Laboratory Geophysics

Laboratory geophysics techniques are performed through  a new advanced oedometer cell, which allows 3D Electric Resistivity Tomography (ERT) and seismic wave velocity measurements: spatial and temporal variation of electrical properties are monitored under controlled mechanical and hydraulic conditions.

The device has an internal diameter of130 mm, and can accommodate samples up to60 mmin height. The cell has 42 electrodes located on its internal boundary; 16 are equally spaced on the sidewall, and 13 are on each of the base and top plates.

The cell allows drainage via the top and base plates. The drainage system is composed of three concentric nonconductive rings with a few micrometres of tolerance between them, resulting in an equivalent permeability of about 6 x 10-6 m/s.

 

 

The Complex Impedance Tomograph used for injecting currents and acquiring potentials was constructed by the Iridium Italy (link) company. It is a very fast acquiring device with a 16 bit resolution. The instrument can perform approximately 200 acquisitions per second (at an operating frequency of 1 kHz) so that it is possible to properly appreciate water content or concentration variations inside samples also for relatively fast transitory phenomena.

The electrical measurements are performed on the basis of a four point measurements scheme. Electrodes placed on the sidewall and plates are used alternatively to inject current and to measure the electrical potential.

After performing a large enough number of independent measurements (~ 800), the electrical conductivity distribution within the sample is estimated with a reconstruction procedure using a commercial software developed by sc-aip, based on a least-squares algorithm with a Tikhonov regularization inversion technique.

Sensors for the measurement of P and S wave velocity are allocated on top and bottom caps of the cell. For S wave measurements cantilever mounted PZT-5A Bimorphs by Morgan Electro-Ceramics (10 by 20 by 0.5 mm3) with a parallel connection are used. The transducers used to generate and receive P waves are a lead zirconate titanate ceramic PZT-5A with a cylindrical shape. The ceramic element is produced by Physik Instrument with a thickness of2 mmand a diameter of8 mm. Both seismic sensors are allocated in an opposite space in the bases and covered by a thin surface of epoxy in order to insulate the piezoceramic from interstitial water.

The equipment was realised in collaboration with Universitat Politècnica de Catalunya.

 

This new equipment has been used to perform some tests:

  • detecting water content changes in homogeneous samples, both in stationary and transient conditions:

as for stationary condition, ERT measurements have been performed to evaluate the degree of saturation. Experiments have been conducted on homogeneous samples compacted at different value of water content. For each sample, ERT and wave velocity measurements have been executed;

as for transient condition, ERT measurements have been used in conjunction with a finite element simulation to infer the water retention curve and the unsaturated hydraulic conductivity of coarse and fine homogeneous samples.

  

  • monitoring of salt diffusion in a homogeneous and heterogeneous saturated soil.

Tests have been used to study the chemical behaviour of geomaterials and to evaluate the clay barriers performances;

 

 

 

 

 

  • monitoring of compression and swelling under mechanical loads.

Test have been performed on a preconsolidated kaolinite homogeneous saturated sample to valuate the variation of porosity during oedometer test.

 

 

 

 

Experimental tests have been conducted in collaboration with:

 Ph.D. Cesare Comina (Assistant Professor) – Department of Earth science, Università degli Studi di Torino,Turin,Italy

 Ph.D. Gabriele Della Vecchia (Assistant Professor) Department of Structural Engineering, Politecnico di Milano,Milan,Italy

 

Current status of the research

Nowadays, a new 3D ERT oedometer cell is building, in collaboration with Universitat Politècnica de Catalunya. The new cell will allow performing tests on unsaturated soils controlling either matric or total suction, through the axis-translation technique or vapour transfer technique, respectively.

People

Publications

2013
  1. Electrical Resistivity Tomography: combined field and laboratory experiments for the characterization and monitoring of hydrocarbon pollution
    Proceeding

    Arato, Alessandro; Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Godio, Alberto; Musso, Guido
    In: Geotechnical and Geophysical Site Characterization 4
    CRC Press (Taylor & Francis Group)
    4th International Conference on Site Characterization, ISC'4 (Pernambuco; Brazil) 18-21 September 2012
    Vol.2 pp.8 (pp.1789-1796)

2012
  1. Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography
    Article

    Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido
    GEOTECHNIQUE
    Thomas Telford
    Vol.62 pp.12 (pp.583-594) ISSN:0016-8505 DOI:10.1680/geot.10.P.066

2011
  1. Misure elettriche tomografiche in laboratorio per la stima della efficienza delle barriere argillose nei processi di diffusione.
    Proceeding

    Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido; Comina, Cesare
    In: Titolo volume non avvalorato
    Incontro Annuale dei Giovani Ingegneri Geotecnici IAGIG (Salerno (Italia)) 27-28 Maggio 2011

