Tunnel Roof Research Articles

Analytical solutions and 3D numerical analyses of a shallow tunnel excavated in weak ground: a case from Turkey

Due to the increasing population and resulting transportation needs, the number of subway and high-speed railway projects has also increased. The geometric constraints of such projects have caused many tunnels to be built in weak ground. Thus, weak ground tunnelling has attracted the attention of tunnel engineers and researchers. The main purposes of this study are to analyse the T4 tunnel excavated in weak ground and to compare the results obtained from the analytical solutions and 3D numerical analyses. This study specifically considers the T4 tunnel support system used in the Ankara İzmir High Speed Railway Project (Afyonkarahisar-Banaz Section). The T4 tunnel route encounters weak ground composed of layers of extremely weak mudstone, clayey sand, weakly cemented sandstone, and silty–clay matrix with pebbles. The tunnel overburden ranges from 10 to 35 m, which is shallow. After the excavation work of the T4 tunnel, severe deformation and critical stability problems in the shallow part (where the overburden is approximately 10 m) were encountered inside the tunnel, leading to a halt in construction. This was followed by revisions to the tunnel support system, leading to successful completion of the tunnel excavation. Numerical simulations of the low overburden section are performed using the commercially available FLAC3D program that uses the finite difference method. The characteristics of insufficient/ineffective support systems and adequate support systems for shallow tunnels excavated through weak ground are discussed in this study. Additionally, problems that pertain to the tunnel itself and its support system are discussed. The results of the 3D numerical analyses and analytical solutions are compared, and the advantages of 3D numerical analyses are discussed. The importance and necessity of tunnel face stability and roof stability for tunnel stability in weak ground is illustrated. Consequently, solutions based on analytical and numerical analyses are presented, and the analysis methodology and solutions proposed in the study can help guide weak ground tunnelling design and evaluation.

A review on the performance of the underground tunnels against blast loading

The tunneling system has become an important part of the present infrastructure system in all over the world. Therefore, it has become important to ensure the safety of the tunnels against any type of man-made blasting activities or other accidental blasting occurrence. In order to evaluate the performance of the tunnels against blast loading, a detailed review is carried out. Based on the review in the last couple of decades, the various parameters such as tunnel lining materials, tunnel shapes, tunnel lining thickness, tunnel burial depth, charge weight and standoff distance are high influences on the performance of underground tunnels against blast loading. It was observed that the tunnel roof and the tunnel wall center are most vulnerable to the blast loads. Also, it was found that more of the tunnel lining thickness results in lesser deformation at the tunnel roof and the tunnel wall center. The increase in the burial depth of the tunnel would reduce the extent of damage to the tunnel caused by effects of surface blast loading. The stiffness and strength of the ground media may be enhanced against the effects of blast loading by grouting measures. The studies revealed that the lining materials possessing blast waves absorbing properties can be best suited to be used in tunnel linings. Further, it was observed that more damage was caused to the tunnels due to the magnitude of the charge weight. An increase in the blast load causes a significant increase in the fracture area, residual stress and lateral displacement caused to the tunnel by the action of blast load. The standoff distance of the blast load from the tunnel also plays a significant role in the damage of the tunnel. More is the distance between the charge and the tunnel, lesser damage caused to the tunnels. In addition to that, the lining thickness was predicted and the trend was calibrated and fitted logarithmically with the available results. Based on the observation from the literature, it is concluded that the use of a single lining material in the tunnel against blast loading was studied predominantly in the couple of decades. Further, the performance of the tunnels in combination of different tunnel lining materials against blast loading was found limited. The influence of barriers to save the underground tunnels against blast loading was found limited.

