Tunnel Support Research Articles

The deformation and failure characteristics of tunnels in layered rock with gentle dip angles after freeze–thaw cycles: Physical model tests and numerical investigation

When a tunnel passes through layered rock with a gentle dip angle in cold regions, the occurrence of multiple freeze–thaw (F–T) cycles can easily cause fatigue damage to the rock bedding surfaces and seriously affect the rock stability. One of the engineering problems that needs to be solved is to determine the deformation and failure mechanisms of such surrounding rock under F–T cycles. Based on the similarity principle, the mechanical response of the tunnel lining structure and the progressive failure process of the surrounding rock under long-term F–T action were studied by performing physical model tests and numerical simulations. The results show that the model tunnel lining partially separates from the surrounding layered rock with a gentle dip angle under the action of F–T cycles. Moreover, the load bearing capacity of the model weakens after undergoing F–T cycles. Additionally, the bending moment and axial force evolution characteristics of the tunnel and surrounding rock model are consistent with the deformation characteristics, which agree with the actual mechanical and deformation characteristics of a real tunnel under F–T cycles. After establishing numerical calculation models for surrounding rock with three bedding angles (0°, 10°, and 20°) and verifying the numerical models based on the test results, the horizontal and vertical displacements of the surrounding rock in the tunnel entrance section under ground stress conditions at a depth of 400 m were calculated. The research results accurately reflect the long-term deformation characteristics of layered rock with gentle dip angles surrounding tunnels in cold regions and can provide theoretical guidance for the application of corresponding tunnel support measures in cold regions.

Study on mechanical properties of composite support structures in TBM tunnel under squeezing soft rock conditions

As more and more TBM tunnels are constructed under complex conditions such as high stress and fault fracture zones, large deformation disasters of squeezing soft surrounding rocks occur frequently. However, TBM method shows poor adaptability to major engineering challenges. Equipment damage, track deviation and support structures failure are widely observed. It is important to propose an effective support scheme and to fully clarifying the mechanical properties of the support structures in TBM tunnel. In this case, this paper aims to conduct laboratory and numerical tests considering steel–concrete interface bond-slip behavior so as to verify the effectiveness of the proposed support scheme. Thus, the quantitative relationship between arch type, arch spacing, longitudinal connection strength, concrete strength, steel fiber content, and tunnel surrounding rock deformation can be obtained. The research results show that the support scheme proposed in this paper shows good applicability for deformation control of TBM tunnels under squeezing soft rock conditions, which provides a reference for TBM tunnel support under squeezing soft rock conditions.

Expanding the Scene of Tunnel Behaviour Through the DEM Model: a Case Study from ZaB-Zentrum Am Berg

The displacement of a tunnel plays a crucial role in conventional tunneling methods, serving as a key parameter for support requirement. Therefore, analyzing tunnel displacement is important for ensuring safety and optimizing costs by determining the appropriate level of tunnel support and installation time. Numerical analysis methods are commonly employed for assessing tunnel displacement, and two widely recognized approaches used worldwide are the continuum and discontinuum methods. While previous studies have highlighted differences in the analysis results obtained from these two methods, the magnitude of such disparities has not been extensively explored. Hence, the objective of this study is to quantify the extent of variation between the two methods through various scenarios, encompassing unsupported and supported excavated ground. Specifically, the focus is on tunnel displacement and the tensile force generated on axial tunnel supports, such as rock bolts. To facilitate this investigation, three tunnel sections from the Zentrum am Berg, tunnel research centre located in Austria, are utilized. The results show that discontinuum models exhibit higher displacements and higher tensile loads on axial support than continuum numerical models of the same tunnel geometry and equivalent rock masses. We show that discontinuum models can also capture asymmetric behaviour, and thus should be preferentially used in fractured rock masses where displacement of rock blocks dominate the rock mass behaviour.

