Tunnel Design Research Articles

Numerical Simulation Study of Midas-Based Tunnel Section Structural Forces and Deformations

The burial depth significantly influences the structural forces and deformations of tunnel sections, playing a crucial role in the safe operation of tunnels. This study focuses on the structural design and deformation analysis in underground tunnel engineering. Utilizing Midas modeling techniques, tunnel models were designed for experimentation to comprehensively explore the impact of tunnel burial depth and key design parameters on structural deformations and safety.(1) The research reveals that design parameters such as tunnel diameter are the dominant factors affecting deformation, lining pressure, and structural displacement.(2) With an increase in tunnel diameter, substantial deformation occurs, and the lining pressure distribution evolves from a "fan-shaped" pattern to a "peach-shaped" pattern. The bottom structure transitions from uplift to slight settlement. (3) The study results provide a rational range of parameter values for tunnel design. Simulation outcomes highlight areas with higher deformation, offering insights for proposing corresponding remedial measures.

Effect of hydrogen ratio on leakage and explosion characteristics of hydrogen-blended natural gas in utility tunnels

Based on computational fluid dynamics technology, the effect of hydrogen blending ratio (HBR) on the concentration distribution of leaked gas diffusion in utility tunnels was investigated, and based on this, the explosion characteristics of hydrogen-blended natural gas (HBNG) were studied in an inhomogeneous concentration field. The results showed that the concentration field of HBNG gradually stabilized in the downstream of the leak site, and the peak concentration increased linearly with HBR. When HBR≤5%, a high concentration region above the upper explosive limit is formed inside the gas cloud. This characteristic of the distribution induces secondary combustion in utility tunnels. The maximum flame velocity and steady acceleration distance increase with the increase of HBR. The flame shape is significantly affected by the concentration field distribution. The explosion overpressure induced by the real concentration field created multiple peak structures that exacerbated the explosion disaster complexity. The first overpressure peak at the ends was formed by the superposition of the precursor shock wave and its reflected wave, and those at other locations are caused by the shock waves. However, all maximum overpressure peaks are formed by the superposition of multiple reflections of the explosion wave. The maximum peak overpressure at both ends of the tunnel is higher than that in the middle. The explosion overpressure induced by the inhomogeneous gas cloud is lower than that caused by homogeneous gas cloud under the same volume. The research results can provide an effective reference for the anti-explosion design and risk assessment of utility tunnel.

Prediction of geomechanical changes in faulted rock mass around underground structures subjected to earthquakes

Faults are a type of geological structure that often leads to geological disasters in underground structures under normal conditions and especially when earthquakes occur, thereby requiring careful study.This article introduces some numerical simulation results on the seismic wave propagation process, on changes in stress and displacement states in the rock mass with a small fault of a dip angle of 45o, around a circular cross-section tunnel, using the discrete element method (Universal distinct element Code - UDEC). Three cases are simulated: a) The tunnel is located in the hanging wall rock, the fault is located 10m from the centre of the tunnel on the vertical axis; b) The fault runs through the centre of the tunnel and c) The tunnel is located in the footing wall rock, the fault is located 10m from the centre of the tunnel on the vertical axis. The results obtained show a very clear influence of the position and location of the fault on the geomechanical changes in the rock mass around the tunnel, contributing to the reasonable design of tunnels subjected to earthquakes.

Excavation method optimization and mechanical responses investigating of a shallow buried super large section tunnels: a case study in Zhejiang

The construction of super large section (SLS) shallow buried tunnels involves challenges related to their large span, high flat rate, and complex construction process. Selecting an appropriate excavation method is crucial for ensuring stability, controlling costs, and managing the construction timeline. This study focuses on the selection of excavation methods and the mechanical responses of SLS tunnels in different types of surrounding rock. The research is based on the Yangjiashan tunnel project in Zhejiang Province, China, which is a four-line highway tunnel with a span of 21.3 m. Three sequential excavation methods were proposed and simulated using the three-dimensional finite difference method: the “upper first and lower later” side drift (SD) method, the central diaphragm method, and the top heading and bench (HB) method. The mechanical response characteristics of tunnel construction under these methods were investigated, including rock deformation, rock pressure, and the internal forces acting on the primary support. By comparing the performance of the three construction methods in rock masses of Grades III to V, the study aimed to determine the optimal construction method for SLS tunnels considering factors such as safety, cost, and schedule. Field tests were conducted to evaluate the effectiveness of the optimized construction scheme. The results of the field monitoring indicated that the “upper first and lower later” SD method in Grade V rock mass and the HB method in Grade III to IV rock mass are feasible and cost-effective under certain conditions. The research findings provide valuable insights for the design and construction of SLS tunnels in complex conditions, serving as a reference for engineers and project managers.