Osseous morphology of the medial epicondyle: an anatomoradiological study with potential clinical implications

The cubital tunnel is limited anteriorly by the medial epicondyle (ME), laterally by the medial collateral ligament, and superiorly by Osborne's fascia and the cubital tunnel retinaculum. Previous studies were mostly dedicated to the roof of the cubital tunnel, in the way that the study of the groove for ulnar nerve and ME anatomy is relatively scarce in the literature. We sought to describe the radiological anatomy of the groove for ulnar nerve and ME in healthy volunteers with multiplanar computed tomography (CT). We analyzed 3D CT images of 30 healthy volunteers (mean age 39years, range 18-66years). Nine variables were measured from the right elbow, including sizes, areas and angles in two different planes (coronal and axial). Mean ME width and length were 17.3 ± 3.5mm and 31.7 ± 4.5mm, respectively. According to categorical correlation studies, ME width (X) was deemed the most representative morphological characteristic because of the positive correlation to five other different anatomical measurements. A three-tiered anatomical classification was proposed based on data distribution. Large individual variation is found in the shape of ME, both in coronal and axial planes. The knowledge of individual osseous morphology is of great value potentially contributing to the surgical decision-making in patients affected by cubital tunnel syndrome.

The study of anatomy of tarsal tunnel in human fetuses by dissection method

Background: The flexor retinaculum of foot extends from the medial malleolus to the calcaneus to form the roof of tarsal tunnel. The structures passing through the tunnel are tendons of tibialis posterior, flexor digitorum longus & flexor hallucis longus, the tibial nerve & the posterior tibial artery with its venae comitantes. In order to understand the pathogenesis and improve the treatment of tarsal tunnel syndrome, we investigated the tarsal region of human foetuses anatomically. Methodology: The study was done on aborted/ stillborn foetuses in the Department of Anatomy of Sapthagiri Institute of Medical, Sciences, Bangalore. The structures passing under the flexor retinaculum of foot were dissected in 68 normal limbs of 34 foetuses of gestational age ranging from 10 weeks to term. Results: It was noted that the structures were arranged in two planes. Most commonly the superficial plane contained the tendon of tibialis posterior, posterior tibial artery & tibial nerve from medial to lateral side. In the deeper plane were the tendons of flexor digitorum longus medial to that of flexor hallucis longus. The bifurcation of tibial nerve mostly occurred under cover of flexor retinaculum and that of posterior tibial artery was distal to it. Conclusion: The understanding of arrangement of structures under cover of flexor retinaculum is important for diagnosis and treatment of tarsal tunnel syndrome in adults and also for the surgical correction of clubfoot, poliomyelitis & other deformities of foot in children.

Limit Analysis of Collapse Mechanisms for Tunnel Roofs Subjected to Pore Water Pressure: A Numerical Approach

The collapse mechanism of a circular unlined tunnel roof subjected to the pore water pressure under plane strain conditions is investigated in this article. First, the model of calculating the function expression of the detaching surface for the collapsing block is formed in the framework of the upper bound theorem of limit analysis and the extremum principle. The analytical solution of the pore water pressure around the tunnel in a two‐dimensional steady seepage field is employed in the equations of the model. Then, the numerical approach based on the Runge–Kutta algorithm and traversal search method is proposed to solve the complex equations. The obtained expression of the detaching surface for the collapsing block provides the shape of the collapsing block and a theoretical basis for designing the support force for tunnels. The proposed limit analysis method and numerical approach are verified by comparing with existing theoretical solutions and the numerical simulation result, and they are suitable for deep, shallow tunnels and layered strata. Moreover, the effects of different parameters on the collapse mechanism are investigated, and qualitative results are provided.

Roof Tunnel Stability by Wedge Analysis

Roof Tunnel Stability by Wedge Analysis

Stability of rectangular tunnel in Hoek–Brown rocks under steady-state groundwater flow

This research study aims to determine the stability of a rectangular tunnel excavated in rock masses obeying Hoek–Brown yield criteria under steady-state groundwater flow using lower bound limit analysis. During tunnelling in the presence of groundwater table (GWT) seepage forces are generated, which causes a decrease in the stability of rock mass. The total head distribution due to seepage is obtained by using two-dimensional finite element software Optum G2. The stability has been presented by a non-dimensional number σci/γ′maxH obtained for various combinations of B/h, H/h, Hw/h, σci/γwh, mi, GSI and D where B and h are width and height of the tunnel, respectively, H is the depth of the tunnel from the ground surface and Hw is the height of GWT from the tunnel roof, respectively, σci and γ′ are uniaxial compressive strength and submerged unit weight of rock, respectively, γw is the unit weight of water and mi, GSI and D are the Hoek–Brown parameters.

