INTRODUCTION: In this paper, a method of settlement analysis for buildings with a mat foundation is described by considering the rebound of the ground. When a building is constructed on soft ground, pile foundations are used to avoid the undesirable effects of ground settlement. In this case, however, a building may become detached from the ground. Various problems caused by this phenomenon have been reported. As a result, mat foundation has recently been employed for construction in consideration of these effects. A building with mat foundation, however, is greatly influenced by settlement. To counteract this, a method is being employed in which a large amount of earth is excavated from the building site of a structure in order to reduce the extent of settlement caused by its weight. Generally the ground rebound and the settlement are caused by the excavation and the weight of a structure, respectively. To estimate their effects, it is necessary to investigate how the excess pore water pressure in the clay layer varies with the time and to analyze the interaction between the ground and structure. We present the correlation between the mean consolidated pressure, and the coefficient of volume compressibility, mv, and the coefficient of consolidation, cv, based on the results of the cyclic consolidation test. And we have calculated the rebound and the settlement of buildings with a mat foundation from the excess pore water pressure obtained from mv and cv. From these results, we obtained that the properties of the ground settlement were changed from excavation period and starting time of the construction of the building and affected largely by the ground rebound. CYCLIC CONSOLIDATION CHARACTERISTICES OF DILUVIAL CLAY We presented cyclic consolidation characteristics of alluvial clay in a previous report 1).

ABSTRACT: The ground replacement method reinforced by geonet is based on field experiences so that a theoretical consideration has been required to adapt for use with the geonet. In this study, we have considered the mechanical behavior of the geonet based on the cable theory. As a result, obtained equations express the deformation and the stress distribution of the geonet. INTRODUCTION Sand replacement on dredged and reclaimed marine clay has been used for some time. It is easy to construct the land on the soft clay, the replacement method dumping the sand into the reclaimed marine clay easily. However, this conventional replacement method has been gradually decreasing because of the unreliable sand shape. In recent years, budgetary cutback of public undertaking has occurred so that this method is new employed by using the geonet, which can restrict the replaced sand and achieved a sand shape (Yasuhara et al., 1982). Hereafter, we call it the Geonet Replacement Method (GRM). GRM is shown in Figure 1. Theoretical consideration of this method was based on the application of the expression of the sheet method on the soft clay ground (Yamanouchi et al., 1979). However, it seems that the mechanism of GRM is different from the sheet method on the soft clay ground. Therefore, a theoretical consideration has been required to adapt to the geonet. In this study, we have considered the mechanical behavior of the geonet on a basis of the cable theory and derived the differential equation from the equilibrium condition of the geonet on the soft clay ground. COMPARISON OF THE CALCULATION AND OBSERVATION Verifying the validity of both the geonet deformation and the tensile stress distribution that were obtained by the above theoretical considerations, we compared the calculation result and the observation data.

PROBLEM In covered karst regions the causes of structural damages are often in coherence with the effect of seepage-water movement in the underground. In such regions, where a karsted and/or fissured hard rock is overlain by cohesionless soil, hydraulic induced erosion and suffosion processes occur within the overburden. Erosion is the hydraulic induced mobilisation and transportation of all diameters of grains in soil. It results in total destruction of the grain skeleton of the soil. Suffosion is also a hydraulic induced process, but only the small grains of a loose soil get mobilized and transported in the pores of the skeleton of the coarse grains. As a consequence of these processes, an abrupt or creeping material displacement from the underground to the cavities in the deeper underground is possible. The situation is characterized by känozoic, especially quarternary loose soil, overlying a karsted sulphate of carbonate rock (MOLEK ET AL., 1997). The hydraulic conditions in the underground can be generally characterized by - in the most cases - vertical seepage water movement to a deeper aquifer (Fig. 1). This water may derive – for example - either from natural rainfall infiltration or from leaky sewer pipes. At surface these processes result in - more or less widespread - depressions or in form of collapse craters with endangering of the stability in built-up areas. The developement of such depression- and collapse forms is discribed by REUTER & MOLEK (1980). Because of these described effects, water has generally two different possibilities for direct or indirect influence to buildings by endangering either their stability or at least by restricting their use (FISCHER ET AL., 1991; VOGEL & KAST, 1994). The same effects of erosion and suffosion as described before, with comparable consequences at surface, can also run within the layers of stratified river deposits.

ABSTRACT: The geomechanical models for slope design, which was mainly based on shear strength parameters estimated by using RMR classification system, are compared with the real post Ð construction conditions of cuts. The results of this study show that RMR classification system generally leads in a rock mass quality underestimation, which mainly due to the rating adjustment for discontinuity orientations as especially proposed for rock slopes. The case records evaluation indicate that the rock mass rating without taking into account the discontinuities adjustment give a more realistic rate of rock mass shear strength characteristics for preliminary slope stability analysis. Also, the shear strength parameters, as determined by the use of GSI, seems to lead in an overestimation of slope stability of these limestone cuts. INTRODUCTION The determination of representative shear strength parameters of a rock mass is often a time consuming, costly and difficult process. Large-scale in situ shear tests are desirable but very expensive. It is known that there are the following lines of approach that can be used to obtain information on in situ behaviour of the rock mass for slope design: direct measurements by means of field and laboratory tests, evaluation by means of mathematical simulations, evaluation of stable and unstable natural and excavated slopes and, empirical methods using rock mass classification systems. The last approach is often applied in many cases for the preliminary design of high rock slopes in Greece and mainly for heavily jointed rock masses assuming isotropic rock mass behaviour. The Geomechanics Classification Rating (RMR) system developed by Beniawski (1976, 1979, 1989) is the common way to obtain the range of shear strength parameters and then to estimate the safety factors by using slope design charts for circular failure surface or other calculation methods (Hoek and Bray, 1974).

