Box Tunnel Research Articles

Analytical solution of overlying pressure for shallowly buried underwater box tunnel: A case study of box jacking in Suzhou, China

Accurately predicting the overlying pressure is crucial for determining an appropriate cover depth of underwater box tunnels to avoid the uplifting failure. Based on the project of box jacking crossing the Beijing-Hangzhou Grand Canal in Suzhou, the characteristics of overlying pressure variation during tunneling are investigated. The monitoring results reveal that the fluctuation of overlying pressure is weakened during the rapid tunneling process. A modified analytical model for vertical earth pressure is conceived, in which the active and passive limit states for multi-layered soils are both considered. The probable range of overlying pressure obtained by the proposed model is suitable to cover the actual values. The anti-floating behavior of underwater box tunnels for two different working conditions is discussed by calculating the minimum cover depth. Using the calibrated analytical models, a parametric study is conducted to explore the influence of injection pressure, hardened slurry unit weight, soil internal friction angle, soil cohesion, and tunnel geometry. It is found that the injection pressure during the construction process is crucial for determining the necessary cover depth, and the change of box tunnel height makes it easier to trigger the variation of minimum cover depth.

Rapid damage state classification for underground box tunnels using machine learning

This study develops and compares the performance of eight machine learning (ML) models to rapidly predict the seismic damage state of underground box tunnels. Nonlinear time history analyses of 24 soil-tunnel configurations subject to 85 ground motions were performed to generate the dataset for the ML models. The aspect ratio, buried depth, flexibility ratio, and 23 ground motion intensity measures (IMs) are employed as input variables of ML models. The output variables are four damage states, namely ‘none’, ‘minor’, ‘moderate’, and ‘extensive’. Among the eight ML models, LightGBM is found to yield the most favorable prediction of the damage states, resulting in an accuracy of 91%. The effects of earthquake IMs were also examined. Results show that the spectral acceleration () and spectral displacement () at the fundamental period of the site (T 1) have the strongest correlation with the damage prediction. Finally, the effect of reducing the input variables to two groups (i.e. combinations of soil-tunnel configuration parameters with top five and top ten ranked IMs) on the model prediction capability was investigated. Accordingly, ), acceleration spectrum intensity, spectral velocity, and velocity spectrum intensity were identified as the key parameters representing the ground-motion characteristics needed for the predictive model.

Influence of extreme shallow jacked box tunnelling on underlying metro tunnels: A case study

The application of jacked box tunnelling for underground passages has grown rapidly in recent years in China. In this study, the design of an extreme shallow jacked box tunnel traversing the underlying metro tunnels was introduced. An innovative additional soil filling above the ground surface was carried out to overcome the overlying-soil-carrying effect of the extreme shallow jacked box tunnelling. The structural safety of metro tunnels during the jacking process was analyzed through in-situ monitoring. It indicated that the overlying-soil-carrying effect was successfully alleviated. The metro tunnels generally showed horizontal displacement towards the receiving shaft, uplift and horizontal stretch during the jacking process. The stop of jacking machine in front of obstacles generally contributed to the decrease of horizontal displacement, uplift and horizontal stretch of metro tunnels. The largest horizontal displacement (1.3–1.6 mm), uplift (1.5 mm) and horizontal convergence (1.6–1.8 mm) generally occurred when the reception of jacking machine was completed, and they all met the requirement of 2 mm for this project. The design and construction of this shallow jacked box tunnel project could provide references for future similar projects.

Stability Analysis of Box Tunnel Working Face under Non-Uniform Support Pressure

For rectangular section tunnel construction, soil bin pressure fluctuates under biaxial emergence conditions. Support pressure is difficult to uniformly distribute, and it can easily cause instability of the tunneling face. The Silo-wedge model is used to perform horizontal strip splitting of parts of the soil at risk for instability under unsupported conditions. In the ultimate equilibrium analysis, the strength discounting method is introduced, a new expression for the safety factor is derived by combining the horizontal strip splitting equilibrium equations, and the safety factor is solved numerically. When the opening range is greater than 0.75 and the effective internal friction angle of the soil is less than 25°, the safety coefficient is less than 1, and destabilization damage is likely to occur. The field application of a box tunnel project in Suzhou demonstrates that the research results have good engineering applicability to the issue.

