Most classical predictive models of unsaturated hydraulic conductivity conceptualize the pore space as either bundles of cylindrical tubes of uniform size or assemblies of cylindrical capillary tubes ...of various sizes. As such, these models have assumed that liquid configuration is the same in both the wet and dry ranges and that a single concept can be used to describe water transport over the entire range of matric head. Yet theoretical and experimental findings suggest that water transport in wet media, which mostly occurs in water saturated capillaries, is quite different from that in dry media, which occurs in thin liquid films. Following these observations, this paper proposes a new model for predicting the hydraulic conductivity of porous media that accounts for both capillary and thin film flow processes. As with other predictive models, a mathematical relationship is established between hydraulic conductivity and the water retention function. The model is mathematically simple and can easily be integrated into existing numerical models of water transport in unsaturated soils. In sample calculations, the model provided very good agreement with hydraulic conductivity data over the entire range of matric head. Two other well‐supported models, on the other hand, were unable to conform to the experimental data.
A dam's responses can be amplified by the geometry and flexibility of its surrounding canyon. To modeling a canyon as an elastic unbounded domain, the radiation damping condition should be satisfied, ...and in this regard, the Scaled Boundary Finite Element Method (SBFEM) is a powerful tool. In this article, a substructure method was used to combine the standard Finite Element Method (FEM) with the SBFEM, resulting in the hybrid FEM‐SBFEM technique. This hybrid technique treats an earth dam by using FEM and a corresponding elastic unbounded canyon by SBFEM. The proposed approach was verified by data available in the literature. The seismic response of an earth dam‐flexible canyon system was investigated by employing a 3D FEM‐SBFEM method. Several amplification functions corresponding to different canyon conditions were obtained by applying a uniform displacement for the canyon boundary, and a comprehensive study was performed to examine the effects of canyon geometry and flexibility on the steady‐state response of the dam, as these two effects influenced the amplification functions. While the flexibility of the canyon significantly affects the maximum amplification function value for a dam, this value does not change for earth dams in canyons with different shapes but the same length. In addition, the lateral response of earth dams in the time domain was computed in order to analyze the aforementioned effects under an actual earthquake. The proposed amplification functions were used to compare the recorded response spectra of the El Infiernillo dam under the two earthquakes in 1966 with the calculated amplification function, and a reasonable agreement was observed between them.
A number of investigations have shown that the shear strength of unsaturated soils can be defined in terms of effective stress. The difficulty in this approach lies in quantifying the effective ...stress parameter, or Bishop’s parameter. Although often set equal to the degree of saturation, it has recently been suggested that the effective stress parameter should be related to an effective degree of saturation, which defines the fraction of water that contributes to soil strength. A problematic element in this approach resides in differentiating the water that contributes to soil strength from that which does not contribute to soil strength. To address this difficulty, the paper uses theoretical considerations and experimental observations to partition the water retention function into capillary and adsorptive components. Given that the thin liquid films of adsorbed water should not contribute to effective stress, the effective stress parameter is solely related to the capillary component of water retention. In sample calculations, this alternative effective stress parameter provided very good agreement with experimental data of shear strength for a variety of soil types.
A one-dimensional model for the consolidation of thawing soils is formulated in terms of large-strain consolidation and heat-transfer equations. The model integrates heat transfer due to conduction, ...phase change, and advection. The hydromechanical behaviour is modelled by large-strain consolidation theory. The equations are coupled in a moving boundary scheme developed in Lagrangian coordinates. Finite strains are allowed and nonlinear effective stress – void ratio – hydraulic conductivity relationships are proposed to characterize the thawing soil properties. Initial conditions and boundary conditions are presented with special consideration for the moving boundary condition at the thaw front developed in terms of large-strain consolidation. The proposed model is applied and compared with small-strain thaw consolidation theory in a theoretical working example of a thawing fine-grained soil sample. The modelling results are presented in terms of temperature, thaw penetration, settlements, void ratio, and excess pore-water pressures.
In this study, new empirical predictive relationships for earthquake-induced crest settlement of earth-core rockfill dams (ECRDs) were developed. A case history database of 19 dams that had been ...subjected to earthquakes was utilized. The presented relationships correlate the intensity measure (IM) of the earthquake records with the observed settlements, and thus, employing IMs that appropriately describe the severity of ground motion is of vital importance. It is well known that the dynamic properties of an ECRD can change significantly depending on the severity of an earthquake, and that this phenomenon can substantially impact the dynamic responses of dams. Accordingly, two IMs were suggested, taking into account the essential characteristics of ground motions affecting the nonlinear behaviour of ECRDs. The results indicate that the proposed relationships effectively address the limitations of the existing ones, and that they are practical tools that efficiently predict the seismic settlements of ECRDs.
