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Valley, Benoît

Nom
Valley, Benoît
Affiliation principale
Site web
Fonction
Professeur ordinaire
Email
benoit.valley@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/943
_
0000-0003-4632-0504

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  • Publication
    Métadonnées seulement
  • Publication
    Accès libre
    A comparison of FBG- and Brillouin-strain sensing in the framework of a decameter-scale hydraulic stimulation experiment
    (: American Rock Mechanics Association, 2018-6-18)
    Krietsch, H.
    ;
    Gischig, V.
    ;
    Jalali, R.
    ;
    Doetsch, J.
    ;
    Valley, Benoît 
    ;
    Amann, F.
    In the framework of the In-situ Stimulation and Circulation (ISC) experiment Fiber-Bragg-Grating (FBG) and Brillouin strain sensing systems were installed to monitor deformation during six hydraulic shearing and six hydraulic fracturing experiments. Three boreholes were dedicated to strain monitoring. Both systems are installed in the same boreholes, offering a unique opportunity to compare these systems with respect to their applicability in hydraulic stimulation tests. A total of 60 FBG sensors with 1 m base length were installed across fractures, shear zones and intact rock. Along the entire borehole length, pre-stressed optical cables for Brillouin distributed strain (DBS) sensing were embedded in grout with two installation methods: a bare cable and a cable packed and fixed with glue every 0.65 m. The strain signals were compared as time series for a given borehole depth and as profiles along the borehole axis. The study reveals that the FBG system gives a high accuracy (0.04 µ-strain) and temporal resolution (>1s) with pointwise measurements. The bare DBS leg yield good quantitative strain data with poorer strain accuracy (>500 times poorer than FBG) and poorer temporal resolution (factor of >100). The packed DBS leg provide no meaningful information about the strain field.
  • Publication
    Métadonnées seulement
  • Publication
    Métadonnées seulement
  • Publication
    Métadonnées seulement
  • Publication
    Métadonnées seulement
    The Propagation of Seismic Waves in the Presence of Strong Elastic Property Contrasts
    (2012-12-1)
    Saleh, Ramin
    ;
    Jeyaraj, R.
    ;
    Milkereit, Bernd
    ;
    Liu, Q.
    ;
    Valley, Benoît 
    In an active underground mine there are many seismic activities taking place, such as seismic noises, blasts, tremors and microseismic events. In between the activities, the microseismic events are mainly used for monitoring purposes. The frequency content of microseismic events can be up to few KHz, which can result in wavelengths on the order of a few meters in hard rock environment. In an underground mine, considering the presence of both small wavelength and strong elastic contrasts, the simulation of seismic wave propagation is a challenge. With the recent availability of detailed 3D rock property models of mines, in addition to the development of efficient numerical techniques (such as Spectral Element Method (SEM)), and parallel computation facilities, a solution for such a problem is achievable. Most seismic wave scattering studies focus on large scales (>1 km) and weak elastic contrasts (velocity perturbations less than 10%). However, scattering in the presence of small-scale heterogeneities and large elastic contrasts is an area of ongoing research. In a mine environment, the presence of strong contrast discontinuities such as massive ore bodies, tunnels and infrastructure lead to discontinuities of displacement and/or stress tensor components, and have significant impact on the propagation of seismic waves. In order to obtain an accurate image of wave propagation in such a complex media, it is necessary to consider the presence of these discontinuities in numerical models. In this study, the effects of such a contrast are illustrated with 2D/3D modeling and compared with real broadband 3-component seismic data. The real broadband 3-component seismic data will be obtained in one of the Canadian underground mines in Ontario. One of the possible scenarios investigated in this study that may explain the observed complexity in seismic wavefield pattern in hard rock environments is the effect of near field displacements rather than far field. Considering the distribution of seismic sensors in a mine and the presence of seismic events within a mine, the recorded wavefield may represent a near-field displacement, which is not the case for most of seismic studies. The role of receiver characterization on the recorded event near the surface or around fault zones is also investigated. Using 2D/3D modeling, the effects of Vp/Vs variation on vertical and horizontal components of recorded amplitude has been shown.
  • Publication
    Métadonnées seulement
  • Publication
    Accès libre
    Capturing non-linear stress-strain response of brittle rocks due to closure of coring-induced micro-cracks using 3D bonded block model
    (: ARMA, 2020-6)
    Bahrani, N.
    ;
    Valley, Benoît 
    The stress-strain curves of brittle rocks can be divided into five regions: 1. crack closure, 2. elastic region, 3. crack initiation, 4. crack damage, and 5. peak and post-peak region. The initial non-linear section of the stress-strain curve is known to be due to the closure of pre-existing micro-cracks. This non-linear section may or may not be present depending on the density and geometry of pre-existing micro-cracks. It is known that some of these micro-cracks may form due to the stress redistribution and tensile stresses generated inside the cores during drilling from deep and high stress grounds. The presence of such micro-cracks may affect the properties of rock specimens determined from laboratory tests. Therefore, the knowledge of the level of core damage (micro-crack density) and associated changes in the laboratory properties of brittle rocks is of paramount importance for reliable designs of deep underground excavations. In this paper, the discontinuum numerical program 3DEC and its Bonded Block Model (BBM) is used to explicitly simulate drilling-induced core damage. The laboratory test data from the well documented case of the AECL's Underground Research Laboratory (URL) is used for numerical simulation and model calibration. The numerical simulations involve: 1) calibrating a 3D BBM to the properties of undamaged Lac du Bonnet (LdB) granite under an unconfined condition, 2) simulating core drilling and associated micro-cracks in the cored specimen (i.e., BBM), and 3) uniaxially loading the damaged BBM and comparing its mechanical properties with those of damaged LdB granite. It is found that the initial region of the stress-strain curve of the damaged BBM is non-linear. This is interpreted to be due to the closure of micro-cracks generated during core drilling simulation. The results of numerical study presented in this paper demonstrate the capability of the proposed modeling approach for a realistic simulation of drilling-induced core damage and associated non-linear stress-strain response of brittle rocks