Quality control of a dam geodetic surveying system

Abstract

Geodetic surveying systems used to monitoring displacements at large concrete dams must be carefully designed and materialized, not only as a response to required submilimeter accuracies but also in regard as to their lifetime, witch is expected to last as long as the dam. This special care should be extended to the choice of the measurement equipment and procedures and to the use of adequate adjustment and quality control procedures. The most common sources of errors are: instrument calibration, atmospheric conditions, operative methods, human errors and mistakes and, last but not the least, the unexpected behaviour of the reference frame. This paper deals with a real situation, which took place in the geodetic surveying system of a Portuguese dam, where unexpected variations of its horizontal control network’s observables, suggesting an apparently abnormal behaviour of the dam, were detected by means of statistical quality control tests. The paper describes the “Monte Novo” dam geodetic surveying system, the measurements carried out along time and its quality control statistical tests, and presents an explanation to the apparently abnormal behaviour of the dam.