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Ground reaction in terms of stress and displacement analysis is one of the major challenges in tunnel design and is helpful for understanding the stability around the excavation zone. In this paper, the analysis of stress, strain responses and radial displacement around circular tunnel excavated in cohesive-frictional granular materials is discussed via an innovative multi-scale approach (FEM × DEM) that combined finite element (FEM) and discrete element (DEM) methods and compared to other solutions obtained with conventional constitutive laws. Thanks to simulations, (i) the Ground response curve is then established and provides a better understanding of the complex behaviour in the vicinity of the tunnel; (ii) the prediction by FEM × DEM approach differs considerably from conventional constitutive laws; and (iii) in a unique manner, macroscopic and microscopic analyses are simultaneously performed showing that at the macroscopic level (FE mesh), diffuse failure mode are observed, while at the microscopic level (DEM level), microscopic evolutions are observed to be strictly related to the macroscopic behaviour. [ABSTRACT FROM AUTHOR]

A major full-scale experiment called the Tunnelling and Limitation of Impacts on Piles (TULIP) project was conducted in 2020 on Line 16 of the Grand Paris Express project to analyze the tunnel boring machine–soil–pile interactions during tunnel excavation near deep structures. This paper presents the greenfield ground response observed when the tunnel boring machine (TBM) crossed the TULIP site: surface displacements, subsurface displacements, and pore water pressures are presented. The originality of the paper lies in the fact that details are provided not only on the site geological and geotechnical characteristics, but also on the TBM operation: a detailed analysis of the variations in pressure inside the cutting chamber of the earth-pressure balanced machine (EPBM) is proposed. This paper reports factual data without bias induced by a preconceived numerical model, but highlights open questions that challenge the advanced numerical models, that will be required to analyze completely the tunnel–soil–pile interactions. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to accurately quantify the spatial constraint effect of tunnel excavation face, a generalized and improved form of virtual support force method is proposed, and the implementation steps of the method are given in detail. This approach is capable of demonstrating the variations in load release within the excavation section as well as the evolution of load release along the tunnel axis direction under the spatial restrictions of the tunnel face. Simultaneously, the presented approach is examined from the perspective of tunnel deformation and stress, and ultimately, the impact of the enhanced approach on the support timing determination is deliberated. A numerical model of a circular tunnel is established for analysis; the results show that, in terms of deformation and stress path, the enhanced virtual support force method can more closely resemble the actual three-dimensional excavation process than the traditional method. The improved virtual support force method can reduce the volume loss rate error by up to 3.76% and the stress error by up to 15.64% compared to the conventional method. As a result, the tunnel face's spatial limitation may be more accurately described by the enhanced virtual support force approach. The support point computed by the enhanced approach is further away from the tunnel face in the research of establishing the beginning support timing, which may more thoroughly mobilize the surrounding rock bearing and minimize support consumables. [ABSTRACT FROM AUTHOR]

The Tertiary water-rich sandstone has characteristics of poor consolidation, low strength, high water content and susceptibility to softening in contact with water. Unfavorable geological disasters, such as water and mud inrush, are frequently encountered during tunnel construction in Tertiary water-rich sandstone regions. However, the existing research on water and mud inrush disasters in tunnels through the Tertiary water-rich sandstone lacks a thorough analysis of the causal mechanisms and influencing factors. Taking the Wangjiazhai tunnel as an example, the evolution process, triggering factors and disaster modes of water and mud inrush disasters in Tertiary water-rich sandstone areas are investigated combined with the landform, stratigraphic lithology and hydrological conditions. A numerical analysis model considering physical and mechanical parameters is established based on COMSOL Multiphysics software to further reveal the disaster mechanism. The results show that factors contributing to the water and mud inrush disaster include the properties of the water-rich sandstone, groundwater conditions, excavation disturbance and recharge of rainfall. The disaster process can be divided into water-rich zone activation stage, transformation mass seepage stage, seepage-stress failure stage and post-disaster stage. Both the permeability and water pressure head increase as excavation progresses in water-rich zone activation stage. The internal porosity and the rate of change of seepage velocity increase as the excavation distance approaches the water-rich zone in transformation mass seepage stage. The effective plastic zone expands and reaches into the interior of the water-rich zone and the lower bench surrounding rock in seepage-stress failure stage. Based on the engineering geological condition and actual construction situation in the Tertiary water-rich sandstone area, sub-horizontal drainage and advance grouting methods can be adopted to mitigate the risk of water and mud inrush disasters. The research results can provide theoretical support for the development of predictive analysis for early warning systems, the improvement of the finite element model for fluid–structure coupling, and the investigation of new reinforcement materials for water and mud inrush disasters in areas with similar engineering geological conditions. [ABSTRACT FROM AUTHOR]

