ABSTRACT: Citatah landslide was indicated at the section of Km 23, from Bandung Ð Jakarta main road, West Java, Indonesia. Its dimension is approximately 200 m long located at the medium to steep morphology. This present activity affects the roadway, which pass through the landslide body. The detail engineering geological and geophysical investigation have been done in order to study the behaviour of soil and rock creep at Citatah landslide. Resistivity analysis shows that the unstable soil layer has resistivity between 23 Ð 25 W m, the interlayer of clay, silt and sandstone have resistivity between 7 Ð 17 W m, claystone between 2 Ð 7 W m, and andesitic rock, as a sill, is between 40 Ð 85 W m. The rock analysis observed from shallow drilling hole shows correlation with the resistivity of the rock types. The layer of claystone found at the depth of 9 m, within bore hole 1, is indicated the value of resistivity between 3 Ð 7 W m. Within bore hole 2, claystone found at the depth of 14 m. These claystone layers are interpreted as sliding planes. This result of investigation could be considered for the mitigation of landslide around this area. So the proposed road is suggested to be placed on the andesitic rock which is situated in between the claystone layers belong to Batuasih formation. INTRODUCTION Most of Indonesian areas were covered by the youngest formation of the Quaternary deposits. Moreover, the volcanic belt passing through Sumatera and Java islands, Nusa Tenggara and Maluku archipelagos, and North Sulawesi, creates many unstable areas which may cause geological hazards including land movement. The Citatah area, in which the study was carried out, located at West Java Province, passed by road connecting Jakarta and Bandung. This area constitutes one of landslide zones in West Java.

ABSTRACT: The geotechnical factors controlling the design of the open pit slopes of the Pasminco Century Mine near Lawn Hill, Queensland are presented below. Pasminco Century is a stratiform shale hosted zinc deposit in the Lawn Hill Formation which is overlain in part by the Thorntonia Limestone Formation. The deposit is located in a structurally complex regime that consists of a synclinal basin truncated by easterly striking reverse faults through its centre and northern and southern limits and by an unconformity on its eastern and western margins. Deposit geometry and slope stability is further complicated by small scale folding, a pattern of northeast and southeast striking subvertical faults and northeast dipping thrust faults. Fault emplaced blocks of Lawn Hill Formation occur in the limestone overburden. A staged mining approach has been adopted with the excavation of final pit walls around the deposit margins and interim pit walls along the internal boundaries between adjacent stages. Deposit geometry, major discontinuities and groundwater pressure controls the design of the interim and final pit walls. Two and three dimensional limit equilibrium stability analyses were conducted using both deterministic and probabilistic approaches to determine appropriate pit wall design criteria and to select a suitable excavation sequence and schedule. Interim western walls in the northern ore block are extremely sensitive to wall location, inclination and excavation schedule due to deposit geometry and low residual shear strength along tuffaceous clay beds. INTRODUCTION Geotechnical assessment for design of the Pasminco Century Mine open pit slopes commenced in 1991 with the introduction of a basic geotechnical logging system and the establishment of a database for all cored boreholes drilled on the deposit. The level of geotechnical data collection and input into pit design increased as the deposit investigation advanced into detailed feasibility studies.

ABSTRACT: A case study is presented of the geotechnical design, construction and construction monitoring of the drained basement of the Airport Central Sheraton Hotel building at Mascot, Sydney. INTRODUCTION This paper provides brief details of the geotechnical design and construction monitoring carried out for the basement of the Airport Central Sheraton Hotel at Mascot, Sydney (Figure 1). The building is 12 stories high with down to 4 levels (depth of excavation about 12.5m) of basement parking and contains commercial premises as well as a five star hotel. The design and construct tender to build the hotel was won in 1990 by Concrete Constructions, now Walter Constructions who, with Douglas Partners, geotechnical consultants, proposed a drained basement. This nonconforming design eliminated the need for tanking and permanent anchors to resist hydrostatic uplift. It facilitated an accelerated construction program using the "top down" method, the first time this technique was used in Australia. In "top down" construction the external diaphragm wall, load bearing barrettes and piles are installed and the basement floors and internal building structure used for lateral support allowing excavation of the basement and construction of the superstructure to proceed together. SUBSURFACE CONDITIONS The site is a relatively level, approximately egg shaped area of about 7800 square metres, bounded to the north and east by major streets with a railway embankment forming the southern boundary. Geotechnical investigations by Douglas Partners and others meant results from 16 test bores and 10 cone penetration tests were available to characterise the site. Hydraulic conductivities (k) of the various strata were estimated from experience in similar conditions and the results of numerous borehole permeability tests, including rising and falling head tests in piezometers with screens in the sands and clays, and packer tests in the shale/laminite.

ABSTRACT: The Omarugawa Site is the pure pumped storage station which the Kyusyu Electric Power Company of Japan aims to start operating in July 2008. There are landslides recognized geographically from aerial photographs of the slope. The distribution of the landslide cannot be clearly defined from aerial photographs because they show some indistinct geomorphologic features. So as to show that the rock mass of the slope is estimated to be stable during operation, some detailed geological investigations were carried out in this area. The geographically recognized landslides are distinguished into 3 blocks depending on the weathering grade of the rock mass and the continuity of the deteriorated boring core. From the viewpoint of engineering geology, the conclusion was reached that there was no need for the engineering countermeasure to improve the stability of the rock mass in the upper reservoir after the reservoir fills with water because these landslides are located several 100m from the upper reservoir and are not be distributed inside the reservoir. INTRODUCTION The Omarugawa Site is the pure pumped storage station which the Kyusyu Electric Power Company aims to start operating in July 2008, and is located at Miyazaki Prefecture, Kyusyu district, Japan (Fig 1). There are landslides recognized geographically from aerial photographs of the slope. The slope was called the "Iwaidani side", which is behind the right bank of the upper reservoir. Therefore the necessity to investigate the stability of the landslide material after the reservoir fills with water during the operation arose. The distribution of these landslides cannot be clearly defined from aerial photographs because they show some indistinct geomorphologic features. So as to analyze the stability of the rock mass of the slope, detailed geological investigations were carried out on this area.

