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A Simplified Mechanistic Rut Depth Prediction Procedure for Low-Volume Roads

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A Simplified Mechanistic Rut Depth Prediction Procedure for Low-Volume Roads Technical I<eport Documentatian Page 1. Report No. 2. Government Accession No. 3. ,Recipient" s Catalog No. FHWA/TX-89/473-1 4. Title and Subtitle 5. Report Date A Simplified Mechanistic Rut Depth Prediction December 1988 -- -Procedure for Low-Volume Roads 6. Performing Orgoni lolion-Code ~~------------~--~----~ h:--:-:::--;-;--------------------------~ 8. Performing Organi lotion Report No. 7. Author' 5) Kashyapa A. S. Yapa and Robert L. Lytton Research Report 473-1 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Texas Transportation Institute II. Contract or Grant No. The Texas A&M University System Study No. 2-18-87-473 College Station, Texas 77843-3135 r,-;;--;-_---:-_-:-_-:-:__ -:--:-:-:-- ________________-I 13. Type of Report and Period Cayered 12. Sponsoring Agency Name and Addre .. · September 1986 I n t erl.m - Texas State Department of Highways and Public December 1988 Transportation; Transportation Planning Division P.O. Box 5051 14. Sponsori ng Agency Code A'\s1:in TexaR 78763 IS. Supplementary Not.. Research performed in cooperation with DOT, FHWA. Research Study Title: Investigation of the Effects of Raising Legal Load Limits to 80.000 1bs. on Farm-to-Market Roads 16. Abstract In this study, a procedure for predicting the number of passes of a wheel load that will cause a specified rut depth is developed, using information which includes the base layer thickness, the resilient moduli and general classification of the granular base course and the subgrade soils. The procedure is mechanistic but simple, and is based on the permanent deformation characteristics of various types of soils determined in the laboratory and also from test results published by other researchers. Resilient moduli of pavement material layers are obtained from the results of non-destructive testing techniques. The validity of predictions of a number of these techniques is verified by comparing them with laboratory test results. Parametric runs were made using the Mechano-1attice program to form a database of rut depths. The procedure uses a multi-parametric interpolation scheme on the database in order to make predictions. Pavement materials were retrieved from six farm-to-market road sections and permanent deformation tests and resilient modulus tests were carried out. The permanent deformation behavior was modeled as a straight line in a logarithmic plot of the residual strain and the number of load repetitions. Typical slopes and intercepts of this line were determined for various soil materials. If the volumetric aggregate and moisture contents are known, an expression is also proposed to calculate the value of the slope. Expressions are giving for the intercept as a function of the resilient modulus and the soil class­ ification. The Mechano-lattice approach, which takes into account the realistic in­ teraction effects of the permanent deformation behavior of the individual layers, is sh?~,to~produce re~u1ts which differ from the more commonly used approximately m~Y-noo or RunernORirion 17. Key Words 18. Oi stri bution Statement Residual deformation, rutting, Mechano­ No restrictions. This document is lattice analysis, non-destructive available to the public through the testing, resilient modulus National Technical Information Service 5285 Port Royal Road Springfield, Virginia 22161 19. Security Classil. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. P ri ce Unclassified Unclassified 145 Form DOT F 1700.7 (8-72) Reproduction of completed poge outhor; zed A SIMPLIFIED MECHANISTIC RUT DEPTH PREDICTION PROCEDURE FOR LOW-VOLUME ROADS by KASHYAPA A.S. YAPA and ROBERT L. LYTTON Research Report 473-1 Research Study 2-18-87-473 Investigation of the Effects of Raising Legal Load Limits to 80,000 1bs. on Farm-to-Market Roads Conducted for Texas State Department of Highways and Public Transportation in cooperation with the U.S. Department of Transportation Federal Highway Administration by the Texas Transportation Institute The Texas A&M University System College Station, Texas December 1988 METRIC (SI*) CONVERSION FACTORS I APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS TO SI UNITS Symbol When You Know Multlpl, 8, To Find Symbol Symbol When You Know Multlpl,8y To Find Sy",bol LENGTH .. LENGTH mm mllilmetres In Inches 2.54 mlilimetres mm .. 