Abstract Demand of high pressurized gas storage in underground rock caverns is increasing. Compressed natural gas (CNG) and compressed air energy storage (CAES) are one of the promising examples after since lined rock cavern (LRC) concept has been verified through in-situ pilot tests. Two key essential concerns of high pressured gas storage in underground rock caverns are mechanical stability of the cavern against high inner storage pressure and the risk of gas leakage from the caverns. In this study, we introduce our results of numerical simulations so as to investigate the potential of monitoring for gas leakage at a pilot facility for CAES in underground LRCs. The pilot facility was constructed at a comparatively shallow depth of 100 m, compared to the previous cases with several hundreds of meters, aiming at validating the feasibility of the LRC storage concept in which inner sealing liners, consisting of steel plate and concrete linings, are installed inside the excavated rock caverns (KIGAM, 2011). Compressed air may leak through either initial defects of inner containment liners such as imperfect welding regions and in-situ construction joints of the liners, or through structurally damaged points of the liners during the CAES operation where compression and decompression of the caverns are necessarily repeated and their structural robustness can be deteriorated. For this perspective, we carried out a coupled thermodynamic and geomechanical deformation analysis using TOUGH-FLAC simulator, and investigated the effectiveness of strain monitoring method in detecting mechanical failure of liners which may provide major pathways of air leakage. We therefore used an equivalent continuum model to relate the localized tangential strain to fracture permeability changes, which was developed in our early work (Rutqvist et al, 2012). In detecting and characterizing the leakage location, we tested a cross correlation technique using the synthetic pressure responses monitored in case of the failure of the inner liners. From the investigations, we showed that tangential strain, rather than radial, monitoring especially at the inner face of the sealing liners can be more effective in detecting the mechanical failure of the liners. In localizing the leakage point, we noted that the interface between the inner liners and surrounding rock may not be perfectly bonded so as to increase permeability through which any leaking air pressure may migrate more dominantly. We also demonstrated that the cross correlation of the time histories of pressure measurement especially at these interfaces can be useful in identifying the leakage point. These results may provide useful information in overall design of monitoring and alarming system of our upcoming CAES pilot facilities.

Abstract The storage of petroleum products on surface is associated with difficulties and limitations. Accordingly, a viable alternative is to excavate underground space in rock and provide a safe way for oil storage. Soft rocks such as salt domes provide good conditions from environmental and operational points of view. The potential for high-volume storage and low permeability are encouraging aspects for oil storage in salt domes. The complicated shape of oil storage caverns, the complicated behavior of salt rocks, and boundary conditions associated with large underground openings are important challenges in the design of oil storage caverns. The aim of this paper is to delve into the stability and deformation mechanisms of storage caverns created in salt domes. A parametric study of effect of the cavern size, orientation, and depth is carried out as a function of ground stress regime. The stress field and deformation mechanisms are calculated for each case aiming at providing design guideline. Introduction One of the most popular soft rock that is used for underground oil storage is salt rock (halite). Salt rock has particular characteristics which makes it suitable for oil storage. Salt rock has several advantages for oil storage, these are: high production rate, high degree of availability, short filling period, high level of safety and low permeability [1]. The low permeability is due to the fact that halite deforms in a plastic manner over a wide range of pressures, temperatures and rates of deformations. This property prevents joints or gaps opening up in the formation, thus preventing the escape of liquids and gases. The state of stresses around the cavern in salt domes depends on the depth of the cavern (initial stresses and rock mass temperatures are increasing with depth), the in-situ stress state within the rock mass, and the internal oil pressure in the cavern. Furthermore, the salt creep behavior and the cavern geometry are influencing stress redistributions during loading and unloading phases. Rock mass structure, cavern geometry, material behavior and cavern operation patterns require complex physical models to describe the load-bearing behavior of the geomechanical structure. The determination of stress, strain and deformation in the rock mass due to cavern construction and operation are complex problems which can be evaluated employing numerical tools such as the Finite Element Method (FEM) or Finite Difference Method (FDM). In this study, the finite difference method was used to evaluate the behavior of oil storage cavern in salt rock.

