontal convergence at the arch waist by 35.43%, 13.17%, and 58.09%, respectively. Under horizontal-side intrusion conditions, initial support stress increases markedly—nearly doubling compared to other orientations—necessitating targeted reinforcement measures. These findings offer practical guidance for the safe design and construction of tunnels in karst regions. Full article

Loess subgrades are prone to significant strength reduction and deformation under cyclic traffic loads and moisture ingress. Permeable polyurethane polymer grouting has emerged as a promising non-excavation technique for rapid subgrade reinforcement. This study systematically investigated the fatigue behavior of polymer-grouted loess using laboratory fatigue tests and numerical simulations. A series of stress-controlled cyclic tests were conducted on grouted loess specimens under varying moisture contents and stress levels, revealing that fatigue life decreased with increasing moisture and stress levels, with a maximum life of 200,000 cycles achieved under optimal conditions. The failure process was categorized into three distinct stages, culminating in a “multiple-crack” mode, indicating improved stress distribution and ductility. Statistical analysis confirmed that fatigue life followed a two-parameter Weibull distribution, enabling the development of a probabilistic fatigue life prediction model. Furthermore, a 3D finite element model of the road structure was established in Abaqus and integrated with Fe-safe for fatigue life assessment. The results demonstrated that polymer grouting reduced subgrade stress by nearly one order of magnitude and increased fatigue life by approximately tenfold. The consistency between the simulation outcomes and experimentally derived fatigue equations underscores the reliability of the proposed numerical approach. This research provides a theoretical and practical foundation for the fatigue-resistant design and maintenance of loess subgrades reinforced with permeable polyurethane polymer grouting, contributing to the development of sustainable infrastructure in loess-rich regions. Full article

Some expressway emergency lanes adopt simplified pavement structures that fail to meet load-bearing requirements after reconstruction. To address the issue of subgrade reinforcement without excavation, a finite element method was employed to analyze the effects of enlarged-borehole grouting (EBG), considering variations in grouting depth and inter-pile subgrade modulus, on pavement load-bearing capacity. Furthermore, field experiments were conducted to evaluate grouting techniques, including enlarged-borehole micro-expansive cement casting (EB-MECC) and enlarged-borehole steel flower pipe split grouting (EB-SFPSG), and three composite grouting schemes. Results indicated that EBG effectively improved the fatigue cracking life of the semi-rigid base layer. Reinforcement effectiveness was positively correlated with grouting depth and subgrade modulus, with the latter exhibiting a more significant influence. Therefore, a 1.5 m grouting depth combined with splitting or compaction is recommended to enhance subgrade stiffness. Field experiments showed that EB-SFPSG effectively enhanced pile–subgrade interaction and mitigated stress concentration around the pile–pavement interface. Comparison of the three composite grouting schemes revealed that both the scheme employing only EB-SFPSG and the hybrid scheme using EB-SFPSG in the middle row with EB-MECC in the side rows exhibited favorable mechanical performance. The latter, however, was achieved at a lower construction cost. Another hybrid scheme that further replaced the middle row with enlarged-borehole conventional pressure grouting (EB-CPG) provided limited reinforcement and poorer uniformity. Full article

Sequential twin-tunnel excavation has become increasingly common as urban rail networks expand, making both deformation control and construction-phase carbon management essential for sustainable underground development. This study investigates the spatiotemporal development of ground settlement induced by parallel Earth Pressure Balance shield tunnelling in a twin-tunnel section of the Hangzhou Metro, based on long-term field monitoring. The settlement process is divided into three stages—immediate construction settlement, time-dependent additional settlement, and long-term consolidation—each associated with distinct levels of energy input, grouting demand, and embodied-carbon release. Peck’s Gaussian function is used to model transverse settlement troughs, and Gaussian superposition is applied to separate the contributions of the leading and trailing tunnels. The results indicate that the trailing shield induces ahead-of-face settlement at approximately two excavation diameters and produces a deeper–narrower settlement trough due to cumulative disturbance within the overlapping interaction zone. A ratio-type indicator, the Twin-Tunnel Interaction Ratio (TIR), is proposed to quantify disturbance intensity and reveal its environmental implications. High TIR values correspond to amplified ground response, prolonged stabilization, repeated compensation grouting, and increased embodied carbon during construction. Reducing effective TIR through coordinated optimization of shield attitude, face pressure, and grouting parameters can improve both deformation control and carbon efficiency. The proposed framework links geotechnical behaviour with environmental performance and provides a practical basis for risk-controlled, energy-efficient, and low-carbon management of sequential shield tunnelling. Full article

Prestressed flexible support systems have become essential in deep excavation engineering, with the load distributive compression anchor (LDCA) widely adopted to enhance load-bearing performance through effective load dispersion among multiple anchoring units. Structural parameters of the anchor, particularly perforation ratio and height-to-diameter ratio, play a critical role in determining the mechanical behavior of the surrounding grout. In this study, grout located 500 mm behind the anchor body was selected as the test specimen. Unconfined compression tests were conducted to evaluate the ultimate load-bearing capacity under varying anchor configurations. Based on experimental measurements, a numerical simulation model was established and calibrated to investigate the internal stress distribution of the grout under different perforation ratios and height-to-diameter ratios. Results indicate that the perforation ratio significantly influences both the magnitude and location of stress peaks within the grout, with higher perforation ratios shifting the x-directional stress peak toward the anchor orifice and gradually reducing ultimate load-bearing capacity. Reducing the height-to-diameter ratio leads to a more uniform stress distribution, mitigating stress concentration while maintaining near-constant load-bearing capacity, although it increases anchor deformation. Optimal perforation ratio ranges were determined as [11%, 23%], [31%, 37%], and [42%, 50%] for anchors 1, 2, and 3, respectively, and the recommended height-to-diameter ratio is [15%, 17%]. The integration of experimental testing and numerical simulation provides quantitative insights into the effects of anchor design on grout performance, offering practical guidance for optimizing LDCA structures in deep excavation projects. Full article

