Parallel Tunnels Research Articles

Segment Stress Characteristics and Ground Deformation Caused by Constructing Closely Spaced Parallel Tunnels under a Complex Geological Condition

Ground deformation and additional stress on the segments of the firstly constructed tunnel may change significantly due to the construction of another tunnel, which is closely spaced with the existing one. A poor geotechnical condition possibly leads to the interaction between such closely spaced tunnels even making it harder to build such tunnels. A practical project located in Guangzhou City, China, consists of such two parallel tunnels with the smallest distance of 2.6 m, which sat on an upper‐soft and lower‐hard stratum. A 3D finite element model has been proposed to numerically investigate the behavior of these two parallel tunnels. The numerical results predicted by the FE model are in close agreement with that obtained from the field monitoring system, indicating the accuracy of the proposed FE model. The FE model was then used to further analyze the effect of reinforcing piles in eliminating the detrimental effect on both ground deformation and additional stress of the segments of the existing tunnel as a result of the construction of the new parallel tunnel. The research results obtained from the present paper can provide technical support and guidance for urban subway construction.

Analysis of the Influence of New Parallel Tunnels on the Safety of Existing Highway Tunnels

With the increasing number of construction projects in China, the intersection or proximity between new tunnels and existing tunnels is increasing. How to evaluate the impact of existing tunnels and ensure the safe operation of existing tunnels are important issues to be considered in the design of new tunnels. Based on the actual conditions of the new tunnel and the existing Jianshi tunnel of Jinliwen Expressway in the north connection of S49 provincial highway in Zhejiang Province, this paper studied the influence of the new parallel tunnel on the existing highway tunnel by analyzing the net distance between the two tunnels, the change of the supporting structure during the construction of the new tunnel and the vibration caused by the blasting construction, etc., the influence of new parallel tunnels on the safety of existing highway tunnels was studied, which provides a reference for the design and construction of similar short distance parallel tunnels.

Greater-curvature peroral endoscopic myotomy with diverticuloseptotomy for the treatment of achalasia in a patientwith a large epiphrenic diverticulum.

Greater-curvature peroral endoscopic myotomy with diverticuloseptotomy for the treatment of achalasia in a patientwith a large epiphrenic diverticulum.

О новом подходе в оценке поведения большой совокупности параллельных штолен

The problem of assessing the behavior of a large number of underground structures such as parallel tunnels, characteristic of mines for the extraction of minerals, including coal, is considered. Traditionally, studies are performed for a single object, and then the parameters found are accepted for all other objects. At the same time, the multiplicity of such objects can lead to another factor of strength impairment associated with the possibility of localization of the stress-strain state in one of the zones of the structure, leading to excess of the planned strength parameters. In this paper, the theory of calculation of strength properties of such objects is based on the example of underground structures. The research is based on the block element method based on factorization approaches. The problem is reduced to a system of integral equations of the first kind with a difference kernel, which is reduced to a system of Fredholm integral equations of the second kind. By calculating the integrals describing the nuclei of these equations according to the theory of deductions, it is possible to reduce the integral equations to a system of algebraic equations available for analytical analysis, which allows to identify the localization of stresses or displacements. The long-range approach made it possible to find a connection between these equations with the Riemann problem for a set of pairs of analytic functions, the number of which coincides with the number of galleries. In earlier works, the resulting stress-strain state was characterized by calculating only the vertical contact stresses on the supports and the vertical displacements of roof slack charges. In this paper, it is possible to construct an approach that allows us to calculate all three components of the stresses on the supports and all three components of the roof sagging displacement.

Jammed hard-sphere hcp crystals permeated with trivacancy tunnels

Supported by simple table-top experiments involving stackings of ball bearings and theoretical analysis, we have discovered crystal packings of identical hard spheres that are permeated by a high concentration of large tunnels and yet are jammed (mechanically stable). We show that starting with a strictly jammed hexagonal close-packed (hcp) crystal of identical hard spheres, removal of certain subsets of those spheres can produce mechanically stable vacancy arrangements involving compact (equilateral triangle) trivacancies such that they produce linear trivacancy tunnels. These tunnels can extend over the entire macroscopic length of the hcp medium, and their width is sufficient to allow contained “test” hard spheres with diameters less than 5−1=1.23606… to migrate over that entire length without contacting the static tunnel-wall spheres. A search for the stable (strictly jammed) periodic framework that hosts the highest density of parallel trivacancy tunnels has identified a structure exhibiting a packing fraction ϕ=π/32=0.55536…, which is equal to 3/4 of the maximum monovalent sphere packing fraction ϕmax=π/18=0.74048…. In that periodic arrangement, filling the interior of the contained tunnels with movable unit-diameter spheres may approach the greatest possible “rattler” density within jammed monovalent sphere systems subject to periodic boundary conditions. It will be of interest to study the physical and chemical properties of these anisotropic porous crystal structures. Our findings may have practical implications for engineered separation and catalytic processes.