ABSTRACT: Geotechnical engineers are often consulted when the site location has been decided and a geotechnical investigation is required for design input. The site investigation and assessment of the ground parameters represents the key work area of the geotechnical professional. Detailed analysis and design, based on the site investigation report is then carried out by the design engineer. The site investigation phase usually occurs only after considerable planning of the project has already occurred. Planners often base the siting of a development on above ground considerations. The below ground conditions are often considered as a design element that must be dealt with during the detailing phase of the project. The paper discusses the limitations of such an approach, and illustrates projects where early geotechnical input influenced the layout, and siting of the developments. These projects show how the planning developed and considered the geotechnical input as a planning essential rather than a given that had to be designed into the project. Geotechnical involvement for the whole of life project cycle is discussed to show how significant cost savings to projects can be derived. THE LIFE OF A PROJECT Variations to the above would include condensing the various stages to the Design and Construct package which would follow on from the IAS or the Planning Phase. Small to Medium size projects would typically combine the phases into feasibility, design and construction. In the ideal world, the geotechnical input should occur at all stages. Unfortunately, in the world of project management, the site investigation is often simply a deliverable that should be programmed into the schedule as soon as possible. This often means carrying out a site investigation in the early phases although the concept may be changing as the project evolves.

ABSTRACT: The development of quantitative risk assessment (QRA) methodologies has advanced to such a state that it is now a practical risk management tool in geotechnical engineering. Pilot applications of QRA have shown great promise and it has contributed to addressing questions that would otherwise be very difficult to answer using conventional techniques. Resistance against the more widespread use of QRA is real and this is partly due to myths about the technique. The essence is risk-based thinking, be it under a quantitative or qualitative framework. The geotechnical community stands to gain by integrating risk-based thinking and methodologies into current geotechnical practice. This integration will better align the geotechnical profession with many of the other engineering fields that practise risk management in a more explicit manner. 1.0 INTRODUCTION In geotechnical engineering, empirical rules based on precedents are commonly relied upon to solve practical problems. Modelling the full range of factors involved in a real problem in detail is, nearly always, too complicated and not credible. Fortunately, only some of the factors tend to be major in a given problem and these can usually be characterized by indices from standard tests. It is generally deemed that one can obtain a good enough estimate for engineering purposes by discounting the minor factors as unimportant and the extreme factors as unlikely. This pragmatic approach has generally served the geotechnical profession well. However, unpleasant surprises do occur from time to time. "Minor" factors can turn out to be major, and "extreme" events can occur more frequently than expected. Geotechnical failures are not a rarity, and sometimes occur in a disastrous manner. What was judged to be unimportant may actually be very important, at least for the combination of circumstances at hand which might not have been foreseen (but were not necessarily unforeseeable).

ABSTRACT: The rock mass around an underground opening is subjected to a unique stress path that results in low radial confinement and both tangential loading and unloading conditions near the wall. As a result, the rock mass strength near underground excavations is controlled by failure mechanisms dominating at low confinement. Hence, when constructing underground works in hard rock, two general scenarios are encountered: structurally controlled gravity-driven failures; and stress-induced failure with spalling and slabbing. The former process is predominant when both the radial and the tangential stresses are low, where as the latter is prevalent when high tangential stresses drive rock mass failure. Whereas structurally controlled failures are most frequently observed at shallow depths and slabbing failure is commonly found at great depth, mining and tunnelling experience shows that these failure processes may be encountered at essentially any depth. In this keynote the authors provide an overall framework for assessing the stability of underground openings in hard rocks, regardless whether the excavations are required for mining, nuclear waste or civil engineering applications. For the prediction of stress-induced slabbing, a bi-linear failure envelope cut-off is introduced. The resulting failure envelope, combined with numerical modelling, is used to determine the depth of failure near excavations and in pillars, and to examine the effect of rock mass bulking of the failed rock on the displacement demand for support selection. An assessment of rock mass relaxation on structurally controlled failure processes is made with respect to support demand and support capacity. This keynote also includes a brief review of violent failure processes, i.e., rockbursting. Where possible, examples from mining and civil engineering projects are provided to illustrate the design challenges of underground excavations in hard rocks. Guidelines for support design are provided.

ABSTRACT: The use of underground space is not new. Mankind has always used it to solve problems, taking advantage of its fundamental characteristics. Among the many reasons to use underground space are: land use and location reasons, isolation considerations, environmental preservation, and societal aspects. On the other hand, many problems and issues must be considered when using underground space, including: safety, psychological and health aspects, protection of the underground environment, relations between underground structures and the ground surface, construction techniques, site investigations, risk analysis, assessment of the underground structures, etc. All these issues must be considered in the search of "the optimum use of underground space" and, in addition, it must be remembered that the use of underground space is not an end in itself. Geoengineering considerations influence greatly the extent and the conditions of the use of underground space and this paper indicates some of the geotechnical issues that will become more important as the use of underground space intensifies. INTRODUCTION This paper is organized to first review the history and varied rationales for using underground space, then to review interaction of geology and geoengineering design with the planning and execution of underground works. Those familiar with underground space use and the geotechnical design of underground structures will be well aware of most of the issues raised but it hopefully will provide a good review of the reasons why geological and geotechnical input is critical at all stages of the process. In the last part of the paper, particular attention is paid to the trends in underground technology development as well as urban underground space use and what these trends may provide in terms of opportunities for geology and geoengineering professionals to help optimize the long-term use of underground space in urban areas.