Seismic isolation technology of shallow buried large section utility tunnel with soft soils in seismically vulnerable area

Shallow utility tunnels with exceptionally large cross-sections in weak soil can face significantly more severe seismic risks compared to conventional deep tunnels in seismic hazard areas. This study investigates the seismic response and isolation technologies applied to a large section utility tunnel with 4 compartments in one layer, employing seismic simulations. The engineering context, dynamic motions, and measuring points of the numerical simulation were introduced. Subsequently, the finite element method was employed to explore the seismic behaviors of the large section utility tunnel when subjected to strong earthquake excitations under four conditions. The study explored and comparatively evaluated the seismic isolation effectiveness of three proposed schemes: the grouting scheme, the buffer layer, and the assembly of three-quarters buffer layer, cushion and grouting. The analysis included various indexes such as the deformation, the principal and shear stress, and the safety factor. The finding reveals that the assembly seismic scheme exhibits the most significant seismic effect (95.39%), followed by the buffer layer (38.82%), and the grouting scheme (25.66%). The assembly seismic scheme is recommended for the seismic design in the current large-section utility tunnels. These conclusions provide valuable scientific guidance for the seismic design of large-section utility tunnels, aiding in enhancing earthquake resilience.

A multi-scale model for longitudinal seismic design of prefabricated utility tunnel based on multi-point constraints

A multi-scale model for the longitudinal seismic analysis of underground prefabricated utility tunnel was proposed. In this multi-scale model, beam elements were used to model the utility tunnel segments, shell elements were used to model the weak parts, e.g., tunnel intersections, and node frames with multiple springs were used to simulated the behavior of the tunnel joint. The node frames, whose form are the same as that of the prefabricated joint, were established on a basis of the cross-sectional size and the joint form of the tunnel. By arranging multiple sets of nonlinear springs to connect adjacent node frames, the refined model of the utility tunnel joint was established. Based on the multi-point constraint method, the multi-point constraint equations between the structure model and the refined joint model were given. Finally, a specific straight utility tunnel as well as a specific cross-type utility tunnel were taken as the examples to verify the accuracy and applicability of the proposed model. The results indicate that the proposed model is suitable for the longitudinal seismic analysis of the utility tunnels with asymmetric cross-section and intersections, and may provide reference for the longitudinal seismic design of large-scale utility tunnels.

Research on mechanical response and time-space distribution of supporting structure of deep-buried tunnel in naturally water-rich loess

When the water content is small, the strength and stiffness of loess is considerably high. But with the increasing of water content, the shear strength of loess decreases since the matric suction of unsaturated loess decrease. If loess is soaked in water for long time after reaching the saturated state and the linking intensity weakened, the loess would be prone to softening deformation, so as to the stress of the tunnel supporting structure, which will cause the decreasing of the stability and durability of the tunnel. Therefore, the in-situ monitoring of surrounding rock deformation and stress characteristics of supporting structure is very important and was carried out in the deep-buried tunnel in naturally water-rich loess in this paper. The time–space effect of tunnel surrounding rock deformation, mechanical response of primary support, and secondary lining were monitored and analyzed. The results indicated that the deformation of surrounding rock was quite large, and the reserved settlement was insufficient. The analysis and calculation of the surrounding rock pressure and the stress of the steel arch indicated that the primary supporting structure of the upper bench was unsafe, the arch-foot had a trend of bending deformation to the side of the tunnel′s inner contour, and the inverted arch had a trend of uplift. Through the analysis of the contact pressure and the stress of the secondary lining reinforced concrete, the sidewall had a trend to deform to a side of the tunnel′s inner contour due to squeezing of the surrounding rock. The inverted arch had a trend to uplift, indicating the significant change and redistribution of the groundwater and surrounding rock stress field. The stress and deformation of supporting structure were highly complex both in space distribution and time development. The research results could provide specific reference and guidance for the design and construction of deep-buried tunnels in naturally water-rich loess.