ABSTRACT: Water content in fine-grained sedimentary rocks is an important consideration in many engineering projects. It has been well establish that water content of these rocks can significantly changes most aspects of physical and mechanical properties. This paper presents the effect of water content on the mechanical behavior of three different types of fine-grained sedimentary rocks, clayshale, mudshale and mudstone from different locations. Many samples were tested at a wide range of water contents varying from oven-dried to saturated condition. A general equation was developed for this type of fine-grained sedimentary rocks that may be used for predicting uniaxial compressive strength from the available information on water content. INTRODUCTION Fine-grained sedimentary rock in this study includes mudrock or shale. This type of rock is formed in both marine and nonmarine environments and it is one of the most abundant sedimentary rocks. Tucker (1991) reported that mudrock is the most abundant of all lithologies, constituting some 45–55% of sedimentary rock sequences. Because of its abundance, mudrock is the most frequently encountered rock type in engineering construction. King et al. (1994) reported that shales are found in many large civil engineering structures in United Kingdom and elsewhere. Moreover this rock is one of the most problematic materials for geotechnical and petroleum engineers. The compressive strength of this type of rocks under different water content conditions have been studied by many researchers (Van Eeckhout, 1976; Bauer, 1984; Tandanand, 1985; Steiger & Leung, 1990; Zhiyl & Jinfeng, 1993; Hsu & Nelson, 1993; Ghafoori, 1995; Lashkaripour & Ghafoori, 1999). Analysis of their results has shown that water content of these rocks significantly changes most aspects of physical and mechanical properties. Van Eeckhout (1976) studied the effect of water content on the strength of different rocks.

ABSTRACT: An experimental study was conducted to investigate the change in the shear strength of expansive soils with the amount of swell. Two series of tests were performed using two types of expansive soils: shale and bentonite. Swell tests were carried out using a hydraulic triaxial stress path cell on samples having different initial water contents. The soil samples were sheared under strain controlled loading using a motorized screw control cylinder connected to the triaxial apparatus. In each group of tests, five shear tests were performed. In the first test, the soil sample was sheared without allowing for swell to take place (i.e. 0% swell) which is considered as a reference test. In the second test, shearing was conducted after the sample was allowed to swell until the vertical swell ceased (i.e. 100% swell). In the third, fourth, and fifth tests, the samples were sheared when the vertical swell reached, respectively, 25%, 50%, and 75% of the ultimate vertical swell measured in the second test. The ratios of the shear strength of swelled samples to the shear strength of the sample in which no vertical swell was allowed were calculated. Test results showed a significant influence of the amount of swell on the measured shear strength of the tested soils. The average value of the shear strength when the sample reached ultimate vertical swell was approximately 10% of that before swelling for the shale and about 33% for the bentonite. INTRODUCTION Shear strength of soils is needed for many stability problems of the geotechnical engineering, including design of foundations, prediction of the stability of slopes and embankments, and calculation of earth pressures against retaining structures. A review of the available literature indicated that studies concerned with the effect of swelling on the shear strength of soils are limited.

ABSTRACT: Tunnelling through the fragile, weak and jointed rock masses of Himalaya is a challenging task. Almost in all the tunnelling projects of Himalaya some or the other type of tunnelling problems have been encountered and are still being faced; be it a face collapse, chimney formation, water inrush, squeezing, etc. Though it is not a welcoming situation, but there is a lot to learn from such conditions. The experiences of Himalayan tunnelling are briefly presented in the paper. INTRODUCTION The Himalayan region and its adjacent basins straddle a third of India"s land mass and support about half the country"s population. The 100 or more dams across its rivers and tunnels supply almost 50 per cent of the country"s power requirements and irrigate millions of acres. But geologically the Himalaya is among the most unstable mountain range in the world (India Today, 1993). Himalaya occupy a unique position internationally providing substantial power production from hydro-power projects, a highly cost-effective clean and renewable energy resource. Total annual energy potential of the fast flowing rivers has been calculated at roughly 80000 TWh, out of which the economically viable potential has been assessed at 10000TWh. Only about 25 per cent out of this potential has been tapped so far. Almost all the hydro-electric projects in Himalaya have an underground structure, be it a tail race tunnel, a head race tunnel, an adit, a cavern for turbines or transformer hall, shafts, etc. In the paper, the lessons from past and present tunnelling operations have been present in brief to highlight the challenges of tunnelling through Himalaya. THE HIMALAYA The Himalayan range, located to the north of the subcontinent, was formed by the collision of the Indian Plate with the Eurasian Plate.

