POST 2 -Scale effects on the mechanical behavior of rock fractures

Motivation

• Improved models for predicting mechanical behaviour of large rock fractures needed for deep underground applications e.g. nuclear waste repositories, mines, geothermal applications
• Lack of physical experiments supporting development of improved models. Existing knowledge and scaling laws based on low stress & dilation constraint experiments (e.g. Bandis et al 1981)

Few recommendations from POST project, phase 1, year 2014-2016 (Siren et al 2017, Posiva Report 2017-01):

• Use replicas of rock fractures to make parameter studies.
• Experiments of large rock fractures in controlled laboratory environment are necessary to decrease measurement uncertainties.

Method

• Specimens with undisturbed natural fractures and tensile induced fractures in three sizes are extracted from granite blocks. Manufacture replicas of natural rock fractures in ultra high-strength concrete.
• Design and manufacture a shear testing equipment with high stiffness and tight tolerances for testing large fractures.
• Conduct characterizations of the fractures pre-, syn, post- mechanical tests.
• Analyze the results from the different scales and investigation methods and identify scale effects.

Results - examples

• Development and testing of replicas incl. quality check of fracture geometries.
• Manufacturing a new unique shar testing machine and validation of its properties
• Demonstrated nye technique for local measurements of fracture deformations and its impact.
• Experiments on large rock fractures under high stress (CNL & CNS).
• Several publications and presentations at conferences.

Contact and collaburations

Feel free to take contact if you are interestred in properties of large rock fractures, looking for collaborations or want to do experiments.