The Brenner Base Tunnel – geological, construction and logistical challenges and innovations at half time

AbstractThe Brenner Base Tunnel with a total of 230 km of tunnels is a geological, structural and logistical challenge. The transnational project is an additional challenge, considering different planning, approval and construction rules and cultures. From the start of construction in 2007 to the present, today halftime is reached with 100 excavated tunnel kilometers. An overview of selected topics is given in this contribution, such as project optimizations of the emergency areas, geological/geotechnical knowledge transfer from the already driven exploratory tunnel to the following construction lots of the parallel main tunnels, reprocessing and use of Schists as aggregates for the inner lining and shotcrete production, logistics experience with wheel‐bound transport vehicles, measurements during construction with laser tunnel scanners and the service life of the tunnel of 200 years with an increased safety concept defined in the guide conceptual design. Preparations and planning are already at an advanced state for the second half of the project, concerning the next excavation lots, secondary linings as well as interior work with the installation of the technical equipment. The construction work is expected to be completed in 2025 and the end of construction is expected at the end of 2028 (2030 in case of risk occurrence).

Tunneling in Squeezing Ground: Effect of the Excavation Method

Tunnel excavation in squeezing ground exhibits large time-dependent and often anisotropic deformation. Within the context of the Frejus road tunnel and its safety gallery excavated under the Alps between France and Italy, an interesting configuration of two parallel tunnels under squeezing ground conditions is observed. The special feature of this case study lies in the fact that both tunnels have been excavated in similar geotechnical conditions but with different excavation techniques. The road tunnel was excavated with conventional drill and blast methods in the 70s, whereas the safety gallery was excavated between 2009 and 2016 with a single-shield tunnel boring machine (TBM). This paper presents monitoring data processing and numerical simulations of both tunnels with the aim of studying the influence of the excavation method on the time-dependent tunnel response. A calibration of a visco-elasto-plastic anisotropic constitutive model based on the back-analysis of convergence measurements retrieved during the excavation of the Frejus road tunnel is carried out. The identified ground behavior can be extrapolated to the parallel zones of the safety gallery. In particular, we are interested in the prediction of the stress state in the segmental lining of the gallery during its excavation and the comparison with in situ measurements. It is shown that the time-dependent behavior of the ground is affected by the excavation technique. Finally, an attempt to predict the long-term response of both tunnels is proposed.

Fault Stability Perturbation by Thermal Pressurization and Stress Transfer Around a Deep Geological Repository in a Clay Formation

AbstractThe increase of temperature of a low‐permeability, fluid‐saturated media may trigger significant thermal pressurization, where the expansion of pore fluid cannot be accommodated by the thermal expansion of the pore space. With the aid of a coupled thermohydromechanical numerical simulator, we investigate the possible impact of thermal pressurization during the life of a deep geological repository (DGR) for high‐level radioactive waste, characterized by the emplacement of radioactive material‐filled canisters in a series of parallel tunnels, excavated in a low‐permeability clay formation. We represent the fault as a planar structure embedded in a thermoporoelastic material and shear activation evaluated by a strain‐softening Mohr‐Coulomb failure criterion. The results show that stress changes caused by temperature and thermal pressurization of a rock mass around the emplacement tunnels may trigger a slip event on a fault plane in proximity of the geological disposal site: Rupture nucleates at depth, hundreds of meters below the DGR. Stress transfer plays a key role, while a direct hydraulic connection between the repository and the nucleation zone is not necessary in order to trigger rupture. A low stress ratio may favor the occurrence of slip up to a distance of 600 m of the fault from the outermost tunnel. These results highlight the need of investigating hydromechanical properties and local stress conditions at depth to characterize the geomechanical response of weak planes located in the surroundings of a high‐level radioactive waste repository and to provide sufficient knowledge for the safe development of the DGR site.