ABSTRACT: Burnt colliery spoil is a potentially valuable engineering material and is present in significant quantities in the UK. It can be used successfully as general fill or capping layer. However, due to its high quality it may be more suited to use as selected granular fill or sub-base. In particular, cement stabilisation will reduce frost susceptibility and may be a particularly appropriate outlet for burnt colliery spoil for use as sub-base. However, an increase in control and testing may be required, having an effect on the cost of using such materials. Conditions under which burnt colliery spoil should not be used are also identified. Although formulated within the limits of the UK Specification for Highway Works, the advice given should be transferable for use within other specifications. INTRODUCTION Colliery spoil is available in the coal mining areas of the UK in large quantities. The estimated annual production of colliery spoil was 45 million tonnes during 1988/89 (Whitbread et al., 1991). An estimated 3,000 to 3,600 million tonnes is also available in stock piles from past production, some of which has been used in land restoration and is therefore not available for use (Sherwood, 1974; 1994). There are two main types of colliery spoil: burnt and unburnt. Burnt colliery spoil, BCS, (burnt shale or burnt minestone) generally has better engineering properties than unburnt colliery spoil, UCS, (unburnt shale or unburnt minestone) and consequently has a higher utility. The most common rock types found in UCS are mudstones, siltstones, shales, seat earths, sandstone and, in some areas, limestones (West and OÕReilly, 1986). There is also an additional variation arising from combustion in the tip. When combustion occurs the physical properties and chemical composition are changed such that BCS varies considerably from the UCS.

ABSTRACT: The experience of seismic activity associated with stabilizing pillars at intermediate depth, approximately 2000 metres below surface on the Ventersdorp Contact Reef horizon, is summarized. One particular case study is used to describe certain aspects in detail. The evaluation is based On seismic data, closure-ride measurements and the extent and intensity of underground damage. Experience from pillar associated seismicity allows a review of stability criteria of stabilizing pillars at intermediate depth which seem to be dominated by the composition of the footwall strata. INTRODUCTION Stabilizing pillars have proved to be the focus of large seismic events which resulted in considerable damage at Western Deep Levels South (WDLS). The gold mine is situated in the Western Transvaal, about 70 km west of Johannesburg. The mine forms part of the West Wits Line of mines which work two major conglomerate formations, the Ventersdorp Contact Reef (VCR) and the Carbon Leader Reef (CLR). At present, at WDLS, only the VCR is mined between 2000 and 2400 m below surface. The reef dips approximately 21 degrees towards South with a varying channel width of 0,05 to 4,50 m. It is intersected by dykes and some faults of minor throw « 50 m). Both the VCR up dip to the North and the CLR some 900 m stratigraphically below are mined by the adjacent WDL-West and WDL-East mines. WDL has adopted longwall-mining as a general concept which allows a face-advance between 10 and 12 m per month. The mine experiences a relative high incidence of seismicity. Stabilizing pillars became part of Western Deep Levels general mining layout to reduce stress concentrations at the stope faces and hence the incidence of seismic activity. Some major seismic events have occurred with catastrophic damage along these pillars but the circumstances which lead to them have until recently been poorly understood. To shed light on this phenomenon, a study was carried out on pillars and their seismic activity, involving mainly the Lower Carbon Leader Reef at WDL-East and West mines (Lenhardt and Hagan, 1990). General results of this study and from Jantzon et al. (1990) can be summarized as follows: The width of pillars between 20 and GO m has no bearing on the magnitude of pillar related seismic events. Pillar associated events tend to recur some distance behind or close to the advancing stope face, depending on the mining geometry. Pillars of20 m width and greater (the widest pillars on WDL are 60 m) do not crush in a hard rock geological environment such as at WDL but the footwall heaves violently in adjacent excavations. Pillar associated seismicity increases with depth. During investigations of pillar related seismicity, which concentrated on the deeper, CLR, horizon of WDL, it became apparent that pillars at intermediate depth on the VCR also experience stability problems. The results of a special project which was initiated to analyze the nature of this phenomenon is described in the following paragraphs. (Figure in full paper)

ABSTRACT: Drilling problems are frequently encountered throughout the Tertiary section in the North Sea. The problems are mainly to be associated with smectitic shales and tuffaceous sediments. Typical problems are drill tool sticking and lost circulation. The causes of borehole instability can be both of chemical and mechanical nature. Possible causes are fracturing of the formation, borehole collapse and creep or swelling in the borehole wall. Borehole instability take place even with inhibitive oil-based mud systems, so part of the problem is clearly of a mechanical nature. In the paper, we present an experimental investigation of mechanical strength and elastic parameters of shales at stress levels corresponding to depths of wellbore instabilities. Four different clays were selected as analogue materials to those encountered in North Sea Tertiary formations. The pre-failure, peak strength and post failure behaviour of these shale materials have been studied. INTRODUCTION Borehole instability has been a significant contributor to unproductive drilling time during the history of drilling for hydrocarbons. As a consequence, drilling costs have been unacceptably high. This fact has led the oil drilling industry to allocate increasing resources on trying to understand, alleviate and solve the problem of borehole instability. While drilling, unstable boreholes cause a variety of problems. The problems are most likely caused by fracturing of the formation, borehole collapse, large deformations and creep in the borehole wall and destructive rock-fluid interactions between the formation and the mud-system. These destructions result in excessive washing and reaming, hole "packing off", lost circulation and stuck pipe, and in the worst case losing the hole. Observations of drilling problems on the Statfjord field indicate that initial tight hole sections after some time may develop into an oversized borehole. This situation is probably due to further collapse in the borehole Wall. For the purpose of keeping the wellbore mechanically stable, increased mud weight has proven to enhance the situation. Using conventional methods for estimating pore pressures, it has been shown that troublesome shales very often are "overpressured", i.e. its pore pressure has attained a higher pressure level experienced at an earlier stage in the rocks stress history. This means that these shales normally are drilled "underbalanced". Another factor that has proven to reduce borehole instability is to minimize the sail angle through the particular hole sections of troublesome shales. Optimization of casing setting depths with respect to geology/ lithology, formation strength and pore pressure, will also be a contribution to reduced borehole instability problems during drilling. As of today, oil based muds are regarded to be the most inhibitive mud with respect to highly reactive clays, which often is dominant in troublesome shales. Use of oil based mud will reduce the destructive chemical effects of interactions between the rock and the mud. The result is that the wellbore will be closer to the gauge size, which in turn contributes to optimum hole cleaning and improved drilling conditions. To be able to predict potentially instable formations, it is of vital importance to know certain rock parameters.

