Tunnel Circumference Research Articles

Anthropometric characteristics as prerequisites for the development of primary carpal tunnel syndrome

Carpal tunnel syndrome is the most common compressive neuropathy of the upper limb. The etiology of this carpal tunnel syndrome is unknown. All previous studies of this issue were aimed at studying the external and internal risk factors, accompanied by narrowing of the carpal tunnel and compression of the median nerve. However, these studies were carried out without taking into account data regarding the anthropometric parameters of the hand.Material and methods. The study involved 48 participants of both sexes, divided into 2 groups. Group 1 – 28 patients with carpal tunnel syndrome, group 2 – 20 people – healthy volunteers. Participants of both groups underwent the following measurements of both upper extremities: wrist perimeter – level of entry into the carpal canal (cm), perimeter of the hand - level of exit from the carpal canal along the Kaplan line (cm), length of the carpal canal (cm). BMI (body mass index) was calculated and interpreted taking into account age and gender. The obtained morphometric data were subjected to systematization and statistical analysis.Results. It has been proven that the likelihood of developing primary carpal tunnel syndrome increases after the age 57 years old and with BMI values of more than 30. Also, the risk of developing primary carpal tunnel syndrome is higher with a hand perimeter of more than 22 cm (exit from the carpal tunnel) and a carpal tunnel length of less than 3 cm.Conclusion. Age, body mass index, hand and carpal tunnel circumference significantly affect the occurrence of primary carpal tunnel syndrome, which allows us to consider them as predisposing risk factors.

Penetration resistance and damage characteristics of cementitious mortar with partially replaced waste tire rubber as a filler against high-speed impact loading

Concrete, as the sole construction material, demonstrates an inadequate performance against high-speed impact loading. Resistance to such loading can be increased by adding rubber from the waste tire industry. In this study, the performances of cementitious mortar with the addition of waste tire rubber (WTR) powder were investigated against the strike of a high-speed projectile. By setting the target flow above 110 % and air content within a range of 5–7%, mortar with 30 % WTR was selected for high-speed impact test. Selected mortar specimens demonstrated significantly high resistance to damage and penetration against a high-speed projectile at impact speeds of 300 m/s and 420 m/s. Further, an experimental study revealed the contrasting behaviour of mortar specimens with WTR powder from that of conventional specimens, where typical compression occurred due to triaxial stress at the tunnel circumference formed by the intrusion of the projectile. Recommendation is made for composite mortar containing a less-stiff material such as rubber for new variables to be defined in the existing formulae, to quantify penetration in high-speed loading; given that the penetration resistance of specimens with 30 % WTR was larger than that of the control specimen, even with its lower compression strength.

Excess Pore Water Pressure and Ground Consolidation Settlement Caused by Grouting of Shield Tunnelling

This study investigates the effect of shield tunnel grouting on excess pore pressure distributions around tunnel and ground consolidation settlement. First, it presents half-plane excess pore pressure around an unlined tunnel caused by grouting pressure based on the complex variable theory and the conformal mapping method. Second, the analytical solution for the soil consolidation is derived using the conformal transformation method and the consolidation theory of Terzaghi–Rendulic. The drainage conditions of the tunnel lining are idealized into three cases: fully drained, partially drained, and impermeable along the tunnel circumference. The impacts of the burial depth of the tunnel, the permeability coefficient of the tunnel lining and the surrounding soil, the Poisson’s ratio of the soil, the lateral Earth pressure coefficient of the soil, and the shear modulus are investigated.

Analysis of the Stability and Mechanical Characteristics of the Jointed Surrounding Rock and Lining Structure of a Deeply Buried Hydraulic Tunnel

On-site monitoring and numerical simulation have been combined to analyze the stability of the jointed surrounding rock and the stress inside the lining structure of a sample deeply buried hydraulic tunnel. We show that the deformation around the tunnel was mainly concentrated in the range 51.37 mm∼66.73 mm, the tunnel circumference was dominated by shear failure, and the maximum plastic zone was about 3.90 m. When the shotcrete treatment was performed immediately after the excavation, the deformation of the surrounding rock was reduced by 58.94%∼76.31%, and the extension of the plastic zone was relatively limited, thereby leading to improvements in terms of the stability of surrounding rock. When the support was provided at different time points, the stress of the surrounding rock in the shallow part of the tunnel was improved everywhere. In the tunnel section with high ground stress and joint development, when 10 cm steel fiber concrete spray layer and 40 cm C25 concrete secondary lining were used, the maximum tensile stress on the lining structure was 0.89 MPa, i.e., it was less than the tensile strength of concrete, which indicates that the internal force of the lining can meet the overall requirements.

