A novel and versatile apparatus for brittle rock deformation

This paper describes a new biaxial rock deformation apparatus within a pressure vessel, consisting of a
stainless steel vessel with an internal diameter of 40 cm and six main access ports for electronics (
100
pins), pore
fl
uids (three lines), and con
fi
ning oil. The apparatus has to ability to work on large rock
samples, up to 20
20 cm
2
, with horizontal and vertical forces up to 1.5 MN. The maximum con
fi
ning
pressure of the vessel is 70 MPa, and
fl
uid
fl
ow properties and permeability of large-samples can be
tested using up to 8 L of
fl
uids that can be pressurized up to 30 MPa. Sliding velocity during experiments
is in the range 0.1
μ
m/s
–
1.0 cm/s. The machine stiffness is 0.91 kN/
μ
m and 1.3 kN/
μ
m for the vertical
and horizontal axes, respectively. Measurements on friction, velocity dependence of friction and healing
properties of reference material like granite and talc replicate the values presented in the literature.
Triaxial stress state tests with controlled con
fi
ning and pore
fl
uid pressure, and
fl
uid
fl
ow through the
samples have been performed successfully. The machine is extremely versatile, as it works as a uniaxial,
triaxial or true-triaxial apparatus, on rock samples with dimensions ranging from several to tens of
centimetres. Due to the broad number of potential operating conditions, we decided to name the
machine BRAVA: Brittle Rock deformAtion Versatile Apparatus