FACTORS INFLUENCING MEASURED DEFLECTION IN SHROPSHIRE . THIRD INTERNATIONAL CONFERENCE ON BEARING CAPACITY OF ROADS AND AIRFIELDS. PROCEEDINGS, NORWEGIAN INSTITUTE OF TECHNOLOGY, TRONDHEIM, NORWAY, JULY 3-5 1990. VOLUMES 1-2

Several anomalies have been found in the procedure for determining residual life or overlay requirements from the measurement of transient surface deflections. This paper examines various factors that can influence the field deflection measurements of a pavement, to enable a more representative value to be used to determine the residual life or overlay thickness if required. These factors include the following: (1) a significant variation in measured deflection values can occur, because the deflections are not being measured at precisely the same location; (2) deflections measured by a deflectograph are more variable than those measured with a deflection beam, because of the difficulty of locating the position of the deflectograph as it moves; (3) the influence of temperature on measured deflections; (4) the influence of moisture content on measured deflections. The revised deflectograph to deflection beam and temperature relationships, derived from the results, have been incorporated in the Shropshire Deflection Analysis (SDEFA) microcomputer program, which has been used in several major pavement investigations and is now being introduced as an option for the design of all structural maintenance works. The new system provides a more rigorous approach to structural life analysis. (TRRL)