Measuring and calculation methods for landslide volume with 3-D laser scanner in Wenchuan earthquake area

Abstract: The earthquake of moment magnitude (M) 8.0 in Wenchuan, Sichuan Province, on May 12th, 2008 produced massive loose landslides, responsible for failure of agricultural land and damage of farmland facilities, which caused a heavy loss of agricultural economy and threatened the production security of agricultural in earthquake area. In this study, typical landslides were chosen to measure volumes with geometry models. The landslide in Caopo Village, Wenchuan County, as measured by using 3-D laser scanner, was used to do measurement and computational processes. The 3-D laser scanner is HDS-ScanStation2, Leica Company, and its scanning distance reaches as far as 300 m, with an distance measurement accuracy of ±4 mm and a resolution of ±6 mm at 50 m. The scanner was set up in front of the slope of the landslide to be measured. The distances from the scanner to the near end and the far end of the landslide were 25.74 m and 79.00 m, respectively. The scan grid was set to be 20.0 cm in horizontal and 20.0 cm in vertical. The actual scan grid of the measured landslide was 2.6 cm×2.6 cm at the near end and 7.9 cm×7.9 cm at the far end, respectively. The landslide surface and its surrounding terrain were accurately scanned on-site by the 3-D laser scanner. The measured landslide was divided into two parts according to its scanned surface features. The original terrain data of the valley were used to determine the bottom planes of the landslide, including horizontal and the hillslope. The horizontal boundary was determined by the original landscape and hillslope bottom was approximated by fitting the hillslope. Based on the data points measured by scanner, the planes were fitted with eigenvalue method. The geometry model of landslide was formulated in the 3-D coordinate system by the measured data. The volume of the landslide was estimated to be 19018 m3. The method was verified with the value calculated by the built-in method of the 3-D laser scanner. The result shows that the value calculated by the method suggested was 7.3% higher than that by the build-in method. The reasonable accuracy of the method shows that the volume of landslides can be measured reliably by the method. The method and procedures for measuring the landslide volume with 3-D laser scanner provide an important basis for methods and measures of land consolidation of earthquake damaged farmland after the disaster.