Tunnel boring machines (TBMs) are used to excavate tunnels in a manner where the rock is constantly penetrated with rotating cutter heads. Fine particles of the rock minerals are thereby generated. Workers on and in the vicinity of the TBM are exposed to particulate matter (PM) consisting of bedrock minerals including α-quartz. Exposure to respirable α-quartz remains a concern because of the respiratory diseases associated with this exposure. The particle size distribution of PM and α-quartz is of special importance because of its influence on adverse health effects, monitoring and control strategies as well as accurate quantification of α-quartz concentrations. The major aim of our study was therefore to investigate the particle size distribution of airborne PM and α-quartz generated during tunnel excavation using TBMs in an area dominated by gneiss, a metamorphic type of rock. Sioutas cascade impactors were used to collect personal samples on 3 separate days. The impactor fractionates the dust in 5 size fractions, from 10 µm down to below 0.25 µm. The filters were weighted, and the α-quartz concentrations were quantified using X-ray diffraction (XRD) analysis and the NIOSH 7500 method on the 5 size fractions. Other minerals were determined using Rietveld refinement XRD analysis. The size and elemental composition of individual particles were investigated by scanning electron microscopy. The majority of PM mass was collected on the first 3 stages (aerodynamic diameter = 10 to 0.5 µm) of the Sioutas cascade impactor. No observable differences were found for the size distribution of the collected PM and α-quartz for the 3 sampling days nor the various work tasks. However, the α-quartz proportion varied for the 3 sampling days demonstrating a dependence on geology. The collected α-quartz consisted of more particles with sizes below 1 µm than the calibration material, which most likely affected the accuracy of the measured respirable α-quartz concentrations. This potential systematic error is important to keep in mind when analyzing α-quartz from occupational samples. Knowledge of the particle size distribution is also important for control measures, which should target particle sizes that efficiently capture the respirable α-quartz concentration. [ABSTRACT FROM AUTHOR]

The vibration of rock breaking in tunnel excavation may cause serious damage to nearby buildings if it is not controlled properly. With reference to a hard rock tunnel in China, the vibration response to the high-pressure gas expansion method (HPGEM), an emerging rock-breaking approach, was investigated with field tests, theoretical derivations, and numerical simulations, then comparisons with the traditional dynamite blast were performed. Firstly, the vibration velocity prediction formulas of the two methods were fitted based on the field tests. Subsequently, the accuracy of the formula was verified by numerical simulation, and the vibration attenuation law of the HPGEM was explored. Comparisons were made between the blast and HPGEM, particularly the differences in peak particle velocity (PPV) for different agent qualities, distance from the blasting center, and engineering conditions. Furthermore, this study also analyzed the relationship between the agent qualities and the rock-breaking volume under different cases, finding that the HPGEM has slight vibration and good rock-breaking effect. The HPGEM is thus fully capable of replacing dynamite blasting to carry out rock-breaking operations in certain special areas. [ABSTRACT FROM AUTHOR]

The construction of mountain tunnels can lead to groundwater loss and severely impact plant growth. In order to study the limited discharge of groundwater in mountain tunnels for the normal growth of typical herbaceous plants, a tunnel in the alpine meadow area of Qinghai Province was taken as the research objective. Based on transplant experiments, numerical simulations, and the empirical calculation of tunnel discharge limits, the minimum water level required for the normal growth of herbaceous plants, groundwater changes, and grouting parameters during tunnel construction, as well as limited discharge values of groundwater based on the normal growth requirements of plants, were studied. The results indicate that when the groundwater level declined by 0.6–0.8 m, herbaceous plants were able to normally grow. Generally, tunnel excavation lowered the groundwater level so that the normal growth of herbaceous plants was significantly affected. The reasonable grouting parameters were obtained by numerical simulation. They were able to ensure that the groundwater level decline was less than 0.8 m and ultimately recovered to over 90% of the pre-construction level. The herbaceous plants in Qinghai's alpine grasslands were able to normally grow when the groundwater discharge limit was 0.2~4.0 m3/(m·d). This research offers guidance and support for managing groundwater discharge during tunnel construction in ecologically fragile areas, such as the Three Rivers Source in Qinghai. [ABSTRACT FROM AUTHOR]

Tunnel Boring Machines (TBMs) have been successfully applied in the excavation of deep shaft roadways in coal mines, yielding substantial socio-economic benefits. However, technical bottlenecks remain that hinder their further promotion and application. In response to the challenge of current support structures and techniques failing to simultaneously meet the requirements of support efficiency, strength, and construction costs, which impedes the full utilization of TBM speed advantages, a research team has developed a novel steel pipe segment assembly support structure. Large-scale model tests of the new prefabricated support structure were conducted to ascertain the deformation and failure patterns under loaded conditions, and the support structure was optimized based on the test results. Numerical simulations were performed to evaluate the reliability of the new support structure under TBM tunneling conditions. Industrial trials were subsequently conducted to field-test the feasibility of the new steel pipe segment support structure for TBM-excavated roadways in coal mines. The test results indicate that the maximum tensile strain of the surrounding rock is 803 με, and the deformation of the steel pipe support structure is less than 1 mm. The new support structure can be installed quickly, with the installation of one ring of segments (1.5 m) completed within 90 minutes, significantly enhancing the support strength in TBM-excavated roadways and the adaptability to strata conditions. This research provides a technical reference for further increasing the tunneling speed of coal mine roadways and ensuring the continuity of coal mining operations.

