Horizontal Tunnel Research Articles

Experimental investigation of particle dynamics in particle-laden turbulent boundary layer

In a horizontal wind tunnel, experiments were performed on both particle-free and particle-laden flows at the same incoming velocity. Glass micro-spheres were carried by air along the turbulent boundary layer at a high Reynolds number (Reτ=3200). The Stokes numbers of the solid particles considered were O(10) and O(102). Under a similar volume fraction, Φv=O(10−5), the velocity and spatial distribution of solid inertial particles were investigated using simultaneous particle image/tracking velocimetry measurements and time-resolved particle imaging. This allowed for the exploration of particle dynamics and their corresponding spatial structure in the particle-laden turbulent boundary layer. The results showed that particle–wall (P-W) interaction occurs in both types of particle-laden flows. However, the particle Stokes number directly affects the intensity of the P-W interaction, significantly altering the behavior and spatial organization of particles. The results from the Voronoi tessellation technique confirmed that preferential clustering still happens for the small particle case. In particular, the premultiplied spectra for the particle concentration showed that the temporal pattern of particle clustering presents a similar time-scale to very large-scale motion (around 22δ, where δ is the boundary layer thickness) in the near-wall region.

Endoscopic flexor hallucis longus tendon transfer with horizontal calcaneal fixation and suturing onto itself

Endoscopic flexor hallucis longus (FHL) tendon transfer to replace the calcaneal tendon is being increasingly performed. The main advantage is minimisation of approach-related morbidity. Fixation of the FHL tendon is usually achieved with a tenodesis screw placed in a vertical calcaneal tunnel. Here, we describe an endoscopic technique with FHL fixation by tenodesis in a horizontal calcaneal tunnel combined with suturing of the tendon onto itself. Level of evidenceIV.

Short-term Clinical Outcomes after Flanged Intrascleral Fixation of Intraocular Lenses Using Oblique Intrascleral Tunnels

Purpose: To report the short-term clinical outcomes after intrascleral fixation of intraocular lenses (IOLs) using oblique intrascleral tunnels.Methods: We retrospectively studied 17 patients (18 eyes) who underwent flanged intrascleral IOL fixation from October 2019 to October 2021. The patients were divided into those who underwent fixation using horizontal (group A) and oblique (group B) intrascleral tunnels. We compared the best-corrected visual acuities (BCVAs), cylindrical powers, refractive errors (the differences between the targeted spherical equivalents [SEs] and postoperative SEs) before and 3 months after surgery, and operating times.Results: At 3 months vs. preoperatively, there were no significant differences in BCVA (-0.83 ± 0.43 vs. -0.48 ± 0.59), refractive error (-0.06 ± 0.97 diopter [D] vs. -0.05 ± 0.80 D), cylindrical power (-0.42 ± 3.81 D vs. -0.33 ± 1.20 D), or operating time (83.33 ± 28.05 minutes [min] vs. 66.33 ± 20.57 min) between groups A and B, respectively.Conclusions: In terms of the short-term clinical outcomes after use of horizontal and oblique intrascleral tunnels, we found no significant differences in any parameters studied. However, use of an oblique intrascleral tunnel may shorten the operating time.

Refined explicit solution for the stress field around an elliptical cylindrical tunnel with a moderate depth

We consider a horizontal elliptical tunnel buried in a medium under gravity and lateral pressure (perpendicular to the generatrix of the tunnel). The stress field in the medium is generally treated as the superposition of an initial stress field induced by the gravitational body force and lateral pressure before tunnel excavation and the perturbation stress field after the introduction of the tunnel. Closed-form solutions for the perturbation stress field are available if the interaction between the tunnel and the surface of the medium is neglected. The initial stress field is usually assumed to be constant in deriving closed-form solutions for the perturbation stress field since it is often believed that the interaction between the tunnel and the surface of the medium is negligible only for a deep-buried tunnel. However, it is indicated from the literature that the interaction between the tunnel and the surface of the medium is insignificant in determining the stress distribution around the tunnel as long as the distance between them exceeds the diameter of the tunnel’s cross section. Consequently, we are motivated to derive in this paper a refined closed-form solution for the perturbation stress field by admitting a realistic initial stress field that varies linearly in the depth direction. The refined solution may lead to more accurate results in predicting the gravity-triggered stress concentration around a moderate-depth tunnel. The refined solution is compared with the classical solution (obtained by using a constant initial stress field) in calculating the hoop stress around the tunnel via several numerical examples.