Hydraulic conductivity of frozen air‐free porous media is a rather elusive property that remains largely undefined in much of the literature. According to modern science, water transport in frozen ...porous media occurs mostly in ice‐free capillaries at temperatures close to the freezing point of pure water and through a thin liquid interlayer, between solid particle and ice, at lower temperatures. In accordance with this understanding, this paper extends the capabilities of an existing capillary and thin film flow model to include the prediction of hydraulic conductivity in frozen air‐free porous media. As such, hydraulic conductivity of the frozen porous media is predicted with a simple capillary bundle model as well as with a new hydrodynamic model of thin interlayer flow in which film thickness is controlled by both London‐van der Waals and ionic‐electrostatic forces. As with other predictive models of hydraulic conductivity, most model parameters are derived from more easily measured water content data in either ice‐free (water retention function) or air‐free (water freezing function) porous media. Model results showed very good agreement with observed values of hydraulic conductivity taken at thermal equilibrium, and illustrated the importance of thin interlayer flow at lower temperatures.
Key Points
A hydraulic conductivity model for air‐free frozen porous media is developed
A method for scaling water retention and water freezing functions is proposed
Thin liquid interlayers are vital in explaining flow at colder temperatures
The finite element method (FEM) is a powerful tool for the nonlinear modeling of dynamic problems. In the present work, the equivalent linear method (EQL) has been implemented into the FEM. For ...stratifying the radiation damping condition and rigorously modeling canyon as an elastic unbounded domain, the scaled boundary finite element method (SBFEM) was utilized. The FEM‐SBFEM technique, wherein FEM is coupled with SBFEM, has been extended to take into consideration the effect of earth dam material nonlinear behavior. It was observed that the nonlinear behavior greatly affects the natural frequency, the amplification function (AF), and peak crest acceleration of the earth dam located in canyons. The effects of canyon geometry and flexibility on the nonlinear behavior were examined, and it was seen that by increasing the flexibility of the canyon, the effect of nonlinearity was decreased. The El Infiernillo dam was modeled by 3D proposed technique, and a comparison of the crest AF obtained by the proposed method with the recorded data shows the accuracy of the methodology.
A simple, yet complete framework is introduced with the aim of modelling grain breakage in soils and crushable granular materials. The evolution of grain breakage is measured using a specific ...parameter of the grain-size distribution. The evolution of this new breakage parameter is related to the applied mechanical work, which allows the predictions to be independent of the stress paths. The correlation function proposed is trilinear, and is capable of describing the initiation, development, and stabilization of breakage. The initial state, coupled with three additional parameters, is used to calibrate this function. The three parameters are related to a grain specific quantity representing the strength of the particles that form the granular medium. The theory of fractal fragmentation is adopted, and the final state is considered to be unique and described by a single parameter: the fractal dimension. When tested against experimental results, this model was able to correctly predict the crushable behavior of a sand.
This study investigates three aspects of the dynamic response of earth-core rockfill dams (ECRDs) under earthquake loadings, including induced shear strain, increased fundamental period, and shear ...modulus reduction. A database of the recorded ground motions of ECRD cases in Japan is analyzed to carry out this study. The required response parameters as mentioned above are extracted by analyzing the acceleration time histories recorded at the dams’ crests and foundations. Subsequently, statistical analyses are performed to achieve the objectives of this study. A graph is developed describing the change in the dam’s fundamental period with the induced shear strain, and it is observed that the increase of the dam’s period is dependent on the increase in the shear strain levels. A relationship is established to estimate the anticipated levels of shear strain from the intensity measure (IM) of the earthquake signals. In the proposed predictive relationship, a new IM is used that can adequately characterize the severity of an earthquake. Finally, a curve and a range are suggested for the average shear modulus degradation of the ECRD’s core materials. The presented empirical graphs and relationships in this study are valuable tools to obtain an appropriate perception of dams’ nonlinear behaviour under strong earthquake excitations.
This paper intends to develop a generalized thermal conductivity model for moist soils that is based on the concept of normalized thermal conductivity with respect to dry and saturated states. This ...model integrates well the effects of porosity, degree of saturation, mineral content, grain-size distribution, and particle shape on the thermal conductivity of unfrozen and frozen soils. The thermal conductivity for saturated soils is computed with the use of a well-known geometric model that includes the unfrozen water content in frozen fine-grained soils. Nearly 220 experimental results available from the literature were analysed to develop a generalized empirical relationship to assess the thermal conductivity of dry soils. A general relationship between the normalized thermal conductivity of soils and the degree of saturation using a soil-type dependent factor was used to correlate the normalized thermal conductivity for more than 650 test results for unfrozen and frozen moist soils, such as gravels, sands, silts, clays, peat, and crushed rocks.Key words: heat transfer, soils, degree of saturation, mineral content, unfrozenfrozen, thermal conductivity.
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