ABSTRACT: This paper presents a dam safety decision-makers, and owners, perspective of the emerging and arguably juvenile discipline of dam risk management using formal, analytically based methods of risk analysis. It is founded on almost ten-years of detailed investigations into all aspects of risk analysis as applied to dams including several experimental applications of proposed approaches by BC Hydro. The paper provides a basis for concluding that while formal analytically based dam risk management can be expected to endure in the long term, its form will continue to evolve and necessarily will be somewhat different to what was (and still is by some) envisaged in the early to mid-1990's. INTRODUCTION This paper focuses on water retaining embankment dams in keeping with the geotechnical theme of the conference. Although some of the principles discussed regarding dam risk management will equally apply to tailings impoundments and concrete dams. According to the world register of dams there are about 30,000 significant water retaining embankment dams throughout the world. Collectively these dams have provided tremendous benefit to the development of civilization, and continue to provide for our improving standard of living. The earliest known dams from about 4000 B.C. until well into the 1800's A.D. were used primarily for irrigation and water supply. Some of the ‘ancient’ dams are still in use today, a testament to potential longevity of embankments if well designed, sited, constructed and maintained. It was not until about the first millennium A.D. that dams exceeded 10 m in height. Near the end of the 19th century, both numbers and heights of dams began to increase, reaching heights of more than 20 m, and with the later introduction of concrete dams the trend to increasing height became marked. The 1920's saw the increasing construction of large dams for hydroelectric power.

ABSTRACT: Landfill disposal creates a repository of elements at significantly elevated levels. Entropy dictates that elements at elevated concentrations will be emitted into the surrounding environment. Most regulatory authorities stipulate generic or site specific concentration criteria to determine whether a landfill is causing contamination. However, if the mass flux of such elements is sufficiently less than surrounding natural or anthropogenic flux levels the environmental impact of the landfill may be significantly less than that based upon concentrations alone. The approach presented is an alternative way to look at the impact of landfills and potentially other waste processing facilities. It allows the long term impacts to be assessed and provides the ability to look at comparative impact for a given element. The approach also enables impacts to be assessed in terms of mass flux rather than concentration. This consideration may yield a more appropriate consideration of the environmental impacts. INTRODUCTION A landfill owner is generally liable for any damage due to contamination for the Ôactive lifeÕ of the landfill. In this context the Ôactive lifeÕ refers to the polluting life of the landfill which is very much dependent upon the landfill design philosophy. These philosophies make no distinction between individual elements (Carbon, Nitrogen, metals etc). Consequently the active landfill life will be the time taken for all elements to achieve acceptable concentrations. An significant development in landfill in Europe and elsewhere is the use of a landfill philosophy termed final storage quality . This philosophy approaches landfill design in a revolutionary way in that the elemental fluxes are analysed individually. However, if the mass flux of such elements is sufficiently less than natural or anthropogenic flux levels the environmental impact may be significantly more or less than that based upon concentrations only.

ABSTRACT: Ore passes at Premier Mine are located in the norite country rock fairly close to the Contact with the kimberlite pipe. They are usually excavated by initially raise boring a 2.1 m diameter hole, and then enlarging this to the required size by blasting. The problems which have been experienced with the ore passes include both blockage of the initial raise bore, and blockage of the enlarged pass. In some cases failure has occurred before the passes have been used. This has required excavation of replacement passes. To remedy the problems, consideration was given to support of the passes. Initially conventional forms of support such as lining were considered. However, it was noted that the norite in which the passes are located is a competent, tough rock with good wearing properties, and the necessity for lining was questioned. An alternative approach, which is described in the paper, was therefore adopted. This involved the measurement of the rock structure, and, from these data, the assessment of the probability of Occurrence of potentially unstable blocks of rock in the walls of passes. This allowed the determination of the required spacing of support elements to reduce the probability of failure of the rock to acceptable block sizes and volumes. The results were expressed as a design curve correlating support spacing and likely failure volume. INTRODUCTION Ore and waste passes are extremely important components of the mining system. They are often critical elements, and their blockage or failure may cause major losses of production. In high stress mining environments, with hard, abrasive Ore and waste, problems of excessive scaling and blockage have been experienced (Gibbon 1977). In similar operations, geological structure has played a significant role in the failure of the passes (Schoombee and van Wyk 1983, Stringer and Lategan 1983). Repair of passes is costly, time consuming and sometimes not practical. Premier Diamond Mine has had experience with the raiseboring of holes for various purposes in felsite, gabbro and norite rock types. Major problems have occurred with some of the holes in the norite, which is a strong and hard rock material, but which is blocky with well-defined Jointing. The problems which have occurred have been a function of the diameter of the hole and the use to which it was put. Numerous 1.8 m diameter ventilation shafts have been bored, and no problems have been experienced with these holes. However, in two separate 6 m diameter raise-bored ventilation shafts major collapses occurred in the norite sections of the shafts. Twenty-four raisebore holes have been drilled on the north side of the Mine as part of the pass system for development and production ore and waste from the underground block cave mining operation. All of these holes were drilled to a diameter of 2.1 m and vary in length from 90 m to 120 m. One of the holes collapsed shortly after it had been drilled, and it was subsequently found that it intersected a 1 m wide shear zone.

