Tunnel Depth Research Articles

Three-dimensional finite difference analysis of shallow sprayed concrete tunnels crossing a reverse fault or a normal fault: A parametric study

Urban tunnels crossing faults are always at the risk of severe damages. In this paper, the effects of a reverse and a normal fault movement on a transversely crossing shallow shotcreted tunnel are investigated by 3D finite difference analysis. After verifying the accuracy of the numerical simulation predictions with the centrifuge physical model results, a parametric study is then conducted. That is, the effects of various parameters such as the sprayed concrete thickness, the geo-mechanical properties of soil, the tunnel depth, and the fault plane dip angle are studied on the displacements of the ground surface and the tunnel structure, and on the plastic strains of the soil mass around tunnel. The results of each case of reverse and normal faulting are independently discussed and then compared with each other. It is obtained that deeper tunnels show greater displacements for both types of faulting.

Numerical simulation of the effect of confining pressure and tunnel depth on the vertical settlement using particle flow code (with direct tensile strength calibration in PFC Modeling)

In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. Acircular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof. The maximum of settlement occurs when center of tunnel was situated 15 m below the ground surface. The settlement decreases by increasing the distance between tunnel center line and measuring circles in the ground surface. The minimum of settlement occurs when center of circular tunnel was situated 60 m below the surface ground. Its to be note that the settlement increase by decreasing the confining pressure.

A Novel Experimental Study on the Effects of Soil and Faults’ Properties on Tunnels Induced by Normal and Reverse Faults

Due to the world population increasing considerably, there is a need for efficient public transportation, such as the subway. However, it has become a major concern to geotechnical engineers that the development and construction of subways are held underground where faults exist, as it will be a major risk to any structure if the fault is still active. Several seismic events, such as the earthquakes in Taiwan in 1999, China in 2008, and Malaysia (Sabah) in 2015, caused by fault ruptures, signify the importance of this study. In this paper, a physical model of 1000 mm in height, 3000 mm in length, and 1000 mm in width, which is the largest single gravity (1g) model for simulation faults (normal and reverse) ever built, was fabricated to evaluate the influence of various soil properties, various fault angles, and tunnel depths on tunnels affected by normal and reverse faults. The effects of various soil properties, such as water content, particle size, cohesion, and friction angle, had revealed major changes (approximately by 34%, 39%, 64%, and 39%, respectively) in tunnel displacements. Results also showed that increasing of fault angle could increase the tunnel displacement as much as two times. In addition, when a tunnel is located close to the ground surface, 22% less displacement was found to have occurred to the tunnel. With the results obtained from the physical model, simulation had been made using plane strain and axial symmetry (PLAXIS) software. The comparison made between rock and soft soil showed that soft soil imposed two times more displacements than rock, and an existence of foundation in soft soil and rock can decrease the tunnel displacements by 6% and 4%, respectively. This paper asserts that besides the structural design of a tunnel, the geotechnical design also has a major impact on the safety and robustness of the tunnel, in which aspects such as soil properties, tunnel depth, and fault angle have a strong influence on tunnel damages which were not considered in previous research, despite their importance.

Correction and Regularity of Influence Coefficient for Double-Line Tunnel Settling

In the construction of most double-tunnel subways and postexcavation tunnels, settlement deformation is an important problem. In this study, we analyzed the problem using monitoring data from the Huai’anqiao-Xisanjiao section (an anhydrous sand layer) of the first phase of China’s Shijiazhuang Rail Transit Line 3 project. First, FLAC3D software was used to establish a numerical model. Grouting pressure was assumed to be uniformly distributed. The settlement value of a measured point was calculated as the test data, and the range of the correction factor was obtained by an influence coefficient formula. The correction factor was revised in accordance with the measured data, and the correction factors for the properties of Shijiazhuang sand were obtained. For the first tunnel measuring point, the correction factor was –0.2; for the rear of the tunnel point the correction factor was 0.2. Finally, different numerical models were established, and the influence on the correction factor of such factors as tunnel depth and horizontal spacing, slope ratio, and tunnel spacing were established by using a control variable method.

