Displacement Measurement of Soil Nail Walls using Close Range Photogrammetry

Displacement measurement of the soil nail walls is very important in monitoring the slightest movements in excavations to prevent disastrous accidents like wall collapsing. Usually in building construction projects, the micro-geodesy and instrumentation methods are used in measurement of vertical and horizontal movements of the walls. Limitations like high cost, long time, limited accuracy, low flexibility and high dependence on the project conditions are the causes of the low control on the movements of walls in many projects. Unfortunately in some cases adverse accidents occurs because of this reason. In this research, for the first time, the use of close range photogrammetry in displacement measurement of the soil nail walls has been proposed and experienced. For this purpose, a photogrammetric system has been designed and examined on a building construction project in Tehran, Iran. The results of monitoring of one the suspicious walls in the project in different time epochs of the excavation and its comparison with the consequences of the micro-geodesy method confirmed the accuracy of the proposed method (7.7 mm). According to this fact that the proposed method has solved the many limitations of the traditional methods, the close range photogrammetry as an efficient method is introduced as an alternative to the existing method in construction projects.