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Introducing: Laboratory Testing Services
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H-M coupling

We are excited to announce a new business activity for Geomechanica: rock laboratory testing services. Geomechanica’s personnel have extensive rock laboratory testing experience, which enabled Geomechanica to begin offering rock testing services in 2015. These services provide clients with the data needed for the design and analyses of various civil and mining engineering projects.

From weak shales to hard crystalline rocks, Geomechanica offers a full array of standard rock mechanics laboratory testing services, including:

  • Uniaxial compression testing
  • Triaxial compression testing
  • Brazilian disc testing
  • Direct shear testing
  • Slake durability testing
  • Cerchar abrasivity testing
  • Point load testing

Email us at lab@geomechanica.com or call us at +1-647-478-9767 for more information about our testing capabilities or to request a brochure.




 
Video demo of Irazu to simulate hydraulic fracturing
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Irazu is an advanced general-purpose rock deformation and fracturing simulation software. In this video, an application of Irazu to simulate fluid injection into a permeable, fractured rock mass is presented (i.e., hydraulic fracturing).

The software is capable of capturing: fluid-driven fracturing of intact rock; energy dissipation due to fluid viscosity and fracture toughness; fluid leak-off into permeable matrix and natural discontinuities; interaction between natural and induced fractures; influence of rock mass fabric on stimulated volume.

Make sure to watch in HD, full-screen and listen to the narrative.




 
A new fully-coupled hydro-mechanical formulation for the Irazu software
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We are excited to announce that we have been working on the introduction of hydro-mechanical (H-M) coupling in our Irazu FDEM software. The introduction of H-M coupling arguably makes the Irazu software one of the most sophisticated simulation software currently available for geomechanical applications as a multitude of multi-physics processes can be taken into account, including:

  • Rock elasticity, including isotropic and transversely isotropic material models
  • Physics of discontinuous and heterogeneous systems, including the interaction between newly-created and existing discontinuities
  • Brittle fracture processes (e.g., Mode I, Mode II, mixed-Mode fracturing)
  • Coupled flow through porous media and effective stresses
  • Fluid-driven fracture nucleation and growth (both toughness-dominated and viscous-dominated regimes)
  • Emergent rock mass seismicity

The H-M coupling is based on a two-way explicit coupling approach obtained by alternating between the mechanical and hydraulic solvers while marching forward in time. The approach is fully-coupled in the sense that:

  • the mechanical calculations are affected by the presence of a fluid pressure acting inside the rock, thus resulting in the natural development of effective stresses within the model; and
  • the flow calculations are affected by the mechanical deformation of the rock through variations, for example, of hydraulic fracture aperture and flow network geometry.
H-M coupling
Two-way hydraulic-mechanical coupling implemented in Irazu.

In the fluid flow algorithm, a flow channel is assumed to exists at the interface between the triangular finite elements. The flow through each channel is idealized as a laminar viscous flow between two parallel plates using a cubic law approximation. The flow solver can capture the transient flow of a compressible fluid through newly-created fractures, existing rock mass discontinuities, and intact porous matrix.

To exemplify the full H-M coupling, we consider the injection of water through a deep well in an initially dry, permeable rock mass. The in-situ stress field is characterized by a maximum and minimum in-situ principal stresses oriented in the horizontal and vertical direction, respectively: σ1h=20 MPa and σ3v=15 MPa. In a first simulation case, the rock mass is assumed to be homogeneous and isotropic with stiffness and strength property values typical of a brittle rock. The animations below show that the pressurization of the well causes the nucleation of a bi-wing tensile fracture parallel to the direction of σ1. The simulation results highlight the effect of the rock mass permeability k on the hydraulic fracture propagation process. As expected, a higher k value leads to a higher leak-off of fluid from the growing fracture, thus resulting in a slower fracture propagation speed and larger area of influence around the fracture.

HF simulation 1
Example of fluid-driven fracturing in a homogeneous and isotropic rock mass with permeability k = 4.5e-12 m2.
HF simulation 1
Example of fluid-driven fracturing in a homogeneous and isotropic rock mass with permeability k = 5.6e-13 m2.

