Research the Integration of Geodetic and Geotechnical Methods in Monitoring the Horizontal Displacement of Diaphragm Walls

Abstract

This article investigates the integration of geodetic and geotechnical methods for monitoring the horizontal displacement of diaphragm walls. The results show that when the horizontal displacement is measured by the geotechnical method using an inclinometer sensor, the center point at the bottom of the guide pipe is usually chosen to be the origin to calculate displacements of the upper points. However, it is challenging to survey the bottom point for checking its stability directly. If this bottom point moves, the observation results will be incorrect. Thus, the guide pipe must be installed in the stable rock layer. But in the soft ground, this rock layer locates more deeply than the diaphragm walls, so the guide pipe cannot be laid out at the required location. Geodetic methods can directly observe the displacement of the center point on the top of the guide pipe with absolute displacement values at high accuracy. Because the displacements of observation points are determined at stable benchmarks, these values are considered the pipe's displacement. Thus, an integrated solution allows the center point on the top of the pipe to be the origin to calculate the displacements of different points located inside the diaphragm wall. Then, the calculated values are calibrated back to the inclinometer observed values to achieve highly reliable displacement, which reflects the moving of diaphragm walls. An experiment integrating the geodetic and geotechnical methods is conducted with an observation point at a depth of 20 meters at a construction site in Ho Chi Minh city. The deviations of the top point that are observed by the two methods are - 4.37 millimeters and - 3.69 millimeters on the X-axis and the Y-axis, respectively. The corrected observed results prove that the integrated solution has a good efficiency in monitoring the horizontal displacement of diaphragm walls. The bottom point observed by an inclinometer is unconfident enough to choose to be a reference point.