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Proceedings Papers

Paper presented at the 12th ISRM Congress, October 16–21, 2011

Paper Number: ISRM-12CONGRESS-2011-384

...

**ground****surface**borehole drill bit azimuth azimuth drill bit location Directional Drilling Drilling production well exploration geophone Harmonising Rock Engineering and the Environment Qian & Zhou (eds) © 2012 Taylor & Francis Group, London, ISBN 978-0-415-80444-8 Real-time microseismic...
Abstract

ABSTRACT Directional drilling of a deep hole in coal bed methane production can be difficult, risky and costly. One of the key issues to ensure the success of the drilling is the steering of the drill bit to the correct direction. The steering of the drill bit is now based on traditional magnetometer techniques. The disadvantages of this technology are its short survey range (<40 m) and that it must be operate down in a well if the operating bit is in deep underground. In this paper, microseismic techniques are proposed for the drill bit navigation and results from a trial of a seismic are presented. The results have shown that seismic signals associated with the drilling can be sufficiently detected when the drill bit was more than 120m from the geophones deployed in the target well and the azimuth of in-coming seismic rays can be determined in real-time using seismic waveform polarities. The drill bit location can then be obtained from the azimuth and distance of the drill string inside the coal seam.

Proceedings Papers

Paper presented at the 12th ISRM Congress, October 16–21, 2011

Paper Number: ISRM-12CONGRESS-2011-213

... the propagation of low-frequency waves through a rock mass near a tunnel. A single period sinusoidal wave was applied as dynamic source on the floor of the tunnel. Observation points were located on the

**ground****surface**and around the tunnel. The influence on wave propagation from overburden, position...
Abstract

ABSTRACT The vibrations generated by a moving train in a tunnel will radiate into the surrounding ground which, in densely populated areas, will reach nearby buildings and its residents. Analyses are commonly made where the aim is to estimate the ground-borne noise and vibrations levels that may occur in nearby buildings. A common assumption is to treat the rock mass as an isotropic, homogeneous, and linear elastic material. Thus, the influence of discontinuities on the propagation of waves is not considered in the analyses. Within this study, numerical simulations were performed to study the propagation of low-frequency waves through a rock mass near a tunnel. A single period sinusoidal wave was applied as dynamic source on the floor of the tunnel. Observation points were located on the ground surface and around the tunnel. The influence on wave propagation from overburden, position of a discontinuity in relation to the tunnel, and normal and shear stiffness of the discontinuity, was studied by using the Universal Distinct Element Code (UDEC). The results show that increasing overburden reduces the vibration levels on the ground surface. Furthermore, the influence of the normal and shear stiffness of discontinuities depends on where the horizontal discontinuity is positioned in relation to the tunnel. If the horizontal discontinuity is positioned above the dynamic source (e.g. above tunnel or in the tunnel wall) the vibration levels on the ground surface will be reduced but if the horizontal discontinuity is located below the dynamic source (e.g. below the tunnel) the vibration levels on the ground surface will be enhanced. In our analyses, discontinuities only have an impact on the wave propagation if the normal and shear stiffness of is ≤10 GPa/m.

Proceedings Papers

Paper presented at the 11th ISRM Congress, July 9–13, 2007

Paper Number: ISRM-11CONGRESS-2007-144

... is a fully threedimensional model for single block dynamics (Nishimura, et al. 2003). The driving force is gravity. trajectory numerical simulation roadway probability

**ground****surface**three-dimensional numerical simulation procedure average vehicle velocity rockfall probabilistic...
Abstract

ABSTRACT A probabilistic rockfall encounter model using a three-dimensional numerical simulation is presented to study the traffic safety for roadways in mountainous terrain. The model consists of a rockfall simulation and an encounter analysis. The three-dimensional rockfall simulation produces all possible trajectories and end points of potential falling rocks to delimit the endangered zone at a given site. The probability of encounter is dependent on the probability that a vehicle and a rock will be in the same spatial section along the road in the zone. The location of the most endangered section is considered to be the location where the number of the calculated trajectories which intersect a trial-section is the largest zone. Vehicle presence in the section is assumed to be based on average vehicle velocity and average daily traffic volume at the site. To estimate the length of the section, we require the average vehicle velocity. 1 INTRODUCTION Rockfall is a significant hazard to roadways in mountainous regions. The protection of human life and traffic lines is a major task in rock engineering. When assessing rockfall hazards, at first, the detection of potential falling rock blocks on slope is important, and it is also important to estimate travel distance of the rock blocks and their velocities at any points on the topographical map (Jaboyedoff et al. 2005). Estimations of them affect protection measures against rockfall. Often numerical simulations are conducted with considerations of uncertainty of input parameters (Dudt & Heidenreich, 2001). The statistical outputs, such as flight height and kinetic energy, can be used for the design of protective measures at a given site. However, we, engineers, often face with the comparison of conditions at several rockfall sites to make decisions related to the allocations of the protective measures with limited resources. Some contributions on this issue have already reported (e.g. Neil & Steven, 2003). A probabilistic rockfall encounter model using a threedimensional numerical simulation is presented to study the traffic safety for roadways in mountainous terrain. The model consists of a rockfall analysis and an encounter analysis. The three-dimensional rockfall analysis produces all possible trajectories and end points to delimit the endangered zone on the road at a given site. The probability of encounter is dependent on the probability that a vehicle and a falling rock will be in the same section in the zone. When destabilizing factors, e.g. piezometric pressure, temperature variations and external forces acting to rock block (e.g. earthquake), exceed the stability of rock block, rock will start falling.These factors are not introduced to this procedure. It is important to recognize that the probabilistic model should be regarded as a tool to provide a comparison of relative risk to moving vehicles from rockfall at several sites. 2 A THREE-DIMENSIONAL SIMULATION The numerical model described here is a fully threedimensional model for single block dynamics (Nishimura, et al. 2003). The driving force is gravity.

Proceedings Papers

Paper presented at the 10th ISRM Congress, September 8–12, 2003

Paper Number: ISRM-10CONGRESS-2003-192

... storage cavern excavation hydro-fracturing test in-situ stress measurement principal stress Fracture design and containment vertical stress

**ground****surface**measuring point stress state stress measurement tunnel 1109 Song, W.K. et al., In-situ stress measurements in underground an oil storage...
Abstract