ABSTRACT: Wedges of rock are defined when two joints intersect each other in the vicinity of an excavation. Due to the variability of joint length, spacing and strength, probability methods are required to estimate the frequency of failure of wedges in a rock slope. The point estimate method allows rapid analysis of the effects of variability on strength parameters but the variation of geometry cannot be assessed Using this technique. The Monte Carlo method was used to evaluate geometrical variations of wedges. The frequency of wedge formation was determined by taking into consideration joint continuity and spacing. Finally the total volume of failure was estimated by taking into consideration the number of unstable wedges in different size intervals and accounting for small wedges which may be contained in larger wedges. The technique showed that the probability of failure of wedges is more sensitive to variations in joint geometry than joint strength. The frequency of wedge formation and hence total volume of failure was shown to be very sensitive to the continuity of joints. INTRODUCTION Instability in rock slopes may occur if two joints intersect near the slope face and result in a wedge of rock which is able to slide into the excavation. If jointing is continuous then very large wedges can be formed which could result in disastrous collapse of an entire slope face. The failure of relatively small wedges of rock could result in instability in individual benches. This paper describes a method of identifying wedges in rock slopes from joint data so that the risk to the functionality of the slope and safety of Workers can be assessed. The method of analysis was encoded into a computer Program which allows rapid computation of potential wedges in rock slopes at any inclination or orientation. Joint orientations vary considerably as do the strength parameters of joints. In any analysis it is important to take these variations into consideration. Probability methods were employed to account for variability. Probability methods can also be used to quantify the effect of uncertainty in input data, for it is seldom that one has accurate data on all the relevant parameters which affect wedge stability. VARIABILITY OF JOINT PROPERTIES Frictional properties Joints are weak planes which are found in most rock masses. Joints can be a few centimeters long or can be several hundred meters long. Joints planes are assumed to consist of a discontinuity part and a rock bridge part, as shown in Figure 1. The discontinuity part can be assigned strength parameters according to the frictional properties of the two sides of the discontinuity. The rock bridge is assumed to have the strength of the surrounding intact rock. Intact rock strength is at least an order of magnitude greater than the shear strength of a discontinuity. In this paper it is assumed that if a rock bridge exists, then shear will not take place through the rock bridge.

ABSTRACT: This General Report, complemented by invited lectures by Dr. J. C. Roegiers and Dr. R. Hart, surveys some recent developments in analytical and numerical approaches to the study of the deformation and stability of deep excavations in rock, both small (boreholes) and large (tunnels, caverns). Emphasis is given to the classical closed-form analytical solution of elastic-plastic (inelastic) behaviour of rock around excavations to illustrate the influence of various factors that affect the constitutive behaviours, both elastic and inelastic, of the rock. Consideration of discrete discontinuities is essential to understanding of the stability of large excavations. INTRODUCTION One of the goals of this Symposium is to strengthen the dialogue between petroleum engineers and mining or civil engineers concerned with the development of stable excavations in rock at great depth. An obvious difference between the two concerns is, of course, the cross-sectional area of the excavations; the small petroleum boreholes and the much larger tunnels, stopes and caverns of mining and civil engineering. In the former, deformation and stability of the excavation are dependent principally on the mechanical properties of the rock material itself, whereas in the latter, controlling influence. Significant progress is being made in studies of both small-scale (borehole) stability and large excavation stability, but each tends to have a different 'flavour'. Borehole stability is amenable to laboratory investigation, for example, whereas behaviour of the large excavations require direct observation in the field for confirmation of analysis. In considering how best to review the progress being made in each, whilst also examining points of common concern to both, it was decided to supplement this report with two special lectures. One, by Dr. J. C. Roegiers, reviews recent developments in excavation stability research, with emphasis on borehole stability and petroleum engineering. The second, by Dr. R. Hart, reviews recent developments in discontinuum studies, with applications to large excavations in mining and civil engineering. This report will focus on a general discussion of stability around excavations, broadly applicable to both small and largescale excavations. CLASSICAL ELASTO-PLASTIC ANALYSIS Much of the discussion concerning stability of underground excavations, both small scale and large scale, starts from the classical problem of a circular hole in an homogeneous, isotropic, elasto-plastic medium loaded in plane strain by a uniform external compression P at infinity, and a uniform internal pressure Pi'. As P is increased, the strength of the rock at the wall of the excavation is eventually exceeded and an annulus of broken rock develops around the inner radius a, i.e. forming the 'plastic' [or 'inelastic' in Fig.1] zone. The thickness [(b - a) in Fig. l] of the inelastic zone to achieve this equilibrium at the interface will depend on the constitutive behaviour of the broken rock in this zone. A wide variety of modifications to this distribution (some for example showing discontinuities in the tangential stress at the elastic/inelastic interface), are possible, depending again on the constitutive behaviour of the broken rock [See, for example, Brady and Brown (1985)].

ABSTRACT: A method is suggested for estimating the stress-strain state of rock foundations weakened by periodic systems of parallel oblique joints. The method is bas ed on the analytical solution of the relevant boundary problem of the elasticity theory. Different types of rock foundation models are considered. A procedure is developed for determining pliability and crack resistance of rock foundations and stress intensity factors at the joint tips. Rock foundations of hydraulic structures constitute rock masses which, in their natural condition, comprise a number of discontinuities in the form of joints or various geomechanical defects. Rock jointing can be of different nature but in many cases rock masses are found to be heavily weakened by systems of parallel or nearly parallel joints (Goodman, 1987). Construction of large dams on rock foundations, excavation of large underground cavities and driving high-pressure tunnels suggest an ever increasing employment of strength and deformation properties of the rocks (Sapegin et e. l, 1972). Optimum utilization of rock mechanical pro- Perties, provision for safety and stability. of the structures to be built, their cost-effectiveness are impossible without comprehensive studies on strength and deformability of rock masses. The object of this paper is to develop a method for calculating the stress-strain state of a rock mass weakened by a peri- odic system of Oblique joints and for finding stress intensity factors at the joint tips. The paper considers a possible model of jointed rock masses, i.e. an elastic range weakened by a system of parallel oblique joints. The calculation procedure described below is based on the analytical solution obtained by Sapegin et al. (1987). The latter is the solution of a mixed elasticity theory problem for the elastic isotropic plane XY with Poisson's ratio v and shear modulus G weakened by a periodic system of semi-infinite parallel tight joints. The joint tips fallon the same straight line, the joints being inclined to the line at an angle of x 0 < x≤ π The adjacent joints are spaced at a distance of 2 (Figure 1) (Figure in full paper) Thus, as distinguished from the continu- ous foundation, the jointed foundation features horizontal pliability from vertical loads and vertical pliability from horizontal loads. The combined use of the elasticity theory boundary problem solutions for the Plane with the foregoing periodic system of joints at periodic load and the analytical solution of a similar boundary problem received by Kamysheva & Nuller (1979) for non-periodic load has made it possible to consider the following models of jointed rock foundations: (Equation in full paper) is considerably lower than, which enables us to employ the solutions of the periodic and non-periodic problems on deformation of an elastic plane weakened by a periodic system of oblique semi-infinite joints. Applied to the upper boundary of the foundation is the distributed load б y = − q, q > O. 1.1. Let us assume that the strips are resting on the non-deformable foundation. In this case normal displacements of the strip faces are taken to be equal to zero.

