Hard Crystalline Rocks Research Articles

A new true triaxial cell for testing mechanical properties of rock, and its use to determine rock strength and deformability of Westerly granite

Abstract 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.

Recent experiments in hard rocks to study the excavation response: Implications for the performance of a nuclear waste geological repository

Major excavation response experiments in granitic rocks have recently been finalized in Canada, Japan and Sweden. There is good understanding of the physical processes involved in developing a failed and damaged zone around an underground opening in crystalline hard rocks. Useful and feasible investigation methodology exists for the description of the mechanical response. The effect of drill-and-blast and mechanical excavation on the extent of the damaged zone is also clarified. However, accurate description of the hydrogeological response to the excavation may warrant further studies. The results derived from the experiments are useful to assess the overall impact on the post-closure performance of a geological repository for high-level, long-lived nuclear waste. Whether or not an excavation failed/damaged/disturbed zone exists is not crucial to the overall safety of a geological repository, but excluding the zone may result in non-conservative estimation of maximum radiation dose. The experiments in Canada, Japan and Sweden have not yet dealt explicitly with consequences of the repository being operated for several decades before closure, nor with the thermomechanical effects. Such effects may also be of importance for the long-term post-closure function of the repository.

Modeling stress-dependent permeability for anisotropic fractured porous rocks

Most of deep geological engineered structures, such as rock caverns, nuclear waste disposal repositories, metro rail tunnels, multi-layer underground parking, are constructed within hard crystalline rocks because of their high quality and low matrix permeability. In such rocks, fluid flows mainly through fractures. Quantification of fractures along with the behavior of the fluid flow through them, at different scales, becomes quite important. Earlier studies have revealed the influence of sample size on the confining stress–permeability relationship and it has been demonstrated that permeability of the fractured rock mass decreases with an increase in sample size. However, most of the researchers have employed numerical simulations to model fluid flow through the fracture/fracture network, or laboratory investigations on intact rock samples with diameter ranging between 38 mm and 45 cm and the diameter-to-length ratio of 1:2 using different experimental methods. Also, the confining stress, σ3, has been considered to be less than 30 MPa and the effect of fracture roughness has been ignored. In the present study, an extension of the previous studies on “laboratory simulation of flow through single fractured granite” was conducted, in which consistent fluid flow experiments were performed on cylindrical samples of granitoids of two different sizes (38 mm and 54 mm in diameters), containing a “rough walled single fracture”. These experiments were performed under varied confining pressure (σ3 = 5–40 MPa), fluid pressure (fp ≤ 25 MPa), and fracture roughness. The results indicate that a nonlinear relationship exists between the discharge, Q, and the effective confining pressure, σeff., and Q decreases with an increase in σeff.. Also, the effects of sample size and fracture roughness do not persist when σeff. ≥ 20 MPa. It is expected that such a study will be quite useful in correlating and extrapolating the laboratory scale investigations to in-situ scale and further improving theoretical/numerical models associated with fluid flow through rock masses.

Glacial striae, glacigenous sediments and Weichselian ice movements in southernmost Sweden

The southernmost part of Sweden is a classical area to study ice-movement patterns. During the course of time, different hypotheses about glacial events and ice dynamics have been proposed, and there is still no consensus of opinion. The author has tried to integrate studies of glacial erosional features registered on bedrock with glacigenic sediments on top of the eroded rock-surfaces. This paper concentrates on ice directions according to glacial striae and clast fabrics from the Hardeberga quarry in Skåne. The results from Hardeberga are discussed in a regional context. The youngest ice movement registered comes from the SW (striae, fabrics, overturned sandwedges and displaced shattered bedrock). Most probably this flow direction is due to quite different ice flow conditions in the flat and low-lying areas south of the Fennoscandian Border Zone (environment with deforming-bed conditions), in contrast to the ice dynamics in the higher crystalline shield-areas and the horst ridges of hard Palaeozoic and crystalline rocks crossing Skåne from NW to SE.

