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Forsmark – Laboratory tests for investigation of the influence of rock type, oxidation, and other factors in borehole breakouts. Boreholes KFM01A, KFM04A, KFM05A and KFM24. Thermal properties by TPS method and uniaxial compression and indirect tensile strength tests of intact rock
RISE - Research Institutes of Sweden, Safety and Transport, Safety.ORCID iD: 0000-0003-4526-4061
RISE - Research Institutes of Sweden, Safety and Transport, Safety.
2019 (English)Report (Other academic)
Abstract [en]

The density, thermal and mechanical properties were determined on water saturated specimens from boreholes KFM01A, KFM04A, KFM05A and KFM24 in the Forsmark site investigation area. The tests have been concentrated to sections where borehole breakouts have been observed. The rock types in the selected sections were amphibolite (102017), granite to granodiorite (101057) and skarn (108018).

All specimens had a more or less foliated rock structure. The cores were sampled from a depth ranging between 308–929 m.

The specimens were water saturated using tap water and all subsequent measurements were conducted at this moisture condition. The density was determined on 41 specimens followed by measuring the thermal properties of 20 pairs of specimens. The thermal conductivity and diffusivity were measured and the volumetric heat capacity was calculated from the thermal conductivity and diffusivity. The testing ended with 35 indirect tensile tests yielding the indirect tensile strength and three uniaxial compression tests including the post-peak response yielded the Young’s modulus, Poisson ratio and the uniaxial compressive strength.

Three specimens aimed for the indirect tensile tests had a major crack and fell apart after measuring the density and the mechanical properties were not tested.

Some variation of rock material along the short cores could be seen, which is reflected in the measured data. The density at a water saturated condition was 2 640–2 814 kg/m3 for granite to granodiorite, 2 768–3 033 kg/m3 for amphibolite and 2 787–2 920 kg/m3 for skarn.

Thermal properties were measured at ambient temperature (22 °C) and under water saturated conditions. The determination of the thermal properties is based on a direct measurement method, the so called “Transient Plane Source Method” (TPS).

Thermal conductivity and thermal diffusivity at 22 °C were in the range of 1.6–3.5 W/(m, K) and 0.9–1.9 mm2/s, respectively. The volumetric heat capacity, which was calculated from the thermal conductivity and diffusivity, ranged between 1.6 and 2.6 MJ/(m3, K). Variations are most likely due to both depth and variations in rock type.

The indirect tensile tests were conducted such that every second specimen was tested with the diametrical compression along and every second across the foliation planes, with higher values for the indirect tensile strength on the specimens with loading across the foliation. The ratio between the strength measured on specimens with loading across over along the foliation was up to 1.6 for granodiorite and possible higher for the amphibolite. The strength variation in the amphibolite was large. The indirect tensile strength was 8.07–14.5 MPa for the granite to granodiorite, 1.18–16.2 MPa for amphibolite and 4.49–8.51 MPa for skarn.

Two of the uniaxial compression test specimens of amphibolite got a diagonal failure and the third had a spalling failure. The maximum axial compressive stress was 61.5 and 68.5 MPa for the specimens with a diagonal failure and 238.7 MPa for the specimen with a spalling failure. The Young’s modulus for the same specimens was 61.6 and 57.5 GPa, respectively 91.0 GPa and the Poisson ratio 0.288 and 0.407, respectively 0.375.

Abstract [sv]

Densiteten, termiska och mekaniska egenskaper har bestämts på vattenmättade prover from borrhål KFM01A, KFM04A, KFM05A och KFM24 i Forsmarks platsundersökningsområde. Provningarna har koncentrerats till avsnitt där s k ”borehole breakouts” har observerats. Bergarterna i de valda avsnitten är amfibolit (102017), granit till granodiorit (101057) och skarn (108018). Samtliga prover hade en mer eller mindre folierad bergstruktur. Proverna har tagits på djupnivåer mellan 308–929 m.

Proverna vattenmättades med kranvatten och alla efterföljande mätningar gjordes vid denna fukthalt. Densiteten mättes på samtliga 41 prover följt av mätning av de termiska egenskaperna på 20 par prover. Termisk konduktivitet och termisk diffusivitet mättes varefter den volumetriska värmekapaciteten beräknades. Provningen avslutades med 35 stycken indirekta test av draghållfastheten som gav den indirekta draghållfastheten och tre enaxiella kompressionsförsök inkluderat efterbrottsbeteende som gav värden på elasticitetsmodul, Poissons tal och enaxiell tryckhållfasthet.

Tre prover som var avsedda för indirekta dragförsök hade initialt en spricka och föll isär efter mätningen av densiteten och ingen mekanisk provning genomfördes.

En viss variation av bergmaterialet kunde ses på de korta kärnorna som visade sig i uppmätta data. Densiteten i ett vattenmättat tillstånd var 2 640–2 814 kg/m3 hos granit till granodiorit, 2 768–3 033 kg/m3 hos amfibolit och 2 787–2 920 kg/m3 hos skarn.

Termisk konduktivitet och termisk diffusivitet har bestämts vid rumstemperatur (22 °C) och vattenmättnad. Mätningarna av egenskaperna utfördes med den direkta metoden “Transient Plane Source” (TPS).

Termisk konduktivitet och termisk diffusivitet vid 22 °C bestämdes till 1.6–3.5 W/(m, K) respektive 0.9–1.9 mm2/s. Den volumetriska värmekapaciteten (produkten av densitet och specifk värmekapacitet), som beräknades från konduktivitet och diffusivitet, varierade mellan 1.6 and 2.6 MJ/(m3, K). Variationerna beror antagligen både på djup och på variationer i materialtyp.

De indirekta dragförsöken utfördes så att vartannat prov belastades med diametral kompression längs med och vartannat tvärs foliationsplanen. Kvoten mellan styrkan mätt med belastning tvärs och längs med foliationen var upp till 1,6 för granit till granodiorit och möjligen högre för amfibolit. Styrkevariationen var stor hos amfibolit. Den indirekta draghållfastheten var 8,07–14,5 MPa hos granit till granodoiorit, 1,18–16,2 MPa hos amfibolit, och 4,49–8,52 MPa hos skarn.

Vid de enaxiella kompressionsförsöken fick två av amfibolitproverna ett diagonalt brott och det tredje ett spjälkningsbrott. Den högsta axialspänningen var 61,5 och 68,5 MPa hos proverna som hade ett diagonalt brott och 238,7 MPa hos provet med ett spjälkningsbrott. Elasticitetsmoduluen var 61,6 och 57.5 GPa respektive 91,0 GPa och Poisson’s tal var 0,288 och 0,407 respektive 0,375.

Place, publisher, year, edition, pages
Solna, 2019. , p. 61
Series
SKB, ISSN 1651-4416 ; P-18-08
Keywords [en]
Thermal properties, Uniaxial compression test, Tensile strength test
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-38175OAI: oai:DiVA.org:ri-38175DiVA, id: diva2:1295497
Funder
Swedish Nuclear Fuel and Waste Management Company, SKBAvailable from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-13Bibliographically approved

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