Excavation-induced fault instability has been known as a major barrier for underground engineering in deep rocks. A comprehensive understanding of unloading-induced stress changes on a pre-existing fault is a critical clue to reveal the mechanism of excavation-induced fault instability. Here we established a machine learning model based on eXtreme Gradient Boosting (XGBoost) to predict changes in normal stress, shear stress, and Coulomb failure stress along the fault due to tunnel excavation. We first created the training datasets based on discrete-element modeling and tested machine learning models to select a better performing model. We then conducted a relative importance analysis and showed that the horizontal stress on the model and the coordinates along the fault are two critical factors to predict the stress changes. We used the XGBoost model to further investigate the fault-slip rockburst during the construction of Jinping II Hydropower station and demonstrated the relationships between the stress changes and the failure locations. Finally, we discussed an interesting correlation between the stress changes (reduction-dominated and rotation-dominated) and the failure locations (initiation and termination) along the fault, which is crucial to understand the mechanism of excavation-induced fault instability and to forecast the fault failure during tunnel excavation. Highlights: Excavation-induced stress changes are critical to reveal the mechanism of fault instability. A XGBoost machine learning model is established to predict the stress changes along the fault. Correlation between stress changes and failure locations is revealed as a mechanism of fault instability. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An empirical model for describing the soil movements induced by tunneling is proposed, then the mathematical relationship between horizontal displacement and vertical displacement is obtained. By analyzing 25 sets of data from field engineering and 35 sets of data from model tests, the formula for the maximum settlement Sv, max(z) is optimized to adapt to different ground conditions. The Modified Gaussian function is developed by introducing the existing width coefficient of the settlement trough i(z) and the optimized Sv, max(z) to describe the surface and subsurface vertical displacement. Subsequently, the formula for the horizontal displacement is derived based on the Modified Gaussian function. H(z) representing the position of the oriented point of the soil movement is a variable in the formula for horizontal displacement. Based on measured results, a logarithmic function and a quadratic polynomial function are proposed to describe the variation of H(z) with depth in the clay stratum and sand stratum, respectively. Then, the rationality of the proposed method is validated by 4 sets of in-situ data and 4 sets of test data. Finally, the implementation process of the proposed method is illustrated, and the inversion results of the ground displacement field in Beijing Metro Line 12 are presented. [ABSTRACT FROM AUTHOR]

According to various human needs, such as mineral supply, transportation, and underground storage, tunnel excavation has become commonplace today. However, one of the undesirable phenomena encountered during tunnel excavating, particularly when employing drilling and blasting techniques, is the overbreak phenomenon (OBP). This phenomenon not only compromises the safety of the work environment but also leads to increased operating costs. Therefore, accurately predicting the occurrence of OBP in tunnel excavation is of utmost importance. Due to the numerous uncertainties and complexities associated with rock formations, traditional methods have limited accuracy in predicting OBP. Consequently, this research used the rock engineering system (RES) method to comprehensively understand the physical and mechanical characteristics of the rock mass at any given point. By employing the RES method, accurate modeling of the OBP can be achieved in a time- and cost-efficient manner without requiring extensive and complicated coding. To construct the model using the RES method, 217 data points from three case studies were utilized: the Tarzeh underground coal mine in Iran, the Azad tunnel on the Tehran-North road in Alborz, Iran, and an Indian mine. The parameters considered in this study that affect the OBP (%) included perimeter hole powder factor (PPF, kg/m3), spacing-to-burden ratio of contour holes (S/B, kg), tunnel section area (A, m2), specific drilling (SD, m/m3), and rock mass rating (RMR, %). To compare and evaluate the RES method, various regression methods were also employed. Statistical criteria revealed that the RES method (RMSE = 0.0046, MSE = 0.068, R2 = 0.945) demonstrated high accuracy compared to other regression methods. Consequently, it can be concluded that the RES is a highly valuable and essential tool for rock engineers. [ABSTRACT FROM AUTHOR]

Rainfall infiltration greatly affects the stability of the surrounding rock in the construction of water tunnels in loess areas. The unsaturated seepage theory and numerical simulation method were used to study the deformation and seepage field evolution of the surrounding rock under the coupling influence of extreme rainfall infiltration and the excavation disturbance of loess gully area tunnel, and the coupled flow-solidity analysis was carried out through the Plaxis3D model to analyze the mechanical properties of the surrounding rock and the initial support process in the construction of Xin'ao method under rainfall infiltration. The results show that the higher the rainfall level is, the larger the pore water pressure change of the surrounding rock is, and the more unfavorable it is to the stability of the surrounding rock, rainfall infiltration and excavation disturbance will accelerate the redistribution process of seepage and stress fields in the soil layer. Based on the catchment characteristics of the trench, the water content of the surrounding rock of the tunnel shows a stepwise increase in the first 5~10 d, and the maximum deformations at the top of the arch, the waist of the arch, and the toe of the arch are 17. 8 mm, 28. 2 mm, and 24. 6 mm, with maximum shear deformations at the top, waist, and toe of the arch, 24. 6 mm, the maximum shear stress is 150. 6 kPa, 182. 5 kPa, 175. 3 kPa, rainfall end about 15~20 d perimeter rock deformation rate gradually reduce convergence to a specific value, but the stress of the perimeter rock continues to increase, in order to avoid plastic deformation of the perimeter rock, so can be carried out in the 15~20 d of the second lining support. The results of this study can provide reference for the safety control of tunnel construction in loess gully area during extreme rainfall. [ABSTRACT FROM AUTHOR]

A simplified two-stage method was employed to provide an explicit solution for the time-dependent tunnel-rock interaction, considering the generalized Zhang-Zhu strength criterion. Additionally, a simplified mechanical model of the yielding support structure was established. The tunnel excavation is simplified to a two-stage process: the first stage is affected by the longitudinal effect, while the second stage is affected by rheological behavior. Two cases are considered: one is that the rigid support is constructed during the first stage, and the other is that constructed at the second stage. Distinguished by the support timing at the seconde stage, different kinds of the “yield-resist combination” support method are divided into three categories: “yield before resist” support, “yield-resist” support, and “control-yield-resist” support. Results show that the support reaction of “control-yield-resist” is much higher than that of “yield before resist” if the initial geostress is not very high, but the effect is not obvious on controlling the surrounding rock deformation. So, the “yield before resist” support is much more economical and practical when the ground stress is not very high. However, under high geostress condition, through applying relatively high support reaction actively to surrounding rock at the first stage, the “control-yield-resist” support is superior in controlling the deformation rate of surrounding rock. Therefore, in the high geostress environment, it is recommended to construct prestressed yielding anchor immediately after excavation, and then construct rigid support after the surrounding rock deformation reaches the predetermined deformation.

