Micromechanics of steady state, collapse and stress-strain modeling of soils

Increased evidence of the influence of their discrete nature on the observed behavior of soils has prompted a number of investigators to look at these materials at the microstructural level of these materials. This study follows along this line of approach. The soil material behavior and response is considered herein as the resultant of the behavior of microsystems. It is shown that a comprehensive description of particulate media can be achieved via two measures: a scalar measure giving the mean value of a fabric descriptor, and a tensor measure giving its distribution. The development allows the fabric descriptors based on the solid phase or the void phase to be treated in a unified manner. The description based on void phase is shown to be more powerful because its parameters are easier to determine experimentally. A technique based on an extension to the classical stereological principle is presented to determine the parameters from observations made with an image analyzer or scanning electron microscope. Examples illustrating its use in soil mechanics are highlighted. A simplified fabric parameter derived from the tensor measure is shown to be powerful in studying the evolution of fabric of soils under shear deformation. Based on the evolution of this fabric parameter, it is proposed that irrespective of their insitu nature of fabric, soils do tend to attain an ultimate structural arrangement specific to an imposed shear loading path. These developments on the mathematical characterization of fabric are used to evaluate some important concepts in soil mechanics in detail, including the question of the uniqueness of the critical state line and the state boundary surface. A generalized concept of an ultimate state surface for soils is proposed. It is shown that this surface reduces to the classical critical state line when fabric effects are neglected. Finally, the application of thermomechanics as an alternative to plasticity theory in developing simple constitutive models for soils is discussed. This theory allows the systematic incorporation of fabric concept and leads to the development of a simple stress-strain model for soils. The new model is a simple extension to the Modified Cam-Clay model with the consideration of fabric change. For simplicity in presentation the model is developed for axi-symmetric conditions. It could however be extended to a general three-dimensional space and incorporated in numerical codes

Determination of Creep Compliance and Indirect Tensile Strength for the Mechanistic-Empirical Pavement Design Guide (MEPDG)

This report provides details of the research, including data analyses and results, conducted into creep compliance and indirect tensile strength tests for use in the Mechanistic Empirical Pavement Design Guide (MEPDG). The study was conducted on field cores from the Idaho Transportation Department as part of an ongoing project at the University of Idaho. The data reported in this study were provided to University of Idaho researchers for use in the AASHTOWare Pavement ME thermal cracking database. By means of this database thermal cracking models in the AASHTOWare Pavement ME can be calibrated for the mixes used by the state of Idaho. Such local calibration will increase the reliability of these models for pavement design in Idaho.Pacific Northwest Transportation Consortiu

Development of Asphalt Materials to Mitigate Studded Tire Wear of Pavements

This study deals with the PacTrans theme of “Developing Data Driven Solutions and Decision-Making for Safe Transport.” Currently, all four northwestern states, including Alaska, Idaho, Oregon, and Washington, allow the use of studded tire. Studded tire can dig into asphalt pavement and pick out the small aggregate and eventually result into pavement rutting (1). Rutting was reported as one of the most important reasons of vehicle hydroplaning and loss of skid resistance in wet weather and can be closely related with traffic accidents during night and accidents under rain weather conditions (2, 3). Each year, millions of dollars are spent to repair/rehabilitate the wear from the studded tire. Developing pavement surface materials that resist studded tire wear will greatly improve the conditions of pavements, and reduce the traffic accidents and repair/rehabilitation costs associated with the studded tire wear. Therefore, the objectives of this proposed study is to determine potential material and mix design variables towards development of a wear-resistant asphalt mix.Pacific Northwest Transportation Consortiu

Nonlinear analysis for a single vertical drain including the effects of reloading considering the compressibility and permeability of the soil

In this paper, the free strain radial consolidation theory incorporating the changes of compressibility and permeability of the soil with the change in effective stress via time dependent surcharge preloading is presented. In contrast to the conventional analysis, the current study highlights the nonlinear characteristics of the soil during the consolidation process. A comparison of the nonlinear radial consolidation model, with the conventional theory and the equal strain theory i.e. constant volume compressibility, mv and constant coefficient of horizontal permeability, kh is presented. Finally, a case history at Muar coastal plain, Malaysia is analysed on the basis of the current solution. This case history indicates improved accuracy of the predictions in relation to the field measurements and observations