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Knowledge of Geological test / Test of inclinometer measurement


In terms of investigation in water resources planning, inclinometer monitoring is commonly used employed in wide applications of monitoring on dams, side slopes, retention walls etc. in areas with potential landslides, for example, in side slopes in watersheds where deep-seated landslide may occur, in the dams of reservoirs whose stability is assessed, or in high retention walls with concerns over slide, the use of only the methods like geological interpretation, boring reports, image analysis or surface crack investigation cannot produce affirmative judgment on slide surfaces, nor can it completely comprehend the speeds or directions of underground deformation. Hence, the monitoring by using inclinometer currently is still the most effective and direct and often used method in Taiwan.

The apparatus and measuring method

An inclinometer comprises the digital data capturer (Datamate), the inclinometer probe, the electric cable and the inclinometer casing. The inclinometer casing is provided, on its inside, with four grooves, each 90 degree apart from another (in A0, B0, A180 and B180 directions), for inserting the glide wheels of the inclinometer probe, as Figure.1 shows, whereby the angle of inclination of the casing and the distance between the slide wheel sets are calculated for relative horizontal distances. Such distances continually measured at the respective distance-angles inside the bore are added to result in cumulative deviation.

Figure.1 Diagram for cross-section of inclinometer casing in various directions

Figure.1 Diagram for cross-section of inclinometer casing in various directions

When analyzing the data, it is normally necessary to establish initial values, against which the measurements taken at different time are compared to learn of magnitudes and directions of shifts. Generally the Japan landslide countermeasure technology association’s (1979) “Table of recommendation for determining shift rates and slope stabilities” is used to assess the mobility and recommend pre-alert against disasters (as Table 1).

Table 1: Table of recommendation for determining shift rates and slope stabilities (Japan landslide countermeasure technology association, 1978)
Type of change, Daily shift Daily shift (mm) Monthly shift (mm) Cumulative inclination in certain direction Judgment of mobility Summary
Urgent change Over 20 Over 500 Very significant Rapidly collapsing Collapse type
mud flow type
Affirmed change Over 1 Over 10 Significant Actively moving Colluvial
soil slide
deep-seated landslide
Quasi-certain change Over 0.1 Over 2.0 Slightly significant Slowly moving Clay landslide 
Backfill landslide
Potential change Over 0.02 Over 0.5 Slight To be continuously observed Clay landslide Talus slide