To investigate the soil displacement rule caused by shield tunneling in soil–rock composite strata, the convergence mode of the shield excavation surface was analyzed. The research accounts for the variations in the slopes of the tunnel and the rock–soil interface along the excavation direction. Based on the stochastic medium theory, the calculation formula of soil displacement under different depths is derived. Surface subsidence was computed and evaluated using three engineering case studies. The results show that the calculated surface subsidence curves exhibit strong symmetry and are similar to the distribution pattern of the measured data. When tunneling through composite strata, the segments are prone to an upward floating motion, leading to a convergence pattern in the cross-section that tends toward a non-equal radial convergence mode with top tangency. Within the same project context, the grouting filling rate (δ) diminishes as the hard rock ratio (B) increases, exhibiting an approximate linear correlation. An increase in the hard rock ratio results in reduced values for lateral and longitudinal subsidence, the width of the lateral subsidence trough, and the main impact zone of the shield tunneling operations. Full article

Accurate prediction of the shield attitude is critical for controlling the excavation direction, ensuring construction safety, and advancing the sustainability of shield tunneling by reducing energy and environmental disturbance. Traditional prediction methods for the shield attitude have a certain lag and low prediction accuracy, and existing machine learning methods lack research on the varying importance of different parameters affecting the shield attitude, while also ignoring the global information characteristics of the data. To accurately predict the shield attitude and support sustainability-oriented operations, this study proposes a novel prediction model based on a project in Shenyang, China. The model utilizes a channel domain attention mechanism to learn the importance of various influencing parameters and extracts spatial features via a convolutional neural network. Additionally, it captures long-range dependency and local temporal features using a transformer augmented with a bidirectional long short-term memory network. Experimental results show that the proposed model achieves lower MAE and RMSE and higher R² compared with baseline and sub-models. Its generalization and reliability are further validated using data from another shield tunnel section. From a sustainability perspective, timely and high-fidelity predictions enable proactive steering that reduces unnecessary corrective actions and extreme operating states (e.g., thrust/torque spikes), which are associated with higher energy use, accelerated consumable wear, over-grouting, and potential surface disturbance. Finally, integrating the model’s predictions with onsite adjustment measures effectively mitigates alignment deviations, contributing to more energy-efficient, resource-conscious, and low-disturbance trajectory control. Full article

This study addresses the stability and deformation control of the Xiling auxiliary shaft in the Sanshandao Gold Mine during excavation, under the complex geological conditions of high in situ stress, high pore pressure, and elevated geothermal gradients. A thermal–hydraulic–mechanical (THM) coupling numerical model is developed to investigate the stress distribution, deformation mechanisms, and long-term stability of the surrounding rock under multi-physical interactions. Meanwhile, the influence of excavation rate on rock stability is analyzed. The results indicate that excavation induces significant stress redistribution, with stress concentrations in high-elastic-modulus strata, where the maximum compressive and tensile stresses reach 15.9 MPa and 14.1 MPa, respectively. The maximum displacement occurs in low-stiffness rock layers (around 1400 m depth), with a total magnitude of 1139 mm, primarily resulting from unloading relaxation, pore pressure reduction, and thermal contraction. Excavation rate strongly affects the temporal evolution of deformation: faster excavation leads to greater instantaneous displacements, whereas slower excavation suppresses displacement due to the sustained influence of thermal contraction. Based on these findings, particular attention should be paid to the low-stiffness strata near 1400 m depth during the construction of the Xiling auxiliary shaft. A combined support system consisting of high-prestress rock bolts, lining, and grouting is recommended for deformation-concentrated zones, while excavation rates should be optimized to balance efficiency and safety. Furthermore, long-term monitoring of temperature, pore pressure, and displacement is essential to achieve dynamic risk control. These results provide valuable theoretical and engineering insights for the safe construction and stability management of deep mine shafts. Full article

This paper systematically analyzes the challenges of stabilizing tunnel excavations in zones with low overburden in urban environments, through an engineering-validated case study of the Kobilja Glava Tunnel. A combined approach involving the New Austrian Tunneling Method (NATM) and the pre-installation of steel pipe umbrellas was applied as the primary pre-support measure under complex geotechnical conditions. The design, drilling, grouting, and formation of the temporary support arch were thoroughly documented, along with the implementation of shotcrete, lattice girders, self-drilling anchors, and reinforcement meshes. A numerical analysis was performed using the PLAXIS 2D software package, encompassing the modeling of deformations, shear forces, axial forces, and bending moments, with precisely defined support parameters. Geodetic monitoring recorded maximum surface settlements of up to 70 mm at an overburden of less than 3 m, while deformations were reduced to 28 mm at an overburden of 20 m. The numerical model confirmed soil plasticization within a 3 m wide zone, with maximum displacements reaching 6.3 cm, consistent with field measurements. Calculated tensile strain and angular distortion were classified according to established building damage criteria, confirming minimal structural impact on adjacent buildings. The applied combination of the NATM and the pipe umbrella pre-support system proved to be an effective and reliable solution for controlling deformations and ensuring excavation stability under conditions of limited rock cover and dense urban development. The obtained results provide a verified framework and practical recommendations for future tunneling projects in similar geotechnical and urban conditions, aiming to enhance safety, stability, and cost-effectiveness. Full article