Application of UAV Photogrammetry in Displacement Measurement of the Soil Nail Walls Using Local Features and CPDA Method

Farid Esmaeili,Hamid Ebadi,Farzin Kalantary,Mohammad Saadatseresht

doi:10.3390/ijgi8010025

Abstract

The high cost of land across urban areas has made the excavation a typical practice to construct multiple underground stories. Various methods have been used to restrain the excavated walls and keep them from a possible collapse, including nailing and anchorage. The excavated wall monitoring, especially during the drilling and restraining operations, is necessary for preventing the risk of such incidents as an excavated wall collapse. In the present research, an unmanned aerial vehicle (UAV) photogrammetry-based algorithm was proposed for accurate, fast and low-cost monitoring of excavated walls. Different stages of the proposed methodology included design of the UAV photogrammetry network for optimal imaging, local feature extraction from the acquired images, a special optimal matching method and finally, displacement estimation through a combined adjustment method. Results of implementations showed that, using the proposed methodology, one can achieve a precision of ±7 mm in positioning local features on the excavated walls. Moreover, the wall displacement could be measured at an accuracy of ±1 cm. Having high flexibility, easy implementation, low cost and fast pace; the proposed methodology provides an appropriate alternative to micro-geodesic procedures and the use of instrumentations for excavated wall displacement monitoring.

Highlights

During the past two decades, with the emergence of professional digital cameras and advanced digital photogrammetric methods, the use of photogrammetric images, especially close-range photogrammetric images taken from or just above the ground surface, has become a typical practice in various applications [1]
Displacement measurement of large-scale structures is an important application of the close-range photogrammetry, where high precision on the feature is subject to appropriate network design and local feature extraction and matching on the convergent images taken from the feature
A unmanned aerial vehicle (UAV) photogrammetry method was proposed for excavated wall displacement monitoring

Summary

Introduction

During the past two decades, with the emergence of professional digital cameras and advanced digital photogrammetric methods, the use of photogrammetric images, especially close-range photogrammetric images taken from or just above the ground surface, has become a typical practice in various applications [1]. Displacement measurement of large-scale structures is an important application of the close-range photogrammetry, where high precision on the feature is subject to appropriate network design and local feature extraction and matching on the convergent images taken from the feature. Given that most excavation projects are performed within urban areas due to the high cost of land across such areas, the spatial limitation imposed by the presence of neighbouring constructions affects the success of reference photogrammetric imaging from the ground surface. Under such condition, application of available space by UAVs to reach suitable positions for imaging is of paramount importance in making such projects feasible

Methods

Discussion

Conclusion