Three-dimensional (3D) roughness of discontinuity affects the quality of the rock mass, but 3D roughness is hard to be measured due to that the discontinuity is invisible in the engineering. Two-dimensional (2D) roughness can be calculated from the visible traces, but it is difficult to obtain enough quantity of the traces to directly derive 3D roughness during the tunnel excavation. In this study, a new method using Bayesian theory is proposed to derive 3D roughness from the low quantity of 2D roughness samples. For more accurately calculating 3D roughness, a new regression formula of 2D roughness is established firstly based on wavelet analysis. The new JRC3D prediction model based on Bayesian theory is then developed, and Markov chain Monte Carlo (MCMC) sampling is adopted to process JRC3D prediction model. The discontinuity sample collected from the literature is used to verify the proposed method. Twenty groups with the sampling size of 2, 3, 4, and 5 of each group are randomly sampled from JRC2D values of 170 profiles of the discontinuity, respectively. The research results indicate that 100%, 90%, 85%, and 60% predicting JRC3D of the sample groups corresponding to the sampling size of 5, 4, 3, and 2 fall into the tolerance interval [JRCtrue–1, JRCtrue + 1]. It is validated that the sampling size of 5 is enough for predicting JRC3D. The sensitivities of sampling results are then analyzed on the influencing factors, which are the correlation function, the prior distribution, and the prior information. The discontinuity across the excavation face at ZK78 + 67.5 of Daxiagu tunnel is taken as the tunnel engineering application, and the results further verify that the predicting JRC3D with the sampling size of 5 is generally in good agreement with JRC3D true values.

Tunnel construction adjacent to the fault fracture zone is prone to water inrush disasters, which pose a serious threat to the safety of tunnel construction. To provide theoretical support for the early warning and prevention of water inrush disasters of the tunnel adjacent to the water-rich faults, a numerical analysis based on the three-dimensional discrete element method (DEM) was performed to study the evolution of the displacement and seepage fields of the water-resistant rock mass of a tunnel adjacent to a water-rich fault during the water inrush process by taking the Xianglushan tunnel as the research project. With reference to the obtained results, a grouting reinforcement scheme was developed, and its effectiveness was evaluated. The results indicated that as the tunnel face approached the water-rich fault fracture zone, the effect of water pressure gradually became obvious, and the displacement at the face continuously increased. When the tunnel face was excavated to the position 5 m from the fault, the displacement at the center of the face changed suddenly with a sudden increase in water pressure. The water-resistant rock mass ahead of the center of the face was damaged, and a water inrush disaster occurred in the tunnel. Numerical simulation results demonstrated the feasibility of the grouting reinforcement scheme. The assessment based on the borehole acoustic waves, borehole TV, geological radar detection, and convergence monitoring as well as the excavation results confirmed that the water inrush disasters in the 2# adit of Xianglushan tunnel adjacent to the water-rich fault were effectively prevented and controlled, which can provide a reference for the prevention and treatment of the frequent water inrush disasters in underground projects constructed in the water-rich fault area. [ABSTRACT FROM AUTHOR]

During new Austrian tunnelling method excavation, it is necessary to carry out an analysis of the compliance of the actual surfaces with the theoretical lines prescribed in the support types for each tunnel excavation step. With our own software solutions, we created point clouds of the excavation and shotcrete of the primary tunnel support through the automated process of photogrammetric data. Together with the tunnel axis and theoretical profiles, the georeferenced and filtered point clouds were then used in the analysis of the deviation from the theoretical lines of excavation and primary support shotcrete and shotcrete thickness. The final products of the independent analysis are deviation profiles and unwrapped extrados views with numerical results and a color legend. [ABSTRACT FROM AUTHOR]

The content of this study combines city safety, optimum excavation situation, mining, geology, and civil engineering principles. Tunnel boring machines (TBM) are the most commonly used machines in the excavation of urban tunnels. These machines prevent the inward movement of the tunnel face and control the amount of settlement formed on the ground by applying pressure to the tunnel face. The most important question here is to determine the amount of pressure to be applied to the tunnel face. There are many widely accepted formulas used in the calculation of the face pressure and these formulas generally attempt to limit the settlements on the ground by using parameters such as groundwater level, overburden thickness, physical and mechanical properties of the surrounding rocks, etc. In this study, a new formula was developed. This new formula calculates the face pressure required to be applied by EPB to the tunnel face in order to prevent damage to a structure located on the route and within the area to be affected by tunnel excavation, instead of only preventing settlements on the surface. In the formula, produced within the scope of this study, in addition to other studies, 3D distances of the structure to which the deformation limitation will be made to prevent damage is also one of the parameters. [ABSTRACT FROM AUTHOR]