Beetle borings in wood with host response in early Permian conifers from Germany

Wood boring represents a common feeding and survival strategy in several lineages of beetles. The larvae of wood-boring beetles hatch and excavate tunnels in wood during their development. The origin and evolutionary history of this life habit, however, remain poorly understood to date, as the fossil record is scarce. We present new silicified conifer wood specimens containing complex borings from the lowermost Permian Manebach Formation of the Thuringian Forest Basin in central Germany and the lower Permian Donnersberg Formation of the Saar–Nahe Basin in southwestern Germany. Additionally, this distinctive type of wood boring is recorded from the Carboniferous/Permian of the Czech Republic, Poland and China. For these borings, the new fodinichnion or agrichnion Pectichnus multicylindricus igen. et isp. nov. is established. It is characterised by several parallel cylindrical tunnels in a longitudinal arrangement, branching from a tangential primary tunnel oriented perpendicularly. The borings contain frass as coprolites made up of undigested wood cells. The conifer trees responded to the borings with callus production that subsequently filled or enclosed the tunnels. This is the earliest record of this specific life habit of ancient insects. The novel wood-boring strategy required structural modification and physiological adaptation; it probably emerged when insect diversity expanded considerably as terrestrial environments changed dramatically.

STRESSED STATE OF A SYSTEM OF THREE PARALLEL TUNNELS WITHOUT DRAWING FROM OWN WEIGHT OF AN ANOTROPHONE ROCK MASSIF

Objectives. The aim of the study is to carry out a parametric analysis of the stress state of an anisotropic rock massif on the contours of the workings of a system of three parallel circular tunnels without lining due to the mass of the massif, for various ratios of the elastic characteristics of the rock massif in orthogonal directions, and at different distances del transverse isotropic medium. Method. The calculation of a system of three parallel tunnels without a large extension lining, laid in a strong transversely isotropic rock massif, is reduced to the problem of plane deformation of the theory of elasticity for a transversely isotropic medium containing parallel workings. A model of a transversely isotropic medium (a special case of an anisotropic medium) is used, in which the rock massif in one plane has the characteristics of an isotropic medium (the isotropy plane), and in the perpendicular direction, characteristics different from the isotropic medium. The stress state was investigated by the finite element method using the ANSYS software package. The sizes and type of the finite element suitable for calculation on the basis of the solution in the program complex of the verification task were previously determined. The Kirsch problem was accepted as the verification problem. Result. The relative tangential stresses on the contours of three parallel tunnels were determined depending on the degree of anisotropy of the rock mass and depending on the distance between parallel tunnels. The influence of the distance between the tunnels on the stress state on the contours of three parallel tunnels was evaluated, depending on the degree of anisotropy.Conclusion. The results of a parametric analysis of the system of three parallel free-flow tunnels without lining, depending on the degree of anisotropy of the rock mass and the distance between the tunnels, show that the stress state is significantly affected by the degree of anisotropy of the elastic properties of the soil massif and the distance between the tunnels. When designing underground structures, it is necessary to take into account the anisotropy of the elastic properties of the soil mass. It is also necessary to determine in more detail the physical and mechanical properties of rocky soils and pay special attention to elastic characteristics. As studies have shown, taking into account transverse-isotropy and the distance between the tunnels leads to both an increase and a decrease in tangential stresses on the contours of parallel tunnels. At some ratios of elastic characteristics in orthogonal directions, regardless of the distance between the tunnels, there are no tensile stresses on the contours of the tunnels, which favorably affects the operation of the hydraulic tunnel.

Medial Patellofemoral Ligament Reconstruction in Traumatic Patellar Dislocation without Patellar Fixation.

Acute traumatic patellar dislocation is a common injury, and spontaneous reduction may occur at the time of injury or may be reduced at the field of the accident by someone. It may be associated with osteochondral fractures and rupture of medial patellar stabilizers leading to recurrent patellar instability. The aim of this prospective study was to evaluate the outcomes of medial patellofemoral (PF) ligament (MPFL) reconstruction in recurrent traumatic patellar dislocation. Forty-five patients presented with PF instability as a result of traumatic rupture MPFL with normal patellar tracking underwent MPFL reconstruction without patellar fixation hardware through two parallel transpatellar tunnels and one screw in femoral tunnel. All patients were evaluated clinically preoperatively and at a minimum follow-up of 24 months, and International Knee Documentation Committee (IKDC) and Kujala scores were used to assess the clinical results. All patients were available for evaluation at a minimum of 24 months (up to 36 months). The mean age of these patients at the time of surgery was 22.82 years (range: 18-34 years). All patients gave history of trauma of their knees. Mean IKDC scale showed significant improvement as it rose from 47.17 preoperatively to 77.94 postoperatively, and mean Kujala score rose from 53.88 preoperatively to 86.24 postoperatively (p < 0.001). No recurrence of dislocation was recorded. Only three patients had mild atrophy of thigh and one patient had some difficulty in jumping. Reconstruction of MPFL by this method provides good clinical result in the treatment of PF instability by using autologous graft (semitendinosus and gracilis). Less hardware were used with less complications.