An analytical method of continuous upper bound limit analysis for the stability of shallow shield tunnels in cohesive-frictional soils

For stability analysis of shallow shield tunnels in cohesive-frictional (clayey–sandy) soils, an analytical method of continuous upper bound limit analysis is developed to determine the most critical slip line position and the minimum required tunnel support pressure. The ground displacement field due to composite volume loss is calculated using a complex variable solution, and the optimization problem is solved by employing the particle swarm optimization technique. Energy dissipation at the potential slip boundary, which is determined through a system of tracking schemes, and in the corresponding potential plastic zone is taken into account. Example calculations are carried out to verify the proposed method via finite element simulations and comparisons with solutions from existing methods, and to study the effects of soil strength properties and tunnel size and depth. The results show that both the internal friction and the cohesion of the surrounding soil may help reduce the range of the potential collapse zone and the magnitude of the necessary support pressure. This study represents the first attempt to deal with cohesive-frictional soils via an analytical and continuous approach, and the developed method can be extended for various tunnel and other geotechnical stability problems involving cohesive-frictional soils.

Anatomic limitations of biceps tenodesis using an interference screw for Asian people: a cadaveric study

BackgroundBiceps tenodesis using an interference screw has been commonly performed in clinical practice because of pathologic changes. Especially, the tenodesis distal to the bicipital groove, such as suprapectoral tenodesis (SPT) and subpectoral tenodesis (SBT), has been performed to avoid residual anterior shoulder pain. However, the techniques were developed based on research tested on Western population, and it is unknown whether they are applicable to Asian individuals, who have a smaller humerus than Western. The purpose of this study was to investigate the anatomic limitations of the biceps tenodesis using an interference screw for Asians.MethodsWe analyzed 22 fixed Japanese cadavers. We measured the length of the suprapectoral tenodesis zone (STZ), which is the area from the distal end of the lesser tuberosity to the proximal border of the insertion of the pectoralis major muscle tendon (PMMT) along the course of the biceps tendon, for the SPT. We also measured the bone tunnel depths (BTDs) for the SPT just distal to the lesser tuberosity along the course of the biceps tendon and, similarly, for the SBT just distal to the PMMT insertion. Finally, we analyzed the sexual differences and correlations of the measured values with the entire humeral length.ResultsIn 9 shoulders (40.9%), the proximal border of the PMMT insertion was attached more proximally than the distal end of the lesser tuberosity, and the length of the STZ was negative. The mean BTDs in the SPT and SBT zones were 19.6 and 14.9 mm, respectively. In 11 shoulders (50%), the BTD in the SBT zone was shorter than 15 mm. The lengths of the STZ or BTDs in the SPT and SBT zones did not show statistical differences between sexes and were not correlated with the entire humeral length.ConclusionAsian patients would have anatomic limitations as follows for the biceps tenodesis regardless of their sex or body size. In anomalous PMMT cases, when the SPT was performed just proximal to the PMMT insertion, the bone tunnel entered into the bicipital groove. On the other hand, when the SPT was performed distal to the lesser tuberosity, a part of the PMMT insertion would be injured. Regarding the SBT, an interference screw with a length of ≥12 mm, which is commonly used in Western countries, is too long for Asians.

Three-Dimensional Analysis of Circular Tunnel Headings Using Broms and Bennermark’s Original Stability Number

The stability of a tunnel face is described by the combined effects of surcharge load, self-weight of the soil, and internal supporting pressure. This combination can cause failure in either blowout or collapse. Since the plastic shearing in undrained soils is independent of loading directions in homogeneous soils, this paper studies Broms and Bennermark’s original stability number for the circular tunnel heading in cohesive soil using three-dimensional upper and lower bound finite-element limit analysis. Dimensionless ratios are used in this study to cover practical soil parameters and tunnel depths for collapse and blowout analyses. Numerical results of critical stability numbers are compared with two-dimensional and three-dimensional solutions available in the literature. Stability design charts and tables produced in this paper can be used to estimate safety factors for various design parameters.