ABSTRACT: The paper deals with problems of concrete dams rock foundations safety: statistics of failures and use of obtained information in safety analysis as well as the results of geomechanical investigations into the rock foundations properties. The safety of structure is ensured in of existing structures and upgrading investigations, surveys, construction the safety criteria, of elaboration and operation periods by employment of new methods of investigation, of experience accumulated in the past by adequate safety criteria. Extensive potentialities of the engineering practice have been attested to by the successful filling of the Inguri Dam storage reservoir, 1.03 cub. Km in storage capacity, in August,1987. The resulting load on the highest arch dam of the world amounted 9.8 mill. t. Nevertheless the dam failures still are occurring. E.g.,rupture of 11 Small dams in USA in October, 1986, caused by a flood of 0.2 per cent probability (the design probability being 1.0–0.5 per cent) in the foundation grouping was estimated to be 141 mill. doll. Investigations into the mechanism of possible failures is too of importance for such small dams as the Sargazon embankment dam impounding a storage reservoir, 3mill. m 3 in storage capacity. The dam rupture has resulted from the dam crest overtopping due to clogging of water outlets by mudflow materials. Accound for actual cases of limiting and beyond-the-limit conditions in the practice of designing is one of the possible ways of improvement of decreasing the failures risk, developing more economical designs of structures. However to be employed in the safety analysis and in the structures designing the information on the failure cases is to be differentiated in respect to external forces, the structure capacity to resist and to properties of the structure members. Various "errors" of speacialists made in the mentiod above terms should be considered from the standpoint of the possible effect of them on the elements of the "environment-structure" system which is under the specialist control. The safety of the structure may be impaired, for instance, in the case the operator will not raise the spillway gates in good time and the dam is overtopped. The "structure" system safety may be impaired more gravely if some kinds of required investigations are neglected in the design studies, this resulting in a considerable underestimation of the external actions on the structure or in structure resistance. Concrete dams on rock foundations are characterized by a high degree of safety featuring Longevity, trouble-free service and maintainability. The criteria of dam safety were formed in The course of more than 30 centuries of the dam building practice evolution. According to Data of ICOLD, the total risk of dam failures is 7.5×10 −2 (Deterioration…1984), the risk of failures of concrete dams on rock foundation during the dam service life (according to data of the Author) is 3.8xl0–2, the risk of complete failure being 2.2xl0–3 These data may characterize the level of dams safety in comparison with the level of risk of failures of other types of structures and the risk of natural calamities.

ABSTRACT The paper deals with mathematical modelling of interaction of hydraulic tunnel linings with the surrounding rock mass with different kinds of static loads and earthquake seismic effects, as well as design methods for linings regarded as elements of a single deformable "liningrock" unit subject to loads and other effects. INTRODUCTION The principle of interaction treating the rock mass and the lining as elements of a single deformable "lining- rock" unit sensitive to all external loads and actions is assumed as a basis for mathematical models and design procedures for linings of underground structures. According to the above principle the design scheme (physical problem statement) for an underground structure (hydraulic tunnel) is a pattern of contact lining-rock interaction. The scheme can serve as a basis for a mathematical model of an underground structure (analytical solution) or for a numerical experiment (using the finite element method). The scheme of lining-rock interaction can be also realized in the form of a physical model of an 'underground structure of optically active (photoelastic method) or equivalent materials. The most important feature of the contact interaction schemes is that stresses at the lining-rock contact (loads, pressure acting on the lining) are not given a priori, but are determined in the course of analysis (modelling). Schemes of contact interaction of linings (supports) of underground structures with rock masses are studied within the scope of underground structure mechanics - a scientific discipline developed in the Soviet Union (Bulychev 1982). The paper discusses mathematical models simulating the rock mass by a linearly deformable medium including viscoelastic one. So each mathematical model is the result of analytical solution of the corresponding plane problem of the elasticity theory. The models and design procedures for linings are realized as computer programs enabling one to perform multivariant designs of underground structures. Reliability of the mathematical models and design procedures for linings is ensured both by qualitative and quantitative correspondence of the design values to the results of model experiments and in situ measurements. In addition, these mathematical models enable one to solve inverse problems using in situ measurements of stresses or displacements in linings. ARBITRARILY SHAPED TUNNEL LININGS The design scheme for tunnel linings (Fig. 1) is one of the contact interaction of an arbitrarily shaped elastic ring, with one axis of symmetry, having the characteristics EI (modulus of deformation), VJ (Polsson's ratio), simulating the Iining and supporting a hole in a linearly deformable homogeneous medium having the characteristics E, V, and simulating the rock mass The mathematical model considers rock rheologic characteristics within the scope of 269 H Figure 1.