Local Site Effect of Fault Site and Its Impact on Seismic Response of Fault-Crossing Tunnel

ABSTRACT The areas where tunnels crossing faults are especially susceptible to seismic damage. Local site effects associated with fault site notably contribute to the unfavourable impact on the seismic behaviour of tunnels. In this study, large-scale shaking table tests were conducted to investigate the fault site effect and its impact on the seismic response of tunnels. Real earthquake records, synthetic seismic wave, and sinusoidal waves were selected as input motions, excited in both transverse and longitudinal directions of the tunnel. The local site effect of the fault site was evaluated by time-frequency analysis. The test results indicate that the acceleration response within the fault is significantly greater than those on both sides, regardless of excitation direction. Dynamic characteristics of different regions of the fault site exhibit distinct variations under different excitation directions, with the dynamic behaviour of the strata within the fault playing a crucial role. Marked waveform distortion and trapped waves can be observed within the fault, attributed to harmonic distortion, waveform conversion at fault interfaces, and varying seismic wave propagation pathways. The region of maximum seismic response of the fault-crossing tunnel predominantly occurs near the interface between the fault and the hanging wall. The seismic response of the tunnel located in the hanging wall exceeds that in the footwall. The dynamic characteristics of the fault-crossing tunnel are significantly affected by the dynamic characteristics of the strata around the tunnel, highlighting the necessity of comprehending strata dynamics in the seismic design of such tunnels. The aforementioned findings could offer valuable insights for the seismic design of mountain tunnels crossing fault zones.

Macro-micro analysis of ground response to circular tunnel excavation in granular media

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.

Thermal performance of geothermal energy tunnel in unsaturated soils

Energy tunnel provides an innovative and efficient approach to harvesting geothermal energy. Understanding its performance and identifying the key influential factors are important to the application of this sustainable technology. In practice, soils surrounding an energy tunnel are often unsaturated, while previous studies either focus on fully saturated conditions (FS analysis) or simplify the soils above the water table as completely dry (CD analysis). These analyses may lead to inaccurate evaluation of thermal performance in unsaturated conditions because soil's thermal properties are moisture-dependent. Moreover, the effects of soil moisture conditions on thermal performance are expected to depend on various factors like soil and operational conditions. To address these problems, this study developed a coupled thermo-hydraulic finite element code to investigate the thermal performance of energy tunnel in unsaturated soils. The effects of soil property, groundwater, tunnel’s internal airflow environment (TIAE), heat carrier fluid, and pipe conditions were investigated. Comprehensive results show that TIAE is one of the most important factors affecting the thermal performance in unsaturated soils. Another dominant factor is the groundwater flow velocity and fluid inlet temperature when the water table is relatively high (above tunnel crown) and low (below tunnel invert), respectively. Moreover, in the cases with a high water table and high TIAE (e.g., heat transfer coefficient ≥ 5.3 W/(m2∙K)), the conventional CD and FS analysis can give an acceptable performance evaluation for the sand and clay, respectively. In other cases, however, significant underestimation and overestimation, with a maximum value of 70 % and 130 %, are induced by the CD and FS analysis, respectively. These findings suggest that soil unsaturation should be properly considered in the design of energy tunnels.

Empirical design for the excavation method and support system at Budong-Budong Dam Diversion Tunnel, Central Mamuju, West Sulawesi Province

Budong-Budong Dam, located in the West Sulawesi Province of Indonesia, was designed to use a tunnel to divert river flow during the dam construction. The Rock Mass Rating was used to examine the tunnel design with a less detailed drill core investigation. The rock strength parameter is only based on the field estimation. The entire diversion tunnel will pass through Breccia with weak strength. Evaluation is required using integrated and precise data to guarantee safety during and post-construction. The RMR classification was used to determine the excavation and preliminary tunnel support, while the Q-System was used to compare the support of the tunnel. Those classifications were used to anticipate the geological conditions uncertainty. Geological data were collected by geological mapping, evaluation of subsurface drilling, and laboratory analysis. The tunnel will pass through a Tuffaceous Breccia and Tuffaceous Sandstone insert of Tuffaceous Siltstone. In addition, a poor-quality rock was found around the inlet and outlet, and a fair-quality rock in the middle of the tunnel. Hence, drilling and blasting were recommended for the excavation. The tunnel’s proposed support system included shotcrete, wire mesh, and rock bolts in the middle of the tunnel. Steel sets are added around the inlet and outlet.

