Poromechanical Approach Research Articles

Poromechanical approach to blast‐induced dynamic fracture in concrete

AbstractThis study introduces a novel poromechanical approach to analyze blast‐induced dynamic fracture in concrete considering gaseous kinetics. The objective is to establish a framework for examining the fracture mechanisms during demolition. The simulation employs finite element analysis, incorporating three‐dimensional non‐orthogonal multidirectional cracks induced by gas inflation, through which the gaseous media flows too. The study investigates the principles governing crack network development and the influence of pressurized gas using a multiphase scheme and verifies its findings experimentally. It was also emphasized that benchmark blast experimental data are essential for validating the model, for practical applications in the demolition and renovation of existing structural concrete.

Onsager’s reciprocal relationship applied to multiphysics poromechanics

Onsager’s theory of linear irreversible thermodynamics has been successfully applied to explain findings from experiments. However, its application to multiphysics processes in deformable porous media is a non-trivial undertaking. This contribution presents an extension of Onsager’s theorem to include the flux of the matter of weakly coupled two-phase porous systems. It also relates Onsager to Ziegler’s nonlinear approach including the classical acoustic tensor criterion for localisation phenomena in such nonlinear media. The results are illustrated by Terzaghi consolidation problem using the well established modified Cam-Clay plasticity model. We show that a generalised dissipative stress can act as an appropriate thermodynamic force quantity rendering the non-associated yield envelope into Onsager’s associated form ensuring the thermodynamic condition of no-work free plastic deformation. We present in this contribution an attempt of using the theory of thermodynamics of internal state variables to develop a generic poromechanics approach that relaxes isothermal constraints for weakly coupled problems. This approach lends itself to a promising future extension of a dynamic Onsager diffusional operator for conditions where the multiphysics processes are strongly coupled in the porous system and emergent phenomena may occur.

Pore pressure built-up in hydrate-bearing sediments during phase transition: A poromechanical approach

Due to the density contrast between the hydrate and methane gas, the pore pressure is accumulated in the sediment during the decomposition process of methane hydrate. This accumulation of pore pressure decreases the magnitude of effective stress, further triggering potential geological disasters such as landslide. This paper establishes a theoretical framework to investigate the evolution of fluid pressure in the hydrate-bearing sediments during the decomposition process. This model consists of two parts: an unsaturated thermo-poromechanical constitutive law as well as a phase equilibrium equation. Compared with the existing studies, the present work incorporates the effect of pore volume change into the pressure built-up model. In addition, the capillary effect is considered, which plays a nontrivial role in fine-grained sediments. Based on this model, the evolution of fluid pressure is investigated in undrained conditions. It is shown that four mechanisms mainly contribute to the pressure built-up: the density contrast between decomposing hydrate and producing fluid, the variation of pore volume, the compaction of hydrate due to variation of capillary pressure, and the thermal deformation of pore constituents induced by temperature change. Among these mechanisms, the density contrast dominates the pore pressure accumulation. Under the combined effect of these contributions, the evolution of fluid pressure exhibits a strong nonlinearity during the decomposition process and can reach up to dozens of mega Pascal. Nevertheless, this high-level pressure built-up results in a significant tensile strain, yielding potential fracturing of the sediment.

Ultrasonic characterization of frozen soils using a multiphase poromechanical approach

The ability to quantitatively and non-invasively characterize complex multiphase geomaterials is still a major challenge to the engineering, construction, and geophysical fields. In the context of accelerating climate change, construction on permafrost requires remedial measures and an appropriate characterization of permafrost (e.g., ice content, unfrozen water content, porosity, ice lenses, soil type, and mechanical properties). Current techniques are insufficient for efficient characterization of permafrost samples. Here, we propose an ultrasonic sensing technique and a signal interpretation method based on an inverse multiphase poromechanical approach to overcome critical gaps in permafrost characterization. This technique allows us to interpret the measured electrical signal using a theoretical transfer function obtained through an efficient multiphase poromechanical forward solver. Our study demonstrates the potential of the ultrasonic sensing technique for the rapid characterization of permafrost samples in terms of both physical and mechanical properties.