ABSTRACT: The influence of confining pressure on the indentation response of rocks is analyzed. Special attention is given to shales which often cause problems during drilling. To take into account the influence of failure mechanisms during indentation, two indentation parameters are defined. The first one measures the non-localized deformation under the tooth; in shales, its value is predicted by a rigid-plastic theory. The second parameter measures the deformation related to highly localized mechanisms. This parameter is dominant at low confining pressure. It cannot be predicted by a continuum formulation. INTRODUCTION Field observable changes in drilling response which are related to changes in rock mechanical properties and environmental conditions are measured in rocks (Falconer et al, 1988). Therefore, one might expect to obtain information on the lithology being drilled, or on any other relevant in-situ parameters such as pore pressure in shales, from an interpretation of the drilling response of bits. Models have already been developed in order to calculate state of the bit and formation strength from a real-time interpretation of the rate of penetration and bit torque (Winter et al, 1987; Falconer et al, 1988). However, due to a lack of knowledge of the understanding of the mechanisms which are involved in the rock fragmentation under the bit teeth, these models use empirical parameters which cannot always satisfactorily provide information on intrinsic rock properties. An understanding of the failure mechanisms which occur during indentation is needed to determine the fundamental parameters which control the drilling process. In particular, the determination of the influence of rock Properties and differential pressure (the mud pressure minus the far-field pore pressure) on the indentation parameters is recognized to be a key subject due to its application to measurement while drilling. Gnirk and Cheatham (1963), Maurer (1965), and Gnirk and Cheatham (1965) have demonstrated that the indentation response of rocks is a function of confining pressure. However, their studies provided little information on shale behaviour, though shales often cause problems during drilling. It is the main purpose of this study to describe the behaviour of shale during indentation and to compare its behaviour with that of other rocks. ROCK PROPERTIES Three rocks have been selected for this study: Carrara marble, a Lower Jurassic shale, and an Upper Jurassic shale. Results from Gnirk and Cheatham (1965) on Indiana Limestone are also reported. The Lower Jurassic shale has been tested both dry and saturated. Carrara marble, and Indiana limestone contain mainly calcite. The Lower Jurassic shale and Upper Jurassic shale contain respectively 51% and 40 % clay, primarily illite and kaolinite, 35 % and 32 % quartz, and 5% and 15% calcite. Due to the mineralogic composition of these Jurassic shales, the influence of the chemical environment on their mechanical behaviour is expected to be very limited. The permeability of the shales is in the order of nanoDarcies. Porosity, Young's modulus at atmospheric pressure and uniaxial strength are shown on table 1.

ABSTRACT: Advances in wellbore stability and shale technology have long been sought because shale instability has consistently produced the highest drilling trouble costs. Most wellbore stability problems occur in shales. Wellbore instability in deep, shale formations is the major cause of stuck pipe, high torque and drag, hole enlargement, poor log quality and poor primary cement jobs. Major improvements in wellbore stability predictions and shale technology are required to significantly impact drilling risks and costs, particularly in expensive wells under high-angle, extended-reach and severe tectonic conditions. This paper presents an overview of recent advances in shale technology and results that show relationships between cuttings index properties and shale mechanical properties determined by special triaxial tests. In addition, it presents an overview of wellbore stability technology with a discussion of practical solutions to wellbore stability problems by qualitative and quantitative applications of theory. INTRODUCTION One of the greatest needs in the petroleum industry is a predictive method to prevent wellbore failure during the drilling operation (Cheatham 1984 and Pearson 1988). Well bore collapse causes problems such as stuck pipe, high torque and drag, hole enlargement, poor log quality and poor primary cement jobs. Critical wells are often sidetracked or abandoned before reaching their objectives because of severe well bore failures. Most of the problems occur in weaker formations, predominately shales. These failures lead frequently to excessive drilling and completion costs that cannot be sustained in the current economic climate drilling engineer is often frustrated with the problem of trying to understand and predict the behavior of rock of uncertain composition at great depth under uncertain loading conditions with theoretical models of uncertain validity or viability. In the past, the well bore stability research area was considered high risk with a low probability of successfully finding practical solutions to the problem. Research progress in recent years has reduced some of the uncertainties. There has been increased development of theoretical concepts (Fairhurst 1964, Gnirk 1972, Bradley 1979, Risnes et al. 1983, Zoback et al. 1986 and Vardoulakis et al. 1988), significant advances in understanding and quantifying shale mechanical behavior (Steiger & Leung 1988) and more widespread experience in field applications and tests of concepts that show promise by Exxon and others (Maury & Sauzay 1987 and Fuh et al. 1988). These results provide encouragement and optimism that more practical predictive methods can be developed to prevent wellbore failure. However, major improvements in wellbore modeling and shale mechanics technology are required to implement practical predictive techniques to significantly impact drilling risks and costs, particularly in expensive wells under high-angle, extended-reach and severe tectonic conditions. 2 WELLBORE STABILITY PREDICTIONS - RETROSPECTIVE 2.1 Mechanical versus chemical stabilization Over the past few decades considerable research effort has been expended on both the chemical and mechanical aspects of wellbore stability. Substantial benefits have accrued from the development and widespread use of inhibitive drilling fluids (Clark et al. 1976, Steiger 1982, Bailey et al. 1987, Grinrod et a1. 1988 and Colins & Stone 1989).

