Rock Tunnel Research Articles

Study on the Support Strategy of NPR Cable Truss Structure in Large Deformation Soft Rock Tunnel Across Multistage Faults

Study on the Support Strategy of NPR Cable Truss Structure in Large Deformation Soft Rock Tunnel Across Multistage Faults

Stability Analysis of Surrounding Rock and Initial Support of Tunnel Undercrossing Multi-Situational Goafs: A Reference of Construction Guidance

To ensure the construction and operational safety of tunnel undercrossing multi-situational goafs, the Huaying Mountain High-Speed Rail Tunnel, a critical section of the Xi’an-Chongqing High-Speed Railway, was taken as a case study. Based on a three-dimensional finite difference numerical simulation platform, twelve situations were established to analyze the effects of three factors: distance, scale, and angle. The stability analysis was conducted by examining the displacement and deformation characteristics of the surrounding rock, stress changes, and axial forces of the initial support for each situation. The results show that in tunnel undercrossing multi-situational goafs, the vertical deformation, horizontal convergence of the surrounding rock, and the maximum axial force of initial support are all affected. Within a certain range, changes in distance significantly impact subsidence and settlement deformation of the surrounding rock. However, as the distance increases, the horizontal and vertical displacements of the tunnel and the axial force of the initial support tend to decrease. Conversely, the scale and angle of the goaf have an opposite effect on the surrounding rock: as the scale and angle increase, the stability of the surrounding rock deteriorates. In this case study, when the distance exceeds 1.13 times the tunnel span, the influence of the goaf on the stability of the surrounding rock gradually decreases. When the angle exceeds 45°, vertical displacement decreases, and the increasing trend of horizontal displacement gradually diminishes. The conclusions of this paper can provide guidance for designing reinforcement schemes for tunnels crossing through multi-situational goafs. The findings provide valuable insights and guidance for similar engineering projects.

Effects of fissure locations on the crack propagation morphologies of 3D printing tunnel models: Experiments and numerical simulations

Hidden fissures widely exist in the surrounding rock of tunnels, and the propagations and interactions of the fissures will directly affect the safety and stability of tunnels. However, experimental and numerical simulation studies are scarce on the tunnel-fissure interactions under complex stress conditions. Based on this background, circular tunnel specimens with different prefabricated fissure locations are prepared by three-dimensional (3D) printing technology. Uniaxial compression fracture tests are conducted utilizing Digital Image Correlation (DIC) technology to obtain strain distributions. An improved Smoothed Particle Hydrodynamics (SPH) method is employed to simulate the crack propagation processes of the tunnel-fissure interactions. The results demonstrate the following: 1) Upper main cracks, upper side cracks, and lower side cracks are produced around the tunnel, and wing cracks initiate from the prefabricated fissure tips. 2) For the different intersection positions, wing crack propagation length decreases as the intersection position moves upward, while the lower side crack propagation length increases. 3) For different distances d, upper side crack does not appear, and the propagation length of upper main crack increases with the increase of the distance d. 4) For different fissure inclination angles α, upper main crack does not appear when α = 15°. The propagation length of wing crack increases with the increase of inclination angle α. 5) The peak stress increases as the intersection position moves upward, while it decreases with the increase of inclination angle α. With increasing distance d, the peak stress initially increases and then decreases. Finally, the crack initiation mechanisms under different fissure orientations and inclinations are discussed. These research findings provide valuable insights into the tunnel-fissure interaction mechanisms under complex stress conditions and the applications of the SPH method in underground engineering simulations.

Development and Mechanical Performance Study of a New Type of Flexible Protective Geogrid for Tunnel Rock Burst

Development and Mechanical Performance Study of a New Type of Flexible Protective Geogrid for Tunnel Rock Burst

Modelling on vibration and failure of rock tunnel under high stress release

This study aimed to analyze the vibration and deformation resulting from high stress release around a circular tunnel. A two-dimensional model was developed using modal superposition and integral transformation to address this issue. The theoretical results indicated that high initial stress and rapid release rate led to considerable PPV around the tunnel. Under the same stress circumstance and unloading period, the instantaneous unloading rate of the unloading path significantly affects the vibration around the tunnel. Then, the FEM software, LS-DYNA, was employed to visualize the distribution of plastic deformation around the tunnel under transient dynamic unloading. The numerical results showed the damage tends to occur in the direction perpendicular to the major principle stress, which coincided with a low particle vibration velocity and high stress concentration area, and higher initial stresses led to more strain energy converted into kinetic energy for particle vibration during dynamic excavation. In addition, the P- and S-waves generated by dynamic unloading and their propagation were also analyzed and discussed. The findings of this work provide mechanistic insight into the geotechnical hazards caused by high stress release during underground ground space excavation and provide a reference for opening design and disaster prevention and mitigation in deep engineering.

