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In the years 1969–1973, the City of Helsinki constructed about 1.5 km distant from the city centre, three oil storage caverns with 250.000 m3 total capacity. In the excavation work difficulties were encountered owing to the state of high horizontal stress in the rock (15 MN/m2). In view of this fact extensive rock stress studies were carried out. The existence of the horizontal stressed state, which has been observed at numerous points of measurement in Helsinki, is explainable as caused by the dome landform. The experience gained regarding the horizontal stresses in the bedrock have also been utilized in other major cavern building projects. La ville de Helsinki construisit dans les annees 1969–1973 a env. 1.5 km du centre de la ville 3 reservoirs souterraines de petrole d'un volume de 250.000 m3. Dans le travail de derochement on se heurta a des difficultes en raison du grand etat de contrainte horizontale du roc (15 MN/m2). Pour cette raison il fut procede a de vastes recherches sur l'etat de contrainte du roc. L'existence de l'etat de contrainte horizontale constatee a Helsinki en plusieurs endroits de mesure peut etre expliquee par le phenomene de formation de dome (diapire). Les experiences acquises en rapport avec l'etat de contrainte horizontale ont egalement ete mises a profit dans d'autres grands projets de construction de reservoirs souterraines. Die Stadt Helsinki legte wahrend der Jahre 1969–1973, 1.5 km von der Stadtmitte entfernt, drei olkavernen mit insgesamt 250.000 m3 Fassungsvermogen an. Bei den Felssprengarbeiten begegnete man Schwierigkeiten infolge von hohen Horizontalspannungen (15 MN/m2) im Gestein. Angesichts dessen wurden ausgiebige Gesteinspannungsuntersuchungen durchgefuhrt. Das Vorhandensein des horizontalen Spannungszustands, der an zahlreichen Messstellen in Helsinki wahrgenommen wurde, lasst sich als Auswirkung der Domung erklaren. Die betreffs der horizontalen Spannungen im Felsgrund erworbenen Erfahrungen sind auch bei weiteren grossen unterirdischen Hohlbauten verwertet worden.

Observations made during drilling and subsequent testing of the USW G-1 drill hole, Yucca Mountain, Nevada, provide qualitative insights into the insitu geomechanical characteristics of the layered tuff units penetrated by the hole. Substantial drilling-fluid losses, and the occurrence of drilling-induced fracturing, are understandable in terms of the low, minimum horizontal stress magnitudes interpreted from six hydraulic-fracturing stress measurements conducted between hole depths of 640 and 1300 meters. Although not confirmed directly by the hydraulic-fracturing data, other observations suggest that the minimum stress magnitudes in the more densely welded and brittle tuff layers may be even smaller than in the less welded and more ductile rocks. Stress-induced borehole ellipticity observed along most of the length of USW G-1 indicates that the horizontal stress components are not equal, and that the concentration of these stresses around the hole is sufficient to locally exceed the yield strength of the rock. The low, minimum horizontal stress magnitudes, perhaps variable with lithology, and the indications from borehole ellipticity of a high in-situ stress/strength ratio, indicate the need for further studies to characterize the structural and geomechanical properties of the rocks at depth in Yucca Mountain.

In situ stress measurements were made at 6 locations in Austria, which were chosen in such a fashion as to yield information on the neotectonic stress in the country. Because of a strong influence of the Alpine topography, it was necessary to apply finite-element calculations for the interpretation of the field results. At three locations, significant tectonic stresses were found which could not be explained by gravitational effects alone. The orientation of the tectonic stresses is in conformity with that found by other methods (joint orientations, earthquakes) in Europe (greatest compression NW — SE).

Directions of maximum horizontal stress SH derived from borehole breakouts are presented. For seven boreholes in the Central and Viking graben we found a clear preference of EW direction of SH, nearly perpendicular to the graben axes. EW directions were also estimated at four locations close to the Voering plateau and in the north Norwegian margin. Occurrence of breakouts in a borehole are not related to lithology, but salt inclusions change the SH-direction in adjacent layers.

