Flexible Tunnel Research Articles

An integrated framework for improving the efficiency and safety of hydraulic tunnel construction

Drilling and blasting is the most flexible tunnel construction method considering the excavation of tunnel size and shape. Schedule and safety are two critical issues for project stakeholders during construction. To evaluate construction quality, various tools such as Building Information Modelling (BIM), schedule simulation, and numerical analysis are commonly employed. However, in current practices, these processes are often independent of each other, requiring data conversion and operation between multiple platforms. In this paper, we present a novel integrated framework for improving the safety and efficiency of hydraulic tunnel construction. To this end, a geometric tunnel model with time attribute is created, which connects the schedule information obtained by construction simulation via secondary development. Then a numerical simulation method coupled with construction schedule is introduced to the integrated framework, which can automatically process the numerical model and perform analysis and calculation combined with the schedule information. In addition, this paper proposes a parameterization method of the rock bolt numerical model to realize the evaluation of different support schemes. The proposed method can avoid tedious manual operations to reduce possible errors. Finally, we propose a multistep prediction model of surrounding rock deformation based on Long Short-Term Memory (LSTM). The framework integrates the above functions via secondary development, scripting, and other technologies, and demonstrates the reliability of the framework with a tunnel project. The proposed integrated framework provides an intuitive and efficient tunnel construction management method hence promoting the information flow of multiple participants and multiple professionals in tunnel construction and providing decision support.

Uncertainty quantification of tunnel seismic deformations in random soils

Tunnel damages are increasing worldwide in major earthquakes, some of which may result from the underestimated seismic actions and uncertainties associated with the design parameters. Opposite to traditionally performed deterministic analysis, this paper introduces stochastic dynamic time-history analysis to quantify the variability of seismic-induced tunnel deformations in a probabilistic framework. Two-dimensional nonlinear finite difference models combined with the Monte Carlo simulation are employed to assess the influence of parameter uncertainty. Analyses are performed for a wide range of soil shear wave velocities, ground motion intensities, lining Young’s moduli, correlation structures, distribution types, and coefficients of variation. The results indicate that the parameter uncertainty can have a significant impact on tunnel seismic deformations. Increased motion intensity leads to an increased standard deviation, especially for flexible tunnels. The influence of shear strength parameters is insignificant, despite a slightly larger standard deviation appears for the positive correlation. The distribution type effect increases sharply for the cases with high variation degrees, and the lognormal distribution generally predicts a lower mean, standard deviation, and probability of exceedance. The results also show that the soil parameter uncertainty can be properly considered by introducing a factor of safety. These findings may provide a useful reference for the reliability-based seismic design of tunnels.

Effect of flexibility ratio on seismic response of rectangular tunnels in sand: Experimental and numerical investigation

The flexibility ratio(F) is defined as the stiffness of a structure relative to that of soil, a critical factor affecting the soil–structure interaction. This study aimed to investigate the effect of F on the seismic response of rectangular tunnels constructed in sand. Shaking table tests were performed based on a scale model of a tunnel with different stiffness values. A 3D finite element model was established using ABAQUS, and the numerical results were compared with the test results. Subsequently, the verified model was implemented in a parametric study. The results showed that tunnels with lower F have higher acceleration responses in the high frequency-range of input motions. In addition, the amplification of the ground acceleration decreases with an increase in F, and the maximum response occurs in a longer period relative to the free-field. The distribution of the dynamic earth pressure along the tunnel lining with different F is relatively complex; nevertheless, overall, rigid tunnels have greater values than flexible tunnels. The dynamic bending moment along the tunnel sidewall decreases with increasing F, but it has the same trend along the sidewall. The presented results may lead to a better understanding of the seismic response of rectangular tunnels constructed in sand, providing practical references for the seismic design of similar underground structures.

BIM-Based Tunnel Information Modeling Framework for Visualization, Management, and Simulation of Drill-and-Blast Tunneling Projects

AbstractTunnel construction fundamentally differs from building and aboveground civil infrastructure projects. Drill-and-blast is one of the most common and flexible tunnel construction methods. Ho...