Study on fracture characteristics of surrounding rock of twin tunnels under various crack inclination and location conditions

In some practical projects, two neighboring tunnels are often constructed in natural rock bodies that have a significant number of fractures with unpredictable inclination angles and locations. To study dynamic fracture characteristics of the surrounding rock mass of the twin tunnels containing a crack with different crack inclinations and crack locations, an experimental model of a cracked twin tunnel was designed and proposed, dynamic experimental analyses were carried out by using a traditional split Hopkinson pressure bar (SHPB) device and digital image correlation (DIC) method, followed by simulation conducted by using LS-DYNA code. The findings indicate that the spandrels and corners of the twin tunnels nearest the pre-cracks are more vulnerable to failure under dynamic loads, resulting in tunnels joining the ends of the pre-cracks. With various crack inclinations and crack locations, the initial cracks are typically produced at the roof and floor of the tunnel, as well as at the points of the pre-cracks. The specimen's kind of crack and its emergence site are connected. Crack inclination and location have little influence on the maximum displacement value in the twin tunnels. The study's findings could offer a fresh theoretical direction for evaluating the stability of twin tunnels when there are numerous joints and flaws.

Hybrid deep learning approach for rock tunnel deformation prediction based on spatio-temporal patterns

The ability to predict tunnel deformation holds great significance for ensuring the reliability, safety, and sustainability of tunnel structures. However, existing deformation prediction models often simplify or overlook the impact of spatial characteristics on deformation by treating it as a time series prediction issue. This study utilizes monitoring data from the Grand Canyon Tunnel and introduces an effective data-driven method for predicting tunnel deformation based on the spatio-temporal characteristics of the historical deformation of adjacent sections. The proposed model, a combination of graph attention network (GAT) and bidirectional long and short-term memory network (Bi-LSTM), is equipped with robust spatio-temporal predictive capabilities. Additionally, the study explores other possible spatial connections and the scalability of the model. The results indicate that the proposed model outperforms other deep learning models, achieving favorable root mean square error (RMSE), mean absolute error (MAE), and coefficient of determination (R2) values of 0.34 mm, 0.23 mm, and 0.94, respectively. The graph structure based on intuitive spatial connections proves more suitable for meeting the challenges of predicting deformation. Integrating GAT-LSTM with transfer learning technology, remains stable performance when extended to other tunnels with limited data.

Development and characteristic research on new thermal insulation and anti-permeability grouting material for tunnels in cold regions

The surrounding rock of tunnels in cold regions are susceptible to the freeze–thaw cycle resulting from the combination of low temperatures and moisture during tunnel service. The phenomenon will not only lead to the expansion of pores and fissures in the surrounding rock of the initial tunnel, but also destroy the integrity of the rock. This destruction will have a serious impact on tunnel structure and rail transit operation safety. At present, the commonly used thermal insulation measures have some problems such as maintenance difficulties, low economic efficiency, and safety hazards. Therefore, it is urgent to develop a kind of tunnel maintenance grouting material with insulation and anti-permeability, which has the characteristics of simple operation, easy preparation and application. We independently developed a composite grouting material composed of polyurethane (PU), epoxy resin (E-51) and acrylic powder (PMMA). Through the material combustion test, magnesium hydroxide was selected as the flame retardant additive. Moreover, we measured the thermal conductivity, water absorption, apparent density, porosity and strength characteristic parameters. The thermal insulation and anti-permeability characteristics of the composites were also analyzed. The results indicated that the thermal conductivity of the new composite grouting material is 6.3% lower than the PU before adding flame retardant. Compared with the PU with flame retardant, the water absorption decreased by 74.4% and the ultimate strength increased by 33.3%. For the area with an average temperature lower than − 10 °C, we recommend the ratio scheme of E-51: 3%; PMMA: 15%. For the area with high water content in the surrounding rock of the tunnel, we recommend the ratio scheme of E-51: 15%; PMMA: 3%. This study provides new ideas for material preparation and tunnel insulation methods for anti-freezing measures in tunnels during their operational period in cold regions.