Abstract: The effect of partially dehydrated clays on the adsorption potential of shales is presented, along with the resulting movement of fluids and the generation of swelling pressures. An experimental test cell is described which measures fluid diffusion rates for shale-fluid systems under temperatures to 350°, and confining and well bore pressure to 15,000 psi. Results for three fluids in contact with one shale are presented. 1 INTRODUCTION Wellbore instability problems are believed to be caused by mechanical and chemical factors. Previous researchers (Bradley 1979, Aadnoy 1987) have shown that mechanical effects depend on in-situ earth stresses, pore pressure, wellbore pressure, and hole angle. This area is fairly well understood, unfortunately the chemical effects which manifest themselves in shale-mud chemical reactions are not well known, and very few analytic solutions exist. The balanced activity oil muds which surfaced in the 70's (Chenevert 1970) provided solutions which eliminated the aqueous chemical reactions by building muds which had osmotic potentials which counteracted the adsorptive potentials of the shales. A second quality of such oil muds was the providing of membrane films which prevented ionic movements from the internal water phase of the mud into the shales. In this water-in-oil emulsion mud both water and ion movement was prevented, and no chemical reactions occurred. Water muds, on the other hand, have not been able to stop the flow of water and ions in such a total manner mainly because of the absence of semipermeable membranes which would restrict ionic flow. Also, the transfer of both water and ions has made analysis of such systems very difficult. 2 SHALE-FLUID REACTIONS 2.1 Shale adsorption potential Shales are sedimentary rocks which usually contain large amounts of clays. As these rocks are dewatered during the geologic compaction process, individual clay platelets within the shale are forced closer together thereby increasing their potential to adsorb polar molecules. The electrical double layers with their exchangeable cautions and interfacial water provide a negatively charged environment which attracts positively charged ions and water (which is dipolar). When such de-watered shales are exposed to certain drilling fluids adsorption and subsequent swelling results. Shown in Figure 1 is the electrical potential on the surface of a completely hydrated platelet as a function of distance from the surface. Such platelets no longer react with fluids because their surface charge is completely satisfied with its adsorbed cautions and water envelope. During geologic compaction, however, water and ions are expelled, adjacent clay platelets are forced closer together, and there is a potential developed midway between the platelets. Figure 2 shows how the adsorptive potential "U" increases with a decrease in spacing between platelets (Mitchell 1976). As the potential between the platelets increases, many changes occur for the clay-fluid system, one being the lowering of the vapor pressure of the water phase. One way to determine a shale's potential to adsorb water is to measure its water vapor pressure, or its relative vapor pressure (p/po)also referred to as its water activity.

ABSTRACT: A comparison has been made of the natural stresses measured in the rock damsite of the arch dam being built for the Houdoni hydropower station using the geological, geophysical and geomechanical methods, on one hand, and the gravitational stresses found by the solution of the plane and spatial problem within the scope of the elastic theory, on the other hand. It is noteworthy that the measured natural stresses are generally higher than the calculated gravitational stresses, especially in the horizontal directions. The damsite section of a 200 m high arch dam of the Houdoni hydropower station consists in a V-shaped canyon with a floor 15 to 20 m wide. The slopes of the canyon are mainly composed of volcano-tufogene rocks of the Bajocian stage formation interlaid with tuff and lava breccia, porphyrites, tuff sandstone and shale. Shale and sandstone of the upper Lias are exposed on the northern periphery of the section. The Bajocian stage rock depth at the damsite section is characterized by a non-uniform petrographical composition and structure. It is divided into four benches in the descending stratigraphical sequence. The first bench being only exposed at upper and medium elevations of the left slope represents mass green and grey porphyrites found as dense, tough and slightly fractured. The second bench consists in tuff sandstone with rare fine-fractioned interlayers of tuff breccia and brown and grey tuff shale. The depth of the left slope bench is 40 to 50 m, and that of the right is 100 to 110 m. These rocks are almost completely exposed on the right slope, and overlapped by drift beds and alluvion on the left. The third bench, the thickest, 120 m deep is lava breccia comprising fine porphyrites based on the lava cement. These rocks are well exposed on both slopes of the valley. The fourth bench is made up of alternating tuff sandstones and shales, and rather thin tuff breccia interlayers. The depth is 40 to 50 m. The aforesaid types of rock with the exception of lithology differ by the degree of schistosity and jointing and possess various indexes of physical-mechanical properties. All rock types in the massif are extremely changed resulting in a large variety of rock properties in the natural bedding. Surface relaxation and weathering are other factors strongly affecting the rock properties and condition in their natural bedding. This results in pronounced heterogeneity of rock physical-mechanical properties of the surfacial part of the profile. A whole complex of investigations was carried out in the determination of the natural stress field at damsite using the geological, geophysical and geomechanical methods. The geomechanical studies using hydrofracture were carried out in two boreholes at depth interval from 50 to 150 m (ref. to Prof.F. Rummel, W. Germany). For the determination of the natural stresses in the massif the following values found in the hydrofracture experiments will be considered as reference: the fracture pressure P e ' the refracture pressure Pr and the static pressure Psl with the closed estuary.

