Abstract Biot's theory of poroelasticity has gained new prominence in rock mechanics to understand the hydro-mechanical (H-M) response of fluid flow and deformation in tunneling in deep saturated ground. Numerically, explicit coupling technique has been widely used for simulating this coupled interaction. However, the technique is conditionally stable and requires small time steps, making it inefficient for simulating large-scale H-M problems. To improve the efficiency, the unconditionally stable alternating direction explicit (ADE) scheme could be used to solve the flow problem. The standard ADE scheme, however, is only moderately accurate and is restricted to uniform grids and plane strain problems. Thus, it is impractical for large-scale domains and inapplicable for axisymmetric problems. This paper aims to remove these drawbacks by developing a novel high-order ADE scheme capable of solving the flow problem in an axisymmetric non-uniform grid. The new scheme is derived by performing a fourth-order finite difference approximation for the spatial derivatives of the axisymmetric fluid-diffusion equation in a non-uniform grid configuration. The implicit Crank-Nicolson technique is then applied to the resulting approximation, and the subsequent equation is split into two alternating direction sweeps, giving rise to a new high-order axisymmetric ADE scheme. The pore pressure solutions from the new scheme are then sequentially coupled with an existing geomechanical simulator in the computer code Fast Lagrangian Analysis of Continua (FLAC). This coupling procedure is called the sequentially-explicit coupling technique based on the fourth-order axisymmetric ADE scheme or SEA-4-AXI. When applied for simulating an advancing tunnel in deep saturated ground, SEA-4-AXI reduces computer runtime up to 42% that of FLAC's basic scheme without numerical instability while also producing high numerical accuracy with average differences of 0.6–1.8% for pore pressure and displacement. 1. Introduction Biot's theory of poroelasticity (Biot, 1941) has gained new prominence in rock mechanics to understand the coupled response of fluid flow and deformation in deformable porous media (i.e., soils and rocks). Consolidation and subsidence induced by fluid extraction from underground formations are the most common examples of this coupled hydro-mechanical (H-M) interaction. In these examples, the transient fluid flow affects deformation in the ground and vice versa (Wang, 2000; Gutierrez and Lewis, 2002; Neuzil, 2003). Thus, consideration of this H-M interaction is essential for the safe design of underground structures such as deep tunnel in saturated ground.

Abstract Due to long and linear properties of tunnel, pre-geological investigation of it is sometimes insufficient and contractors sometimes have to change the plan depending on the geological condition they face during excavation. Especially, as to groundwater, misjudgment of its condition ahead of tunnel face might cause tremendous disaster. However, in the case of large-scale tunnel, it is quite difficult to set monitoring wells on the surface due to its huge overburden. Here, in this study, several types of innovated groundwater surveying and monitoring technique from tunnel inside are developed. At first, the horizontal pilot boring in the tunnel was categorized into three types as boring distance. Then, the special devices to measure ground water pressure for each boring type are respectively developed. Therefore, devices for each boring type have different concept and structure depending on the purpose and timing of each horizontal boring. There three types of devices were respectively tested in tunnel site and were verified their good performance. In the future, the system that combines these three different devices will help site staffs to estimate the ground water condition ahead and judge the appropriate counterplan, and that must leads to safety tunnel excavation. 1. Introduction Since mountain tunnels are long and linear structures, it is often difficult to accurately predict geological, groundwater, and other subterranean conditions through pregeological investigations alone. This means construction plans are often modified in response to unexpected geological conditions encountered during excavation. Of various possible factors, groundwater can cause sudden and high-pressure water inflow during the construction of a large-scale mountain tunnel, resulting in major construction delays or, in worst-case scenarios, disasters. Since it is not always possible to drill monitoring wells from the ground surface due to large overburden, it is critical to obtain reliable groundwater information from inside the tunnel via horizontal boring during the construction phase. In recent years, horizontal bores of various lengths have been drilled during tunnel construction for various purposes, including extra-long horizontal bores. 1)-3) We have developed a system of water inflow research monitoring (SWIReMo) capable of acquiring accurate water inflow information; this system comprehensively evaluates conditions ahead of the tunnel face and provides water inflow information to help ensure safe excavation. Various measurement technologies and horizontal bores of different lengths were required to enable SWIReMo to obtain the information needed based on the construction period and purpose. We tested individual techniques and systems in field tests.