Optimizing Tunnel Design in Sharp Curves: A Numerical Simulation of Fluid-Structure Interaction

Optimizing Tunnel Design in Sharp Curves: A Numerical Simulation of Fluid-Structure Interaction

Seismic Isolation Materials for Bored Rock Tunnels: A Parametric Analysis

Most recent tunnel designs rely on more thorough analyses of the intricate rock interactions. The three principal techniques for excavating rock tunneling are drill-and-blast for complete or partial cross-sections, TBM only for circular cross-sections with full faces, and road header for small portions. Tunnel-boring machines (TBM) are being utilized to excavate an increasing number of tunnels. Newer studies have demonstrated that subterranean structures such as tunnels produce a variety of consequences during and after ground shaking, challenging the long-held belief that they are among the most earthquake-resistant structures. Consequently, engineering assessment has become crucial for these unique structures from both the geotechnical and structural engineering standpoints. The designer should evaluate the underground structure’s safety to ensure it can sustain various applied loads, considering both seismic loads and temporary and permanent static loads. This paper investigates how adding elastic, soft material between a circular tunnel and the surrounding rock affects seismic response. To conduct the study, Midas/GTS-NX was used to model the TBM tunnel and the nearby rock using the finite element (F.E.) method to simulate the soil–tunnel interactions. A time–history analysis of the El Centro (1940) earthquake was used to calculated the stresses accumulated in the tunnels during seismic episodes. Peak ground accelerations of 0.10–0.30 g, relative to the tunnel axis, were used for excitation. The analysis utilized a time step of 0.02 s, and the duration of the seismic event was set at 10 s. Numerical models were developed to represent tunnels passing through rock, with the traditional grout pea gravel vs. isolation layer. A parametric study determined how isolation material characteristics like shear modulus, Poisson’s ratio, and unit weight affect tunnel-induced stresses. In the meantime, this paper details the effects of various seismic isolation materials, such as geofoam, foam concrete, and silicon-based isolation material, to improve protection against seismic shaking. The analysis’s findings are discussed, and how seismic isolation affects these important structures’ performance and safety requirements is explained.

A New Method for Calculating the Load Shared by the Primary Support of Deep-Buried Rheological Soft Rock Tunnels by Considering the Flexible Primary Support

The gap between the theoretical solution of the load and the field measurement is too large to guide the support design while the primary support of deep-buried soft rock tunnels shares a large surrounding rock load. In this study, the flexible support effect of the primary support and the rheological effect of the surrounding rock were considered. The calculation procedure of load shared by the primary support when the surrounding rock is in the accelerated, uniform velocity and decelerated stages was proposed. Then, the reliability of the computational method of the study was verified by numerical simulation methods. The analysis shows that the surrounding rock in the accelerated, uniform and decelerated stages of the load sharing of the primary support presents increasing, unchanged and decreasing states and that the formation of the primary support load is mainly concentrated in the stage of accelerated movement of the surrounding rock. Enhancement of the primary support parameters, while significantly increasing the support safety factor, has a limited effect on reducing load shared by the primary support. Thus, it is recommended that the advanced support can be strengthened to reduce the pre-deformation of the surrounding rock in the unsure soft rock section to reduce the load shared by the primary support. The primary support design of tunnels with rheological rock should account for the long-term rheological load effect of the surrounding rock. The results of this study can provide guidance for the prediction of primary support load sharing for dynamic tunnel construction.

Displacement-based Design of Shield Tunnel Lining Considering Mobilized Strength of Undrained Clay

This paper presents a displacement-performance design method for the shield tunnel based on the mobilized strength design (MSD) theory. Firstly, the nonlinear relationship between the ground volume loss caused by tunnel excavation and the earth pressure was constructed to obtain the real earth pressure on the tunnel lining. Secondly, the nonlinear relationship between the convergence displacement of the lining and the ground resistance was built to acquire the subgrade reaction working on the tunnel lining. Finally, the proposed method was verified by orthogonal numerical experiments and compared with the finite element method (FEM) results. Compared with the FEM, the average deviation of the bending moment and the axial force are about 9% and 1%. The average variation of the bending moment can be reduced to 1% after calibration. The results calculated by this developed method are better than the traditional beam-spring model. Its accuracy is close to the FEM based on the strata-structure concept. Therefore, the proposed method based on MSD theory in this paper has the characteristics of high efficiency and simplicity, which provides a new auxiliary design approach for the structural design of shield tunnels in clay areas.