ABSTRACT: This paper comments generally on the inherent difficulties of interpreting in-situ stress determinations. These difficulties arise primarily from geological complexity and the localized significance of individual measurements. Frequently the stress state information is sought as input for excavation design studies. In such cases, greater emphasis should be placed on assessing the effect of in-situ stresses, and stress variations, in combination with several other factors (rock strength, excavation geometry,...) which influence design. Observation of the overall response of the rock mass to the combined effect of these variables is then more important than the specific determination of stress state. RESUME: Ce rapport offre des remarques en general sur les difficultes inherents d''interpreter les determinations des contraintes ''in-situ'' dans les roches. Ces difficultes arrivent primitivement a cause du complexite geologique, et le caractere ponctuel des essais individuels. Frequemment, on se sert de l''information qui concerne des contraintes pour dessiner les excavations. Dans tels cas, plus d''effort doit etre attacher au jugement des effets des contraintes in-situ, aux variations des contraintes de point a point, en combinaison avec des autres facteurs (la resistance des roches, la geometrie de l''excavation...)qui peuvent influencer le dessin. Les mesures de la reponse en total du massif rocheux aux effets integrals de ces variables sont encore plus important que la me sure specifique de la contrainte in-situ. ZUSAMMENFASSUNG: Dieser Beitrag ist uber die innliegenden Schwierigkeiten in der Ausdeutung des Messungen der "in-situ" Spannungen. Diese Schwierigkeiten kommen erstens von der Geologischen Complexitat und von der lokaler Wichtigkeit der einzelnen Messungen. Die Information an den Spannungszustand wird oft gesucht als Eingabe zu den Aushohlung Entwurf Studien. In diesen Fallen sollte ein grosseres Gewicht gelegt sein an die Auswertung der "in-situ" Spannungen und an die Spannungs wechseln, welche, in Kombination mit anderen Einflussen (Gebingsfestigkeit, Form der Hohle u.s.w) den Entwurf beinflussen. Die Besichtigung der uberall Reaktion der Gebirgsmasse zu dem kombinierten Effekt dieser Variablen ist dann wichtiger als die spezifische Messungen des Spannungszustandes. 1. INTRODUCTION Study of the deformation and failure of rock masses has relied traditionally on concepts of continuum mechanics. These concepts are powerful and can provide valuable insights for rock engineering. It is important to appreciate, however, that continuum mechanics, and engineering design procedures based on continuum mechanics, developed within the context of a concern for engineering materials and/or situations quite different from those often encountered in rock engineering. Care must be taken, therefore, to ensure that these design procedures are not applied inappropriately to rock. In many classical design problems (e.g. design of buildings, bridges, pressure vessels, air frames...) the applied loads are known and remain constant independent of the displacements (so called ''following loads/). The energy available to propagate rupture continuously exceeds the energy that can be stored or absorbed within the structure (Fig. l(a). In this case, onset of rupture, (at load F a ) is synonymous with collapse. It is important, therefore, to ensure that at no point in the structure does the applied load (or stress state) exceed the resistance (i.e. strength) of the structural material. Classical stress analysis is possible; the structural material adequately satisfies the requirements of homogeneity, continuity, and elasticity. The dimensions and locations of all components are well defined. Classical stress analysis is possible; the structural material adequately satisfies the requirements of homogeneity, continuity, and elasticity. The dimensions and locations of all components are well defined. Material properties (deformability, anisotropy, strength) can be determined reliably from laboratory tests on specimens of a size comparable to the prototype structure (or at least to components of it), and taken from the same material; strength variability can be determined and, together with other uncertainties in the analysis, can be accounted for by an appropriate "safety factor" in the analysis, thus assuring that loads in the structure are everywhere well below the limit (F a ) i.e., everywhere on the rising portion of the load-deformation curve. 2. IN-SITU STRESS DISTRIBUTION IN ROCK MASSES Rock engineering problems are much less well defined than those described above. The rock mass has usually been subjected to numerous epochs of loading throughout geological time, producing fracture and faulting of systems of different orientations in space, resulting in a 3-dimensional network of interconnected blocks. The scale of fractures or joints is such that direct laboratory testing of a "representative volume" of the rock mass is impossible. Groundwater influences the pressure distribution in the rock mass. Undulating topography will also affect both vertical (gravitational) and lateral load distributions. In some cases, (e.g. dam foundations, rock slopes) the applied loads have a "following" character. Here it is important to ensure that discontinuities are not so loaded (both by solid and fluid forces) that alone or in combination (e.g. as a wedge or connected planes) they begin to slide and, hence, collapse.

