Tunnel Design Research Articles

Influence of geological uncertainty on longitudinal deformation of tunnel based on improved coupled Markov chain

The complex geological condition encountered during excavation is the key challenge for tunneling projects. Therefore, tunnel design and construction require a comprehensive understanding of the subsurface geology. This study aims to reveal the effect of geological uncertainty on tunnel longitudinal deformation based on a reconstruction geological model using the improved coupled Markov chain method. The improved coupled Markov chain method makes the predicted results more suitable for the possible stratigraphic distribution by optimizing the transition probability matrix, and breaks through the limitations of non-coaxial predicted cell updating in traditional methods. A mapping method was proposed to establish a matching relationship between the irregular grids of the geological model and the numerical tunnel model. Then, a long tunnel in Shenzhen was selected as a case study to demonstrate the effectiveness of the proposed framework. The correlation coefficient was used to verify the relationship between tunnel deformation and the surrounding stratum with different tunnel cover depths. The geological uncertainty of various strata was quantitatively measured based on the proposed geological uncertainty index. The three-dimensional strata surrounding the tunnel were reconstructed based on exceedance probabilities for adverse geological conditions. Quantitative analysis was conducted on the tunnel vertical convergence during the excavation process.

Analysis of mechanical response and failure characteristics of tunnels crossing active faults considering axial force and geometrical nonlinearity

Tunnels subjected to active fault dislocation may experience significant damage. This paper establishes a novel methodology and solution procedure for analyzing the mechanical response and failure characteristics of tunnels subjected to active fault dislocation based on an elastic foundation beam model. The proposed methodology includes axial, transverse, and vertical soil-tunnel interaction terms, in addition to geometrical nonlinearity and axial force terms in the governing equation. This approach has a significantly extended application range, effectively addressing the problems encountered in tunnels crossing active faults with diverse crossing angles, dip angles, and fault types. The proposed methodology is verified by comparison to a 3D FEM model with various fault types, experimental tests, and on-site case, and the results are in excellent quantitative and qualitative agreement with the numerical, experimental, and on-site results. When fault displacement is below 0.5 m, disregarding geometric nonlinearity results in calculation errors of approximately 10% to 17% for peak axial force (Nmax), 18% to 22% for peak shear force (Vmax), and 20% to 30% for peak bending moment (Mmax). Finally, the responses caused by different factors, i.e., fault type, fault displacement, tunnel stiffness, and tunnel diameter, are investigated in detail to better understand tunnels crossing active faults. The results show that amongst the various fault types, the Vmax and the Mmax experienced by tunnels subjected to oblique slip-fault dislocation surpass those of other fault types, accompanied by the most extensive failure range. The augmentation of fault displacement, tunnel stiffness, and tunnel diameter precipitates a corresponding escalation in the Nmax, Vmax, Mmax, and failure range. Under oblique-slip fault dislocation, the tunnel undergoes an initial phase of shear failure, followed by tension-bending failure, delineated by distinct fault displacement thresholds of 0.1 m and 0.2 m, respectively. The proposed methodology provides the advantage of reliable stability analysis and design of tunnels crossing active faults.

Correlation Analysis of Tunnel Deformation and Internal Force in the Earthquake Based on Tunnel Inclination

An increasing number of studies have shown that the seismic response of shield tunnels differs from that of aboveground structures. While the seismic response of aboveground structures is mainly influenced by the peak acceleration and frequency of the earthquake, the seismic response of shield tunnels is more influenced by the ground displacement due to the surrounding soil layers. In this study, it is not appropriate to follow the seismic concept of aboveground structures. Dynamic time-history analysis is a powerful and effective method to study the seismic response of tunnels in the typical subway in this paper. The analysis results show that the overall levelling of the tunnel will not affect the tunnel too much, and the seismic response of the tunnel is mainly related to the relative displacement of the ground around the tunnel. The analysis results show that the internal force of the tunnel and the tunnel inclination have a good linear relationship, and the tunnel inclination can be used to measure the magnitude of the seismic response of the tunnel. In the seismic design of shield tunnels, the inclination of the tunnel can be taken into account to evaluate the change in the internal forces of the tunnel during earthquakes, which avoids the need for complex dynamic time-history analysis and greatly improves the efficiency of the seismic design of shield tunnels.

