Development of Draw-wire Type Displacement Instrument for Monitoring Subsurface Settlement

In the subsurface settlement monitoring of field soaking test in collapsible loess regions, the traditional subsurface settlement monitoring pole can only measure the settlement of a single position in a hole, and the electromagnetic settlement gauge has some disadvantages, such as large measurement error and so on. Therefore, a new type of draw-wire type displacement instrument for monitoring subsurface settlement is developed. The basic principle of the new instrument is to excavate a vertical exploration well at the monitoring site. Subsurface settlement monitoring positions are evenly set along the circumference of the exploration well, and the anchor head is installed on the side wall of the exploration well at the measuring position. When the soil layer is collapsible, the deformation is first transmitted to the measuring wire by the anchor head, and then to the slide block on the column by the measuring rope. Finally, the subsurface settlement of each measuring position is obtained by measuring the relative displacement between the fixed support and the sliding block on the column, and combined with the geometric leveling results. Based on field tests for comparing the new instrument and the traditional subsurface settlement monitoring pole, it is concluded that the new instrument with the advantages of working principle is clear, and structure is simple, and measurement range is adjustable, and precision is high, which not only meets the needs of multi-position measurement in a single hole, but also improves the reliability of measurements. Finally, the existing problems of the new instrument are discussed and suggestions for improvement are put forward.