Date of Award
Doctor of Engineering (DEng)
Materials and Infrastructure Systems
The purpose of this project was to study the effects of fines (minus #4 sieve) on permeability and stiffness characteristics of unbound base materials and to propose an optimumgradation that will satisfy these two parameters. One type of highway base material--crushed limestone--was used in the study. A total of 75 laboratory tests were conducted and distributed--25 respectively on permeability, resilient modulus and unconfined compression. The permeability test data were collected using a low-head permeameter. The resilient modulus and unconfined compression test data were collected by the mean of the MTS (Machine Testing System) with a load cell capacity of 22-kips. The major steps of the research are summarized as follows: (A) Conduct intensive laboratory testing on open and dense-graded materials with respect to their drainage (permeability) and stiffness (resilient modulus and unconfined compressive strength) characteristics. The determination of permeability is necessary if an evaluation of drainage capability of an existing or new base layer is needed. The determination of the resilient modulus is necessary because it is an input data for pavement design using the AASHTO procedure. (B) Perform permeability and resilient modulus tests to study the effect of introducing fines (percent passing #4) to open-graded base layers on permeability and resilient modulus. (C) From the data collected from these tests on both drainage and strength characteristics, perform regression analysis to develop formulas that relate percent fines to permeability and to resilient modulus. (D) Combine the tests results from permeability and resilient modulus to provide a range of percent fines gradation band that will satisfy the two parameters as pavement design inputs. (E) Provide some tools and techniques used to prevent the base course from being contaminated by subgrade material and to check whether the proposed base course is able to drain water as quickly as possible. The project produced some formulas that predict the coefficient of permeability for pavement base materials, unconfined compression strength, and resilient modulus. The study also provided an optimum gradation, permeable enough to withstand heavy traffic. A highway engineer can use these equations to estimate the coefficients of permeability and resilient modulus of aggregate bases for preliminary design or for evaluation of an existing unbound pavement layer.
Issa, Moussa, "" (1999). Dissertation. 749.