Abstract Laboratory tests were performed to explore the effects of frequency on the deformation property of rock salt subjected to cyclic loading under confining stress condition. A two-stage (transient and steady) evolution law of axial cumulative strain was obtained through cyclic stress-strain curves complied from the loci of minimum load of each cycle. The unloading modulus decreases with loading cycles/time as a negative exponential function. The damage of rock salt under cyclic loading is reflected by the degradation of elastic modulus. A unified damage evolution equation considering the effects of frequency and time was established based on the experimental results. A new creep damage model for rock salt was proposed by introducing the non-stationary modular components in Burgers creep equation according to the Lemaitre equivalent strain theory. Comparative study indicates that the new model can accurately describe the creep deformation and damage evolution of rock salt under different loading frequencies. This paper provides a more reasonable model and relevant mechanical parameters for the stability analysis of compressed-air storage cavern in the injection and withdrawal durations. Introduction The time-dependent properties of rock salt play a key role in long-term cavern stability and safety. The typical creep deformation consists of the transient, the stationary, and the accelerated phases. The internal variable theory and elasto-viscoplastic component method have been frequently used to formulate the constitutive equation of the primary creep of rock salt (Aubertin et al., 1996; Munson et al., 1996; Cristescu, 1993; Musso & Vouille, 1974). The steady state creep relationship of rock salt is mainly built based on the creep mechanism of metal material (Pfeifle & Senseny, 1983). In 1990s, continuum damage mechanics (CDM) approach was introduced in the study of the creep characteristics of rock salt (Chan et al., 1992). Generally, the mechanical parameters of the constitutive models for representing inelastic flow due to coupled creep, damage, and damage healing in rock are assumed to be constant. However, the elastic modulus, strength, and the viscosity of rock mass subjected to multi-field stress and weathering tend to decrease with time (Sun, 2007). The reduction of mechanical parameters objectively reflects the degradation of mechanical properties. Therefore, the damage evolution could be described by introducing variable parameters into the stationary creep constitutive model, which is a new method for investigating the creep damage property of rock material (Zhang et al., 2009; Yan et al., 2010; Zhu et al., 2010; Li & Wang, 2009).

Abstract Nonlinear time-dependent response analysis of salt cavern under extreme loads in disaster mode is of great importance to the safety and disaster prevention of gas storage group. Uncontrolled blowout is one of the extreme conditions for compressed-air cavern operation. Based on the geological structure of Jintan salt deposit, China, the numerical model of the complete process of water solution, cyclic operation, and internal pressure runaway was developed. The effects of rapid unloading on the stress filed, the progressive failure of surrounding rock, the volume convergence of storage cavern, and the ground subsidence were simulated employing an elasto-viscoplastic damage constitutive equation for rock salt. The results indicate that the damage and failure zones propagate much larger in the mudstone interlayer than in the host salt. The volume of damage and failure zones surrounding salt cavern induced by unloading process is 5~6 times that of cyclic injection and withdrawal process. The average volume convergence rate of salt cavern reaches 0.012%/d~0.013%/d, which is 6~6.5 times that induced by cyclic operation. The ground subsidence exhibits a typical funnel curve. The affected region of ground subsidence due to rapid unloading in the blowout period is about two times the maximum cavern diameters. Furthermore, double cavern analysis reveals that the interaction between adjacent caverns may be ignored so long as the pillar width is larger than two times the maximum cavern diameters. Introduction Underground solution-mined salt caverns are widely accepted and utilized as the highly secure strategic storage for natural resources. Despite there are many advantages of underground salt storage, such as high security, economy and durability over other energy reserve methods, the catastrophic accidents about salt storage cavern (e.g., oil/gas seepage, cavern collapse, and ground subsidence) have happened from time to time ever since 1950s. Besides, they usually caused great economic losses and secondary environmental disasters. According to the global statistical events, the probability of heavy accident about single cavern during construction and operation phases is 1.51% (Yang et al., 2013). With the development of large-scale construction of energy storage groups in China, the issue rock salt cavern safety and stability becomes increasingly prominent. It is well established that the geometric design parameters (storage shape, depth, roof and floor thicknesses, pillar width, etc.), operating conditions (minimum and maximum internal pressure and injection-production rate, etc.) and the characteristic and distribution of interlayer are the main factors affecting the stability of salt cavern in bedded rock salt. Rock rheological mechanics and the numerical simulation were applied to study the relationship between the internal pressure and the convergence deformation property and the stability of the rock salt gas storage cavern by Lux (Lux, 1984). Ehgartner (1991) performed finite element analysis to study the effects of cavern spacing and internal pressure on the ground subsidence and cavern volume loss. An exponential relation between the ground subsidence and cavern spacing was obtained. Hoffman stated that the ground subsidence and the rate of volume loss increased with an increase of the buried depth, while the ground subsidence decreased with an increase of the ratio of cavern spacing to diameter (Hoffman, 1992; Hoffman, 1992; Hoffman & Ehgartner, 1997). Moghadam et al. (2013) employed an elasto-viscoplastic constitutive model by a Lagrangian finite element formulation to calculate the stress variation and ground movement during creep of surrounding rock salt of storage cavern. Wang et al. (2011) discussed the deformation differences that occur due to the presence of thin mudstone layers in bedded rock salt cavern. Deng et al. (2014) simulated the time-dependent deformation and quantitatively evaluate the global stability if rock salt cavern with the deformation reinforcement theory.

Abstract The demand for gas storage operations with high withdrawal rates and operation modes different to a seasonal storage regime requires a more detailed rock mechanical consideration of thermal induced stresses in the vicinity of the caverns. This means that the change of gas temperatures during operation and the consequences of these temperature changes on the stressing of the salt rock mass must be taken into account in the rock mechanical dimensioning. Within the rock mechanical calculations a loading history, i.e. a pressure versus time dependency, has to be defined. As rock salt has a time dependent material behavior stress redistributions in the rock salt mass take place even under constant internal pressure conditions. Therefore not only withdrawal and filling periods but also the duration of phases with nearly constant internal pressure is significant for the resulting state variables. Within the paper the differences and consequences for the rock mechanical recommendations are discussed. As a result it can be concluded that recommendations with respect to minimum operation pressure as well as for maximum withdrawal rates can be answered only in connection with the respective time intervals. Introduction There are many different aspects to be taken into account when performing a rock mechanical analysis for the design of a gas storage cavern in rock salt. On the one hand high withdrawal and filling rates of the caverns are desirable. The optimization for this goal will be performed for a so-called free operation range where no restrictions about permissible time periods have to be regarded. On the other hand the cavern investment requires a minimization of cushion gas and therefore small minimum internal pressures. An acceptable compromise is concentrating the trading in the free operating range, i.e. between maximum pressure P max which is identical to the upper limit of the free operating range and its lower limit P lfor . Below this pressure range time restrictions apply. Nevertheless this range can be used for a certain time period during each year of operation.

