DEVICE FOR MONITORING COLLAPSE OF NATURAL GROUND IN UNDERGROUND EXCAVATOR

摘要

A device for accurately monitoring a collapsed portion when an underground excavator advances. Three or more combinations different from one another of a pair of conductive electrodes and a pair of detecting electrodes out of electrodes (1-8) are successively selected, and, for every combination, an electric power (17) and a voltmeter (16) are successively and switchingly connected. A specific resistance of a collapsed portion (24) is calculated for every combination on the basis of a detected voltage for each selected combination. A specific resistance for every combination as calculated above and the distance between selected conductive electrodes for every combination are successively substituted into an operational expression showing the interrelations between the calculated value of a specific resistance, the distance between selected conductive electrodes, a real specific resistance of the collapsed portion (24) in muddy water, a real specific resistance in the natural ground (22) of the collapsed portion (24) and the depth of muddy water, so that three or more expressions can be obtained. The depth of muddy water is calculated on the basis of these three or more expressions. As described above, the value of a real specific resistance is not a known one, but regarded as an unknown one, whereby the depth of muddy water is calculated. Therefore, even if the real specific resistance of the collapsed portion (24) is changed with the progress of excavation, the change can be accommodated and the depth of muddy water can be constantly and accurately calculated.