A two-dimensional experimental study of active progressive failure of deeply buried Qanat tunnels in sandy ground

As an ancient underground hydraulic engineering facility, the Qanat system has been used to draw groundwater from arid regions. A qanat is a horizontal tunnel with a slight incline that draws groundwater from a higher location and delivers it to lower agricultural land. During long-term water delivery, the qanat tunnel has experienced different degrees of aging and collapse, which may result in the significant ground settlement and even disasters. This paper developed a two-dimensional laboratory system to investigate the influence of progressive failure on the stability of deeply buried qanat tunnels. The developed system is fully instrumented with a particle image velocimetry (PIV) system and earth pressure and displacement monitoring. A special cylindrical membrane tube is designed and connected to an advanced pressure–volume controller to simulate the step-wise failure process of the tunnel. Three model tests were conducted on a dry sand considering the buried qanat tunnels at three different depths. Experimental results clearly show the progressive evolution of soil arching effect in the dry sand associated with the progressive failure of the tunnels. The failure of the Qanat ground starts from the vault and develops upwards, which is closely related to the evolution of stress contour at three consecutive stages. Ground surface settlement and volume loss corresponding to three burial depths were compared. A deeply buried qanat tunnel has a small effect on surface settlement. Earth pressure evolution on the 2D plane shows the load redistribution when the qanat collapses. The maximum arch and the initial point of the limit state correspond to a volume loss of 12.5 % and 50 %, respectively. For the collapse of the deep buried qanat tunnel, ground earth pressure evolution can be divided into a stress-increasing region, stress-decreasing region, and no redistribution region. Furthermore, a multi trap-door model considering soil expansion is proposed to describe the progressive failure behavior and its effects.

Numerical study on the effects of blocking ratio and spraying angle on the smoke flow characteristics of new energy vehicle fires in tunnels

Compared with traditional fuel vehicle fires, new electric vehicle fires have a fast flame propagation rate and higher smoke toxicity. Thus, higher requirements need to be implemented when designing tunnel fire protection. In this study, a horizontal highway tunnel with a rectangular cross-section is taken as the research scenario, and the FDS numerical simulation method is used to study the effects of different blocking ratios and key parameters of the water mist system in a rectangular tunnel under longitudinal ventilation on the smoke temperature and flow state near the fire source area. The results indicate that the average velocity of smoke in the vicinity of the fire source in the tunnel is mainly related to the cross-sectional size of the obstruction, and changing the spray angle does not affect the state of the smoke flow field. The relationship between the cross-sectional size of the blocked vehicles in the tunnel and the spray angle is proposed. In addition, when the blocking ratio reaches 25%, the back-layer length of smoke corresponding to the subsequent blocking ratio remains basically unchanged. Setting a reasonable spray angle can significantly reduce the CO mass fraction in the tunnel, while the visibility of the tunnel will also decrease. Using the dimensionless analysis method, a critical velocity correction model based on the blocking ratio factors is proposed. These research results provide a theoretical reference for the design of longitudinal ventilation and smoke exhaust for new energy-electric vehicles in highway tunnels.

Experimental and numerical studies on the seismic response of adjacent horizontal parallel tunnels

Several studies have investigated the seismic performance of single-tunnel structures. However, few studies have focused on the interactions between adjacent tunnels during earthquakes. The interaction mechanisms and influence ranges between tunnels during earthquakes are not clear. Shaking-table tests and numerical parameter analyses were employed to explore the interaction mechanism between two horizontal parallel tunnels during an earthquake. The main influencing factors were tunnel factors (tunnel net spacing, diameter, and buried depth), ground motion factors (type and amplitude), and site soil types. The calculation and analysis results indicate that the net spacing of the horizontal parallel tunnels is a key factor in determining the interaction of close-distance tunnels. The interaction was most apparent when the net spacing of the tunnels was between one and two times the tunnel diameter, which is the most common net spacing used in practical engineering. In addition, the tunnel diameter, buried depth, ground-motion type, amplitude, and soil type can significantly influence the tunnel response. The results of this study can serve as a reference for the seismic design of adjacent horizontal parallel tunnel structures.