An unusual talar fracture is presented along with a review of the literature concerning talar fractures. In evaluating certain ankle injuries, close scrutiny of the talar head, especially the mortise view, is emphasized.

Hydraulic fracturing stress measurements and a borehole televiewer log were obtained in hole USW G-2 at Yucca Mountain, Nevada, to depths of 1200 m. Results indicate that at the depths tested, the minimum and maximum horizontal stresses are less than the vertical stress, corresponding to a normal faulting stress regime. Drilling-induced hydrofractures seen in the televiewer log imply a least horizontal principal stress direction of N 60° W to N 65° W. For reasonable values of the coefficient of friction, the magnitude of the least horizontal stress is close to the value at which slip would occur on preexisting faults of optimal orientation (strike N 25° E to N 30° E and dipping 60° to 67°). The prominent drilling-induced fractures seen in the televiewer log are believed to have been caused by excess downhole pressures applied during drilling the hole. Many throughgoing fractures are also seen in the televiewer log; most of these are high angle, stringking N 10° E to N 40° E. These fractures show a general decrease in angle of dip with depth. Stress-induced wellbore breakouts are seen at depths below 1050 m. The average N 60° W azimuth of these breakouts agrees very closely with the N 60° W to N 65° W direction of least horizontal principal stress inferred from the drilling-induced hydrofracs.

A flat jack method has been used to determine the principal stress axes in the Jurassic limestone of the basin of Paris and in neighbouring regions. The results have been compared with a few overcoring measurements in boreholes of a few meters.

The Building Research Establishment (BRE) has, for a number of years, been investigating the pressuremeter test, its interpretation and the application of its results for assessing soil properties relevant to design. The work originated with studies on London Clay (Marsland and Randolph, 1977), developed through various research programmes into offshore site investigations (e.g. Henderson et al., 1979; Marsland, 1979) and has continued by returning to the land-based application (Powell et al., 1983).

Horizontal fracture of the anterior arch of the atlas can be easily overlooked on lateral radiographs. The fracture is not associated with neurological deficit but may be the cause of severe pain. A review of the literature reveals only 3 previously reported cases. Seven new cases, including 2 without other cervical spine fractures, indicate a much higher incidence than was previously thought. Hypotheses about the mechanism of injury are discussed.

Accurate formation fracture gradient prediction in abnormally pressured wells is one of the most critical considerations involved in planning a successful drilling operation. Shallow abnormal pressure, coupled with deep geologic objectives, requires an accurate fracture gradient prediction to insure casing setting depths are correctly determined in order to carry sufficient mud weights to successfully reach the deep objectives. In an effort to better meet these requirements, a study of formation fracture gradients was made for the Western and Central Gulf of Mexico. As a result of this study, a new technique was developed which accurately predicts fracture gradients in the abnormally pressured formations. This technique is based on an empirical correlation of Effective Horizontal Stress Gradient to Effective Vertical Stress Gradient.

The functional behavior of removable partial denture is destined to be transmitted directly to the abutment tooth as a stress via clasp because of most of its retention being dependent upon the clasp retainer. Therefore, the influence of the clasp on the behavior of the abutment tooth is supposed to be more important according to its designs.Thus, using a bend strain measuring system according to 2 gauge Active-Active method developed previously by the Author and 4 kinds of clasp with a high applicability to cases of distal extention, the Author examined, on experimental models, possible difference horizontal stress on the abutment tooth according clasp designs.The results are as follows:1. Both clasp of Supra-bulge type with distal rest and Infra-bulge type with mesial rest exerted respectively to make the abutment tooth incline distolingually.2. It was showed that the horizontal stress put on the abutment tooth reduced Aker's clasp, Wire combination clasp, Kratochvil I-bar clasp and Krol I-bar clasp in turn, and for the Infra-bulge type clasp was smaller than for Supra-bulge type clasp.

