Soil Model (soil + model)

Distribution by Scientific Domains


Selected Abstracts


Measurement and computation of ground resistances at 161/23.9,11.95-kV indoor-type substations

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2009
Cheng-Nan Chang
Abstract The purpose of this paper is to compare the calculated and actual ground resistances at two 161/23.9,11.95-kV indoor-type substations in the system of Taiwan Power Company. For the calculated ground resistances, one- and two-layer soil models based on Sverak and Schwarz equations, the method of images and the current distribution electromagnetic grounding and soil structure analysis (CDEGS) program are performed. As for the actual ground resistances, they are found by subtracting the measured ground resistances which are obtained by the fall-of-potential method from the earth mutual resistances. As a result, the calculated ground resistance based on the method of images as the observation point located at the lower layer of the two-layer soil model is approximately equal to the actual ground resistance measured by the fall-of-potential method with the potential electrode buried at the lower layer. In addition, the ground potential rises (GPRs) at both substations are computed and compared with the minimum touch voltages for assessing the grounding system safety. The result shows that the design of the grounding system at both substations is unsafe under the one-layer soil model for humans with 50 and 70,kg body weight. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Assessing the impact of the hydraulic properties of a crusted soil on overland flow modelling at the field scale

HYDROLOGICAL PROCESSES, Issue 8 2006
Nanée Chahinian
Abstract Soil surface crusts are widely reported to favour Hortonian runoff, but are not explicitly represented in most rainfall-runoff models. The aim of this paper is to assess the impact of soil surface crusts on infiltration and runoff modelling at two spatial scales, i.e. the local scale and the plot scale. At the local scale, two separate single ring infiltration experiments are undertaken. The first is performed on the undisturbed soil, whereas the second is done after removal of the soil surface crust. The HYDRUS 2D two-dimensional vertical infiltration model is then used in an inverse modelling approach, first to estimate the soil hydraulic properties of the crust and the subsoil, and then the effective hydraulic properties of the soil represented as a single uniform layer. The results show that the crust hydraulic conductivity is 10 times lower than that of the subsoil, thus illustrating the limiting role the crust has on infiltration. Moving up to the plot scale, a rainfall-runoff model coupling the Richards equation to a transfer function is used to simulate Hortonian overland flow hydrographs. The previously calculated hydraulic properties are used, and a comparison is undertaken between a single-layer and a double-layer representation of the crusted soil. The results of the rainfall-runoff model show that the soil hydraulic properties calculated at the local scale give acceptable results when used to model runoff at the plot scale directly, without any numerical calibration. Also, at the plot scale, no clear improvement of the results can be seen when using a double-layer representation of the soil in comparison with a single homogeneous layer. This is due to the hydrological characteristics of Hortonian runoff, which is triggered by a rainfall intensity exceeding the saturated hydraulic conductivity of the soil surface. Consequently, the rainfall-runoff model is more sensitive to rainfall than to the subsoil's hydrodynamic properties. Therefore, the use of a double-layer soil model to represent runoff on a crusted soil does not seem necessary, as the increase of precision in the soil discretization is not justified by a better performance of the model. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Wave propagation in nonlinear one-dimensional soil model

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2009
J. Ahn
Abstract The objective of the research conducted by the authors is to explore the feasibility of determining reliable in situ values of shear modulus as a function of strain. In this paper the meaning of the material stiffness obtained from impact and harmonic excitation tests on a surface slab is discussed. A one-dimensional discrete model with the nonlinear material stiffness is used for this purpose. When a static load is applied followed by an impact excitation, if the amplitude of the impact is very small, the measured wave velocity using the cross-correlation indicates the wave velocity calculated from the tangent modulus corresponding to the state of stress caused by the applied static load. The duration of the impact affects the magnitude of the displacement and the particle velocity but has very little effect on the estimation of the wave velocity for the magnitudes considered herein. When a harmonic excitation is applied, the cross-correlation of the time histories at different depths estimates a wave velocity close to the one calculated from the secant modulus in the stress,strain loop under steady-state condition. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Skin friction features of drilled CIP piles in sand from pile segment analysis

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2008
Sungjune Lee
Abstract Numerical pile segment analysis is conducted in this study with an advanced soil model to investigate the skin friction behaviour of a drilled Cast-In-Place (CIP) pile installed in sand. Although the interface between the sand and pile is considered rough, thin elements adjacent to the pile are used to include effects of localized shear. Unit weights of fluid concrete and accompanied changes in stress are considered as the effects of pile installation. Changes in effective stresses are the most prominent effect due to pile installation with a change in direction of the major principal stress from the vertical to the radial direction. Shear behaviour of the sand at the interface during the early shear stage is related to the contractive tendency of the sand at small strain levels. Changes in the stress field around the pile with little changes in volumetric strain take place during the early shear stage. Stress redistributions during the early shear stage depend on the direction of the major principal stress before shear. Results of the pile segment analyses for drilled CIP piles show good agreement with design methods. Parametric studies are used to characterize the effects of sand density and pile diameter on the skin friction behaviour of drilled CIP piles. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Generalized trapezoidal numerical integration of an advanced soil model