Numerical investigation on the responses of existing single piles due to adjacent twin tunneling considering the lagging distance

This paper presents an assessment of the influence of the lagging distance between two horizontal tunnel faces of the side-by-side twin tunnels on the responses of the adjacent existing single pile by a series of three-dimensional numerical analyses. Two different relative positions between the pile tip and the tunnel are considered to cover the short and long pile behaviors. The responses of the existing pile in terms of pile head settlement, axial force, lateral movement and bending moment are considered and discussed. The numerical results indicate that the lagging distance between twin tunnel faces significantly affects not only the soil movements but also the responses of the existing single pile. The critical case that produces unsatisfactory pile responses due to twin tunneling is when the lagging distance between the second tunnel and the preceding tunnel equals to the shield length. It is recommended that the lagging distance be not less than three times of shield length when the two tunnels need to be concurrently excavated.

Assessment Method Integrating Visibility and Toxic Gas for Road Tunnel Fires Using 2D Maps for Identifying Risks in the Smoke Environment

This study proposes an assessment method to quantify the risks of the smoke environment for road tunnel fire safety based on previous studies. The assessment method integrates visibility and toxic gases to address the hazards of smoke distribution more comprehensively. Considering that the hazards of visibility reduction and toxic gases for tunnel users vary with exposure time and location in a fire event, the smoke environment (SE) levels are defined as a function of longitudinal location and time. The SE levels simplify smoke distribution as calculated from 3D computational fluid dynamics (CFDs). For easily identifying SE risks, SE levels are illustrated on a 2D map to analyze the potential hazard by quantifying specific areas and times of smoke exposure. To demonstrate the applicability of the assessment method of this study, cases are carried out using CFD simulation to investigate the risks associated with tunnel fires with various tunnel cross-section types, longitudinal velocities, and gradients. In the analysis of the SE level in different cross-section types and longitudinal velocities under the condition of no vehicle, a velocity of 0.9–1.1 m/s can maintain a less serious SE level both upstream and downstream in a horizontal rectangular tunnel, and 0.3–0.5 m/s in a horizontal horseshoe-shaped tunnel. Both rectangular and horseshoe-shaped tunnels reveal an obvious rise within 10–15 min. In the case of inclined tunnels, for both rectangular and horseshoe-shaped tunnels, the SE level near the fire source obviously deteriorates. Thus, the longitudinal velocity range for the purpose of maintaining a relatively less serious SE level should be slightly reduced for inclined tunnels compared with horizontal tunnels.

New records of Ctenopholeus in the early Devonian Hunsrück Slate of Bundenbach, SW Germany

The rare trace fossil Ctenopholeus kutscheri Seilacher & Hemleben, originally described from the type area of the early Devonian Hunsrück Slate at Gemünden (Germany), refers to initially open horizontal tunnels with vertically to obliquely oriented serial shafts opening to the sediment-water interface. Occurrences of frequent and partly exceptionally large specimens from Bundenbach, tentatively assigned here to C. kutscheri, reveal that these burrows, were constructed in larger numbers in the Hunsrück Slate. This happened when environmental conditions were favorable for the producer(s). Contributing factors presumably include substrate cohesion and stability being suitable for the maintenance of open burrow systems, as well as sustainable food resources during the time interval when the burrows were occupied. The new material confirms that the course of the shafts in C. kutscheri varies from almost straight to slightly bent to circular in cleavage plane view and may overlap with morphologies observed in Heliochone hunsrueckiana Seilacher & Hemleben. Holothurians and, more likely, crustaceans are discussed as possible producers of C. kutscheri from the Hunsrück Slate.

Study on the Air Inlet Velocity and Temperature Distribution in an Inclined Tunnel with Single Shaft under Natural Ventilation

The emergence of inclined tunnels under natural ventilation has brought many new fire safety issues. The smoke movement in the tunnel is affected by the chimney effect induced by the shaft and the downstream tunnel. The characteristics of temperature distribution in inclined tunnels are different from horizontal tunnels, which is worthy of further study. A series of conditions were carried out in an inclined model tunnel with a single shaft to investigate the temperature distribution characteristics. In this study, the longitudinal air inlet velocity is used to replace the longitudinal ventilation wind velocity. Results showed that the variation of fire source location Lf,, shaft height Ls, and the tunnel slope φ have obvious effect on the air inlet velocity. Based on the previous theories and the non-dimension analysis, the formulas of the dimensionless longitudinal inlet air velocity and the distribution of the maximum smoke temperature under the ceiling are proposed, which show good consistency with the simulation results. The reduced-scale experiments were conducted to validate the results of numerical simulation. The error range between the theoretical results and the simulation results is less than 20%.