Patellar tendon ruptures : Internal bracing and augmentation technique

To report asurgical technique for the treatment of patellar tendon ruptures augmented with an internal brace suture tape. Acute patellar tendon ruptures, fractures of the distal patellar pole, chronic insufficiency of the patellar tendon or revision surgery for failed repairs. Severe damage to the surrounding soft tissue. Local infection. Life-threatening conditions. Direct longitudinal anterior approach to the patellar tendon. Two parallel transosseous bone tunnels are drilled in the patella and tibial tuberosity with a2.4 mm drill bit. Two separate FiberTapes® (Arthrex, Naples, FL; USA) are shuttled through the proximal and distal bone tunnels around the tendon in "X" and "O"type configuration. Patellar height is reestablished under fluoroscopic control and both FiberTapes are tied down. Both tendon ends are debrided and readapted with absorbable sutures. Passive motion exercise to 90° of flexion from day1. Partial load to 20 kg of body weight with knee in locked full extension brace during first 2weeks. Isometric exercises from week3. Passive flexion to 110° from week4 (adapted to pain). Free active range of motion and weight bearing from week7. In more than 10 years of clinical application, positive results were continuously found in acute as well as chronic patellar tendon ruptures. These results are consistent with those in the current literature.

Ground Settlements due to Construction of Triplet Tunnels with Different Construction Arrangements

Combining two or three shield tunnels that are drilled consecutively at small intermediate distances into a single open cross section creates a larger useful tunnel area, while keeping the total construction area rather compact. However, the combination of several bored tunnel tubes into a singular cross section results in a complicated construction procedure. Current methodologies address the evaluation of the settlement trough for one single tunnel or two parallel tunnels only. This study aims at expanding the current methodologies to the multiple‐tunnel geometry. Various construction orders and intermediate distances between the tunnels are evaluated using finite element analyses. The grout pressure method is applied in combination with the hardening strain with the small strain stiffness (HS small) constitutive model to investigate the relative magnitude of the settlements due to shield tunneling. It is concluded that the configuration with a Top‐Left‐Right construction sequence is the optimal arrangement. It results in 22.4% and 36.9% lesser settlements when compared to the equivalent horizontal twin tunnels spaced at 3D and the Left‐Right‐Top sequence, respectively.

Rethinking the Water Leak Incident of Tunnel LUO09 to Prepare for a Challenging Future

Incident often occurs while deepening excavation pit and/or tunnelling underground pipelines although serious attention from practitioners, engineers, and scientists has received. Prevention and mitigation of incident have thus been deemed to be the key in developing sustainable infrastructure in urban areas. This study analyses and discusses an extensive water leak incident taken place throughout the parallel tunnels LUO09 construction in the soft alluvial deposits in Kaohsiung, Taiwan. Dumping sand bags and quick‐set cement intervened the incident but in vain. The water leak incident is initiated by the piping. The existing vehicle underpass causes the jet‐grout columns installed not exactly in the plumb. Their overlapping is estimated to be less than the design value of 60 cm, and some seepage‐prone weak zones are thus developed. The measured hydraulic gradient being equal to 12.1 and existence of seepage‐prone weak zones are deemed as the main cause initiating the water leak incident. The pinhole test results highlight not only the nonplastic nature of the Kaohsiung silt but also its vulnerability to piping under large hydraulic gradients. Some bullet points that indicate what engineers should do or avoid are learned and summarised.