Single-Level Station Complex Structure for Application of Through Driving Construction Method

Metro Service has a huge impact on the development of urban transport infrastructure. The need to increase the efficiency of passenger transportation is caused by the rapid growth in passenger turnover as well as an increase in the distance from the outskirts of the city to the center. In connection with the need to develop a metro service network in Minsk city, which is confirmed by research in the area of passenger traffic in the main areas of the city, the CSM Bessac tunnel boring machine was purchased, which allows significantly to increase the speed of tunnel driving. The use of a mechanized tunnel boring machine in the traditional concept of the metro network construction, in which driving of tunnels is carried out after construction of stations, does not allow to use a shield with maximum economic efficiency due to the small extent of tunnels. There is also a need to build assembly-shield chambers and carry out works on disassembling and assembling the shield. The application of the new concept developed by Yu. S. Frolov and called “through driving” is actual in the conditions of the use of a mechanized tunnel boring machine. Its essence lies in the continuous driving of tunnels on the line section under construction and the consecutive construction of each station complex as the tunnel boring machine passes through it. To implement the concept of “through driving”, it is relevant to use a semi-closed construction method, in which the floor structure is constructed in an open way, and the other elements are closed. The available solutions of the metro stations constructed while using a semi-closed method of work have been analyzed in the paper. A detailed analysis has been carried out with due account of the adaptation to the construction conditions in Minsk, and the development of structural elements and assemblies of the platform area of the station, which is a two-cantilever vault with a developed transom part, resting on pile-columns of a circular cross section. Forces from the open ring of flexible tunnels lining are supported by a cantilever part of an arch and a bottom plate. The paper considers a design of a metro station, its main elements, their purpose and specificity of work, as well as optimization issues and the results of the design feasibility study.

Shaking Table Test Study on Flexible and Rigid Immersed Tube Tunnel in Liquefiable Soil Layer

To study the seismic response law of the immersed tunnel under different structural stiffnesses, three groups of shaking table models of immersed tunnel are carried out, including free-field model, flexible tunnel model, and rigid tunnel model. The similarities and differences of the pore water pressure and acceleration time-history between the free site and liquefiable soil layer around the flexible and rigid immersed tube tunnel are analyzed. The results show that, compared with the soil layer at the same position in the free-field, both the amplitude of acceleration and frequency component in the surrounding soil layer are affected by the stiffness of tunnel, and the influence comes greater with the larger stiffness of tunnel. When the input amplitude of seismic ground motion is small, the soil layer in the free field and the flexible tunnels share the same acceleration amplification law. The development law of pore pressure in the soil layer of test 1 was similar to test 2 but was quite different from test 3. Specifically, when the tunnel stiffness is smaller, the surrounding soil layer is easier to liquefy, with greater influence of the tunnel stiffness on the development law of pore pressure in the surrounding soil layer. The lower the soil buried depth is, the faster the pore pressure dissipates. The growth rate of tunnel strain is related to the stiffness of the structure. Generally speaking, the strain growth rate of the structure with smaller stiffness is higher under moderate earthquakes. The smaller the tunnel stiffness is, the more adaptable the tunnel is to the movement of the surrounding soil layer.

Precisely Controlled Two-Dimensional Rhombic Copolymer Micelles for Sensitive Flexible Tunneling Devices

Nanoscale two-dimensional (2D) organic materials have attracted significant interest on account of their unique properties, which result from their ultrathin and flat morphology. Supramolecular 2D ...

Soft soil layer-tunnel interaction under seismic loading

Understanding the soft soil layer-tunnel seismic interaction in the multi-layered ground is an important issue for a safe seismic design. However, this issue remains unclear since most of the previous studies considered homogeneous grounds. In this regard, the paper aims at investigating the seismic behavior of tunnels when they intersect a soft soil layer. Three soft soil layer-tunnel intersection scenarios (i.e., at the crown, springline, and invert) are respectively considered based on an academic case. Two-dimensional numerical analyses are performed for a wide range of soft soil layer thicknesses and shear wave velocities, assuming various flexibility ratios. The effect of soil nonlinearity is also involved. The results reveal that the presence of a soft soil layer generally increases the internal forces and deformations, particularly when a very soft soil layer passes through the flexible tunnel at the springline. The findings of this work may have a certain reference value for seismic design practice of tunnels.

