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1

A Method of Optimal Design for the Base Network in Structural Deformation Monitoring at Song Hinh Hydroelectricity, Vietnam

Pham Quoc Khanh

Inżynieria Mineralna

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2022

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no. 2

13--20

EN

The article mentions a method of optimal design for the base network in horizontal displacement monitoring at hydroelectric works, based on the average residual level of the measured values. When the target function is the weakest positional error, the obtained result after optimizing is the unique plan that no depends on the designers and their experience. Thus, this is helpful for the production units because they no need to have experts in designing the network. Experiment for the base network of deformation monitoring at Song Hinh hydroelectricity shows that 44%, 50% and 60% of the initial measurement can be reduced when the average residual level is chosen 0.5, 0.4 and 0.3, respectively. The weakest position error of the network after optimizing is 2.4 mm, 2.5 mm and 2.6 mm, respectively, all are smaller than requirement ±3.6mm. This method is mainly applied for the side-angle network that was measured by total station, without considering the optimal design network in the priority direction.

PL

W artykule przedstawiono metodę optymalnego projektowania sieci bazowej w monitoringu przemieszczeń poziomych elektrowni wodnych na podstawie średniego poziomu rezydualnego zmierzonych wartości. Gdy funkcją docelową jest najsłabszy błąd pozycjonowania, uzyskany wynik po optymalizacji jest unikalnym planem, który nie zależy od projektantów i ich doświadczenia. Jest to więc pomocne dla jednostek produkcyjnych, ponieważ nie potrzebują one ekspertów do projektowania sieci. Eksperyment dla podstawowej sieci monitorowania deformacji w elektrowni wodnej Song Hinh pokazuje, że 44%, 50% i 60% początkowego pomiaru można zmniejszyć, gdy średni poziom pozostałości zostanie wybrany odpowiednio 0,5, 0,4 i 0,3. Najsłabszy błąd pozycji sieci po optymalizacji wynosi odpowiednio 2,4 mm, 2,5 mm i 2,6 mm, wszystkie są mniejsze niż wymagane ±3,6 mm. Metodę tę stosuje się głównie dla sieci kątów bocznych, które zostały zmierzone przez tachimetr, bez uwzględnienia optymalnej sieci projektowej w kierunku pierwszeństwa.

2

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

Pham Trung Dung, Pham Quoc Khanh, Cao Xuan Cuong, Nguyen Viet Hung, Ngo Sy Cuong

Inżynieria Mineralna

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2021

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no. 2

495--504

EN

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.

3

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

Pham Quoc Khanh, Tran Ngoc Dong, Nguyen Thi Kim Thanh, Pham Van Chung

Inżynieria Mineralna

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2021

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no. 2

331--340

EN

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.