Combined adjustment of GNSS observation results and slit meter measurements for the displacement detection at the Dniester HPP dam

Abstract

The paper considers the combined adjustment problem both of GNSS and geotechnical sensor (slit meter) measurements to detect the deformations at large engineering structures. The study offers mathematical apparatus and formulates the basic restrictions for combined processing of geodetic and geotechnical data. A preliminary assessment indicates a significant improvement in the displacement detection accuracy (up to 1 mm in planar and vertical direction). The approbation of the proposed method was performed using time series of measurements of GNSS receivers and slit meters located on the Dniester hydroelectric power plant (HPP) dam for the period from 2017 to 2019. Gross errors were excluded before processing from all the time series of observations in the semi-automatic mode using a specially designed filter. Additionally, the high-frequency noise was removed by low-pass filter (period 0.2 years). The analysis of obtained adjustment results proved the effectiveness of the proposed method. However, a number of shortcomings were identified, related to non-compliance with the main restrictions: systematic errors in the input data, lack of strict parallelism of slit meters axis to the coordinates axis of local reference system, and violation of monolithic conditions of separate blocks of the objects where slit meters are installed.