Two methods of stress measurements have been executed on the surface and underground to construct an oil storage cavern using hydro-fracturing and overcoring method. The first measurement has been performed to make a design of the caverns before excavating and the second to confirm the stress state during excavation. Six measurements have been carried out in the hydro-fracturing test at the depths between -17.8 and 54.5m from the sea level and a single measurement in the overcoring test in a single borehole at the depth of -21m from the sea level. The ratios of the maximum horizontal to vertical stress measured using hydro-fracturing and overcoring method are 2.95 and 3.1, respectively. Also, the orientations of the maximum horizontal stress are N53E and N58E. These measurements show that both methods give almost same results and significant horizontal stresses are acting on this cavern. Deux methodes de mesure de contrainte ont etè executees sur la surface de terrain et sous la terre pour construire une cavite de stockage de petrole en utilisant l'hydro-fracturing et l'overcoring. La première mesure a etè faite pour le plan des cavites avant l'excavation et le seconde pour confirmer l'etat de contrainte durant l'excavation. Six measures ont etè faites dans le teste de l'hydro-fracturing à la profondeur entre -17.8 et 54.5m depuis l'elèvation maritime. Une seule mesure a etè faite dans le teste de l'overcoring dans une seule trou de songdage à la profondeur de -21m. Le ratios de la maximale contrainte horizontale à la contrainte verticale mesure par les deux methodes sont 2.95 et 3.1, respectivement. Les orientations de la maximale contrainte horizontale sont N53E et N58E. Ce montre que les deux methodes donnent presque m me resultats et la contrainte importante est activee sur ces cavites. Zwei Druckmessungen wurden durchgefuehrt auf der Erdoberflache und im Innern von Ölspeicher- kavernen unter vergleichender Anwendung des Hydrofraktionierungs- und des Kernbohrungsver- fahrens. Die erste Messung wurde durchgefuehrt um einen Plan der Kavernen vor der Herstellung zu erstellen und die zweite um die Druckverhaltnisse wahrend der Bohrung zu ueberpruefen. Sechs Messugnen wurden mit der Hydrofraktionierungsmethode bei einer Tiefe von 17,8m und 54,5m unter dem Meeresspiegel und eine einzige Messung mit der Kernbohrungsmethode in einem Bohr-loch bei einer Tiefe von 21m unter dem Meeresspiegel vorgenommen. Das Verhaltnis von maxi- malem horizontalem zu vertikalem Druck bei der Hydrofraktions- und der Kernbohrungsmedthode ist 2,95 bzw. 3,1. Die Bezugspunkte des maximalen horizontalen Drucks in beiden Verfahren sind N53E und N58E. Introduction It is essential to measure virgin stresses for the purpose of stability analysis of underground caverns in numerical way. Hydro-fracturing and overcoring methods are largely used for stress measurement in Korea. As the stress state depends closely on the geological structure, different stress values might be obtained according to measuring points even in a small area. To avoid this, several tests should be carried out in different points but few measurements could be made in a project because of the expenses. Another way to obtain a representative data is to measure and compare the stresses using two different methods. Cai et al.(1997) presented a case study of in-situ stress measurement by hydro-fracturing and overcoring tests for the design of an underground mine. In this study two methods, hydro-fracturing and overcoring, have been adopted to obtain reliable data of virgin stresses for the proper design of an underground oil storage cavern. Hydro-fracturing test has been performed before excavating the cavern (Choi et al., 1999) and overcoring test during the excavation. This paper reports the comparison of the results obtained by two methods. Measuring Site In-situ stress measurements have been made to construct a large underground facility for the oil storage.

Proceedings Papers

Paper presented at the 9th ISRM Congress, August 25–28, 1999

Paper Number: ISRM-9CONGRESS-1999-319

... ABSTRACT: This paper summarizes some phenomenological research results from underground nuclear explosion tests in rock. These include effects on the rock in the free field, rock deformation and rupture near the

**ground****surface**, hydrological effects, and damage in the vicinity of the...
Abstract

ABSTRACT: This paper summarizes some phenomenological research results from underground nuclear explosion tests in rock. These include effects on the rock in the free field, rock deformation and rupture near the ground surface, hydrological effects, and damage in the vicinity of the underground cavity/chamber due to the stress wave induced by the explosion. Problems to stress wave in rock, such as the empirical rules, geologic effects, the methods of numerical analysis, and the equation of state and constitutive relationships for rock, are discussed. Topics where further research is needed are also outlined. 1 INTRODUCTION This paper discusses the mechanical underground nuclear explosions, as observed underground testing. Underground nuclear explosions generate dramatically changed conditions of high temperature and high pressure in the rock. The nuclear tests have provided an abundance of insights and information on rock dynamics and physical means to know the nature and protect the environment. Underground nuclear tests create exceptional natural conditions for study of many complex dynamic phenomena and catastrophies that arise in rock. Release/transfer of radiation and propagation of a high pressure dynamic disturbance are the two main basic physical phenomena that occur in underground nuclear explosions. Phenomena that are close associated the the dynamic disturbance include the effects on use the free field, deformation and damage of the rock near the ground surface, hydrodynamic effects in the rock, damage of the underground cavity/chamber, etc. The dynamic disturbance induced by the explosion i.e. the stress wave, exhibits special rates of propagation and attenuation. These topics are reviewed below. 2 PHENOMENOLOCY OF A NUCLEAR EXPLOSION IN ROCK 2.1 Effects on rock in the free field An underground nuclear explosion releases a very large quantity of energy, essentially instantaneously. Effects of this release can be divided into a number of zones or regions according to the radial distance from the point of explosion, as follows: gasification zone, liquefaction zone, explosion cavity, chimney, compaction zone, crushed zone, fractured zone, and plastic deformation zone. 2.1.1 Macroscopic effects on the rock mass in the free field The shape and size of the cavity formed in an explosion varies with the explosive yield, the boundary conditions of the explosion chamber, and the rock type. For explosions in hard rock, the radius (in) of the cavity is about 8 to 12 times the cube root of the equivalent explosive energy in (kt)¹. The height of the chimney that results from the collapse of rock in the upper half of the cavity depends on the rock type. For a typical granite, for example, the chimney height is 2 to 3 times the cavity diameter. In limestone, the scaled radius of the compact here the rock is distorted and crushed into different varies typically over the range R = 9.7~13.6 A large number of radial and circumferential cracks are formed in the rock and filled with vitrified rock. Many frictional planes and slickensided (scratched) surfaces can be observed. The crushed zone in limestone extends over a radial range of R=13.6~28.3 (m/kt¹/ 3 ); a large number of cracks are formed and shear cracks with scratches can also be observed. Slip along major discontinuities is also seen. Planar surfaces extending radially are clearly the result of tangential tension induced by the explosion. The residual stress zone (fractured zone, cracked zone) extends over an approximate range R=28.3~64.0 few tensile cracks are observed in this zone. Post-explosion drilling reveals that rock core obtained from near the explosion center has a consistency similar to round cake. Outside the residual stress zone is the elastic zone. 2.1.2 Results of geophysical logging The results of acoustic wave logging before and after nuclear explosions in granite shows that the wave velocity is reduced by explosions in the rock from 80m below the ground surface.

