EXTERNAL REFERENCE MEASURING SYSTEMS FOR ACCURATE CONTROL OF FWD MEASURING RESULTS . THIRD INTERNATIONAL CONFERENCE ON BEARING CAPACITY OF ROADS AND AIRFIELDS. PROCEEDINGS, NORWEGIAN INSTITUTE OF TECHNOLOGY, TRONDHEIM, NORWAY, JULY 3-5 1990. VOLUMES 1-2

This paper reports an investigation by Phoenix Pavement Consultants, Denmark, and the Technical University of Norway to compare the deflections measured by the falling weight deflectometer (FWD) with the deflections to which roads are actually subjected. An indoor test road was constructed, equipped with very accurate instruments for measuring both deflection and force under controlled climatic conditions. This paper (1) considers the construction of the test road; (2) describes how the test road functions and can be applied to accurate control of FWD measuring results; (3) discusses some of the problems that arose in connection with the very accurate and stable FWD used. Preliminary tests show that FWDs produced until now give satisfactory results, when the prescribed calibration routines are observed. The present study shows the need for comparative tests, especially if FWDs of different brands are to be used for measuring roads successively. This is confirmed by the fact that several FWD calibration equipments are to be constructed in connection with the Strategic Highway Research Program (SHRP) in the USA, so that different types of FWDs can be applied to measure various SHRP roads. The next stage of the authors' study will be to test and adjust their own FWDs. (TRRL)