Shear testing on rock tunnel models under constant normal stress conditions

Large shear deformation problems are frequently encountered in geotechnical engineering.To expose the shear failure mechanism of rock tunnels,compression-shear tests for rock models with circular tunnel were carried out,including single tunnel and adjacent double tunnels.The failure process is recorded by the external video and miniature cameras around the tunnel,accompanied by real-time acoustic emission monitoring.The experiments indicate that the shearing processes of rock tunnel can be divided into four steps:(i)cracks appeared around tunnels,(ii)shear cracks and spalling ejection developed,(iii)floor warping occurred,and(iv)shear cracks ran through the tunnel model.Besides,the roughness of the sheared fracture surface decreased with the increase in normal stress.Corresponding numerical simulation indicates that there are tensile stress concentrations and compressive stress concentrations around the tunnel during the shearing process,while the compressive stress concentration areas are under high risk of failure and the existence of adjacent tunnels will increase the degree of stress concentration.

Numerical Investigation of the Effects of Wind Tunnel Model Vibrations on the Measured Aerodynamic Properties of Airfoils and Wings

This paper presents a numerical prediction of the unsteady flow field around oscillating airfoils at high angles of attack by solving unsteady Reynolds-averaged Navier-Stokes equations with SST turbulence model in order to simulate the effects of wind tunnel model vibrations on the aerodynamic properties of airfoils,especially high-aspect-ratio wings in a wind tunnel.The effects of the phase lagging between different modes of oscillations,i.e.,the airfoil plunging oscillation mode,the pitching oscillation mode,and the forward-backward oscillation mode,are also studied.It is shown that the vibrations (oscillations) of airfoils can cause the unsteady shedding of large-size separated vortex to precede the stationary stall incidence,hence lead to a stall onset at some earlier (lower) incidence than that in the steady sense.The different phase lagging has different effect on the flow field.When the pitching oscillation mode has small phase lagging behind the plunging oscillation mode,the effect of vibrations is large.Besides,if the amplitude of the oscillations is large enough,and the different modes of vibrations match or combine appropriately,the unsteady stall may occur 2° earlier in angle of attack than the case where airfoils keep stationary.

Evaluation of a Micro-scale Wind Model's Performance over Realistic Building Clusters Using Wind Tunnel Experiments

The simulation performance over complex building clusters of a wind simulation model（Wind Information Field Fast Analysis model, WIFFA） in a micro-scale air pollutant dispersion model system（Urban Microscale Air Pollution dispersion Simulation model, UMAPS） is evaluated using various wind tunnel experimental data including the CEDVAL（Compilation of Experimental Data for Validation of Micro-Scale Dispersion Models） wind tunnel experiment data and the NJU-FZ experiment data（Nanjing University-Fang Zhuang neighborhood wind tunnel experiment data）. The results show that the wind model can reproduce the vortexes triggered by urban buildings well, and the flow patterns in urban street canyons and building clusters can also be represented. Due to the complex shapes of buildings and their distributions, the simulation deviations/discrepancies from the measurements are usually caused by the simplification of the building shapes and the determination of the key zone sizes. The computational efficiencies of different cases are also discussed in this paper. The model has a high computational efficiency compared to traditional numerical models that solve the Navier–Stokes equations, and can produce very high-resolution（1–5 m） wind fields of a complex neighborhood scale urban building canopy（～ 1 km ×1km） in less than 3 min when run on a personal computer.

Trend analysis and comparison of basic parameters for tunnel blast design models

One of the most important factors influencing on a tunnel blast efficiency is the proper design of blasting pattern. Among blasting parameters, blasthole diameter and tunnel face area are more significant so that any change in these parameters could finally affect on specific charge and specific drilling. There are mainly two groups of methods for tunnel blast design categorized based on the parallel cuts and angular cuts. In this research, a software for tunnel blast design was developed to analyze the effect and sensitiveness of blasthole diameter and the tunnel face area on blasting results in different blast design models. Using the software, it is quickly possible to determine specific charge, specific drilling and number of blastholes for each blast design model. The relations between both of blasthole diameters and the tunnel face area with the above parameters in different blast design models were then investigated to yield a set of equations with the highest correlations to compare the methods. The results showed that angular method requires more blasthole numbers than parallel method in similar condition(blasthole diameter and tunnel face area). Moreover, the specific charge values yielded by the two methods are approximately the same and very close together.

