Tunnel Face Research Articles

MCS-based quantile value approach for reliability-based design of tunnel face support pressure

This paper develops a new approach for reliability-based design (RBD) of tunnel face support pressure from a quantile value perspective. A surrogate model is constructed to calculate the collapse pressures of the random samples generated by a single run of Monte Carlo simulation (MCS). The cumulative distribution function (CDF) of the collapse pressure is then obtained and the support pressure aiming at a target failure probability is chosen as the upper quantile value of the collapse pressures. The proposed approach does not require repetitive reliability analyses compared to the existing methods. Moreover, a direct relationship between the target failure probability and the required support pressure is established. An illustrative example is used to demonstrate the implementation procedure. The accuracy of the reliability-based support pressures is verified by direct MCS incorporating with three-dimensional numerical simulations. Finally, the influencing factors, including the sample size of MCS, the correlation coefficient between random variables, the choice of experimental points, and the surrogate model, are investigated. This method can play a complementary role to available approaches due to its advantages of simplicity and efficiency.

Evolution Law and Grouting Treatment of Water Inrush in Hydraulic Tunnel Approaching Water-Rich Fault: A Case Study

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.

RCEAU-Net: Cascade Multi-Scale Convolution and Attention-Mechanism-Based Network for Laser Beam Target Image Segmentation with Complex Background in Coal Mine.

Accurate and reliable pose estimation of boom-type roadheaders is the key to the forming quality of the tunneling face in coal mines, which is of great importance to improve tunneling efficiency and ensure the safety of coal mine production. The multi-laser-beam target-based visual localization method is an effective way to realize accurate and reliable pose estimation of a roadheader body. However, the complex background interference in coal mines brings great challenges to the stable and accurate segmentation and extraction of laser beam features, which has become the main problem faced by the long-distance visual positioning method of underground equipment. In this paper, a semantic segmentation network for underground laser beams in coal mines, RCEAU-Net, is proposed based on U-Net. The network introduces residual connections in the convolution of the encoder and decoder parts, which effectively fuses the underlying feature information and improves the gradient circulation performance of the network. At the same time, by introducing cascade multi-scale convolution in the skipping connection section, which compensates for the lack of contextual semantic information in U-Net and improves the segmentation effect of the network model on tiny laser beams at long distance. Finally, the introduction of an efficient multi-scale attention module with cross-spatial learning in the encoder enhances the feature extraction capability of the network. Furthermore, the laser beam target dataset (LBTD) is constructed based on laser beam target images collected from several coal mines, and the proposed RCEAU-Net model is then tested and verified. The experimental results show that, compared with the original U-Net, RCEAU-Net can ensure the real-time performance of laser beam segmentation while increasing the Accuracy by 0.19%, Precision by 2.53%, Recall by 22.01%, and Intersection and Union Ratio by 8.48%, which can meet the requirements of multi-laser-beam feature segmentation and extraction under complex backgrounds in coal mines, so as to further ensure the accuracy and stability of long-distance visual positioning for boom-type roadheaders and ensure the safe production in the working face.

Effect of advance rate on excess pore water pressure induced by TBM tunnelling in saturated sand

The stability of tunnel face can be significantly influenced by the excess pore water pressure induced by tunnel boring machine (TBM) tunnelling in saturated sand. This article aims to investigate the effect of TBM advance rate on the variation of such excess pore water pressure. Numerical and analytical solutions are given for the situations of TBM advance rate faster and slower than the slurry infiltration velocity, respectively. It appears that the excess pore water pressure at the tunnel face maintains constant with time when the TBM advance rate exceeds the slurry infiltration velocity and the gradient close to the TBM decreases with distance. In the opposite situation, there is a temporal decrease in excess pore water pressure at the tunnel face, accompanied by a more gradual spatial drop in pressure. In addition, the gradient close to the TBM remains constant. Notably, a larger extent of excess pore water pressures is present in the latter situation, augmenting the risk of a blow-out during tunnelling. Comparative analysis of field measurements and theoretical calculations indicates that the conditions at Green Heart Tunnel align with the latter situation. Furthermore, for the latter situation, a slower TBM advance rate will result in a higher discharge and thus a higher pore water pressure.