Non-linearity of strain in hard crystalline rocks : F. F. Gorbatsevich, International Journal of Rock Mechanics & Mining Sciences, 33(1), 1996, pp 83–91

Non-linearity of strain in hard crystalline rocks : F. F. Gorbatsevich, International Journal of Rock Mechanics & Mining Sciences, 33(1), 1996, pp 83–91

The Tsergo Ri landslide: an uncommon area of high morphological activity in the Langthang valley, Nepal

The large-scale mass movement of Tsergo Ri (Langthang valley, central-north Nepal) was investigated from the viewpoint of morphological activity for the first time. The Quaternary mass-movement (fission track age: about 4 × 104 yr) only affected crystalline hard rocks (gneisses, migmatites and leucogranites) of a dimension of 1010 m3. During the mass displacement an extreme shattering of the rocks happened, which is mainly responsible for the high actual morphological activity in the Tsergo Ri landslide deposit area. Three different zones of highest morphological activity (= the sum of the presently occurring geomorphic processes) can be distinguished: 1.(A) High, very steep slopes (mainly in bedrock) show usual morphological activity, except when they were affected by the landslide event - e.g., the barrier where the sliding mass crashed against: E-slope of Pangshungtramo Peak.2.(B) Slopes and erosional channels underneath glaciated or perennial firn areas, or areas which are snow covered most of the year show a permanent or seasonal morphological activity - e.g., the area in front of the Yala Tsang.3.(C) The zone with the biggest extension of actual morphological activity is the area of the Tsergo Ri landslide deposit with intense rock shattering of the sliding mass - e.g., the Dranglung valley or the S- and SW-slopes of Tsergo Ri.Zones A and B come up to the noral expectations of morphological activity for high mountain regions. Zone C makes the whole Tsergo Ri landslide deposit area an outstanding terrain of the upper Langthang valley with extremely high morphological activity.

Non-linearity of strain in hard crystalline rocks

Non-linearity of strain in hard crystalline rocks

Geotechnical investigations for a deep radioactive waste repository: in situ stress measurements

Abstract Comprehensive geotechnical investigations of potential repository sites for deep disposal of low- and intermediate-level solid radioactive wastes at Sellafield, Cumbria and Dounreay, Caithness included drilling and testing cored boreholes up to 2000 m deep. The investigation at Sellafield included the measurement of in situ stresses using the overcoring technique at various depths in a 250 m deep, vertical borehole drilled from the surface. The measuring instrument and method used for overcoring had, therefore, to perform reliably under high hydrostatic heads. The equipment used to carry out these measurements was the Swedish Borre Probe. Previous work with this equipment has been carried out in slim holes and hard crystalline rocks. In contrast, this project required in situ stress measurements to be taken in a relatively large-diameter borehole, drilled in weak sedimentary rocks by wireline drilling techniques, and consequently, significant adaptations to the installation equipment. The paper describes the adaption of the Borre Probe and its successful application in this project up to the end of 1992. Possible future applications of the technique are discussed.

Accounting for excavation responses in developing an underground repository in hard crystalline rock : Simmons, G R Proc NEA Workshop on Excavation Response in Geological Repositories for Radioactive Waste, Winnipeg, 26–28 April 1988P47–66. Publ France: OECD, 1989

Accounting for excavation responses in developing an underground repository in hard crystalline rock : Simmons, G R Proc NEA Workshop on Excavation Response in Geological Repositories for Radioactive Waste, Winnipeg, 26–28 April 1988P47–66. Publ France: OECD, 1989

Nature and Behaviour of Fractured Hard-Rock Aquifers of the Kandy District, Sri Lanka

Abstract This paper deals with the hydrogeological properties of the groundwater resources of the Kandy District of Sri Lanka. The main groundwater resources of the district are fractured crystalline hard-rock aquifers. These crystalline hard-rocks comprise quartzites, charnockites, granites, granitic gneisses, khondalites, quartzo-feldspathic rocks, gneisses, migmatites, calc-silicate rocks, and marbles of Precambrian age. The behaviour of these rocks as fractured aquifers is completely different from rock to rock, and is, to a great extent, controlled by the tectonic lineaments (fracture zones, joint zones and fault zones) of the area. It would appear that a considerable amount of groundwater, the yield ranging from 50 l/min. to over 1500 l/min., can be exploited along the lineaments.

