Monitoring Slope Failure at Kadoorie Agricultural Research Centre with a 3D Laser Scanner

Abstract

A loosely compacted fill slope with an angle of 33° was constructed at the Kadoorie Agricultural Research Centre of The University of Hong Kong. The height and width were 4.75 m and 9 m respectively. It was constructed by end-tipping method and resulted in a loose state with an initial dry density of 70% of the maximum dry density. Two rows of grouted nails were installed at a grid of 1.5 m x 1.5 m at an inclination of 20° from the horizontal. The slope was brought to failure by subjecting it to surcharge at the slope crest in combination with induced rise in groundwater table and precipitation. Heavy instrumentation comprised in-place inclinometer, vibrating wire piezometers, vibrating wire extensometer, earth pressure cell, tensiometer and strain gauges along soil nails and they had been monitored throughout the test. Surface movement was monitored using a GPS system and a 3D laser scanner. This paper focuses on the use of 3D laser scanner in capturing the formation of cracks and surface movement during the failure. It is found that by overlapping the point clouds generated from the scanner at different time intervals, the surface movement of the slope can be accurately recorded without the need of physically accessing the slope surface. When the slope reaches failure, the use of laser scanning can safely and quickly record the movement and dimension of washout and cracks, providing advantages over conventional survey method. This study shows that the movement obtained from the scanner agrees very well with that from conventional inclinometer reading at the surface. The travel distance of the surcharge block can be easily measured and point cloud can be easily modeled into geometrical shape for further rendering.