Total deformation prediction of the typical loess tunnels

The total deformation of loess tunnels is an essential basis for determining reasonable support timing, optimizing support parameters, and predicting collapses. Accurately predicting the total deformation is of considerable significance to the safe design and construction of loess tunnels. In this paper, a representative data sample set of the total deformation in loess tunnels was obtained using numerical simulations, and a back-propagation neural network (BPNN) was adopted. The input parameters were the bulk density, water content, elastic modulus, Poisson’s ratio, cohesion, internal friction angle of the loess, tunnel depth, and primary support strength. The output parameters were the total vertical and horizontal convergence deformation of the loess tunnel. The prediction results showed that the BPNN model could effectively predict the total deformation of a typical loess tunnel. Finally, the sensitivity analysis of the impact factors showed that the primary support strength and internal friction angle were parameters affecting the total deformation the most and least, respectively. This study can provide targeted guidance for the safe construction of loess tunnels.

Parametric Study of Pile Response to Side-by-Side Twin Tunneling in Stiff Clay

A three dimensional coupled-consolidation numerical parametric study was carried out in order to gain new insight of single pile response to side-by-side twin tunneling in saturated stiff clay. An advanced hypo plasticity (clay) constitutive model with small-strain stiffness was adopted. The effects of relative to the pile tunnel depths were investigated by simulating the twin tunnels near the pile at various depths of tunnels, namely near the pile shaft, adjacent to the pile toe, and below the pile toe. It was found that the second tunneling in each case resulted in a larger settlement than the one due to the first tunneling with a maximum percentage difference of 175% in the case of twin tunneling near the mid-depth of the shaft. This occurred due to the degradation of clay stiffness around the pile during the first tunneling. Conversely, the first tunneling-induced bending moment was reduced substantially during the second tunneling. The most critical location of twin tunnels relative to the pile was found to be below the pile toe.

The effect of engineering geology on the rock load and squeezing potential in Lot2 of Imamzadeh-Hashem tunnel

The load entering from the ground surrounding on the tunnel’s lining is one of the effective parameters in the designation of a tunnel. The amount of this parameter, which is called Rock load in a rocky environment, depends on several factors such as the overburden thickness, geological and geomechanical conditions and the depth of tunnel. In the present study, the amount of rock load for the Lot 2 of Imamzadeh Hashem Tunnel (L2IHT) has been evaluated using various methods and the effect of geological characteristics of the rock units on the tunnel route has been investigated. For this purpose, different methods for estimating the rock load were introduced firstly, and then the amount of this parameter for the tunnel was estimated using these methods. To evaluate the thickness of the plastic zone around the tunnel, the numerical method, finite difference code of FLAC3D software, has been used. Comparison of the results obtained from different methods and their analysis indicates that the rock load applying from H-4 and H-10 rock units is more than the other units. This happens because of the specific geological characteristics of these rock units such as high degree of crushing due to the geological factors and being in the faulted zone. Therefore, it is required for the stronger lining of the tunnel in the range of these units.

Effect of structures density and tunnel depth on the tunnel-soil-structures dynamical interaction

Abstract This paper studies the presence effects of two or more adjacent structures on the tunnel responses and vice versa due to surface and underground traffic loads. The study is numerically carried out by using Finite element Plaxis2D software©. The obtained results demonstrate that the dynamical interaction between the tunnel and the structures is significantly influenced by varying the number and distance between the adjacent structures, the depth of the tunnel and the location of the traffic load. These results can be considered and used in realistic and practical cases and also to help build efficient and more comfortable construction projects.

Theoretical and Experimental Study on Rock Resistance Coefficient of Soft Rock Tunnel Considering Creep Effect

Creep deformation properties of soft rock are studied based on the visco-elastoplastic model. Combining with the generalized Hoek–Brown criterion, the calculation formula for rock resistance coefficient (RRC) of soft rock tunnel is deduced based on the creep effect, and the formula is applied to Tianjiashan tunnel, which is a typical soft rock tunnel. Besides, the influences of creep effect and tunnel buried depth on RRC are discussed. As shown in the results, the RRC which takes creep effect into consideration is declined, and the RRC decreases with the increase of tunnel depth and in situ stress. After the creep effect of surrounding rock is fully developed, the values of RRC are from 140.92 to 24.09 MP m−1 at different buried depth, which indicates that although soft rock tunnels have poor stability, the surrounding rock still possess certain elastic resistance and self-bearing capacity.