Scattering of SH waves by elliptical cavity and type-III crack in deep anisotropic geology

Most of the underground rock formations are anisotropic, and the study of the dynamic response of anisotropic geology containing internal defects is necessary for the development of underground tunnels or caverns. In this paper, the wave function expansion method, the complex function method, and the Green's function method are used to solve the problem of scattering of SH waves in anisotropic rock in the presence of elliptical cavity and type-III crack. Boundary conditions for solving the problem are given using the conformal transformation method, and crack in the medium is constructed using the "crack cutting" technique. The scattered wave field generated by the crack is constructed based on the Green function method, and the displacement and stress fields in the model are obtained by the wave field superposition principle in the case of SH wave incidence. The dynamic stress concentration factor (DSCF) on the boundary of the elliptical cavity and the dynamic stress intensity factor (DSIF) at the crack tip are derived. The correctness of the method is verified by degenerating it to a classical analytic solution. Finally, the effects of the anisotropic strength of the rock mass, the dimensions of the cavern, and the incidence angle and wave number of the SH wave on the DSCF and DSIF are analyzed by numerical calculations in both the frequency and time domains. The results show that the anisotropy of the rock mass, the shape of the cavern and the defects of the surrounding medium have a great influence on the dynamic response of the underground structures, which should be given enough attention in the development and design of deep underground caverns or tunnels.

Development of correlations between various engineering rockmass classification systems using railway tunnel data in Garhwal Himalaya, India

Engineering rockmass classifications are an integral part of design, support and excavation procedures of tunnels, mines, and other underground structures. These classifications are directly linked to ground reaction and support requirements. Various classification systems are in practice and are still evolving. As different classifications serve different purposes, it is imperative to establish inter-correlatability between them. The rating systems and engineering judgements influence the assignment of ratings owing to cognition. To understand the existing correlation between different classification systems, the existing correlations were evaluated with the help of data of 34 locations along a 618-m-long railway tunnel in the Garhwal Himalaya of India and new correlations were developed between different rock classifications. The analysis indicates that certain correlations, such as RMR-Q, RMR-RMi, RMi-Q, and RSR-Q, are comparable to the previously established relationships, while others, such as RSR-RMR, RCR-Qn, and GSI-RMR, show weak correlations. These deviations in published correlations may be due to individual parameters of estimation or measurement errors. Further, incompatible classification systems exhibited low correlations. Thus, the study highlights a need to revisit existing correlations, particularly for rockmass conditions that are extremely complex, and the predictability of existing correlations exhibit high variations. In addition to augmenting the existing database, new correlations for metamorphic rocks in the Himalayan region have been developed and presented that can serve as a guide for future rock engineering projects in such formations and aid in developing appropriate excavation and rock support methodologies.

Theoretical semi-quantitative risk assessment methodology for tunnel design and construction processes

Theoretical semi-quantitative risk assessment methodology for tunnel design and construction processes

Ice shedding tests for the assessment of hybrid ice protection systems

In technical areas, the prevention of atmospheric icing on structures is imperative due to safety risks and potential technical failures it poses. Recent development projects have focused on hybrid ice protection systems, combining active elements (heaters/mechanical actuators) with passive icephobic coatings. However, there is a lack of test strategies for the early development stages of these coating materials. An efficient test design for an ice wind tunnel is described here, developed to quantitatively assess the ice shedding effects facilitated by icephobic surfaces in electro-thermal ice protection systems. Dependencies on test and surface parameters are explored, laying the groundwork for defining test procedures for subsequent surface evaluations. During testing, utilizing a hydrophobic model coating, a reduction in energy of over 30% was observed compared to uncoated aluminium. This finding highlights the potential effectiveness of icephobic surfaces in mitigating icing effects. The presented test serves as a valuable tool for pre-selecting the most promising surfaces for further advanced tests, particularly those involving aerodynamic profiles within the ice wind tunnel test facility. It constitutes a vital component of a comprehensive test pyramid, encompassing ice-related tests with increasing complexity. Furthermore, the results obtained from these tests are utilised to establish correlations with surface properties, thereby enhancing our understanding of the significance of these findings. This approach provides a well-founded testing strategy for evaluating and advancing icephobic surface technologies.

Flow features of a horseshoe tunnel bend

Previous research on bend flow has mainly focused on rectangular channels or circular conduits with small bend radii. This study investigates the dynamics of bend flow in an unexplored geometry: the horseshoe cross-section with large bend radii, a typical configuration in hydraulic tunnels. We examine two critical flow features, energy losses and superelevation, employing theoretical equations and dimensional analysis based on experimental data collected on a physical model of a diversion tunnel. The findings reveal an exponential decrease in the bend loss coefficient with increasing Reynolds numbers and shockwaves within the bend for Froude numbers exceeding 1.945. These findings are relevant in a hydraulic tunnel design with similar features and offer insights to minimize energy losses and maintain stable flow conditions.

