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Pavement Behavior Evaluation During Spring Thaw Based on the Falling Weight Deflectometer Method

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Pavement Behavior Evaluation During Spring Thaw Based on the Falling Weight Deflectometer Method Pavement Behavior Evaluation during Spring Thaw based on the Falling Weight Deflectometer Method Degree Project in Highway Engineering Berglind Ösp Sveinsdóttir Division of Highway and Railway Engineering Department of Civil and Architectural Engineering Royal Institute of Technology SE-100 44 Stockholm TRITA-VBT 11:02 ISSN 1650-867X ISRN KTH/VBT-11/02-SE Stockholm 2011 Pavement Behavior Evaluation during Spring Thaw based on the Falling Weight Deflectometer Method Berglind Ösp Sveinsdóttir Division of Highway and Railway Engineering School of Architecture and the Built Environment Royal Institute of Technology (KTH) SE - 100 44 Stockholm [email protected] i ii Abstract: The bearing capacity of a road decreases greatly during spring thaw, when the previously frozen road begins to thaw. The extent of this decrease can be evaluated by making Falling Weight Deflectomter (FWD) measurements on the road, measuring the deflection of the road when an impact load is applied to it. The bearing capacity of the road can then be evaluated by backcalculating the layer modules with backcalculation programs, or through more simple calculations based on the deflection basin indices. Both analyses were carried out in this thesis with data from FWD measurements which were carried out on county road Lv 126 in Southern Sweden during the year 2010. The temperature and moisture content of the road were monitored during the same time. The aim with the thesis was to compare the two ways of analyses, and to find out if there is some relationship between them and the measured environmental data. The results showed that the base course layer and subbase decreased in stiffness during spring thaw about 50% while the decrease in the subgrade was 20%, compared to the backcalculated summer and autumn value. The results of the simple calculations from the deflection basin indices were well comparable to the backcalculation results. By comparing the backcalculated stiffness values to the moisture content measurements it was stated that the stiffness decreased as the moisture content increased. KEY WORDS: Falling Weight Deflectometer (FWD), multilayer elastic theory, backcalculation, deflection basin indices, EVERCALC, spring thaw weakening, bearing capacity of roads, moisture content, temperature. iii iv Sammanfattning: Vägens bärförmåga minskar markant under tjällossningsperioden, då den tidigare frusna vägen börjar tina. Omfattningen av minskningen kan utvärderas genom fallviktsmätningar, där vägens deformation mäts då den blir utsatt för en pålagd last. Bärförmågan bedöms genom att bakberäkna lagers moduler med bakberäknings program, eller genom mer enklare beräkningar baserad på deflektionsindexen. Båda dessa analyser har tillämpats i detta examensarbete med data från fallvikstmätningar från länsväg 126 i södra Sverige utförda under år 2010. Vägens temperatur och fukthalt kontrollerades under samma period. Syftet med examensarbetet var att jämföra de två analysmetoderna och se om det finns något samband mellan dem och uppmätt klimatdata. Resultaten visade att bär- och förstärkningslagrets bärförmåga minskade med 50% under tjällossningen, medan minskningen i terrassmaterialet var 20%, detta jämfört med bakberäknade sommar- och höstvärden. Resultaten av de enkla beräkningarna från deflektionsindexen stämde väl överens med bakberäkningsresultaten. En jämförelse mellan de bakberäknade styvhetsvärdena och fukthaltsmätningarna visade att styvheten minskade då fukthalten steg. NYCKELORD: Fallviktsdeflektometer, linjär elasticitetsteori, bakberäkningar, EVERCALC, deflektionsindex, tjällossningsperiod, vägens bärförmåga, fukthalt, temperatur. v vi Acknowledgements I would like to express my gratitude to those who helped me on this thesis and give special thanks to: Sigurður Erlingsson – for his excellent guidance and interest in the project. Michael T. Behn – for his review and helpful comments. Sweco – for accommodating me. My family and friends – for all their help and support throughout my studies. vii viii List of Symbols Normalized basin area Η Constant of integration for layer i Contact radius Base Curvature Index Base Damage Index Η Constant of integration for layer i Constant = 0.065 Η Constant of integration for layer i Η Constant of integration for layer i / Deflection i Π Diameter on the particle-size distribution curve, representing % fines ͤ Maximum deflection " Depth Elastic modulus of a bounded layer Έ Elastic modulus of the asphalt layer at a certain temperature Έ°£¤ Reference modulus of the asphalt layer at the reference temperature ΠΓΔ # Void ratio ͦ Deflection factor for a two-layer system Thickness of all layers