Performance of segmental and shotcrete linings in shallow tunnels crossing a transverse strike-slip faulting

Abstract In this paper, three-dimensional numerical modeling is performed to study the effects of strike-slip fault movement on the performance of shotcrete and segmental linings in shallow tunnels that transversely cross the fault. For this purpose, a parametric study is conducted on lining thickness, soil geo-mechanical properties, tunnel depth, and fault dip angle to assess their influence on the tunnel movements and deformation. A comparison between the segmental and the shotcrete tunnels is made to highlight their performance. The results show that the greater strike-slip fault dip angle increases the separation of the lining segments. As well, after faulting, the maximum tunnel displacement in denser soils is greater than in loose soils.

Prediction of the tunnel displacement induced by laterally adjacent excavations using multivariate adaptive regression splines

Excavations may cause excessive ground movements, resulting in potential damage to laterally adjacent tunnels. The aim of this investigation is to present a simple assessment technique using a multivariate adaptive regression splines (MARS) model, which can map the nonlinear interactions between the influencing factors and the maximum horizontal deformation of tunnels. A high-quality case history in Tianjin, China, is presented to illustrate the effect of excavation on the tunnel deformation and to validate the FEM. The hypothetical data produced by the FEM provide a basis for developing the proposed MARS model. Based on the proposed model, the independent and coupled effects of the input variables (i.e. the normalized buried depth of tunnels Ht/He, the normalized horizontal distance between tunnels and retaining structures Lt/He, and the maximum horizontal displacement of retaining structures, δRmax) on the tunnel response are analysed. The prediction precision and accuracy of the MARS model are validated via the artificial data and the collected case histories.

Validity of computed tomographic measurements and morphological comparison of cubital tunnel in idiopathic cubital tunnel syndrome

BackgroundUlnar neuropathy is a common reason for referral to hand surgeons, and 10 to 30% of cubital tunnel syndrome (CuTS) is idiopathic. We hypothesized that the cause of idiopathic CuTS is in the bony structure.MethodsWe analyzed 79 elbows (39 idiopathic CuTS and 40 without CuTS symptom) using computed tomography and Materialize Mimics software to compare the differences between the two groups. We proposed a new bony cubital tunnel with a new boundary that could play a role in ulnar nerve compression symptom.ResultsThe mean cubital tunnel volume was 1245.6 mm3 in all patients, 1180.6 mm3 in CuTS patients, and 1282.3 mm3 in the control group. A significant difference (p = 0.015) between two groups was found. Bony cubital tunnel cross-sectional area, cubital tunnel depth, and cubital tunnel angle also showed significant differences.ConclusionThe shape of the bony cubital tunnel is an important cause of CuTS, and the normal variation of the volume and cross-sectional area of the cubital tunnel and cubital tunnel angle could influence the occurrence of idiopathic CuTS.

Prediction Model for Deformation Risk Grade of the Soft Rock Tunnel Based on GRA - Extension

The soft rock tunnel is affected by geological factors and construction factors and it is easy to produce large deformation, which leads to cracking and spalling of the primary support, distorting the steel frame, uplifting the tunnel bottom, and cracking of the secondary lining, and has a serious impact on the safety of tunnel construction and operation. In this paper, the surrounding rock strength, rock mass integrity, groundwater condition, tunnel depth, excavation method, support strength and primary support closure time were chosen as the main factors affecting the deformation of soft rock tunnels. According to the actual monitoring and measurement data of the tunnel, the factor weights were calculated using GRA. Extension theory is used to establish the prediction model for the soft rock tunnel deformation risk. According to the comparison between actual deformation and model prediction deformation, the prediction model of tunnel deformation risk grade has high applicable performance in tunnel deformation risk assessment, which provides a reference for construction optimization of soft rock tunnel.