Proceedings Papers

Paper presented at the 9th ISRM Congress, August 25–28, 1999

Paper Number: ISRM-9CONGRESS-1999-021

... property excavation

**ground****surface**lock chamber boundary condition excavation process Dimensional Behavior Gorge Project coordinate system stability ship lock deformation Three dimensional behavior of the high slopes of ship locks in Three Gorges Project Le comportement tridimensionnel des...
Abstract

ABSTRACT: The permanent shiplock is an important part in the Three Gorges Project The excavation of the high slopes may result in the stress relief and the excessive deformation as well as the failure of rock masses, which may further affect the safety of the lock and the shipping traffic. In this paper, three-dimensional modeling has been carried out to study the stress and deformation behaviors of the slopes and their stability at each step excavation. An anchoring system has been proposed and discussed for diminishing the failure zones and the slope deformation. RÉSUMÉ: Le navire-ecluse permanent est une partie importante au projet de Trois Gorges. La fouille des pentes hautes pourrait resulter dans le soulagement du stress et la deformation excessive ainsi que la panne de la masse de roche, qu'influencerait plus la sûrete de l'ecluse et le trafic maritime. Dans ce papier, le modele tridimentionne a ete effectue pour etudier le stress et la fonctionnement de la deformation des pentes et leur stabilites à chaque demarche de la fouille. Un systeme du mouillage a ete propose et discute pour diminuer les zones de la panne et la deformation de la pente. ZUSAMMENFASSUNG: Der permanent Schiffschlos ist ein wichtiger Teil in dem Drei Tal Projekt. Der Abbau der hohen Gebirgswaenden kann die Entlastung und die uebermaessige Gebirgesdehnung sowohl den Gebirgesbruch verursachen, die die Gebirgssicherheit und den Verkehr beeinflussen kann. Dieser Artikel befasst sich mit einer drei-dimentionalen Nachbildung des Spannungs- und Dehnungsverhaltens der Gebirgswaenden sowohl der Stabilitaet nach jedem Abbau. Ein Ankersystem ist vorgeschlagen worden, um die Bruchszone und die Gebirgsdehnung zu verkleinen. INTRODUCTION The Three Gorges Project(TGP), being under construction from 1993, is a key project in the development and harnessing of the Yangtze River, China. The concrete gravity dam site is situated in Sandouping of Yichang City, Hubei Province, about 40km upstream from the Gezhouba Project which has been constructed in 1988. The permanent facilities for navigation are to be set at the left bank, and consist of a shiplift and a double-line, five-stage shiplock system with a bulkhead pier of 60m in widtht(see Figure 1), the dimension of each lock chamber is 280m in length, 34m in width and 5m in water depth(CTGPC,1996). The two sides of the lock chamber are rock slopes approximately l.5km long with a maximum height of 170m and be excavated in a deep cut through granite in different slope according to the weathering degree. The stability and deformation of these high and steep rock slopes after excavation and during operation is one of the major technical problems of TGP. A number of numerical and model experimental analyses have been performed to judge the slope stability(Dong,1994). Most of them, however, adopted the two-dimensional simulations so that the influences of excavation process and the topography of the dam site area could not be investigated correctly. In this paper, a three-dimensional numerical analysis by using the finite difference method is carried out to exactly simulate the excavation process of the high rock slopes.

Proceedings Papers

Paper presented at the 9th ISRM Congress, August 25–28, 1999

Paper Number: ISRM-9CONGRESS-1999-070

..., concrete; footings with. loads , up I to., 11000 kN/footing on the

**ground****surface**. The rock overburden is about 11 - 13 m, less than .half the width of the station. The rock mass mainly consists of heavily foliated and jointed micaceous schist and gneiss. 1. ll:; "1' 1 , I,' 'h ,>1. .The rock excavation...
Abstract

ABSTRACT: The authors of the paper present the rock excavation and rock support works of the underground train stations for the Arlandabanan Project, a fast railway link between the Stockholm City and the Arlanda Airport. The project was the first major BTO (Build-Transfer-Operate) project in Sweden. The underground complex in the airport area consists of three 23 m span underground stations and the connecting single and double track tunnels. The train stations are located directly under the terminal buildings. The rock excavation works and rock support design of one of the three underground stations, "Shuttle Station 2" located under Terminal 5, will be presented in this paper. RÉSUMÉ: Les ecrivains de l'article presentent le creusement de roc et les travaux de support du roc des stations de trains souterrains du Projet de ‘Arlandabanan’, un lien de chemin de fer de grande vitesse entre Ie centre de Stockholm et l'Aeroport de Arlanda. Le projet constitue Ie premier projet majeur de BTO (Batir-Transferer-Operer) en Suede. L'ensemble souterrain aupres de la zone de l'aeroport comprend trois stations souterrains de 23 m de portee ainsi que les tunnels de connexion de simple et de doubles voies. Les stations de train se trouvent directement en dessous des batiments d'aerogare. Les travaux de creusement de roc et la conception de support du roc d'une des trois stations souterrains, "La Station Navette no 2", qui se trouve en dessous de I'Aerogare 5, seront presente dans cet article. ZUSAMMENFASSUNG In diesem Dokument sind die Tunnelbohrungs- und Bewehrungsarbeiten der Untergrundbahnhöfe des Arlandabanan-Projekts, eine Schnellzugverbindung zwischen Stockholm Stadtmitte und Flughafen Arlanda, beschrieben worden. Das Projekt ist das Erste grosse BTO (Build-Transfer-Operate) Projekt in Schweden. Das untererdische Baukomplex am Flughafen besteht aus drei Bahnhöfe, jeder mit einer Breite von 23 M, und die dazu gehorenden ein- und doppelspurigen Verbindungstunnels. Die Bahnhöfe sind gerade unter den Terminalgebauden des Flughafens belegen. Die Tunnelbohrungs-arbeiten und die Konstruktion der Bewehrung eines der drei Untergrundbahnhöfe,. die unter Terminal 5 belegene „Shuttle Station 2", sind in diesem Dokument beschrieben worden. INTRODUCTION The Arlandabanan Project is a fast railway link between Stockholm City and the Arlanda airport. The project is the first major BTO (Build-Transfer-Operate) project in Sweden. The underground complex in the airport area consists of three underground stations with 23 m span, single/double track tunnels and 1.shafts for elevators and escalators. The underground train stations are located directly, under the terminal buildings. The total rock excavation volume was about 800 000 m 3 . This paper will present the rock excavation work and the design of rock support, for the underground stations. Especially one of the three underground stations, "Shuttle Station 2", will be described. The Shuttle Station 2 is 165 m long and is located under the international terminal, Terminal 5. The, terminal building is grounded on concrete footings with loads up to 11000 kN/footing on the ground surface. The rock overburden is about 11 - 13 m, less than. half the width of the station. The rock mass mainly consists of heavily foliated and jointed micaceous schist and gneiss. The rock excavation work was planned and executed with great concern to the nearby terminal buildings. The design of rock support was conducted in parallel with, the excavation works.