Abstract This paper discusses the design of underground salt caverns, opened by solution mining, for the production of brine and storage of natural gas under high pressures. The caverns are located in the salt basin in Maceio City, Alagoas State, at the northeast region of Brazil. Special attention is given to the geomechanical structural design of the caverns using computer codes specially developed for the simulation of excavations in salt rock formations, considering validated constitutive creep laws under different initial stress states and temperatures. The behavior of sedimentary rocks intercalations presented in the salt layer is simulated using elastic-plastic models. The excavation of the caverns by solution mining is also simulated starting from a geostatic initial equilibrium state of stresses, with a unique formulation only implemented in these computer codes, without the need of the application of boundary stresses to the model in order to develop the initial state of stresses. These computer codes have being used in the design of several clusters of caverns for brine production used as raw material of Poly Vinyl Chloride (PVC) of the Chemical Industryin Brazil. These computer codes and methodology were also applied to the design of the underground conventional potash mine in the state of Sergipe, overlying tachyhydrite and carnallite with very high creep strain rate. They have also been used in the design of the pre-salt oil wells through thick layers of stratified salt rock in Santos Basin, for the exploration and production of the pre-salt reservoirs in Brazil. The constitutive creep equations implemented in the codes are based on a double mechanism creep law. The creep constants adopted in the simulation are taken from a previous investigation carried out on an experimental panel of the potash mine, considering the stratified geology with different salt rocks of the basin where the mine is located. These constants were also obtained by lab tests under different confined and differential stresses and temperatures.

ABSTRACT Uniaxial and triaxial compression tests are performed to assess the loading rate effect on the strength and deformability of the Maha Sarakham salt. The salt specimens with a nominal dimension of 5.4×5.4×5.4 cm3 are compressed to failure using a polyaxial load frame. The lateral confining pressures are maintained constant at 0, 3, 7, 12, 20 and 28MPa while the axial stresses are increased at constant rates of 0.001, 0.01, 0.1, 1.0 and 10MPa/s until failure occurs. The salt elasticity and strength increase with the loading rates. The elastic modulus varies from 15 to 25 GPa, and the Poisson's ratio from 0.23 to 0.43. The elastic parameters tend to be independent of the confining pressures. The distortional strain energy at dilation and at failure from various loading rates varies linearly with the mean strain energy. The proposed empirical criteria are applied to determine the safe maximum withdrawal rate of a compressed-air energy storage cavern.

ABSTRACT Engineering geology plays a key role in planning, design and construction of underground cavern storage facilities. The geological assessment of the site is made not only during investigation but also corroborated and updated during construction. In case of cavern storage project, relatively smaller dimensioned water curtain tunnels, which lie above the main storage cavern, are always excavated in advance before excavation of the main large storage caverns. This water curtain tunnel acts as a pilot tunnel and helps assessment of the likely geological setting in advance. As part of the water curtain system, large numbers of boreholes are drilled from the water curtain tunnel and are hydraulically charged to maintain a saturated rock mass surrounding the storage caverns, revealing additional information about the geological and hydro-geological setting above the cavern. Thus a 3D geological (structural) model of the site is updated through an active design process with focus on geological hot spots intersecting the cavern. During construction of caverns, a careful approach is adopted along these hot spot segments. These adverse rock mass conditions are probed, assessed and supported in accordance with special design supports. The geological model is further updated during excavation of cavern heading and becomes useful for excavation of benching, for verification of the rock support in heading and in further optimisation of rock support during bench excavations. The paper presents two case studies of underground storage cavern sites, where in the active design process has been adopted for geological assessment of both the sites.

ABSTRACT The world's increasing demand for natural gas has made the research on the temporal evolution of storage group damage and the corresponding protection theory of great significance. At present, researches on the overall stability and temporal evolution of underground caverns are relatively few. Relating experimental study has not been reported yet. This paper simulated the injection-production cycles of 4-cavern reservoir group under different internal pressure with small block masonry. The variation of the displacement and strain of the bedrock and the cavern group is automatically recorded by the displacement meters and the strain gauges buried in the model. Cavern stability under different gas production process, the failure pressure of the caverns and the impact of mudstone interlayer on cavern stability are analyzed.