  2. 3D-electrical resistivity tomography monitoring of salt transport in homogeneous and layered soil samples
    Article

    Comina, Cesare; Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido
    ACTA GEOTECHNICA
    Springer
    Vol.6 pp.9 (pp.195-203) ISSN:1861-1125 DOI:10.1007/s11440-011-0146-3

  3. La tomografia elettrica in laboratorio come tecnica per la caratterizzazione idraulica dei mezzi porosi ed il monitoraggio dei processi transitori
    Proceeding

    Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido
    In: Innovazione tecnologica nell'ingegneria geotecnica
    Edizioni Agi
    XXIV Convegno nazionale di geotecnica (Napoli) 22-24 giugno 2011
    Vol.2 pp.8 (pp.687-694) ISBN:9788897517009

2010
  1. Hydro-chemo-mechanical processes in soil samples: monitoring through electrical resistivity tomography
    Article

    Comina, Cesare; Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido
    EPJ WEB OF CONFERENCES
    pp.6 ISSN:2100-014X DOI:10.1051/epjconf/20100622012

  2. Detecting water content changes in sand samples by means of Electrical Resistivity Tomography
    Proceeding

    Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido
    In: Proc. 5th International Conference on Unsaturated Soils
    5th International Conference on Unsaturated Soils (Barcelona (Spain)) September 6-8
    Vol.CD-Rom

  3. Monitoring transient hydro-chemo-mechanical processes in porous media using electrical resistivity tomography
    Proceeding

    Comina, C; Cosentini, RENATO MARIA; DELLA VECCHIA, G; Foti, Sebastiano; Musso, Guido
    In: Proc. 14th International Conference on Experimental Mechanics (ICEM 14)
    14th International Conference on Experimental Mechanics (ICEM 14) (Poitiers, France) July 4-9
    Vol.CD-Rom

  4. Electrical Tomography as laboratory monitoring tool
    Article

    Comina, C; Cosentini, RENATO MARIA; Foti, Sebastiano; Musso, Guido
    RIVISTA ITALIANA DI GEOTECNICA
    Vol.44 (pp.15-26) ISSN:0557-1405

2009
  1. Analisi della variazione del grado di saturazione mediante misure di tomografia elettrica
    Proceeding

    Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido
    In: Titolo volume non avvalorato
    Incontro Annuale dei Ricercatori di Geotecnica (Roma) 9-11 Settembre 2009

  2. Monitoraggio di prove geotecniche di laboratoriotramite tecniche geofisiche in cella edometrica (EITEDOMETER)
    Proceeding

    Comina, Cesare; Cosentini, RENATO MARIA; Foti, Sebastiano; Musso, Guido
    In: Titolo volume non avvalorato
    28° Convegno nazionale GNGTS (Trieste) 16-19 novembre 2009
    (pp.561-564)

  3. Monitoring transient hydro-mechanical processes in porous media using electrical resistivity tomography
    Article

    Comina, Cesare; Cosentini, RENATO MARIA; DELLA VECCHIA, Gabriele; Foti, Sebastiano; Musso, Guido
    PURE MATHEMATICS AND APPLICATIONS
    Vol.20 pp.3 (pp.165-167) ISSN:1218-4586

2008
  1. EIT oedometer - an advanced cell to monitor spatial and time variability in soil
    Article

    Comina, Cesare; Foti, Sebastiano; Musso, Guido; Romero, E.
    GEOTECHNICAL TESTING JOURNAL
    Vol.31 (5) ISSN:0149-6115 DOI:10.1520/GTJ101367

  2. Monitoring 3D diffusion processes with high speed electric tomography
    Article

    Comina, Cesare; Festa, C; Foti, Sebastiano; Musso, Guido
    THE LEADING EDGE
    Vol.31 (pp.468-471) ISSN:1070-485X

2005
  1. Imaging heterogeneities with electrical impedance tomography: laboratory results
    Article

    A., Borsic; Comina, Cesare; Foti, Sebastiano; Lancellotta, Renato; Musso, Guido
    GEOTECHNIQUE
    ICE
    Vol.55 pp.9 (pp.539-547) ISSN:0016-8505 DOI:10.1680/geot.2005.55.7.539

  2. IMAGING HETEROGENEITIES AND DIFFUSION IN SAND SAMPLES
    Proceeding

    Comina, Cesare; Foti, Sebastiano; Lancellotta, Renato; Musso, Guido
    In: Titolo volume non avvalorato
    Proceedings of the 11th International Conference of the International Association of Computer methods and Advances in Geomechanics IACMAG2005 (Torino)
    Vol.2 (pp.27-34)

Total: 16