Abstract
Local scour is the removal of soil around bridge foundations under the erosive action of flowing water. This hydraulic risk has raised awareness of the need for developing continuous monitoring techniques to estimate scour depth around bridge piers and abutments. One of the emerging techniques is based on monitoring the vibration frequency of either bridge piers or a driven sensor in the riverbed. The sensor proposed in this study falls into the second category. Some unresolved issues are investigated: the effect of the geometry and material of the sensor, the effect of the embedded length and the effect of soil type. To this end, extensive laboratory tests are performed using rods of different materials, with various geometries and lengths. These tests are conducted in both dry sand and a soft clayey soil. Since the sensor will be placed in the riverbed, it is crucial to evaluate the effect of immersed conditions on its response. A numerical 3D finite-element model was developed and compared against experimental data. This model was then used to compute the ‘wet’ frequencies of the sensor. Finally, based on both the experimental and numerical results, an equivalent cantilever model is proposed to correlate the variation of the frequency of the sensor to the scour depth.
Highlights
Scour is considered as the main cause of bridge damages [1] and accounts for nearly half of all bridge collapses in the USA [2]
The present study focuses on the effect of scour on the dynamic response of sensor-rods partially embedded in soil, on the correlation between the variation of the first frequency and the current scour depth
The reported study proposes a continuous monitoring technique of scour by means of rods embedded in the riverbed
Summary
Scour is considered as the main cause of bridge damages [1] and accounts for nearly half of all bridge collapses in the USA [2]. Several monitoring devices already exist and are used in the field such as: float-out devices [9], radar [10,11], sonar [12], time domain reflectometry [13,14], magnetic sliding collar [15,16], electrical conductivity devices [17] and fiber optic [18,19] Those methods have several limitations such as: high sensitivity to noise, difficulties in result interpretations and not being suitable to high sediment concentration conditions. An emergent technique based on the dynamic response of the structure is the main method proposed in this paper
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