SUMMARY: Failures occuring with underground openings of large section without locking depend on stress field, its orientation, the physical characteristics of the rocky environment of openings, the geometry of openings and the character of discontinuity. In this case the quantity, orientation and quality of discontinuity is meant by the character of discontinuity. Rheological properties of rocks and discontinuity are mainly responsible for failures. Consequently, stress field, deformation field and displacement field after driving the opening should be determined by considering the rheological properties of rocks. As next step the assessed system of discontinuity should be drawn around the Opening and rock bloks tending to move off potentially should be subjected to stability investigation. It is made possible by test results that by considering the character of the surfaces of discontinuity and its frequency the sections of openings requiring locking can be indicated. ZUSAMMENFASSUNG: Die bei den Untergrundhöhlen mit grossem Profil ohne Sicherung eintretenden Einbrueche haugen vorn primaren Spannungsfeld, von dessen Orientierung, von den physikalischen Eigenschaften der Gesteinsumgebung der Anlage, der Geometrie der Höhle sowie vom Character der Klueft igkeit ab. Beim Eintreten der Einbrueche spielen rheologischen Eigenschaften des Gesteinkörpers und die Klueftigkeit die Hauptrolle. Dementsprechend muss das Spannungs- Deformations- und Verschiebungsfeld nach Strecken abbau mit Beruecksichtigung der rheologischen Eigenschaften des Gesteins bestimmt werden. Es ist der folgende Schritt, das bemcssene Kluef''tigkeitssystem um die Höhle zu zeichnen und diejenigen Gesteinblöcke, die potentiell zur Verschiebung geneigt sind, einer Stabilitatsuntersuchung zu unterwerfen. Als Ergebnis der Untersuchung können mit Beruecksichtigung des Charakters und des Haufigkeitswerts der Klueftigkeitsflachen diejenigcn Strecken angesetzt werden, an denen Versicherungsanlagen gebaut werden muessen. RESUME: Les ruptures de toit des cavites souterraines de grande dimensions dependent du champ de contraint primaire et de son orientation, des proprietes de I'' environnement rocheux, de la g eometric de la cavite ainsi que de la presence des discontinuites. La discontinuite doit être exprimee par les mesures, I'' orientation et la qualite. Ce sont le comportement rheologique et la discontinuite qui jouent le rôle plus important au cours des ruptures. Les champs de contraint et de mouvernent doivent être dêterminês en tenant compte des propriêtês rheologiques des roches. Le pas suivant doit être de projeter le systerne de disco ntinuite rnesure autours de la cavite, et executer une analyse de stabilite des blocs potenciellement prêts aux movements. Les sections, où un soutènernent doit être assure peuvent être determinees à I'' aide de caractère et de frequence des discontinuites comme le resultat de notre consideration. STRESS FIELD IN THE ROCKY ENVIRONMENT OF OPENINGS The choice of safety system in case of underground openings, caves of large section is made possible by knowing the primary state of stress, the rock-physical characteristics, and the regularity of mechanical processes due to geological effects. In favourable conditions it is not necessary to ensure the safety of openings by the means of special built-in mechanism, because the developing state of stress does not cause any failure in the environment of the opening. Even in such cases local failure may occur in some sections. The driving of openings is accompanied by failures expanded in time. This phenomenon can be explained by discontinuity dividing rock bodies into bloks, consequently mechanical regularities due to geological effects should be investigated. PRIMARY STATE Rocky environment before starting building activity is inactive and this state of stress is called primary state of stress (if rocky environment is disturbed e. g. by other mining caverns, then the state of stress before starting building is considered as quasi-primary state). This state at depth H is represented by stress tensor F p (H) having as a rule general orientation instead of horizontalvertical one

SUMMARY: The underground position of the hydroelectric and pumped storage power plants has become considerably widespread, mainly in the rock. The paper presents a brief description of a number of existing, under construction and planned underground power plants in the USSR. The.sizes and significance of such structures demand a complex analysis which involves analytical technique, modelling, in-situ investigations, and which takes into consideration the experience gained in construction and operation. principal requirements are formulated for the components and the precision of the geological survey which should pro- vide information on the strength and deformability of the rocks, the systems of joints (Special attention should be paid to the tectonic joints adjacent to the cavern), and of the initial state of stress of the rock mass. The final stage of the studies is both the in-situ measurements of the cavern contour displacements and of the anchor forces, and the analysis. The statements mentioned in the paper are illustrated with specific examples of the powerhouse caverns investigation. ZUSAMMENPASSUNG: Die unterirdische Anordnung der Maschinenkavernen fuer wasserkraftwerke und pumpspeicherwerke hat sich hauptsachlich in Felsgesteinen immer starker durchgesetzt. Im vorliegenden Bericht werden einige in der UdSSR im Betrieb stehende, im Bau befindliche und projektierte unterirdische Maschinenkavernen kurz beschrieben. Wegen der grossen Dimensionen und der wirtschaftlichen Bedeutung solcher Bauwerke ist eine komplexe Betrachtungsweise unter An- Wendung von Berechnungsverfahren, Modellierung, in-situ-Versuchen und unter Berucksichtigung der langjahrigen Erfahrungen im Bau und Betrieb erforderlich. Es werden grundsatzliche Forderungen an die Zusammensetzung und Genauigkeit der ingenieurgeologischen Erkundungen zusarnmengefasst, die ueber die Festigkeits- und Deformations-eigenschaften der Gesteine, Kluftsysteme (unter besonderer Beachtung der tektonischen Kluefte in der Nahe der Maschinenkaverne), den natuerlichen Spannungszustand des Felsverbandes Aufschluss geben muessen. Der Sachverhalt des Berichtes wird an einigen konkreten Beispielen der untersuchung der Maschinenkavernen fuer die Wasserkraftwerke klargelegt. RESUME: Une disposition souterraine des centrales hydroelectriques et des centrales à accumulation par pompage s''est repandue largement, surtout quand il s''agit des terrains rocheux. Dans le rapport les auteurs donnent une breve description de quelques usines souterraines, deja mises en service, à construire et à projeter en URSS. De grandes dimensions et l''importance de tels ouvrages demandent une analyse complexe, qui comporte des methodes theoriques, modelisation et investigations in situ et qui tient compte de l''experience, acqUise pendant la construction et l''exploitation. Les auteurs formulent des exigences essentielles, concernant la composition et la precision de la reconnaissance du terrain qui doit aussurer l''information sur la resistance et la deformabilite des terrains, sur le systeme de joints (une attention essentielle doit etre pretee aux fussures tectoniques à proximite des cavernes), sur l''etat de contrainte initial du massif rocheux. L''expose est illustre par d''exemples concrets relatifs aux etudes des cavernes. A number of various large under ground workings intended for Accommodation of machine halls, transformer halls as well as of gate chambers of hydroelectric power plants in a variety of geological conditions has been constructed or is at present under construction in the USSR. Recently the underground machine hall of the Inguri hydroelectric power plant, 127 m long, 22 m wide and 51 m high, has been put into service (Maysuradze & Potskhoveria 1977, 1978). The machine hall is situated in jointed water-bearing limestone and covered with a rein- forced concrete vault, 1 m thick, on which crane beams are suspended. In the diversion and spillway Tunnels of the Nurek hydroelectric power plant large underground gate chambers (for permanent, emergency and repair gates) are provided (Iliushin 1977; Gurtovnik, Shuten-kov, Mel''nikov 1980). The chambers are 25 m high, 14 m wide and 45 m long and are spaced at 52 m intervals between centre-lines. The chambers are situated in interbedding sandstones and aleurolites of medium hardness and the rock mass around the chambers is rock-bolted. The underground machine hall ofthe Ust-Khantaisk hydroelectric power plant was built under severe climatic conditions of the North,in dolerite of large-block structure (Kelmi & Vittenberg 1975). Theclear span of the machine room is24 m, the maximum height - 48 m,the length - 148 m. The workingwalls are rock-anchored, the vaultis of reinforced concrete.