ACL graft with extra-cortical fixation rotates around the femoral tunnel aperture during knee flexion.

An understanding of the behavior of a new ACL graft in the femoral tunnel during knee motion and external loading can provide information pertinent to graft healing, tunnel enlargement, and graft failure. The purpose of the study was to measure the percentage of the tunnel filled by the graft and determine the amount and location of the graft-tunnel contact with knee motion and under external knee loads. Single bundle anatomical ACL reconstruction was performed on six cadaveric knees. Specimens were positioned with a robotic testing system under: (1) passive flexion-extension, (2) 89-N anterior and posterior tibial loads, (3) 5-Nm internal and external torques, and (4) 7-Nm valgus moment. The knees were then dissected, repositioned by the robot and the geometry of the femoral tunnel and graft were digitized by laser scanning. The percentage of tunnel filled and the contact region between graft and tunnel at the femoral tunnel aperture were calculated. The graft occupies approximately 70% of the femoral tunnel aperture and anterior tibial loading tended to reduce this value. The graft contacted about 60% of the tunnel circumference and the location of the graft-tunnel contact changed significantly with knee flexion. This study found that the graft tends to rotate around the tunnel circumference during knee flexion-extension and contract under knee loading. The "windshield-wiper" and "bungee cord" effect may contribute to femoral tunnel enlargement, affect graft healing, and lead to graft failure. There can be a considerable motion of the graft in the tunnel after surgery and appropriate rehabilitation time should be allowed for graft-tunnel healing to occur. To reduce graft motion, consideration should be given to interference screw fixation or a graft with bone blocks, which may allow an earlier return to activity.

Sensitivity Analysis Of Influencing Factors On Tunnel Stability In Bad Geological Slope Sections

Based on a tunnel through slope of Yongji highway project, relying on ABAQUS geotechnical numerical analysis software, using the appearance of plastic penetration area for instablilty criterion, choosing 11 typical influential factors as independent variables to tunnel stability, the orthogonal test array L50(511) is used to analyze sensitivity of influence factors under evaluating indexes of safety factor to the tunnel stability and the maximum principal tensile on the inner surface of surrounding rock. Research results show that: there are some certain differences between calculation results of safety factor and maximum principal tensile, but overall presentation represents favorable consistency, and the sensitivity of influence factors to the stability of tunnel through unfavorable geological slope can be preferably annlyzed by orthogonal test. The influence of the cohesion of rock c, the horizontal distance d between tunnel centerline and slope toe, the inclination angle of slope α are significant. Comprehensive consideration of safety factor and maximum principal tensile of tunnel circumference is more perfect than one-sided safety factor when performing the analysis of tunnel stability. The research results of this paper can provide reference to design, construction of similar tunnels.

Cicatrisation des greffes de DT4 dans le tunnel tibial et dans l’échancrure : évaluation clinique et IRM à 4 ans minimum des DT4 fixés par fixation de suspension versus vis d’interférence

Success of ACL reconstruction requires Graft healing in the joint and a solid graft incorporation within the tunnels. Resorbable interference screws (RIS) provide limited tendon-bone contact because much of the tunnel circumference is occupied by the screw itself, while adjustable suspensory fixation (ASF) systems provide larger contact zones and stiffer fixation which favor graft healing. Purpose To evaluate ligamentization of four-strand semitendinosus (4ST) using MRI, fixed with ASF compared to RIS. Study Design Prospective comparative study; Level II. Methods The authors prospectively enrolled 57 patients undergoing primary ACL reconstruction using single bundle 4ST. The femoral graft was fixed using suspensory fixation in all knees. The tibial graft was fixed using ASF in 28 knees and using RIS in 29 knees. The groups were similar in term of age and gender. Minimum 4 years postoperatively, GNRB® knee laxity measurements were taken and MRI scans were performed to assess graft incorporation within the tibial tunnel and in the notch. Results There was not significant difference on the Functional results IKDC and Lysholm. The IKDC Global score A + B 96.4 % was better in the ASF group than in RIS 82.1 % (p = 0.04). Mean side to side Laximetry test was none significant p = 0.18 (−0.13 vs 0.35). Tunnel enlargement was no significant between the two groups 10.7 mm in ASF group and 11.5 mm in RSI group. Howell graft signal assessment in the notch was excellent (Grade I + II) in 91 % of cases in the ASF Group and in 73 % of cases in the RIS group (p = 0.04). In the tibia the SNQ was 2.25 ± 4.05 in the ASF group and 10.28 ± 18.98 in the RIS group (p = 0.02). In the notch the SNQ was 2.57 ± 2.80 in the ASF group and 6.62 ± 10.99 in the RIS group (ns). There were 6 consistent tibial cysts related to the screw (20 %) in the RSI group and no cyst in the ASF group. Conclusion ASF provides more favorable conditions than RIS for incorporation and ligamentization of 4ST grafts within the tibial tunnel with more residual cysts in the RSI group. In the notch, the Howell grade was better in the ASF group, although the SNQ were not significatively better. the objective IKDC Score was significatively better in ASF group, however functionals results are similar.