Due to the complex urban geological environment and physicochemical interactions, the physical and mechanical parameters of the cohesive soil layer in the adjacent construction area show strong spatial variability and correlation. In addition, the actual exploration and test data are very limited because of limited technical and economic conditions. This severely restricts the ability to evaluate the stability of adjacent structures and to prevent and control instability disasters during subway construction. In this study, a generation method of limited sample data for the cohesive soil layer in the adjacent construction area is proposed. The spatial variability and correlation of uncertain mechanical parameters for the clay layer are quantified using incomplete probability data. A calculation method of uncertain settlement for the cohesive soil layer in the adjacent construction area is developed. The distribution fitting tests of settlement characteristics are conducted with different joint distribution functions and correlation structure. A reliability analysis and risk assessment methodology for the settlement of the cohesive soil layer is presented. The reliability value and failure probability induced by undercrossing tunnel excavation are analyzed and predicted. The results show that the bootstrap simulated sampling and random field method can quantify the cohesive soil layer heterogeneity reasonably under limited investigation data. Different joint distribution and correlation structure functions have different effects on the distribution fitting test. The uncertain settlement of the upper center of the tunnel is the largest, and the failure disaster is most likely to occur. The effects of a copula structure and correlation parameter on the failure probability of the cohesive soil layer are sensitive. This research can provide scientific support for public safety and sustainable development in urban subway construction. [ABSTRACT FROM AUTHOR]

Grouting is a widely used approach to reinforce broken surrounding rock mass during the construction of underground tunnels in fault fracture zones, and its reinforcement effectiveness is highly affected by geostress. In this study, a numerical manifold method (NMM) based simulator has been developed to examine the impact of geostress conditions on grouting reinforcement during tunnel excavation. To develop this simulator, a detection technique for identifying slurry migration channels and an improved fluid-solid coupling (F–S) framework, which considers the influence of fracture properties and geostress states, is developed and incorporated into a zero-thickness cohesive element (ZE) based NMM (Co-NMM) for simulating tunnel excavation. Additionally, to simulate coagulation of injected slurry, a bonding repair algorithm is further proposed based on the ZE model. To verify the accuracy of the proposed simulator, a series of simulations about slurry migration in single fractures and fracture networks are numerically reproduced, and the results align well with analytical and laboratory test results. Furthermore, these numerical results show that neglecting the influence of geostress condition can lead to a serious overestimation of slurry migration range and reinforcement effectiveness. After validations, a series of simulations about tunnel grouting reinforcement and tunnel excavation in fault fracture zones with varying fracture densities under different geostress conditions are conducted. Based on these simulations, the influence of geostress conditions and the optimization of grouting schemes are discussed.

Shield machine may deviate from its design axis during excavation due to the uncertainty of geological environment and the complexity of operation. This study therefore introduced a framework to predict the attitude and position of shield machine by combining long short-term memory (LSTM) model with attention mechanism. The data obtained from the Wuhan Rail Transit Line 6 project were utilized to verify the feasibility of the proposed method. By adding the attention mechanism into the LSTM model, the proposed model can focus more on parameters with higher weights. Sensitivity analysis based on Pearson correlation coefficient was conducted to improve the prediction efficiency and reduce the irrelevant input parameters. Compared with LSTM model, LSTM-attention model has higher accuracy. The mean value of coefficient of determination (R2) increases from 0.625 to 0.736, and the mean value of root mean square error (RMSE) decreases from 3.31 to 2.24. The proposed LSTM-attention model can provide an effective prediction for attitude and position of shield machine in practical tunneling engineering.

The sanding process caused by karstification in dolomite creates a special sandy dolomite stratum, where the frequent catastrophic instability of the surrounding rock occurred during tunnel construction. In this study, the micro-origin and macro-performance of the sandy dolomite stratum are first discussed. Then, a numerical model based on the coupling method between the discontinuous deformation analysis and smoothed particle hydrodynamics is proposed to depict the heterogeneous dolomite formation with different sanding degrees. Following, the mechanical behaviors of the heterogeneous dolomite samples under uniaxial compression are studied after calibrating the numerical parameters with the two single materials sampled from the tunnel site respectively. Further, the instability disasters of the dolomite surrounding rock with different sanding degrees are reproduced, and the failure behaviors of tunnels are explained with respect to the stress distribution and plastic zone. The obtained results show that the rotation and dislocation of the remained dolomite block contribute to the unsmooth stress–strain curve and deterioration in uniaxial compressive strength. However, the block serves as the skeleton in the transmission of field stress in underground space, which improves the stability of the formation.

In order to accurately quantify the spatial constraint effect of tunnel excavation face, a generalized and improved form of virtual support force method is proposed, and the implementation steps of the method are given in detail. This approach is capable of demonstrating the variations in load release within the excavation section as well as the evolution of load release along the tunnel axis direction under the spatial restrictions of the tunnel face. Simultaneously, the presented approach is examined from the perspective of tunnel deformation and stress, and ultimately, the impact of the enhanced approach on the support timing determination is deliberated. A numerical model of a circular tunnel is established for analysis; the results show that, in terms of deformation and stress path, the enhanced virtual support force method can more closely resemble the actual three-dimensional excavation process than the traditional method. The improved virtual support force method can reduce the volume loss rate error by up to 3.76% and the stress error by up to 15.64% compared to the conventional method. As a result, the tunnel face’s spatial limitation may be more accurately described by the enhanced virtual support force approach. The support point computed by the enhanced approach is further away from the tunnel face in the research of establishing the beginning support timing, which may more thoroughly mobilize the surrounding rock bearing and minimize support consumables.