Generally, the speed and efficiency with which a well is drilled are dependent upon the formation balance gradient/mud density relationship. The safety factor also depends primarily on this relationship. With the costs of wells continually escalating (particularly offshore), drilling time and material costs are minimized through engineering practices which attempt to produce maximum penetration rates as cheaply as possible. Instances have arisen where safety margins were negated when preference was given to cost/time activities rather than to established safety levels. Because safety should always come first, knowledge of kick tolerance is of paramount importance.

A new technique for calculating hydraulic properties of unsaturated fractured formations is proposed as an alternative to the common approach involving steady-state analysis of multi-rate gas injection tests. This method is based on graphical analysis of unsteady-state pressure-time data from an injection-falloff test sequence. Both gas and water injection testing are considered. Flow in a horizontal fracture of limited lateral extent, bounded above and below by an impermeable matrix, and intersected by a cylindrical borehole is described by two analytical models developed in this study. The first model corresponds to the early-time infinite acting radial flow period, and the second to the late-time linear flow period. Interpretive equations are derived for computing fracture conductivity and volumetric aperture from early-time pressure data, and fracture width from late-time pressure data. Effects of fracture inclination and gravity are studied numerically and found to be practically negligible for gas as well as water injection. Two simulated injection-falloff tests are analyzed using the suggested procedure. Results are found to be in good agreement with simulator input values. 13 refs., 14 figs., 4 tabs.

The contract between the Dow Chemical Company and the Department of Energy to investigate the feasibility of recovery of energy from the Antrim shale by an in situ process includes a task titled, In Situ Fracturing and Assessment. This task required Dow to conduct and evaluate three fracturing techniques: hydraulic fracturing followed by explosive fracturing; chemical underream followed by explosive fracturing; and explosive underream and fracturing. The work carried out in the chemical underream subtask is summarized. Two distinctly different field methods were attempted. Hydrochloric acid treatment in the limestone section resulted in creating a cavity less than of the expected size. An attempt to produce a horizontal fracture in the limestone failed to establish the communication required to solution mine the limestone section between the injection and four production wells. Communication between the wells was an essential ingredient for success. In the second field trial, not having achieved this, neither the acidization or the originally planned explosive fracturing experiments were attempted. It was concluded that with current technology applied to these particular field conditions, the other two techniques offered the best short-term potential for success.

A state of high horizontal stress prevails in many of the Silurian, Ordovician and Precambrian rocks of Ontario, Canada. Tunnel and cavern construction in these rock types generally results in a concentration of horizontal compressive stresses in the roof and the floor, as manifested by field observations. In addition, caverns used for the storage of hot fluids will also be subjected to a state of tangential compressive stress as a result of geometric constraint. These effects of thermal and residual stresses on rock mass stability are discussed in the paper, along with a case study of oil storage caverns for a large thermal plant in Ontario, Canada. Il regne dans beaucoup des roches Siluriennes, Ordoviciennes et Precambriennes de l'Ontario, Canada, un etat de tension horizontale elevee. Selon les observations faites sur le chantier, la construction de tunnels et de cavernes dans les roches de ces genres entraine generalement une concentration de tensions comprimees horizontales dans la voute et le plancher. De plus, les cavernes utilisees pour le stockage de fluides chauds seront egalement soumis a un etat de tension comprimee par suite de la contrainte geometrique. Ces effets des tensions thermique et residuelle sur la stabilite de la masse des roches feront l'objet de ce rapport, ainsi que l'etude du cas particulier de cavernes de stockage de le petrol destinees a une grande centrale thermique en Ontario, Canada. In einem grossen Teil des Silurischen, des Ordovizischen und des Prakambrischen Gesteines in Ontario, Kanada, herrscht ein Zustand der hohen horizontalen Spannung. Gemass der Beobachtungen auf der Baustelle hat das Anlegen von Tunneln und Hohlen in diesen Arten von Gestein ublicherweise eine Konzentration von horizontalen Druckspannungen in deren Decke und Boden zur Folge. Ausserdem werden Hohlen, die zur Lagerung von heissen Flussigkeiten benutzt werden, auch einem Zustand der tangentialen Druckspannung durch geometrischen Zwang augesetzt. Es wird uber diese Einwirkungen von warme-und Restspannungen auf die Stabilitat der Felsenmasse und auch uber eine Einzelfallstudie von Heizollagerungshohlen fur ein grosses Warmekraftwerk in Ontario, Kanada, berichtet.