Subsea tunnelling for oil: the petromine concept

Abstract Small-scale tunnelling for oil has been performed onshore since the turn of the century. In the late 1970s and in the 1980s, several proposals were set forth for using subsea tunnels in the exploitation of offshore oil and gas fields. A prefeasibility study carried out for the Troll oil and gas field in the North Sea has yielded interesting results for the subsea oil tunnel concept. This article describes how existing geological knowledge combined with geophysical measurements and exploratory oil well data have given a surprisingly large amount of information regarding ground conditions where the “geology” is hidden by deep water. The expected ground conditions have been used to work out specifications for development of a tunnel boring machine and equipment to tackle the prevailing ground conditions, which include squeezing rocks and, possibly, running ground and shallow gas. A tunnelling progress of 5 km/yr in hard crystalline rocks and up to 10 km/yr in the soft sedimentary rocks offshore is regarded as possible, given active development of the equipment to be used. Many future offshore oil and gas fields—especially those in arctic areas exposed to icebergs and extreme weather conditions—can be exploited advantageously by using subsea tunnels.

Computer model for vedavati ground water basin. Part 2. Regional model

A computer model for regional ground water resource evaluation, based on the leaky aquifer concept, is presented for the Vedavati basin which is a crystalline hard rock area of 24,200 km2 in Peninsular India. The model can handle nonhomogeneity, anisotropy, varied pumping, rainfall and river stages. The model is calibrated based on regional water level observations for one year. The calibrated model is used to determine the distribution of safe yield, overexploited regions and regions of maximum potential over the basin. Regions which are most affected by drought conditions are also identified.

Delayed failure in rock loaded in uniaxial compression

The long-term response to sustained compressive loading of two crystalline hard rocks of the Canadian Shield has been investigated. Static fatigue tests conducted on granite and anorthosite have shown that in a humid environment the long-term strengths of these crystalline igneous rocks could be less than 60 percent of their dry instantaneous strengths. Such reduction in strength has implications for the design and construction of deep tunnels, mines and other underground installations. The particular case of a nuclear fuel waste vault located at a depth of one kilometer is considered. Considering a service life of 1,000 years, a vault one kilometer deep in granite could suffer time-dependent spalling in highly stressed regions of the rock where the maximum principal stress exceeds about 130 MPa. Anorthosite has a lower instantaneous strength than granite and it is sensitive to static fatigue as well. A vault in anorthosite would be subject to time-dependent spalling of the perimeter rock in places where the maximum principal stress is above 80 MPa.

Near-field thermomechanical response of a waste vault

The near-field thermomechanical response of an immobilized waste disposal vault in crystalline hard rock was numerically studied taking into account the nonlinear behaviour of the host rock. The results of analyses indicate that the temperature dependence of rock properties has relatively little effect on the transient temperature distributions but may increase the thermal stresses and displacements substantially. However, no deep-seated major overstressed zones are expected.