Seismic damage evaluation of double-box metro tunnel accounting for soil stiffness using three-dimensional finite element analysis

Development of a generalized damage state and index system for prediction of the seismic performance levels of box tunnels that accounts for coupled axial - flexural - shear response of the reinforced concrete lining and soil stiffness is a challenge. The objectives of this study are to develop physics-based definitions of damage states for double-box metro tunnels and associated damage indices (DIs) accounting for the soil-tunnel relative stiffness and inelastic behavior of concrete lining. A rigorous three-dimensional (3D) finite element (FE) model that simulates concrete structure and steel rebar cage individually is used to monitor the damage accumulation. It is proposed to utilize both the structural element response and seismic capacity curve to define four performance levels. Because the drift ratio, a widely used DI, is demonstrated to be sensitive to soil stiffness, an alternative index is linked with the damage states. The recommended DI is the ratio of the elastic moment (M) to the yield moment (My), because it less dependent on the soil stiffness compared with the drift ratio. Another advantage of M/My is that the performance level can be determined from an elastic analysis, whereas an inelastic simulation must be performed to calculate the drift ratio.

Working Face Stability of Box Shield Tunneling under Non-Uniform Support Pressure

This paper proposes a theoretical model for the stability analysis of a box tunnel face in non-cohesive soils considering the uneven distribution of support pressure caused by multiple cutter heads and screw conveyors. The support pressure distribution on the tunnel face is concave. Accordingly, the failure mechanism is composed of a prism and a wedge, both including three blocks. The relatively smaller support pressure acting on the middle blocks lead to the tendency of slide. Assuming that the support pressure acting on the side blocks is obtained using the active earth pressure coefficient, the support pressure acting on block II can be achieved by limit equilibrium analysis considering the interactions between the blocks. The influences of strength parameters and geometric parameters on the tunnel face stability are discussed in the parametric analysis. For comparison, numerical analysis is conducted in the commercial software OptumG3. It is found that the results given by the proposed model agree well with those from the numerical model. Therefore, the rationality of the proposed model in predicting the collapse geometry is verified.

A model test on an open-cut tunnel structure under the effect of a stick-slip normal fault

PurposeLarge displacement misalignment under the action of active faults can cause complex three-dimensional deformation in subway tunnels, resulting in severe damage, distortion and misalignment. There is no developed system of fortification and related codes to follow. There are scientific problems and technical challenges in this field that have never been encountered in past research and practices.Design/methodology/approachThis paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation based on the open-cut tunnel project of the Urumqi Rail Transit Line 2, which passes through the Jiujiawan normal fault. The test simulated the subway tunnel passing through the normal fault, which is inclined at 60°. This research compared and analyzed the differences in mechanical behavior between two types of lining section: the open-cut double-line box tunnel and the modified double-line box arch tunnel. The structural response and failure characteristics of the open-cut segmented lining of the tunnel under the stick-slip part of the normal fault were studied.FindingsThe results indicated that the double-line box arch tunnel improved the shear and longitudinal bending performance. Longitudinal cracks were mainly distributed in the baseplate, wall foot and arch foot, and the crack position was basically consistent with the longitudinal distribution of surrounding rock pressure. This indicated that the longitudinal cracks were due to the large local load of the cross-section of the structure, leading to an excessive local bending moment of the structure, which resulted in large eccentric failure of the lining and formation of longitudinal cracks. Compared with the ordinary box section tunnel, the improved double-line box arch tunnel significantly reduced the destroyed and damage areas of the hanging wall and footwall. The damage area and crack length were reduced by 39 and 59.3%, respectively. This indicates that the improved double-line box arch tunnel had good anti-sliding performance.Originality/valueThis paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation. This system increased the similarity ratio of the test model, improved the dislocation loading rate and optimized the simulation scheme of the segmented flexible lining and other key factors affecting the test. It is of great scientific significance and engineering value to investigate the structure of subway tunnels under active fault misalignment, to study its force characteristics and damage modes, and to provide a technical reserve for the design and construction of subway tunnels through active faults.