Abstract Evaluation of the distribution of fractures in a rock mass ahead of a tunnel face is required for safe and reasonable tunnel excavation. To evaluate not only the position of fractures, but also their inclination before tunnel excavation, a directional borehole radar may be a suitable technique. A directional borehole radar can determine the inclination of fractures with a single pilot boring because it can estimate the arrival direction of the waves reflected by fractures, which are measured by a dipole array antenna with multiple elements. In this study, we first confirmed experimentally that glass fiber reinforced plastic (GFRP) tubes with steel joint couplers can be used as borehole casings for measurements with radar. Then, a directional borehole radar was applied to the survey of fractures in granite in a horizontal borehole drilled in the sidewall of a tunnel in order to confirm its applicability for evaluating the three-dimensional distribution of fractures. The results show that the strike and dip of each reflector estimated by the directional borehole radar measurements approximately correspond to the fractures observed with a borehole scanner. Therefore, it was concluded that a survey with a directional borehole radar in a horizontal borehole can evaluate the three-dimensional distribution of fractures surrounding the borehole. 1. Introduction Because the collapse of a tunnel face has occurred after the unexpected appearance of faults or fractures, evaluation of the distribution of fractures in the rock mass ahead of a tunnel face is required for safe and reasonable tunnel excavation. A survey of a pilot boring has been widely applied to evaluate the geological conditions ahead of a tunnel face (Fig. 1). Although the position where a fracture intersects with a pilot boring can be detected by the survey, it is difficult to evaluate its inclination with this method. As shown in Fig. 1, if a fracture intersects a tunnel at a low angle, it will appear on the tunnel face at a different position than that detected by the pilot boring. This suggests that it is important to evaluate not only the position of fractures, but also their inclination, before tunnel excavation. On the other hand, although the inclination of fractures may be evaluated by a survey with two or more pilot borings, the cost becomes high. Therefore, a geological technique capable of evaluating the inclination of fractures in a single pilot boring is needed. A directional borehole radar may be a suitable technique for evaluating the inclination of fractures because it can estimate the arrival direction of the reflected waves, which are measured by a dipole array antenna with multiple elements. This study first examined the application of a directional borehole radar to investigate within a single pilot boring. Next, a directional borehole radar was used to survey fractures in granite in a horizontal borehole drilled in the sidewall of a tunnel in order to confirm the applicability of the directional borehole radar for evaluating the three-dimensional distributions of fractures.

Abstract The authors developed a system for predicting geological conditions not just of excavated areas but also ahead of the tunnel face by processing drilling data using Ordinary kriging, a geostatistical approach, and by visualizing conditions in real time. Using auto-controlled face drilling rigs, the authors confirmed the easy and rapid acquisition of drilling data from blast holes and rock bolt holes, along with three-dimensional coordinates. The authors deployed the system in real time to decide whether pre-supports such as forepoling and facebolts would be necessary for a strongly sheared slate area at tunnel faces of the Shin-Kuzakai Tunnel (provisional name). The prediction provided information essential for decisions on construction methods. It also enabled safe streamlining of the process of deploying pre-supports. The authors also compared the applied support systems with P-wave velocity distributions of the rock mass derived from specific energy of drilling and rock mass classification distributions. 1. Introduction Choosing appropriate support systems and pre-supports are the key to ensuring quality, stability, and safety in tunnel construction projects. Typically, the tunnel face is observed during the excavation to evaluate geological conditions. The tunnel face is generally observed once a day, while excavations usually occur around four times a day. This means changes in geological conditions may be overlooked. In addition, as demonstrated by past incidents, the presence of a weak layer behind a tunnel face or a side wall may result in the collapse or significant deformation of a tunnel face or wall. With respect to the geological conditions behind a side wall, hardness is determined empirically from drilling data for rock bolt holes. However, acquiring and analyzing this data requires a great deal of time and labor. Obtaining information on geological conditions that would allow real-time decisions on construction plans tends to pose extreme difficulties. Using auto-controlled face drilling rigs whose use is increasingly common, we found a way to quickly and easily acquire drilling data from blast and rock bolt holes. We established a system that predicts geological conditions not just in excavated areas, but ahead of the tunnel face; this method visualizes conditions in real time by processing drilling data based on a geostatistical approach called Ordinary kriging. We applied this system to the construction site for the Shin-Kuzakai Tunnel (provisional name) on the Miyako-Morioka Cross Road and confirmed that the system provides essential information for construction plan decisions.