Numerical simulation of a continuously released ethanol spill fire in an inclined tunnel with longitudinal ventilation

Under the influences of the chimney effect and longitudinal ventilation, the risks of continuous spill fires in inclined tunnels are catastrophic with great complexity and uncertainty. In this paper, the spread and combustion behaviour of a continuous spill fire under the effect of longitudinal ventilation in an inclined tunnel is studied and compared with that in a horizontal tunnel through fire dynamics simulator (FDS) software. The critical time shrink point (SP) to reach the maximum combustion area (MCA), the change rates of the dimensionless combustion area A* and stable combustion area (SCA), the flame propagation speed, and the dimensionless burning rate W* values and heat transfer mechanisms of the combustion fuel layer, tunnel wall and flame smoke are analysed; the prediction equation between the dimensionless burning rate W* and the dimensionless wind speed V* of the upstream and downstream spill fire are identified. The results show that longitudinal ventilation leads to a nonlinear increase in the MCA, and the longitudinal slope leads to a great decrease in the critical time SP. In the stable combustion stage, the SCA in the downstream spill fire is greater than that in the upstream spill fire. Additionally, there are significant differences in the flame propagation phenomenon of spill fires. On the windward side, the maximum flame propagation speed of the upstream spill fire is 3.8 times that of the downstream spill fire; however, on the leeward side, the maximum flame propagation speed of the upstream spill fire is only 18% of that of the downstream spill fire. According to the prediction equation, with the increase in the dimensionless wind speed V*, the dimensionless burning rate W* decreases gradually; the dimensionless burning rate W* of the upstream spill fire is always greater than that of the downstream spill fire. The increase in thermal feedback caused by the inclined flame is the main reason for the significant difference in the spread of the spill fire in the ventilated inclined tunnel, causing the flame propagation speed of the −10% slope on the leeward side to gradually approach that of the −5% slope.

An innovative design of mega shaft boring machine (SBM) cutterhead based on TRIZ and AD theory

Cutterhead is the key component of the mega shaft boring machine (SBM), whose complex structure and huge size lead to high manufacturing difficulty and cost, and its reliability is difficult to guarantee under huge loads. It is difficult to design the cutterhead only referring to the existing small horizontal tunnel boring machine cutterhead. In order to brainstorm innovative ideas, the paper incorporates the TRIZ into AD to address the following issues. Firstly, engineering conflicts in designing process are eliminated by TRIZ tools to generating innovative ideas. Then, the decomposition of functional requirements and design parameters are employed based on independence axiom of AD, transferring the abstract ideas into concrete design solutions. Moreover, fuzzy comprehensive evaluation is adopted to choose a better design scheme from alternatives of critical component. Finally, the feasibility and practicality of the proposed approach has been demonstrated through case study of designing a novel mega SBM cutterhead. The cutterhead structure is significantly improved with embedded movable cutter boxes, which can excavate step by step to reduce the driving torque, and the manufacturing and transportation cost has been greatly reduced. The method can help designer to innovative design the key components of large-scale underground tunneling equipment.

Inchworm‐Like Soft Robot with Multimodal Locomotion Using an Acrylic Stick‐Constrained Dielectric Elastomer Actuator

Inchworm‐like robots have been increasingly investigated in recent years. However, most studies have focused on one or several locomotion modes, lacking in terms of inverted climbing, movement with a heavy load, and climbing a vertical plane. Herein, an inchworm‐like soft robot is actuated with multimodal locomotion using an acrylic stick‐constrained dielectric elastomer actuator (ASCDEA). By assembling the ASCDEA with a flexible support frame, a soft saddle‐like shape body is designed to provide the shape deformation ability for the robot. This design enables the robot to move under a heavy load. Two electroadhesion actuators are designed to implement the anchoring action. Additionally, a coordination control strategy is developed to synchronize the shape deformation and electroadhesion for multimodal locomotion. Experimental results confirm that the designed robot can move at a maximum velocity of 39.55 mm s−1 (0.53 body length s−1) on an inverted plane. Moreover, the robot is capable of multimodal locomotion, including inverted climbing, vertical climbing, horizontal crawling, turning locomotion, and rapid movement with a heavy load. The developed soft robot can navigate through a confined horizontal tunnel while carrying a payload, cross a gap, circumvent obstacles, and is particularly robust owing to its compliance.