Proceedings Papers

Paper presented at the 8th ISRM Congress, September 25–29, 1995

Paper Number: ISRM-8CONGRESS-1995-113

... formula for calculating the thickness of the broken zone on the basis of the strain-sofening and volume expansion properties of rockmass and analyses its affecting factors. Finally, the authors introduce a supporting practice of a deep roadway lying at a depth of 1155m below

**ground****surface**. RESUME I En...
Abstract

ABSTRACT: In this paper the thickness of a broken zone is used as the index to evaluate the stability of surrounding rock of a deep roadway. The paper gives a theoretic formula for calculating the thickness of the broken zone on the basis of the strain-softening and volume expansion properties of rockmass and analyses its affecting factors. Finally, the authors introduce a supporting practice of a deep roadway lying at a depth of 1155m below ground surface. RESUME: En utillsant Iepaisseur de Ia zone de crevassement comme I'lndice de Ia stabillte des parois rocheuse de Ia galerie aux grandes Profondeurs, sur Ia base de Iàdoucissement de deformation rocheuse et de dilatation volumetrique, ce memoir donne une formule de sa theorie et annallse ses facteurs d'Influence. Enfin, làuteur presente Ia pratique du supportage de galerie d'une profondeur de 1155m. ZUSAMMENFASSUNG: In diesem Artikel benutzen die Autoren die Dicke der Brechen zone des Gesteins als Index ziffer der Stabilitat des Nebengestein vom Streckenumfang in groβer tiefer Grube. Under der Beruecksichtigung des Weichens und raumlicher Ausdehnung von Gestein, geben die Autoren eine theoretisihe Formel zur kaikulierung von Dicke der Brechen zone des Gesteins. Zum Schluβwird eine beispiel ueber die stuetzungpraxis in der 1155 Meter tiefen gelegenen Strecke von den Autoren weitergeben. 1. INTRODUCTION A key problem to deep mining is that the stability of surrounding rock becomes poorer and roadways are difficultly maintained. The stability of roadway surrounding rock is decided by states of surrounding rock under the interaction of stresses in surrounding rock and its strength. If its surrounding rock is in an elastic or plastic state after a roadway is driven, the surrounding rock is stable and the roadway needs not to be supported theoretically. However, if its surrounding rock is in a broken state after the roadway is driven, the surrounding rock is unstable. In this case, the roadway needs to be supported and the support to it must fit in with the deformation of the roadway. The greater the broken range in surrounding rock is, the poorer stability will be and the more difficult supporting of the roadway will be. Lots of in-situ observation data show that there is widely a broken zone in surrounding rock of roadways. Therefore, we may use its thickness as a comprehensive index of stresses and strength of surrounding rock to evaluate the stability of surrounding rock of a deep roadway. 2 STABILITY (BROKEN ZONE) ANALYSIS OF SURROUNDING ROCK OF A DEEP ROADWAY 2.1 Theoretic calculation of the thickness of a broken zone Surrounding rock of a deep roadway may be divided into broken, plastic and elastic zones on the basis of their states, their surrounding rock being in elastic, strain-softening and residual strength states, respectively. Thus surrounding rock within the broken zone is the direct object of supporting. 2.2 Major factors affecting the stability of surrounding rock of a deep roadway For a deep roadway located in bottom strata without mining disturbance, mining depth, H, (or in-situ stresses) is still a major factor affecting the stability of surrounding rock. The strength of rockmass is another major factor affecting the stability of a deep roadway. As shown in Fig. 2, the strength of rockmass may greatly influence its stability. However, it must be pointed out that concerning the strength of rockmass we mean not only the ultimate strength of rockmass but also its residual strength and strain-softening level.

Proceedings Papers

Paper presented at the 8th ISRM Congress, September 25–29, 1995

Paper Number: ISRM-8CONGRESS-1995-119

... with those obtained from the dynamic experiments. Some considerations are given regarding the experimental results, and new facts are found. 2 STATIC EXPERIMENTS 2.1 Experimental method and device Fig. 1 shows the experimental device used. Half of the shallow ground with a

**ground****surface**is...
Abstract

ABSTRACT: Three-dimensional static and dynamic model experiments on a tunnel with a shallow depth have been conducted to clarify the failure mechanism of the tunnel face. In the dynamic failure experiments, an ultra-highspeed video camera is employed. Through a comparison of the results obtained by both types experiments, new facts on the failure mechanism have been made clear. Resume: On a effecttue des essais experimentaux statique et dynamique en trois dimensions surdes modèles de souterrain de couverture peu profonde afin d'elucider Ie mecanisme de l'effondrement du front de souterrain. L'essai dynamique a ete effectue en employant un camerade video de grande ouverture. Par comparaison des resultats obtenus de ces deux essais, de nouveaux faits sur Ie mecanisme de l'effondrement ont ete mis en clair. AbriB: Dreidimensionale statische und dynamische Modellversuche fuer einen Tunnel mit geringer Tiefe sind durchgefuehrt worden, um den versagensmechanismus der Abbauwand des Tunnels zu klaren. In den dynamischen Versuchen wurde eine ultraschnelle Videokamera verwendet. Durch Vergleich der in beiden Experimenten erhaltenen Erqebnisse sind neue Tatsachen in Bezuq auf den Versaqensmechanismus geklart worden. INTRODUCTION A ground with a shallow depth near the foot of a mountain may show its mechanical characteristics as soils or the mixture of soils and rocks. When a mountain tunneling method such as NATM is applied to such a ground, maintaining the stability of the tunnel face becomes very important. In this paper, three-dimensional static and dynamic model experiments on grounds with different depths have been conducted ¹- 2 , in order to clarify the mechanism of the stability and the failure phenomena of a shallow tunnel face. In the static experiments, the earth pressure and the ground movement are measured, while in the dynamic failure experiments, the world's fastest high-speed video camera (with a maximum speed of 40,500 pictures per second) is employed to analyze the dynamic behavior of the tunnel face. The results obtained from the static experiments are compared with those obtained from the dynamic experiments. Some considerations are given regarding the experimental results, and new facts are found. 2 STATIC EXPERIMENTS 2.1 Experimental method and device Fig. 1 shows the experimental device used. Half of the shallow ground with a ground surface is treated here. An acrylic plate is installed on the symmetrical plane through the tunnel axis, through which the ground movement is observed. In a practical tunnel excavation, the initial stress of the ground in the tunnel axial direction decreases with the approach of the tunnel, and finally becomes zero. In order to express this tendency approximately, a half-circle tunnel-face-retaining plate (diameter 13cm) is set at the tunnel face in the tunnel lining (diameter 14cm). By slowly moving the face retaining plate to the right, the ground movement near the face is recorded by a camera. The initial ground is prepared by letting sand fall from a height of 30 cm. The strength of the ground is controlled by changing the later content of the various sands used. In order for the camera to catch the ground movements clearly, black-colored sand, which are the same type of sand used in the experiments, is horizontally placed at 3 cm intervals, and vertical and horizontal lines are painted on the acrylic plate at 1 cm intervals. Seven kinds of experiments have been conducted, they are shown in Table 1, where H/D is the relative tunnel depth (H: tunnel depth, D: tunnel diameter) and w, C, and are the later content ratio, cohesion, the unit weight of the ground and the friction angle, respectively.