Abstract Appropriate construction of tunnel requires accurate determination of crack distribution, rock strength, and weathering grade. Tunnel face evaluations are commonly based on subjective visual inspections, the results of which are likely to vary from person to person. While quantitative methods based on laser measurements or photographic surveys to accurately determine crack distributions are available to eliminate these variations, these methods are time-consuming. To achieve the fast, simple, and consistent determination of crack distributions on tunnel faces, we developed a quantitative analytical method based on image analysis. The method divides the tunnel face into several areas. An image of each area is rotated, and the directions of the major cracks are read numerically. We found that applying this method at an actual tunnelling site identified the principal crack directions and determined crack intervals in about one minute. 1. Introduction Appropriate construction of tunnel requires accurate tunnel face evaluations. With conventional evaluation methods, a tunnel face is assigned scores for various parameters, including rock strength, weathering grade, and distribution of major cracks based on preestablished criteria. The results of this approach are inconsistent and likely to vary from person to person. To eliminate these variations, we devise a quantitative analytical method that does not depend solely on subjective visual inspections. Rock strength and weathering grade can be assessed via simple quantitative analysis due to recent technical developments. Rock strength is determined quantitatively by an in situ test like the point load test. Weathering grade is determined quantitatively by a process that combines color analysis and X-ray diffraction analysis (Tobe et al., 2014). Regarding crack distribution, the strike and dip of a given crack can be identified by laser measurements or photographic surveys (Ishihama et al., 2016). This method is highly accurate, but the associated measurement and analysis require considerable time. The measurements require suspending excavation work, with repercussions for construction timetables. With this approach, cracks are analyzed one by one to determine the principal direction, based on an image of a tunnel face form obtained from a survey. It takes several tens of minutes to several hours to complete this analysis. If the goal were simply to identify crack directions and intervals in a manner consistent from inspector to inspector, this approach would be excessive. Based on our investigation of fast, simple ways to quantitatively determine crack distributions on tunnel faces that do not affect construction timetables and eliminate inconsistency of results from different individuals, we devised a quantitative method based on image analysis of photographs of tunnel faces.

Abstract Rock mass characterization is very important in rock engineering. The characterization encompasses the description of the apparent joint network as well as the spatial distribution of ground types or lithologies. Currently, the rock mass is documented and mapped either on-sight or with digital mapping-software like ShapeMetriX 3D on the desktop. In the latter, digital images are used to generate 3D point clouds and manually map the joint planes or traces. With an increasing trend to automate the mapping procedure, the analysis of the digital images experiences a digital rebirth. In this paper, digital image processing is applied to detect edges in the images of two selected tunnel faces, clusters the signals and a structure map is generated which can be used for determining joint orientations, spacings and trace lengths. The applied method resulted in both cases in a very good detection joint traces, which could be distinguished into four distinct joint sets in the first step and reduced into three joint set in the second clustering process. In total, 743 (case study I) and 1233 (case study II) joint traces were detected automatically. However, in the current application, the segment linking process is incomplete and leads to scattering of the orientation values due to short line segments. Additionally, no effort was made yet to exclude artificial color changes, like caused by chiselling, from the analysis. However, with the large number of measurements, their influence is considered negligible. The applied method shows strengths especially in detecting geological features, which do not per se occur as joint planes and which will be missed in an automated vector analysis of the point clouds. 1. Introduction The extraction of joint traces from photographs of rock masses is nothing new in rock mass characterization (e.g. Franklin et al., 1988, Reid & Harrison, 2000, Lemy & Hadjigeorgiou, 2003, Deb et al., 2008). However, the analyses were restricted in dimension (2D) and heavily affected by different light and rock mass conditions. With the up come of photogrammetry in rock mass characterization and an increased trend for automatic rock mass characterization (e.g. Kemeny & Post, 2003, van Knapen & Slob, 2006, Riquelme et al., 2014), digital image processing experiences a digital rebirth for rock engineering purposes (Vasuki et al., 2014, 2017), still facing the old problems (e. g. exposition and light condition, rock mass conditions), but with the possibility to include spatial analyses like the determination of the joint trace and plane orientations in point clouds.

