Landslide Monitoring Using Moiré Technique

In this work a new method for measuring landslide displacements using moiré technique is presented. A linear periodic pattern (carrier grating) is pasted on the surface of a wall that has a crack due to the landslide displacements. The crack has been opening in the last few years. Lines of the carrier grating are in parallel with the line of the crack. A suitable imaging system takes the image of the carrier grating and superimposes it on a physical grating (probe grating). A moiré pattern is formed. The displacements continually distort the image grating and the moiré fringes greatly magnify the displacements. By processing the relative displacements of the moiré fringes on both sides of the crack in successive frames, one can measure the amount of crack opening through time with high accuracy. The implementation of the technique is straightforward; displacements can be magnified by more than a factor of ten in a comparatively simple and reliable way. The method is applied to study the landslide of the village of Gholghati in Zanjan Province in the summer and the fall of 2009. The total amount of crack opening during the mentioned time 4 mm was measured. In this work, the measurement precision of crack opining was about 0.04 mm.