Osborne’s ligament: a cadaveric study and literature review

First described in 1957 by Dr Geoffrey Osborne, the Osborne ligament is defined as a band of tissue that connects the two heads of the flexor carpi ulnaris, which forms the roof of the cubital tunnel, between the medial epicondyle and the olecranon. We retrieved data from 16 elbows of 8 cadavers, measuring the length of the Osborne’s ligament in both maximum extension and in 90º flexion. Using this data, we managed to compare the differences between the left and right arm and also between male and female specimens. Our goal was to find statistically significant differences between the variables: males vs females; right vs left elbow; flexion vs extension. To our knowledge, no prior study has compared the length of this ligament between both elbows.

Evaluation of blast-resistant ability of shallow-buried reinforced concrete urban utility tunnel

To check the protective performance of shallow-buried steel bars reinforced concrete urban utility tunnel (UUT) under accidental explosion, a scaled shallow-buried UUT was designed, constructed and tested. In-field explosion experiments were carried out on this UUT. Dynamic responses, damage evolutions and failure styles of the UUT were revealed by the experiments. The tunnel roof is the most vulnerable component with longitudinal main cracks developing along the tunnel. When the scaled distance was larger than 1.10 m/kg1/3, no cracks appeared and the UUT was intact. When the scaled distance was reduced, the damage degree became more and more serious with longitudinal crack number developing from one at 1.000 m/kg1/3, two at 0.881 m/kg1/3, to three at 0.800 m/kg1/3. At 0.557 m/kg1/3 the width of the central crack abruptly increased to 11.2 mm and the UUT was seriously damaged. Damage level can be classified by the mid-span displacements of the roof, the width and number of the roof cracks, the accelerations and the maximum strains. The roof was simplified as an elastically restrained one-way slab. The Euler beam theory was adopted to analyze the dynamic responses, which are in agreement with the experiments in the first three cases.

Time-dependent deformation analysis of the surrounding rock mass around a tunnel

A numerical time-dependent model is established by incorporating the stress corrosion model into the three-dimensional discrete element grain-based model (3DEC-GBM) to analyze the fracture evolution and instability mechanism of the surrounding rock mass around a circular tunnel. The surrounding rock of the tunnel is assumed to be made from intact Yunnan sandstone formation, whose material properties were found using laboratory experiments (ignoring scale effects). The mesoscale mechanical stress corrosion parameters in the model are calibrated to reproduce the time-independent and -dependent deformation and failure of Yunnan sandstone observed in a laboratory. The model is validated against laboratory data and then further applied to analyze the time-independent and -dependent deformation of the surrounding rock of the tunnel. The fracture evolution around the tunnel instability is numerically visualized. The failure zone around the tunnel gradually extends deeper into the surrounding rock with time, and the location of failure at the roof and floor of the circular tunnel becomes more evident as the lateral pressure coefficient increases. We conclude that the model is not only able to simulate the location of the concentrated tensile and shear stress around the tunnel but also has important theoretical guidance and practical significance for the long-term stability study of tunnels.

Numerical analysis of coupled thermo-hydro-mechanical behavior in single- and multi-layer repository concepts for high-level radioactive waste disposal

A multi-layer repository concept is proposed as an alternative to the single-layer repository concept to improve the disposal density of high-level radioactive waste (HLW) in Korea. Numerical simulations are performed to compare the coupled thermo-hydro-mechanical (THM) behavior in the existing Korean reference HLW disposal system (KRS) based on the single-layer repository concept to that in the new multi-layer repository concept. The applicability of the multi-layer repository concept, such as double- and triple-layer repositories, for the disposal of HLW is analyzed with respect to a maximum temperature criterion of 100 °C, evolution of saturation and pore pressure, and mechanical stability. Maximum temperatures are below 100 °C in the double- and triple-layer repository concepts, as in the single-layer reference, although two peaks in simulated temperatures are observed during the evolution of the thermal pulse, resulting from superposition of decay heat at different vertical levels in the multi-layer repository concept. There is no significant difference in the evolution of pore pressure and saturation among the three concepts. The evolutions of mean effective stress at the bentonite blocks and backfill materials are also not significantly different between the single-, double-, and triple-layer repository concepts, because the hydraulic behavior is quite similar, resulting in almost the same change in swelling pressure. Stress states in the rock mass near the tunnels and deposition holes remain below the Mohr-Coulomb failure envelopes at the repositories of 500 m depth in the single-, double-, and triple-layer repository concept simulations. However, the stress states exceed the Mohr-Coulomb failure envelopes at the repositories below 500 m depth (beneath the top layer) in the double- and triple-layer repository concepts. Also, mechanical analysis shows high potential for spalling failure around the deposition holes and tunnel roof in the double- and triple-layer repository concepts. Subsidence in the double- and triple-layer concepts due to the construction of repositories is much deeper than that in the single-layer concept, and uplift induced by heating the rock mass due to the decay heat in the double- and triple-layer concepts is much higher than in the single-layer concept. These results indicate that multi-layer repositories with larger depth intervals between layers are a feasible alternative to the KRS to safely achieve higher disposal density.