SCOPE: A simple case history. What is the required stability of a wellbore? Key factors of instability. Recent progress and review 1) A SIMPLE CASE HISTORY Even if this does not happen on a routine basis, wellbore instability is unfortunately quite a common feature of drilling. It seems interesting to start the general report on this subject by a short description of a case of instability, without any specific worsening problem. This case is from the Norwegian North Sea, but it will look familiar to any drilling engineer. The Hordaland group is a thick formation (about 1500 m) which covers most of the reservoirs in the North Sea. Even if it is of course variable from one place to another, it is mainly composed of clayey formation, claystone at the top and more indurated shale at the bottom. In that particular case, the well was drilled with a 12" 1/4 bit. The bottom of the Hordaland group was at about 2000 m. The sequence of events is reported on the following table (Figure 1). This sequence of event is quite typical of a wellbore instability. The hole was drilled through the shale on day 1 with a mud weight of 1.13, and the well deepened into the underlying formation. The trip to the surface was smooth. While running the new bit down, it was necessary to redrill the hole down from 1950 m. This may indicate that instability started during the trip. However the mud weight was slightly raised because shale "cavings" (chips of rocks producted by hole wall caving) were coming on the shakers. A "wiper trip" was decided to control the hole stability after the well had been circulated "bottom up", i.e. for a sufficiently long time to bring all the cuttings to the surface. While pulling out, the pipe got stuck when the bit was at 2232. It was impossible neither to rotate the pipe, nor to circulate. After a while, circulation was restored, and lots of cavings came to the surface with a high viscous pill. After some time working on the stuck pipe, it was decided to disconnect the stuck part of the pipe ("back off"), to cement the hole above the "fish," and to start a new hole at 1980 m.(side-track). On day 19 the drilling reached the previously reached depth on day 11. Even for a simple instability, this means a loss of 8 days, on an offshore rig where 70 persons are working permanently. This is why wellbore stability is considered as a serious concern by most of the oil industry operators. In this particular well, caliper logs revealed that at the bottom of the shaly Hordaland group the hole was largely caved. The instability must have started during the first trip but was not causing serious problems to the drilling operation. It seems however that large "cavings" were produced, which cannot be carried up to the surface by a regular mud flow.

ABSTRACT: Drained triaxial tests, including stress path studies, have been conducted on a selection of sedimentary rocks to investigate strength behaviour with reference to wellbore instability. The tests were undertaken using 'state-of-the-art', servo- controlled equipment, and specimens were subjected to conditions of elevated temperatures, stresses and pressures. From data obtained, established failure models were compared to alternative models developed from the critical state concept. Stress distributions around a wellbore have been computed, using finite element solutions, to investigate the influence of different peak strength criteria. 1 INTRODUCTION The occurrence of mechanical instabilities, which can result in complete or partial collapse of wellbores, remains a continuing problem in the drilling of deep petroleum boreholes. Instabilities may occur during or shortly after drilling, or may develop later during the operation of the well. Such time dependency can be introduced by creep or swelling behaviour, or by a gradual increase in the effective stresses around the wellbore as pore pressures are reduced on production. Amongst the most important factors governing the integrity of a borehole at any time is the load bearing capacity of the rock immediately around it. Similarly, of vital importance in predictive modelling or back analysis of wellbore instability, is the availability of appropriate and reliable strength data, and the selection of criteria which can describe the peak strengths of the materials. Pan and Hudson (1988) have reviewed a number of strength criteria, any of which could be applied to the problem of wellbore instability, but it is the long-established criteria, including those by Drucker-Prager and Mohr-Coulomb, which remain those most commonly used in wellbore applications. however, many such criteria were developed to describe not only the strength behaviour a sedimentary rocks, but also of igneous and metamorphic rocks, soils and engineering materials. Consequently, they are often inadequate for describing the peak strength of weak rocks, such as those in which wellbore instabilities often occur. One such criterion, and an alternative semi-empirical criterion, are considered in this paper to describe the behaviour of some sedimentary rocks tested under simulated petroleum environments. Several individual and joint programmes of research have been undertaken at Imperial College (Santarelli et al. 1986, Nakken et al. 1989) to investigate many aspects of the mechanical behaviour of intact sedimentary rocks in petroleum applications. This paper focuses data from two such projects (Marsden, Wu), in which strength behaviour of sedimentary rocks in wellbore environments, and the application of critical state concepts to borehole instability, have being investigated. The work has included a large number of high quality laboratory tests, including conventional and stress path triaxial studies, at room and elevated temperatures. The sedimentary rocks investigated were a limestone, a shale and several sandstones with varying degrees of anisotropy. The tests, were undertaken using a 'state of- the-art', closed-loop, servo-controlled rock mechanics test facility, capable of high quality thermo-hydro-mechanical acoustic testing under conditions of elevated temperature and pressures, for a wide range of petroleum, civil and mining engineering applications.