Analysis of working face stability during obstruction removal from a box tunnel machine

Analysis of working face stability during obstruction removal from a box tunnel machine

Deformations of Subway Tunnels Induced by the Overcrossing Jacked Box Tunnels

The rectangular utility tunnels have been increasingly built in urban areas in recent decades. In this paper, a case of jacked box tunnels built closely over-crossing the existing subway tunnels in Suzhou, China, is presented. The tunneling-induced deformation of the subway tunnels is measured and analyzed. The measurement indicates that the subway tunnels are uplifted and subjected to the overcrossing box tunneling. As compared, the longitudinal deformation of the range that locates under the box tunnels is more significant than that outside the range. The tunneling-induced deformation of the left subway tunnel is relatively higher than that of the right one. The numerical simulation is performed for validation. The numerical result is agreed with the in-situ measurements. Moreover, the simulation reveals that the presence of friction in jacked tunnels causes the extra uplift deformation of subway tunnels. The higher the friction, the is the deformation. It is affirmed that using the effective lubrication not only facilitates the tunnel jacking but also inabilities the tunneling-induced deformation of underlying tunnels

Theoretical prediction models for ground settlement during box jacking

Box tunnels, compared with circular tunnels, can increase the space utilization ratio by approximately 20% and have been increasingly used in urban underground space. Box jacking generates more ground loss due to its special geometric shape, inducing larger ground settlement, compared with circular pipe jacking. Accurate prediction of ground settlement during box jacking is a key aspect for the success of a project. This paper proposes the ground settlement prediction models during box jacking based on stochastic medium theory and cavity expansion theory, and compares the applicability of the models. The comparison shows that the modified Verruijt model based on the cavity expansion theory can provide a relatively accurate prediction for the magnitude and trough width of the ground settlement. The analytical model is validated through numerical simulation and field instrumentation using the project of Shilianjie Station of No. 5 metro line in Suzhou, China as a testbed. The validation shows that the analytical predictions compare reasonably well with the numerical simulation results and field measurements with a maximum error within 13%. The analytical model in this paper can provide a quick estimate on the ground settlement during box jacking.

Behavior Characteristics of a Booted Sleeper Track System According to Substructure Deformation

In booted sleeper floating track systems wherein the concrete bed, rail, and sleeper are structurally separated, mismatches can occur between the substructure and track owing to deformations. Nevertheless, the mutual behavior between substructures and track systems has not been studied extensively. To address this limitation, the effect of substructure uplift and subsidence on the deformation of a boosted sleeper floating track system installed in a subway box tunnel was analyzed using finite element analysis. A detailed three-dimensional model consisting of all track system components was constructed to determine the interaction between the rail and concrete bed. The sleepers were observed to rotate in response to substructure deformation, and their resulting contact conditions on the concrete bed were analyzed to determine the track status accordingly. The zones of likely tension and shear cracking in the concrete bed were then determined to provide focus areas for track design and maintenance efforts. The results of this study can be used to improve the design and inspection of floating track systems to ensure the safety and functionality of railway tunnels in areas likely to experience uplift or subsidence.

Savonius wind turbines: A review of recent advances in design and performance enhancements

The energy crisis due to a rapid globalization and adverse effects of global warming has led to an increased need for the non-conventional sources of energy. In the recent times, significant research activities are carried out in the renewable energy field, mostly in solar and wind power generation. Wind turbines are categorised into vertical axis wind turbines (VAWT) and horizontal axis wind turbines (HAWT). Savonius rotor (S-type) is a type of VAWT and its function depends on the drag force. It has many advantages of easy installation, simplicity in design, good self-starting capability, low speeds operation and independency of direction of wind. Although, the negative torque produced on the returning blade leads to its low efficiency. Researchers have conducted several investigations to improve the functioning of Savonius rotor for satisfying large-scale energy demands. The parameters affecting the performance, such as, overlap ratio, aspect ratio, tip speed ratio and blade shapes, are improved by undergoing various designs. Several augmentation techniques, such as, end plates, shielding obstacle, guide box tunnel, deflecting plate, curtain plate, quarter blades and nozzles, have been used to enhance the performance of S-type VAWT. With the installation of these augmentation devices, the negative torque acting on the blades was reduced and the starting ability of the rotor was improved. These devices in turn help in increasing the power output as well as the torque coefficient of various rotor configurations. It has been reported in the literature that the coefficient of power of the conventional Savonius rotor lies in the span of 0.12 to 0.18. By using different methods for optimizing its design or installing the augmentation devices, the coefficient of performance can be improved to a value of 0.52. In this article various performance influencing parameters and the power augmentation techniques used for S-type VAWT have been studied and reported studies on these techniques have been reviewed. The article concludes with proposed directions for future research.