Radiography using cosmic-ray electromagnetic showers and its application in hydrology

In-situ measurements of soil water content provide important constraints on local/global hydrology. We demonstrate that the attenuation of the underground flux of cosmic-ray electromagnetic (EM) particles can be used to monitor the variation of soil water content after rainfalls. We developed a detection system that preferably selects EM particles by considering the coincidence of distant plastic scintillators. The calibration test beneath the water pool revealed that the count rate decreased by 0.6–0.7% with a 1 cm increase in the water level. The field measurement performed in the horizontal tunnel showed that the count rate dropped according to 48-h precipitation, after correcting the effects originating from atmospheric and water vapour pressures. These characteristics were confirmed using dedicated Monte Carlo simulations. This new method is called cosmic electromagnetic particle (CEMP) radiography.

Study on large deformation and failure mechanism of deep buried stratified slate tunnel and control strategy of high constant resistance anchor cable

Aiming at the significant deformation problem of deep buried stratified soft rock tunnel, taking the No.3 inclined shaft of Muzhailing tunnel as background, the deformation and failure mechanism of the tunnel and the control strategy of high constant resistance anchor cable are studied. The deformation and failure mechanism of stratified tunnel surrounding rock is studied by physical model test, including the tunnel's temperature field, strain field, and displacement field from excavation to failure. Lateral stress significantly influences the deformation of the surrounding rock of the horizontal stratified tunnel. The surrounding rock of the tunnel forms a dumbbell-shaped tensile stress zone under the action of stress. The high tensile stress of the roof and floor leads to dislocation and layer separation, which causes floor heave failure and temperature change. The indoor tensile test verified the super strength characteristics and large deformation of the high constant resistance anchor cable. Based on the excavation compensation method and the coupling control mechanism of high constant resistance long and short anchor cables, a new high prestress constant resistance coupling control strategy is proposed. The numerical simulation and field test studies according to the new design are presented, which show that the high constant resistance anchor cable coupling support significantly reduces the tensile stress zone, effectively controls the deformation of tunnel surrounding rock, and avoids the damage of supporting structure and the cracking and deformation of the lining. The research results can provide a reference for constructing and supporting deep-buried, stratified soft rock tunnels.

Efficiency investigation of mitigation effect of isolation piles on tunneling-induced ground settlements

In order to study the control efficiency of isolation pile on the settlement of the surface and deep soil, we analyze the implementation method of simulated isolation pile in Plaxis^2d, and establish the finite element model of the tunnel and isolation pile interaction to study the effects of the pile length, pile diameter, buried depth of pile top, pile horizontal position and tunnel buried depth on the control effectiveness. The results show that the control effectiveness of the isolation pile on the ground surface and deep soil strata subsidence is different. Under the uniform radial contraction mode of the tunnel, the pile length has the most obvious impact on the ground surface. In practical projects, it should be at least one radiu at the bottom of the deep tunnel to ensure the control effect on surface subsidence. The closer the isolation pile is set to the tunnel, the better the control efficiency is, especially to the settlement of deep soil. Within 0.6 ~ 1.4 m pile diameter changes on the isolation is of little influence on the pile settlement control effectiveness. The control efficiency of buried isolation pile on ground settlement is not much different from that of non-buried one, but the control efficiency of deep soil settlement in the ground is obviously better than that of the non-buried isolation pile. For the same isolation pile, the deeper the tunnel is buried, the lower the control efficiency of the isolation pile on surface settlement. In this study, the control efficiency of isolation piles on the settlement of deep soil mass is basically negative, indicating that the placement of isolation piles increases the original settlement of deep soil mass, instead, resulting in negative effects. The research can provide a reference for the design and construction of isolation pile.