Directional Drilling Equipment and Techniques for Deep, Hot Granite Wells

Summary Conventional directional drilling technology has been extended and modified to drill the first well of a subsurface geothermal energy extraction system at the Fenton Hill, NM, hot dry rock (HDR) experimental site: Ambitious borehole geometries, extremely hard and abrasive granite rock, and high formation temperatures combined to provide a challenging environment for directional drilling tools and instrumentation. Introduction Completing the first of a two-wellbore HDR system has resulted in the definition of operational limitations of many conventional directional drilling tools, types of instrumentation, and techniques. The successful completion of the first wellbore, Energy Extraction Well 2 (EE-2), to a measured depth of 15,300 ft (4.7 km) in granite reservoir rock with a bottomhole temperature of 600°F (315°C) required the development of a new high-temperature downhole drilling motor and modification of existing wireline-conveyed steering tool systems. Conventional rotary-driven directional assemblies were modified successfully to accommodate the very hard and abrasive crystalline rocks encountered during drilling of a nearly 8,500-ft (2.6-km) directional hole to a final inclination of 35° from vertical at a controlled azimuthal orientation. Drilling Objectives The HDR geothermal resource is derived from a subsurface region that exhibits a relatively high geothermal gradient. At the Fenton Hill site, granitic basement rock is encountered at a depth of 2,400 ft (730 m) and exhibits a static geothermal temperature of 600°F (315°C) at a true vertical depth (TVD) of 14,500 ft (4.42 km). Hydraulic fractures in the granitic rock are vertical and preferentially oriented in a northwesterly direction. The rock matrix is slightly porous (<1%) but has very low permeability (from 1.0 to 0.0 µd). The method of heat extraction experiments currently under way at the Fenton Hill site requires that two boreholes - one injection well and one production well - be drilled to a depth exhibiting an economically attractive reservoir temperature. To enhance reservoir production objectives, the two wells will be inclined 35° from the vertical through the reservoir region at an azimuthal direction normal to the preferred fracture orientation. The wells will be drilled vertically coplanar with a constant separation of 1,200 ft (370 m) between the underlying injection well and the overlying producer. Fig. 1 illustrates the already described geometry of the Well EE-2/Well EE-3 extraction system in the 11,000- to 14,500-ft (3.35- to 4.42-km) reservoir region. The sequentially formed interconnecting fracture system will be inflated hydraulically, and water will be circulated at a total flow rate of approximately 1,500 U.S. gal/min (95 dm3/s). Drilling Problems The implications for drilling-related problems1 during the construction of such a system are significant. The flow capacity requirements of the system require a minimum production drilled-hole diameter of 8 3/4 in. (22.2 cm) and a minimum intermediate drilled-hole diameter of 12 1/4 in. (31.1 cm). The extremely hard and abrasive rock requires that all roller cone bits have a tungsten carbide cutting structure. All drilling tools, bottomhole assembly components, and the drill string are subjected to severe abrasive wear that limits useful life.

Natural Analogues—A Way to Increase Confidence in Predictions of Long-Term Performance of Radioactive Waste Disposal

ABSTRACTNo exact analogue to a radioactive waste disposal system exists but by studying natural analogues of the most important components or subsystems of a waste repository, confidence in long-term predictions can be increased. The U.S. Nuclear Regulatory Commission (NRC) is supporting research on igneous intrusions into proposed repository-type host rock (basalt, tuff, crystalline hard-rock, and salt), on uranium ore body analogues, on actinide solubility as a function of natural complexing agents in closed basin lakes and on field migration of radionuclide species at low-level waste and uranium mill tailings disposal sites. The NRC is studying analogues to ensure that important parameters which might be overlooked in laboratory tests and in modeling because of problems with scaling time, space and geologic complexity can be identified and their importance bounded.

Geological engineering aspects of the conceptual design of a radioactive waste vault in hard crystalline rock

Geological engineering aspects of the conceptual design of a radioactive waste vault in hard crystalline rock

