Physical and hydraulic characteristics in compacted clay soils

To determine and compare the differences in soil water suction between uncropped and cropped plots, a 52-plot experiment was used. Three average tyre to soil contact pressures of 31, 41 and 62 kPa as well as four numbers of machines passes (1, 5, 10 and 15) and control plots of zero traffic were used as pre-seeding machinery compaction treatments for the investigation. Soil dry bulk density, soil moisture content, soil suction, rainfall, water table depth and corn yield were all measured. The results showed that, with increasing tyre contact pressure, there was a corresponding increase in soil suction during the growing season in both uncropped and cropped plots. A family of curves was drawn for soil suction versus tyre contact pressure for different numbers of days and also for soil suction versus volumetric water content at varying contact pressures and times of the season. Growth performance of corn plants was best in moderately compacted plots. Dry bulk density and penetrometer resistance were related to traffic treatments.     

Morphology of horizontal cracks in swelling soils

Horizontally formed cracks in the network of cracked swelling soils tend to influence water and solute transport. An approach is suggested for estimating the mean width and volume of horizontal cracks. It is assumed that the nearly horizontal cracks appear as a result of inhomogeneous soil subsidence caused by rapid drying and shrinkage of thin layers at the walls of vertical cracks. Compared with the moist soil matrix, at the same soil depth, horizontal cracks originate as ruptures in stretched layers of the drying walls of vertical cracks. A characteristic of the average inhomogeneity of soil subsidence, i.e., the mean potential relative subsidence (MPRS) depending on the soil depth is defined. It is calculated on the basis of linear shrinkage in the clay soil matrix and at the walls of vertical cracks of different depths, and on two geometrical parameters of crack networks. They are namely the maximum crack depth and the thickness of the upper intensive-cracking layer. The absolute value and sign of the derivative of the MPRS function with respect to soil depth determine the specific volume of horizontal cracks (horizontal-cracks porosity), and their mean width as functions of depth. Model predictions are obtained using published data on variation of linear shrinkage with depth in 19 soil profiles. For lack of data specific to horizontal-crack characteristics model, predictions were compared with data on vertical cracks and subsidence at the soil surface. Satisfactory agreement was obtained for all soil depths up to the maximum crack depth.     

Mixture theory and unsaturated flow in swelling soils

The current state of knowledge on various aspects of mixture theory applied to unsaturated/saturated swelling soils is discussed. Two and three phase problems are studied. On the smallest scale (micro) the individual platelets and adsorbed (vicinal) water exist as separate phases. On the intermediate scale (meso) the platelets and vicinal water are homogenized to form a saturated particle where vicinal water and solid are overlaying continua. On the macroscale, bulk water, water vapor, and the mesoscale particles are homogenized resulting in three overlaying continua for solid, bulk water, vicinal water, and water vapor. Stress tensor formulations and Darcy’s laws are presented at the mesoscale and macroscales. A theoretical formulation for surface crusting is presented at the mesoscale. General viscoelastic mesoscale and macroscale models are discussed and related to classical approaches.     

Study of the swelling behavior of a compacted soil using flexible odometer

This paper includes an experimental study of the swelling behavior of a compacted soil. The study is performed using a flexible odometer, which allows for lateral deformation during soil expansion and the measurement of the lateral swell pressure. The paper is composed of two parts. The first one describes the flexible device used in this study while the second presents experimental results and discusses the influence of the rigidity of the odometer ring on the swelling behavior of a compacted soil.     

Torque reduction during the excavation of dense cohesionless soils

In this paper, water jet has been used to achieve a reduction in the magnitude of the excavation torque, also known as the torsional resistance, imparted on the cutting wing of an excavation machine during rotational excavation of cohesionless soils. This was accomplished by injecting a controlled water jet along the front plane of the cutting wing during the excavation of a model sandy ground. Experimental excavation was performed on compacted completely saturated sand samples using a prototype excavation machine and the torque required for excavation was measured. Within the experimental limitations, the results showed that water jet could successfully be used to reduce torque during excavation of dense sandy soils.     

Potential method in the linear theory of swelling porous elastic soils

This paper deals with the isothermal linear theory of swelling porous elastic soils in the case of fluid saturation. Internal and external boundary value problems of steady vibrations are investigated using the potential method. The uniqueness and existence theorems of classical solutions of the aforementioned problems are proved.     