The Use of Slag in Accelerated Shotcrete for Rock Support: A Pilot Study on the Influence on the Early Compressive Strength

Abstract Today, the world is facing an enormous challenge where the emissions of greenhouse gases must be reduced significantly to stop the increasing mean temperature. For the construction industry, this challenge means that structures must be designed more carefully, and materials must be used and produced more efficiently. Concrete is one of the most widely used materials, and cement production alone contributes to around 8 % of the world’s total CO2 emissions. This paper presents a pilot study in which part of the cement clinker content in accelerated shotcrete is replaced with ground granulated blast furnace slag (GGBS). Shotcrete is widely used as part of the rock support for tunnels in hard rock and has a large cement content. Thus, the environmental impact must be reduced significantly to meet future demands. However, introducing GGBS will slow down strength development, which is a crucial part of shotcrete. Thus, this paper aims to investigate the early strength development, i.e., after one and seven days. The results show that an average compressive strength of 18 MPa can be reached after 24 hours when 35 % of the cement clinker content is replaced with GGBS. Finally, some important topics for further studies are pointed out.

Study of Tunnel Support Methods Based on RMR and Q-System Methods at Kerinci Merangin Hydropower Jambi Province

Excavation of tunnel construction at the Kerinci Merangin Hydropower in Jambi Province is a complex job, because it will use the tunnel as a waterway which will always be faced with unstable conditions. One of the way to deal with instability is to classify the mass and determine the type of support on the roof and walls using empirical methods. The parameters in rock mass classification include mapping the structure, physical and mechanical properties of the material. Empirical analysis was carried out using the Rock Mass Rating (RMR) classification and the Q-System to determine the condition of the rock mass in the tunnel and determine the type of support that will be used and in accordance with the rock mass class. The rock mass classes in the study area of STA 8+869, 8+872 and 8+879 based on the RMR classification are included in rock class III, namely rocks that have moderate conditions (fair quality rock mass) and rock class IV, namely rocks that have poor conditions (poor quality rock mass). Meanwhile, the rock mass class based on the Q-System includes very poor rock mass.The recommendation for supporting the tunnel face according to RMR in the study area is to use a combination of rockbolt, shotcrete and wiremesh supports, while the support recommendation according to the Q-System uses a combination of rockbolt and shotcrete supports.

Dynamic characteristics of basalt fibre-reinforced polymer cement mortar bolts and its applicability for bolt defect detection

Basalt fiber reinforced polymer (BFRP) bolt has the advantages of high tensile strength, low quality and corrosion resistance. This kind of bolt has a potential application prospect in tunnel and underground engineering support. However, there is no effective method for non-destructive testing of anchoring quality of BFRP cement mortar, which restricts the application of this kind of anchor. Based on the propagation principle of stress waves in solids, the feasibility of the impact elastic wave method in detecting the length and compactness of bolts is theoretically demonstrated. Then, numerical simulation and test methods were used to study the propagation characteristics of stress waves in bolts under impact load and its application in the anchorage quality inspection of BFRP bolts. The results show that the elastic wave method can be used to detect the length of BFRP bolts and the detection accuracy meets the engineering requirements. In terms of anchoring compactness of cement mortar, this method can identify the location of defects, but the detection accuracy needs to be further improved. The research results presented in this paper can promote the application of BFRP bolts in tunnel and underground engineering support.

Experimental investigation on corroded and non-corroded RC tunnels under different loading conditions

Underground reinforced concrete (RC) structures, such as tunnels and pipelines, are frequently employed in urban areas and are designed to withstand both static and seismic loads, including those that occur during earthquakes. However, the inspection of deteriorated underground structures has yielded valuable findings for the civil engineering community, highlighting the need for further experimental investigation of the various damage mechanisms affecting RC tunnels under different loading conditions. This research presents a comprehensive experimental study aimed at elucidating the damage mechanisms of underground RC structures exposed to various loading conditions. Specifically, the study includes experimental testing of the corrosion of tunnel reinforcement and an investigation into the overall performance of corroded tunnels. The experimental results indicate that existing vertical loads significantly impact the lateral carrying capacity and ductility of RC tunnels.

Deformation Law of Tunnels Using Double-Sidewall Guide Pit Method under Different Excavation Sequences

The double-sidewall guide pit method finds extensive application in the construction of large cross-section tunnels in soft rock strata due to its minimal disruption to the surrounding rock, thereby enhancing tunnel stability. To investigate the loading and deformation patterns of the surrounding rock and tunnel support using the double-sidewall guide pit method, this study compares the impacts of various construction sequences on surface settlement, surrounding rock stress, and lining stress using indoor model tests. The experimental results show that after excavating the upper guide hole on one side, the excavation of the lower guide hole on the same side is carried out. The upper and lower support structures form a closed loop, and the structure can better constrain the surrounding rock and control the deformation of the surrounding rock, whereas the lower structure can share the stresses suffered by the upper structure. Therefore, compared with the upper and lower excavation methods, the surface settlement caused by the left and right excavation methods is smaller, the disturbance to the surrounding rock is smaller, and the supporting structure is more evenly and stably stressed in the excavation process.