Proceedings Papers

Paper presented at the 7th ISRM Congress, September 16–20, 1991

Paper Number: ISRM-7CONGRESS-1991-134

... deformation due to the decline in piezometric head. However, surface subsidence will occur as a result of three dimensional propagation of the deformation of confined aquifer, characterized by an influence factor within a limit angle Ψ, as shown in Figure 1.

**ground****surface**groundwater time factor...
Abstract

ABSTRACT: It is known that pumping of deep groundwater which contains natural gas has caused surface subsidence. And, houses, roads, bridges etc. on the ground have been often damaged. Surface subsidence in natural gas fields has been caused by extensive decline in water level(piezometric head) in confined aquifer. In this study, a new system for simulating surface subsidence has been developed. This system consists of a quasi three dimensional finite element seepage analysis and an influence function method to estimate the incidental surface subsidence. Contour maps of water level in gas seam and surface subsidence can also be obtained. This system has given useful results based on past, present and future conditions and made a contribution to the development of gas field without environmental hindrance. RESUME: Pompage de l"eau souterraine qui contient du gaz naturel cause l"affaissement du sol et il cause des dommages aux maisons, routes, points etc. qui sont construits sur le sol. L"affaissement du sol dans le gisement de gaz naturel est cause par la baisse de niveau de l"eau(hauteur piezometrique) dans la zone etendue en aquifère. Nous avons perfectionne le système qui simule l"affaissement du sol. Le système se compose du programme qui analyse le fluide penetrant par des elements finis de demi-trois dimensions et de la methode des fonctions d"influence. On peut obtenir de lui une carte avec contour d"eau souterraine et d"affaissement du sol dans la couche du gaz naturel. Le système donne des resultats efficaces qui sont fondes sur la condition passee, presente et future, et il contribue à l"exploitation de gisement de gaz naturel sans la destruction de l"environnement. Zusammenfassung: Es ist bekannt, daß der Extraktion von erdgashaltigem grundwasser ein betrachtliches· Absinken des Wasserspiegels (piezometrischer Head) im Grundwasserleiter folgt und dadurch Gelandeabsenkungen verursacht werden. Diese Arbeit stellt ein neuentwickeltes System zur Simulation von Gelandeabsenkungen vor, das aus einem quasi drei-dimensionalen FE-Programm zur Analyse von Sickerungsvorgangen besteht und mit Hilfe einer Einflussfunktion die dabei auftretenden Absenkungen abschatzt. Eine Darstellung von Contour-Maps sowohl der Absenkungsbetrage als auch des Wasserspiegels in den gasfuehrenden Schichten ist möglich. Mit Hilfe dieses Systems konnten wertvolle Ergebnisse fuer verschiedene fruehere, heutige und zukuenftige Untergrundbedingungen und technische Möglichkeiten gewonnen werden, und es kann dazu beitragen, Erdgasfelder ohne eine Beeintrachtigung oder Schadigung der umwelt zu konzipieren. 1 INTRODUCTION Natural gas resources exist through the world. In Japan since the 1930"s, groundwater containing natural gas has been developed in different places, such as Hokkaido, Niigata, Chiba, Miyazaki, Okinawa. Following the advance of industry, the amount of pumped groundwater and extracted natural gas have increased rapidly. The overdevelopment of groundwater and natural gas has resulted in a type of mining damage, i.e. surface subsidence. Especially in Niigata, surface subsidence exceeded 50 cm per year, and in Chiba the total surface subsidence amounted to over 100 cm. Therefore, many studies on surface subsidence in natural gas fields have been carried out, and useful methods which are able to know the ground movement have been also proposed. Nishida et al., for example, developed the horizontal two dimensional model. The results by their model were very coincident with in situ measurement data. They assumed that the amount of surface subsidence was equal to the gas seam deformation due to the decline in piezometric head. However, surface subsidence will occur as a result of three dimensional propagation of the deformation of confined aquifer, characterized by an influence factor within a limit angle Ψ, as shown in Figure 1.

Proceedings Papers

Paper presented at the 7th ISRM Congress, September 16–20, 1991

Paper Number: ISRM-7CONGRESS-1991-033

... Sweden rock mass tunnel repository Magnitude

**ground****surface**Earthquake waste repository loading glaclatlon Modelling of rock masses for site location of a nuclear waste reposit~ry Modell eines GebirgskOrpers im Bereich einer unterirdischen AtommOlldeponie Modelisation des massifs rocheux pour...
Abstract

ABSTRACT: To provide a better understanding of the rock mass behaviour for deposition of nuclear waste in hard rocks, five important events occurring in the life-time of the waste repository, i.e. glaciation, earthquakes, repository excavation, thermal loading, and bentonite swelling pressure, are modelled numerically in three different scales. The 2-D and 3-D distinct element codes (UDEC and 3DEC) are used. Faults, fracture zones and joints in the rock mass are considered. Based on the modelling results, the consequences of all above events are discussed with respect to their effects on the stability of a repository. Glaciation and thermal loading from the waste are found to have major impact on the rock mass stability in the vicinity of the repository. Swelling pressure of bentonite in the deposition hole and dynamic loading from earthquakes are less important to the stability of the tunnel and deposition hole. RESUME: Poor mieux comprendre le comportement des massifs rocheux pour le stockage de produits radioactifs, cinq phenomènes lmportants (glaciation, tremblements de terre, excavation du site de stockage, chargement thermique, pression de gonflement du à la bentonite) le produisant pendant la duree du vie d"un site de stockage, sont modellses d"une façon numerlque à trois echelles dlfferentes. La methode des elements distincts à deux et trols dlmenslons (UDEC et 3DEC) à ete utilisee. A l"ald,e des resultats du modèle, l"importance de ces phenomènes est presentee en ce qul concerne leurs effets sur la stabilite et la securite des sites de stockage de produits radioactifs. Ou a trouve que la glaciation et le chargement thermique du au produits radioactifs ont un impact sur la stabilite des massifs rocheux dans la proximite du site de stockage. Les pressions de gonflement de la bentonite dans les trous de stockage et le chargement dynamique de aux tremblements de terre sont moins importants pour la stabilite des tunnels et trous de stockage. ZUSAMMENFASSUNG: Zum besserenVerstandnis des Verhalters eines Geblrgskörpers, in dem Atommuell gelagert werden soll, wurden 5 Hauptereignisse, die wahrend der Lebensdauer solch einer Deponie auftreten können, wie z.B. Vergletscherung, Erdbeben, Hohlraumausbruch, Temperturbeanspruchungen und Bentonit-Schwelldruck, in 3 verschiedenen Masstaben mit numerischen Modellen untersucht. 2-D und 3-D Distinct Element Kodierungen (UDEC und 3DEC) wurden benutzt. Verwerfungen, Bruchzonen und Kluefte wurden im Gebirgskörper berueckslchtlgt. An Hand der Modellergebnisse wurden die Konsequenzen der obigen Ereignisse bezueglich Stabilitat und Sicherheit der Atommuelldeponie diskutiert. Es zeigte sich, dass Vergletscherung und Temperaturbeanspruchungen infolge des radioaktiven Muells einen grossen Einfluss auf die Stabilitat des Gebirges in der Umgebung der Lagerungsraume haben. Schwelldruecke des Bentonits in den Lagerungshohlraumen und dynamische Beanspruchungen durch Erdbebend agegen beinflussten nur in"geringem Masse die Stabilitat der Tunnel und Deponiehohlraumme. 1. INTRODUCTION The deposition of spent nuclear fuel is a task which calls for high security within the whole process of design for the control of the finite repository. For this reason, a comprehensive understanding and estimation of the mechanical response of the jointed rock mass to all kinds of events occurring now and in the future is necessary. During the period of time when the waste is toxic, the important events are glaciation, earthquakes, thermal loading from waste heat release, repository excavation, and the swelling pressure of buffer material in the tunnel and deposition hole. Each of these events affect the rock mass differently, therefore, all of them must be treated respectively. The distinct element method which is specially suitable for dealing with jointed rock mass is employed. This method was developed for rock material by Cundall (1971) and currently has been developed to encompass three dimensional problems including thermal loading. All the events listed above, except the earthquake, are modelled in three dimensions with the three dimensional distinct element code (3DEC) the response of the repository to earthquake is modelled in two dimensions with the two dimensional code UDEC.