• Elastic field for layered composite rock with excavated tunnels is predicted by a semi-analytical method. • The layer and tunnel are considered as inhomogeneities of different elastic moduli through employing the EIM. • A yield approximate index is used to evaluate safety of layered composite rock with excavated tunnels. • Effects of parameters of the layer and tunnel on the elastic field and plastic zones are discussed. Tunnels excavation in layered composite rock subjected to ground loads to make the best of underground space is an important engineering problem in more and more mega-cities. Such a three-dimensional case, layered composite rock with excavated tunnels, is usually simplified as a two-dimensional plane strain problem in mechanics. The present study reports a Semi-Analytical Method (SAM) to predict elastic field of an excavated layered composite rock with the assistance of the Equivalent Inclusion Method (EIM) that can handle elastic field of the layers and tunnels simultaneously. In the EIM, the layer and tunnel are considered as inhomogeneities of different elastic moduli from the base rock, and the inhomogeneities are further equivalent to inclusions of identical elastic modulus to the base rock but including eigenstrains. Effectiveness of the SAM is examined by the Finite Element Method (FEM) through comparing their results. Moreover, a yield approximate index (YAI) is introduced to evaluate safety of excavated layered composite rock and acoustic emission (AE) event is used to count the number of plastic yield elements. Finally influences of depth of and distance between the tunnels, thickness, elastic modulus, number of the layer, range of ground load on principal stress, YAI , plastic zones are discussed, which may have potentials to provide guidance for practical engineering applications of tunnel excavation. [ABSTRACT FROM AUTHOR]

Recently, global urbanization and industrialization have resulted in excessive groundwater exploitation, and the occurrence and damage of land subsidence to human life and property are increasing accordingly. The present study assessed the impact of tunnel excavation on the groundwater system and potential land subsidence in a Korean metropolitan area. A numerical model was established to predict groundwater level variations with tunnel excavation, and the mechanisms and cases of land subsidence worldwide were reviewed. The established model adequately represented the groundwater system in the study area. The tunnel excavation decreased the groundwater level along the tunnel line, and significant groundwater drawdown primarily occurred up to 6.1 m at locations with high permeability, leading to the temporary development of a large depression cone. The study area has favorable conditions for land subsidence, and curved tunnel excavation may induce ground disturbance, resulting in groundwater inflow and soil loss in the region. In addition, the risk of land subsidence is expected to persist owing to the lag time caused by the creep phenomenon, even though the groundwater level recovers. Efforts to effectively reduce land subsidence damage in urban areas are crucial, requiring measures such as controlling land subsidence occurrence and implementing prevention measures through early recognition, including artificial recharge of groundwater, underground cavity observation with ground penetrating radar, land subsidence observation with a borehole extensometer, and groundwater level monitoring systems. [ABSTRACT FROM AUTHOR]

To study the stability of roof areas in the process of rapid driving in coal roadways, the deformation law of roof areas under the interaction of different factors is systematically analyzed through mechanical analysis, numerical calculation, and industrial testing, yielding a reasonable selection basis of the critical parameters of roof space stability. The roof is difficult to control when the unsupported roof distance exceeds 2.0 m and the roof thickness is less than 0.9 m. Considering the tunnel excavation safety and effectiveness, the support technology principles of "large-angle control span" and "classification control technology of roadway surrounding rock stability" based on the support "small-step" excavation method were realized in the case study of the 150,802 machine roadway of Liuzhuang Coal Mine, China. The resulting rapid tunneling system made it possible to increase the tunneling speed from 300 to 500 m/month, i.e. by 67%. The whole roadway remained relatively stable, verifying the proposed approach feasibility. [ABSTRACT FROM AUTHOR]

Taking mechanical property differences of rock and soil layers into consideration, a method of calculating ground settlement caused by tunnel excavation in composite strata by means of uniting complex variable function and stochastic medium theory is proposed. Firstly, via complex variable function the analytical solution of rock strata under the conditions of self-weight of upper soil layer and non-uniform deformation of tunnel can be obtained, and the settlement deformation of rock-soil interface is gotten, and regard the area surrounded by the interface as “unequal thickness excavation”. Then, with the use of stochastic medium theory, surface settlement value is calculated. By summing up two examples of tunnel excavation in composite strata and analyzing the differences between calculated results and measured values, it can be noted that the agreement between calculated results and measured values of geotechnical stratification method is obviously better than the calculation method considering rock and soil layers as medium. In addition, it is concluded that the tunnel convergent deformation influences strata deformation more and surface less by considering the influence of different tunnel convergent deformation modes, soft-hard ratio of overlying strata and influence angles of soft soil on strata deformation. The soft-hard ratio of overlying strata has a great influence on strata deformation and influence zone. The larger the influence angle of soil layer is, the larger surface deformation will go, and the influence zone of ground surface will reduce with it. [ABSTRACT FROM AUTHOR]

The method of surface displacement prediction of tunnel convergence displacement is used to make up for the failure of tunnel convergence displacement monitoring in the construction process, to supplement and verify the tunnel monitoring data, and to guide the construction. Firstly, some sets of systolic displacement and surface displacement data are obtained by field monitoring, which is used to calculate the parameter vector to be determined. The corresponding mathematical model is established and the systolic displacement of tunnel is predicted according to the monitoring data of surface displacement. Combined with field tunnel displacement monitoring and surface displacement monitoring, the correlation of displacement curve is analyzed, and the corresponding mathematical model is established. Combined with Matlab programming, the corresponding program language is written, the user interface is compiled, and the method of predicting tunnel convergence displacement by the ground displacement is realized. [ABSTRACT FROM AUTHOR]

The application of explosive blasting for rock breaking works was not possible in densely populated areas, which caused problems in urban tunnel construction. In the application of dry ice powder thermal shock breaking in tunnel excavation, a vibration monitoring system was employed to monitor the vibration response of the tunnel structure during the breaking process, and it was used to extract the signal characteristics by Hilbert-Huang transformation. Experimental results are as follows: 1) The peak vibration speed was below 50 mm/s for concrete structures safe as long as it was farther than 10 m from the burst hole in the support concrete. 2) Aggregate decay of vibration velocities caused by thermal shock breaking of rock with dry ice powder corresponded to the decay law of the power function. The range of influence of the vibration was considerably smaller compared to that of drilling and blasting the rock; 3) The new rock-breaking technology induced damage can be divided into three regions, with radial fractures generated by high-energy fluids dominating. 4) Hilbert Huang transform extracted signal features more objectively and accurately, with excellent reference for the safety monitoring of tunnel structures. [ABSTRACT FROM AUTHOR]