Seismic physics-based characterization of permafrost sites using surface waves

Abstract. The adverse effects of climate warming on the built environment in (sub-)arctic regions are unprecedented and accelerating. The planning and design of climate-resilient northern infrastructure, as well as predicting deterioration of permafrost from climate model simulations, require characterizing permafrost sites accurately and efficiently. Here, we propose a novel algorithm for the analysis of surface waves to quantitatively estimate the physical and mechanical properties of a permafrost site. We show the existence of two types of Rayleigh waves (R1 and R2; R1 travels faster than R2). The R2 wave velocity is highly sensitive to the physical properties (e.g., unfrozen water content, ice content, and porosity) of active and frozen permafrost layers, while it is less sensitive to their mechanical properties (e.g., shear modulus and bulk modulus). The R1 wave velocity, on the other hand, depends strongly on the soil type and mechanical properties of permafrost or soil layers. In situ surface wave measurements revealed the experimental dispersion relations of both types of Rayleigh waves from which relevant properties of a permafrost site can be derived by means of our proposed hybrid inverse and multiphase poromechanical approach. Our study demonstrates the potential of surface wave techniques coupled with our proposed data-processing algorithm to characterize a permafrost site more accurately. Our proposed technique can be used in early detection and warning systems to monitor infrastructure impacted by permafrost-related geohazards and to detect the presence of layers vulnerable to permafrost carbon feedback and emission of greenhouse gases into the atmosphere.

Numerical modelling the influence of water content on the mechanical behaviour of concrete under high confining pressures

The present paper focuses on the hydro-mechanical behaviour of concrete under high confining pressures. By using the poromechanics approach, an elastoplastic model is adopted to describe the mechanical behaviour of concrete under different saturation conditions and high confining pressures. A hydrostatic compression test with the measurement of interstitial pore pressure is firstly used to identify the model’s parameter. After that, three quasi-oedometric tests with different water contents are simulated. The obtained numerical results exhibit that the mechanical behaviour of concrete is strongly coupled with its hydraulic responses. For instance: the saturation kinetics is accelerated by the plastic deformation related to pore collapse and volumetric compaction. The numerical predictions and discussions can help engineers to enhance their understandings on the influence of interstitial pore pressure on the vulnerability of concrete structures subjected to near-field detonations or impacts.

Numerical investigation and design of reinforced concrete beams with non-uniform frost damage on the compression and tension sides

This paper aims to investigate the bending behaviour of a reinforced concrete (RC) beam with different non-uniform frost damages. A multi-scale poromechanical approach is developed to build a bridge between the material deterioration process and the structural mechanical performance by considering the global heat and moisture transport and rebar confinement, as well as the local phase changes and poromechanical deformation. The real-time frost damage process is first simulated and experimentally validated for different depths of exposure on both the compression and tension sides and then used for testing the residual bending behaviour. The failure modes, load-carrying capacity and strain distribution of the reinforcement are fairly consistent with the experimental results. The bearing capacity decreases with the increment of the freeze-thaw cycles (FTC) and the frost exposure depth. Reinforcing bars can restrain not only crack propagation but also frost damage. Thus, the bearing capacity of the damaged beam on the compression side drops more than that on the tension side for the same exposure depth. Finally, an indirect method for the use of the equivalent deteriorated mechanical properties is compared with the detailed real-time simulation, and a simple design method is proposed for RC beams with partial frost damage.

Coupled Modeling of Sedimentary Basin and Geomechanics: A Modified Drucker–Prager Cap Model to Describe Rock Compaction in Tectonic Context

The aim of basin modeling is to characterise fluids and rocks in a basin considering its history and data partly describing its present state. In usual basin simulators, only a simplified description of geomechanics based on the hypothesis of oedometric strain is used. To both enhance the modeling of basin history and to characterise actual in situ stresses, the effect of stress redistribution, horizontal stresses, and strain variations during basin history should be considered. To address this point, a coupled basin-geomechanics framework based on a new constitutive law is proposed in this paper using the prototype simulator $$\mathrm{A}^{2}$$ . This framework has been built to provide relevant results for various kinds of basin cases including tectonic loading. A finite strain poromechanical approach is considered along with an modified Drucker–Prager Cap model to describe rock compaction under natural sedimentation, erosion, and tectonics. The constitutive model can be seen as a tensorial extension of the compaction models of Athy or Schneider as it allows to recover the same behaviour in oedometric context. Simple test cases are modeled considering typical sand or shale properties, emphasizing the effect of tectonic loading on the present-day pore pressures and in situ stresses. It appears that even relatively moderate tectonic loading ( $$5\%$$ of horizontal strain) can lead to overpressures of several hundreds of bars and to a complete change in in situ stress regime for deeply buried layers (above a depth of 2000 m).

On the mechanism of plastic shrinkage cracking in fresh cementitious materials

In this study, a continuum poromechanics approach is presented to model the plastic shrinkage cracking of fresh cementitious materials. The boundary conditions are according to the modified ASTM C1579–13 standard for mortars. The restrained deformations are linked to the restraint stresses according to the Cauchy-Navier equations of elasticity, assuming an incremental stress-strain relationship. The Bresler-Pister and Rankine failure criteria are utilized to model failure. The material parameters are adapted according to the Drucker-Prager and Griffith criteria. The crack initiation and propagation is verified experimentally by X-ray radiography. Eventually, the cracking mechanism is discussed and a safe capillary pressure limit is proposed. It is found that capillary pressure stiffening occurring before air entry, when deformations take place in the saturated state, is the predominant cause of plastic shrinkage cracking in the drying state.

