Duc-Phi Do

A closed-form hydro-mechanical solution for deep tunnels in elastic anisotropic rock

In this work, a closed-form hydro-mechanical solution for stresses and displacements around a deep tunnel excavated in an anisotropic poro-elastic medium is presented. The developed analytical solution is conducted by using the well-known complex potential approach and including the hydraulic effect. The validation of this analytical solution is done by comparing with the numerical results obtained from the finite element method Aster-Code. Through some numerical applications, the effect of the anisotropic poro-elastic behaviour of rock mass on the distribution of stresses and displacements around the tunnel will be detailed. The obtained results demonstrated the essential role of pore pressure and the hydro-mechanical coupling on the response of the tunnel and the analytical solution developed in this contribution would be useful for tunnel design thanks to its quick evaluation of the stress and displacement fields in the medium.

Modelling of two-phase flow in capillary porous medium by a microscopic discrete approach

The aim of this work is to study the fluid flow in porous media by a microscopic approach. For that, the microstructure of a porous material is represented by a network of capillary pipes with geometric and flow characteristics chosen in such a way as to fit both the pore volume and water saturated hydraulic conductivity of a studied porous material. In saturated state, a pipe is supposed to have a Kozney–Carman hydraulic conductivity. In partially saturated conditions, the “menisci model” as proposed by has been used. Such a representation is sufficient to satisfactory reproduce mostly of laboratory results on flow properties of a porous material in saturated and partially saturated conditions as demonstrated by our numerical results on a porous stone.

Damage assessment of cement-based geomaterial during loading by ultrasonic tomography

Damage assessment of cement-based geomaterials during loading was conducted in this work by using the through-transmission ultrasound. For this purpose a built up system of ultrasound consisting of 96 channels and the specific sensors allowing to measure at the same time three types of waves (a bulk wave and two shear waves) were used. The continuous measurements enable to assess the damage of material through the constructed image of ultrasonic velocity as well as the attenuation of each wave during loading. The difference tomography method using the differential arrival times or relative amplitudes with respect to the initial stage confirms its efficacy through this work. The results show that all three types of wave can be used to capture the progressive damage in material but the bulk wave seems to be more sensitive than the shear waves.

On the Modeling of Transition from a Diffuse to a Localized Damage

An approach to model long term hydromechanical behavior of rock masses around underground excavations is proposed. Implemented in a classical finite element numerical code this approach combine in one hand a continuum model to describe the progressive damage and strain localization and a fracture mechanics XFEM based numerical procedure to model the behavior of fractured mass once the macrofracturing takes places.

Fractured Reservoirs Modeling by Embedded Fracture Continuum Approach: Field-Scale Applications

In this paper, the recently developed Embedded Fracture Continuum (EFC) approach will be used to model the fractured reservoir at the large scale. This novel approach borrows the concept of continuum models and incorporates the effect of fractures explicitly by using the fracture cell concept which represents the grid mesh intersected by one or many fractures in the medium. Each fracture cell presents a porous medium that has its own properties calculated from the contributed properties of intact matrix and fractures. The considered problem consists of simulating the primary depletion of fractured reservoir in which the short and medium fractures will be accounted for implicitly in the homogenized porous medium through the upscaling procedure while the embedded long fracture networks are explicitly taken into account. Through this application, we demonstrate and highlight the performance of the EFC approach.

P and S wave anisotropy to characterize and quantify damage in media: laboratory experiment using synthetic sample with aligned microcracks

Damage characterization in solid media is studied in this work through ultrasonic measurements. A synthetic 3D printed sample including a system of horizontally aligned microcracks is used. In contrast to other manual fabrication methods presented in the literature, the construction process considered here ensures a better control and accuracy of size, shape and spatial distribution of the microcracks network in the synthetic sample. The acoustic measure-ments were conducted through a specific device using triple acoustic sensors, which allows to capturing at each incident direction three wave-modes. The evolution of the ultrasonic velocities with respect to incident angle accounted for the damage-induced anisotropy. The experimental results are then compared with some well-known effective media theories in order to discuss their potential use for following studies. Finally, we highlighted and compared the accuracy of these theories used for inversion procedure to quantify damage in the medium. This article is protected by copyright. All rights reserved

P- and S-wave anisotropy to characterise and quantify damage in media: laboratory experiment using synthetic sample with aligned microcracks: P- and S-wave anisotropy

Damage characterization in solid media is studied in this work through ultrasonic measurements. A synthetic 3D printed sample including a system of horizontally aligned microcracks is used. In contrast to other manual fabrication methods presented in the literature, the construction process considered here ensures a better control and accuracy of size, shape and spatial distribution of the microcracks network in the synthetic sample. The acoustic measure-ments were conducted through a specific device using triple acoustic sensors, which allows to capturing at each incident direction three wave-modes. The evolution of the ultrasonic velocities with respect to incident angle accounted for the damage-induced anisotropy. The experimental results are then compared with some well-known effective media theories in order to discuss their potential use for following studies. Finally, we highlighted and compared the accuracy of these theories used for inversion procedure to quantify damage in the medium. This article is protected by copyright. All rights reserved

Assessment of Mechanical Properties of Interphase in Compositelike Geomaterials by Ultrasonic Measurement and the Extended Multi-Inclusion Model

This work aims at assessing the mechanical properties of interphase in a compositelike geomaterial by using a nondestructive characterization technique by ultrasound and an inversion procedure based on the theoretical multi-inclusion model. This latter model is extended here and adapted for the multiphase heterogeneous materials which may contain an arbitrary number of interphases between each inhomogeneity and matrix phase. Some numerical applications on a cement-based geomaterial show that this procedure can be used as a complementary method to characterize the properties of interphase.

Modeling Damage by Crack Nucleation and Growth in Porous Media

While crack propagation is considered as the predominant mechanism of damage in quasi brittle rocks, recent observation on cracking evolution on porous rocks have shown that nucleation of new cracks and back-sliding mechanism of cracks are perhaps as important as the crack propagation. The model proposed here tends to explain the laboratory results that could not be explained within framework of crack-sliding model. A crack nucleation mechanism is then considered to generate an increasing number of cracks based upon a statistical distribution of strain energy cumulated on grain to grain contacts. The increasing role of crack growth and crack coalescence is modeled by an avalanche like mechanism that leads finally to the failure of a porous rock. Predictions of the model are compared with experimentally results in terms of strains and acoustic emission