Influence of Grouting Sequence on the Correction Effect of Horizontal Tunnel Displacement by Grouting in Granite Residual Soil

Shield tunnels are vulnerable to large displacements induced by surrounding environmental changes. Grouting is an effective way to correct excessive shield tunnel displacement, while the grouting scheme design, especially the grouting sequence, is the key factor affecting the correction efficiency. A finite element simulation method considering the construction of multiple grouting zones is verified by the engineering case of Shenzhen Metro Line 1, and the influence of the grouting sequence on the correction effect on the horizontal tunnel displacement is further studied. The results show that the proper grouting efficiency of sandy clay, completely decomposed granite, and strongly decomposed granite is 5.5%, 2.8%, and 1.1%, respectively. The adjacent newly-built grouting zones are significantly constrained by the reinforcement created during the preceding grouting process. It is more efficient to correct excessive tunnel displacement in the “from far to near” sequence and excessive tunnel convergence in the “from near to far” sequence with increasing reinforcement stiffness. The correction effect improves greatly as the elastic modulus of the reinforcement increases up to 100 MPa.

Revision Anterior Cruciate Ligament Reconstruction Using Bone Dowels

Background: Revision anterior cruciate ligament (ACL) reconstruction is technically challenging and may require the use of bone dowels in either 1 or 2 stages. Indications: The indications for bone dowels include tibial or femoral tunnel malposition or widening of the tunnels. In the patient case, the tibial tunnel aperture was positioned far medial to the native ACL insertion with a horizontal tunnel trajectory and the femoral tunnel was vertical. In addition, there was tunnel widening to 12 mm of both tibial and femoral tunnels. Technique Description: A bone-patellar tendon-bone autograft was harvested and diagnostic arthroscopy was performed. The previous tibial tunnel was sequentially reamed from 8 to 12 mm to adequately overdrill the previous widened tunnel. Next, the femoral tunnel was reamed to 12 mm in similar fashion. Using a tamp and guide pin, a 12 × 30-mm allograft bone dowel was then malleted into the femoral tunnel until it was flush with the medial aspect of the lateral femoral condyle. Another 12 × 30-mm bone dowel was then advanced into the tibial tunnel until it was just below the native articular margin. With the bone dowels securely in place, the ACL reconstruction using the harvested bone-patellar tendon-bone autograft was performed. Results: Werner et al reported a study of 12 patients who had excellent incorporation of femoral tunnel allograft bone dowels and comparable objective and subjective scoring to 2-stage techniques. Dragoo et al reported a study of 18 patients with tibial tunnel allograft bone dowels that demonstrated significant increases in patient-reported outcome measures and a significant decrease in tunnel widening. Discussion/Conclusion: Revision ACL reconstruction may require bone dowels if there are malpositioned tunnels or if there is tunnel widening. Overall, the literature demonstrates that 1-stage revision outcomes have been comparable to reported 2-stage revision outcomes, both of which are satisfactory.

Mechanical Behavior of the Special Segment Structure during Upward Shield Tunnel Construction

The upward shield method in horizontal tunnels has the advantages of small ground space occupation, low construction cost, and short construction period, which expresses substantial economic benefits. The special segments of horizontal shield tunnels corresponding to the upward shield method construction area have special design requirements, and different internal force calculations and analyses should be carried out. To determine the mechanical behavior of the special segment structure of horizontal shield tunnels during the construction of upward shield tunnels, the theoretical calculation formula of the internal force of the special segment structure is deduced based on the average uniform rigidity ring method. Moreover, the bending moment and axial force of special segments are numerically simulated and analyzed using Midas GTS NX software. Finally, the theoretical formula and finite element calculation results are compared and analyzed. The results show that the internal force values of the open segment ring and the adjacent segment ring of the special segment are quite different during upward shield tunnel construction. Furthermore, compared with the arch crown and arch bottom of the segment ring, the stress at the arch waist of the segment ring is the most unfavorable. The stress difference between the open segment ring and the adjacent segment ring may cause unbalanced deformation, leading to damage to the segment ring radial joint. In the design and construction, attention should be given to the shear strength of the segment ring radial joint and the bending stiffness of the ring joint at the arch waist.