Proceedings Papers

Paper presented at the 5th ISRM Congress, April 10–15, 1983

Paper Number: ISRM-5CONGRESS-1983-188

... Test site The test site where trial blasting has been conducted is shown in Fig.3. Upstream Oil & Gas

**ground****surface**detonation pressure Reservoir Characterization frequency detonation velocity maximum particle velocity analytical contribution reservoir geomechanics relation...
Abstract

SYNOPSIS: In this paper an analytical approach to forecasting the dynamic behaviour of an existing tunnel due to adjacent blasting is proposed, taking detonation velocity, weight of charge and three-dimensional blasting effects into account. High accuracy of the proposed approach is assured through field measurements. RESUME: Dans cet article, une approche analytique sur la prevision du comportement dynamique des tunnels existants suite aux abattages à proximite est proposee, en tenant compte de la vitesse des detonations, du poids de la charge et des effets tridimensionnels de l'abattage. L'exactitude de l'approche ainsi proposee est verifiee par des mesures en reel. ZUSAMMENFASSUNG: Es wird eine analytische Methode beschrieben, die das Verhalten eines Tunnels bei in der Nahe vor sich gehenden Sprengarteiten voraussagt. Sie beruecksichtigt die Explosionsgeschwindigkeit, das Gewicht der Sprengladung und den raumlichen Sprengeffekt. Die große Genauigkeit der vorgeschlagenen Methode wird durch Gelandemessungen bestatigt. 1. INTRODUCTION When construction works are conducted by blasting near an existing old tunnel, much attention should be paid not to cause any serious damages on the existing tunnel. For this purpose, an observational approach has been employed, in which the weight of charge and the method of blasting are controlled by monitoring the particle velocity of tunnel linings. This approach however, is difficult to apply to such a special tunnel as water supply, tunnel in which the monitoring is unable to operate. And also, in this approach, an allowable value of the particle velocity for the safety margin of the lining is not reasonably determined, so that the sufficient planning of blasting operation can not be made prior to blasting. The objective of this study is to propose an analytical approach to forecast the dynamic behavior of existing tunnel linings due to an adjacent blast operation. In this approach, a finite element method (FEM) is employed, in which such executive conditions as weight and detonation velocity of charge, distance between existing tunnel and blasting point, and three dimensional blasting effects are taken into consideration. Then, the results obtained by this approach are compared with those of field measurements. 2. ANALYTICAL APPROACH In this study, the dynamic behavior of existing tunnel linings is analyzed by FEM, in which θ-method is employed (Wilson et al.,1973), and the time length Δt for one step in numerical integration is taken to be 15/106 Sec.. A plane strain condition is assumed so that two dimensional analysis is done in a plane perpendicular to the tunnel axis, which passes through blasting points. In the two-dimensional analysis, however, unrealistically greater energy would be applied to the ground, because in reality the explosive energy propagates and attenuates three dimensionally in the ground. To avoid this shortcoming the following method is proposed introducing the equivalent radius r of blasting hole, instead of using the actual radius of borehole in which blasting operates. Therefore, the dynamic behavior of the tunnel linings can be easily analyzed by FEM in which the equivalent radius r obtained by Eq.(3) is used. According to this method, accurate results can be expected, because the geometrical and geological conditions near the tunnels are easily taken into account, and the equivalent radius of the blasting hole corresponding to the weight of charge is also considered. 3. DETERMINATION OF IMPUT DATA 3.1 Mechanical properties of ground and lining Mechanical properties of rock specimen in general are quantitatively, very different from those of rock masses, because they are very much affected by the specimen size as well as the arrangement of microscopic particles which compose the rock, and, on the other hand, the mechanical properties of rock masses depend mainly on macroscopic structural characteristics such as joints and faults. Therefore, the mechanical properties of rock masses should be directly evaluated by in situ tests. On the other hand, damping characteristics are determined as follows. Fig.1 shows the experimental results for several different types of rock indicating the relationship between the frequency ft of harmonic applied stress and coefficient of viscosity η which is evaluated by assuming the ground to be Voigt type viscoelastic material (Hayashi et al.,1973). Vibrations caused by blasting are limited in a local area of the ground and different from those of earthquake in which the ground vibrates in a widely spread region. The frequency of vibration measured in rock due to blasting of dynamite ranges from about 10 to 1000Hz, and its spectrum shows the peak value at about 200Hz (Ito et al.,1971). Therefore, in determining the frequencies in Eqs(5) and (6), it is unfavorable to use the minimum value of natural circular frequency of the ground, which is usually used in earthquake problems. 4. APPLICATION OF THE PROPOSED METHOD To verify the accuracy of the proposed method, analytical results are compared with field data. 4.1 Test site The test site where trial blasting has been conducted is shown in Fig.3.