Finite-State Markov Wireless Channel Modeling for Railway Tunnel Environments

In recent years,high-speed railways(HSRs)have developed rapidly with a high transportation capacity and high comfort level.A tunnel is a complex high-speed rail terrain environment.It is very important to establish an accurate channel propagation model for a railway tunnel environment to improve the safety of HSR operation.In this paper,a method for finite-state Markov chain(FSMC)channel modeling with least squares fitting based on non-uniform interval division is proposed.First,a path loss model is obtained according to measured data.The communication distance between the transmitter and receiver in the tunnel is non-uniformly divided into several large non-overlapping intervals based on the path loss model.Then,the Lloyd-Max quantization method is used to determine the threshold of the signal-to-noise ratio(SNR)and the channel state quantization value and obtain the FSMC state transition probability matrix.Simulation experiments show that the proposed wireless channel model has a low mean square error(MSE)and can accurately predict the received signal power in a railway tunnel environment.

Examining the effect of adverse geological conditions on jamming of a single shielded TBM in Uluabat tunnel using numerical modeling

Severe shield jamming events have been reported during excavation of Uluabat tunnel through adverse geological conditions, which resulted in several stoppages at advancing a single shielded tunnel boring machine(TBM). To study the jamming mechanism, three-dimensional(3D) simulation of the machine and surrounding ground was implemented using the finite difference code FLAC3D. Numerical analyses were performed for three sections along the tunnel with a higher risk for entrapment due to the combination of overburden and geological conditions. The computational results including longitudinal displacement contours and ground pressure profiles around the shield allow a better understanding of ground behavior within the excavation. Furthermore, they allow realistically assessing the impact of adverse geological conditions on shield jamming. The calculated thrust forces, which are required to move the machine forward, are in good agreement with field observations and measurements. It also proves that the numerical analysis can effectively be used for evaluating the effect of adverse geological environment on TBM entrapments and can be applied to prediction of loads on the shield and preestimating of the required thrust force during excavation through adverse ground conditions.

Model test study of frost heaving pressures in tunnels excavated in fractured rock mass in cold regions

Based on the similarity theory, taking the horseshoe, city-gate and round linings as examples, the value and distribution regularities of normal frost heaving pressures （hereinafter as frost heaving pressures） in tunnels excavated in fractured rock mass in cold regions under different constraints and freezing depths were studied by a test model. It was found that the larger the frozen depth, the larger the frost heaving pressure, and the stronger the top constraint, the larger the frost heaving pressure. For the horseshoe lining and city-gate lining, the top constraint has a greater effect on the frost heaving pressures on the arch and the inverted arch. For the round lining, the influences of the top constraint on the frost heaving pressure in all linings are almost the same. The frost heaving pressure is maximum on the city-gate lining and minimal on the round lining. The largest frost heaving pressure all occur near the foot of the inverted arch for the three kinds of lining. Thus, the test data basically coincide with the observed in situ data.

A unified critical state model for geomaterials with an application to tunnelling

This paper is prepared in honour of Professor E.T.Brown for his outstanding contributions to rock mechanics and geotechnical engineering and also for his personal influence on the first author’s research career in geomechanics and geotechnical engineering.As a result,we have picked a topic that reflects two key research areas in which Professor E.T.Brown has made seminal contributions over a long and distinguished career.These two areas are concerned with the application of the critical state concept to modelling geomaterials and the analysis of underground excavation or tunnelling in geomaterials.Partially due to Professor Brown’s influence,the first author has also been conducting research in these two areas over many years.In particular,this paper aims to describe briefly the development of a unified critical state model for geomaterials together with an application to cavity contraction problems and tunnelling in soils.

Fisher discriminant analysis model and its application for prediction of classification of rockburst in deep-buried long tunnel

A Fisher discriminant analysis (FDA) model for the prediction of classification of rockburst in deep-buried long tunnel was established based on the Fisher discriminant theory and the actual characteristics of the project.First, the major factors of rockburst,such as the maximum tangential stress of the cavern wall σ_θ, uniaxial compressive strength σ_c, uniaxial tensile strength σ_t, and the elastic energy index of rock W_(et), were taken into account in the analysis.Three factors, Stress coefficient σ_θlσ_c, rock brittleness coefficient σ_c/σ_t, and elastic energy index W_(et), were defined as the criterion indices for rockburst prediction in the proposed model.After training and testing of 12 sets of measured data, the discriminant functions of FDA were solved, and the ratio of misdiscrimination is zero.Moreover, the proposed model was used to predict rockbursts of Qinling tunnel along Xi'an-Ankang railway.The results show that three forecast results are identical with the actual situation.Therefore, the prediction accuracy of the FDA model is acceptable.