Performance of the suspension method in large cross-section shallow-buried tunnels

Large cross-section tunnel construction induces ground surface settlements, potentially endangering both subterranean projects and nearby above-ground structures. A novel tunnel construction method, known as the suspension method, is introduced in this paper to mitigate surface settlement. The suspension method employs vertical tie rods to establish a structural connection between the initial tunnel support system and the surface steel beam, thereby exerting effective control settlements. To analyze the performance of the proposed method, systematic numerical simulations were conducted based on the practical engineering of Harbin Subway Line 3. The surface settlement and vault settlement characteristics during construction are investigated. The results show a gradual increment in both surface and vault settlement throughout the construction process, culminating in a stabilized state upon the completion of construction. In addition, compared to the double-side drift method and the Cross Diaphragm Method (CRD) method, the suspension method can obviously reduce the surface settlement and vault settlement. Moreover, the surface settlements and the axial force of tie rods were continuously monitored during the construction process at the trial tunnel block. These specific monitoring measurements are illustrated in comparison to numerical analysis results. The monitored results show great agreement with the numerical predictions, confirming the success of the project. This research can serve as a valuable practical reference for similar projects, offering insights and guidance for addressing ground surface settlements and enhancing construction safety in the domain of large cross-section tunneling.

Viscos-elastic-plastic solution for deep buried tunnels considering tunnel face effect and sequential installation of double linings

Tunnels excavated in soft rock under high in situ stress are usually accompanied by large time-dependent deformation, slow convergence, and long periods of increased support load due to the strong rheological properties of the surrounding rock. This paper presents a time-dependent solution for deeply buried supported circular tunnels excavated in viscoelastic-plastic strain-softening rock masses, in which both the whole process of longitudinal excavation and the sequential installation of two elastic linings are considered. In the solution, the surrounding rock obeys a Burger-creep viscous elastic–plastic strain-softening model and two stages, referring to the “tunnel face influence stage” and the “creep stage”, are divided to derive the explicit expressions of the time-dependent tunnel convergences and support loads, in which the former stage accounts for the effect of stress release based on the elastic–plastic analysis, and the latter concentrates on the long-term response induced by the viscous behavior of the ground. To account for the different rock qualities, tunnel face advance rates, and lining tunnel support locations, the elastic–plastic strain-softening solution in the former stage is divided into three cases and the viscos-elastic–plastic solution in the creep stage includes two sub-solutions depending on the evolutions of stress paths being considered or not. For validation purposes, the provided analytical solutions are compared with the numerical results by finite-difference simulations and previous solutions. Following that, parametric studies are conducted to compare the stresses, deformations, and support loads under different stages and solutions. Finally, to further verify the applicability of the solutions in practical tunnels, the convergences, support loads and lining stresses of a typical tunnel cross-section in the Saint Martin La Porte access adit are successfully predicted. Overall, the proposed solutions in this study provide a profitable idea for deriving various viscoelastic-plastic or elasto-viscoplastic explicit solutions that can simultaneously account for both the rock rheology and tunnel face effect.

Calcium phosphate cement promotes the stability of osteoporotic lumbar pedicle screw by enhancer-injecters with different number of holes

