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Rock Mass Response to Coupled Mechanical Thermal Loading: Äspö Pillar Stability Experiment, Sweden
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Jord- och bergmekanik.
2007 (engelsk)Doktoravhandling, monografi (Annet vitenskapelig)
Abstract [en]

The geological disposal of nuclear waste, in underground openings and the long-term performance of these openings demand a detailed understanding of fundamental rock mechanics. A full scale field experiment: Äspö Pillar Stability Experiment was conducted at a depth of 450 m in sparsely fractured granitic rock to examine the rock mass response between two deposition holes. An oval shaped tunnel was excavated parallel to the σ3 direction to provide access to the experiment and also provide elevated stress magnitudes in the floor. In the tunnel floor two 1.75-m diameter 6-m deep boreholes were excavated so that a 1-m thick pillar was created between them. In one of the holes a confinement pressure of 700 kPa was applied and in the other displacement transducers were installed. The pillar volume was monitored by an Acoustic Emission System. Spatially distributed thermocouples were used to monitor the temperature development as the pillar was heated by electrical heaters. The excavation-induced stress together with the thermal-induced stress was sufficient to cause the wall of the open borehole to yield. The temperature-induced stress was increased slowly to enable detailed studies of the rock mass yielding process. Once the rock mass loading response was observed, the rock mass was unloaded using a de-stress slotting technique.

This thesis focuses on the in-situ study of the rock mass response to coupled mechanical thermal loading and thermal-mechanical unloading. The experiment, its design, monitoring and observations are thoroughly described. An estimate of the yielding strength of the rock mass is presented and compared with laboratory test and results from other rock mass conditions reported elsewhere in the open literature. General conclusions about the effect of the confining pressure and the observations from the unloading of the pillar are also presented.

Important findings are that the yielding strength of the rock mass has been successfully determined, low confinement pressures significantly affects the onset of yielding, the primary mode of fracture initiation and propagation is extensional, no significant time dependency of the yielding process was observed. The unloading studies also indicated that what appeared to be shear bands likely was a propagating zone of extensile failure that weakened the rock so that displacements in the shear direction could occur.

sted, utgiver, år, opplag, sider
Stockholm: Byggvetenskap , 2007. , s. xx, 180, 16, 20, 34, 5
Serie
TRITA-JOB PHD, ISSN 1650-9501 ; 1008
Emneord [en]
Yielding, Spalling, Rock mass strength, Confinement, Fracturing, Tensile failure, Shear failure, Displacement, Acoustic Emission, Heating, Stress, Back calculation, Radial expansion
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-4287OAI: oai:DiVA.org:kth-4287DiVA, id: diva2:11635
Disputas
2007-03-02, Lokal Ekholmen, Äspölaboratoriet, Oskarshamn, 10:00
Opponent
Veileder
Merknad

QC 20100622

Tilgjengelig fra: 2007-02-28 Laget: 2007-02-28 Sist oppdatert: 2016-12-09bibliografisk kontrollert

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