ACCURACY OF FIELD DEFORMATION MEASUREMENTS

Abstract

THIS IS A STATE-OF-THE-ART REPORT CONCERNING THE ACCURACY OF MEASUREMENT OF SETTLEMENT, LATERAL MOVEMENT, AND CHANGE OF POSITION OR CHANGE OF DIMENSION. METHODS AND EQUIPMENT EMPLOYED IN FULL-SCALE FIELD OPERATIONS DESCRIBED. ACCURACY REQUIRED IN A FIELD PROBLEM IS COMPARED TO THAT PROVIDED BY DIFFERENT MEASURING METHODS. EXAMPLES OF FIELD OBSERVATIONS ARE PRESENTED. FACTORS WHICH CHARACTERIZE AND INFLUENCE ACCURACY SUCH AS PHYSICAL CHARACTERISTICS OF THE DEVICE, INSTALLATION PROCEDURES, EXTERIOR INFLUENCES, CONFORMANCE, DATA REDUCTION, OBSERVER ERROR, AND VERIFICATION PROCEDURES ARE DETAILED. ACCURACY REQUIRED OF SETTLEMENT MEASUREMENTS ON BUILDINGS, EMBANKMENT DAMS AND IN ROCKS ARE DISCUSSED. A REVIEW OF MEASUREMENTS BY CONVENTIONAL SURVEYING METHODS AND GEODETIC TECHNIQUES INTRODUCES A DISCUSSION OF SPECIFIC INSTRUMENTS. THE LATTER ARE CATEGORIZED INTO VERTICAL- TUBE SETTLEMENT GAGES, REMOTE SETTLEMENT GAGES, HORIZONTAL MOVEMENT GAGES INCLINOMETERS AND EXTENSOMETERS. VARIOUS ASPECTS OF THIS REPORT ARE DISCUSSED. THE IMPORTANCE OF A SYSTEMATIC APPROACH TO PLANNING EXTENSOMETER MEASUREMENTS FOR LARGE OPENINGS IN ROCK IS EMPHASIZED. ADDITIONAL PROCEDURAL DETAILS FOR EMBANKMENT DISPLACEMENT MEASUREMENT ARE REVIEWED. THE USE OF ELECTRONIC DISTANCE MEASURING DEVICES IS RECOMMENDED. ACTUAL CASES ARE PRESENTED TO ILLUSTRATE COMMENTS ON PLANNING AND EXECUTING A FIELD MEASUREMENT PROGRAM. THE ACCURACY OF TENSIONED-WIRE EXTENSOMETER IS DISCUSSED. THE NEED FOR AN EVALUATION OF THE FIELD PROBLEM IN DESIGNING AN INSTRUMENTATION PROGRAM IS INDICATED. THE OBSERVATION IS MADE THAT THE PLANNING OF A USEFUL OBSERVATION PROGRAM IS CONSTRAINED BY ADMINISTRATIVE AND POLICY CONSIDERATIONS.