Design and Fabrication of Low-Speed Wind Tunnel (LSWT)

The design and fabrication of a low-speed wind tunnel (LSWT), which is a critical component for testing and comprehending aircraft aerodynamics, is presented in this study. Despite the increasing prominence of computational fluid dynamics (CFDs) in manufacturing engineering, wind tunnels remain essential for the intricate development of aircraft and automobile designs with complex flow interactions. Using SolidWorks, we focused on controlling flow turbulence approaching the test section, emphasizing performance and quality parameters. The construction of the wind tunnel used plywood with an axial fan regulating the airspeed, and Arduino facilitated data acquisition. The drag and lift on the Y Clerk Airfoil were quantified by two load cells along the XY-axis, complemented by a Pitot Static Tube and a multitube inclined plane manometer for pressure and velocity calculation. Fusion 360 simulation software was used to analyze pressure and velocity profiles at speeds ranging from 10 to 20 m/s, providing a comprehensive quantitative evaluation of the wind tunnel’s capabilities. By emphasizing both design innovation and quantitative performance metrics, this study underscores the continuing significance of wind tunnels in engineering.

Design and validation of a wind tunnel for viral aerosol filtration testing

Design and validation of a wind tunnel for viral aerosol filtration testing

Comparative analysis of adaptability of open TBM small curve turning radius

Aiming at the problems of difficult operation and low excavation accuracy of open TBM in the process of small curve cornering, the structural mechanism, and motion characteristics of the traditional Horizontal main beam type TBM and the new 8-SPS V-type TBM mainframe were compared and studied. Based on the drainage channel project of a pumped storage power station, the factors affecting the minimum turning radius of TBM were analyzed by establishing two TBM main engine turning direction models. Secondly, the design of two open TBM mainframes with a diameter of ϕ3530 mm is improved. Finally, the relationship between the displacement and velocity change between the cutterhead and the propulsion cylinder under the straight-line boring condition and the small curve turning boring condition of TBM was analyzed by ADAMS software. The results show that when the tunnel design axis has a large turning radius and is dominated by straight segments, the TBM propulsion system with horizontal main beam type has higher excavation efficiency. The 8-SPS V-type TBM cutterhead attitude change is more flexible, which is more suitable for complex and changeable small curve corner boring. Moreover, the 8-SPS propulsion system is symmetrical, and the speed of each cylinder changes more gently during the turning process, the cylinder attitude of TBM is easy to control during the small curve turning and propulsion, the boring accuracy is higher, and the propulsion system compliance is better.

Mechanical Behaviors and Structure Safety of a Tunnel Crossing a Water-Rich Fault Fracture Zone—A Case Study

To study the potential disasters caused by tunnels crossing water-abundant fault areas, this study takes the Jinyunshan Tunnel as an example, and studies the groundwater flow law between different rock layers, the interaction between surrounding rock hydrostatic pressure and soil pressure, and the mechanical features and safety of the lining during construction by combining field tests and finite element simulation analysis. The results show that the displacement change rate of the tunnel vault reaches 2.8 mm/d, and the maximum earth pressure and hydrostatic pressure are 2.3 MPa and 1.15 MPa, respectively, both at the bottom of the tunnel in section II. When the tunnel enters the fault fracture zone from the V surrounding rock, the bending moment of the lining increases by 222.78% at the left haunch and 60.87% at the bottom of the right wall. The axial force of the right spandrel increases by 2579.2%, and the left spandrel increases by 221.18%. The safety factor of the two sections is greater than 2.4, indicating that the overall structure is in a safe state, but the safety factor of the second right shoulder is 2.54, which is close to the safety threshold of 2.4. The research results provide a basis for the safety design and construction safety of tunnels through water-rich sections in similar fault fracture zones, and provide a reference for reducing groundwater loss and protecting ecological vegetation.

An evaluation of cutting head design of current tunnel Boring machines and suggestions to improve machine Performance

ABSTRACT This paper evaluates cutterhead design of current tunnel boring machines (TBMs) in considerations with the actual cutting action of discs observed on the most common cutter heads. The discs on the current TBM cutter heads were found to predominantly perform asymmetrical cutting action, which generates excessive sideway forces impairing steering action of the machine. The effective s/p ratios related to actual cutting action of discs emerge to be significantly higher than those of the laboratory-determined values, and this consequently leads to adverse cyclic deepening effect. The gross lateral loads arising from excessive side forces were stated to be minimised if the adjacent discs are arranged to cut in symmetrical position by adopting appropriate cutterhead design methods suggested in this paper. Furthermore, a dynamic analysis was carried out in terms of reaction forces on cutter heads of different geometries, and it was indicated that flat face cutter heads have better steering abilities than conical or domed types, in mixed face conditions. Similar analysis on disc angular spacing also inferred that scattered type disc arrangements with equal angular spacing are preferable to cutterheads with spoke or star type lacing, in terms of cutterhead balance.