Forward and inversion approach for direct current resistivity based on an unstructured mesh and its application to tunnel engineering

AbstractThe accurate identification of water‐bearing structures is urgently required for the safe construction of tunnel engineering. Currently, the direct current resistivity method is an effective method for detecting water‐bearing structures in tunnels. In the advanced detection of the direct current resistivity based on the finite element method, the traditional hexahedron mesh performs poorly for the discretization of models of complex tunnel structure sections such as horseshoe‐shaped and round sections. Therefore, this study adopts unstructured grid generation technology combining tetrahedra and hexahedra to achieve more accurate modelling of complex structures, such as round and horseshoe‐shaped sections, and establishes a forward modelling method of the direct current resistivity in tunnels based on an unstructured mesh. The maximum error between the numerical simulation and theoretical results for an infinite tabular body in full space is less than 0.8%. It is more complicated to calculate the sensitivity matrix and model constraint term for the inversion region containing two types of grid than for one. For this purpose, the sensitivity matrix of different types of grid areas is calculated, a model constraint term based on the dual constraints of volume and distance is constructed, and finally, a partitioned domain‐weighted least‐squares inversion method based on an unstructured mesh is proposed. Synthetic examples of typical water‐bearing structures are analysed, and the results show that the proposed forward and inverse methods of the direct current resistivity in tunnels based on an unstructured mesh can effectively capture the position and morphology of the water‐bearing structure. Finally, an on‐site application was conducted in the Yellow River Diversion Project in central Shanxi. The proposed method could effectively identify the water body in front of the tunnel face and guide the on‐site construction of the project. These results can improve the interpretation of the direct current resistivity data in tunnels and play a positive role in promoting the use of the direct current resistivity method to prevent and control water‐inrush disasters in tunnels with complex structures.

An extended discontinuous deformation analysis for simulation of grouting reinforcement in a water-rich fractured rock tunnel

Grouting has been the most effective approach to mitigate water inrush disasters in underground engineering due to its ability to plug groundwater and enhance rock strength. Nevertheless, there is a lack of potent numerical tools for assessing the grouting effectiveness in water-rich fractured strata. In this study, the hydro-mechanical coupled discontinuous deformation analysis (HM-DDA) is inaugurally extended to simulate the grouting process in a water-rich discrete fracture network (DFN), including the slurry migration, fracture dilation, water plugging in a seepage field, and joint reinforcement after coagulation. To validate the capabilities of the developed method, several numerical examples are conducted incorporating the Newtonian fluid and Bingham slurry. The simulation results closely align with the analytical solutions. Additionally, a set of compression tests is conducted on the fresh and grouted rock specimens to verify the reinforcement method and calibrate the rational properties of reinforced joints. An engineering-scale model based on a real water inrush case of the Yonglian tunnel in a water-rich fractured zone has been established. The model demonstrates the effectiveness of grouting reinforcement in mitigating water inrush disaster. The results indicate that increased grouting pressure greatly affects the regulation of water outflow from the tunnel face and the prevention of rock detachment face after excavation.

Numerical Simulation of Tunnel Face Support Pressure in Layered Soft Ground

In shield construction, the limit support pressure of the tunnel face has an important influence on ground settlement and construction safety. In this study, MIDAS GTS NX software was used to conduct a series of three-dimensional finite element simulations to investigate variations in excavation face support pressure under different layered ground conditions. By changing the shear strength parameters of the top or bottom layers, the influence of composite layers with different formation boundaries on the support pressure of the excavation face was studied. It was observed that when the formation boundary is placed above the axis, the support pressure of the excavation face is more sensitive to a change in the parameters in the lower part of the formation than in the upper part. Conversely, when the formation boundary lies below the axis, this sensitivity becomes reversed. Additionally, we derived a robust and accurate equation to estimate the limiting face support pressure in layered soft ground based on numerical modeling.

Methodical principles of experimental-analytical research into the influence of pre-drilled wells on the intensity of gas-dynamic phenomena manifestations