ABSTRACT The current status and development trend of natural gas pipelines and storage in China is summarized briefly. With the development of economy, the natural gas demand in China increases rapidly; the construction of long distance natural gas pipeline enters a fast development period. To support long transportation gas pipelines, a group of natural gas storages have been built or building in China. The success of the Jintan salt cavern gas storage project in old caverns validates that bedded salt rocks as well as salt domes can be utilized as host rocks of underground gas storage. Then, the advances in researches of the mechanical behaviors of deep bedded salt rocks in China are reviewed comprehensively. Some researches on the mechanical characteristics of bedded salt rocks have been present recently for feasibility studies of gas storage in deep bedded salt rocks. Those studies validate strongly the feasibility of gas storage in bedded salt rocks, and also provide useful technical supports for the construction of gas storages in salt caverns.

ABSTRACT In order to assess the global stability of underground cavern group for energy reserves, deformation stability theory which considers the strength reduction approach of finite element method (FEM) is developed. Global stability criterion of cavern group is established based on the K~Δ E relation, where K is the strength reduction factor and Δ E is the plastic complementary energy. For the state of instability, the unbalanced forces clearly exhibit the position and pattern of the local failure. We study the global stability and local failure of the single cavern, double cavern, multi-cavern and Jintan oil and gas storage cavern group in salt deposit. Multiple influencing factors such as cavern diameter, cavern spacing, weak intercalation, internal pressure, pressure loss and cavern layout were considered. As a result, the maximum cavern diameter, the minimum cavern spacing, the minimum stable internal pressure and the optimal layout mode of cavern group was determined.

ABSTRACT The visualized model test of gas storage cavities destruction process in salt rock is more difficult than the ordinary geo-mechanical model test, which demands the air tightness of cavities, the visibility of destruction process and the similarity of rheological property and self-healing between model material and as salt rock. The authors have excogitated an air impermeable and transparent material, which imitates the self-healing and rheological property of salt rock after large numbers of tests. In this article, techniques of constructing the physical model by utilizing this model material are introduced, and the load control system is also described in detail. A kind of non-disturbed 3-D deformation measurement method which bases on Digital Speckle Correction Method (DSCM) and pre-embedded displacement sensor method is put forward. Besides these, the system of measuring model internal deformation and monitoring the destruction process are illustrated.

ABSTRACT: A three-dimensional hydrogeological modelling method for the large LPG storage project is developed in order to predict the hydraulic behaviors around the caverns precisely for the observational design and construction from a hydrogeological point of view. The Namikata LPG storage cavern under construction, one of the world's largest LPG storage caverns is the subject of this study. More than a thousand of hydraulic conductivity data have already been obtained from the site investigation.The geostatistical technique is employed to deal with a large amount of the spatial data that can be obtained at each stage of the project. The ordinary kriging (OK) is implemented to obtain a spatial distribution of hydraulic conductivity and that of its estimation error at each stage. The sequential indicator simulation (SIS), one of the widely used geostatistical simulation methods, is also implemented to assess the uncertainty of hydraulic conductivity. A set of realizations, which are generated using different series of random numbers, gives a map of the upper tail probability above a specific threshold value. This map is convenient for the risk assessment related to the uncertainty of hydraulic conductivity. Furthermore a new hybrid modelling methodology considering geostatistical and hydrogeological correlations between a pair of spatial data at different locations is proposed to obtain a geostatistically and hydrogeologically relevant model that can enable to predict the hydraulic behaviors in the subsequent stage of the project precisely.The models based on the realizations of SIS are used to simulate the observed hydraulic behaviors of the site by FiniteVolume Method. The most relevant model is identified and validated by comparing the measured and the computed values of pore pressure at the specific positions. The validated SIS model shows lower hydrogeological connectivity than theOKmodel that has an unfavorable smoothing effect and is apt to overestimate the hydrogeological connectivity due to that effect. In fact the computed pore pressure from the validated SIS model shows better agreement with the measured value than that from the OK model. Thus the higher performance of the modelling method is clarified. 1 INTRODUCTION The constructions of the Namikata and the Kurashiki LPG storage caverns are two of the world's largest underground LPG storage projects being operated by JOGMEC in Japan. To maintain the air tightness of the storage caverns at normal temperature and high storage pressure, JOGMEC designed the water containment system. The system of water curtains is established above the LPG storage caverns and provides higher surrounding water pressure than storage pressure to maintain the air tightness, instead of using concrete and steel of lining works. The LPG storage pressure is designed as 0.95MPa for keeping the propane (boiling point is 15° at 0.75MPa) in liquid phase at normal temperature. To ensure the air tightness of LPG tank and the water containment ability of water curtains, it is important to grasp the hydrogeological structure in site-scale.