SUMMARY: This paper is intended to present a description of the historical development and progress of the design approaches for the construction of a total of nine (9) underground power Caverns in Taiwan over the past three decades. The design approaches of the caverns in Taiwan are roughly classified into the classical and the more recent methods for discussion in this paper. The first five caverns constructed during the period of 1955 through 1973 were mostly designed in accordance with the classical approach. The other four power caverns, however, were designed in accordance with the more recent approach based on recently developed principles and theories of rock mechanics. As an illustration of this more recent design approach, the design procedure of the Minghu power cavern, which is 20 m in clear span and about 120 m in length, are discussed in detail in this paper. Tech- Cal problems related to geological investigation and orientation of the power caverns built in Taiwan are also reported in this paper. Furthermore, for reference purposes, the paper also embodies a description of the progress of rock mechanics tests, construction method and sequence which have been undertaken in Taiwan for construction of power caverns as well as the instrumentations installed in the caverns in Taiwan over the past 30 years. ZUSAMMENFASSUNG: In diesem Beitrag soll fuer die letzten 3 Jahrzehnte die geschichtliche Entwicklung und der Fortschritt beim Entwurf von Kavernen anhand von neun unterirdischen Kraftwerkskavernen in Taiwan dargestellt werden. Die Entwuerfe fuer die Kavernen in Taiwan werden in diesem Beitrag grob in klassische und modernere Methoden unterteilt. Die Entwuerfe der ersten fuenf Kavernen, die im Zeitraum von 1955 bis 1975 gebaut wurden, lehnen sich an die klassiche Methode an. Die anderen 4 Kraftwerkskavernen wurden in Übereinstimmung mit den modernen Verfahren, die nach den Theorien und Prinzipien der Felsmechanik entwickelt wurden, gebaut. Zur Anschauung dieser moderneren Entwurfsmethoden wird hier der Planungsablauf bei der Minghu Kraftwerkskaverne, mit einer Spannweite von 20 m und einer Lange von 120 m, im Detail durchgesprochen. Von den technischen Problemen bei der geologischen Erkundung und bei der raumlichen Orientierung der in Taiwan gebauten Kraftwerkskavernen wird in diesem Beitrag ebenfalls berichtet. Weiterhin beinhaltet der Bericht fuer ahnliche Falle eine Beschreibung der Entwicklung von felsmechanischen Untersuchungen, Baumethoden und -ablaufen, als auch eine Beschreibung der in den letzten 30 Jahren in den Kavernen von Taiwan eingebauten Messeinrichtungen. RESUME: Cet expose a pour but de presenter une description du developpement et de la progression historique des approches de dimensionnement dans la construction d''un total de neuf (9) centrales souterraines à Taiwan durant les trois dernieres decades. Les approches de dimensionnement de ces usines souterraines sont classees approximativement parmi les methodes classiques et les plus recentes à discuter dans cet expose. Les cinq premieres centrales, construites durant la periode 1955 à 1973, ont ete dimensionnees selon l''approche Classique. Cependant les quatre autres ont ete calculees d''apres une approche plus recente, basee sur les theories et les principes de la mecanique des roches. Comme illustration de cette plus recente approche de dimensionnement, les procedes de calcul de l''usine souterraine Minghu, d''une portee de 20 m et d''une longueur approximative de 120 m, sont discutes en detail-dans cet expose. Les problemes techniques relatifs à l''investigation geologique et à l''orientation des centrales souterraines construites à Taiwan sont presentes dans cet expose. De plus, à des fins de references, cette etude embrasse egalement une description de la progression des essais de mecanique des roches, de la sequence et de la methode de construction qui ont ete appliquees à Taiwan lors de l''execution des usines souterraines ainsi qui les instruments installes dans les centrales de ce pays durant les 30 dernieres annees. INTRODUCTION In Taiwan, a total of six underground power caverns have so far been successfully completed and are presently in service. In addition, two more caverns are being designed and constructed and one more cavern is in the geological exploration and preliminary design stage. Highlights of the underground power caverns in Taiwan are summarized in Table 1. Of the aforementioned nine power caverns, seven are for conventional hydro power schemes with the clear span ranging from 7.5 m to 21.0 m. Two other caverns, the Minghu and the Mingtan caverns, which are respectively in the detailed and preliminary design stages, are for pumped storage schemes. These two caverns involve the construction of caverns of relatively large spans (20.0 m and 22.8 m clear span) in sandstone stratum with fairly developed joint systems occasionally intercalated with clay seams. Construction of the first underground power cavern in Taiwan may be traced back to the 1950s. At that time, the science of rock mechanics was still in its embryonic stage. Consequently, no rigorous theories, standardized testing methods, and sophisticated testing instruments were available to evaluate the rock properties for design use.