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2008
Yunming Yang
Abstract This paper investigates the numerical performance of the generalized trapezoidal integration rule by using an advanced soil model. The generalized trapezoidal integration rule can include many other integration algorithms by adjusting a single parameter , ranging from 1 to 0. The soil model used is the recently developed middle surface concept (MSC) sand model which simulates different soil response characteristics by using different pseudo-yield functions. The generalized trapezoidal rule and MSC sand model are used to simulate the responses of sand samples with different relative densities under various initial and loading conditions. Instead of a single step, multiple loading steps bring the sample to the vicinity of failure. These comprehensive investigations examine and compare the influences of various values of , on the numerical solution of integrated constitutive equations, the convergence of Newton's iterative scheme, and the integration accuracy. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Load-displacement and bearing capacity of foundations on granular soils using a multi-surface kinematic constitutive soil model

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2006
M. Banimahd
Abstract A finite element approach based on an advanced multi-surface kinematic constitutive model is used to evaluate the bearing capacity of footings resting on granular soils. Unlike simple elastic-perfectly plastic models, often applied to granular foundation problems, the present model realistically accounts for stress dependency of the friction angle, strain softening,hardening and non-associativity. After the model and its implementation into a finite element code are briefly discussed, the numerical difficulty due to the singularity at the footing edge is addressed. The bearing capacity factor N, is then calculated for different granular materials. The effect of footing size, shape, relative density and roughness on the ultimate bearing capacity are studied and the computed results compare very favourably with the general experimental trends. In addition, it is shown that the finite element solution can clearly represent counteracting mechanisms of progressive failure which have an important effect on the bearing capacity of granular foundations. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Development of hyperplasticity models for soil mechanics

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2006
S. Likitlersuang
Abstract Hyperplasticity theory was developed by Collins and Houlsby (Proc. Roy. Soc. Lon. A 1997; 453:1975,2001) and Houlsby and Puzrin (Int. J. Plasticity 2000; 16(9):1017,1047). Further research has extended the method to continuous hyperplasticity, in which smooth transitions between elastic and plastic behaviour can be modelled. This paper illustrates a development of a new constitutive model for soils using hyperplasticity theory. The research begins with a simple one-dimensional elasticity model. This is extended in stages to an elasto-plastic model with a continuous internal function. The research aims to develop a soil model, which addresses some of the shortcomings of the modified cam-clay model, specifically the fact that it cannot model small strain stiffness, or the effects of immediate stress history. All expressions used are consistent with critical state soil mechanics terminology. Finally, a numerical implementation of the model using a rate-dependent algorithm is described. Copyright © 2005 John Wiley & Sons, Ltd. [source]


A three-phase soil model for simulating stress wave propagation due to blast loading

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2004
Zhongqi Wang
Abstract A three-phase soil model is proposed to simulate stress wave propagation in soil mass to blast loading. The soil is modelled as a three-phase mass that includes the solid particles, water and air. It is considered as a structure that the solid particles form a skeleton and their voids are filled with water and air. The equation of state (EOS) of the soil is derived. The elastic,plastic theory is adopted to model the constitutive relation of the soil skeleton. The damage of the soil skeleton is also modelled. The Drucker,Prager strength model including the strain rate effect is used to describe the strength of the soil skeleton. The model is implemented into a hydrocode Autodyn. The recorded results obtained by explosion tests in soil are used to validate the proposed model. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Involutions resulting from annual freeze,thaw cycles: a laboratory simulation based on observations in northeastern Japan

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2007
Yoshiko Ogino
Abstract A pilot laboratory experiment using a reversed two-layer soil model simulated small-scale involutions formed in a seasonal frost environment during the last glacial period. At the modelled site, the interface between the upper aeolian sandy loam and the lower volcanic pumice constitutes small-scale involutions that display upward-extending tapered projections and downward-extending round hollows. Two scale-reduced laboratory models were subjected to three accelerated annual freeze,thaw cycles with monitoring of frost heave, soil temperature, moisture and pressure. Ice segregation near the layer interface induces upheaving of coarse pumice grains on freezing and earlier settlement of mobilised loam on thawing, resulting in deformation of the interface. A reconstructed 3-D interface displays mounds and depressions with a diameter of 15,20,cm and a height increasing with freeze, thaw alternations. The experimental results imply that the repetition of differential heave and soft-loam settlement promotes decimetre-scale involutions in near-saturated soils subject to deep seasonal frost penetration. Copyright © 2007 John Wiley & Sons, Ltd. [source]