Influence of bedding planes to EDZ-evolution and the ... - Andra

P/EDZ/1
Rock matrix
(Visco-)elasto-plastic material model
it describes as afunction of the plastic strain :
Axial stress σ 1 (MPa )
Volumetric strain V/V (%)
60,0
40,0
30,0
20,0
10,0
Stoffansatz :
Minkley, W.; Menzel, W.; Konietzky, H.;
te Kamp, L.(2001)
Figure 1: Our modelling approach to describe the mechanical evolution of the EDZ for aspecific drift
situation at the Mont Terri site.
damage) and hydraulical properties seems unlikely. Gas-transport is controlled by two-phase flow. In
addition, aunique permeability /porosity relationship is not available.
Finally, asshown inFigure 1,anew modelling approach ispresented consisting of two parts, i.e. of a
(visco-)elasto-plastic constitutive model, comprising the hardening/softening behaviour and dilatancy
effects of the rock mass, and aspecific friction model, which described displacement- and velocitydependent
shear strength softening for the bedding planes (Minkley &Mühlbauer, 2007). Using our sitespecific
material parameters, EDZ phenomena for alocal drift situation in the Mont Terri lab could be
nicely simulated.
However, literature results reveal alarge scattering of mechanical strength date ofindurated clay, e.g. from
the Mont Terri Site, which isattributed besides others mainly tothe possible influence ofpore pressures
or de-saturation. From the experimental point of view the knowledge regarding coupling between
mechanical (e.g. damage) and hydraulical properties is not sufficient i.e. the effective Biot-coefficient is
unknown. Preliminary tests with application of pore pressures demonstrate the difficulty ensuring stable
conditions in short term tests due to the low rock permeability. This implies that more experimental work
is necessary to quantify the respective parameters and processes.
References:
Popp, T.&Salzer, K., 2006. Anisotropy of seismic and mechanical properties of Opalinus clay during
triaxial deformation in amulti-anvil apparatus. Proceedings International Symposium: "Using Natural
and Engineered Clay-based Barriers for the Containment of Radioactive Waste ",Tours, 14-18 March
2005. Physics and Chemistry of the Earth, Parts A/B/C, available online 6October 2006.
Minkley, W.&Mühlbauer, J., 2007. Constitutive models todescribe the mechanical behavior of salt rocks
and the imbedded weakness planes. In Proc. 6th Conference onthe Mechanical Behaviour of Salt,
Hannover, 22-25 May 2007, in press. Rotterdam: Balkema.
Page 522
⎛
50,0
σ Max − σ ⎞ D
σ1= σ D + ⎜ 1 +
⎟ σ 3
⎝ σ ϕ + σ
⎟
3 ⎠
⋅
⎛
50,0
σ Max − σ ⎞ D
σ1= σ D + ⎜ 1 +
⎟ σ 3
⎝ σ ϕ + σ
⎟
3 ⎠
⋅
⎛
50,0
σ Max − σ ⎞ D
σ1= σ D + ⎜ 1 +
⎟ σ 3
⎝ σ ϕ + σ
⎟
3 ⎠
⋅
0% plast. Verformung
0,04% plast. Verformung
0,1% plast. Verformung
0,24 plast. Verformung
0,4% plast Verformung
ε p (%) 0,00 0,04 0,10 0,24 0,40
σ D (MPa ) 10,5 8,6 6,0 2,0 0,0
σ φ (MPa (MPa (MPa ) 5,0 5,0 5,0 5,0 5,0
σ Max (MPa ) 55,0 48,0 43,0 38,0 35,0
0,0
0 2 4 6 8 10 12 14 16 18 20
2,5
2,0
1,5
1,0
0,5
Confining stress σ 3 (MPa )
ε p (%) 0,00 0,04 0,10 0,24 0,4
σ ψ (MPa ) 3,2 3,1 2,9 2,5 2,0
tan β° 0,15 0,3 0,5 1,0 2,0
0% plast. strain
0,04% plast. strain
0,1% plast. strain
0,24 plast. strain
0,4% plast strain
0,0
0 2 4 6 8 10 12 14 16 18 20
Confining pressure σ 3 (MPa )
• hardening
• softening
• dilatancy
⇒ Implementation
of pore pressures ?
(Konietzky, 2001)
Bedding plane properties
Newdeveloped shear model
to describe the behaviour ofweakeness planes
on the basis of:
τ = μ 1 + Δ μ ⋅ σ +
μ K
adhesion
=kinetic friction
Δμ =adhesive friction
c =cohesion
K
( ) c
τ
Shear stress (MPa )
INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCE
CLAYS IN NATURAL &ENGINEERED BARRIERS
FOR RADIOACTIVE WASTE CONFINEMENT
N
σ N
Normal Normal stress
stress
σ σ Ν Ν = = 10 10 MPa
MPa
Shear displacement (mm)
Medium Medium 1
1
Medium Medium 2
2