Effect of Voids Behind Lining on the Failure Behavior of Symmetrical Double-Arch Tunnels

The presence of voids behind lining seriously affects the safety of the symmetrical double-arch tunnels during service life. It is essential to find out the impact of voids on tunnel safety due to the increasing demand for the construction and maintenance of symmetrical double-arch tunnels. Model tests and numerical analyses were conducted in this research. The results attained were explored including earth pressure, internal force, and lining failure. Results reveal that the presence of voids has a large influence on the internal force in the lining of symmetrical double-arch tunnels, generally in the form of asymmetrical failure patterns of the lining. The failure patterns of the lining are greatly influenced by the size and location of voids with respect to the symmetrical double-arch tunnel circumference. Significant changes in the lining internal forces were found at the areas in the close vicinity of the void whereas a few changes were found at the bottom of the sidewall, the invert, and the central wall far away from the void. The propagation laws of lining cracks of asymmetrical double-arch tunnels are more complicated than symmetrical tunnels with a void behind the central wall. The location of the initial cracking of symmetrical and asymmetrical double-arch tunnels is the same, while the lining failure of the large-section tunnel is the most complicated.

Mechanical Analysis of the Circular Tunnel considering the Interaction between the Ground Response Curve and Support Response Curve

The viewpoint that the ground initial elastic displacement and the interaction between the ground response curve (GRC) and support response curve (SRC) in the surrounding rock should be considered at the same time in the mechanical analysis of the circular tunnel is proposed, and its solution method is also established. Meanwhile, in order to consider the effect of the intermediate principle stress, Drucker-Prager criterion is introduced to describe the yield property of the surrounding rock. The calculation example indicates that the final radial displacement of the tunnel circumference will increase when the ground initial elastic displacement in the surrounding rock is considered before the support structure is applied, which indicates that it is necessary to consider the ground initial elastic displacement in the surrounding rock before the support structure is applied. With increasing the support resistance force and the initial field stress, the plastic zone radius in the surrounding rock and the radial displacement of the tunnel circumference will decrease and increase, respectively, while with increasing the rock internal friction angle and cohesion, the plastic zone radius in the surrounding rock and the radial displacement of the tunnel circumference both decrease. Meanwhile, with the stress Lode parameter increasing from −1 to 1, the plastic zone radius in the surrounding rock and the radial displacement of the tunnel circumference both greatly decrease and then slightly increase. It indicates that the intermediate principle stress has some effect on the calculation results.

Évaluation IRM comparative des greffes de DT4 fixées par vis résorbable vs. fixation de suspension ajustable

Background Success of ACL reconstruction requires solid graft incorporation within the tunnels to enable graft remodeling. Resorbable interference screws (RIS) provide limited tendon-bone contact because much of the tunnel circumference is occupied by the screw itself, while adjustable suspensory fixation (ASF) systems provide larger contact zones which favor ligamentization. Purpose To evaluate ligamentization of four-strand semintendinosus (4ST) within the tibial bone tunnel using MRI at 6 postoperative months, fixed with ASF compared to RIS. Study design Prospective comparative study; level II. Methods The authors prospectively enrolled 121 consecutive patients undergoing primary ACL reconstruction using single bundle 4ST. The femoral graft was fixed using suspensory fixation in all knees. The tibial graft was fixed using ASF in 67 knees and using RIS in 44 knees. Six months postoperatively, knee laxity measurements were taken and MRI scans were performed to assess graft incorportation within the tibial tunnel. Results At 6 months follow-up, MRI scans of 109 knees were available for analysis. Tunnel enlargement in the ASF group was 2.3 ± 1.1 mm (range, 0.5–6.0), while in the RIS group it was 4.7 ± 2.8 mm (range, 0.5–19.0) ( P > 0.001). Howell graft signal assessment was excellent in 97% of cases in the ASF Group and in 25% of cases in the RIS group ( P > 0.001). The SNQ was 0.078 ± 0.62 in the ASF group and 0.671 ± 0.83 in the RIS group ( P > 0.001). Conclusion ASF provides more favorable conditions than RIS for incorporation and ligamentization of 4ST grafts within the tibial tunnel. The ASF system used showed very little tunnel widening, which suggests that it grants stabilization. The SNQ was also considerably better in the ASF group, mainly due to tight graft folding that prevented synovial fluid penetration in the graft-bone interface. Clinical relevance The findings are relevant for choice of tibial fixation device for ACL reconstruction particularly in patients that need to resume athletic activities.