Finite-Element Studies on Factors Influencing the Response of Underground Tunnels Subjected to Internal Explosion

The role of underground metro tunnels in a modern urban society is indispensable. Nowadays, these populous metro tunnel networks are becoming a prime target for terror strikes around the world. Considering these terror threats, it is crucial to study the vulnerability of tunnels when subjected to an internal explosion. This paper evaluates the vulnerability of underground metro tunnels exposed to an internal explosion using the explicit finite element (FE) method. The developed FE model has been validated with the field data reported in the literature for free-field blast wave propagation. Parametric studies were also carried out using the developed models to investigate the effect of lining material, lining thickness, lining shape, and type of surrounding of soil on the blast response of tunnels. A typical metro tunnel of 5.0 m internal diameter embedded at a depth of 9.0 m below the ground level is considered for the analysis. Numerical analysis shows that reinforced cement concrete (RCC) tunnels suffer severe damage when compared with the cast-iron tunnels. Box tunnels are extremely vulnerable to internal explosion when compared with circular and horseshoe tunnels. RCC tunnels embedded in medium dense sand are less vulnerable when compared with soft saturated clayey soil.

Tunnels in Arcadia: Isambard Kingdom Brunel's Portal Designs for the Great Western Railway

AbstractFrom the 1830s, the British landscape was transformed by the development of the steam-hauled railway system, which necessitated bridges, viaducts and tunnels. Of such structures, tunnel entrances feature little in serious studies of railway architecture. However, rich archival evidence exists relating to the designs of Isambard Kingdom Brunel for the tunnel portals on the Great Western Railway between London and Bristol, including numerous pencil and ink drawings in sketchbooks held by the Brunel Archive, University of Bristol, and watercolour elevations in the Network Rail Archive in York, as well as lithographs of the portals by John Cooke Bourne for his History and Description of the Great Western Railway (1846). Brunel's drawings, unique among nineteenth-century engineers, range from the classical style for Box and Middle Hill tunnels in Wiltshire, through the Gothic for Twerton in Somerset, to the Romanesque for Brislington on the edge of Bristol, his so-called ‘Tunnel No. 1’. In their variety and careful design, Brunel's portals represent an important part of Britain's railway and industrial architectural heritage.

Seismic Damage Analysis of Box Metro Tunnels Accounting for Aspect Ratio and Shear Failure

We performed a series of inelastic frame analyses for single, double, and triple reinforced concrete box tunnels to investigate their unique damage mechanisms. We focused our interest on the influence of the aspect ratio of box tunnels and the occurrence of a shear structural failure. This is a follow-up study of Lee et al. (2016), where damage analyses of box tunnels with an aspect ratio of unity were performed by considering only the flexural failure. We show that only flexural failures occurred in single box tunnels, whereas shear structural failures were produced at the inner column for double and triple box tunnels. The inner column failed in shear after flexural plastic hinges were formed at all four outer corners, and might cause a brittle collapse. A structural collapse was not observed in single box tunnels. An increase in the aspect ratio was demonstrated to cause associated increment in the seismic resistance. The moment and shear strains at which plastic hinges formed an increase by up to 5% and 20%, respectively. We proposed revised damage indices (DIs) corresponding to three damage states for single box tunnels, where DI is defined as the ratio of the elastic moment to the yield moment. The collapse damage state and corresponding DI for double and triple tunnels are newly presented.

Assessment of Soil Tunnel Interaction in Sand Soil

In this study, series of shaking table tests were carried out to investigate the effect of tunnel model depth and direction of ground acceleration on the ground surface settlement and the dynamic earth pressure on the tunnel wall. Box tunnel model is embedded in dry and saturated soil (Karbala Sand). It subjected to three input sinusoidal motions 0.05g, 0.1g, and 0.2g. Two relative densities were used, 30% for the upper layer and 70% for the lower layer. The results obtained indicate that the settlement of soil surface increases with an increase in ground acceleration. The increase in tunnel model depth leads to an increase in settlement especially at 0.2g earthquake loading (for saturated and dry soil). The change of direction of seismic loading leads to a small change in the settlement for dry soil. The results appear that dynamic earth pressure (DEP) was positive in dry soil and negative in saturated soil in all test. In saturated soil, the effect of direction of ground acceleration and depth of tunnel model on DEP in 0.2g is quite little.