Numerical modeling of time-dependent deformation and induced stresses in concrete pipes constructed in Queenston shale using micro-tunneling technique

Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids（LFs） used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio（K;）, and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining.The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling.

Three dimensional modeling and developing of tunnel based on objectarx technique

Studied the methods of 3D modeling in tunnel of underground and realized the3D visual expression of tunnel using language Object ARX CAD.

Anomaly-based model for detecting HTTP-tunnel traffic using network behavior analysis

Increasing time-spent online has amplified users' exposure to the threat of information leakage.Although existing security systems(such as firewalls and intrusion detection systems) can satisfy most of the security requirements of network administrators,they are not suitable for detecting the activities of applying the HTTP-tunnel technique to steal users' private information.This paper focuses on a network behavior-based method to address the limitations of the existing protection systems.At first,it analyzes the normal network behavior pattern over HTTP traffic and select four features.Then,it presents an anomaly-based detection model that applies a hierarchical clustering technique and a scoring mechanism.It also uses real-world data to validate that the selected features are useful.The experiments have demonstrated that the model could achieve over 93%hit-rate with only about 3%falsepositive rate.It is regarded confidently that the approach is a complementary technique to the existing security systems.

An analytic model for gate-all-around silicon nanowire tunneling field effect transistors

An analytical model of gate-all-around （GAA） silicon nanowire tunneling field effect transistors （NW-TFETs） is developted based on the surface potential solutions in the channel direction and considering the band to band tunneling （BTBT） efficiency. The three-dimensional Poisson equation is solved to obtain the surface potential distributions in the partition regions along the channel direction for the NW-TFET, and a tunneling current model using Kane＇s expression is developed. The validity of the developed model is shown by the good agreement between the model predictions and the TCAD simulation results.

Train crossing modeling based on measurements and best numerical approximation in subway tunnels

Communication based train control systems(CBTC) must work even in the worst situation—train crossing.This paper models the propagation characteristics in one of the most common and pivotal scenarios—train crossing in subway tunnels which is rarely mentioned in previous publications.Firsdy,measurements for train crossing scenario at 2.4 GHz in a real subway line in Madrid have been made.The field measurement is the most reliable way to reveal the propagation characteristics involving shadowing effect and fast fading.Moreover,to precisely describe the fast fading distribution and eliminate the inevitable weak points of traditional fitting way,a best numerical approximation method using Legendre orthogonal polynomials has been proposed.Comparisons show that this method works better and is of greater physical significance.Finally,a complete statistical model is given and all the coefficients can be applied by system designers for the link and system level simulations.

Model test to investigate failure mechanism and loading characteristics of shallow-bias tunnels with small clear distance

Based on the similarity theory,a tunnel excavation simulation testing system under typical unsymmetrical loading conditions was established.Using this system,the failure mechanism of surrounding rock of shallow-bias tunnels with small clear distance was analyzed along with the load characteristics.The results show that:1) The failure process of surrounding rock of shallow-bias tunnels with small clear distance consists of structural and stratum deformation induced by tunnel excavation; Microfracture surfaces are formed in the tunnel surrounding rock and extend deep into the rock mass in a larger density; Tensile cracking occurs in shallow position on the deep-buried side,with shear slip in deep rock mass.In the meantime,rapid deformation and slip take place on the shallow-buried side until the surrounding rocks totally collapse.The production and development of micro-fracture surfaces in the tunnel surrounding rock and tensile cracking in the shallow position on the deep-buried side represent the key stages of failure.2) The final failure mode is featured by an inverted conical fracture with tunnel arch as its top and the slope at tunnel entrance slope as its bottom.The range of failure on the deep-buried side is significantly larger than that on the shallow-buried side.Such difference becomes more prominent with the increasing bias angle.What distinguishes it from the "linear fracture surface" model is that the model proposed has a larger fracture angle on the two sides.Moreover,the bottom of the fracture is located at the springing line of tunnel arch.3) The total vertical load increases with bias angle.Compared with the existing methods,the unsymmetrical loading effect in measurement is more prominent.At last,countermeasures are proposed according to the analysis results: during engineering process,1) The surrounding rock mass on the deep-buried side should be reinforced apart from the tunnel surrounding rock for shallow-buried tunnels with small clear distance; moreover,the scope of consolidation should go beyond the midline of tunnel(along the direction of the top of slope) by 4 excavation spans of single tunnel.2) It is necessary to modify the load value of shallow-bias tunnels with small clear distance.