Purpose.The research aims to substantiate the general provisions on coordination of the experimental-analytical research results of the influence of pre-drilled wells on the intensity of gas-dynamic phenomena manifestations (using the example of the mining-geological conditions of the phenomena at the PJSC Mine Administration Pokrovske, Ukraine). Methods. The research uses an integrated methodology consisting of indirect experimental methods for studying the adjacent rock mass state and tendencies. Findings. It has been proven that indirect experimental indicators of the rock mass state around the tunneling face are related to the peculiarities of the distribution of its stress-strain state components. Based on this research, the well lengths of up to 10-15 m has been determined to effectively and safely de-stress the rock mass. The experimental research validity is confirmed by conducted computational experiments, in the course of which the dependence of the propagation parameters of the stress-strain state component concentrations on the degree of hardness of the lithotypes is revealed, and a geomechanical substantiation to the tendencies of propagation of rock pressure anomalies near stoping and tunneling faces is given. The new knowledge obtained is the basis for creating a method for calculating rational parameters for the location of de-stressing pre-drilled wells. Originality. An objective assessment of the degree of adequacy and reliability of the computational experiment results has been made under the condition of using a new geomechanical model with mine studies of seismic-acoustic signal parameters and the initial gas release velocity. The main tendencies of vertical σу, horizontal σх and σz, as well as stress intensity propagation have been identified. The obtained results of exploring the bottom-hole mass are aimed at substantiating the parameters of anti-outburst measures for all preparatory mine workings. Practical implications. The conducted research is implemented in creation of a calculation method and recommendations for the selection of rational parameters for the location of de-stressing pre-drilled wells for the purpose of weakening the rock mass, surrounding the tunneling face, and reducing the probability of gas-dynamic phenomena occurrence due to the controlled weakening of adjacent rocks.

АНАЛИТИЧЕСКИЙ ПОДХОД К ОПРЕДЕЛЕНИЮ ПРОДОЛЬНОГО СМЕЩЕНИЯ СУЩЕСТВУЮЩЕГО СБОРНОГО ТОННЕЛЯ ПРИ ВЫЕМКЕ КОТЛОВАНА ПО ВСЕЙ ДЛИНЕ

In the realm of urban construction employing excavation techniques, safeguarding existing underground structures from detrimental consequences arising from surface construction operations poses a formidable challenge. The reduction of loads due to excavation activities can induce unintended responses, potentially jeopardizing subterranean infrastructure, particularly high-safety-demanding structures like Tunnel Boring Machine (TBM) tunnels. This article introduces an uncomplicated method for ascertaining the axial displacement of TBM tunnels amidst concurrent surface excavation activities. Primarily, the approach entails the identification of stress variations encountered during soil excavation at the tunnel face. Subsequently, employing the solutions derived for the determination of tunnel deformation subjected to concentrated loads, the deformation incurred by the tunnel due to alterations in excavation-induced stress is quantified. The analytical outcomes are meticulously juxtaposed against results generated from a three-dimensional computational model. The comparative analysis demonstrates that the displacement values and axial deviations calculated using the proposed analytical method exhibit only marginal disparities of 4,3% and 1%, respectively, when compared to those obtained through finite element analysis. This study underscores the efficient predictive capabilities of the analytical method in assessing tunnel deformations, enabling a preliminary estimation of critical parameters associated with the excavation pit. These findings have significant implications for mitigating adverse impacts on existing subterranean infrastructure in densely populated urban areas.

Limit equilibrium model for active failure of large-size rectangular tunnel face considering effect of height–width ratio

The stability of a rectangular tunnel face (RTF) has received less attention than that of circular tunnels; in particular, the stability of RTFs with different height–width (H/W) ratios has not yet been investigated comprehensively. In this study, extensive numerical simulations are conducted to investigate the limit support pressure (Pa) of the active failure of an RTF with different H/W ratios and to determine the appropriate failure mechanism without assuming the failure shape in advance. The result shows that, as the H/W ratio increases, Pa decreases gradually for specified heights and overburden depths of the RTF. The failure shape of the soil in front of the RTF is determined by analyzing the contours at plastic points of the soil. Subsequently, three types of failure modes, namely, partial semicircular, semicircular, and supersized semicircular modes, are identified based on the progression of plastic points in the soil. Corresponding failure models are established using the limit equilibrium method. Compared with relevant theoretical models, the proposed model predicted results that are more consistent with the numerical simulation results. Furthermore, a parametric study is performed to investigate the stability of the RTF. Finally, the predicted results are compared and analyzed with the pressure monitored inside the chamber, thus providing a theoretical reference for the jacking construction of the Shasan project.

Profiling of weathered argillaceous limestone rock with MWD data from advanced drilling for tunnelling along Wu-Kai expressway in Chongqing, China

Advanced drilling was employed for the ongoing excavation of a tunnel on Wu-Kai Expressway in Chongqing, aiming to characterize the ground condition ahead of the tunnel face and avoid potential geohazards. Measurement While Drilling (MWD) system and the hydraulic rotary crawler drilling machine are used for the advanced drillhole in the weathered argillaceous limestone rock mass. However, the MWD data exhibits random variations in penetration rate and cannot be correlated with ground conditions. In addition, there is little MWD data on the weathered argillaceous limestone with time-series algorithm in relevant open literature. This paper presents further analysis of the MWD data, resolves the random variation issue in penetration rate, and re-interprets the MWD data along three advanced drillholes in this tunnel project. The re-calculated penetration rate with the time-series algorithm for each drillhole is a stepped function of the drillhole depth. The constant penetration rates for the different homogeneous zones can be further correlated with the weathering degrees of the rock and compared with those from other five ground sites with different ground conditions in China and London. The findings of the paper can enhance the general applicability of MWD data for accurate profiling of weathered argillaceous limestone rock mass for safe tunnelling.

