2013 Session: 480

• Resilient and Permanent Deformation Characteristics of Unbound Pavement Layers Modified by Geogrids
  Abstract: The benefits of geogrids in reducing permanent deformation of flexible pavements are generally recognized and have been shown in numerous laboratory and field studies. On the other hand, although the resilient moduli of unbound pavement materials are important property inputs in the mechanistic-empirical (ME) pavement design process, the impact of geogrids on unbound layers’ resilient behavior remains unclear according to previous studies. The focus of this paper is on resilient behavior of unbound layers and permanent deformation of soft soil subgrade modified by geogrids placed at the base-subgrade interface. Two sets of reduced-scale accelerated pavement tests were conducted on scaled pavement structures built over two types of soft soil subgrade. Each set of accelerated tests consists of four sections, among which three sections were modified with different geogrids and one section left unmodified as a control. Instruments were embedded in the subgrade to measure resilient and permanent deformations of the subgrade. Nondestructive tests using a lightweight deflectometer (LWD) were conducted on pavement layers along with the progression of construction. Surface deflections and subgrade resilient deformation under the impulsive LWD loads were recorded. The test sections were then subjected to repetitive moving wheel loading by means of a one-third-scale model mobile load simulator (MMLS3). Subgrade resilient and permanent deformations were measured at intervals of the wheel load applications. The surface deflection measurements and instrumentation measurements of subgrade resilient deformation under the LWD load indicate that the geogrids did not have an appreciable impact on the resilient behavior of the base layer and subgrade. Subgrade resilient deformations measured along with the repetitive wheel loads also suggest that the effects of the geogrids on the resilient responses of the subgrade were not evident. However, through the two sets of accelerated tests, two of the geogrids consistently exhibited benefits in reducing the permanent deformation in the subgrade.
  Authors: Tang, Xiaochao; Stoffels, Shelley M.; Palomino, Angelica M.
  Authors: Tang, Xiaochao; Stoffels, Shelley M.; Palomino, Angelica M.
  Year: 2013
  Document Type: Paper
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-0479
• Evaluation of Permanent Deformation Characteristics of Unbound Granular Materials from Multistage Repeated-Load Triaxial Test
  Abstract: A simple time hardening approach was used to model the accumulation of permanent deformation of unbound granular materials (UGM) in multi-stage (MS) repeated load triaxial (RLT) tests. Some of the existing permanent deformation models were used to implement this method and one model was slightly modified to better suit this approach. These models were calibrated using data from MS RLT tests on three different UGM used in base layers of flexible pavement structures. The material parameters of the models were optimized using least square curve fitting method. The shakedown ranges for each stress path of the RLT tests were calculated and the models were compared to see how well they simulate these ranges. Generally, very good fit was obtained for these models with the modified model showing the best agreement.
  Authors: Erlingsson, Sigurdur; Rahman, Mohammad Shafiqur
  Authors: Erlingsson, Sigurdur; Rahman, Mohammad Shafiqur
  Year: 2013
  Document Type: Paper
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-1472
• Comparison of Isotropic and Cross-Anisotropic Analysis of Pavement Structures
  Abstract: In most existing pavement design methods, including South African Mechanistic Design Method (SAMDM), pavements are analyzed using linear elastic multilayer theory. In this approach, it is assumed that isotropic conditions are present in the structural layers of the pavement section. There are however numerous researchers that disagree with this statement and their research have proven that there are inherent and induced anisotropic material behaviors in the structural layers of a pavement section. The problem facing the SAMDM is that this anisotropic behavior of material may reduce the predicted life of pavement sections as described in the South African Technical Recommendations for Highway (TRH 4). The objective of this study was to determine if cross-anisotropic conditions induced in the pavement layer reduced the predicted life resulting in gross overestimation of the SAMDM in South Africa. During this study pavements were analyzed using cross-anisotropic conditions in the layers. The results from the analysis showed that the asphalt surfacing layer is very sensitive to cross-anisotropic conditions. The tendency is to reduce the predicted life drastically with any variation of stiffness modulus relative to each direction. The granular layer tends to reduced predicted life resulting in overestimation of current values in the TRH 4. The cemented layers show some increase in predicted life in the cemented phase but an overall tendency in decreased predicted life. The main conclusion evident from each layer is that the current design method in the SAMDM must include cross-anisotropic analysis to achieve more realistic values of predicted life for pavement sections.
  Authors: Steyn, Wynand Jacobus van der Merwe; Maina, James William; Repsold, Anton
  Authors: Steyn, Wynand Jacobus van der Merwe; Maina, James William; Repsold, Anton
  Year: 2013
  Document Type: Paper
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-1871
• Evaluation of Seasonal Variation in Pavement Mechanistic Responses Using Falling Weight Deflectometer Data
  Abstract: Pavement structures in regions with severe and frequent freeze and thaw cycles are prone to prompt damage. The pavement structure is in its weakest conditions right after the start of the thawing season each year. The existing practice followed by many highway agencies is to enforce spring road ban (SRB) during the critical thawing period. Alberta Transportation performs an extensive Falling Weight Deflectometer (FWD) test program during the spring to enhance SRB decision making process. In this study, the results from the FWD tests for multiple highway sections in Alberta from 2000 and 2006 were analyzed to investigate the effect of seasonal variation on pavement stiffness and mechanistic responses. The FWD data was used to backcalculate the pavement layers’ moduli and to predict two critical pavement responses of tensile strain at the bottom of the Asphalt Concrete layer and compressive strain at the top of the subgrade in spring and summer. The Asphalt Institute’s predictive models for fatigue cracking and rutting failures were used to relate the pavement responses to the allowable number of load repetitions (Nf for fatigue and Nd for rutting). The comparison of Nf and Nd between the spring and summer shows differences of as high as 88 percent for Nf and 98 percent for Nd. Further analysis showed that a 50% reduction in the load during the critical period of spring can result in about a 90% increase in the Nd and Nf.
  Authors: Norouzi, Meisam; Nassiri, Somayeh; Bayat, Alireza
  Authors: Norouzi, Meisam; Nassiri, Somayeh; Bayat, Alireza
  Year: 2013
  Document Type: Paper
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-3346
• Resilient and Permanent Deformation Characteristics of Unbound Pavement Layers Modified by Geogrids
  Authors: Tang, Xiaochao
  Authors: Tang, Xiaochao
  Year: 2013
  Document Type: Presentation
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-0479
• Comparison of Isotropic and Cross-Anisotropic Analysis of Pavement Structures
  Authors: Repsold, Anton
  Authors: Repsold, Anton
  Year: 2013
  Document Type: Presentation
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-1871
• Evaluation of Permanent Deformation Characteristics of Unbound Granular Materials from Multistage Repeated-Load Triaxial Test
  Authors: Erlingsson, Sigurdur
  Authors: Erlingsson, Sigurdur
  Year: 2013
  Document Type: Presentation
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-1472
• Evaluation of Seasonal Variation in Pavement Mechanistic Responses Using Falling Weight Deflectometer Data
  Authors: Nassiri, Somayeh
  Authors: Nassiri, Somayeh
  Year: 2013
  Document Type: Presentation
  Subject: Design; Pavements
  Session: 480
  Paper Number: 13-3346