Abstract The application of effective tunnel reinforcement method is essential to stabilize the face when digging into loose ground by the NATM. In Japan, long face bolts (usually 76mm in diameter) are frequently used as the reinforcement of tunnel face. The bolt, made by GFRP (Glass Fiber Reinforced Plastic) pipe, is popularly used because GFRP has sufficient tensile strength and can be easily cut and removed during excavation. The length is generally about 12m per 1 shift in order to get sufficient anchoring, and the bolt is divided into 3 or 4 units and jointed. However, tensile strength of screw joints of GFRP pipe is low and the strength of the bolt is inevitably reduced as a result. Therefore, we have newly developed a high-strength face bolt by using steel pipe. Firstly, the relationship between the extrusion of the face and the axial force of the face bolt is discussed based on the results of field measurements and three dimensional FDM analyses. In a case of tunneling in mudstone at great depth, the face extrusion by more than 200mm and great changes in axial forces on face bolts were measured associated with the extrusion. By analyzing the performance of the face bolt, the requirements for the face bolt in such squeezing ground is identified. Secondly, the new steel pipe bolt, which we have been developed to meet the requirements, is described. The new face bolt has been developed to have high strength and adhesion resistance. It was confirmed that the strength of the screw joints and the adhesion resistance were larger than that of conventional face bolts according to the results of tensile test and pull out test. Additionally, assuming the application to deeper squeezing ground, the additional development to further reinforce the steel face bolt is also reported.

Abstract It is difficult to predict detailed ground conditions of a mountain tunnel with a large overburden from a surface geological survey only. The ground conditions ahead of a tunnel face must be predicted for efficient and safe tunnel construction. The authors have proposed a simple forward prediction method that uses tilt sensors installed at the tunnel crown near the cutting face. Moreover the effectiveness of the method has been verified in practice. The field tests have been carried out at three mountain tunnel projects under construction to confirm that the trend of the inclination angle variation shows the transition portent of the ground ahead of the face, as predicted by a preliminary numerical study (Kudoh et al., 2012a). The trends of inclination angle measured in the field are practically consistent with those in the numerical analysis for an unsupported elastic ground (Tani et al., 2012). This paper first shows the proposed prediction method and the necessary measurement devices, and mentions the principle of prediction by tilt sensors. It then presents the capability of prediction, and discusses the effectiveness of this method in two different types of deformation modes.

Abstract Tunnel construction involves various drilling works such as for installing rock-bolts and blast explosive charges. An examination of rock-bolt hole drilling at a tunnel face showed that drilling efficiency is greatly influenced by the geological conditions of the surrounding rock mass. Therefore, by assessing the geological conditions around a tunnel, the drilling efficiency could be estimated quantitatively. Accordingly, we have developed a geological drill survey and 3-dimensional visualization system (GENESIS/GSV), which gathers data related to drilling works, processes it and visualizes the 3-dimensional geological structure. This paper outlines GENESIS/GVS and its practical use, and shows examples of identifying the geological structure based on daily drilling work using the system. The validity of using the system for tunneling is also discussed..