Application of Radon Transform in in-seam Wave Advanced Detection Technology

In view of the increasingly high degree of mechanization of coal mining and the increasing difficulty of mining, seismic exploration based on ground seismic method is not applicable in coal seams. Therefore, a trough wave seismic detection method of geophysical prospecting method is introduced into coal mine tunneling roadway, which provides a method and means for ascertaining the geological anomalies in front of the tunnel face. Combined with modern geological information, seismic data can be visualized and interpreted by geological personnel, which can identify geological anomalies such as faults, collapse columns, goafs and water inrush areas in the process of coal seam excavation and mining, and reduce the occurrence of disasters and accidents in the mining process.

Modeling of spalling failure of in-situ rock mass for quantification of the source mechanics with flat-joint model and moment tensor

Spalling failure caused by excavation unloading in tunnels under high in situ stress is a common phenomenon. Here, we attempt to use a three-dimensional flat-joint model (FJM3D) combined with a moment tensor to simulate the process of spalling failure. FJM3D simulation showing the process of micro-crack initiation and propagation in the surrounding rock from a micro-perspective. The nature of the source mechanism is quantitatively assessed by moment tensor analysis. There are a large number of micro-cracks extending deep at the shoulder and foot of the tunnel. This model reproduces similar thin slabs and fracture orientations in Mine-by Experiment (MBE). The excavation disturbed zone (EDZ) characteristics around the MBE show that the tunnel crown and invert are dominated by tensile mechanisms, the tunnel sidewalls are dominated by implosive and shear mechanisms, and the tunnel shoulders are butterfly shaped with tensile and implosive sources. The nature of these sources are not purely tensile/shear cracks, but some isotropic/deviatoric components also play a role. The magnitude and orientation of the principal stress near the excavation face are linked to the advancement of the tunnel face and are related to the direction of micro-cracks initiation and propagation, which sheds new light on the failure mechanics of spalling failure.

Numerical and analytical studies on the coupling effects of unloading and cutterhead vibration on tunnel face in dry sandy ground

When tunnelling in difficult ground conditions, shield machine would inevitably produce significant ground loss and vibration, which may disturb the ground ahead of the tunnel face. In this paper, discrete element models calibrated by model tests were established to investigate the response of tunnel face under the coupling effects of unloading and cutterhead vibrations. The results show that the friction angle reduction under cyclic loading and vibration attenuation in the sandy ground are significant and can be estimated by the fitted exponential functions. Under cutterhead vibration, the tunnel face stability is undermined and the limit support pressure (LSP) increases to 1.4 times as that in the static case with the growth of frequency and amplitude. Meanwhile, the loosening zone becomes wider and the arching effect is weakened with the reduction of peak horizontal stress and the increase of vertical stress above the tunnel. Based on the numerical results, a pseudo-static method was introduced into the limit equilibrium analysis of the wedge-prism model for calculating the LSP under vibration. With an error rate less than 5.2%, the proposed analytical method is well validated. Further analytical calculation reveals that the LSP would increase with the growth of vibration amplitude, vibration frequency and covered depth but decrease with the increase of friction angle. This study can not only lay a solid foundation for the further investigation of ground loss, ground water and soft-hard heterogeneous ground under cutterhead vibration, but also provide meaningful references for the control of environmental disturbance in practice.

Volume Loss Prediction for a Longitudinally Inclined Tunnel Face Advancement in Undrained Clay

Volume Loss Prediction for a Longitudinally Inclined Tunnel Face Advancement in Undrained Clay

The Stability Analyses of Tunnel Faces in Saturated Soils with Soil Arching Effect

The undesirable effect on the stability for cross-river tunnel faces considering pore water pressure was observed with the consideration of the soil arch effect by using the discrete technology for the first time. In light of the upper bound of plastic theory, an improved failure mechanism of the deep-buried tunnel face was established. A new discrete technology approach taking account into the soil arching effect was proposed to estimate the stability for cross-river tunnel faces subjected to pore water pressure. The presented approach is validated by comparing with the existing solutions as well as showing great improvements. After verification, based on the failure mechanism, this paper discusses the impact of the changing water level and the soil parameters on the normalized supporting pressure and meanwhile analyzes the variation of the shape of collapsing domain of soils ahead of the tunnel face considering the soil arching effect. The results illustrate that soils with the bigger friction angle form the arch more easily during excavation, and with higher water height, the soil arching effect appears not as obvious as expected, particularly on those soils with the smaller friction angle.