0.039 Inches in ft feet 0.3048 metres m m metres 3.28 feet ft yd yards 0.914 metres m -.. m metres 1.09 yards I yd - km ml miles 1.61 kilometres km .. kilometres 0.621 miles ml AREA AREA mm2 mililmetres squared 0.0016 square inches in" In2 square Inches 645.2 mllUmetres squared m' metres squared 10.764 square feet ftl ft2 square feet 0.0929 metres squared km' kilometres squared 0.39 square miles mil 2 yd square yards 0.836 metres squared ha hectores (10000 m2) 2.53 acres ac ml2 square miles 2.59 kilometres squared ac acres 0.395 hectares MASS (weight) .. g grams 0.0353 ounces oz MASS (weight) kg kilograms 2.205 pounds Ib Mg megagrams (1 000 kg) 1.103 short tons T oz ounces 2a35 grams g ::: Ib pounds 0.454 kilograms kg .. T short tons (2000 Ib) 0.907 megagrams Mg ... VOLUME ml mlIII litres • 0.034 fluid ounces floz VOLUME l lUres 0.264 gallons gal m3 metres cubed 35.315 cubic feet ft· m3 fl oz fluid ounces 29.57 mlllilltres .. metres cubed 1.308 cubic yards yd' gal gatlons 3.785 IItres fta cubic feet 0.0328 metres cubed .. a TEMPERATURE (exact)· yd cubic yards 0.0765 metres cubed • NOTE: Volumes greater than 1000 l shall be shown In ma. ., °C CelSius 915 (then Fahrenheit temperature add 32) temperature .. OF OF 32 . 98.6 212 TEMPERATURE (exact) - ~, , , ? , , ,I ~ I ' , ~, f. ,1~, I ,1~, , Ii ( iii iii , i , 2?OJ u -.a -20 0 20 40 60 60 i 100 Fahrenheit 519 (after Celsius "C 37 "C temperature subtracting 32) temperature These factors conform to the requirement of FHWA Order 5190.1A. • SI Is the symbol for the International System of Measurements ABSTRACT Rutting has always been recognized as a major problem in low-volume roads. Thin pavements can easily face rapid deterioration because of rutting caused by in­ creased overweight vehicle traffic. The present trend in pavement design and analysis is towards describing material properties in terms of resilient moduli. In this study, a procedure for predicting the number of passes of a wheel load that will cause a specified rut depth is developed, using information which includes the base layer thickness, the resilient moduli and general classification of the granular base course and the subgrade soils. The procedure is mechanistic but simple, and is based on the permanent deformation characteristics of various types of soils determined in the laboratory and also from test results published by other researchers. Resilient moduli of pavement materials are obtained from the results of non-destructive testing techniques. The validity of a number of these techniques is verified by comparing them with laboratory test results. Parametric runs were made using the Mechano-Iattice program to form a database of rut depths. The procedure uses a multi-parametric interpolation scheme on the database in order to make predictions. Pavement materials were retrieved -from six farm-to-market road sections, and permanent deformation tests and resilient modulus tests were carried out. The per­ manent deformation behavior was modeled as a straight line in a logarithmic plot of the residual strain and the number of load repetitions. Typical slopes and intercepts of this line were determined for various soil materials. Typical values for the slope are given for different soil types. If the volumetric aggregate and moisture contents are known, an expression is also proposed to calculate the value of the slope. Expres­ sions are given for the intercept as a function of the resilient modulus and the soil classification. The Mechano-Iattice approach, which takes into account the realistic interaction effects of the permanent deformation behavior of the individual layers, is shown to produce results which differ from the more commonly used approximate method of superposition. 11 SUMMARY Rutting has always been recognized as a major problem in low-volume roads. Thin pavements can easily face rapid deterioration because of rutting caused by in­ creased overweight vehicle traffic. As a part of a previous study by Texas Transporta­ tion Institute, "Load Rating of Light Pavement Structures" (Study No. 2-8-80-284, sponsored by Texas State Department of Highways and Public Transportation), a computer program, "LOAD RATE" , was developed. It predicts the rut depth of a low-volume pavement using an empirically developed database. This study refines that process by using a mechanistic approach for predicting rut depth. This procedure predicts the number of passes of a wheel load that will cause a specified rut depth, using information which includes the base layer thickness, the resilient moduli and general classification of the granular base course and the sub­ grade soils. The procedure is mechanistic but simple, and is based on the permanent deformation characteristics of various types of soils determined in the laboratory and also from test results published by other researchers. Resilient moduli of pavement material layers are obtained from the predictions of nondestructive testing techniques. The validity of predictions of a number of these techniques is verified by comparing these predictions with laboratory test results. Parametric runs were made using the Mechano-lattice program to form a database of rut depths. The procedure uses a multi-parametric interpolation scheme on the 'database in order to make predictions. Pavement materials were retrieved from six farm-to-market road sections, and permanent deformation tests and resilient modulus tests were carried out. The per­ manent deformation behavior was modeled as a straight line in a logarithmic plot of the residual strain and the number of load repetitions.
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