A computer model has been fitted to the regional horizontal stress trajectories mapped by Aldrich and Laughlin. The model has then been used to estimate the minimum horizontal principal stress direction at Fenton Hill. The result is approximately 100 deg E of N, +/- about 5 degrees. This is an interim report. Further results are expected.

In the ambit of CISM mainly the mechanical aspects, the principles and the theory of the rock mechanics research work is of interest. But it would not be advisable to treat mechanical matter mathematically and in an abstract way without binding it on a real view and concrete imagination.

The principal axes of stress and strain are inferred for the seismotectonic zones of the Friuli–Venezia Giulia region, which forms the eastern part of the European Southern Alps. This region corresponds to a polyphase deformational belt formed during the Meso- and Neoalpine compressions (from the Eocene to Plio-Quaternary). Several distinct seismotectonic zones are recognized by comparing seismological and tectonic characteristics. Inference of the stress and strain tensors is based on 243 fault-plane solutions, corresponding to earthquakes occurring between 1984 and 2001 (magnitude range: 2.1–5.6). The analysis reveals two main regional stress patterns: a strike-slip regime active in the eastern and northwestern parts of the area under study and dominant thrusting processes in the central and western zones. The orientation of the maximum principal stress varies from north-northwest–south-southeast to north-northeast–south-southwest. The stress magnitude ratio of the calculated stress tensors varies from 0.4 to 0.7. The orientation of the maximum shortening axis is generally north-northwest–south-southeast, changing to north-northeast–south-southwest in the southeastern part of the region. For most seismotectonic domains, the inferred strain pattern is quite concordant with the surface tectonics. The orientations of the principal axes of stress and strain are in most cases similar. The complex regional tectonic structure, consisting of two indented tectonic wedges, appears to control the patterns of horizontal stress and strain.

A new true triaxial cell has been designed, fabricated, calibrated, and successfully tested. Its main feature is very high loading capability in all three orthogonal directions, enabling the testing to failure of hard crystalline rocks subjected to large least and intermediate principal stresses. All three principal stresses applied to rectangular prismatic specimens, 19×19×38 mm in size, are servo controlled. The cell was used to conduct an extensive series of tests in Westerly granite. A new true triaxial strength criterion for the rock was obtained that takes into account the effect of the intermediate principal stress. This turns out to be so significant that it raises serious questions about the suitability of criteria such as those named after Mohr, Coulomb, Griffith, and others. Measurements of strain in all three principal directions revealed that the onset of dilatancy relative to the major principal stress at failure rises substantially as the intermediate principal stress increases. The true triaxial tests also demonstrate that for the same least horizontal stress the main fracture dip angle in Westerly granite increases as a function of the intermediate principal stress, suggesting a strengthening effect. Limited thin section and SEM study shows that microcrack propagation, crack localization, and main fracture characteristics are basically similar to those observed in common triaxial tests.