Vertical displacement reduction of cohesionless overburden soil by nails in box jacking

ABSTRACT The cohesionless soil overburden experiences large vertical displacements when shallow jacked box tunnel is constructed through it. A modelled steel box tunnel was jacked through cohesionless soil filled tank in different conditions. The overburden soil was reinforced with ‘one’ and ‘two’ rows of steel nails to control its displacements during box jacking operation under loading. The study shows that the vertical displacement of overburden with ‘two’ rows of nails were reduced by 81% as compared to ‘without nail’ conditions for a typical loading intensity of 365 kN/m2. The load carrying capacity of overburden soil was also increased by 134% corresponding to a particular value of displacement as 5.6 mm from ‘without nail’ to ‘two’ rows nailed case. The results of the model study have been validated with PLAXIS 3D and were found in good agreement.

Seismic vulnerability assessment of rectangular cut-and-cover subway tunnels

This study develops fragility curves for rectangular cut-and-cover tunnels from nonlinear frame analyses. Fragility curves are generated for single, double, and triple boxes constructed for the subway system. A wide range of site profiles is used to evaluate the effect of soil characteristics on the calculated fragility curve. The fragility curves are developed for minor, moderate, and extensive damage states. The damage indices defined in a previous study as the ratio of the elastic moment demand to the yield moment at the critical section of the tunnel lining was used in the analyses. Fragility curves of the tunnels are generated in terms of surface peak ground acceleration (PGA), peak ground velocity (PGV), and PGV/Vs30 (Vs30 is the time-averaged shear-wave velocity to 30 m depth). The results highlight that the fragility curve is highly sensitive to the site profile, and that PGA based curves result in the largest scatter. The effect of the site profile is significantly reduced when PGV/Vs30 is used, where the fragility curves for all site profiles fall within a narrower band. This is because both the intensity of the ground motion and the soil stiffness is accounted for in the parameter PGV/Vs30. Considering the importance of site amplification characteristics, it is recommended that PGV/Vs30 be used instead of PGA and PGV in the generation of fragility curves of underground structures. Comparisons also demonstrate that multi-box tunnels are more vulnerable to earthquake damage compared with single box tunnels because the seismic demand is always larger.

Effect of Flexibility Ratio on Seismic Response of Cut‐and‐Cover Box Tunnel

Equivalent linear time history analyses are conducted to calculate the seismic response of various types of cut‐and‐cover single box tunnels. A finite‐element numerical model is calibrated against the results of centrifuge tests. The calculated tunnel responses compare favourably with the measurements. A validated model is then used to quantify the seismic response of box tunnels. The flexibility ratio (F) is illustrated to have a governing influence on the tunnel response. It is shown that the previously developed relationship between F and the racking ratio (R) is applicable for a wide range of F up to 20. It is also shown that an increase in F accompanies corresponding increase in R, the spectral acceleration in the tunnel lining, and the shear stress along the tunnel lining‐soil interface. The thrust in the tunnel lining is also revealed to increase with F, although the calculated value is significantly lower than the pressure on yielding walls. Additionally, the surface settlement is shown to increase with an increase in F.

Reduction in Lateral Displacement of Cohesionless Soil at Box Tunnel Face Using Nails in Overburden

The construction of shallow box tunnel underpass below rail/road traffic using jack pushing has become a quite common technique these days to create an uninterrupted flow of traffic in metropolitan cities. During the driving of shallow box tunnel underpass, the overburden cohesionless soil experiences large stresses and excessive lateral displacements at the box tunnel face, which sometime causes an accident leading to loss of lives. In order to overcome this problem, a laboratory model study has been conducted. A steel tank of size 450 mm × 300 mm × 300 mm, filled with cohesionless soil was used, in which a square steel box tunnel of size 34 mm × 34 mm (inner) with 1 mm wall thickness was moved through jacks. This tunnel was slowly pushed into the soil mass with the help of jack. Three vertical offsets from top of soil surface as well as three horizontal offsets from center of loading. To restrict the excessive lateral displacement, the overburden soil above the box tunnel was reinforced with 8 mm diameter tor steel nails prior to pushing of box tunnel. The lateral displacement of soil at tunnel face was found reduced from 6.92 mm in case of ‘without nailed’ to 0.23 mm in case of ‘with nailed’ overburden soil. Further, there was also a gain in load carrying capacity of soil in case of reinforced overburden soil. The study shows that if, overburden soil is reinforced with nails prior to the driving of box tunnel, the chances of collapse or lateral displacement at box tunnel face soil can be minimized for construction of shallow underpass.