Evaluation of Measured Results of Pipe-Strain Gauges

Abstract

In case of landslide investigations, a confirmation of existing depth of slide surface is one of the most essential investigation. For the purpose of pipe-strain gauges are usually used in the most landslide areas in Japan. On the basis of these observational results, the existing depth of slide surface is definited and these data are presented for planning and designing landslide preventive works. However, recently we have been able to see many column diagrams of strain variation which have some unreasonable measured results of those pipe-strain gauges.
Thereupon, on the basis of these observational examples, we carried out comparison between the measured results of these pipe-strain gauges and geological column, and measured results by inserting-type-strain meter, examination of the insulation resistance of the circuit including pipe-strain gauges and lead wires, and measurement of the resistance of each strain gauge. Further, we considered causes why such unseasonable column diagrams of strain variation were obtained.
As a result of these examinations, the main causes of such unreasonable columns are as follows:
1) Scratch or disconnection of lead wires and treatment parts of waterproof and dampproofing of strain gauges when inserting a pipe-strain gauge into a borehole or when pulling out a casing pipe from a borehole.
2) Deteriorative phenomena of insulation resistance of lead wires and treatment parts of gauges for a long time.
3) Abrasion phenomena of strain gauges from vinyl chloride pipe for long time.