Erratum to: A Comparative Study of Soft Rock Tunnel Control Methods Using NPR High Preload Anchor Cables: Analysis of Multiple Cases

Erratum to: A Comparative Study of Soft Rock Tunnel Control Methods Using NPR High Preload Anchor Cables: Analysis of Multiple Cases

Design of Rock Support in Hard and Layered Rock Masses Using a Hybrid Method: A Study Based on the Construction of the New Skarvberg Tunnel, Norway

AbstractHard rock formations with layered, anisotropic geological structures are rather common in Norway. The design of tunnel rock support under such ground conditions has been traditionally done with an empirical approach and assisted with engineering rock mass classification. In most cases, rock stability has been achieved with the use of fiber-reinforced sprayed concrete combined with rock bolts, sometimes supplemented with ribs of reinforced sprayed concrete (RRS) and bolt spiling. However, the discontinuous character and more complex ground behavior of layered rock can lead to design challenges as experienced during the construction of the new Skarvberg highway tunnel in Northern Norway. A significant portion of the tunnel exhibited consistent overbreak, delamination problems and a tunnel failure. In this article, the ground behavior and rock support performance at different locations of the tunnel are investigated to find a basis for design optimization of rock support under similar ground conditions. For this purpose, a thorough site investigation program was carried out, which formed the basis for further assessments and analyses with a hybrid design methodology and the numerical code UDEC (Itasca). As a result, the main challenges of classification systems to capture ground behavior and derive optimal support design in layered rocks were identified. As such, this study has investigated design optimization possibilities, which resulted in the development of, among others, a specific ground behavior classification for layered grounds and a new, optimized RRS-support concept for layered rock masses of very poor quality (e.g., Q ~ 0.1–1).

Study on the Stress and Deformation of Surrounding Rock and Support Structure of Super Large Section Tunnels Based on Different Excavation Methods

Study on the Stress and Deformation of Surrounding Rock and Support Structure of Super Large Section Tunnels Based on Different Excavation Methods

Compensation mechanics application of NPR anchor cable to large deformation tunnel in soft rock

NPR anchor cable is a new type of support material with negative Poisson's ratio effect, which is widely used in mine support because of its superb compensating mechanical effect. In order to study more deeply the support effect of NPR anchor cable in soft rock large deformation tunnel, indoor test, numerical simulation and field monitoring were used to study the strong weathering carbonaceous slate tunnel in Min County. The study shows that NPR anchor cable has extraordinary compensating mechanical behavior for soft rock large deformation tunnel, which can control the deformation of tunnel surrounding rock below 300 mm and keep the constant resistance value around 350 kN, which has obvious effect on the control of broken rock. To provide a basis for other research on support for large deformation tunnels in soft rock.

Analysis of progressive collapse disaster and its anchoring effectiveness in jointed rock tunnel

AbstractThe complexity and variability of the structural distribution and combination characteristics of jointed rock masses make the response mechanism of tunnel rock collapse different, and there is a lack of systematic research on the existing perimeter rock instability mode and bolt support scheme. Based on numerical simulations of the block system structure of a nodular rock mass, the existing theory of bolt support is compared and analyzed to explore the scope of their respective applications. Combined with the spatial and temporal transport law of block instability, a new batch instability model of jointed rock tunnels is proposed, which reveals the progressive collapse catastrophe evolution mechanism of a collapsed interlocking block system after the instability of the key blocks and elucidates the coupling mechanism between the bolts and the block system structure as well as their anchoring effectiveness. Finally, for the actual tunnel project, the instability batches of the surrounding rock are identified, and the corresponding optimized design of the bolt support is presented, which has achieved good support effects. The research results can provide important theoretical guidance and practical engineering value for risk avoidance, disaster identification and targeted prevention and control of dangerous rock fall and chain collapse instability disasters in jointed rock body tunnels.