Abstract In this study, which is based on their mountain tunnel construction project, the authors applied the extremely long pre-supporting system (ELPS) excavation method to a tunnel portal located in a weak ground area to ensure the stability of the tunnel crown and prevent subsidence of the surface ground. The ELPS method enables installation of pre-supporting steel pipes with a length of approximately 50 m. On the basis of this method, pre-supporting steel pipes are installed parallel to the tunnel axis with great precision to resolve some of the issues posed by the traditional all ground fastening (AGF) forepoling method, such as poor economic efficiency of the steel pipe overlap, the separation of pre-supporting steel pipes from the tunnel, and delays in the excavation process. During construction, the authors measured strain on the pre-supporting steel pipes using pulse pre-pump-Brillouin optical time domain analysis (PPP-BOTDA) optical fiber sensing. This process enabled the authors to monitor the behavior of the pre-supporting steel pipes during tunnel excavation and verify the pre-supporting effectiveness of the ELPS method by comparing numerical analysis results.

Abstract It is difficult to understand the geological condition accurately ahead of the tunnel face during tunnel excavation. Accordingly, for the safe and economical tunnel excavation, particularly in complicated ground conditions, survey techniques should be effectively used because they would enable us to avoid large costs and unexpected collapses. In recent years, a seismic refraction survey and a seismic reflection survey, which are conducted on the ground surface and inside a tunnel, has been customarily carried out as a preliminary survey method. However it does not sufficiently provide proper information of faults and fracture zones. In order to solve this problem, the authors developed the "Tunnel to surface seismic tomography", which is the new survey method using seismic tomography technique between the inside of a tunnel and the ground surface above the tunnel. This new method enables us to grasp P-wave velocity and more proper prediction over a wide area ahead of the tunnel face. In order to conduct seismic tomography analysis, arrival time of seismic wave has to be precisely calculated and, for that reason, the wave -generation and reception systems must be synchronized with each other. It is the simplest to use wired channels, but, in reality, it is difficult to synchronize them with wire connection because the receivers on the ground are usually located far away from the source points inside a tunnel. The authors consequently developed a new time synchronization system using GPS satellite time with wireless data transmission solutions. Furthermore, the authors have improved this system so that vibrations from blasting for excavation could be used as a survey source. This new system contributed to extending the survey limit for depth and improving the survey precision. Furthermore, it is remarkable that this system can be performed without interrupting tunnel excavation.

Abstract The Kitanomine Tunnel (tentative name) will be a 2928m-long tunnel in Furano City, part of the Asahikawa-Tokachi Road running N-S in central Hokkaido. The area that surrounds the tunnel is rich in water resources. Thus, a 740m-long watertight structure is designed in the middle of the tunnel alignment to minimize the impact of the tunnel excavation on the groundwater environment. It is expected that the groundwater level will be recovered in the long term due to the watertight structure which does not allow the groundwater to flow into the tunnel. At the south end of the watertight structure section, pre-grouting had been conducted from the ground surface before the section was excavated. The length of the pre-grouting section was 200m. Nano-fine cement grout and chemical grout were injected into sandy soil and highly weathered welded tuff to decrease the permeability and improve the stability of the ground. In this paper, we report the quality assessment of the grouting effect conducted by resistivity tomography and in-situ permeability tests. The results of the both investigations concluded that the grout had been injected into the ground homogeneously as designed and the pre-grouting actually decreased the permeability of the original ground. Furthermore, we report the result of the excavation of the pre-grouting and non-pre-grouting sections. By observing the tunnel face continuously, it was reconfirmed that the nano-fine cement grout permeated homogeneously into sandy soil and highly weathered welded tuff as designed. In addition, the amount of water inflow was smaller than management standard value. In the non-pre-grouting section, however, the water inflow into the tunnel significantly increased, which required additional grouting from the tunnel face.