Saudi Aramco is drilling horizontal wells along the minimum horizontal stress direction in an attempt to generate multiple transverse fractures during stimulation to increase gas production and enhance recovery. However, drilling operations in these wells are difficult due to wellbore instability because of the higher mud weights required to minimize formation breakout due to prevailing in-situ stress conditions. Increased mud weight also led to higher differential pressure across the variably depleted reservoir layers, which when coupled with formation instability, created greater challenges for the drilling team. These conditions resulted in a significantly increased number of stuck pipe incidents, incurring noticeably high nonproductive time including loss of bottomhole assemblies in the hole. To address these problems, an integrated approach between drilling expertise, applied geomechanics, and advanced mud logging technology was applied to successfully overcome stuck pipe events arising from wellbore instability and differential sticking. Additionally, the drilling and tripping practices were customized to confront borehole instability issues. Further, to account for formation heterogeneity and varying in-situ stresses, the predrill Mechanical-Earth-Model (MEM) was updated during drilling using Real-Time Drilling Geomechanics (RTDG). In addition, advanced cutting return-monitoring technology was used, which helped hole cleaning to minimize the risk of stuck pipe due to formation failure (excessive cuttings). An insight into the planning, challenges encountered, and procedures implemented to successfully drill the planned horizontal wells will be presented.

This paper describes new developments of a wireline tool for stress measurements. The tool was initially designed for open-hole tests and its application was limited to very low permeability formations (up to 50 μd). Since then the capabilities of the tool have been extended to handle both impermeable formations and permeable formations (currently up to 400 md). New testing and interpretation procedures make it possible to obtain reliable measurements of the minimum horizontal stress and also the maximum horizontal stress in an open-hole environment or to conduct tests in a cased hole environment. These new developments make detailed stress measurements possible in a wide range of formations, providing input to numerous applications: design of hydraulic stimulations, stability of deviated wells, screenless completions for sand control and enhanced recovery programs.

Background Fractures of the pelvic ring in elderly patients have increased in frequency over time. These injuries are associated with a high morbidity and have a socio-economic impact. The diagnostic procedures and their influence of therapy decisions are still controversial. Methods In a retrospective study, we investigate the value of additional MRI examination on therapy decision of fragility fractures of the pelvis. The evaluation of all patients with pelvic fractures without adequate trauma and with performed CT and MRI was conducted at three large German hospitals. The imaging procedure took place within a maximum interval of 4 weeks. After evaluation of the imaging, the resulting therapeutic consequences either based on CT alone or on CT and MRI were reviewed by experienced pelvic surgeons. Results Of 754 patients with pelvic injuries, 67 (age 80 +/- 9.7 years, f: m 54:13) could be included. The detection of vertical fractures in CT (n = 40 unilateral, n = 11 bilateral) could be increased by the additional MRI (n = 44 unilateral, n = 23 bilateral). A horizontal fracture component was identified in CT in 9.0% (n = 6) vs. MRI in 25.4% (n = 17) of the cases. An anterior pelvic ring injury was detected in 71.6% (n = 44; 4x bilateral) in CT, in 80.6% in MRI (n = 50, 4 bilateral). Additive MRI imaging increased the decision rate for surgical therapy from 20.9% (n = 14) to 31.3% (n = 21). Conclusions The results of this study further support the value of bone marrow edema detection by MRI diagnostics (or dual source CT which showed promising initial results) for the detection of pelvic ring fractures. For the first time, the study identifies an additional therapeutic consequence by an increased rate of surgical procedures.

The Victoria microplate between the Eastern and Western Branches of the East African Rift System is one of the largest continental microplates on Earth. In striking contrast to its neighboring plates, Victoria rotates counterclockwise with respect to Nubia. The underlying cause of this distinctive rotation has remained elusive so far. Using 3D numerical models, we investigate the role of pre-existing lithospheric heterogeneities in continental microplate rotation. We find that Victoria’s rotation is primarily controlled by the distribution of rheologically stronger zones that transmit the drag of the major plates to the microplate and of the mechanically weaker mobile belts surrounding Victoria that facilitate rotation. Our models reproduce Victoria’s GPS-derived counterclockwise rotation as well as key complexities of the regional tectonic stress field. These results reconcile competing ideas on the opening of the rift system by highlighting differences in orientation of the far-field divergence, local extension, and the minimum horizontal stress.