BackgroundsThis study aimed to compare whether Calcium phosphate cement (CPC) promotes the stability of osteoporotic lumbar pedicle screw by enhancer-injecters with different number of holes.MethodsThrough a self-designed bone cement injection device, the pedicle screw canal was strengthened with calcium phosphate bone cement, and divided into 4-hole group, 6-hole group, 8-hole group, straight pore group and the control group. The screw was inserted into the mechanical test module, the Maximum insertion torque and Maximum axial pull-out strength were recorded, and the distribution of calcium phosphate bone cement was analyzed by CT and X-ray. The data results were analyzed using SPSS19.0 statistical software package.ResultsThe distribution of bone cement in different reinforcement groups was different and showed regularity. The bone cement in the 4-hole group was roughly located in the head 1/3 of the screw, the 6-hole group was located in the middle 1/3 of the screw, and the 8-hole group was located in the caudal 1/3 of the screw. Compared with the control group, the maximum axial pull-out force of screws in the lateral hole and full screw tunnel reinforcement group was significantly increased. There was no significant difference between the 4-hole, 6-hole and straight pore groups. There was no difference in the screw-in torque between the reinforcement groups, and they all increased significantly compared with the control group, and the difference was statistically significant. After the screw was pulled out, the interface between the bone cement and the polyurethane material was fractured, and a tight package was formed with the screw.ConclusionsEnhancer syringes with different hole numbers combined with CPC bone cement injection can significantly increase the maximum screw pull-out force. The 8-hole group has a smaller pull-out force and is relatively prone to leakage of reinforcing material, which lacks safety in use. The local reinforcement of 4-hole and 6-hole sheath can play a similar role to that of total nail tunnel reinforcement.

Study on the time‐dependent interaction between surrounding rock and yielding supports in deep soft rock tunnels

AbstractAs yielding supports can deform without being damaged, the yielding principle has attracted significant attention for tunnelling in squeezing ground compared with the heavy support method. The deformation energy of surrounding rock can be managed using yielding supports that maintain the rock pressure within the bearing capacity of the supports. However, although the yielding principle has been often applied in practical scenarios, a design method for yielding supports has yet not been well developed. This study discusses interaction between the squeezing ground and yielding supports and investigates the influence of the time‐dependent behaviour of rock on the yielding supports. The yielding supports can be implemented by the movement of sliding joints of steel arches or by shortening the yielding elements inserted in shotcrete linings. The deforming process of yielding supports can be divided into three stages: elastic a, yielding, and elastic b. A three‐stage pressure‐displacement relationship of yielding supports is proposed and a method is provided for the calculation of the support stiffnesses of yielding supports in different stages. Furthermore, a unified design approach for the yielding supports is presented and the theoretical model is established after simplifying the asymmetry of problem. The analytical solution for tunnel displacement and support pressure in a tunnel supported by the yielding supports is obtained. The proposed design method for the yielding supports is successfully applied to the Saint Martin La Porte access tunnel, and the mean tunnel deformation in this tunnel is appropriately predicted by the analytical solution. Additionally, a parametric investigation is performed based on the analytical solution, and the effects of yielding path, yielding displacement, support thickness, and installation time of the yielding supports are discussed. Finally, certain highlights of the analytical model of yielding supports in this study are identified, compared with other researches, and recommendations for the design of the yielding supports are provided. The outcome of this research has potential applications in the preliminary design of deep tunnels in squeezing ground.

Target spectrum-based risk analysis model for utility tunnel O&M in multiple scenarios and its application

Current utility tunnel operation and maintenance (O&M) risk management suffers from low quality and inefficiency and still lacks a robust analysis method to address various risks. Therefore, this study proposes a theoretical model to build an adaptive system of algorithms and models based on global data linkage and a decision-making system for the target spectrum of intelligent O&M of utility tunnels. In addition, a risk prevention and control platform for utility tunnel O&M is formed, and remote centralized data collection, monitoring, emergency decision-making and other functions are realized to improve the safety of utility tunnel O&M. Finally, the model is validated using data from three typical scenarios, and the Beijing International Horticultural Exhibition utility tunnel is chosen as an example. The findings demonstrate that the model offers effective and adaptable decision support for utility tunnel O&M risk management.

Embodied carbon assessment on road tunnels using integrated digital model: Methodology and case-study insights

With the constant increasing road tunnel construction in China, embodied carbon emissions of tunnels play an important role in addressing the issue of the low-carbon construction. This study determined the carbon emission boundary based on the characteristics of road tunnels and proposed a digital model based framework for evaluating embodied carbon emissions in road tunnels, thus realizing the rapid calculation and visualization of tunnel carbon emissions. Through two typical region cases of road tunnels in different regions, the usability and universality of this framework are verified. Based on the carbon emission calculation results of the tunnels, a systematic analysis was conducted on the proportion of carbon emissions in each stage of the tunnel and the carbon emission characteristics of the whole construction process. The results show that the material production stage of road tunnel has the largest carbon emissions proportion, accounting for about 79%-87%, among which the carbon emissions contribution of concrete is the highest, followed by steel. Concrete and steel together account for about 90% of carbon emissions during the tunnel material production stage. The carbon emissions of road tunnel increase with the deterioration of the surrounding rock. The embodied carbon in the secondary support step of road tunnel contributes the most to the total embodied carbon, and the carbon emissions difference of different tunnels is mainly reflected in the two steps of primary support and secondary support of road tunnel. The visual presentation of embodied carbon in road tunnel by digital model can help to achieve the purpose of reducing carbon emissions in tunnels.