Abstract In general, the seismic survey of a tunnel excavation requires careful arrangement of seismic sources and receivers, which causes interruption of tunnel excavation work. However, when blasting is used for excavating the tunnel, the blasts themselves can be used as the seismic survey source, and it becomes possible to continuously evaluate the geological features ahead of tunnel. We called this method -the Seismic While Excavating using SSRT method (SWE-SSRT). Recently, research has focused on the seismic interferometry method as this does not need a strong single seismic source and can utilize non-blast construction noises. The seismic noises of the tunnel construction could be adopted as a seismic source for the geological survey ahead of a tunnel face. And seismic interferometry is useful for SWE-SSRT as it requires fewer, less-complicated measuring devices. In this paper, we carried out numerical analysis of an acoustic field simulating both single and multiple-steps blasting. The result shows that the seismic interferometry for SWE-SSRT could have applicability to the survey ahead of a tunnel face.

Abstract Although a spherical tunnel face has been reported to enhance the stability of tunnels where the tunnel is excavated using Sequential Excavation Method, the effect of the shape of the tunnel face on the deformation behavior, mechanical stability, and ease of construction for the tunnel has yet to be quantitatively clarified. The Shin-Takarahama Tunnel was excavated through granite by full-face advanced drill and blast while varying the shape of the spherical tunnel face and blasting pattern. As a result, full-face advanced drill and blast in combination with a spherical tunnel face enhanced tunnel stability and improved the efficiency of work in front of the tunnel face. This paper clarifies the characteristics of mechanical behavior of a tunnel with a spherical tunnel face and its ease of construction so that the effectiveness of the spherical tunnel face method is hereby quantitatively verified.

Abstract The seismic refraction survey from the ground surface has been routinely applied to planning of tunneling as a preliminary survey. A tunnel support pattern is designed based on seismic wave velocity of the ground obtained by seismic refraction survey. Where overburden on a tunnel is large, the resolution in velocity structure by this technique becomes poor. The authors developed a new exploration method by the use of drilling vibration data called T-SPD (Tunnel Seismic Probe Drilling) to estimate seismic wave velocity distribution ahead of the tunnel face to be utilized for designing tunnel support patterns. The field tests of T-SPD have been carried out at three tunneling sites. In this paper, the authors will report two field tests using the drill machines, one with 100m and the other 1,000m capacities. P-wave velocity distribution estimated by T-SPD was found to agree with P-wave velocity distribution estimated by seismic refraction survey from the ground surface and on the roadbed in the tunnel. Two field tests confirmed T-SPD can be an alternate exploration method of seismic refraction in case seismic refraction from the ground surface is difficult to be applied due to large overburden.

ABSTRACT Under the observational design and construction method, original tunnel design is immediately verified or modified based on the prediction results of geological conditions from in-situ data sequentially obtained during construction, such as seismic profiling, probe hole drilling and geological ratings at tunnel faces. Because data used and its processing method for geotechnical prediction change according to purposes, this study proposes the integrated prediction system for geological conditions ahead of tunnel faces, which is composed of long-interval, middle-interval, and short-interval prediction subsystems. The long-interval prediction subsystem is used for master planning, such as estimation of the total period and cost of a project. The middle-interval prediction subsystem is used for detailed planning, such as judgment of execution of preliminary reinforcement and selection of tunnel support pattern. The short-interval prediction subsystem is used for final decision making, such as confirmation or modification of the detailed plan and determination of tunnel excavation parameters. The applicability of those subsystems is verified with actual field data obtained in the motorway tunnel project, where Cretaceous granite occurs, involving a main tunnel excavated by the drill and blast method, and an accompanied evacuation tunnel excavated by a TBM in advance of the main tunnel.

