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With a structure’s foundation and supporting ground generally being critical to its design and construction, understanding how soil behaves under various stress and drainage conditions is imperative. It is well known that certain characteristics and behaviors of soils with fines are highly dependent on water content and liquid limit is one of the important soil index properties to define such characteristics. However, conventional liquid limit measurement techniques can be easily affected by the proficiency of the operator, potentially leading to disastrous consequences. The dynamic properties of soils are required in numerous applications, and current testing techniques frequently call for specialized lab equipment, which is often pricy and delicate to test conditions. To address these concerns and advance the state of the art, this study explores a novel method to determine the liquid limit of cohesive soil by employing video-based vibration analysis which may precisely measure and identify the status of a soil’s water content. In this research, the modal characteristics of cohesive soil columns are extracted from videos by phase-based motion estimation. By utilizing the proposed method that analyzes the optical flow in every pixel of the series of frames that effectively represents the motion of corresponding points of the soil specimen, the vibration characteristics of the entire soil specimen could be assessed in a non-contact and non-destructive manner. The experimental investigation results compared with the liquid limit determined by the conventional method verify that the proposed method reliably and straightforwardly identifies the liquid limit of clay. It is envisioned that the proposed approach could be applied to measuring liquid limit of soil in practical field, entertaining its simple implementation that only requires a digital camera or even a smartphone without the need for special equipment or techniques that may be subject to the proficiency of the operator.
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