Calculating of the tunnel face deformations reinforced by longitudinal fiberglass dowels: From analytical method to artificial intelligence

Deformation calculation of the reinforced tunnel is always the key and difficult problem in tunnel support design. To achieve simple and rapid tunnel performance evaluation, this paper attempts to establish a novel calculation system based on the artificial intelligence, which is transitioned from an analytical method named the Convergence-Confinement Method (CCM) based on the spherical symmetry hypothesis. 200 simulations were completed by using an analytical method to describe the reinforced tunnel behavior and seven parameters were considered to calculate the tunnel face deformation. The Boruta algorithm with a random forest (RF) model was utilized to eliminate unnecessary parameters in the analytical method to build high-precision prediction model. The performance evaluation results indicated that the prediction model based the artificial intelligence has obtained excellent accuracy for estimating the deformation of the tunnel face reinforced by the longitudinal fiberglass dowels. Furthermore, the Geological Strength Index (GSI) is the most important parameter for predicting the deformations of tunnel face in the weak rock masses. Interestingly, the tentative parameter, rock type (mi), cannot be ignored when using the proposed artificial intelligence model to predict the deformations of a tunnel face reinforced by longitudinal fiberglass dowels. In general, this successful transition helps popularize the application range of analytical methods and improve the prediction accuracy for the deformations of reinforced tunnel.

Composite interpretability optimization ensemble learning inversion surrounding rock mechanical parameters and support optimization in soft rock tunnels

The mechanical parameters of the surrounding rock of a tunnel are the premise and foundation of the supporting design in soft rock tunnel engineering. To obtain the mechanical parameters of the surrounding rock accurately and quickly, a composite inversion model is proposed, and different models are used to invert different mechanical parameters. In this paper, first, the Latin hypercube and Monte Carlo sampling methods are used to construct the mechanical parameter samples from the surrounding rocks. The numerical simulation of the water diversion project in central Yunnan is carried out by using FLAC3D, and the corresponding displacement data are obtained, three sets of effective inversion datasets are formed along with the mechanical parameter samples. Second, the adjusted coefficient of determination and the symmetrical mean absolute percentage error are used as the performance evaluation indices. The Bayesian 10-fold cross-validation iteration is used to optimize the five regression model hyperparameters for the three sets of inversion parameters. The base model of the best performance is selected for inverting the friction angle (φ) and cohesion (c). For the deformation modulus (Em) inversion parameters, LIME interpretability is used to optimize the weights and integrate the five models. Finally, by developing a calculation tool for the elastic modulus of tunnel support, an orthogonal experimental design is applied based on the verified engineering numerical model. The results show that the average error of the inversion results of the mechanical parameters of the surrounding rock by the proposed composite model is 9.32%, the minimum error is only 0.81%, and the error is within 15%. The inversion trend is similar to the actual displacement height, and the optimized support scheme provides a reference for the engineering site.

Excavation and Construction Technology of Diversion Tunnel under Complex Geological Conditions

