Moisture sensitive and stress dependent behavior of pavement unbound materials from in situ falling weight deflectometer tests

Publisher's full text
Farhad Salour

In an instrumented flexible pavement with subsurface drainage system, a field study was performed to investigate the influence of water on the response of the pavement structure. The drainage system of the structure was clogged during a three-month period, allowing the groundwater to rise and the structure to undergo high moisture conditions. Thereafter the drainage was reopened allowing the structure to approach its previous draining hydrological state. Along with subsurface groundwater level and moisture content monitoring, the structural response of the pavement was studied by conducting frequent Falling Weight Deflectometer tests with multilevel loads. The stress sensitivity of the unbound layers and the influence of moisture on their stiffness were studied using the data with an effort to determine the unbound materials nonlinear parameters through a backcalculation algorithm. The groundwater level rose rapidly after the drainage was clogged. It significantly affected the overall stiffness of the pavement structure and the backcalculated stiffness of the unbound layers decreased as their moisture content increased. It was further observed that the unbound layers exhibited stress-dependent behavior to multilevel loads. The subgrade showed stress-softening response in unsaturated condition and stress-independent behavior in saturated state. The granular layer exhibited stress-hardening behavior. Backcalculation of the unbound nonlinear parameters according to the universal extended k-? model revealed that the k1 parameter decreased with increasing moisture content for both the unbound granular layer and the unsaturated fine grained subgrade material.



Shipping and the environment – research meets reality

Centre for Transport Studies (CTS) in co-operation with Ports of Stockholm invite you to the seminar Shipping and the environment – research meets reality.



Simulation of cut-in by manually driven vehicles in platooning scenarios

A study in a VTI-driving simulator has showed that a platoon will be able to handle a cut in from a manually driven car. The results of this study have recently been presented at two conferences in Japan.



The five-year anniversary of European Road Profile Users' Group (ERPUG) Forum will take place at Ramboll head quarter, Copenhagen, Denmark October 19-20, 2017.


Self-driving buses in Sweden next year?

A self-driving, fossil-free bus. This idea might become reality through a forthcoming collaborative project involving the Swedish National Road and Transport Research Institute (VTI), Linköping University and several other participants. The project group aim...


New climate-proof solutions for hard surfaces in cities

High-density road infrastructure that emphasise maximum durability and minimum maintenance create inflexible systems, which put increased stress on urban trees and lead to increased risk for flooding. Over the past five years, the ‘Climate-proof solutions for...


VTI is preparing for automated vehicles

Automation of traffic systems will lead to major changes. The European Union’s (EU) CoEXist research project began in June 2017 with the aim of preparing cities and road operators for the introduction of self-driving vehicles. The Swedish National Road and...


Vehicle Driver Monitoring: sleepiness and cognitive load

To prevent road crashes it is important to understand driver related contributing factors, which have been suggested to be the critical reason in 94 per cent of crashes. The overall aim of the project Vehicle Driver Monitoring has been to advance the...