Towards future circular colliders

The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) presently provides proton-proton collisions at a center-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics program will extend through the second half of the 2030’s. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ∼100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCCee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3 S n superconductor, for the FCC-hh hadron collider, and a highly-efficient superconducting radiofrequency system for the FCC-ee lepton collider. Following the FCC concept, the Institute of High Energy Physics (IHEP) in Beijing has initiated a parallel design study for an e + e − Higgs factory in China (CEPC), which is to be succeeded by a high-energy hadron collider (SPPC). At present a tunnel circumference of 54 km and a hadron collider c.m. energy of about 70 TeV are being considered. After a brief look at the LHC, this article reports the motivation and the present status of the FCC study, some of the primary design challenges and R&D subjects, as well as the emerging global collaboration.

Incorporation of Hamstring Grafts Within the Tibial Tunnel After Anterior Cruciate Ligament Reconstruction

Background: The success of anterior cruciate ligament (ACL) reconstruction requires solid graft incorporation within the tunnels to enable graft remodeling. Resorbable interference screws (RIS) provide limited tendon-bone contact because much of the tunnel circumference is occupied by the screw itself, while adjustable suspensory fixation (ASF) systems provide larger contact zones, which favor ligamentization. Purpose: To evaluate ligamentization of a 4-strand semitendinosus (4ST) graft fixed with ASF compared with RIS within the tibial bone tunnel at 6 months postoperatively using magnetic resonance imaging (MRI). Study Design: Cohort study; Level of evidence, 2. Methods: We prospectively enrolled 121 consecutive patients undergoing primary ACL reconstruction using a single-bundle 4ST graft. The femoral end of the graft was fixed using suspensory fixation in all knees. The tibial end of the graft was fixed using ASF in 67 knees and RIS in 54 knees. Six months postoperatively, knee laxity measurements were taken, and MRI was performed to assess graft incorporation within the tibial tunnel. Results: At 6-month follow-up, MRI scans of 109 knees were available for analysis. The mean tibial tunnel enlargement in the ASF group was 2.3 ± 1.1 mm (range, 0.5-6.0 mm), while in the RIS group, it was 4.7 ± 2.8 mm (range, 0.5-19.0 mm) (P < .001). The Howell graft signal assessment findings were excellent in 97% of knees in the ASF group and in 25% of knees in the RIS group (P < .001). The mean signal-to-noise quotient (SNQ) was 0.078 ± 0.62 in the ASF group and 0.671 ± 0.83 in the RIS group (P < .001). Conclusion: ASF provides more favorable conditions than RIS for the incorporation and ligamentization of 4ST grafts within the tibial tunnel. The ASF system used showed very little tunnel widening, which suggests that it grants stabilization. The SNQ was also considerably better in the ASF group.

Design Study of a 16-T Block Dipole for FCC

Author(s): Sabbi, G; Blomberg Ghini, J; Gourlay, SA; Marchevsky, M; Ravaioli, E; Ten Kate, H; Verweij, A; Wang, X | Abstract: The Future Circular Collider (FCC) study at CERN is investigating the design of a proton-proton collider with a center of mass energy of 100 TeV and a tunnel circumference of 100 km (FCC-hh). Nb3Sn arc dipoles with 50-mm aperture and 16-T operating field are required for this application. Among the possible magnetic layouts, block coils offer attractive features, in terms of conductor packing, separation between high-field and high-stress locations, use of flat cables, and simpler geometries for windings and parts. In order to assess these potential advantages, the HD series of block-coil models was developed at LBNL. These models achieved fields of 15-16 T in technology tests, and 13-14 T in accelerator relevant configurations, with bore diameters of 36-43 mm. In this paper, we discuss the implications of increasing the bore diameter to 50 mm, which is consistent with the latest FCC-hh design targets. A detailed quench protection analysis is performed using the new coupling-loss-based CLIQ system, expanding the safe parameter space with respect to the traditional approach based on quench heaters. Finally, alternative magnet design options, and further studies required to select among them, are outlined.