In a second simulation case, the presence of a 20-m-long cohesive-type discontinuity (fault) is incorporated into the model with higher permeability (k = 4.5e-12 m2). The strength properties of the discontinuity are lower than those of the rock mass. As highlighted in the animation below, the seepage flow around the hydraulic fracture causes a progressive decrease of the normal effective stress acting along the fault plane, thus gradually reducing the mobilized frictional resistance. After about 76 seconds of injection, the fluid pressure induces fault slip (reverse faulting).

HF simulation 1
Example of fluid-pressure-induced fault slip (rock mass permeability k = 4.5e-12 m2).




 
A pragmatic methodology to abstract the EDZ around tunnels of a geological radioactive waste repository
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Geomechanica is launching a guest blog series, written by experts and numerical modellers in the field of rock engineering. In the first post of this series, we’re showcasing the work of Andrés Alcolea on “A pragmatic methodology to abstract the EDZ around tunnels of a geological radioactive waste repository – Application to the HG-A experiment in Mont Terri.”

Andres Alcolea

Andrés Alcolea is a Civil Engineer and Hydrogeologist with more than 20 years of experience in numerical modelling of groundwater, contaminated aquifers and geothermal reservoirs. He is the Head of the “Groundwater and Geothermal” Division with TK Consult AG, a consulting company in Zürich (Switzerland).

The Excavation Damaged Zone (EDZ) around the backfilled underground structures of a geological repository represents a possible release path for radionuclides, and corrosion and degradation gases which needs to be addressed adequately in Safety Assessments (SA). The hydro-mechanical phenomena associated with the creation and temporal evolution of the EDZ are of high complexity, precluding the detailed representation of the EDZ in conventional SA modelling tools. Thus, simplified EDZ models able to mimic the safety-relevant functional features of the EDZ, are required.

In this context, TK Consult AG has developed a versatile and heuristic modelling approach with the goal of representing the creation and evolution of the EDZ in an abstracted and simplified manner. The key features addressed are the stochastic character of the excavation-induced fracture network and the self-sealing processes associated with the re-saturation after backfilling of the underground structures.

The methodology consists of three main steps (Figure 1). Firstly, using Geomechanica’s hybrid finite-discrete element method (FDEM) code, the geometry and geomechanical conditions of the discrete fracture networks forming the EDZ are simulated (Figure 1a). Secondly, the geometry and hydro-geomechanical properties simulated by the FDEM are mapped onto a finite element mesh (Figure 1b), which allows the fluid motion equations in the excavation near-field to be solved. A prominent feature of the methodology is that hydraulic parameters of both fracture and matrix evolve with time as a response to resaturation of the tunnel surroundings. Finally, an abstraction of the complex model is made upon the late time behavior (after full resaturation) of the system (Figure 1c). The main outcomes are:

  • Spatio-temporal distributions of hydraulic parameters and corresponding specific fluxes towards the tunnel, with special emphasis on the late time behavior (i.e., the one relevant for SA).
  • The abstraction of the EDZ at late times: a piece-wise homogeneous model with hydraulic behavior identical to that of the complex initial FDEM model is defined.
Cavern design using FEMDEM
Figure 1: Concept of the EDZ abstraction process for Safety Assessment (SA) applicable for a circular tunnel: (a) Representative fracture patterns are simulated for relevant repository configurations with a discrete element model (FDEM by Geomechanica Inc.); (b) The discrete fracture patterns are converted to heterogeneous porosity and conductivity distributions; (c) In a final abstraction process, the heterogeneous porosity / conductivity distributions are converted to a shell defined by a radius and homogeneous porosity / conductivity..

The abstraction methodology relies on a good initial discrete representation of the fracture network. The methodology has been tested on a range of generic repository settings in the context of a sensitivity study, aimed at investigating the impact of repository depth and in-situ stress conditions on the hydraulic significance of the EDZ after repository closure. Finally, the model has been benchmarked with a data set from an in-situ self-sealing experiment at the Mont Terri Underground Rock Laboratory (URL), demonstrating the ability of the modelling approach to mimic the hydraulic response of the EDZ around a backfilled tunnel section during the re-saturation phase. Only two model parameters are calibrated: the rate of fracture closure and the skin factor around the tunnel. An example of the fit attained with such a simple model is displayed in Figure 2.

Cavern design using FEMDEM
Fig. 2: (a) Pressure fits at observation borehole HG-A2 for simulations HG-A and HG-A-F; (b) number of closed fractures vs. time. In the inset, the discrete fracture networks.