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: Several underground hydroelectric plants in the Niagara Falls region are showing signs of structural distress as a result of preexisting high horizontal stresses and time-dependent rock deformation upon stress relief. Thus, a major emphasis in the feasibility and preliminary design studies toward the construction of a new power plant has been the measurement of the in-situ stress using both overcoring and hydrofracturing. This paper reports the results of the first comprehensive stress measurements in the area, confirming that high horizontal stresses prevail, but also showing that substantial jumps in stress magnitudes exist between rock units, and that stress changes, especially with respect to direction, may occur along the route of the planned power tunnels. These results have been incorporated in the design analysis of the power plant underground components. RESUME: Fortes contraintes horizontales à Niagara Falls, leur mesure, et la conception d''une nouvelle generatrice hydro-electrique. Plusieurs génératrices hydro-electriques souterraines dans le région de Niagara Falls montrent des signes de de''tresse de structure résultant de fortes contraintes horizontales et de la déformation de la roche causée par le reláchement de ces contraintes. Par Conséquent, les études préliminaires de faisabilite et de conception pour la construction d''une nouvelle génératrice ont mis l''accent sur la mesure des contraintes en place, par le sur-carottage et la fracturation hydraulique. Cette communication rapporte les resultats des premières mesures d '' ensemble dans la région, lesquels confirment que les contraintes hori zontales sont en général éleveés, mais aussi demontrent qu il existé des variations substantielles dans l''intensité de ces contraintes dans les diverses roches, et que des variations de contraintes peuvent done surveni er le long des tunnels proposés. Ces resul tats furent incorpores dans l''analyse de tous les composants sous-terrains du groupe electrogèe. ZUSAMMENFASSUNG: Einige Untergrund - Wasserkraftwerke im Gebiet der Niagara- Fälle zeigen Anzei chen der Baufälligkeit als Resultat der vorgegebenen hohen horizontalen Spannungen und der zeitabhangigen Felsdeformation in Folge des Spannungsabbaus. Daher wird bei vorläufigen Design - Studien bei der Konstruktion eines neuen Kraftwerks der Messung der in-situ Spannung unter Benutzung von "overcoring" und "hydrofracturing" besondere Beachtung geschenkt. In diesem Artikel wird über die ersten vergleichenden Spannungsmessungen berichtet, welche bestätigen, daβ hohe horizontale Spannungen vorherrschen und euβerdem zeigen, daβ groβe Unterschiede in der Höhe der Spannungen verschiedener Felseinheiten bestehen und richtungsabhängige Spannungsanderungen entlang der geplanten Druck-tunnel aufreten können. Diese Ergebnisse wurden in die Designanalyse der Untergrundkomponenten des Kraftwerkse ingebaut. INTRODUCTION The Niagara Falls region has long been recognized for its scenic attractions and hydroelectric resources. A number of power plants were completed at the turn of the century. Of those owned by Ontario Hydro - the provincial electric utility - the Toronto Power Generating Station has already been retired, and the Ontario Power Generating Station is coming close to retirement. To make efficient use of the available water, Ontario Hydro is currently evaluating the feasibility of building a new hydraulic plant in the region known as Sir Adam Beck Niagara Generating Station No. 3 (SAB #3). Similar to the 1400 MWSAB #2 plant built in the 1950''s, the proposed SAB #3 project will involve a system of hydraulic tunnel s and canal. The SAB #2 project included twin 9 km long tunnels, each with 15.5 m excavated and 13.7 m finished diameters. As illustrated in the geologic section in Figure 1, the twin tunnels were excavated in horizontally bedded sandstone, shale, dolomite and limestone units of the Silurian age. The new tunnels for the proposed SAB #3 project will likely be excavated in the underlying Queenston shale formation, with the Whirlpool sandstone as the roof. The reference scheme favours a twin tunnel system with a finished diameter of 10.7 m. Alternatively, a single 15 m diameter tunnel could also be contemplated, the limiting factors being excavation cost and machine tunnel technology. Figure 2 shows the 1ayout of the existing SAB #2 as well as the proposed layout schemes for the SAB #3. 2. ROCK ENGINEERING DESIGN CONSIDERATIONS Rock structure performance in the region over the years clearly suggested that there are two major rock mechanics factors in the design of the underground openings for the SAB #3. The first is the state of high horizontal stresses in the sedimentary units, the second being the time-dependent deformation properties of some shale and shale limestone units. It has been recognized that high horizontal stresses exist in many of the bedrock units in Southern Ontario and adjacent areas (Haimson and Lee 1980; Lee 1981; Lo 1978). Buckling failure may also occur in some quarry floors and rock outcrops (Lee 1981). The origin of this state of stress is not well defined. A number of mechanisms have been postulated, including viscoelastic deformation under glacial loading, changes in the Earth''s curvature due to continental glaciation, erosion, and plate tectonics (Lee 1978b; Lee and Asmis 1979; Asmis and Lee 1980).