ABSTRACT: According to the requirement of theWest-East GasTransmission Pipeline Project in China, 6 existing salt caverns in Jintan Salt Mine, Jiangsu province, were selected as natural gas storages. In the paper, the feasibility of this use is evaluated through the geological investigation of salt rock occurrence, the mechanical experiments and numerical simulating.A positive conclusion is given. 1 INTRODUCTION Salt rocks are generally recognized to be the ideal geologic host rocks for storage of gas and crude oil and are also being considered to be used in the disposal of radioactive waste. So far, numerous foreign researchers have already carried out many studies [1−11] on the strength and deformation characteristics of salt rocks in laboratory and field and established constitutive models of relationships among the damage, deformation and permeability of salt rocks. However, the sedimentary characteristics of salt rocks in China are much different from those in Europe and North America. So those preexisting models can not be applied directly to the construction of salt caverns in China. In this paper, the feasibility study of the Jintan gas storage project was in detail introduced. The project is to use some existing solution-mined caverns in Jintan Salt Mine as gas storages. 2 EXISTING CAVERNS IN JINTAN SALT MINE 2.1 Geologic conditions According to the borehole data, the salt rock of Jintan Salt Mine is relatively steady along the horizontal direction and the vertical direction. The salt rock deposit occupies an area of 60.5 km2: the long axis 12 km and the short axis 5.6 km, with the thickness varying from 67.85m to 230.95 m. The central part of the salt rock deposit, with a range of 180–230 m, is thicker than the other parts. The depth of the top surface is 850m~1100 m. From bottom to top there are three major salt layers: I, II, and III. The average thickness of layer I is 58m. Layer II is uniformly distributed, with the thickness varying between 50mand 80 m, averaging 64 m.This layer has caverns to be capable of being used as gas storages. Layer III is only 30m~50m thick. 2.2 Caverns To satisfy the requirement of structure and volume of gas storage, about 15 salt caverns for gas storage were selected from 30 old solution-mined caverns. Among these selected caverns, 6 caverns, namely caverns West-1, West-2, East-1, East-2, Gang-1and Gang-2, were chosen as research objects for evaluating the usability of these caverns as gas storage. The in-situ sonar measures of the cavern boundary were carried out. As an example, the sonar measure result of cavern East-1 is shown in Figure 1. Caverns West-1and West2 are in Xizhiqiao well field of Jintan Salt Mine and about 104.43mapart. 3 MECHANICAL PROPERTIES AND CONSTITUTIVE MODEL OF SALT ROCK 3.1 Mechanical properties To investigate the mechanical properties of salt rocks, a series of laboratory test including uniaxial compression, triaxial compression, and creep experiment by the XTR01 Electricfluid Serving Compression Machine were carried out.

ABSTRACT The underground LPG storage plant is one of the new style energy storage facilities, which have large rock caverns with high internal gas pressure. The gas storage design basically relies on the water pressure in the surrounding rock being more than the ‘escape’ pressure of the stored gas. Therefore, it is important to prevent gas leakage through the conductive fracture networks formed by fracture initiation, propagation and coalescing phenomenon due to the fluid pressure. Distinct Element Method (DEM) using Bonded Particle Model (BPM) is convenient to simulate such process of fracturing as the progressive breaking of discrete bonds. Potyondy & Cundall (1999) suggested the hydro-mechanical coupled formulation that utilizes DEM and channel and domain network concept. However, this formulation has never been extended to the threedimensional rock deformation and fracturing issue caused by the interaction of gas and liquid. Thus, in this study, the authors develop the three-dimensional hydro-mechanical coupled analysis that can express rock deformation and fracturing coupled with fluid flow of gas and liquid. The applicability of this method is examined through the case study of the actual air cushion surge chamber (ACSC), which has experienced not only the leakage of high pressured air from the rock cavern but also the air leakage-control with water curtain. The proposed method shows high performance to evaluate the air leakage and air tightness. 1 INTRODUCTION The underground LPG storage plant and CAES (Compressed Air Energy Storage) plant are new style energy storage facilities, which have large rock caverns with high internal gas pressure. The gas storage design basically relies on the principle ofwater pres-sure in surrounding rock being more than the ‘escape’ pressure of the stored gas. However, the surrounding fracture network effects air tightness performance of storage cavern, the leakage mechanism is governed by fracture initiation, propagation and coalescing phenomenon resulted from the variation of fluid pressure. Therefore, for the planning and designing of gas storage caverns with high internal pressure, it is required to predict the generation of fracture network due to internal gas pressure and evaluate the amount of gas leakage through the fracture network with taking the effect of groundwater flow that governs the gas penetration to rock mass into account. Particle flow code (PFC) described by Cundall & Strack (1979) is convenient to treat such process of fracturing as the progressive breaking of discrete bonds. Potyondy & Cundall (1999) suggested the hydro-mechanical coupled formulation that utilizesDEMand channel-domain network concept. 2 FORMULATION 2.1 Basic concept The concept of the hydro-mechanical coupled model formulated by Potyondy & Cundall (1999) is shown as in Figure 1. Rock mass is represented by the bonded particle assemble. A closed loop surrounded by the bonded particles, is called a ‘domain’ that acts as a notational void in rock mass. A segment that links two neighboring domains is called a ‘channel’that acts as a notational crack with a specific aperture.