Proceedings Papers

Paper presented at the 5th ISRM Congress, April 10–15, 1983

Paper Number: ISRM-5CONGRESS-1983-180

... away from the well known Larderello geothermal reservoirs. In addition to the high temperature of the virgin rock mass (75°C at 500 m depth below sea level, near to 800 m below

**ground****surface**), a strong influence on the temperature conditions underground is that due to the heavy mechanized systems used...
Abstract

SYNOPSIS: The heat transfer in the rock mass around mine openings is studied with reference to the Campiano Mine (Grosseto, Italy), where the geothermal gradient was measured to be approximately 0.08°C per meter depth. The following problems are considered: Laboratory tests carried out in order to determine the thermo-physical properties of the rock. In situ tests performed to measure the temperature distribution in the rock mass around mine openings and to evaluate the most important thermo-physical parameters of the rock mass. Analytical and numerical modelling performed in order to interpret the in situ tests and to predict the temperature distribution in the rock mass around mine openings. RESUME: On etudie la diffusion de la chaleur dans la roche autour des vides miniers dans le cas de haut gradient de temperature (0.08°C/m) dans la mine de Campiano (Grosseto, Italie). L'etude a ete realisee par: 1) essais en laboratoire pour deduire les proprietes thermo-physiques de la roche; 2) essais in situ pour mesurer la distribution de la temperature dans la roche autour des vides miniers et d'evaluer les plus importants paramètres thermiques au niveau de la roche in situ; 3) mise au point des modèles analytiques et numeriques ayant pour but d'interpreter les essais in situ et de predire la distribution de la temperature dans la roche. ZUSAMMENFASSUNG: Der Warmeaustausch im Gebirge um bergmannische Hohlraume wird in Bezu auf die Campiano Grube (Grosseto, Italien) untersucht, wo der geothermische Gradient einer Temperaturzunahme von 0.08°C je Meter Tiefe - nach eigenen Messungen - zu enbsprechen scheint. Man hat deswegen die folgenden Untersuchungen durchgefuehrt: 1) Laborversuche, um die Warmeeigenschaften des Felsens zu bestimmen. 2) In situ Messungen, um die Warmeverteilung in der Umgebung von bergmannischen Hohlraumen festzustellen und die wichtigsten Warmeparameter des Gebirges abzuschatzen. 3) Analytische und numerische Modelle wurden hergestellt, um die in situ Messungen wissenschaftlich zu erklaren und um die Ternperaturverteilung um Grubenhohlraume vorhersagen zu können. INTRODUCTION A number of very important engineering problems relate to heat transfer in rock masses. Among the most interesting examples, the following may be recalled: 1. the stabilization of rock by artificial freezing, for the purpose of excavation of wells and tunnels; 2. the industrial use of geothermal reservoirs; 3. the choice of underground spaces for radioactive waste storage; 4. the exploitation of minerals in deep mines, with high temperature conditions. With reference to the problem of evaluating the thermomechanical behavior of rock masses (i.e.) stress analysis and heat transfer of rock masses), the present state of knowledge is limited. For example, rock thermo-physical properties (e.g. thermal diffusivity and/or thermal conductivity; specific heat) are less known than mechanical properties (e.g. stress-strain laws, failure criteria, etc.). The need for obtaining additional data on rock thermo-physical properties in the laboratory and in situ is therefore well recognized. At the same time, appropriate analytical and numerical methods and solutions are to be developed for the study of heat transfer in rock masses around underground openings. This paper describes a number of problems relating to the analysis of heat transfer around underground openings in a deep mine near to Grosseto (Italy). The purpose is to obtain the basic data needed for predicting the temperature distribution in the rock mass and in the air where a mine opening is being excavated. The following problems are considered: Laboratory tests carried out in order to determine the rock thermo-physical properties. In situ tests performed to measure the temperature distribution in the rock mass around mine openings and to evaluate the rock mass thermo-physical parameters. Analytical and numerical modelling performed in order to interpret the in situ tests and to predict the temperature distribution in the rock mass around mine openings. THE MINE UNDER STUDY The mineral deposit is formed of pyrite, mixed (Pb, Zn, Cu) sulphurs, and pyrite and magnetite, with a total of 25 Mt presently estimated reserve. An evaporitic series, made mostly of anhydrite with dolomites, is above the deposit, with phyllitic rocks being below. A very high geothermal gradient (approximately 0.08 °c per meter-depth) is present. It is to be noted that Campiano is located approximately 20 km away from the well known Larderello geothermal reservoirs. In addition to the high temperature of the virgin rock mass (75°C at 500 m depth below sea level, near to 800 m below ground surface), a strong influence on the temperature conditions underground is that due to the heavy mechanized systems used for excavation purposes. For the purpose of the present study, the heat transfer problem in situ was examined, mainly by considering the rock mass thermal behavior around a drift (spiral decline) of a 20 m 2 cross section, created in order to reach the orebody, Fig. 2. However, in a few cases, also the openings located in the ore and neighbouring rocks were considered.

Proceedings Papers

Paper presented at the 4th ISRM Congress, September 2–8, 1979

Paper Number: ISRM-4CONGRESS-1979-237

... tons per square meter for overburden, sandstone and siltstone respectively; average unit weight 2.60 tons per cubic meter; and ambient stress coefficient equal to 1.00. The material layers are considered parallel to the