Geological Model of Mae Tang-Mae Ngad Diversion Tunnel Project, Northern Thailand

Most of infrastructure projects around the world have to focus on a clear understanding of geological model which may be determined from various sources of information. The limitation in geotechnical data and budget affects the accuracy of the geological model, particularly for projects of long and deep tunnel of which accessibility to the excavation points is difficult and far reaching. Therefore, an approach adopted for interpretation plays an important role in the level of uncertainty of the derived geological model. This paper focuses on the determination of the geological models at the site of a long water diversion tunnel project in a complex geologic setting in northern Thailand from an approach to understand the relationship between regional tectonic setting and local tectonic condition so that geological structures and rock mass conditions along the tunnel alignment can be assessed for a better planning of tunnel design and construction. The paper describes tectonic settings at regional scale (Northern Thailand and Eastern Myanmar), tectonic features and geologic condition in project area, geotechnical investigation and data along tunnel alignment and predicted tunnel ground behavior.

Random Vibration Analysis of Urban Underground Tunnels Under Vertical Earthquake Excitations Based on Mass–Damper–Spring Model

In this paper, the verticalseismic effects on tunnels are studied based on a classic mass–damper–spring model. An analyticaldiscrete modelof urban underground tunnels subjected to verticalearthquake excitations is proposed by considering the first verticalvibration mode. Taking a light railproject in Tianjin as an example, this study uses the proposed discrete modelto analyze the displacements of tunneland soilunder verticalearthquake excitations. The soildisplacement responses at different tunnellocations are analyzed with linear random vibration theory.The computationalcost is greatly reduced using the proposed model. It can be seen that different from the case of horizontalearthquakes, the displacement responses under verticalearthquake excitations keep growing after seismic acceleration reaches its peak for a short duration, and then,they begin to decay. The soils at different positions around the tunnels have large relative displacement under verticalearthquake excitations. Moreover, a finite-element modelis also established for displacement responses using ABAQUS.The comparison with the results of the finite-element modelshows that the results of the proposed discrete modelare available.

侧部注浆对已建盾构隧道受荷变形影响试验研究

采用侧部注浆法整治盾构隧道横椭圆变形超限过程中,盾构隧道周围附加土压力及隧道变形特性暂不明晰。通过几何相似比为1∶10的缩尺寸模型试验开展了侧部注浆对已建盾构隧道的影响试验研究,试验结果分析表明:在注浆挤压作用下,将导致隧道周围的土压力在注浆点处局部增大,两边有一定程度的减小,产生了明显的水平被动土拱现象;在注浆附加荷载影响下,模型盾构隧道在注浆点附近发生了竖椭圆变形,而在离注浆点较远处则发生了横椭圆变形,且隧道发生了反弯现象;注浆过程中发生了“渗透→挤密→劈裂”扩散模式与“挤密→劈裂→渗透”扩散模式,并阐明了两种浆液扩散模式的扩散机制;隧道外壁附加荷载主要由浆液通过渗透扩散与劈裂扩散的浆液压力所形成,同时浆液挤压土体变形对隧道周围的浆液也将形成一定的挤压荷载。

浅埋暗挖交叉相贯隧道施工力学行为试验研究

为完善浅埋暗挖交叉相贯隧道在施工过程中的受力形式及变形特征,依托青岛某地铁工程,根据所选地铁车站的地质条件及衬砌结构特点浇筑衬砌模型并配制围岩相似材料,利用模型试验对采用全断面法在Ⅴ级围岩环境下进行的风道和车站主体开挖过程的力学行为展开研究,并从隧道衬砌结构变形及地层内部位移变化规律两方面分析了浅埋暗挖交叉相贯隧道全断面开挖施工的力学行为。结果表明:对于交叉相贯位置处的隧道结构,已有隧道结构将改变后续施工隧道衬砌结构应变最大值及其出现位置;位于交叉相贯隧道结构附近不同象限内的围岩分别处于水平变形累加区和往复区;地表竖向变形最大点位于后续施工的车站上方且与交叉相贯位置存在一定距离,而在交叉相贯位置处的地表竖向变形值稍小;模型试验明确了交叉相贯隧道在施工过程中围岩及衬砌结构的变形特征,给出了隧道结构地表最大变形与施工步序间的时空关系;研究结果可为相关交叉相贯隧道结构的施工及设计提供依据。