Scaling behavior of circular colliders dominated by synchrotron radiation

The scaling formulas in this paper — many of which involve approximation — apply primarily to electron colliders like CEPC or FCC-ee. The more abstract “radiation dominated” phrase in the title is intended to encourage use of the formulas — though admittedly less precisely — to proton colliders like SPPC, for which synchrotron radiation begins to dominate the design in spite of the large proton mass. Optimizing a facility having an electron–positron Higgs factory, followed decades later by a p, p collider in the same tunnel, is a formidable task. The CEPC design study constitutes an initial “constrained parameter” collider design. Here the constrained parameters include tunnel circumference, cell lengths, phase advance per cell, etc. This approach is valuable, if the constrained parameters are self-consistent and close to optimal. Jumping directly to detailed design makes it possible to develop reliable, objective cost estimates on a rapid time scale. A scaling law formulation is intended to contribute to a “ground-up” stage in the design of future circular colliders. In this more abstract approach, scaling formulas can be used to investigate ways in which the design can be better optimized. Equally important, by solving the lattice matching equations in closed form, as contrasted with running computer programs such as MAD, one can obtain better intuition concerning the fundamental parametric dependencies. The ground-up approach is made especially appropriate by the seemingly impossible task of simultaneous optimization of tunnel circumference for both electrons and protons. The fact that both colliders will be radiation dominated actually simplifies the simultaneous optimization task. All GeV scale electron accelerators are “synchrotron radiation dominated”, meaning that all beam distributions evolve within a fraction of a second to an equilibrium state in which “heating” due to radiation fluctuations is canceled by the “cooling” in RF cavities that restore the lost energy. To the contrary, until now, the large proton to electron mass ratio has caused synchrotron radiation to be negligible in proton accelerators. The LHC beam energy has still been low enough that synchrotron radiation has little effect on beam dynamics; but the thermodynamic penalty in cooling the superconducting magnets has still made it essential for the radiated power not to be dissipated at liquid helium temperatures. Achieving this has been a significant challenge. For the next generation p, p collider this will be even more true. Furthermore, the radiation will effect beam distributions on time scales measured in minutes, for example causing the beams to be flattened, wider than they are high. In this regime scaling relations previously valid only for electrons will be applicable also to protons.

Ground and tunnel responses induced by partial leakage in saturated clay with anisotropic permeability

Finite element analysis was conducted to study the ground and tunnel response to partial tunnel leakage coupled with anisotropic soil permeability, a novel and little-known approach that was developed from in-situ inspections of shield tunnel leakage in the Shanghai Metro system. The ground and tunnel settlements, which were caused by water leaking into the tunnel, significantly degraded both the serviceability and safety of the tunnel and its surroundings. In a typical analysis, such leakage is commonly assumed to be uniform along the tunnel circumference with a soil permeability that is isotropic. Numerical simulation results obtained in this paper indicated that partial tunnel leakage in only one side of the shield tunnel caused a greater pore pressure reduction at the tunnel spring line and a larger ground surface settlement than otherwise caused by uniform tunnel leakage with the same rate of water inflow. Indeed, observations showed that partial leakage in only one side of the shield tunnel caused remarkable lateral movements of the tunnel. Our analysis showed that coupling leakage boundary conditions with favorable soil permeability anisotropy could significantly decrease the maximum ground settlements induced by the leakage, which leads to an increase in the width of the surface settlement trough. Furthermore, the effect of soil permeability anisotropy on ground settlement was found more profound for cases involving partial tunnel leakage boundary conditions.

Analytical solutions of stresses and displacements for deep circular tunnels with liners in saturated ground

To investigate the displacement and stress distributions for deep circular tunnels with liners in saturated ground, an analytical model is proposed. For a deep tunnel with drainage conditions, plane strain conditions at any cross-section of the tunnel and the elastic regime of the linear elasticity for the remaining liner are assumed, while the ground is assumed to be linearly elastic and perfectly plastic with a failure surface de?ned by the Mohr-Coulomb criterion. The post-yield behavior of the ground follows the non-associated flow rule defined by the dilation angle. To solve the proposed problem, two procedures are presented. An axisymmetric model for a deep circular tunnel with a steady-state seepage condition is considered, and then a simple closed-form analytical solution is obtained with a common theoretical framework for the boundary conditions of a constant total head along the tunnel circumference. Assuming that certain ground displacements along the tunnel circumference have occurred before the installation of the liner, analytical solutions of stresses and displacements are derived with particular emphasis on the seepage and the stress release effect induced by tunnelling. The proposed analytical model is validated by numerical simulation.

