SEDL / STP / STP1026-EB / STP19801S

Using the Multidepth Deflectometer to Verify Modulus Backcalculation Procedures

Scullion, T
Associate research engineer, Texas Transportation Institute, Texas A&M University, College Station, TX

Briggs, RC
Engineering assistant of Pavement Management, Austin, TX

Lytton, RL
Professor of civil engineering and research engineer, Texas Transportation Institute, Texas A&M University, College Station, TX

Pages: 12    Published: Jan 1989

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Abstract

This paper describes the use of a multidepth deflectometer (MDD) for determining the resilient modulus of pavement layers. The MDDs are installed in specially drilled holes, and up to six modules may be placed in a single hole. This device measures the relative deflection of each layer with respect to an anchor point located approximately 2.1 m (7 ft)⁴ below the pavement surface. In this paper are results obtained from two instrumented pavement sections at the Texas Transportation Institute's Research Annex. By obtaining MDD deflections under falling weight deflectometer (FWD) loadings, two independent procedures are available for estimating layer moduli.

A procedure for automatically calculating layer moduli from MDD measurements is described, and the results obtained are compared with those obtained from three backcalculation schemes using FWD surface deflection data. When a semi-infinite depth subgrade was specified, all three procedures predicted subgrade moduli approximately 50% higher than those estimated from MDD measurements. When a finite depth was specified, a rock layer at 6 m (20 ft), all three procedures calculated subgrade moduli values very similar to the MDD values. The ELSDEF program with finite subgrade also produced comparable values for the moduli of base and subbase layers.