Framework for determining the safety distance of karst caves adjacent to tunnels

Karst caves pose safety issues for tunnels in karst areas. Karst caves at a certain distance from the tunnel must be treated fully to mitigate risks. A threshold of 3 m is typically adopted; caves within this threshold are fully treated, while those beyond are left untreated, regardless of the geological environment, cave features, tunnel design, operating conditions, etc. This poses risks to tunnel safety during construction and operation. This paper proposes a novel framework based on the aforementioned aspects to determine the treatment distance for caves from the perspective of uncertainty and risk. Geological conditions include the soil and rock type, weathering degree, underground water system, and pH. Karst caves primarily include the size, shape, distance, spatial distribution, density, and filling condition; the tunnel aspect refers to the tunnel diameter, construction method, design life, importance, lining, and tolerable criterion; and operation conditions refer to the vehicle speed, operation time, vehicle load, and maintenance. Herein, the parameters/indices for these aspects and methods to quantify their values are described. A decision-making process is illustrated to revive the mindset of risks in tunnel engineering. The proposed framework is effective for optimizing decision-making in karst cave treatment for tunnels in karst areas.

Seismic Response of Utility Tunnel in Trapezoidal Backfilled Soil Under P Wave and Amplification Effect of Ground Motion

ABSTRACT For the seismic risk of utility tunnel in trapezoidal backfilled soil and its possible amplification effect of ground motion, the seismic response of utility tunnel in trapezoidal backfilled soil under P wave is studied by a high-precision indirect boundary element method (IBEM) with the idea of “partition fit.” The results show that the peak surface displacement appears on the backfill surface, and the softer the backfilled soil, the greater the peak surface displacement; the peak vertical displacement at oblique incidence is generally smaller than that at vertical incidence; the existence of utility tunnel can restrain the incidence wave to a certain extent, especially for the low-frequency wave; the peak displacement and stress of utility tunnel in the soft backfilled soil are all greater than that in stiff backfilled soil; the peak stress of utility tunnel at oblique incidence is greater than that at vertical incidence; the stress concentration occurs at the axillary corner; and the stress in the inner wall of utility tunnel is greater than that in the outer wall. The similar conclusions could be further confirmed from the time history analysis. The research results can provide some reference for the seismic design of utility tunnel in the backfill site and the evaluation of seismic performance of near surface pipeline, etc.

Dimension-Reduction Spectral Representation of Soil Spatial Variability and Its Application in the Efficient Reliability Analysis of Seismic Response in Tunnels

Reliability analysis of tunnels considering soil spatial variability was traditionally carried out using Monte Carlo simulations, which are computationally expensive. This study proposes a dimension-reduction spectral representation method (SRM) for simulating parameter stochastic fields to capture uncertainties in soil properties, which can be coupled with the probability density evolution method (PDEM). Additionally, the PDEM is employed to conduct seismic reliability assessments of tunnels in a more efficient manner. By integrating a non-intrusive dynamic random finite element method (FEM), this study explores the horizontal drift angle and vertical relative settlement of tunnel dynamic response under different coefficient of variations (COVs) and horizontal autocorrelation lengths of elastic modulus (E). Results show the changes in COVs have more pronounced effects on the mean and standard deviation of horizontal drift angle and vertical relative settlement of tunnel than alterations in horizontal autocorrelation lengths. A limit state pertaining to the horizontal drift angle and vertical relative settlement is established through the use of a probability density function (PDF) and cumulative distribution function (CDF). The results suggest that the combination of soil spatial variability and PDEM can serve as an effective approach for practical tunnel design.

Evaluating the anisotropic thermal–mechanical coupling strength of slate: A discrete element method approach

This study utilizes the discrete element method (DEM) to explore the thermal–mechanical coupling behavior of slate. Initially, a series of triaxial compression tests are conducted on slate specimens with varying orientation angles, temperatures, and confining pressures. Subsequently, the DEM is employed to replicate the mechanical and failure characteristics of the slate under identical laboratory conditions. The DEM constitutive models incorporate the parallel bond model for the rock matrix and the smooth-joint model for foliation. A thermal-degradation function for the parallel bond model is proposed, reasonably capturing the temperature's effect on the strength and failure characteristics of the slate. The simulation results exhibit a series of U-shaped curves in peak strength at different orientation angles, mirroring experimental findings. The study's findings indicate that orientation angles significantly influence the mechanical behavior and failure characteristics of slate. Elevated temperatures have minimal effects on strength anisotropy. Furthermore, applying high confining pressure is observed to mitigate the impact of high temperatures on bond weakening. This proposed method provides a useful tool for tunnel designs and geothermal energy development.