Reliability analysis of shallow foundation in the vicinity of the existing buried conduit

ABSTRACTThe present study proposes reliability-based approach for assessing the performance of shallow foundation placed in the vicinity of an existing buried flexible pipe or utility tunnel. Performance function for the reliability analysis is defined in terms of % bearing capacity loss in the load carrying capacity of the shallow foundation due to the presence of buried flexible pipe or utility tunnel, and, allowable bearing capacity loss in load carrying capacity that can be tolerated. For the reliability analysis, an explicit functional relationship between input variables, such as geotechnical parameters of in situ soil as well as material properties of pipe, and, output response, i.e. % bearing capacity loss in load carrying capacity of foundation soil is needed. Using concept of response surface methodology (RSM) combined with the results of the numerical analysis; such an explicit functional relationship is easily established. Thereafter, reliability analysis can be performed, conveniently, using standard First Order Second Moment (FOSM) approach and performance of the foundation soil system with buried flexible pipe, present in the vicinity, can be assessed in terms of an index, popularly known as ‘reliability index (β)’.

Response characteristics of rectangular tunnels in soft soil subjected to transversal ground shaking

A numerical parametric study was conducted on diverse soil-rectangular tunnel systems, aiming to shed light on critical response characteristics of rectangular tunnels subjected to transversal ground shaking. Salient parameters that affect the dynamic response, such as: (i) the soil-tunnel relative stiffness and interface properties, (ii) the shape, dimensions and burial depth of the tunnel section, (iii) the soil deposit characteristics, and (iv) the input motion characteristics, were accounted for in this study. This paper summarizes the key findings of this investigation, focusing on the complex deformation modes of the tunnels during shaking, the dynamic earth pressures and the soil dynamic shear stresses developed around the tunnel, and the dynamic lining forces. The numerical results indicated a combined racking-rocking deformation pattern for the tunnels during shaking, while inward deformations of the slabs and the side-walls were also observed for flexible tunnels, when soil inelasticity was encountered. To quantify the racking deformation of rectangular tunnels, a series of numerical racking ratio - flexibility ratio (R-F) relations were developed and compared with existing analytical and empirical ones. The rocking response of rectangular tunnels was quantified by means of dimensionless relations (θ/γff-F), similar to the R-F relations. The soil-tunnel relative stiffness, the interface characteristics and the soil yielding affected significantly the above relations, as well as the dynamic earth pressures, the soil dynamic shear stresses and the dynamic forces developed on the lining during shaking. The presented results lead to a better understanding of the seismic response of rectangular tunnels in soft soil, while the proposed relations contribute towards the improvement of the R-F analysis method.

Seismic response of box-type tunnels in soft soil: Experimental and numerical investigation

A series of dynamic centrifuge tests were carried out at the geotechnical centrifuge facility of IFSTTAR in Nantes, to investigate the response of box-type tunnels embedded in dry sand under sinusoidal and seismic excitation, as affected by soil-tunnel relative flexibility and soil-structure interface rugosity. The system under investigation was analyzed by means of full dynamic time history analyses, implementing rigorous finite element models. The numerical models were calibrated on the basis of back analysis of tests, while the numerical predictions were compared with experimental data, in terms of soil and tunnel horizontal acceleration, soil shear strains and tunnel deformations. The validated numerical models were then employed to further investigate several aspects of the system seismic response. Results indicate a rocking deformation mode coupled with the well-known racking distortion of box-type tunnels under seismic shaking. The effect of the soil-tunnel interface characteristics and soil yielding on the racking deformation of the tunnel, the dynamic earth pressures and shear stresses around the tunnel, as well as on dynamic lining forces is also reported. Soil yielding leads to post-shaking, residual, dynamic earth pressures, shear stresses and lining forces, especially in the case of flexible tunnels, while interface characteristics affect the distributions of these response parameters around the perimeter of the tunnel section. The ability of simplified seismic design methods for tunnels to predict the response is finally discussed, by comparing their predictions with the recorded data and the numerical results.

