FINITE ELEMENT ANALYSES OF PAVEMENTS

AN APPLICATION IS DESCRIBED OF THE FINITE ELEMENT TECHNIQUE TO THE ANALYSIS OF SYSTEMS REPRESENTATIVE OF PAVEMENT STRUCTURES. USE IS MADE OF A DIGITAL COMPUTER PROGRAM WHICH GENERATES SUITABLE FINITE ELEMENT CONFIGURATIONS FOR AXISYMMETRIC STRUCTURES AND ACCOMMODATES APPROXIMATIONS OF NONLINEARITY WHICH APPEAR APPROPRIATE TO REPRESENT THE BEHAVIOR OF GRANULAR BASE AND COHESIVE SUBGRADE MATERIALS UNDER CONDITIONS CORRESPONDING TO MOVING TRAFFIC. EXAMPLES ARE PRESENTED FOR SYSTEMS WITH LINEAR MATERIAL PROPERTIES SHOWING COMPARISONS BETWEEN DISPLACEMENTS AND STRESSES COMPUTED USING THE FINITE ELEMENT TECHNIQUE AND THOSE COMPUTED USING ELASTIC HALF-SPACE AND LAYERED SYSTEM ANALYSES TO ESTABLISH CRITERIA FOR BOUNDARY CONDITIONS IN THE FINITE ELEMENT PROCEDURE. FOR THE ELASTIC HALF-SPACE SUBJECTED TO A UNIFORM CIRCULAR LOAD, DISPLACEMENTS AND STRESSES COMPUTED BY THE FINITE ELEMENT TECHNIQUE COMPARE FAVORABLY WITH THOSE DETERMINED FROM THE BOUSSINESQ SOLUTION WHERE THE NODAL POINTS IN THE FINITE ELEMENT PROCEDURE ARE FIXED AT A DEPTH OF 18 RADII FOR THE BOTTOM BOUNDARY AND CONSTRAINED FROM MOVING RADIALLY ON THE VERTICAL BOUNDARY AT A DISTANCE OF ABOUT 12 RADII FROM THE CENTER. TWO ANALYSES ARE PRESENTED FOR DEFLECTION DETERMINATIONS FOR AN INSERVICE PAVEMENT NEAR GONZALES, CALIF., ONE FOR A CONDITION WHERE THE ASPHALT CONCRETE WAS AT A COMPARATIVELY HIGH TEMPERATURE (STIFFNESS MODULUS IN THE RANGE 120,000 TO 280,000 PSI), AND THE OTHER WITH THE MATERIAL AT A LOW TEMPERATURE (STIFFNESS MODULUS APPROXIMATELY 1,500,000 PSI). NONLINEAR MATERIAL PROPERTIES, DETERMINED FROM THE RESULT OF REPEATED LOAD TRIAXIAL COMPRESSION TESTS, WERE USED TO REPRESENT THE BEHAVIOR OF THE UNTREATED GRANULAR BASE AND SUBBASE AND THE FINE-GRAINED SUBGRADE SOIL. DEFLECTIONS PREDICTED BY THE FINITE ELEMENT PROCEDURE ARE IN THE SAME RANGE AS THOSE MEASURED WITH THE CALIFORNIA TRAVELING DEFLECTOMETER INDICATING THAT THE METHOD HAS POTENTIAL TO SIMULATE ACTUAL PAVEMENT BEHAVIOR TO A REASONABLE DEGREE. THE ANALYSIS ALSO INDICATES THAT WHEN THE EXTENSIONAL STRAINS IN THE ASPHALT CONCRETE ARE LARGE FOR THIS PAVEMENT (I.E., WHERE THE STIFFNESS OF THE ASPHALT BOUND MATERIAL IS LOW), THE GRANULAR MATERIAL EXHIBITS A VERY LOW MODULUS UNDER THE LOADED AREA AND A LARGE PROPORTION OF THE SURFACE DEFLECTION CAN BE ATTRIBUTED TO DEFORMATIONS WITHIN THIS MATERIAL. ON THE OTHER HAND, WHEN THE ASPHALT LAYER IS STIFF, THE MAJORITY OF THE SURFACE DEFLECTION IS CONTRIBUTED BY THE SUBGRADE. AN ANALYSIS IS ALSO PRESENTED FOR THE RESULTS OF PLATE LOAD TESTS ON A TWO- LAYER PROTOTYPE PAVEMENT CONSISTING OF GRANULAR BASE AND A COHESIVE SUBGRADE SOIL USING THE SAME NONLINEAR CHARACTERIZATION FOR MATERIAL PROPERTIES AS FOR THE IN- SERVICE PAVEMENT. /AUTHOR/