Taking the twin-tunnel shield tunnel of the urban rail transit in Lanzhou City as an example, this article applies the hardening soil small criterion and utilizes finite element software to simulate the excavation process of the undercrossing Yellow River tunnel. The analysis focuses on the deformation effects and axial force variations of nearby bridge foundations in three directions: vertical to the tunnel, along the tunnel, and the vertical direction. The simulation results are compared with monitoring data. The findings indicate that shield tunnel construction increases the deformation of bridge foundations in the vertical and tunnel directions, while mitigating the deformation in the vertical direction. The influence is more significant as the distance between the tunnel and the foundations decreases. The redistribution of stress due to soil disturbance causes foundation deformation, and the magnitude of foundation deformation reflects the extent of soil disturbance. The simulated vertical displacement of the pile head is consistent with the trend observed in the field measurements. The simulation results generally align with the conclusion that the tunnel has minimal impact on the soil beyond a distance of 3–5 times the tunnel diameter.

Abstract Surrounding rock mass fracture characteristics play a significant role in the understanding of the CO2 geological storage and utilization (CGSU) engineering practices in abandoned mines. The combined finite discrete element method (FDEM) shows advantages in simulating fracture and fragmentation of rock-like materials, however, many computational parameters and a lack of basis for accurate values affect the simulation results. For systematic explorations of the influence of the effect of model parameters with different time steps, this study conducted different loading rate specimen tests and unloading rate tests both in laboratory-scale tests and field-scale based on the CUDA-based GPU parallel FDEM program. In laboratory-scale uniaxial compressive strength (UCS) tests, a smaller loading rate ensures a quasi-static loading process and should be below 0.1 ms−1 for simulation. Then, continuous optimization and improvement of the GPU parallel FDEM in tunnel excavation were proposed, and the model parameters reflect the continuous improvement of the simulation results. In the process, the tunnel excavation simulation method with the reduction rate of the opening zone’s Young's modulus in the excavation was performed to investigate the unloading mode and rate by continuing to optimize the GPU parallel FDEM program and model parameters. Besides, the main factor in fracture mode and failure mechanism of the surrounding rock mass also was calibrated. The results indicate that the system kinetic energy of the model is maintained at a small level with the reasonable unloading mode and critical threshold set at a small value, the damping parameters, dissipation mechanism, and excavation fractures are clearer and reasonable, and the computational cost is significantly reduced with GPU parallel FDEM.

The construction of mountain tunnels can lead to groundwater loss and severely impact plant growth. In order to study the limited discharge of groundwater in mountain tunnels for the normal growth of typical herbaceous plants, a tunnel in the alpine meadow area of Qinghai Province was taken as the research objective. Based on transplant experiments, numerical simulations, and the empirical calculation of tunnel discharge limits, the minimum water level required for the normal growth of herbaceous plants, groundwater changes, and grouting parameters during tunnel construction, as well as limited discharge values of groundwater based on the normal growth requirements of plants, were studied. The results indicate that when the groundwater level declined by 0.6–0.8 m, herbaceous plants were able to normally grow. Generally, tunnel excavation lowered the groundwater level so that the normal growth of herbaceous plants was significantly affected. The reasonable grouting parameters were obtained by numerical simulation. They were able to ensure that the groundwater level decline was less than 0.8 m and ultimately recovered to over 90% of the pre-construction level. The herbaceous plants in Qinghai’s alpine grasslands were able to normally grow when the groundwater discharge limit was 0.2~4.0 m3/(m·d). This research offers guidance and support for managing groundwater discharge during tunnel construction in ecologically fragile areas, such as the Three Rivers Source in Qinghai.

The vibration of rock breaking in tunnel excavation may cause serious damage to nearby buildings if it is not controlled properly. With reference to a hard rock tunnel in China, the vibration response to the high-pressure gas expansion method (HPGEM), an emerging rock-breaking approach, was investigated with field tests, theoretical derivations, and numerical simulations, then comparisons with the traditional dynamite blast were performed. Firstly, the vibration velocity prediction formulas of the two methods were fitted based on the field tests. Subsequently, the accuracy of the formula was verified by numerical simulation, and the vibration attenuation law of the HPGEM was explored. Comparisons were made between the blast and HPGEM, particularly the differences in peak particle velocity (PPV) for different agent qualities, distance from the blasting center, and engineering conditions. Furthermore, this study also analyzed the relationship between the agent qualities and the rock-breaking volume under different cases, finding that the HPGEM has slight vibration and good rock-breaking effect. The HPGEM is thus fully capable of replacing dynamite blasting to carry out rock-breaking operations in certain special areas.