During the construction of a diversion tunnel, geological problems often include faults, fragile strata, hard rock formations, karst landforms, etc., which may have adverse effects on the excavation and construction of the diversion tunnel. Based on the analysis of the engineering overview, this study designed a new construction technology for the excavation of water diversion tunnels in hard rock layers and high-karst areas. Based on tunnel seismic prediction (TSP) technology to achieve advanced geological prediction, combined with actual geological conditions, construction difficulties are analyzed. Then, detection technology is used to collect two-way travel time, amplitude, and waveform data. By processing and analyzing the detection image, the spatial orientation and length of the main tunnel during the construction of the diversion tunnel are calculated. After completing the construction ventilation and wind, water, and electricity layout, the excavation construction procedure is designed. In the specific excavation design, the tunnel curtain excavation technology, tunnel body excavation and support technology, excavation grouting technology, important unfavorable geological tunnel section excavation technology, upper/lower flat section excavation technology, upper/lower curved section excavation technology, and vertical shaft section excavation technology were elaborated. Finally, a plan was made for the reuse process of slag material and a construction quality control system was established. During the testing process, it was found that the antidamage coefficient of the side wall was above 0.9 after using the technology described in this article. Therefore, it indicates that the excavation construction technology designed in this article can ensure the support capacity of the side wall of the diversion tunnel, which is suitable for the excavation of the main tunnel during the construction of the diversion tunnel.

Numerical Simulation Analysis of Construction Support of Intersection Section in Extra-long Water Diversion Project Tunnels

The selected Middle Yellow River Diversion Project is an important backbone project of the planning and construction of the modern water network in Shanxi Province. The project is composed of water source project and water transmission project, the water transmission project is about 400 kilometers long, there are about 200 kilometers of total dry, about 100 kilometers of East Dry and West Dry each, with an average depth of about 400 meters. The intersection section studied in this paper is located under the ridgeline of Lvliang Mountain with a burial depth of more than 600 meters. Whether to support the excavation of the tunnel intersection section was simulated by three-dimensional numerical simulation analysis of different sections. The stress field of surrounding rock and liner and the distribution of plastic zones in surrounding rock were simulated and calculated. The research results provide a technical reference for the design of tunnel support and the formulation of construction schemes, which is of great significance for the construction safety and operation management of water diversion tunnels.

Simulation of bench stepping and optimization of bolt parameters based on multiple geological information fusion

In the stability analysis and design of rock support for tunnels, the establishment of a refined numerical model relies on reliable and accurate geometrical information of structural planes. To better analyze and optimize the tunnel construction method and support mode, it is crucial to establish a refined numerical model for the tunnel. Based on the developed geotechnical intelligent analysis and multi-interpretation system, the feature extraction and interpretation of the rock mass structural surface are achieved. Meanwhile, coupled with multiple geological information, the comprehensive analysis and judgment of rock mass structural surface information are achieved through continuous dynamic tracking. According to this method, based on grade IV fractured rock data collected from the construction site of Dapuling tunnel, the safe distance of step in bench excavation method has been optimized based on the numerical modelling, and the corresponding bolt support design. The optimized tunnel excavation process is more stable and safer, providing a scientific basis for predicting, identifying, controlling, and preventing rockfall disasters during the excavation process of tunnels and underground caverns in fractured rock masses.

Effect of compressible layer on time-dependent behavior of soft-rock large deformation tunnels revealed by mathematical analytical method

The application of compressible layers is considered to be the most promising solution for solving the problem of large deformations in deep soft-rock tunnels. However, although significant effort has been devoted to understanding its mechanical working, the effect of the compressible layer has not been completely revealed. This study theoretically predicts the mechanical response of a deep soft-rock large deformation tunnel by applying a compressible layer. The theoretical model involves a circular tunnel, which is supported by a compressible layer and concrete lining, and subjected to a non-hydrostatic stress field. The influence of the tunnel face advancement is described by the stress release coefficient, and the three-stage deformation characteristics (elastic–yielding–compaction) of the compressible layer material are considered in this model. The entire tunnel deformation process is divided into unlined and lined (further subdivided into elastic, yielding, and compaction phases of the compressible layer material) phases. A series of complex potential functions in different media (rock, compressible layer, and concrete lining) and at different phases is provided; subsequently, the unknown coefficients in these functions are determined using the stress balance and displacement continuity conditions at different interfaces. Thus, the analytical solutions for tunnel displacement and support pressure at different phases are obtained. Good agreement between the numerical and analytical results is observed after performing the numerical simulation to validate the reliability and feasibility of the proposed analytical derivation. Finally, a parametric sensitivity investigation is conducted by including the yielding stress of the filling material, yielding length of the compressible layer, and installation time of the support. Adequate attention is paid to the tunnel displacement and support pressure on the 100th day and their development laws at the positions of θ = 90°, 45°, and 0° during the first 100 days. Some interesting findings are presented, and useful design suggestions for the compressible layer are provided.