On the dynamic response of square tunnels in sand

The paper investigates the seismic response of square tunnels in sand by means of dynamic centrifuge testing and numerical analysis. A series of dynamic centrifuge tests, conducted at the University of Cambridge on a square aluminium model tunnel embedded in dry sand, are initially presented. The tests, which were designed to investigate the seismic response of flexible tunnels, are analyzed numerically by means of full dynamic analysis of the coupled soil-tunnel system, using different soil and soil-tunnel interface models. Numerical predictions are compared to the experimental data, so as to better understand the response mechanism and validate the numerical modelling. The validated numerical models are then used to investigate the effect of lining rigidity on the soil-tunnel system dynamic response. The experimental and numerical results reported herein, indicate a non-negligible rocking deformation mode for the tunnels during seismic shaking coupled with racking distortion. The significant effects of the lining rigidity, soil-tunnel interface characteristics and soil yielding on the dynamic earth pressures and the shear stresses developed around the perimeter of the tunnel, as well as on the dynamic lining forces, are also reported and discussed.

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors.

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

An IBEM solution to the scattering of plane SH-waves by a lined tunnel in elastic wedge space

The indirect boundary element method (IBEM) is developed to solve the scattering of plane SH-waves by a lined tunnel in elastic wedge space. According to the theory of single-layer potential, the scattered-wave field can be constructed by applying virtual uniform loads on the surface of lined tunnel and the nearby wedge surface. The densities of virtual loads can be solved by establishing equations through the continuity conditions on the interface and zero-traction conditions on free surfaces. The total wave field is obtained by the superposition of free field and scattered-wave field in elastic wedge space. Numerical results indicate that the IBEM can solve the diffraction of elastic wave in elastic wedge space accurately and efficiently. The wave motion feature strongly depends on the wedge angle, the angle of incidence, incident frequency, the location of lined tunnel, and material parameters. The waves interference and amplification effect around the tunnel in wedge space is more significant, causing the dynamic stress concentration factor on rigid tunnel and the displacement amplitude of flexible tunnel up to 50.0 and 17.0, respectively, more than double that of the case of half-space. Hence, considerable attention should be paid to seismic resistant or anti-explosion design of the tunnel built on a slope or hillside.

Flexible endoscopic single-incision extraperitoneal implant and fixation of peritoneal dialysis catheter: proof of concept in the porcine model.

Peritoneal dialysis (PD) catheters placed in the pelvic space without anchoring present a high rate of migration. We aimed to assess the feasibility of a single-incision approach, using a flexible endoscopic preperitoneal tunneling for catheter implantation and fixation. Eight pigs were involved in this experimental study. A 2/0 Vicryl loop was sutured at the tip of a PD catheter. In 4 pigs, a 1.5 cm incision was made on the left paramedian line and the parietal peritoneal layer was identified by splitting rectal muscles. A gastroscope was inserted in the incision and advanced in the extraperitoneal space. An exit hole was made in the peritoneum over the low pelvic cavity. A guidewire was left in the abdominal cavity, and the PD catheter was inserted over the guidewire. The endoscope was inserted in the tunnel again, and endoscopic clips were deployed over the Vicryl loop to fix the catheter. In 4 pigs, the PD catheter was inserted laparoscopically using a two-port approach. The catheter's tip was fixed with laparoscopic clips on the Vicryl loop. A strain test to assess the force required to detach clips was performed using a digital dynamometer. Operative time for flexible endoscopic tunneling was longer when compared to the laparoscopic implant (29.5 ± 4.43 vs. 22.7 ± 2.51 min). Mean force to displace the catheter was similar after flexible endoscopic fixation when compared to laparoscopic clip fixation (5.57 N ± 2.76 vs. 4.15 N ± 1.76). Flexible endoscopic extraperitoneal tunneling allows for minimally invasive single-incision PD catheter placement and fixation.

Does flexible tunnel drilling affect the femoral tunnel angle measurement after anterior cruciate ligament reconstruction?

