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.



Cost Benefit Analysis (CBA) workshop in Stockholm

An open seminar and workshop in Stockholm will be held on 25-26 April 2018. The workshop deals with the use of CBA as a basis for decision-making in the public sector. The workshop is organized by, among others, Professor Jan-Eric Nilsson, VTI.

The 6st Humanist Conference

The 6th HUMANIST Conference will take place 13-14 June 2018 in the Hague, The Netherlands. The scope of the conference covers a wide range of topics on Human Factors in Transport. Tania Willstrand and Alexander Eriksson will present their research results.



VTI will develop simulators for ambulance staff

VTI has initiated a pilot study for paramedics with the Centre for Teaching & Research in Disaster Medicine and Traumatology and Linköping University. The aim is to give ambulance staff the opportunity to practice critical medical tasks in a moving vehicle in...


Unique electrified road opens in Sweden

The world’s first electrified road recharging the batteries of cars and trucks while driving opened in Sweden. The Swedish Minister for Infrastructure, Tomas Eneroth, was at the formal inauguration of the electrified road on April 11, 2018. VTI is one of 22...


Swedish road safety spreads internationally

Sweden is a leading country in terms of road safety, and the research conducted by the Swedish National Road and Transport Research Institute (VTI) has contributed to increased safety. VTI’s remit includes disseminating research results and keeping up to date...


A greater understanding of cyclists' behaviour

Cyclists are often accused of not following traffic rules and being hooligans on the road. New research shows that there is no support for this perception. "Our observations reveal no such general anarchy" says Sonja Forward, researcher at VTI.


New technology for road surface measurement tested

VTI has tested a new scanning-laser technology for road surface measurement. The tests show the new technology for comprehensive transverse-profile measurement provides dependable values in measuring transverse profile and rut depth.


Ulf Sandberg has been presented with the TTI Lifetime Achievement Award 2018

VTI’s Senior Research Leader Ulf Sandberg has been presented with the TTI Lifetime Achievement Award 2018 for his work on research into tyres and road surface.