Study on the stressing state features of basalt fibre concrete lining structure under sulphate erosion

Basalt fibre (BF) is an environmentally friendly material with excellent corrosion resistance. When tunnels cross gypsum rock strata, the gypsum rock will dissolve sulphate and erode the supporting structure, thus affecting the safe operation of the tunnels in the long term. Adding BF to the supporting structure of gypsum rock tunnels can improve its resistance to sulphate erosion. This paper took Wuzhishan Tunnel as a case, and first determined the sulphate concentration of the gypsum rock stratigraphic environment at the site; then, analysed the change of mechanical properties of basalt fibre concrete (BFC) before and after sulphate erosion by mechanical tests; finally, examined the deformation and force characteristics of the BFC secondary lining structure by numerical simulation. The results showed that the bridging effect of BF fibres and the stable spatial network structure formed inside the concrete enhanced the mechanical properties of BFC and its ability to resist sulphate erosion. However, due to the agglomeration effect of BF fibres, too much BF would reduce the mechanical properties and erosion resistance of BFC. At a BF content of 6 kg/m³, BFC had the strongest ability to resist sulphate erosion, and the cube compressive strength, axial compressive strength, and modulus of elasticity of BFC were the highest, with 47.8 MPa, 33.6 MPa, and 38.7 GPa, respectively. The dense calcium silicate hydrate (C-S-H) gel, generated near the BF, enhanced the connection between the cementitious and the aggregate, inhibited the development of microcracks within the concrete, and reduced the erosion channels for sulphate ions. The maximum displacement of the BFC secondary lining structure was reduced by 20.15 % compared to plain concrete (PC) after sulphate erosion. The secondary lining structures consisting of both BFC and PC were stressed the most at footing. The secondary lining structure composed of BFC had better deformation resistance and higher strength than PC.

Characterizing large deformation of soft rock tunnel using microseismic monitoring and numerical simulation

Surrounding rock deterioration and large deformation have always been a significant difficulty in designing and constructing tunnels in soft rock. The key lies in real-time perception and quantitative assessment of the damaged area around the tunnel. An in situ microseismic (MS) monitoring system is established in the plateau soft tock tunnel. This technique facilitates spatiotemporal monitoring of the rock mass's fracturing expansion and squeezing deformation, which agree well with field convergence deformation results. The formation mechanisms of progressive failure evolution of soft rock tunnels were discussed and analyzed with MS data and numerical results. The results demonstrate that: (1) Localized stress concentration and layered rock result in significant asymmetry in micro-fractures propagation in the tunnel radial section. As excavation continues, the fracture extension area extends into the deep surrounding rockmass on the east side affected by the weak bedding; (2) Tunnel excavation and long-term deformation can induce tensile shear action on the rock mass, vertical tension fractures (account for 45%) exist in deep rockmass, which play a crucial role in controlling the macroscopic failure of surrounding rock; and (3) Based on the radiated MS energy, a three-dimensional model was created to visualize the damage zone of the tunnel surrounding rock. The model depicted varying degrees of damage, and three high damage zones were identified. Generally, the depth of high damage zone ranged from 4 m to 12 m. This study may be a valuable reference for the warning and controlling of large deformations in similar projects.

Frost heaving and crack initiation characteristics of tunnel rock mass in cold regions under low-temperature degradation

Frost heaving and crack initiation characteristics of tunnel rock mass in cold regions under low-temperature degradation

Time-Dependent Reliability Analysis of Anhydrite Rock Tunnels under Swelling Conditions: A Study on Stress, Deformation, and Engineering Solutions

This study presents an analytical approach for evaluating the reliability of anhydrite rock tunnels, focusing on their characteristic swelling behavior. Anhydrite rocks, prone to significant expansion upon moisture exposure, pose a challenge in tunnel construction, potentially leading to structural issues such as floor heave and lining damage. To address this, this research develops an elastic swelling analytical solution based on humidity stress field theory, enabling the assessment of time-dependent stress and deformation changes in anhydrite tunnels. The solution’s applicability is demonstrated through its application to the Lirang tunnel. The investigation into the effects of support pressure, swelling time, and reserved deformation on tunnel reliability reveals that circumferential stress at the tunnel wall increases by 13.94% and 21.86% for swelling periods of 30 and 365 days, respectively. Similarly, radial displacement escalates by 22.97% and 35.93% over these periods, highlighting the significant impact of swelling behavior. Using a spreadsheet-based First Order Reliability Method (FORM) for analysis, this study finds that the original design of the Lirang tunnel did not meet the desired reliability standards under swelling conditions. However, strategic adjustments in construction variables, such as increasing support pressure to 1.2 MPa or enhancing reserved deformation to 59 mm, elevated the tunnel’s reliability to meet safety requirements. This research provides a vital framework for assessing and enhancing the reliability of anhydrite rock tunnels, considering the long-term effects of swelling. It underscores the importance of incorporating swelling behavior in the design and construction of tunnels in anhydrite rock formations, offering valuable insights for optimizing tunnel stability in such challenging geological conditions.