On the spatial behavior in the theory of swelling porous elastic soils

This paper is concerned with the study of the spatial behavior of the processes associated with a mixture consisting of three components: an elastic solid, a viscous fluid and a gas. An appropriate time-weighted surface power function is used in order to describe the spatial behavior of the processes in question. Spatial estimates of Saint–Venant type (for bounded bodies) and Phragmèn–Lindelöf type (for unbounded bodies) with time-dependent and time-independent rates are established. For unbounded bodies the asymptotic spatial behavior of the processes is also studied by means of an appropriate volumetric measure.     

Shrinking–swelling phenomenon of clay soils attributed to capillary-crack network

The shrinking and swelling behavior of clay soil is modeled by considering a capillary-crack network, the hydraulic conductivity of which is accounted for by the network tortuosity and specific crack length tracing a horizontal cross-section. Retention curve is determined by the total crack volume and volume of water filled cracks. Available data on hydraulic conductivity for two clay soils are compared with predictions and the agreements is good.     

Adsorption and strain: The CO2-induced swelling of coal

Enhanced coal bed methane recovery (ECBM) consists in injecting carbon dioxide in coal bed methane reservoirs in order to facilitate the recovery of the methane. The injected carbon dioxide gets adsorbed at the surface of the coal pores, which causes the coal to swell. This swelling in confined conditions leads to a closure of the coal reservoir cleat system, which hinders further injection. In this work we provide a comprehensive framework to calculate the macroscopic strains induced by adsorption in a porous medium from the molecular level. Using a thermodynamic approach we extend the realm of poromechanics to surface energy and surface stress. We then focus on how the surface stress is modified by adsorption and on how to estimate adsorption behavior with molecular simulations. The developed framework is here applied to the specific case of the swelling of CO₂-injected coal, although it is relevant to any problem in which adsorption in a porous medium causes strains.     

Penetration of rigid bodies into loose and layered media

Penetration and motion of rigid bodies in ground media attracts the researchers’ attention because of various problems arising as the technology evolves. In fact, there are two independent directions of studies in this field: (1) the problem of earth excavation when a rigid body of a definite shape slowly moves along a given trajectory in the ground; (2) an impact of a rapidly flying free rigid or deformable body against the ground. In the latter case, to which the proposed studies pertain, it is sometimes of interest to study the medium behavior and the motion of the free body, which moves in the medium after the impact owing to the kinetic energy of itself. In this field, a majority of studies deal with collision and penetration of bodies of various shapes into clay media. An extensive survey of these studies is given in [1]. After this survey appeared, numerous paper dealing with complicated collision conditions have been published [2]. Penetration in loose media has been studied much more rarely. The direct collision with fractured rock was studied in connection with the expected landing of spacecraft on other planets [3, 4]. In this case, the influence of grain dimensions and the density of the filling and vacuum on the penetration was studied for the initial velocities in the range of 1.7–10 m/s. On the other hand, in [5], the results of investigating the penetration of conic bodies in sand at entry velocities of 700–900 m/s are given; these velocities significantly exceed the speed of sound in this medium, which lies in the range of 100–200 m/s for dry sand. Analyzing the experimental results, the author came to the conclusion that it is necessary to use different representations of the drag force in the supersonic and subsonic modes. In the present paper, we do not consider the influence of the grain distribution, sand density, and filling methods on the penetration. But, as follows from the experiments whose results are described in [6] and [7], to represent the results of penetration of rigid bodies at velocities up to several hundreds of meters per second, in addition to the characteristics listed above, it is also required to describe the technology of the experiment preparation, because such media have the property of shape “memory.”     

Elasticity, fracture and yielding of cold compacted metal powders

The behaviour of powder compacts is modelled by explicitly introducing the possibility of plastic loading, elastic unloading and decohesion at contacts. The study is limited to cold compaction and to perfectly plastic materials for which the analysis of Mesarovic and Johnson (J. Mech. Phys. 48 (2000) 2009) is used. We model the compact behaviour both with an analytical approach based upon a mean field assumption and with the discrete element method (DEM) that allows force equilibrium to be treated in a realistic manner. Using these two approaches, we are able to predict the effective elastic properties of a powder compact at the onset of unloading. The knowledge of the conditions that lead to decohesion at the contact scale is used to model the fracture of the powder compact (green strength). It is shown that, in first approximation, green strength is inversely proportional to the size of the powder particles. The two methods are used to generate failure and yield surfaces for axisymmetric conditions. Both isostatic and close die conditions are studied.     

