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Title: Stress measurements in the Stripa granite. Technical project report No. 4

Abstract

Rock stress measurements at the 348 m level of the Stripa Mine have been carried out with the Leeman tri-axial equipment. The largest principal stress is found to be 20.0 MPa and directed parallel with the strike of the contact between the granite and the orebody. The intermediate principal stress is 11.4 MPa and directed almost horizontal and perpendicular to the contact. The minor principal stress has a magnitude of 5.4 MPa. The deduced vertical stress is approximately of the same value as can be theoretically calculated.

Authors:
Publication Date:
Research Org.:
Tekniska Hoegskolan, Luleaa (Sweden)
OSTI Identifier:
6868635
Alternate Identifier(s):
OSTI ID: 6868635
Report Number(s):
LBL-7078; SAC-04
TRN: 78-019612
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 58 GEOSCIENCES; GRANITES; STRESSES; BOREHOLES; MINES; RADIOACTIVE WASTE STORAGE; STRAIN GAGES; STRAINS; SWEDEN; UNDERGROUND STORAGE; CAVITIES; EUROPE; IGNEOUS ROCKS; MANAGEMENT; MEASURING INSTRUMENTS; ROCKS; SCANDINAVIA; STORAGE; WASTE MANAGEMENT; WASTE STORAGE 052002* -- Nuclear Fuels-- Waste Disposal & Storage; 580300 -- Mineralogy, Petrology, & Rock Mechanics-- (-1989)

Citation Formats

Carlsson, H. Stress measurements in the Stripa granite. Technical project report No. 4. United States: N. p., 1978. Web. doi:10.2172/6868635.
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Carlsson, H. Stress measurements in the Stripa granite. Technical project report No. 4. United States. doi:10.2172/6868635.
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Carlsson, H. Tue . "Stress measurements in the Stripa granite. Technical project report No. 4". United States. doi:10.2172/6868635. https://www.osti.gov/servlets/purl/6868635.
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@article{osti_6868635,
title = {Stress measurements in the Stripa granite. Technical project report No. 4},
author = {Carlsson, H.},
abstractNote = {Rock stress measurements at the 348 m level of the Stripa Mine have been carried out with the Leeman tri-axial equipment. The largest principal stress is found to be 20.0 MPa and directed parallel with the strike of the contact between the granite and the orebody. The intermediate principal stress is 11.4 MPa and directed almost horizontal and perpendicular to the contact. The minor principal stress has a magnitude of 5.4 MPa. The deduced vertical stress is approximately of the same value as can be theoretically calculated.},
doi = {10.2172/6868635},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 1978},
month = {Tue Aug 01 00:00:00 EDT 1978}
}
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Technical Report:
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DOI:  10.2172/6868635
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  • ; ;
    Finite element analyses were carried out to assess the possible effects of the Stripa mine openings on the in-situ stress measured in a 400-m-deep borehole drilled from the surface. For this assessment, four 2-dimensional cases were modeled. These cases variously included two horizontal sections, and two separate, idealized vertical sections. An iron ore body in the mine was assumed to be completely extracted, thereby providing conservative estimates of stress concentration effects. Since no in-situ stress measurements were made before mining, overburden weight and horizontal stresses measured by hyrodfracturing were assumed to be the pre-mining state of stress. The stress statemore » resulting from excavation of the mine was calculated by the finite element model. In the cases using horizontal sections, the model predicted a stress concentration factor at the borehole of approximately 1.15, which is negligible considering the difficulty of obtaining accurate stress measurements. For the vertical sections the model predicted higher stress concentration factors at depths less than 200 m. This was expected because the vertical sections chosen brought the borehole unrealistically close to the mine openings, thereby leading to overly conservative estimates. In general, deviations in the magnitudes and orientations of the calculated redistributed principal stresses from the assumed pre-mining state of stress were found to be comparable to the scatter of overcoring data. It is, therefore, recommended that, for near-field stress calculations, the vertical stress due to overburden weight and the horizontal stresses measured by hydrofracturing at the borehole be considered the unperturbed far-field in situ state of stress.« less

  • The mechanical properties of Stripa granite are presented as determined from small (laboratory size), oven-dried specimens, The properties determined include Young's modulus, Poisson's ratio, unaxial compressive fracture stress, and the expansion coefficient, all as a function of temperature, In addition the Brazilian tensile fracture stress, residual shear strength as a function of a normal stress and the rock's anisotropy ratios are presented, Finally ultrasonic determinations at 1 MHz of the rock's dilatational wave velocity are given and the deduced Young's modulus is compared with the static value for room temperature. This report is one of a series documenting the resultsmore » of the Swedish-American cooperative research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and structural effects anticipated from the use of a large crystalline rock mass as a geologic repository for nuclear waste.« less

  • ; ;
    This report is one of a series documenting the results of the Swedish-American cooperative research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and structural effects anticipated from the use of a large crystalline rock mass as a geologic repository for nuclear waste. This program has been sponsored by the Swedish Nuclear Power Utilities through the Swedish Nuclear Fuel Supply Company (SKBF), and the U.S. Department of Energy (DOE) through the Lawrence Berkeley Laboratory (LBL). This is the twelfth report in the series. This paper presents the results of geochemical and isotopic analyses on water samplesmore » from the granite at Stripa, Sweden. Groundwater samples collected from shallow, private wells; surface boreholes; and boreholes drilled from the 330 m and 410 m mine levels were analyzed for their major ion chemistry, dissolved gases, and environmental isotope contents.« less

  • ; ; ; ...
    This report presents the results of laboratory tests on a 1 meter diameter by 2 meters high sample of granitic (quartz monzonite) rock from the Stripa mine in Sweden. The tests were designed to study the mechanical and hydraulic properties of the rock. Injection and withdrawal permeability tests were performed at several levels of axial stress using a borehole through the long axis of the core. The sample was pervasively fractured and its behavior under uniaxial compressive stress was very complicated. Its stress-strain behavior at low stresses was generally similar to that of small cores containing single healed fractures. However,more » this large core failed at a peak stress of 7.55 MPa, much less than the typical strength measured in small cores. The complex failure mechanism included a significant creep component. The sample was highly permeable, with flows-per-unit head ranging from 0.11 to 1.55 cm/sup 2//sec. Initial application of axial load caused a decrease in permeability, but this was followed by rapid increase in conductivity coincident with the failure of the core. The hydraulic regime in the fracture system was too intricate to be satisfactorily modeled by simple analogs based on the observed closure of the principal fractures. The test results contribute to the data base being compiled for the rock mass at the Stripa site, but their proper application will require synthesis of results from several laboratory and in situ test programs.« less

  • The report describes the methodology and results of a detailed study of geologic discontinuities associated with the time-scale heater test at the Stripa mine in Sweden. Mapping of the floor of the experiment tunnel coupled with observation of core samples from beneath the drift indicate that four N-striking shear fractures dip steeply through the 6 x 10 x 25-m rock mass. Oblique-thrust faulting has produced displacements of up to 2 m on one of the surfaces, and its inferred 3-D configuration is consistent with observed slickensiding. Resolution of locally measured principal stresses on the shear plane yields a theoretical shearmore » direction that also coincides with the slickensiding. Four distinct joint sets exist locally, one of which coincides with the shear fractures. Another lies nearly horizontal, and two others are steeply inclined. Fracture length and spacing distributions for the four joint sets are shown to be lognormal. Two of the sets lie perpendicular to principal stress directions. The fact that one of these two joint sets apparently post-dates other fracturing and is normal to the minimum principal stress suggests that it is due to isostatic rebound.« less