ABSTRACT The Government of India has entrusted the National Highway Authority of India (NHAI) with the responsibility of four laning of Chenani to Nashri Section of NH-1A from km 89.00 to km 130.00 including 9km long bi-directional traffic tunnel with a parallel escape tunnel of 9km on BOT (annuity) basis. The project area lies in western Himalayan region. The rock masses along the project of the Chenani-Nashri tunnel, belong to the Lower Murree formation that includes a sequence of interbedded sandstones, siltstones and claystones layers. The tunnel behaviour classification of the rock mass has been performed by Geodata, Italy. These rock behaviour classes has been correlated with the rock mass behavior type of NATM. The supports for various behavior classes have also been designed using the numerical methods as per the requirements. The tunnel construction work was started in August 2011 from South end and in September 2011 from North end. As expected the experience of tunneling in Himalayan mixed geology having bands of sandstone, siltstone, claystone, intermingled siltstone and claystone and sheared siltstone and claystone is not very encouraging. There have been instances of overbreaks and cracks in shotcrete support in the tunnel. Accordingly the designs have been modified. The benefits of displacements/convergence monitoring have been highlighted at the end.

ABSTRACT: The Longitudinal Deformation Profile (DP) is an important component of the Convergence- Confinement method. The present study concerns numerical simulation, by means of the finite difference code FLAX 3D, to calculate the DP curve for an unlined tunnel driven in a Burger viscoelastic rock mass model in various stress fields. Model constants of the Burger rock mass are selected according to a detailed literature review and parameterized in order to simulate different time-dependent situations of rock mass. The results are plotted, analyzed, discussed and compared against known empirical solutions and found in good agreement. 1. BACKGROUND 1.1. Time-dependent response Observed displacement of a specific point in an underground excavation can be expressed as the sum of displacements caused by two effects, the face advance and the time dependent reaction of the ground. In order to describe the time-dependent deformation due to creep in tunnels, various approaches have been established based on analytical, empirical and numerical methods. To briefly report an indicative selection of researches that include time in stability analysis of tunnels, one would start with the basic research that was presented by Salem et al [12]. In their suggested analytical method an explicit solution was proposed for the determination of the radial displacements and the ground pressure acting on tunnel support. It was based on a Kelvin-Voigt theological model. A closed-form solution for the calculation of the pressure acting on tunnel support structures was given by Samurai [10]. He introduced an "equivalent initial stress" in order to solve three-dimensional effects of the tunnel face progression with a two-dimensional plane strain model of tunnel- support structures for elastic and viscoelastic media. Also, by means of a three component viscoelastic model, relations are given for the calculation of tunnel wall displacement and pressure on lining. In another research by Ghaboussi and Gilda [4], the short-term effects that develop when a tunnel is driven in a ground showing viscous behaviour associated with the devi atomic deformations is studied. Also, radial deformation of a lined tunnel when there is an unsupported zone between the face of the excavation and the liner, the effects of a temporary interruption of the excavation process and of various rates of tunnel excavation. More recently, Salami [11] performed viscoelastic analysis with the Abacus code to model ground squeezing through the heavily sheared and fault zones of the Red Pine shale of still-water tunnel (Utah, USA) under an overburden of 700 m. He concluded that the effect of tunnel face advance on the crown displacement extends to a distance of about 2 tunnel diameters behind the tunnel face and 1.5 tunnel diameters ahead of the face. This zone of influence is slightly wider than the zone that has been predicted from elastic analysis. Yiouta-Mitra et al [15] performed viscoelastic analysis of materials with swelling and creep potential to investigate the effects on the tunnel final lining loads. Sophistic numerical code and the viscoelastic Persona model were used on the basis of the convergence-confinement method.