ABSTRACT Underground hydrocarbons storage is a very specific domain for the designer. He is usually free to adjust the section, shape and layout to cope with the geological and geotechnical conditions. This paper presents a panorama of the geotechnical design of mined underground storage caverns, then lists a number of uncommon features encountered in a storage excavated in Sydney, Australia, the Elgas LPG project that had to face major non-isotropic conditions with numerous local variations, impacting on the achievement of the design profiles. Changes in geotechnical design methodology and practice are examined through this project, now in operation, which will have lasted altogether almost ten years. ZUSAMMENFASSUNG Die untertaegige Speicherung von Kohlenwasserstoffen unterliegt in der Planung sehr spezifischen Bedingungen. Der planende Ingenieur hat bei der Dimensionierung und Formgebung der Speicherhohlraeume gewisse Freiheiten, muss jedoch vorgefundene geologische und geotechnische Bedingungen beruecksichtigen. Der vorliegende Beitrag gibt zunaechst einen allgemeinen Ueberblick ueber die geotechnische Planung von bergmaennisch aufgefahrenen Speicherhhohlraeumen. Darueber hinaus werden Besonderheiten betrachtet, mit denen das Elgas LPG-Speicherprojekt in einer bergmaennisch aufgefahrenen Kaverne in Sydney, Australien konfrontiert war. Hierbei ging es um die Beruecksichtigung anisotroper Bedingungen mit zusaetzlichen Heterogenitaeten im Gestein und den daraus erwachsenden Schwierigkeiten, die geplante Hohlraumform zu verwirklichen. Ueber einen Zeitraum von fast 10 Jahren, in denen das jetzt in Betrieb befindliche Projekt unterschiedliche Betriebsphasen durchlaufen hat, wurden verschiedene geotechnische Entwurfsverfahren auf ihre Anwendbarkeit geprueft. RESUME Le stockage souterrain d'hydrocarbures est un domaine très specifique pour le concepteur, car celui-ci dispose d'une large liberte pour adapter les sections, les formes et les implantations aux conditions geologiques et geotechniques de l'environnement choisi. Après un panorama de la conception geotechnique des stockages souterrains d'hydrocarbures par la methode dite des cavites minees, l'accent sera mis sur un certain nombre de particularites rencontrees lors du projet de stockage de GPL de Elgas à Sydney en Australie, creuse dans de très fortes conditions d'anisotropie du massif rocheux, avec de nombreuses variations locales et toutes les implications que cela peut avoir sur le maintien des formes. L'evolution des approches methodologiques geotechniques durant la dizaine d'annees de developpement de ce projet depuis les premières etudes jusqu'à l'exploitation actuelle est egalement presentee. 1. General description of geotechnical design of mined storage The design of underground LPG storage in mined caverns has been presented in various papers [1] [2] [3] [4] with reference to their stability and product containment criteria. In the following, a brief overview of some of the main geotechnical features relating to the design of stable underground caverns in difficult conditions is presented [5]. While the task of the geotechnical engineer or design team for storage caverns is in many ways comparable to that of designers of related works such as tunnels, it can be thought of as being easier in some aspects and more difficult in others. The task is made easier because: the site will usually have been selected in good engineering ground, the designer is generally free to choose the most appropriate layout, especially the geometry and the orientation of the tunnels, cross-sections and locations can be matched to the local geological conditions. (Figure in full paper) In contrast, it is harder because of: the importance of the required hydrodynamic containment conditions (for example, groundwater pressure drawdown when a pervious feature is encountered may not be allowed)

Abstract The formation and mechanism of rock cavern roof arches are studied and effects of rockbolts reinforcement are evaluated. It is concluded that a self-supported roof arch may be formed by the excavation. To stabilize such a roof arch, fully grouted rockbolts are effective. Tensioned cable anchors may have a negative influence on the arch stability. Zusammenfassung Die Formation und der Mechanismus von Deckenbögen in Bergkavernen wird studiert und der Effekt von Verstarkung mit Bergbolzen wird bewertet. Es wird festgestellt, dass die Exkavation einen selbst-stuetzenden / freitragenden Deckenbogen formen kann. Eingegossene Bergbolzen sind effektiv um einen solchen Deckenbogen zu stabilisieren. Spannkabel können unter Umstanden eine negative Einwirkung auf die Stabilitat des Bogens haben. Resume Le mecanisme et la formation de voûtes dans les cavernes rocheures sont etudies et l'effet du renforcement par boulonnage est evalue. Nous arrivons à la conclusion qu'une voûte autosupportêe peut être formee par excavation. Des boulons entièrement scelles par coulis de bêton s'avèrent efficaces pour stabiliser de telles voûtes. Les tirants d'ancrage peuvent quant à eux nuire à la stabilite de la voûte. Introduction When a rock cavern roof is excavated, a self-supported roof arch structure may be formed. The characteristics of the roof arch may inherit from the voussoir arch, in which the voussoir has 'unlimited' compressive strength. The arch shape has advantage to make use of the high compressive strength in order to transfer loads, meanwhile, to compact the arch itself and thus forms a stable structure. To ensure the stability of the arch, conditions that induce tensile stress or/and sliding along masonry joints should be avoided. In stabilization of rock masses, rockbolting is a routine practice as the bolts are inexpensive, flexible to apply in changing ground conditions of underground excavation and easy and fast to install. Rockbolting contributes to the modern rock reinforcement system that is based on assisting the rock mass to form a self-supporting structure such as the cavern roof arch. Rockbolts mobilize the inherent strength of the rock mass by offering confining pressure, increase the stiffness of the rock, provide shear resistance to the rock joints or discontinuities and suspend loosed rock blocks. However, it is important to distinguish the effects of full grouted rockbolts and the tensioned cable anchors in reinforcing the roof arches. Formation of roof arch and reinforcement Formation of voussoir arch and cavern roof arch Voussoir arch (Figure 1) action arises directly from the properties of the material - masonry blocks are laid in weak mortar or placed one on another to form the arch. This method of construction ensured that the structure would sustain no tension and sliding between blocks. Stability of the whole arch is assured by the compaction under gravity of the various elements and high capacity of compressive strength of masonry blocks. Coulomb, in his memoir on statics in 1773, examined the behavior of the masonry structure in the light of three assumptions as (Westergaard, 1964): voussoir has no tensile strength, voussoir has an unlimited compressive strength