Submarine Canyons: Multiple Causes and Long-Time Persistence

The actual investigation of submarine canyons as field work was begun about 50 years ago. A large amount of factual information has accumulated as result of operations of deep diving vehicles, first in the Pacific Coast canyons and more recently in the remarkable dives of the Woods Hole minisubmarine Alvin into East Coast canyons. Taking the results of these recent dives and combining them with earlier investigations, including much work done by the French in the Mediterranean as well as our extensive studies off California and Baja California, we can now say with some confidence that these amazing deep excavations into the sea floor off so many coastal areas can be explained. New methods such as side scanning have also given us a greater understanding of the exact character of submarine canyons, particularly in the Bay of Biscay. The development of multichannel sonar has greatly increased our knowledge of the nature of continental margins and hence their history. This has given us more insight into the history of canyon development, particularly off the east Coast where drilling for oil and gas has become so important. In the past we have seen a great variety of hypotheses for explaining submarine canyons. Unfortunately almost all of these have been based on information from a small selection of the canyons, usually from one area. From the new information, it is evident that canyons are of composite origin and that many of the hypotheses suggested in the past were partly correct but did not appreciate that coordination of other processes was required. Thus there is growing evidence that, in the history of many canyons, there was a period in which subaerial erosion was an important precursor, but that present features are predominantly the result of marine erosion. Those advocating turbidity currents as the unique cause of canyons failed to appreciate that debris flows down the incipient valleys, as ell as other types of landslides, could be an almost equally important factor in marine erosion. The great effect of biologic activity on the rock walls of incipient canyons has been almost completely neglected in explanations, and various types of currents such as those of the tides have been left largely out of the picture. Perhaps the most important feature absent in these various hypotheses has been the realization that canyons may well be the result of a long period of formation, much longer than the short episodes of Pleistocene glacial sea-level lowering features which commonly cut into hard crystalline rock. New information is showing that the canyons may date back to at least the Cretaceous.

Wind-driven sand in Coachella Valley, California: Further data

The last 5 yr (1964–1969) of a 16-yr field experiment involving unidirectional windblown rock and mineral debris focused on study of ground-based objects. A large increase in wind-blown material crossing the plot resulted from accelerated fluvial flooding of the upwind alluvial source area starting in 1964. The plot itself was destroyed by such flooding in early 1969. Maximum cutting of 2.8 cm in 15 yr on a vertical lucite rod occurred on its oblique upwind sides, at 10 to 15 cm above ground. Cutting rate in the last 3 yr was 15 times greater than in the preceding 12 yr, coincident with the increased flux of wind-borne material. A 30-cm gypsum-cement cube showed an 11-fold increase of cutting rate during the last 4 yr (3.6 cm/yr compared to 0.34 cm/yr). Total cutting on the front face was 18 times greater than on the two side faces combined, an average cutting ratio of 36/1. Common red bricks recorded an average front- to side-face cutting ratio of 20/1, and a front-to-top ratio of 45/1. Cutting of 1 to 2 mm occurred on hard crystalline rock within 15 yr, much of it in the last 5 yr. Changes in orientation and position of gympsum-cement cubes and common bricks were produced by basal ground scour, tilting, rotation, creep, and tumbling. Newly placed hydrocal cubes developed upwind tilts as much as 17° in as little as 69 days (d), owing to basal scour. A slow upwind creep of 2 to 3 cm accompanied scour and tilt. A 90° rotation around a near-vertical axis of a brick demonstrated the importance of lever-arm length offered to the wind. Movements of many centimetres and complete reversals, bottom for top, were caused by tumbling. Separation of the base of cubes from the ground by tilting or by perching on residual pebbles, owing to scour or overturn, usually produced an instability favorable to movement.

Ceramic and pure-metal canisters in buffer material for high level radioactive waste

Within the Swedish KBS-project a great effort has been devoted to the development of canisters for the encapsulation of high level vitrified waste or spent unreprocessed fuel. The canisters will, upon final disposal in deep geological formations, provide an extra engineered barrier against the dispersal of radioactive nuclides in the groundwater. Comprehensive studies have been made on two types of pure metal canisters, i.e., lead-titanium for the high level vitrified waste and pure copper for spent fuel. The final disposal is made in hard crystalline rock where the waste canisters are embedded in a buffer material—a clay with good long term stability. For the lead-titanium canister a mixture of quartz sand and bentonite is proposed whereas for the copper canister highly compressed bentonite is preferred. Careful evaluations predicted a lifetime of at least thousands of years for the lead-titanium canisters and probably tens of thousands of years in the actual environment. For the copper canister it is realistic to expect a lifetime of hundreds of thousands of years. Comprehensive studies have also been made of a ceramic canister of alumina for spent fuel. Through hot isostatic pressing it is possible to make a completely tight and joint-free alumina container. Alumina has a very high chemical and mechanical resistance over very long periods of time. Preliminary studies have also been made of a glass ceramic material of the betaspodumenetype.