The behavior and properties of Tehran alluvial soils under cyclic loading of urban vibrations—a case study: Arash-Esfandiar tunnel

Urban vibrations are increasing due to urban developments all over the world. These vibrations are daily applied to all surrounding structures, while their effects are not mainly considered in regular geotechnical analyses. This research will focus on how much urban vibrations cause displacement and strain in soil in a tunnel surrounding. In fact, using a case study data and combination of numerical analyses, empirical equations, and geodetic monitoring, the displacements and strains of soil caused by urban vibrations were calculated, compared, and evaluated. A traffic tunnel in Tehran (Arash-Esfandiar tunnel) was studied, in which a section was monitored by geodetic tools (simple instruments that are glued to the tunnel roof and their displacements measured using a theodolite). To complete the required data, microtremor recording equipment was employed to record real urban vibrations in the site. Then, using numerical modeling, the strains and displacements were obtained by applying the recorded vibrations to the model. The obtained strain values were employed to calculate the constant parameters of two existing empirical equations of Li and Selig and Chai and Miura. The obtained parameters conformed to the results of the previous studies and were all in the ranges given in those studies. Thus, the obtained parameters are proposed for the soil of Tehran for the first time. These parameters could be used for future studies on the effect of urban vibrations on Tehran soil. Furthermore, the calculated displacements were compared with the results of geodetic monitoring, which were in good agreement. The amounts of measured strains and calculated displacements show the importance of studies on the effects of urban vibrations.

Blast resistance evaluation of urban utility tunnel reinforced with BFRP bars

To improve corrosion-resistance of shallow-buried concrete urban utility tunnels (UUTs), basalt fiber reinforced polymer (BFRP) bars are applied to reinforce UUTs. As the UUT must have excellent survival capability under accidental explosions, a shallow-buried BFRP bars reinforced UUT (BBRU) was designed and constructed. Repetitive blast experiments were carried out on this BBRU. Dynamic responses, damage evolutions and failure styles of the BBRU under repetitive explosions were revealed. The tunnel roof is the most vulnerable component and longitudinal cracks develop along the tunnel. When the scaled distance is larger than 1.10 m/kg1/3, no cracks are observed in the experiments. When the BBRU is severely damaged, there are five cracks forming and developing along the roof. The roof is simplified as a clamped-supported one-way slab, proved by the observation that the maximum strain of the transverse bar is much larger than that of the longitudinal bar. Dynamic responses of the roof slab are predicted by dynamic Euler beam theory, which can consistently predict the roof displacement under large-scaled-distance explosion. Compared with the UUT reinforced with steel bars, the BBRU has advantages in blast resistance with smaller deflections and more evenly-distributed cracks when the scaled distance is smaller than 1.260 m/kg1/3 and the steel bars enter plastic state. Longer elastic defamation of the BFRP bars endows the UUT more excellent blast resistance under small-scaled-distance explosions.