Since the early 1970s, Korea has constructed many large-scale tunnels and underground storage caverns in response to the rapid industrial development. The rock mechanics engineers have accumulated valuable experiences in the area of underground space technologies. But they still face technical challenges in environmental and safety aspects. To discuss those challenges in Korea, a brief engineering description of underground space projects including oil and gas storage, food storage, pumped storage power plant, transportation tunnels, waterway tunnels, and radioactive waste disposal is presented. Mechanical and hydrological stability analyses of the storage caverns in Korea are also introduced. Depuis le debut des annees soixante-dix, le developpement industriel rapide en Coree a entraîne la construction de nombreuses galeries et cavernes de stockage souterraines. Les ingenieurs de mecanique minière ont donc accumule des experiences precieuses dans le domaine de la technologie de l'espace souterrain. Cependant, ils font toujours face à de nombreux defis techniques en ce qui concerne les aspects de l'environnement et de la securite. Pour presenter ces defis en Coree, l'etude presente decrit les projets d'espace souterrain, y compris le stockage de petrole et de gaz, de nourriture, centrales de stockage pompe, tunnels de transport, tunnels navigables, et evacuation des dechets radioactifs. Des analyses de stabilite mecanique et hydrologique des cavernes de stockage en Coree sont aussi presentees. Seit Anfang der 70er-Jahre, baute Korea in Folge raschen Industriewachstums viele lange Tunnels und unterirdische Lagerungsraume. Fachkrafte im Bereich Gesteinsmechanik sammelten wertvolle Erfahrungen ueber unterirdische Raumtechnologien. Dennoch stehen sie auch heute noch vor technischen Herausforderungen im Bereich Umweltschutz und Sicherheit. Zur Erlauterung dieser Herausforderungen in Korea folgt eine kurze technische Beschreibung der Projekte zur Schaffung unterirdischen Raumes fuer beispielsweise Öl- und Gaslagerung, Nahrungsmittellagerung, Pumpspeicherwerke, Straßen- und Wasserstraßentunnels, als auch Lagerung radioaktiven Muells. Mechanische und hydrologische Stabilitatsanalysen der Lagerungsraume in Korea werden ebenfalls dargestellt. 1. Introduction Korea is ranked 109th in all countries of the world in size and 70 percent of it consists of mountains and only 30 percent plains. However, it is ranked 26th in population and 13th in gross domestic product (GDP). The need for expanding infrastructure to support the rapid industrialization in the 1970s and the two oil crises stimulated the construction of large underground structures such as the pumped storage power plants, crude oil and liquefied petroleum gas (LPG) storage caverns, the railways, and the road tunnels. The principles of rock mechanics have played important roles in site investigation, designing and construction. Before the 1970s, only small-scale tunnels for mining and railway were built, and principles of rock mechanics were applied in limited areas such as in deep-mining. The first large underground facility project in Korea was the construction of the Chongpyoung pumped storage power plant initiated in 1973. Several underground facilities have been successfully constructed since that time; and many projects on high speed railway tunnels, subway tunnels, oil and gas storage caverns, and waterway tunnels are in progress. For the effective use of land and to overcome the adverse geographical and topographical conditions of Korea.