combined &Η Thickness of layer i ͤ Bessel function of first kind and order 0 Π Resilient modulus of an unbounded layer + Parameter for layered system +Ρ Mass of solids +΢ Total mass of solid and water +Υ Mass of water , Porosity " Point load / Axisymmetric load /ʚ0ʛ Pressure under a rigid plate as a function of 0 ix 0 Radial distance ' Degree of saturation ' Surface Curvature Index Temperature ΠΓΔ Reference temperature = 10°C 3 Displacement in the radial or r direction ) Volume of soil )Ώ Volume of air )Ρ Volume of solids )Τ Volume of voids )Υ Volume of water , Weight of a soil 5 Displacement in the vertical or z direction / Gravimetric moisture content 5Δ Vertical deflection for flexible plate 5Π Vertical deflection for rigid plate 8 Vertical distance MΎ Vertical deflection on the surface of a half-space NΠ Radial strain N΢ Tangential strain NΨ Vertical strain Q Volumetric moisture content U Dimensionless vertical distance, &Η W Poisson Ratio [ Dimensionless radial distance, 0 [Υ Water density [Β Dry density of a material \Π Radial stress \Πͥ Radial stress at bottom of layer 1 ɑ \Πͥ Radial stress at top of layer 2 \Πͦ Radial stress at bottom of layer 2 x ɑ \Πͦ Radial stress at top of layer 3 \΢ Tangential stress \Ψ Vertical stress \Ψͥ Vertical stress at interface 1 \Ψͦ Vertical stress at interface 2 ^ΠΨ Shear stresses on 0 plane in 8 direction Ĝ Stress function ĜΗ Stress function for layer i xi xii List of Abbreviations AC - Asphalt Concrete AADT - Annual Average Daily Traffic APT - Accelerated Pavement Testing BC - Base Course FWD - Falling Weight Deflectometer GPS - Global Position System HWD - Heavy Weight Deflectometer HMA - Hot Mix Asphalt LFWD - Light Falling Weight Deflectometer MABT - Mjuk Asfaltbetong, tät (Soft Asphalt Concrete, tight) NDT - Nondestructive Testing RDD - Rolling Dynamic Deflectometer RMS - Root Mean Square Sb - Subbase Sg - Subgrade USFS - The U.S. Department of Agricultural Service VTI - Statens Väg- och Transportforskningsinstitut (Swedish National Road and Transport Research Institute) WASHO - Western Association of State Highway Officials WESLEA - Waterways Experiment Station Layered Elastic Analysis WSDOT - Washington State Department of Transportation xiii xiv Table of Contents Abstract: .......................................................................................................... iii Sammanfattning: ............................................................................................... v Acknowledgements .........................................................................................vii List of Symbols ................................................................................................ ix List of Abbreviations ..................................................................................... xiii Table of Contents ............................................................................................ xv 1. Introduction .................................................................................................. 1 2. Literature review .......................................................................................... 3 2.1 Nondestructive testing of pavements ............................................................ 3 2.1.1 Static loading method ............................................................................ 4 2.1.2 Steady state loading method .................................................................. 5 2.1.3 Dynamic impulse loading method ......................................................... 5 2.1.4 Factors that influence the measured deflections .................................... 6 2.2 Flexible pavements ....................................................................................... 7 2.3 The history of the Falling Weight Deflectometer (FWD) ............................. 8 2.4 Errors in FWD data....................................................................................... 9 2.5 Backcalculations during spring thaw ............................................................ 9 2.5.1 History of backcalculations ................................................................. 10 2.5.2 Changes in resilient modulus over time and space .............................. 10 2.5.3 The pavement model ........................................................................... 11 3. Theory ........................................................................................................ 13 3.1 Response analysis ....................................................................................... 13 3.1.1 One-layer systems................................................................................ 13 3.1.2 Axisymmetric solutions ....................................................................... 15 3.1.3 Layered systems .................................................................................
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