Multi-scale computational modeling for concrete damage by mixed pore pressures – case of coupled alkali–silica reaction and cyclic freeze/thaw

PurposeThis paper aims to propose a multi-scale simulation approach for the concrete macro-mechanical damage caused by mixed micro-pore pressures, such as the coupled alkali–silica reaction (ASR) and freeze-thaw cycles (FTC).Design/methodology/approachThe micro-physical events are computationally modeled by considering the coupling effect between ASR gel and condensed water in the mixed pressure and motion. The pressures and transport of pore substances are also linked with the concrete matrix deformation at macro-scale through a poro-mechanical approach, and affect each other, reciprocally. Once the crack happens in the nonlinear analysis, both the micro-events (water and gel motion) and the macro mechanics will be mutually interacted. Finally, different sequences of combined ASR and FTC are simulated.FindingsThe multi-chemo mechanistic computation can reproduce complex events in pore structures, and further the macro-damages. The results show that ASR can reduce the FTC expansion for non-air-entrained concrete, but may increase the frost damage for air-entrained concrete. The simulation is examined to bring about the observed phenomena.Originality/valueThis paper numerically clarifies the strong linkage between macro-mechanical deformation and micro-chemo-physical events for concrete composites under coupled ASR and FTC.

Experimental and numerical modeling of creep in different types of concrete

Creep in concrete, play a critical role in estimating losses in prestressed concrete structures, such as bridge girders, nuclear containment vessels, etc. The present study aims at investigating the creep under various environmental conditions in different types of concrete made with different ingredients using an experimental and numerical approach. Seven different concrete mixes have been made for this purpose and among the seven mixes, three mixes are self compacted concrete mixes (35 MPa, 55 MPa and 70 MPa), a high volume fly ash concrete mix (45 MPa), two mixes of normally vibrated ordinary Portland cement (OPC) concrete mixes (35 MPa and 45 MPa) and a heavy density concrete (25 MPa). Studies have been carried out at temperature of 25 °C and two relative humidity (RH) conditions (RH of 60% and 70%). An analytical model has been developed to simulate the drying phenomena in concrete based on a poromechanics approach. The hydration effects in blended cements (containing mineral admixture) is considered while developing the model. The proposed model is capable of predicting the degree of hydration, temperature and relative humidity (RH) over the continuum that required for estimating the creep strain. Micro prestress solidification (MPS) is used to estimate the creep strain. It is found that the proposed model is able to predict the drying phenomena and creep strain in various concretes, and which is in good agreement with the corresponding experimental results. It is found that heavy density concrete shows a higher creep strain than the other concretes. This may be due to the lower porosity of hematite aggregate. Further adding fly ash as a mineral admixture to concrete mix reduces the creep. Creep in a reinforced concrete (RCC) beam tested under sustained loading and reported in the literature is simulated using the present model and it is seen that the model predictions are in good agreement with the test data.

A poromechanics model for plastic shrinkage of fresh cementitious materials

When fresh cementitious materials are exposed to evaporation, drying of the pore fluid leads to capillary pressure development and plastic shrinkage. Plastic shrinkage occurring after the solid percolation threshold plays an important role in the initiation and propagation of plastic shrinkage cracks, which may compromise the durability and decrease the service life of concrete structures.In this study, a poromechanics approach to plastic shrinkage is developed. Novel experimental methods are utilized to quantify the material properties used as model input. An independent set of measurements is further used to validate the developed model. It is shown that the bulk modulus evolution plays a prominent role in controlling the plastic shrinkage of cementitious materials.

Strong Coupling of Freeze-Thaw Cycles and Alkali Silica Reaction - Multi-scale Poro-mechanical Approach to Concrete Damages -

Strong Coupling of Freeze-Thaw Cycles and Alkali Silica Reaction - Multi-scale Poro-mechanical Approach to Concrete Damages -

The significance of pore liquid pressure and disjoining pressure on the desiccation shrinkage of cementitious materials