Analysis on construction of the subway shield underpassing the underground pedestrian passage at close range

Numerical simulation analysis was conducted on the shield tunneling construction of the right line between Tangdong station and Huangcun station of Guangzhou rail transit line 21, the right line subway shield underpassing the underground pedestrian passage at close range. The numerical simulation vertical settlement of the ground and floor outside the foundation pit was compared with the field monitoring. The results show that the numerical analysis of the trend of land subsidence is consistent with the field monitoring, the thickness of the tunnel roof overburden has a great influence on the ground settlement. The ground settlement is mainly subsidence with thick overburden, while the thin overburden, the ground settlement is mainly uplift; the Equivalent Circular Zone formed by simultaneous grouting and secondary grouting has a great influence on the ground settlement. During the site construction, the tunneling parameters should be adjusted according to the site monitoring, and parameters such as soil and water pressure on the tunneling surface, overburden thickness, synchronous grouting pressure and secondary grouting pressure should be taken into comprehensive consideration to control the tunneling of shield underpassing the existing structures at close range.

Planning and Design of Prefabricated Beef Cattle Barns Constructed by Lightweight Concrete for Cold Climate Regions

It is very important to increase the income levels of livestock enterprises and engaged in animal production in our country by producing barns with modern and economic methods. In this study, prefabricated barn types which are built as opposed to traditionally built barns of the cold regions like Erzurum was revealed. Concerning tie-stall type barn, as for the number of animals 10, 20, and 30 headstocks discussed in the study. Moreover, the tie-stall prefabricated barn project is designed by using 50 tunnel type light-weight concrete materials to illustrate an example for commercial enterprises. At the end of the study, it was determined that prefabricated lightweight concrete barns were more economical than produced traditionally classical-type barns. As the number of cattle increased, the cost of barn decreased per cattle for cold climate conditions. The cost reduction percentage for 10-head barns was determined as 38.0% and 38.9% for lightweight concrete cylindrical roof and light concrete tunnel roofed barn types, respectively. These values were calculated as 60.5% - 61.4% for 20 head barns, and 59.9% - 60.4% for the 30 head barns. Among the studied barn types, it was found that the most economically suitable barn combination was a prefabricated barn with tunnel roof and lightweight concrete.

Deformation Mechanism and Stability Control of Roadway Surrounding Rock with Compound Roof: Research and Applications

In view of problems with roadways with a compound roof, such as the occurrence of instability in the roof strata, ease of separation of the layer caving, difficulty of maintenance, and poor safety, we established a mechanical calculation model of a roadway with compound roof using the elastic mechanics theory, taking the stability control of a roadway with compound roof at a coal mine in Guizhou Province, China as the research background, and based on the actual characteristics of the coal seam and the roof and floor slate. Expressions of the separation layer and instability limit load of compound roof were derived, and the calculation and verification were carried out in combination with the actual conditions. By means of numerical simulation, the distribution and evolution laws of stress, displacement and plastic zone of roadways with a compound roof were studied, and the deformation characteristics and instability mechanism of roadways with a compound roof were revealed: (1) in early stage deformation of roadway, the amount is large, the speed is fast, and the scale is wide; (2) compound roofs are vulnerable to abscission and instability, the bearing capacity of the two sides is low due to softness and cracking, the shear failure of side angles and vertex angles weakens the strength of surrounding rock, and the self-bearing capacity of surrounding rock is low; (3) the bolt and anchor bear relatively large tensile force, and the support structure is easy to be broken up. On this basis, the stability control principle of a roadway with compound roof tunnel was put forward: fast and timely support; high-strength bolt strong support; improving the stability of the roof and the bearing capacity of the two sides; restraining the shear failure of the key bearing parts such as the side angles and the bottom angles, and targeted stability control technology for roadways with a compound roof was developed. The field industrial test showed that the deformation of this roadway with a compound roof was effectively controlled and the overall stability of the roadway was effectively improved. The results of this study could provide useful reference for a roadway with a compound roof under similar conditions.