Investigation on the failure mechanism for surrounding rock in small interval tunnels using finite element limit analysis method

This paper presents a case study to evaluate the failure mechanism of surrounding rock in mountain tunnels caused by small interval parallelism and the reinforcement effect of intermediate rock columns. The characteristics and reasons of surrounding rock collapse were analyzed through field investigation, taking Yaoxi Tunnel as a case study. The critical collapse and blowout pressure results obtained by the finite element difference method (FEDM) software FLAC and the finite element limit analysis method (FELAM) software OPTUM were compared based on Mollon’s theoretical solution. The critical support pressure errors for collapse are 18.803% and 8.129%, indicating that OPTUM has a slight advantage in accuracy for solving tunnel collapse. Therefore, the models of small interval tunnels were established by OPTUM to investigate the collapse failure mechanism and progressive failure process of surrounding rock. The effects of tunnel depth ratio (H/D), spacing ratio (S/D), and surrounding rock parameters (γ, φ, c) on critical support pressure, failure mode, and surrounding rock settlement laws were studied through simulation models. It shows that the gradual decrease in mechanical parameters of rock is the main cause of the increase in critical support pressure. The design parameters (H/D, S/D) have a mutagenic effect on the pressure arch of the double tunnel surrounding rock. As the distance between the two holes increases, the joint pressure point in the intermediate rock column gradually rises. Finally, the effectiveness of the reinforcement measures for the intermediate rock column was verified through on-site monitoring. The research results of this study have reference price for similar projects.

The Vibration Response to the High-Pressure Gas Expansion Method: A Case Study of a Hard Rock Tunnel in China

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.

Epiphytic Patterns Impacting Metabolite Diversity of Drynaria roosii Rhizomes Based on Widely Targeted Metabolomics.

Drynaria roosii Nakaike, a fern widely distributed in China and some countries in Southeast Asia, is a commonly used herbal medicine in tonic diets and Chinese patented medicine. The metabolites of its dried rhizomes are easily affected by the epiphytic pattern, whether on rock tunnels (RTs) or tree trunks (TTs). The current research focused on rhizomes from these two patterns, RTs and TTs (further divided into subclasses TA, TB, TC, and TD, based on trunk differences) and conducted a widely targeted metabolomics analysis. A total of 1435 components were identified across 13 categories, with flavonoids, amino acids, and their derivative, lipids, identified as the main components. They accounted for 19.96%, 12.07%, and 12.14% of all metabolites, respectively. The top five flavonoids in TB were eriodicty-ol-7-O-(6″-acetyl)glucoside, quercetin-3-O-sophoroside (baimaside), dihydrochar-cone-4'-O-glucoside, morin, and hesperetin-7-O-glucoside, with relative contents 76.10, 24.20, 17.02, 15.84, and 14.64 times higher than in RTs. Principal component analysis revealed that samples with different epiphytic patterns clustered into five groups. The RT patterns revealed unique metabolites that were not detected in the other four epiphytic species (TA, TB, TC, and TD), including 16 authenticated metabolites: 1 alkaloid, 1 amino acid derivative, 7 flavonoids, 2 lignans, 1 lipid, 1 alcohol, 1 aldehyde, and 2 phenolic acids. These differences in epiphytic patterns considerably affected the accumulation of both primary and secondary metabolites. The comparison of diversity between RTs and TTs can guide the selection of a cultivation substance and the grading of collective rhizomes in the wild. This comprehensive analysis of D. roosii rhizome metabolites also offers fundamental insights for identifying active components and understanding the mechanisms underlying their potential pharmacological activities.