There are several conflicting opinions in the literature concerning the significance and role of bulk pore liquid pressure and disjoining pressure on the desiccation shrinkage of cementitious materials. While the applicability of the Kelvin–Laplace equation in fine pores (due to the unstable nanosized meniscus) has been questioned by some, disjoining pressure has been advocated to be the primary mechanism driving desiccation shrinkage in cementitious materials. In order to elucidate the proper contribution and understanding of these two mechanisms, a thermodynamics-based mechanistic approach has been utilized here to derive expressions for both the bulk liquid pressure and the disjoining pressure. The validity of the poromechanical approach to modeling shrinkage of a porous body has also been examined. It has been concluded that the determination of pore liquid pressure via the Kelvin–Laplace equation does not require the presence of a stable meniscus and is applicable to nanosized pores. As such, the pore liquid pressure is found to be the primary mechanism associated with the desiccation shrinkage of cementitious materials. While disjoining pressure does not induce any change in the bulk liquid stress during drying, it plays a significant role in counterbalancing the liquid pressure in the thin film separating the vapor phase from the pore wall, which justifies poromechanical shrinkage models that consider pressurization to occur only in the portion of the pores containing bulk pore liquid.

The bleeding test: A simple method for obtaining the permeability and bulk modulus of fresh concrete

This paper shows how the well-known bleeding test can be used as a simple and inexpensive method for measuring the permeability and the bulk modulus of fresh concrete, utilizing Darcy's law and a small-strain poromechanical approach. The permeability and the bulk modulus are two essential parameters for understanding the behavior of fresh concrete, in particular plastic settlement and plastic shrinkage cracking. The proposed methods are verified and validated by utilizing experimental data obtained from the literature.

A hygrothermo-mechanical model for wood: Part B. Parametric studies and application to wood welding : COST Action FP0904 2010–2014: Thermo-Hydro-Mechanical wood behavior and processing

The correct prediction of the behavior of wood components undergoing environmental loading or industrial process requires that the hygric, thermal and mechanical (HTM) behavior of wood are considered in a coupled manner. A fully coupled poromechanical approach has been used to perform a parametric study on wood HTM behavior, and the results have been validated with neutron imaging measurements on a moist wood specimen exposed to high temperature. Further, HTM behavior of wood during welding has been simulated by the model. For such a simulation, proper material properties are needed, as some of them, for example thermal conductivity, have a significant influence on the local and temporal behavior of the material.

A hygrothermo-mechanical model for wood: Part B. Parametric studies and application to wood welding

Abstract The correct prediction of the behavior of wood components undergoing environmental loading or industrial process requires that the hygric, thermal and mechanical (HTM) behavior of wood are considered in a coupled manner. A fully coupled poromechanical approach has been used to perform a parametric study on wood HTM behavior, and the results have been validated with neutron imaging measurements on a moist wood specimen exposed to high temperature. Further, HTM behavior of wood during welding has been simulated by the model. For such a simulation, proper material properties are needed, as some of them, for example thermal conductivity, have a significant influence on the local and temporal behavior of the material.

A hygrothermo-mechanical model for wood: part A. Poroelastic formulation and validation with neutron imaging

Abstract The correct prediction of the behavior of wood components undergoing environmental loading or industrial process requires that the hygrothermal and mechanical (HTM) behavior of wood is considered in a coupled manner. A fully coupled poromechanical approach is proposed and validated with neutron imaging measurements of moist wood specimens exposed to high temperature. This paper demonstrates that a coupled HTM approach adequately captures the variations of temperature, moisture content, and dimensions that result in a moist wood sample exposed to one-side heating.

Poroelastic theory applied to the adsorption-induced deformation of vitreous silica.

When vitreous silica is submitted to high pressures under a helium atmosphere, the change in volume observed is much smaller than expected from its elastic properties. It results from helium penetration into the interstitial free volume of the glass network. We present here the results of concurrent spectroscopic experiments using either helium or neon and molecular simulations relating the amount of gas adsorbed to the strain of the network. We show that a generalized poromechanical approach, describing the elastic properties of microporous materials upon adsorption, can be applied successfully to silica glass in which the free volume exists only at the subnanometer scale. In that picture, the adsorption-induced deformation accounts for the small apparent compressibility of silica observed in experiments.

Elastic behavior of saturated porous materials under undrained freezing

The elastic behavior of saturated porous materials under undrained freezing is investigated by using a poromechanical approach. Thermodynamic equilibria are used to describe the crystallization process of the partially frozen solution in bulk state and confined state in pores. By phase transition at freezing, fusion energy, thermal contraction of solid, solution and ice crystals, volume changes of crystallization build up remarkable pore pressure that induces expansion or shrinkage of solid matrix. Owing to the lower chemical potential when pore water mixes with salts, fewer ice forms in pores. Penetration of ice into the porous materials increases the capillary pressure, but limits effect on the pore liquid pressure and the strain of solid matrix. On the contrary, the pore pressure induced by solution density rises as salt concentration increases and causes significant shrinkage of solid matrix.