Breakouts in four wells in Hudson Bay suggest that the Paleozoic section is currently subject to maximum horizontal compression about a northeast–southwest axis, with some local deflection in horizontal stress orientations related to faults. The Paleozoic section does not appear to be detached from the crystalline basement of the Canadian Shield, despite the presence of thick Silurian halite-rich intervals. The northeast–southwest compressional axis documented in the Hudson Bay Basin is compatible with stress orientations mat have been measured in other parts of cratonic North America. Leak-off tests from three wells imply that contemporary horizontal stress magnitudes above 1500 m depth exceed present-day overburden loads; comparable relative magnitudes have been measured elsewhere in central Canada. Finite-element modelling suggests mat this phenomenon is due to the effects of glacial loading, crustal rebound, and spreading of the Mid-Atlantic Ridge.

An interpretive map of the orientation of minimum horizontal stress for the contiguous United States, based on in situ stress measurements, geological data, and earthquake focal mechanism solutions, indicated that the state of stress within the plate is not uniform. The tectonically active western United States was shown to possess a complicated stress pattern, but even in the relatively quiet eastern and central parts of the country, several major variations in orientation of stress were apparent. A new study, based on measurements in North America, Africa, and Australia, revealed that, on the average, maximum sheer stress increases linearly with depth to at least 5 km, with no indication of leveling off.

Over recent years, several geotechnical explorations in clay deposits have shown the flat dilatometer test (DMT) to provide reasonable estimates of in-situ overconsolidation ratio with depth. Why should the horizontal stress index (KD = initial contact pressure minus hydrostatic pressure normalized to the effective overburden stress) show an empirical trend with over consolidation ratio (OCR)? It is postulated that, since the closing pressure and contact pressures are nearly equal, the initial contact pressure in clay is an approximate measure of the total pore pressure induced during penetration of the dilatometer blade. Published data from a clay site tested by a special DMT having a pore-pressure sensor, as well as piezocone/dilatometer data from seven other sites, support this hypothesis. Since the pore-pressure response of clay is influenced by the in-situ OCR, the initial effective DMT contact pressure can be used to profile the stress history.

Focal mechanisms have been determined from P wave first motion polarities for 138 small to moderate (2.6 ≤ M ≤ 4.3) earthquakes that occurred within 10 km of the surface trace of the San Andreas fault in southern California between 1978 and 1985. On the basis of these mechanisms the southern San Andreas fault has been divided into five segments with different stress regimes. Earthquakes in the Fort Tejon segment show oblique reverse sup on east-west and northwest striking faults. The Mojave segment has earthquakes with oblique reverse and right-lateral strikesup motion on northwest strikes. The San Bernardino segment has normal faulting earthquakes on north-south striking planes, while the Banning segment has reverse, strike-sup, and normal faulting events all occurring in the same area. The earthquakes in the Indio segment show strike-slip and oblique normal faulting on northwest to north-south striking planes. These focal mechanism data have been inverted to determine how the stresses acting on the San Andreas fault in southern California vary with position along strike of the fault. One of the principal stresses is vertical in all of the regions. The vertical stress is the minimum principal stress in Fort Tejon and Mojave, the intermediate principal stress in Banning and Indio, and the maximum principal stress in San Bernardino. The orientations of the horizontal principal stresses also vary between the regions. The trend of the maximum horizontal stress rotates over 35°, from N15°W at Fort Tejon to N20° at Indio. Except for the San Bernardino segment, the trend of the maximum horizontal stress is at a constant angle of about 65° to the local strike of the San Andreas fault, implying a weak fault. The largest change in the present stress state occurs at the end of the rupture zone of the 1857 Fort Tejon earthquake. It appears that the 1857 rupture ended when it propagated into an area of low stress amplitude, possibly caused by the 15° angle between the strikes of the San Jacinto and San Andreas faults. The strong correlation between present state of stress and segmentation in previous earthquakes suggests that the stress state is important in controlling rupture propagation.