Mitigation of tunnel support design risks for hydropower projects within high tectonic stress regimes – an empirical analysis

Abstract The study for the design of tunnels in similar geological settings, providing insights into potential challenges that may arise during excavation and offering strategies for mitigating risks in District Kalam on the Ushu River, Khyber Pakhtunkhwa, Pakistan. The methodology involved geological mapping, rock sampling, discontinuity surveys, and laboratory testing for empirical analysis of tunnel parameters at the Weir House, Powerhouse, and tunnel alignment locations. Empirical analysis of tunnel parameters using three rock classification systems, rock mass rating (RMR), rock quality tunneling index, and rock mass index (RMi). Based on the classification, the rock quality was found to be fair, indicating favorable rock properties. The Q-system rated the rock as poor to fair, suggesting low discontinuity intensity, medium rock strength, or medium deformation modulus. According to the RMi, rock was rated as medium to strong, indicating low discontinuity intensity, high rock strength, or low deformability. The support design for the tunnel is based on empirical analysis, it recommends support design for the tunnel reinforcement elements such as rock bolts, wire mesh, and shotcrete lining. Overall, the tunnel is stable and does not have complex structure and weak zones.

A quantitative tunnel support design method considering the safety factor of the surrounding rock

The quantitative support design plays a vital role in tunnel design, while the conventional quantitative framework of tunnel support design through convergence-confinement method (CCM) generally focuses on the safety of the support structure element. Herein, a quantitative tunnel support design method considering the safety factor of the surrounding rock is proposed. First, the solution for the safety factor of surrounding rock element is derived under the CCM framework considering influences of the intermediate principal stress (IPS) and the dilatancy on rock-mass yielding. Second, the allowable safety factor of surrounding rock element is obtained based on the critical support line in the widely used rock quality (Q) system. Then, the framework and procedure of the quantitative tunnel support design method are outlined. Verification of the proposed method is conducted through comparisons with the analytical solution, laboratory model experiment and field monitoring data. Furthermore, a case study is employed to illustrate the proposed method, results indicate that the failure of the whole underground system is caused by the insufficient safety reserve of surrounding rock element. In general, the proposed method provides theoretical guidance for quantitative stability analysis and design optimization of tunnels.

Mechanical testing and engineering applicability analysis of SAP concrete used in buffer layer design for tunnels in active fault zones

Abstract To tackle the challenge of dislocation damage when tunnels traverse active fault zones, this study introduces the concept of using brittle buffer materials for anti-dislocation. Building on this concept, we propose a novel concrete buffer material utilizing large-sized spherical super absorbent polymers (SAP) as a porogen, aimed at ensuring the safety of tunnel structures during active fault dislocations. To investigate the feasibility and superiority of SAP concrete as a buffer material compared to other similar materials, we prepared samples with three different SAP concrete proportions and conducted a series of physical and mechanical tests. The results show that SAP pre-hydrated with 0.2 mol·L−1 sodium carbonate solution exhibits a slower rate of moisture loss in the cement slurry, aiding the hydration reaction of concrete. The permeability coefficient of SAP concrete is approximately 10−7 cm·s−1, slightly lower than foam concrete of the same density level. SAP concrete buffer material demonstrates significant brittleness, in contrast to the mostly ductile nature of other buffers such as foam concrete and rubberized concrete. Utilizing the brittle nature of SAP concrete materials, when applied to tunnels affected by stick–slip active fault dislocations, its instantaneous loss of compressive capacity provides excellent yield performance, thus protecting the tunnel lining from damage. However, under certain circumferential pressure conditions, both the peak and residual strength of SAP concrete significantly increase. High peak and residual strengths do not favor the effective buffering effect of SAP concrete; therefore, an approach involving the intermittent arrangement of precast buffer blocks has been proposed for application.

Evaluation of eye-catching effect in highway tunnel entrance area based on saccade behavior