This paper proposes a temporary support system for improving the efficiency and safety of underground roadway excavation in coal mines. Firstly, this study establishes a calculation model for the initial supporting force of the excavation of roadway temporary support and a gray system-based automatic prediction model for the initial supporting force level, based on the mechanism of temporary support controlling the roof. These models enable the prediction of the required initial supporting force at different locations along the roadway's temporary support area, thereby providing a basis for controlling the initial supporting force of the temporary support system. To achieve efficient and adaptive control of the initial supporting force of temporary supports at different locations, this study designs a support force controller based on Simulated Annealing Particle Swarm Optimization Proportional-Integral-Derivative (SAPSO-PID). This study establishes a mathematical model for the hydraulic cylinder pressure system controlled by the temporary support overflow valve and conducts a stability analysis and model verification. The study constructs a simulation control system for the initial supporting force based on SAPSO-PID using the combined simulation platform of AMESim and Matlab. The simulation results demonstrate that the proposed support force control system efficiently achieves adaptive control of the initial supporting force of temporary supports. An experimental system in the underground roadway of a coal mine is constructed to validate the results of the simulation analysis. [ABSTRACT FROM AUTHOR]

With the growing demand for transportation, there has been a significant increase in road-related projects, leading to potential risks in the safety of existing structures. This paper presents a study on the influence of new tunnel construction on the stability of an adjacent existing tunnel and provides valuable insights for the safety technology evaluation of similar tunnel crossing projects. In order to evaluate the influence of tunnel excavation on adjacent tunnels, the excavation process of a new tunnel near the original tunnel is simulated using the finite element software Midas GTS. This analysis includes the evaluation of static and dynamic responses. The results indicate that the horizontal and vertical displacements caused by the excavation of the railway tunnel are minimal. Furthermore, during the blasting excavation of the railway tunnel, the vibration velocity experienced by the highway tunnel remains below the safe allowable limit. These findings demonstrate that in this project, the influence of blasting excavation for the railway tunnel on the highway tunnel is both safe and manageable. [ABSTRACT FROM AUTHOR]

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The content of this study combines city safety, optimum excavation situation, mining, geology, and civil engineering principles. Tunnel boring machines (TBM) are the most commonly used machines in the excavation of urban tunnels. These machines prevent the inward movement of the tunnel face and control the amount of settlement formed on the ground by applying pressure to the tunnel face. The most important question here is to determine the amount of pressure to be applied to the tunnel face. There are many widely accepted formulas used in the calculation of the face pressure and these formulas generally attempt to limit the settlements on the ground by using parameters such as groundwater level, overburden thickness, physical and mechanical properties of the surrounding rocks, etc. In this study, a new formula was developed. This new formula calculates the face pressure required to be applied by EPB to the tunnel face in order to prevent damage to a structure located on the route and within the area to be affected by tunnel excavation, instead of only preventing settlements on the surface. In the formula, produced within the scope of this study, in addition to other studies, 3D distances of the structure to which the deformation limitation will be made to prevent damage is also one of the parameters.

Tunnel construction adjacent to the fault fracture zone is prone to water inrush disasters, which pose a serious threat to the safety of tunnel construction. To provide theoretical support for the early warning and prevention of water inrush disasters of the tunnel adjacent to the water-rich faults, a numerical analysis based on the three-dimensional discrete element method (DEM) was performed to study the evolution of the displacement and seepage fields of the water-resistant rock mass of a tunnel adjacent to a water-rich fault during the water inrush process by taking the Xianglushan tunnel as the research project. With reference to the obtained results, a grouting reinforcement scheme was developed, and its effectiveness was evaluated. The results indicated that as the tunnel face approached the water-rich fault fracture zone, the effect of water pressure gradually became obvious, and the displacement at the face continuously increased. When the tunnel face was excavated to the position 5 m from the fault, the displacement at the center of the face changed suddenly with a sudden increase in water pressure. The water-resistant rock mass ahead of the center of the face was damaged, and a water inrush disaster occurred in the tunnel. Numerical simulation results demonstrated the feasibility of the grouting reinforcement scheme. The assessment based on the borehole acoustic waves, borehole TV, geological radar detection, and convergence monitoring as well as the excavation results confirmed that the water inrush disasters in the 2# adit of Xianglushan tunnel adjacent to the water-rich fault were effectively prevented and controlled, which can provide a reference for the prevention and treatment of the frequent water inrush disasters in underground projects constructed in the water-rich fault area.

Tunnel construction in karst areas greatly impacts the local hydrological conditions. The drawdown of groundwater levels and the loss of soil water storage due to tunneling limit the available water resources on the karst land surface, and this may affect the function of plants. Here, we evaluated the responses of the radial growth rates of two major tree species (Masson pine and Camphor laurel) to a tunneling induced water stress event in a typical karst trough valley. Meanwhile, to discuss the overall influence of tunnel excavation on plant growth in all vegetation cover types, the dynamics of vegetation productivity around the tunnel were evaluated using remote sensing indices, the Normalized Difference Vegetation Index (NDVI), and Net Primary Productivity (NPP). Furthermore, we estimated the spatial–temporal variations of NDVI and NPP in other tunneling regions of Southwest China. The results showed that the soil moisture contents (SMC) around the Zhongliang Mountain Railway Line 6 (ZMRL6) tunnel had dramatically declined −5.06%∼−10.53% within the areas

The shield machine is clogged frequently when tunneling in cohesive strata. Shield clogging is closely linked to the shear strength exhibited at the clay-metal interface. To investigate the impact of anti-sticking coating technology on the shear strength at the clay-metal interface, a series of direct shear tests were conducted. The obtained test results revealed an initial increase in shear stress at the clay-metal interface as shear displacement increased, eventually reaching a state of stabilization. The shear strength exhibited a gradual increase initially, followed by a significant increase, and eventually reached a plateau with the rise in the consistency index. It was observed that the adhesion between the anti-adhesion coating and clay was relatively weak, but the presence of the anti-adhesion coating effectively reduced the risk of shield clogging.