A STUDY OF PERMANENT DEFORMATION BEHAVIOR OF GEOGRID-REINFORCED FLEXIBLE PAVEMENTS USING SMALL SCALE ACCELERATED PAVEMENT TESTING
Open Access
- Author:
- Tang, Xiaochao
- Graduate Program:
- Civil Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 17, 2010
- Committee Members:
- Angelica Palomino, Dissertation Advisor/Co-Advisor
Angelica M Palomino, Committee Chair/Co-Chair
Shelley Marie Stoffels, Committee Chair/Co-Chair
Maria Lopez De Murphy, Committee Member
Charles E Bakis, Committee Member - Keywords:
- pavements
geogrid
soft soil subgrade
accelerated testing
instrumentation
mechanistic empirical design
finite element - Abstract:
- A total of four different geogrid products were subjected to an in-depth investigation through multi-scale tests: in-air index testing, bench-scale testing, and pit-scale accelerated pavement testing. Basic geometric characteristics and mechanical properties of the geogrids, particularly tensile behavior at small displacements, were tested in air, followed by bench-scale testing, namely pullout and direct shear tests with geogrids embedded in pavement materials to characterize the geogrid-pavement interfaces. The geogrids were further tested within scaled pavement sections using the one-third model mobile load simulator (MMLS3). During the accelerated testing, both elastic and permanent deformations at the top of the subgrade, vertical stress on top of the subgrade, and strains developed in geogrids were measured in addition to the surface rutting/total permanent deformation of the pavement sections at different stages of MMLS3 load applications. A finite element (FE) response model was created and calibrated through an inverse procedure based on the measurement of elastic pavement responses. Compressive strains in the pavement were extracted from the FE models for the subsequent development of subgrade permanent deformation models. A correlation study between the tested geogrid index properties, interface characterizations, and the accelerated tests on subgrade permanent deformation indicates that the geogrid tensile modulus and the geogrid-pavement materials interface shear modulus at small displacements play critical roles in affecting the performance of the geogrids while reinforcing the pavement subgrade. It is noted that the correlation was developed on the basis of a limited number of tested samples. The tensile modulus and interface shear modulus were incorporated into the FE model. In light of the widely-recognized mechanistic-empirical (ME) approach to pavement design, attempts were made to develop a model for predicting permanent deformation of the geogrid-stabilized subgrade. The model adopted in the Mechanistic-Empirical Pavement Design Guide (MEPDG) for permanent deformation of unbound pavement layers was modified to accommodate the testing conditions in this study. The model was then calibrated and verified by using the measurements from accelerated tests. It was found that the model underestimated the subgrade permanent deformation to various degrees, although the model was able to predict the rank of the performance among the sections.