Abstract: The Longitudinal Deformation Profile (LDP) is a graphical representation of the radial displacement versus the distances to the tunnel face for an unsupported tunnel section. LDPs can be computed by numerical models. Also, Vlachopoulos and Diederichs [1] have proposed accurate expressions to calculate LDPs for tunnels excavated in elastic perfectly plastic (EPP) rock masses, as a function of the plastic radius that is induced by the excavation. On the other hand, average quality rock masses behave in a strain-softening (SS) manner. This behaviour produces different Ground Reaction Curves to those obtained for an equivalent EPP material. The aim of this paper is the analysis of LDPs using the numerical code FLAC3D. Comparing the LDPs of different quality rock masses under the same confinement, we have observed that the curves are less steep as the GSI of the rock mass diminishes. These differences increased as far as the confinement is greater. We have also found that the fact of accounting for SS behaviour affects LDPs significantly. Moreover, we have made simulations with different values of the dilatancy parameter for SS, and it seems that this parameter does not have great influence in the LDPs. 1. INTRODUCTION 1.1. Problem Statement The estimation of the stresses involved in a tunnel excavation, the control of the deformation of the rock mass and the determination of the distance from the tunnel face where the installation of support and reinforcement is most efficient are key issues in underground tunneling. The face itself carries a significant portion of the load in its surroundings. This As the tunnel face advances, the support will have to carry a greater proportion of the load. Once the face has advanced far enough, there would be no face effect and the support and reinforcement system will be carrying the design load. Therefore, if the support is installed too close to the tunnel face, it would carry an excessive load and if it is installed too far from the tunnel face, excessive deformations may occur. The three basic components of the convergence-confinement method are: the ground reaction curve (GRC); the support characteristic curve (SCC); and the LDP [2]. The LDP is a graphical representation of the radial displacement (tunnel wall deformation) versus the distances to the tunnel face for an unsupported tunnel section, behind and ahead of the tunnel face, along the axis of the tunnel. An accurate description of this LDP is needed to estimate the optimal distance to the face for installing the support. The profile of radial displacements along the axis of the tunnel can be computed by numerical models -for instance, FLAC3D [16]. Vlachopoulos and Diederichs (V&D, in what follows) [1] have performed a series of numerical simulations to determine the LDP for a wide range of EPP rock masses. This has led them to propose more accurate expressions to calculate LDPs, as a function of the plastic radius that is induced in the rock mass by the excavation (see section 1.2).

ABSTRACT It has been widely reported that fault zones are the most influencing factor of tunnel collapse. This study reviewed the applicability of the 3-D absolute displacement measurement of a tunnel by using digital vision monitoring. Also analyzed is the behavior of a tunnel displacement when passing through a fault zone with various orientations by using 3-D finite element analysis. As a result of analyzing 3-D deformation, it was found that the variation of displacement trend on horizontal/vertical section per measurement section would be larger as it approaches to the core of the fault zone. It was also examined that the variation of crown settlement and trend line would be the most influenced at a point where a tunnel meets fault zone. However, since the variation of crown settlement trend line starts as it is very close to a fault zone(0.5D ~ 1D), it may be difficult to anticipate a fault zone from crown settlement trend line. It was also proposed the move vector concept of a center point in a plane, which is created by connecting displacement measuring points. After applying the proposed monitoring center vector(MCV) to a tunnel section through which a fault zone passes, it was found that the influence would be well reflected depending on the fault zone orientation. In addition, the study suggested the ‘stereonet projection’ as a method to express the move behavior of MCV in a 3-D space and suggested how to anticipate front fault zone through variations of measuring section center point vector on the stereonet projection diagram. The 3-D absolute displacement measurement of tunnel and the displacement analysis using the digital vision measurement developed in the study were applied to a tunnel site. Comparison with the survey results of fault zone showed good 1. Introduction For safe and economic construction of a tunnel in a fault zone, appropriate method have to be employed to predict and prepare for sudden change in ground condition ahead of the tunnel face as early as possible. Studies on the prediction of fault zone ahead of tunnel face using the convergence of tunnel have been conducted since late 1980s. Various methods have been tried, including analysis on the trend line and influence line of the displacement in tunnel axis, analysis on the change trend of the vector orientation which is the ratio between the displacements in radial and advance directions, and so on. Most of the studies on the prediction of fault ahead of tunnel face using tunnel convergence have been focused on the investigation of the deformation behavior of the displacement by excavation at the measuring point. However, it was not possible to take full consideration of the 3-dimensional behavior of displacement by fault zone ahead since the analyses were only limited to the displacement in single or two directions,. In this paper, a 3-dimensional displacement analysis method which can efficiently represent behavior of rock in fault zone is proposed.