Modelling the effect of blasting-caused damage, anisotropy of rock masses and excavation sequence on deformational behaviour and stability of large-scale underground caverns is important in the design and information-oriented construction of the pumped storage power plant. A powerful three-dimensional numerical method that can be applied for that purpose is presented in this paper. Damaged range caused by blasting and mechanical properties of rock masses near to the walls of caverns are determined by using the back analysis approach in which three lines of the measurement results during the arch part excavation process were used to verified the simulations. Finally, applying the improved model and properties of rocks, the cavern stability and reinforcement effect of the preliminarily designed support system are also estimated for the safety in the bench excavation process. La creation de modèles des effets relatifs aux dommages resultant des explosions, à l'anisotropie des masses rocheuses et à la sequence d'excavation quant au comportement à la deformation et à la stabilite des cavernes souterraines de grandes dimensions est une etape importante dans l'etude et la construction sur ordinateur de centrales hydrauliques à accumulation par pompage. Cet article traite d'une methode numerique tri-dimensionnelle puissante applicable à cet effet. La gravite des dommages resultant des explosions et les proprietes mecaniques des roches à proximite des parois de la caverne sont determinees par une analyse du fond dans laquelle les simulations sont verifiees à l'aide de trois lignes de resultats de mesures prises durant le processus d'excavation de la partie arche. Finalement, la stabilite de la caverne et les effets du renforcement du système de support prealablement conçu sont estimes par application du modèle ameliore et des proprietes de la roche, pour application à la securite durant le processus d'excavation en gradins. Nachahmung der Wirkungen von durch Explosionen hervorgerufenen Schaden, Anisotropie der Gesteinsmassen und der Ausschachtungssequenz auf das Verformungsverhalten und die Stabilitat großraumiger Untergrundhöhlen ist fuer das Design und den informationsorientierten Bau von Pumpenkraftwerken wichtig. Entsprechend der Vorgaben in dieser Arbeit kann ein leistungsfahiges, dreidimensionales numerisches Verfahren fuer diesen Zweck eingesetzt werden. Der durch Explosionen und die mechanischen Eigenschaften des Gesteins bedingte Schadensumfang im Bereich der Höhlenwande kann mit Hilfe eines retroversen Analyseansatzes bestimmt werden, bei dem die drei bei der Ausschachtung resultierenden Messlinien dazu genutzt wurden, die Simulationen zu bestatigen. Abschließend wurde außerdem durch Einsatz verbesserter Modelle und Gesteinseigenschaften die Auswirkungen vorlaufig entworfener Unterstuetzungssystem auf die Höhlenstabilitat und Verstarkungswirkungen hinsichtlich der Sicherheit bei Böschungsausschachtung abgeschatzt. Introduction Computer design and information-oriented construction of rock engineering, such as underground pumped storage power station, oil and gas storage caverns, etc.. It has been considering as the practical engineering tool to understand the response of those underground caverns having large-scale sectional areas at depth, and support design and stability assessment. This paper established a powerful three-dimensional numerical method that can be applied for modelling the effect of blasting-caused damage, anisotropy of rock masses and excavation sequence on deformational behaviour and stability of the underground excavation of the objective.

Abstract Short-term strength, damage and healing boundaries for rock salt are experimentally determined and integrated into the Hou/Lux-MDS damage-healing model. This model can be used to describe the mechanical behaviour of rock salt during a damaging process (under high stress to strength ratios) as well as during a healing process (under very low stress to strength ratios with high confining pressure). The development of the damage and the stress to strength ratio in the excavation damaged zone (EDZ) of a storage cavern under a minimum internal pressure as well as the development of the healing of damage and the stress to strength ratio under a subsequent maximum internal pressure are investigated project-related. The results of the investigation make it possible to shift the permissible minimum pressure boundary down, allowing the optimisation of decisive economic characteristics of storage caverns. RÉSUMÉ Le comportement court terme, l'endommagement et les conditions de colmatage pour le sel gemme ont ete etudies experimentalement et integres dans le model endommagement- colmatage Hou/Lux-MDS. Ce modèle permet de decrire le comportement mecanique de sel gemme pendant le processus d'endommagement (sous fort rapport contrainte-resistance) et le comportement du processus de colmatage sous très faible rapport contrainte-resistance avec forte pression de confinement. Le developpement d'endommagement et le rapport de contrainte-resistance dans une zone d'endommagee (EDZ) d'une cavite de stockage avec un maximum de pression de soutènement ont ete etudies. Les resultats de cette etude permettent de conclure qu'il est possible de baisser la pression de soutènement, et par consequent d'optimiser les caracteristiques economiques decisives des cavite de stockage. ZUSAMENFASSUNG Fuer Steinsalz werden Festigkeits-, Schadigungs- und Verheilungsgrenze experimentell ermittelt und in das Schadigungs-Verheilungs-Modell Hou/Lux-MDS integriert. Damit kann das mechanische Verhalten von Steinsalz sowohl bei einem Schadigungsprozess (mit hohen Ausnutzungsgraden) wie auch bei einem Verheilungsprozess (mit niedrigen Ausnutzungsgraden) beschrieben werden. Projektbezogen werden die Schadigungs- und Ausnutzungsgradentwicklung in der Auflockerungszone einer Speicherkaverne unter einem minimalen Innendruck sowie die Verheilungs- und Ausnutzungsgradentwicklung unter einem anschließenden maximalen Innendruck untersucht. Die Untersuchungsergebnisse erlauben, die zulassige Minimaldruckgrenze nach unten zu verschieben, so dass entscheidende wirtschaftliche Kenngrößen von Speicherkavernen optimiert werden können. Introduction It has been determined through laboratory tests, that exceeding the damage boundary under high stress to strength ratios generates, among other consequences, damage, dilatancy and increased creep rates and permeability. However the damage, which already existed in the salt rocks and which developed further due to the stress caused by mining activities, may heal as the healing boundary is undershot under very low stress to strength ratios with a high confining pressure as a result of the stress relief (e.g. due to backfill in conjunction with rock convergence or due to an increased internal pressure in the storage caverns) accompanied by positive effects, such as closing of pores and cracks, decrease of permeability and compacted deformation. Therefore the material damage and its healing are the basis for the description of the mechanical behaviour of rock salt. Both inverse processes must be taken into consideration simultaneously using a joint damage parameter.