Mechanical response and modeling of fully compacted nanocrystalline iron and copper

A comprehensive study on the response of nanocrystalline iron and copper to quasi-static and dynamic loading is reported. Bulk solid nanocrystalline iron and copper specimens used in static and dynamic loading experiments were made by compaction and hot sintering of the nanocrystalline powders. The powders, with grain size 16–96 nm, were obtained by using high energy ball milling. The stress/strain response of dense nanocrystalline iron is found to be grain size and strain rate dependent. The KHL model is modified by incorporating Hall–Petch relation (i.e. yield stress dependence on grain size) and is used to represent the behavior of fully compacted nanocrystalline material. A good correlation with the experimental results is demonstrated.     

Comportement hydromécanique d'un sol gonflant compacté sous très fortes succionsHydromechanical behaviour of a compacted swelling soil under very high suctions

This paper presents a study performed on a compacted swelling material in the range of suctions comprised between 8.5 and 287.9 MPa. Two series of tests were carried out with suction controlled oedometers. The aim of the first series was to study the compressibility as a function of suction. It showed that the apparent preconsolidation pressure and the plastic compression line are greatly affected by the applied suctions. The other series of tests highlighted the influence of complex hydromechanical paths on the compressibility of the studied material that appeared to be greatly influenced by the stress path followed. To cite this article: O. Cuisinier, F. Masrouri, C. R. Mecanique 331 (2003).     

Equilibrium swelling and electrochemistry of polyampholytic pH-sensitive hydrogel

Immersed in an ionic solution, a network of polyampholytic polyelectrolyte imbibes the solution and swells, resulting in a polyampholytic pH-sensitive hydrogel, which can respond to changes in the surrounding environmental pH. The presence of fixed charges and mobile ions due to the dissociation of ionizable acidic and basic groups may give rise to a region called the electrical double layer of a thickness scaled by the Debye length. Owing to the existence of the electrical double layer, when the size of a polyampholytic pH-sensitive hydrogels is comparable to, or smaller than, the Debye length, the behavior of the gel may deviate from that of the gel of a large size. To account of the size effects, this paper develops a field theory for polyampholytic pH-sensitive hydrogels by coupling large deformation of the network, the dissociation of the functional groups and the migration of the ions and the solvent. The theory is then applied to explore the influence of pH, salt concentration, geometric constraint and the effects of the electrical double layer on swelling properties by analyzing a thin layer of a polyampholytic pH-sensitive hydrogel immersed in a solution.     

Relation between extrudate swelling of polypropylene and molecular weight

Six samples of polypropylene produced by Montepolimeri were carefully characterized in dilute solution and studied, with a capillary extrusion rheometer, in large ranges of shear and temperature. The extrudate swelling behaviour is found to be regular as far as its shear stress and temperature dependence is concerned, but the influence of molecular weight is abnormal. With increasing molecular weight the amount of elastic recovery (as measured by the extrudate swell) decreases markedly and the shear modulusG (obtained from the data by making use of simplifying assumptions) appears to be an increasing function ofM _w at all the shear stress investigated. No similar results appear to be reported in the literature.Presented in part at the VIIIth Intern. Congress on Rheology, Naples, September 1–5, 1980.     

A study of swelling and collapse in polyelectrolyte gels

Swelling and collapse of a polyelectrolyte are shown to be the result of a delicate balance of three thermodynamic forces, viz. osmotic pressure, polymer elasticity, and van der Waals attraction. The behaviour of the polyelectrolyte gel is studied under isotropic pressure and under uniaxial and biaxial loading.     

Simultaneous Measurement of Effective Chemical Shrinkage and Modulus Evolutions During Polymerization

A novel method is proposed to simultaneously measure the effective chemical shrinkage and modulus evolutions of advanced polymers during polymerization. The method utilizes glass fiber Bragg grating (FBG) sensors. They are embedded in two uncured cylindrical polymer specimens with different configurations and the Bragg wavelength (BW) shifts are continuously documented during the polymerization process. A theoretical relationship is derived between the BW shifts and the evolution properties, and an inverse numerical procedure to determine the properties from the BW shifts is established. Extensive numerical analyses are conducted to provide general guidelines for selecting an optimum combination of the two specimen configurations. The method is implemented for a high-temperature curing thermosetting polymer. Validity of the proposed method is corroborated by two independent verification experiments: a self-consistency test to verify the measurement accuracy of raw data and a warpage measurement test of a bi-material strip to verify the accuracy of evolution properties.