A new diffusion laser displacement meter (DLDM) has been developed for monitoring rock/ground displacements. It adopts the large diameter and cone angle of laser beams to improve the measurement performance under rainy or foggy conditions and to avoid the harmful effects on human eyes, skin, etc. The resolution of the distance meter is up to 0.1 mm.

Although the authors firstly developed a twin-lens type of DLDM, the newly developed single-lens DLDM has been found to have a higher cost performance. Moreover, the single-lens model has a fewer number of components and a wider range of laser reflection intensity than the twin-lens model.

In this study, experiments were conducted to investigate the measurement performance of the single-lens DLDM under hard rain conditions using an indoor rainfall simulator. The test results showed that this single-lens DLDM was able to measure displacements without missing any data under rainfall intensities up to 200 mm/hr for a baseline length of 30 m and up to 120 mm/hr for a baseline length of 62.5 m.

In order to verify its practical applicability, the DLDM was applied to the landslide monitoring of a large steep slope. It was proven that the DLDM can continuously measure displacements under hard rain, of around 50 mm/hr, and can detect 110-mm displacements together with the local failure of the slope. The performance of the new single-lens DLDM was found to surpass that of surface extensometers.

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