The fitting could be improved by using a 3D extension of the modelling approach (on-going work) or highly parametrized sophisticated models. However, the fact that such a simplistic (and under parametrized) 2D model is capable of reproducing the main experimental trends can be considered a hopeful step towards the abstraction of the Excavation Damaged Zone.

Further reading:




 
Geomechanica at the EUROCK Symposium
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Geomechanica is looking forward to presenting recent research and developments at the European Rock Mechanics Symposium (EUROCK 2015) External link, to be held in Salzburg, Austria, from October 7 to 10, 2015.


On Wednesday October 7, 2015, Dr. Andrea Lisjak will be offering a short course External link on the use of the hybrid finite-discrete element method (FEMDEM) to simulate fracture processes in rocks. The course will cover the theoretical principles of the numerical method and will offer the opportunity to gain valuable “hands-on” experience using Geomechanica’s recently-released Irazu FEMDEM software External link. We encourage petroleum, mining, geological and geotechnical engineers, graduate and post-graduate students with an interest in brittle rock behaviour to attend this short course. The registration fee is only 125 Euro External link.


On Thursday October 8, 2015, Andrea will be presenting Geomechanica’s latest research results on the numerical simulation of the excavation damaged zone (EDZ) in Opalinus Clay with application to underground nuclear waste repositories. The complete conference technical program can be found here External link.

We hope to see you in Salzburg! Please make sure to connect with Dr. Andrea Lisjak.




 
Irazu Cloud simulation software
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Geomechanica is pleased to offer a cloud computing service, Irazu Cloud, for its Irazu simulation software, the innovative simulation package for modelling rock mass deformation and fracturing.

This service employs conventional software applications for model construction and post-processing, together with cloud computing for model execution. With this approach, you will build the Irazu models on your local computer using the Irazu Graphical User Interface, Geomechanica’s intuitive and easy-to-use pre-processing software. The models will then be submitted to the cloud for execution on Geomechanica’s computing infrastructure. As simulation outputs are generated, they will be automatically downloaded to your computer where visualization and post-processing can be carried out.

Main advantages of the Irazu Cloud include:

  • No need for specialized IT infrastructure: avoid the expense of purchasing a dedicated workstation for running models. To use Irazu Cloud, only a simple laptop (running Microsoft Windows or Linux) and an Internet connection are required.
  • Reduced capital costs: pay-as-you-go options are offered in lieu of a large upfront software licensing fee.
  • Greater flexibility: monthly, quarterly, and yearly subscriptions are available to better suit variations in your demand.
  • Improved accessibility: you can submit your models any time and from anywhere.
  • Automatic software updates: you are always running the most up-to-date version of our Irazu software.

To learn more about how you can use Geomechanica’s Irazu software, including a free, one-month trial subscription to Irazu Cloud, please get in touch with us by calling 1-647-478-9767 or emailing us at info@geomechanica.com. Subscribe to our mailing list to get the latest updates from us.

   




 
ARMA 2015: One-day course on rock fracture simulation using Irazu FEMDEM software
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Geomechanica is looking forward to teaching a short course on the application of the hybrid finite-discrete element method (FEMDEM) to simulate fracture processes in rocks at the 49th US Rock Mechanics/Geomechanics Symposium (ARMA 2015) External link to be held in San Francisco, California, USA on 28 June-1 July 2015. The one-day course External link, instructed by Dr. Bryan Tatone, will be held at the Westin St. Francis, San Francisco, California, on Saturday June 27, 2015 from 8:30 am to 4:30 pm. Morning lectures will cover the theoretical principles and main algorithms of the numerical method, with particular emphasis on the role of fracture and fragmentation processes on the overall simulation results. These theoretical lectures will be followed by the presentation of several practical simulation case studies from mining, civil, and petroleum engineering applications. In the afternoon, the participants will learn how to build simple models using Geomechanica’s Irazu FEMDEM software External link, assign correct inputs, and post-process the results.

 
We encourage all petroleum, mining, geological and geotechnical engineers, graduate and post-graduate students with an interest in brittle rock behavior to attend this short course. The registration fee of $499 includes lunch/refreshments, course documentation (course slides and tutorial and verification manuals, and related references.