Seismic capacity assessment of cracked lining tunnel based on the pseudo-static method

Crack is one of the most common lining deteriorations, which is generally regarded as an indicator of tunnel safety. The present study investigated the lining cracks of 11 tunnels which are 200 km away from the Longmenshan fault zone. In order to evaluate the seismic capacity of these tunnels with longitudinal cracks in the permanent lining, a modified deformation-based pseudo-static assessment method was developed. The propagation of lining cracks was simulated by a reconstructed damaged plasticity constitutive model of reinforced concrete. The analyses adopted a two-dimensional finite element model and took tunnel depth, initial crack position, and the interaction between soil and lining structures into account. The analysis results showed that the modified evaluation method could simulate the damage process of lining structures under the action of seismic shear wave well. The results also showed that the failure modes of tunnels with cracked permanent lining were different with different burial depth in an earthquake. The cracks in the spandrel had the greatest impact on the seismic capacity of tunnels and should be reinforced in time before the earthquake. In addition, the interaction between the temporary support and permanent lining had little effect on the damage process of linings but had an impact on the damage speed. This study can provide a reference for the safety assessment of cracked lining tunnels in seismically active areas and help to determine the reinforcement measures and time more reasonably.

Prediction of water inflow in Tsingtao subsea tunnel based on the superposition principle

Prediction of water inflow is a key scientific problem in construction of subsea tunnels. Tsingtao subsea tunnel is taken as the research object, and a calculation method for predicting and analyzing the water inflow based on superposition principle is proposed by applying theoretical analysis, numerical simulation and field monitoring. First of all, the computation model of seepage field and water inflow in the subsea tunnel is established. The permeability coefficients of strongly weathered layer and moderately weathered layer are determined according to the permeability coefficient of slightly weathered layer. Secondly, based on the well flow model of infinite confined aquifer, the double water gushing points calculation model is presented, and then the model is simplified into single water gushing point calculation model. The equivalent calculation formulas of water inflow under the condition of multi-horizontal strata are derived. The water inflow which is affected by the tunnel depth, radius and seawater depth is analyzed. Thirdly, the proposed method is compared with the engineering practice and numerical simulation, which verifies the accuracy and feasibility of the method. The results show that: (1) The water inflow of subsea tunnels increases with the permeability coefficients of strongly and moderately weathered layers. (2) The water inflow of subsea tunnels first decreases and then increases with the tunnel depth increasing. (3) The water inflow of subsea tunnels increases linearly with the tunnel radius and seawater depth.

Study on the Mechanism of Grouting Under Different Tunnel Depth of Cross Passage

Based on a cross passage construction project, numerical simulation and analysis were carried out, which revealed the mechanism of grouting in the construction of the subway cross passage. The effects of different grouting properties, different grouting range and tunnel depth on the reinforcement were studied. According to different tunnel depth, the properties and range of grouting were determined. The characteristics of surface settlement, lining force, stress and plastic zone distribution after cross passage construction were compared. The result shows that: (1) In the case of the above geological properties, for a tunnel with a depth of 9 m (1.5 D), the grouting property is fair and the grouting range is 2 m can prevent the occurrence of failure. (2) Due to the higher stress, larger tunnel depth needs to increase grouting range to prevent the occurrence of failure. This research can provide some reference and guidance for similar projects.

The Volume Loss: Real Estimation and Its Effect on Surface Settlements Due to Excavation of Tabriz Metro Tunnel

A case study including monitoring data of surface settlements induced by tunneling in Tabriz metro line 2 is presented. This study focuses on about 4.6 km EPB-TBM tunneling works from west depot to S5 Station, where the tunnel was being excavated in sandy and fine grained alluvial, generally below the water table. Although volume loss (VL) has an important effect in estimating the ground movements, the prediction of optimum VL relies on the data from previous case studies with similar ground condition. Realizing unavailability of VL data based on Tabriz geological conditions, from the actual occurred settlements, VL was back-calculates by Gaussian empirical equation to get the VL percentage. Also a back-analysis was done to obtain settlement trough width constant K in both longitudinal and transverse sections. Furthermore, face support and tail grouting pressures were monitored, and compared with COB method. Likewise, a 3D finite element multi-step simulation was carried out by ABAQUS to predict surface settlements. There was concluded that, in longitudinal sections, numerical simulation is not capable of reproducing the recorded Smax, applying Mohr–Coulomb model. Smax can be estimated accurately by Gaussian curves, but the distribution of longitudinal surface settlement doesn’t match with these curves. The obtained VL varies from 0.13 to 1.35%, with an average value of 0.46%. The range of the VL increases significantly with the decrease of the tunnel depth. For the studied case, in shallow tunnels (C/D ≃ 1) high values of VL are occurred despite good control of face and grout injection pressures.