Estimation of effect of voids on frequency response of mountain tunnel lining based on microtremor method

Nowadays, aged tunnels keep continuously increasing all over the world, which require effective inspection methods to assess their health conditions. In this study, both in situ acceleration wave measurements and numerical simulations were carried out to study the microtremor characteristics of mountain tunnel lining. Power spectrum density (PSD) of signals was calculated and peak frequencies were identified using the peak-picking method. Discontinuous contacts between rock masses and lining concrete were simplified as weak interfaces with low stiffness, which play the role of elastic supporting during dynamic calculation. Influences of voids, rock type and concrete type on their peak frequencies were evaluated. The results of the numerical analysis show that the normal stiffness of rock–concrete interface has strong correlation with the magnitude of peak frequency. The frequency response of tunnel lining is affected by the presence of voids located around tunnel circumference behind lining. The first peak frequency is dependent on the void size and location. The larger the void size and location angle, the greater the decrease of the first peak frequency. The peak frequency also decreases as the strength of concrete decreases, and is not affected by the change of properties of unweathered rock masses. Additional frequency modes can be identified when voids are not located on the central axis of tunnel. The first peak frequency variation can be considered to be intimately linked with the stress state of the tunnel lining influenced by the existence of voids.

Advance numerical simulation of tunneling by using a double shield TBM

Double shield TBMs are amongst the most technically sophisticated excavation machines in use by tunneling industry. However, using the shielded machine limits access to the walls for observation of ground conditions and presence of shield makes the machine susceptible to entrapment or seizure in weak rocks under high stresses which results in high convergence. To realistically evaluate the possibility of machine seizure in such grounds, the interaction between the rock mass and shields, lining and backfilling need to be understood. This study explains the application of numerical analysis for 3D simulation of mechanized tunneling by using a double shield TBM. For this purpose, a comprehensive numerical simulation is developed to systematically evaluate the potential of excessive ground convergence. Simulation results at five reference points on the tunnel circumference along the tunnel have been examined. The results are including longitudinal displacement profile (LDP) as well as contact force profiles (LFP) on both front and rear shields, frictional forces and required thrust to move the machine, stress history of ground, and estimated loading of the segments. The results also proved that numerical analyses can successfully be used for prediction of loads on the shield during excavation to assess risks of machine entrapment.

3D finite difference model for simulation of double shield TBM tunneling in squeezing grounds

One of the main concerns in using a shielded machine in deep rock tunnels is the possibility of the shield seizure in squeezing ground. To realistically evaluate the possibility of machine seizure in such grounds, the interaction between the rock mass and shield, lining and backfilling need to be understood. This paper will explain the background theories and the application of numerical analysis for 3D modeling of mechanized tunneling by using a double shield TBM in squeezing ground. The discussions will include the effects of advance rate during excavation cycle of a shielded TBM to observe the impact of tunneling rate on the possibility of machine jamming in the squeezing grounds. Simulation results at five reference points on the tunnel circumference along the tunnel or longitudinal displacement profile (LDP) as well as longitudinal contact force profiles (LFP) on both front and rear shields have been examined. Also, maximum thrust force required to overcome friction and drive TBM forward is calculated. This exercise allows for evaluation of the effects of various parameters on convergence and contact forces between the rock and shield, which in turn determines the required propel forces and can define the possibility of machine entrapment.

Effect of drainage conditions on porewater pressure distributions and lining stresses in drained tunnels

This study deals with the effect of drainage conditions on porewater pressure distributions and lining stresses in drained tunnels. Firstly, simple closed-form analytical solutions for the steady-state porewater pressure are re-derived within a common theoretical framework for two different boundary conditions (one for zero water pressure and the other for a constant total head) along the tunnel circumference by using the conformal mapping technique. The difference in porewater pressure distributions among the analytical solutions is investigated. The numerical simulation of a drained circular tunnel under the steady-state groundwater flow condition is made to investigate the effect of porewater pressure distributions on lining stresses. Secondly, the case study of the planned South Blue Line Extension subway tunnel under the steady-state groundwater flow condition is performed for four different drainage conditions (sealed, fully-drained with zero water pressure or a constant total head, and invert only-drained) along the tunnel circumference. The effects of different drainage conditions on porewater pressure distributions, flow nets, and lining stresses are investigated.