SUMMARY The performance of a 235 m deep circular shaft wit~ a finished diameter of 4.3 m, excavated by conventional shaft construction techniques in clay shale, was monitored by measuring the rock mass displacement field, the rock stress changes which occurred during the shaft advance, and the stress build up in the cast-in-place concrete liner. The project, the local geology and the instrumentation program is described. The field observations are discussed with particular emphasis on their interpretation to determine the in situ stress field. ZUSAMMENFASSUNG Ein 235 m tiefer, kreisförmiger Schacht mit einem Durchmesser von 4,3 m wurde mit konventioneller Bauweise in weichem Tonschiefer erstellt. Das Verhalten des Gesteines und des schachtausbaues wurde durch Messungen der Felsverschiebungen mit Mehrfach-Messankern, der Felsspannungsanderungen wahrend des Schachtvortriebes und der Dehnungen im Betonring beobachtet. Das Projekt, die lokale Geologie sowie die Messeinrichtungen sind beschrieben und die Auswertung der Messresultate ist erlautert. Spezielles Gewicht wurde dabei vor allem auf die Bestimmung des urspruenglichen Spannungsfeldes gelegt. RESUME La performance d''un puits circulaire d''une profondeur de 235 m et d''un diamètre de 4,3 m, creuse suivant les techniques conventionnelles de construction de puits enschiste argileux, a ete etudiee par le mesurage du camps de deplacement de la masse rocheuse, les changements de contrainte du roc pendant la construction du puits, et la progression des contraintes sur le revêtement en beton. Le project, la geologie locale et le programme d''instrumentation sont decrits. Les observations sur le terrain sont interpretees pour determiner le champs de contraintes en place. INTRODUCTION The design of underground openings in the soft and weak bedrock underlying large areas of the prairie provinces of western Canada has been primarily empirical and the dimensioning of the opening supports is often based on rules developed for comparable rock types in other parts of the world. Their applicability to the local conditions has never been proven and little quantitative data has been collected to describe accurately the rock properties and to evaluate the performance of existing openings. This inhibits more rational design and construction procedures. The sinking of a vertical shaft at Kipp near Lethbridge in southern Alberta provided an excellent opportunity to collect shaft performance data for the rational design of future adits to this coal mine. For this purpose, it was necessary to determine the in situ stress field, to observe the deformations near the opening, to determine the rock mass deformation properties, to determine the strength properties by laboratory tests, and to monitor the load development on the support to verify lining design. In this paper, we present a brief overview of the project with a qualitative description of the performance of the shaft. This is followed by a detailed interpretation of observations made to evaluate the existing field stresses at the site. PROJECT DESCRIPTION The prospective mine is located approximately ten kilometers north-west of Lethbridge, on the southern edge of the Alberta Plains (Figure 1). The mine is being developed by Petro Canada Exploration Inc. to exploit part of the bituminous coal of the extensive Lethbridge Coal Field. Several coal mines have operated in this area since the early 1880''s but most mines have been inactive over the last two decades. Recent increases in world coal prices make underground mining in this area viable and one additional major project is presently under development nearby. The shaft with a finished diameter of 4.32 m was sunk by Thyssen Mining Construction of Canada Ltd. between February and November, 1980 using conventional shaft sinking methods. The bedrock was excavated by drilling and blasting 1.8 to 2.4 meter deep, half floor benches. The shaft was lined with a cast-in-place concrete lining with variable thickness depending on the overbreak. The specified thickness was (Figure in full paper) 300 mm for the first 70 m, 400 mm to a depth of 130 m and 500 mm, 600 mm, 700 mm to depths of 175 m, 220 m and 235 m, respectively. The lining construction generally followed one to two shaft diameters behind the shaft bottom. Ready-mix concrete with a specified strength of 35 MPa was poured behind segmental slipforms. Shaft sinking through the bedrock progressed at a rate of about 3 to 4 meters per day. Except during 4-day work stoppages, the rock was seldom unsupported for more than 16 to 20 hours.

The development of nuclear power requires safe disposal of large quantities of nuclear waste. A committee of the National Academy of Sciences-National Research Council proposed storing the waste in natural salt formations. However, oil production activities and geologic exploration have left boreholes in the salt beds. A report by Battelle Northwest Laboratories (Schneider and Platt 1974) suggested that. in order to protect waste repositories in salt it would be necessary to restore the formations surrounding the salt to essentially their original state. They proposed the use of compacted natural earthen materials to achieve such a high quality plug. Compacting borehole plugs using natural materials has been evaluated (Martin 1975; Olsen and Martin 1976). Since the essential function of a compacted plug is to keep water out of the salt, the permeability of a compacted plug is its most important property. The referenced studies indicated that adequate plugs (permeability, k ≤.1 μ D) could be compacted in metal molds using the parent shale with high compactive efforts or montmorillonite with low compactive effort. However, when borehole plugging was modelled by compacting a plug into a shale specimen using high effort impact compaction, flow of water in a permeability test of. the composite section was concentrated in the interface zone between the plug. and the surrounding shale. This zone consists of both the outer portion of the plug and the inner portion of shale at the hole wall. The interface flow suggested a difference in lateral confining stress for Plugs compacted in metal molds compared to plugs compacted into the shale formation. The lower confining stress may result from damage to the rock formation during plugging or the lower modulus of the shale. Any cracking or crack propagation during plugging would also allow flow to take place in the shale portion of the interface zone. This paper presents the results of a program to determine the relationship between changes in lateral stress during plugging and the ability of a plug-formation system to restrict the flow of water into the salt. A complete treatment of this subject is presented elsewhere (Olsen 1978). EXPERIMENTAL APPARATUS AND PROCEDURES Lateral Stress Equipment Model tests of coring and plugging were run in a lateral stress cell - shown schematically in Figure 1. This cell was constructed to accommodate a 3.75-inch diameter by 2-inch high cylindrical sample which could be loaded by the top piston'. It was also possible to remove the central portion of the base and top piston for coring, plugging and extrusion while the remainder of the sample remained loaded. A sample borehole l.l-inches in diameter could thus be constructed and plugged. Both ends of the cell have porous stones and fittings to apply water pressures for backpressuring and/or permeability testing. A 0.030-inch stainless steel membrane transferred the lateral pressure on the sample to a fluid in an annular chamber connected to a 1000 psi pressure transducer. Vertical loads were transmitted through and measured by a 10,000 pound capacity load cell.