Dynamic Responses of a Twin-Tunnel Subjected to Moving Loads in a Saturated Half-Space

With the fast development of rail transit, the environmental vibration problems caused by subways have received increasing attention. A 3D finite element model was built in this study to investigate the ground vibrations induced by the moving load operating in the parallel twin tunnels. Compared to the model consisting of a single tunnel that was commonly adopted in the past studies, a pair of tunnels is considered and the surrounding medium of the tunnels is taken as a saturated porous medium. The governing equations of the 3D finite element method modeling of the saturated poroelastic soil have been derived according to Biot’s theory. Computed results showed that the dynamic response of the twin-tunnel model is greater than that of the single tunnel model. And the spacing between two tunnels, tunnel buried depth, and load moving speed are the essential parameters to determine the dynamic response of the tunnel and soil.

Dynamic stability evaluation of underground tunnels based on deformation reinforcement theory

Owing to the rapid and increasing application of underground engineering, the stability of underground tunnels under complex geological and seismic environments is receiving increasing attention. Seismic stability analysis and reinforcement design are important to guarantee engineering safety and operation. Based on the deformation reinforcement theory, a dynamic analysis method of the anti-seismic stability evaluation of underground tunnels is presented. The time history of plastic complementary energy norm is used to identify the instant when the structure is exhibiting the most devastating failure. The unbalanced force is used to represent the local failure of the structure. The reinforcement forces are derived through the distribution of unbalanced forces at the instant with the maximum PCE norm. These evaluation indices are incorporated into a three-dimensional nonlinear finite element analysis program, TFINE, which is designed by an object-oriented approach. Further, an elastoplastic integration algorithm and a comprehensive convergence rule are implemented. Examples of a single tunnel and parallel tunnels subject to earthquake are demonstrated, showing the capability and effectiveness of TFINE in evaluating the structure stability.

Study on the Uplift-resistant Design of Oversized Ultra-deep Underground Structural Foundation above Subway Lines

For an oversized ultra-deep underground foundation in areas with shallow water level and crossing subway lines, an unreasonable anti-floating design may be dangerous to the safe operation of the subway lines. In this paper, numerical analysis is employed to the anti-floating design scheme of the foundation for an actual project, where two parallel and adjacent subway tunnels are laid under the underground structure. Three rows of large diameter bored piles are densely distributed along the sides and centerline of the two tunnels to restrict the foundation excavation. The simulation results show that the displacement of the tunnels caused by foundation rebounding can be limited to 3∼4 mm, the fluctuation of vertical displacement caused by floating ranges from 11.0 to 15.4 mm, and the maximum value of the uplift gradient is only 0.019‰. On the other hand, a reasonable design of anti-floating anchors in the area of excavation far from the subway can be effective to lower bending moment in the integral concrete floor and thereby avoid the appearance of cracks. The scheme of combining design of uplift piles with anti-floating anchors in different regions can not only meet the requirements of anti-floating performance of the foundation and the safe operation of the subway, but also reduce the construction costs. The proposed design scheme can provide practical reference for the design and con-struction of similar projects.

Vibration energy harvesting with piezoelectrets and electrets

We report on vibration energy harvesting with parallel tunnel piezoelectret films and negatively charged wavy shaped electret films made from fluoroethylene propylene (FEP).

A node-based Smoothed Finite Element Method for Stability Analysis of Dual Square Tunnels in Cohesive-frictional Soils

This paper presents an upper bound limit analysis procedure using the node-based smoothed finite element method (NS-FEM) and second order cone programming (SOCP) to evaluate the stability of dual square tunnels in cohesive-frictional soils subjected to surcharge loading. The displacement field of the tunnel problems is approximated by using NS-FEM triangular elements (NS-FEM-T3). Next, commercial software Mosek is employed to deal with optimization problems, which are formulated as second order cone. Collapse loads and failure mechanisms of dual square tunnels were performed by solving the optimization problems with a series of size-to-depth ratios and soil properties. For dual square tunnels, the distance between centers of two parallel tunnels is the major parameter used to determine the stability. In this study, surcharge loading is applied to the ground surface and drained conditions are considered. Numerical results are verified with those available to demonstrate the accuracy of the proposed method.

Stress state of uniformly piecewise homogeneous space with a periodic system of parallel internal cracks

This paper deals with the antiplane stress state of a uniformly piecewise homogeneous space formed by alternate junction of two distinct layers of the same thickness manufactured of different materials which are weakened by periodic parallel tunnel cracks in their middle planes. The governing system of singular integral equations and the ways of solving the system are are given in general form. The closed solution of the problem is obtained in the special case, where there are central cracks of length 2a in heterogenous layers.