Today, as structures with life expectancy of more than 100 years are being constructed, it is vital to gain knowledge about the gradual decline in material properties. Accordingly, to ensure the longevity and safety of these structures, monitoring has been incorporated as a fundamental part of their service life. To monitor structural deformation, various methods have been developed, with the most common being the survey of certain points of a structure during and after construction using a total station. New techniques are now being developed, and one of the most promising ones is photogrammetry because it provides a simple method to monitor a structure using Unmanned Air Vehicles (UAVs). This paper is aimed at sharing the strategic steps followed in monitoring the deflection of a simple secant pile retaining wall during excavation and construction of a basement. The monitoring is performed using a commercial UAV in combination with point cloud formation, georeferencing, and comparison software (cloud compare, I-Site Studio, 3DReshaper etc.). The monitoring results show very good agreement with the traditional inclinometer deflection measurements and numerical analysis, thereby demonstrating the feasibility of the proposed method. The authors believe that in the future, photogrammetry using UAVs can become the standard method for geotechnical monitoring because its speed, lower cost and ease of use, when compared to conventional methods, a non-destructive method, and is easy to learn and use.

A large amount of research has been done on conforming surfaces in rock joints as well as on the contact between individual grains, however, not much exist in nonconforming contact surfaces subjected to friction, such as flat contacts between ballast particles, stone columns or riprap; applications that involve the use of coarse gravel subjected to low vertical stresses. Therefore, this article aims to study changes in contact properties between non-conforming flat contacts between large geomaterial particles that have been subjected to cyclic shearing under a constant low vertical force, using a direct shear apparatus. Two different silica carbide sandpapers that do not loose particles were used, to simulate different morphologies, a nominally fine and a coarse surface texture. The results show a passivation of the shear strength where a constant value of friction coefficient is reached after around 15 to 17 cycles for all tests, except the tests at the lowest vertical force. For the tests at the highest vertical force similar friction coefficients were determined for the coarse and fine surfaces. The mass broken during the 10 th and 20 th cycles was collected at the end of the tests and seem to show a linear relationship with the vertical force used in the test. Particle analysis, determined via microscopy, show that the grading is dependent on the initial topography of the surfaces. Despite being subjected to 10 and 20 cycles of shearing, the broken particles look similar in shape with sharp, jagged edges and having different shapes and roundness values with a large variation, indicating that the breakage was not enough to fill in the space between the particles.