Numerical analyses for three-dimensional face stability of circular tunnels in purely cohesive soils with linearly increasing strength

The tunnel face stability in purely cohesive soils with linearly increasing strength was investigated using three-dimensional finite element limit analysis (FELA). Both the collapse (active failure) and blow-out (passive failure) of the tunnel face were considered in the analysis. The rigorous upper bound (UB) and lower bound (LB) solutions of the load factor were calculated with a wide range of ground conditions to cover a broad scope of practical application. The results showed that the whole surface of the face is at failure in the collapse case; while in the blow-out case, there exists a gradual evolution process from partial failure to global failure within the tunnel face with increasing buried depth. Later, based on 960 finite element limit analysis results, a series of practical equations were proposed for tunnel face stability analysis in purely cohesive soils. These equations can be employed to quickly calculate the UB and LB solutions of the limit support pressure and the stability number of a tunnel face in both the collapse and blow-out cases. Finally, the calculation results from these equations were compared with those from previous studies in detail. The comparisons showed that the proposed equations make an improvement over existing methods and can be used as an efficient tool in practical engineering.

Creep Versus Consolidation in Tunnelling Through Squeezing Ground—Part A: Basic Time Effects

Although squeezing ground may undergo rapid convergences following tunnel excavation, its behaviour is often markedly time dependent due to creep or consolidation. The effects of creep and consolidation on shield tunnelling are comparatively evaluated in two companion papers, with the aim of demonstrating their qualitative similarities and distinctive features. The present, first paper investigates the basic time effects, placing focus on the time development of ground deformations and the complex interaction between ground, tunnel boring machine (TBM) and tunnel support during excavation and during construction standstills. The presented numerical simulations indicate several qualitative similarities between the two mechanisms of time dependency, in respect of the time development of ground deformations, the counter-intuitive behaviour of increasing shield loading with increasing rate of advance under certain conditions, as well as the thoroughly adverse effect of the additional time-dependent deformations taking place during construction standstills on the shield loading. However, they also underscore two prominent differences resulting from the fundamentally different nature of creep (a purely mechanical rheological process) and consolidation (a coupled hydromechanical process): first, the consistently more extensive plastic yielding in consolidating ground, which is partially associated with the seepage forces exerted by the pore water on the solid rock constituents. Second, the role of seepage forces as a potential destabilising agent, particularly for the tunnel face, which does not happen in the case of creep and may be critical for shield and cutterhead jamming. Building upon these investigations, the companion paper compares creep and consolidation with respect to the transferability of experiences about the required thrust force to tunnels of different diameter or to adjacent tunnels.

Three-dimensional stability analysis of tunnel face considering the upper partial failure in layered rock masses

Three-dimensional stability analysis of tunnel face considering the upper partial failure in layered rock masses

Revisiting the face stability of rock tunnels in the Hoek–Brown strength criterion with tension cutoff

AbstractIn this work, the three‐dimensional stability of deep tunnel faces is evaluated in rock masses characterized by the generalized Hoek–Brown (H–B) criterion from the perspective of the limit analysis theorem. Considering that underground engineering is gradually developing towards larger burial depths and larger sizes, and the tensile strength of rocks is usually overestimated, the concept of tension cutoff (T‐C) is introduced to substitute the parabolic form of the H–B envelope in the tensile region with a circular arc. The multitangent technique is used to piecewise approximate the H–B envelope, instead of the conventional linear substitution, accounting for the nonlinear dependence of the shear strength on the pressure. Meanwhile, the earthquake loading is considered by the classic pseudostatic method. The tunnel face stability is measured by a stability number, which is calculated based on a newly developed multicone failure mechanism. Parameter studies indicate that the T‐C has almost no impact on the critical support pressure, while has a significant effect on the critical stability number, especially in the presence of earthquakes. Nearly all stress points back‐calculated from the rupture angles fall within the T‐C region, except for the first stress point associated with the first segment. Interestingly, the influence of the geological strength index (GSI) on the face stability is inverse to that of mi due to the brittleness of rocks. Moreover, the critical stability number is not sensitive to mi, but sensitive with the introduction of earthquake loadings.