Mass movement monitoring

• Levelling in surveying


  The process of determining the height of one level relative to another
• Levelling


  • Heights can be monitored for changes to monitor slope movements
• Surveying


  Relates to the two-dimensional or three-dimensional positions of points, distances and angles between them
• Surveying


  • In the case of 3d, modelling of a mass movement can be undertaken
• Seismic activity


  Small scale seismic (micro seismic) events are monitored and occur when the rocks begin to slide
• Seismic events increase


  In rate and magnitude as a mass movement unfolds
• Borehole distortion


  Monitor tilt in borehole, there is a greater distortion from vertical with strain changes
• Ground deformation


  The investigation of surface deformation is conducted to define the boundaries of the mass movement, size, level of activity, direction of movement and to determine individual moving blocks of slide
• Ground deformation


  • Presence of scarps, cracks and scree are useful for determining whether the potential for future activity exists
• Tilt


  Tiltmeters record changes in the inclination of a wall/face and the ground surface
• Tilt


  • Useful to monitor changes in the rate of increase for a movement
• Ground tiltmeter


  Useful for determining the deformation at the head and toe portions and sometimes along the flanks of the landslide, or to assess the possibility of future deformation
• Ground tiltmeter


  • Level type tiltmeter is most conventional, capable of measuring the N-S and E-W components, magnitude of tilting and tilt directions can be determined directly from the instrument panel
• Tilt results


  Shown chronologically along with the daily rainfall totals
• Creep


  One of the simplest methods to determine mass movement direction is to drive wooden stakes across a tension crack along the direction of slide movement, attach horizontal boards to the stakes, and saw through the boards
• Extensometer

  Used to measure relative movement by comparing the extension of two points
• Extensometers


  • Generally installed across the main scarp, at transverse crack and transverse ridges near the toe or front portion of the slide and parallel to the suspected slide movement
• Extensometers


  • By arranging a series of interconnecting extensometers from the main scarp to the toe of a complex landslide that has many moving slide blocks, the resulting data could aid in clearly delineating the individual slide blocks
• Extensometer measurements


  • Should be accurate to within 0.2mm, and the magnitude of the movement and daily rainfall data should be included to establish the relationship between the measurable movement and the precipitation rate
• Strain gauges


  Convert the applied force, pressure, torque, etc., into an electrical signal which can be measured
• Strain gauges


  • Any small change in the material under the strain gauge results in a change in the resistance of the strain gauge as it deforms with the material
• Electronic distance measurement (EDM)


  A way of determining the length between two points by looking a phase change that occurs as electronic energy waves, which travel from one end of a straight line to the other
• Laser Surveys


  A control point is established along the opposite bank on stable ground and survey stakes are positioned within the slide, changes in distance (decrease) are measured
• GPS and satellite data

  Can be used to determine three-dimensional positioning of the slide, a GPS device can determine the size and displacement of a landslide by setting the boundary points on the GPS and determining the distance between them
• GPS techniques


  • Small landslide features may not be measured as accurately as larger features
• Aerial imagery, such as LiDAR


  Can be used to map landslides and evaluate their mechanics and material properties