Behavior Of Subgrade Research Articles

Receptance behaviour of railway track and subgrade

Vertical dynamic behaviour of a railway track on an elastic halfspace or on a layered halfspace is investigated by a frequency domain analysis. The results are compared with those for a simpler model, where ballast and subgrade are considered as a viscoelastic foundation. In the low- and medium-frequency range up to 250 Hz, great differences are observed between the results of the halfspace model and the results of the viscoelastic foundation model. This is because the damping due to wave propagation and coupling between sleepers cannot be modelled correctly by a viscoelastic foundation. Contradictions observed in the past between measured and calculated results can be explained with the new halfspace model. For frequencies higher than 250 Hz, the influence of the subgrade is negligible, so that here the simpler viscoelastic foundation model can be used.

Load-Carrying Capacity for Concrete Slabs on Grade

A finite-element method is used to analyze a full range of stress and deformation behavior for a concrete slab on grade. The slab is axisymmetrical, one with its circumference restrained horizontally, simulating a portion of a slab with infinite extent. The load is applied on a small circular area located at the center. Winkler's assumption is used to study the subgrade behavior. Using Ottosen's failure criterion for concrete under a multiaxial stress state and considering the nonlinear behavior of concrete, the subgrade reaction, displacement of slab, stresses, bending moments, horizontal thrusts in slab, and position of cracks, and so on are obtained. The analytical results were found to compare well with test observations. Based on this finite-element analysis, a new analytical method for computing the ultimate load-carrying capacity of concrete slabs on grade is proposed.

Simplified subgrade model for three-dimensional soil-foundation interaction analysis

A simple mechanical model is presented for the three-dimensional dynamic soil-structure interaction analysis of surface foundations. The model is made of one-dimensional vertical beams with distributed mass and horizontal springs which interconnect the two adjacent beams. Its parameters are rather uniquely related with the soil properties alone and thus are minimally dependent on the loading condition and the foundation conditions like geometry, flexibility and size. Formulations are provided to determine the model parameters from the soil properties. Solving the governing equations of this model, expressions for the subgrade behavior in response to the applied load and soil-foundation interaction are developed in analytical forms for various cases. The dynamic and static response of three-dimensional surface foundations are computed by these expressions. It is verified that the model is well capable of reproducing the three-dimensional soil-structure interaction behavior.

Steady‐state harmonic response of a rigid plate bearing on a liquid‐saturated poroelastic halfspace

AbstractSoil–structure interaction problems are typically modelled by assuming subgrade behaviour to be either elastic or viscoelastic. Herein, compliance functions that may be used to solve soil–structure interaction problems are evaluated by treating the subgrade as a liquid‐saturated poroelastic material whose behaviour is governed by Biot's theory.The compliances are evaluated for the harmonic rocking and vertical motions of rigid permeable and impermeable plates bearing on a poroelastic halfspace. Comparisons are made with elastic solutions which assume the subgrade to be either completely drained or undrained. Also, solid and fluid contact stresses are reported for the poroelastic case and compared to the solid contact stresses for the elastic cases.

Problems Of Off-Road Transportation

Off-road transportation or land locomotion mechanics differs from the usual concept of highway engineering in regard to the relationship between a motor vehicle and the environment of its operation. The basic philosophy underlying highway engineering is that of modifying the environment by means of pavement design to fit the needs of a wheeled vehicle. Off-road transportation or locomotion differs in that soil is the medium in which the vehicle moves and there is no opportunity to transform the existing conditions, much the same as an airplane cannot modify the air in which it travels. Off-road vehicle performance is directly related to the shearing strength and deformation characteristics of soil as they affect tractive effort and sinkage. The status of some current (1963) mobility research projects dealing with deformable soils is summarized. The soil value measurement and evaluation programs for off-road transportation purposes should prove to be of interest to the highway engineer in a more comprehensive understanding of subgrade behavior relative to pavement choice and design.