Objective This study aimed to investigate the effects of visual attraction in the entrance areas of highway tunnels on drivers’ saccade behavior and driving safety, with the objective of providing insights for tunnel entrance design and driver education. Methods Fifty participants were recruited for the naturalistic driving experiment. Four different visually attractive driving scenarios (baseline, landscape-style architecture, tip slogan, and billboard) were selected. Eye-tracking technology was utilized to record and analyze the scanning behavior of participating drivers. Various metrics, including saccade duration, frequency, amplitude, velocity, and the peak-to-average ratio of saccade velocity (PARSV), were measured and compared across different scenarios. Results The results revealed different patterns of visual scanning dynamics among the four experimental scenarios, reflecting the different levels of visual-cognitive demands and situation awareness of drivers. The visual attraction in the tunnel entrance area resulted in prolonged saccade duration, increased saccade amplitude, reduced saccade frequency, and slower, less stable saccade velocity. Among these, drivers exhibited the most intricate and unstable scanning behavior, accompanied by the lowest level of situational awareness, particularly under the influence of visual attraction of tip slogan. Conclusions The findings highlight the importance of considering visual attraction in tunnel entrance design. Minimizing unnecessary visual attraction can help reduce distractions and maintain driver attention, ultimately enhancing driving safety. Driver education programs should emphasize the significance of adapting to visual attraction at tunnel entrances to promote safer driving practices. Overall, this study contributes valuable insights into the effects of visual attraction on driver scanning behavior, facilitating the development of strategies to improve tunnel design and driver education.

Experimental and Theoretical Investigation of Longitudinal Temperature Attenuation and Smoke Movement in Urban Utility Tunnel Fires

The urban utility tunnel is an indispensable part of modern engineering construction. However, the fire risk cannot be ignored due to the narrow space and limited ventilation of the utility tunnel. A study of smoke filling is performed in a 1/8-scaled utility tunnel (25 m × 0.5 m × 0.45 m). Five heat release rates (5, 10, 15, 20 and 25 kW) and four positions of fire sources are used for tests. The initial position of the one-dimensional smoke movement of strong plume is determined. Based on the traditional model, the longitudinal temperature attenuation model of tunnel smoke is established with consideration of radiation and convection heat losses. The theoretical value of the longitudinal temperature rise of smoke is in good agreement with the experimental value. A one-dimensional spreading velocity model is established that coincides well with the experimental value, and the relative error is less than 20%. The spreading velocity of smoke is increased by the heat release rate. The velocity of the smoke spreading at the near end is smaller than that at the center, due to the long spreading route. The current conclusions disclosed in this study provide important guidance for the ventilation design of utility tunnels for fire smoke scenarios.

The optimal diameter design of high-capacity transmission tunnels based on analysis of cable thermal effects

The optimal diameter design of high-capacity transmission tunnels based on analysis of cable thermal effects

A plastic Stillinger-Weber potential-based discretized virtual internal bond approach for modeling soft rock fracture and its application in tunnel failure

Soft rocks present some undesirable behaviors, such as low strength, high plasticity and softening. These traits pose challenges in the design and construction of soft rock tunnels. To address these issues and model plastic fracture behaviors of soft rocks, we proposed a plastic Stillinger-Weber (PSW) potential and integrated it into the discretized virtual internal bond (DVIB) model. The PSW-DVIB model combines the strengths of the plastic DVIB and the SW-DVIB models. It not only effectively reproduces the plastic fracture behavior but also accurately reflects the Poisson’s ratio. Moreover, due to the inclusion of fracture energy in the PSW potential, the simulation results are basically mesh size independent. The PSW-DVIB model is then utilized to investigate the failure behaviors of soft rock tunnels. The effects of the coefficient of lateral pressure, in-situ stress, Poisson’s ratio and tunnel shape on tunnel failure are investigated. The simulated results indicate that the coefficient of lateral pressure has significant influence on the failure zone distribution of the surrounding rock. With the coefficient of lateral pressure increasing, the failure degree of surrounding rock decreases firstly and then increases. The optimum coefficients of lateral pressure for the stability of circular, arched and square tunnels are about 1.00, 0.75 and 0.75, respectively. When the in-situ stress or Poisson’s ratio is larger, the influence of the coefficient of lateral pressure on tunnel failure is more obvious. The influence of the coefficient of lateral pressure on square tunnels are more significant than the arched tunnels, and then the circular tunnels. These findings provide valuable insights for the design and construction of soft rock tunnels.

Analysis Sequential Excavation Method For Large Span

Modern tunnel design mandates the careful selection of appropriate techniques and technologies for all tunnel projects. The pivotal factor for success in tunnel construction lies in choosing the right excavation methods for extensive-span tunnel projects in soft soil materials. The choice of excavation methods during tunnel construction significantly impacts both the project timeline and associated costs. This study specifically concentrates on the selection of excavation techniques, sequencing, and temporary supports employed during the excavation phase for tunnels located in soft soil environments. Given the considerable diameter of the tunnel, exceeding 200 m2, and the presence of soft soil, traditional methods like the Full-face method and the Central Diaphragm (CD) and Side wall Drift (SD) approach are not feasible. Therefore, this study suggests the application of a Sequential Excavation Method (SEM) for the tunnel construction.