The N30°–35°W trend of three long basaltic andesite dikes in west-central New Mexico indicates a least principal horizontal stress direction of N55°–60°E at the time the dikes were emplaced 28 m.y. ago. This stress direction agrees with recently proposed tectonic models for the region, suggesting that northeast-southwest extension was pervasive over both the early Basin and Range and Colorado Plateau provinces and the southern Rocky Mountains at this time.

Hundreds of millions of cubic meters of natural gas are locked up in low-permeability, natural gas reservoirs. The Multiwell Experiment (MWX) was designed to characterize such reservoirs, typical of much of the western United States, and to assess and develop a technology for the production of this unconventional resource. Flow-rate tests of the MWX reservoirs indicate a system permeability that is several orders of magnitude higher than laboratory permeability measurements made on matrix-rock sandstones. This enhanced permeability is caused by natural fractures. The single set of fractures present in the reservoirs provides a significant permeability anisotropy that is aligned with the maximum in situ horizontal stress. Hydraulic fractures therefore form parallel to the natural fractures and are consequently an inefficient mechanism for stimulation. Successful stimulation may be possible by perturbing the local stress field with a large hydraulic fracture in one well so that a second hydraulic fracture in an offset well propagates transverse to the natural fracture permeability trend.

Ever since the recognition of plate tectonics as a major Earth process, maps of the orientation of stress in Earth's crust have given us one of the most direct clues to the forces that drive plate movements. We now know from these maps that stress orientations are consistent on a regional scale, that the boundaries between provinces of uniform stress direction generally coincide with major physiographic and structural boundaries, and that for many regions the orientation of the maximum compressive horizontal stress generally coincides with directions of plate motion [e.g., Zoback and Zoback, 1989]. On a regional scale, maps of crustal stress have provided striking evidence of the low strength of plate margin at the San Andreas Fault in California [M. D. Zoback et al, 1988]. In industry, maps of stress orientations have been used to plan secondary recovery projects for oil and gas [Bell and Babcock, 1986] and evaluate seismic risk near critical facilities [e.g., Stock et al., 1985].

The in situ stress field was determined at a depth of 837 m (2745 feet) in Devonian Shale ('gray' shale) within the Rome Basin in West Virginia. Logging data and laboratory observations of core samples reveal vertical cracks oriented at N50/sup 0/-60/sup 0/E. Because of these cracks and their preferred orientation a new approach based on fracture mechanics concepts is used to evaluate the in situ stresses from the field and laboratory data. The resulting prediciton of the maximum horizontal stress (sigma/sub H/max) is compared to the maximum horizontal stress predicted by Haimson and Fairhurst's (1967) method; the latter method appears to overestimate the value of this stress component because the effect of loading the faces of any preexisting crack is neglected.

Stress directions have been determined to depths of 4.5 km in eastern North America from borehole elongation measured by dipmeter calipers in 47 wells. The average maximum horizontal stress directions are eastern Canada, N54°E ± 7°; Appalachian Basin, N58°E ± 8°; and the Illinois Basin, N89°W ± 5°. Stress directions determined for the Illinois and Appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions. New results from eastern Canada and the Appalachian Basin show that stress directions are everywhere consistent with the Midcontinent stress province. These data suggest that the maximum horizontal stress does not rotate from the ENE Midcontinent trend to NW near the Atlantic coast. A directional analysis of hydraulic fractures, petal-centerline fractures, and natural fractures from the Appalachian Basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures, centerline fractures, and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures. These observations indicate that borehole elongations provide reliable stress orientations.

The authors' theory would seen] to require the unrealistic (at least for soils in which consolidation is significant) assumption that the soil skeleton is free from "creep at constant effective stress." The presence of such creep implies that strain can no longer be uniquely defined in terms of effective stress and the concept of a unique relationship between effective stress and void ratio is, then, no longer valid. A further consequence is that the horizontal stress, at any specified level of effective stress, is found to vary with such factors as size of specimen, location of element in the stratum, and length of drainage path. These factors would appear to reduce somewhat the practical value of the authors' theory.