Instability mechanism of shallow tunnel in soft rock subjected to surcharge loads

The tunnel instability accidents caused by surcharge loading could even lead to ground settlement or collapse, damage to the existing municipal pipelines or inclination of the surgical buildings. Series of large-scale physical model test was conducted in this paper to reveal the failure mechanism of tunnel in soft rock subjected to surcharge loading. The non-contact full-field displacement measurement (i.e. Digital Image Correlation, DIC) was employed to obtain a detailed deformation of surrounding rock after excavation. A coupled numerical method combing the continuum (Finite Difference Method, FDM) and dis-continuum (Discrete Element Method, DEM) analysis was used to deal with the failure mechanism of tunnel excavation in rock mass. Good agreements between physical model test and numerical analysis approve the accuracy of the proposed FDM-DEM numerical model. It is found that the collapse mainly occurred in tunnel roof rather than in tunnel sidewall. The collapse zone shows a step-type increase with the increase of surcharge loads. The stress loosening zone (SLZ) in tunnel roof is larger than that in tunnel sidewall. The thickness of SLZ in tunnel roof can be used to design the length of the formed pressure anchors. The proposed large-scale model test with DIC method is applicable to the tunnel engineering study. Moreover, the results in this paper give some insights to secure excavation works and optimize supporting structures.

Effects of joint surface roughness and orientational anisotropy on characteristics of excavation damage zone in jointed rocks

Investigating the mechanical behavior of the excavation damage zone (EDZ) in jointed rocks is essential for underground openings. In this numerical study, the effects of joint surface roughness and orientational anisotropy on the size and shape of EDZ in jointed rocks were examined, based on a diversion tunnel excavated in columnar jointed rocks at the Baihetan Hydropower Station. The results showed that failure zones are usually at the two ends of the tunnel roof. Both open and shear zones are dependent on the JRC (Joint Roughness Coefficient) averages and standard deviations. With increasing standard deviations of JRC, the depths and areas of both open and shear zones generally increase. As the jointed rocks changing from anisotropic to isotropic, the shapes of EDZ are similar but rotate in jointed rocks. Under effects of water pressures, larger open zones appear in the lateral tunnel walls, and the depths of shear zones increase.

A theoretical explanation of natural ventilation at roof openings in urban road tunnels

Natural ventilation through openings in the roof of a road tunnel is a green technique that saves energy and greatly improves the air quality inside the tunnel. However, even though multiple tunnels with natural ventilation have been built in China, the theoretical basis for designing and constructing such tunnels is incomplete and there is as yet no uniform and systematic understanding of the natural-ventilation mechanism at the roof openings. Aimed at these problems and based on nearly six years of research and experiments, this paper presents a theoretical explanation of the flow-field characteristics in a road tunnel and the natural ventilation at its roof openings, including (i) the distribution and governing equations for the flow in the tunnel, (ii) the energy governing equation and (iii) the equation governing the natural ventilation at the roof openings. The presented theoretical formulas are consistent with the measured data. The main conclusions are as follows. (1) The airflow in a road tunnel is drag flow resulting from vehicles driving in a restricted space. The flow develops in a bottom-up manner and tends to be stable. The flow velocity is distributed double-logarithmically with height in the tunnel. (2) Moving vehicles are energy sources for the airflow in a road tunnel. Some of the energy transferred from a moving vehicle to the air increases the airflow velocity, while the rest is consumed in turbulence. As the flow develops, the kinetic energy increment decreases gradually and tends to zero, while the energy dissipation decreases gradually and tends to be stable. (3) The air above a road tunnel with roof openings can be sucked into the tunnel by the airflow induced therein by the unidirectional continuous traffic flow. This creates airflow from exterior to interior, but there is no corresponding ‘breathing’ phenomenon. The air inlet velocity at the roof openings differs considerably along the tunnel. It is maximum near the tunnel entrance and decreases gradually along the tunnel, presenting a concave curve.

Support Technology of Long Bolt in Roadway under Crushing Condition

In order to solve the problem that the roadway roof is large and easy to collapse under crushing conditions. Test shows that: Under the crushing condition, a considerable part of roadway surrounding rock deformation is in a given deformation state. The control effect of support resistance on surrounding rock deformation is limited at the level of existing technology. In this kind of roadway support, the deformation method of anchor cable high rigidity support should be abandoned. It is changed to adopt the long bolt with high elongation to adapt to the deformation of surrounding rock, and continue to provide high support resistance to prevent loose rock caving caused by roof collapse. Based on this, the supporting technology of replacing anchor cable with docking bolt is put forward to increase the coordination between supporting member and roadway surrounding rock deformation. The industrial test results of Baode coal mine show that the technology can adapt to the deformation of surrounding rock and effectively prevent the tunnel roof from caving due to the break of anchor cable.