**ground****surface**. The top layer is overburden, the middle layer is sandstone and...
Abstract

SUMMARY: Erosion of a cut in stratified sandstone and siltstone over a ten year period resulted in a surface profile conforming to the zero stress contour calculated in the initial excavation. This paper shows stress contours calculated using a two-dimensional finite-element analysis and the configuration of the eroded cut, demonstrating that the calculated zero stress contour may be used to predict the equilibrium surface of the excavation. SOMMAIRE: L' erosion d' un versant d' excavation au couches greseuses et pelitiques, pendant la duree de 10 ans, a produit une surface de section correspondante à la ligne de tension egale zero, qui a se calcule pour l' excavation primitive. A cette etude se presentent les lignes des tensions egales qui ont calcule par la methode des elements finis à deux dimensions et se conclut par la forme du versant erode, que la ligne de tension egale calculatrice, peut utiliser pour la prevision de la surface d' equilibre d' excavation. ZUSAMMENFASSUNG: Die Erosion an einer von Flysch besetzten Abtragsböschung, hat in dem Zeitintervall von 10 Jahre ein Hangschnitt geschaft, das die Iso-spannungslinie null der Abtragsböschung entspricht. In der vorliegenden Arbeit werden die Spannungslinien dargestellt, die mit Hilfe der zweidimensionalen Berechnung der Finite-Elemente Methode bestimmt wurden. Von der Form der erodierten Abtragsböschung, wird die Schlussfolgerung gezogen, dass die berechnete Spannungslinie null, fuer die Vorbestimmung der standsicheren Abtragsflache benutzt werden kann. INTRODUCTION Unstable regions in rock slopes may be identified through negative minor principal stresses (Bukovansky-Piercy, 1975, Kalkani, 1975) because of the comparative weakness of rock under tension. In case of inclined stratified rock, such as sedimentary formations, the stress condition at the cut surface is determined by the relevant properties of the sequence of layers. A two-dimensional finite-element method incorporating the plane strain assumption and uniformely stressed triangular or quadrilateral elements has been employed for the analysis. Contours of constant stress in the new excavation were derived from these calculations for 2:1 slopes cut in sandstone and siltstone strata. The actual contour of the surface of the cut was measured 10 years after excavation, and it is shown that regions where the rock was in tension have eroded away. SITE CHARACTERISTICS Two cases of excavation for road construction are examined in this study. The road was excavated in a series of Flysch near the Kastraki Hydroelectric project in Greece. The Flysch for this area consists of interbedded sandstones and siltstones of the middle Eocene to the early Miocene. The rock types appearing at the road are weathered siltstone overlying sandstone, which in turn overlies siltstone. The weathered siltstone is light grey and calcareous and contains thin layers of fine grained sandstone. When considerably weathered it is characterized as overburden. The sandstone is grey, possessing a dence texture and contains a few scattered layers of grey shale. The siltstone is grey with fine seams of sandstone, and becomes light grey and friable when exposed. The road excavation cut the flysch series in all directions, and an upslope and a downslope section selected for study are shown in Figures 1 and 2 respectively. In both cases, the cut was at a 2:1 (vertical: horizontal) slope. During the first year after excavation was complete the slope retained its original shape, but shortly afterwards it begun to approach a more stable condition. EXCAVATION STRESSES The excavation stresses were calculated with a two-dimensional finite-element stress analysis. The minor principal stress plots are presented in Figures 3 and 4, which correspond to Figures 1 and 2 respectively. The elevations and distances in Figures 3 and 4 are given in fractions of slope height H from the toe of the cut, while the minor stress σ3 distribution is given in ratios σ3/γh where γ is the average unit weight of the rock. The following properties are used based on values of the same rock at the nearby hydro-electric project: Poisson's ratio 0.20, Modulus of elasticity 1.40E06, 1.60E06, and 2.00E06 in tons per square meter for overburden, sandstone and siltstone respectively; average unit weight 2.60 tons per cubic meter; and ambient stress coefficient equal to 1.00. The material layers are considered parallel to the ground surface. The top layer is overburden, the middle layer is sandstone and lower layer is siltstone. Excavation in Figure 3 results in a narrow tensile stress region along the cut face which widens at the lower siltstone region. In Figure 4, tensile stress regions are formed with smaller widths at the sandstone and larger widths at the siltstone. Cross sections in Figures 5 and 6 show the actual profiles of the slope cuts corresponding to the photographs.of Figures 1 and 2. The excavated slope has reached an equilibrium and the minor principal stress at the surface is zero. This final configuration is compared with the zero stress line of Figures 3 and 4.

Proceedings Papers

Paper presented at the 4th ISRM Congress, September 2–8, 1979

Paper Number: ISRM-4CONGRESS-1979-093

... relation hisatake shear modulus surface settlement equation

**ground****surface**boundary condition surface displacement displacement creep function tunnel excavation settlement viscoelastic ground tunnel center line tunnel anisotropy shallow tunnel excavation initial stress...
Abstract

SUMMARY: In this paper, first, the method of a complex variable taking time dependency and anisotropy of the ground into consideration is newly proposed to estimate surface displacements caused by shallow tunnel driving in soft ground subject to gravity. Secondly, theoretically calculated values are shown to have good agreements with field data. ZUSAMMENFASSUNG: Die oberflachlichen Verschiebungen verursacht durch den Graben des Tunnels in einem anisotropen viskoelastischen Grund werden durch das Berechnungsverfahren der komplexen Veranderlichen gelöst. Dann werden die Feldmessungen mit den theoretischen Resultaten verglichen. SOMMAIRE: Cel article analyse les tassements superficiels induits par le creusement d'un tunnel à faible profondeur dans un sol mou soumis à son poids propre par une methode faisant appel au domaine complexe et incluant les effets de fluage et d'anisotropie du sol. Finalement, plusieurs mesures Sur le terrain sont comparees aux predictions theoriques. INTRODUCTION The excavation of a shallow tunnel in soft ground brings about surface displacements of the ground. Therefore, it may be required, in advance, to estimate the magnitude of surface displacements and their effects on neighboring structures. As surface displacements are affected not only by such geometrical conditions as the depth of burial for a tunnel and inclination of ground surface but also by several geological properties, little information has been available up to now about the accurate estimate of the magnitude of the displacements. It is of importance to take into account the fact with respect to deformation phenomena that the surface displacements over a tunnel in soft ground generally increase with time and are affected, in no small quantities, by directions of sedimentation, stratification and joints which bring out the anisotropic properties of the ground as a whole. In this paper, problems of surface displacements resulting from shallow tunnel driving in soft ground subject to gravity are analyzed by the method of a complex variable, considering time dependency and anisotropy of the ground. Subsequently, the results of several field measurements with respect to displacements are compared with the theoretical ones. METHOD OF ANALYSIS 1. Fundamental relationships for an anisotropicelasticity The authors refer the ground to Cartesian coordinate system (X1,X2,X3) shown in Fig.l. 2. Determination of stress functions The tunnel excavation can be expressed by releasing the initial stresses σijnj which exist on the virtual tunnel boundary B1(Fig.1) before the excavation, where nj are the components of the inward unit vector normal to B1. The initial stresses can be considered as functions of parameter θ having period 2π, and they can be expanded in Fourier series in cos (mθ) and sin(mθ). The expressions of the infinite series on the right-side of the above equations are obtained as a result of the integration of the,initial stresses with respect to arc-length along the contour B1. Then the coefficients bjk (m) become known complex quantities. On the other hand, 1bjo must be determined by the condition that the displacements caused by the tunnel excavation must be equal to zero at infinity. 3. Initial stresses of the ground due to gravity Initial stresses in the anisotropic elastic ground due to gravity can be obtained by considering such conditions: All of the stresses σij are independent of the X1-axis. σ22=0, 012=0, 02,=0 on B2. Strain E11 is caused by σ11 only, which is the normal stress component obtained from equilibrium equations with respect to gravity. ε13=0 in the ground. ε33=0 in the ground. 4. Displacements caused by tunnel excavation in anisotropic viscoelastic ground These equations independent of time correspond to those of anisotropic elastic ground. It has been shown that the way to solve boundary value problems in the theory of viscoelasticity is to apply the Laplace transform, with respect to time, to the time dependent field equations and the boundary conditions. By so doing, the solution to the original problem is reduced to the transform inverse of a solution to the transformed problem. 1. Convergent characteristics of analytical functions Fig.2 shows convergent characteristics of the analytical functions. It may be recognized that the convergent characteristics of analytical functions are fairly good and that if the first two terms of the infinite series of the functions are used, engineering accuracy will be satisfied. In the following analysis the first four terms of the infinite series are used. 2. Analytical results The horizontal and vertical displacements (Uh and Uv respectively) of ground surface are summarized in Figs.3 and 4. From Fig.3 we can see that the value of anisotropic parameter k=C22/22/C11/11 considerably affects the displacements. When the value of k becomes smaller than 1.0 (=isotropic), Uh increases greatly; on the other hand, if the value of k becomes greater than 1.0, Uv decreases remarkably. The directions of sedimentation, stratification and joints which bring out the anisotropic properties of the ground can, therefore, be thought to have very important effects on the displacements.