Geomechanics and Geotechnics

True Triaxial Apparatus

Measuring the pressure and temperature dependence of elastic wave velocities (P- and S-waves), thermal conductivity and  others physical properties of rocks

The multi-anvil pressure apparatus has been developed and designed by Prof. H. Kern at the former Institute of Mineralogy and Petrography. The device allows measurements of elastic wave velocities (Vp, Vs) and volume (density) change of rocks at confining pressure, deviatoric stress and temperature. Measurements can be done simultaneously in three orthogonal directions of a sample cube (43 mm on edges) over a range of pressures up to 600 MPa and temperatures up to 600°C, using the ultrasonic pulse transmission technique.  The transducers operate at 2 MHz and 1 MHz, respectively. In order to measure the directional dependence of wave velocities (anisotropy), particularly in sedimentary (bedded) and metamorphic (foliated) rocks, which are in general  anisotropic,  the three orthogonal measuring directions must be related to the structural reference frame X, Y, Z , where Z is normal  and Y and Z  parallel to bedding  (foliation) [XY-plane]. Shear-wave splitting (Vs1-Vs2), which is a characteristic phenomenon of anisotropy, is measured by two sets of orthogonal polarized shear-wave transducers. Length changes (volume change) of the sample as a function of pressure and temperature is obtained by the piston displacements. A complete set of measured data comprises three P-wave velocities and six S-wave velocities, thermal conductivity along with length changes (volume change) of the sample. The data are important for geophysical, geotechnical, geothermal modelling and for civil and underground engineering.

             

                                   

Specification of the Device    

  • Maximum loading: 2000 kN in 3 orthogonal directions,
  • Sample size : cubes with 43 mm on edges,
  • Maximum pressure: 600 MPa, isostatic (σ1 = σ2 =σ3) and deviatoric (σ1 ≠ σ2 ≠  σ3 )
  • Maximum temperature: 600 °C

 

Results

Density as a function of pressure and temperature for samples A, B, C and D*

Dynamic moduli Young’s modulus, bulk modulus, and shear modulus as a function of pressure and temperature for eclogite sample A*

 

Refrences

  • Zertani, S., John, T., Tilmann, F., Motra, H. B., Keppler, R., Andersen, T. B., Labrousse, L., (2019): "Modification of the seismic properties of subducting continental crust by eclogitization and deformation processes". In: Journal of Geophysical Research: Solid Earth 124, 9731-9754. Agupubs

  • (*)Motra, H. B., and  Zertani, S., (2018) "Influence of loading and heating processes on elastic and geomechanical properties of eclogites and granulites", Journal of Rock Mechanics and Geotechnical Engineering, 10:1, 127-137, Sciencedirect

  • Motra, H. B., Magar, J., Ismail, A., Wuttke, F., Rabbel, W., Köhn, D., Thorwart, M., Simonetta, C., Costantin, N, (2018) "Determining the influence of pressure and temperature on the elastic constants of anisotropic rock samples using ultrasonic wave techniques." Journal of Applied Geophysics, Vol. 159, 715-730. Sciencedirect

  • Motra, H. B., Stutz, H.H., (2018) "Geomechanical Rock Properties Using Pressure and Temperature Dependence of Elastic P- and S-Wave Velocities", Geotechnical and Geological Engineering, 36:6, 3751-3766, Springer

  • Rabbel, W., Jusri, T., Köhn, D., Motra, H. B., Niederau, J., Schreiter, L., Thorwart, M., Wuttke, F., (the DESCRAMBLE Working Group), (2017) "Seismic Velocity Uncertainties and their Effect on Geothermal Predictions, Energy Procedia, 125, 283-290.  Sciencedirect