To quantify the mean difference in femoral tunnel angle (FTA) as measured on knee radiographs between rigid and flexible tunnel drilling after anatomic anterior cruciate ligament (ACL) reconstruction. Fifty consecutive patients that underwent primary anatomic ACL reconstruction with a single femoral tunnel drilled with a flexible reamer were included in this study. The control group was comprised of 50 patients all of who underwent primary anatomic ACL reconstruction with a single femoral tunnel drilled with a rigid reamer. All femoral tunnels were drilled through a medial portal to ensure anatomic tunnel placement. The FTA was determined from post-operative anterior-to-posterior (AP) radiographs by two independent observers. A 5° difference between the two mean FTA was considered clinically significant. The average FTA, when drilled with a rigid reamer, was 42.0° ± 7.2°. Drilling with a flexible reamer resulted in a mean FTA of 44.7° ± 7.0°. The mean difference of 2.7° was not statistically significant. The intraclass correlation coefficient for inter-tester reliability was 0.895. The FTA can be reliably determined from post-operative AP radiographs and provides a useful and reproducible metric for characterizing femoral tunnel position after both rigid and flexible femoral tunnel drilling. This has implications for post-operative evaluation and preoperative treatment planning for ACL revision surgery. IV.

Robust and flexible tunnel management for secure private cloud

Private cloud is cloud infrastructure operated solely for a single organization, whether managed internally or by a third-party and hosted internally or externally. It provides a flexible way to extend the working environment. Since the business process that working on them could be critical, it is important to provide a secure environment for organizations to execute those processes. While user mobility has become an important feature for many systems, technologies that provide users a lower cost and flexible way in joining a secure private cloud are in a strong demand. This paper exploits the key management mechanisms to have secured tunnels with private cloud for users who might move around dynamically without carrying the same machine. A strong authentication with a key agreement scheme is proposed to establish the secure tunnel. Furthermore, the proposed framework also provides mutual authentication, session key renewal between the users and the cloud server. Several related security properties of the proposed mechanism are also presented.

Comparative performance analysis of silicon nanowire tunnel FETs and MOSFETs on plastic substrates in flexible logic circuit applications

AbstractWe report on the fabrication and electrical comparison between flexible tunnel field‐effect transistors (TFETs) and metal–oxide–semiconductor FETs (MOSFETs) on plastic substrates from device to circuit performance by use of fully CMOS‐compatible silicon nanowires (SiNWs) as the channel material. The SiNW TFETs exhibit ION/IOFF ratio of ∼105, which is about an order of magnitude lower than that of their MOSFET counterparts, viz. ∼106, mainly due to their high turn‐on voltage and low band‐to‐band tunneling (BTBT) efficiency. The SiNW complementary TFET (c‐TFET) inverter shows ultralow DC power consumption (at VDD = 3 V, Ppeak = 11.4 nW and Pstby = 26.8 pW, respectively), which are about three to four orders of magnitude lower than those of the SiNW CMOS inverter, viz. 17.4 µW and 0.39 µW, respectively. Due to the different pros and cons for each of these devices, our top–down approach should open up the opportunity to integrate SiNW TFETs with SiNW MOSFETs on one plastic substrate for flexible hybrid SiNW TFET‐MOSFET integrated circuits, where both high‐performance and low‐power functionality are required.

Early encounters of a nascent membrane protein

An unbiased photo–cross-linking approach was used to probe the “molecular path” of a growing nascent Escherichia coli inner membrane protein (IMP) from the peptidyl transferase center to the surface of the ribosome. The nascent chain was initially in proximity to the ribosomal proteins L4 and L22 and subsequently contacted L23, which is indicative of progression through the ribosome via the main ribosomal tunnel. The signal recognition particle (SRP) started to interact with the nascent IMP and to target the ribosome–nascent chain complex to the Sec–YidC complex in the inner membrane when maximally half of the transmembrane domain (TM) was exposed from the ribosomal exit. The combined data suggest a flexible tunnel that may accommodate partially folded nascent proteins and parts of the SRP and SecY. Intraribosomal contacts of the nascent chain were not influenced by the presence of a functional TM in the ribosome.

Dynamics of a three-terminal mechanically flexible tunneling contact

The dynamics of a nanoelectromechanical system in the form of a three-terminal tunneling device is studied by analytical and numerical methods. The main results are the existence of bistable stationary states resulting in directly detectable chaotic behavior.