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2 2021

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

100%

Pham Q. K. , Tran N. D. , Nguyen T. K. T. , Pham V. C.

Inżynieria Mineralna

2021

tom no. 2

331--340

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.

The capability of terrestrial laser scanning for monitoring the displacement of high-rise buildings

88%

Pham T. D. , Pham Q. K. , Cao X. C. , Nguyen V. H. , Ngo S. C.

Inżynieria Mineralna

2021

tom no. 2

495--504

Recently, terrestrial laser scanner (TLS) has been increasingly used to monitor of displacement of high-rise buildings. The main advantages of this technique are time-saving, higher point density, and higher accuracy in comparison with GPS and conventional methods. While TLS is ordinary worldwide, there has been no study of the capability of TLS in monitoring the displacement of high-rise buildings yet in Vietnam. The paper's goal is to build a procedure for displacement monitoring of high-rise buildings and assess the accuracy of TLS in this application. In the experiments, a scanned board with a 60 cm x 60 cm mounted on a moveable monument system is scanned by Faro Focus3D X130. A monitoring procedure using TLS is proposed, including three main stages: site investigation, data acquisition and processing, and displacement determination by the Cloud-to-Cloud method (C2C). As a result, the displacement of the scanned object between epochs is computed. In order to evaluate the accuracy, the estimated displacement using TLS is compared with the real displacement. The accuracy depends on scanning geometry, surface property, and point density conditions. Our results show that the accuracy of the estimated displacement is within ± 2 mm for buildings lower than 50 m of height. Thus, TLS completely meets the accuracy requirements of monitoring displacement in the Vietnam Standards of Engineering Surveying. With such outstanding performance, our workflow of using TLS could be applied to monitor the displacement of high-rise buildings in the reality of geodetic production in Vietnam.