Encardio-rite Borehole Extensometer with Vibrating Wire is used to measure the extension (displacement) that takes place with time in a bored hole or in several bored holes in a rock mass.
We will be looking at the Vibrating Wire Extensometer Installation Procedure in this article.
It consists of one or more anchors and a reference plate. Anchor or anchors are set in same borehole or in different boreholes drilled adjacent to the first borehole. The extensometer helps to accurately measure distance between various anchors with respect to reference plate and thus monitor with passage of time their relative displacement.
Tools & Accessories required for installation
The following tools and accessories are necessary for the vibrating wire extensometer installation procedure:
Soldering iron 25 watt
Rosin 63/37 solder wire
Thread sealant (Loctite 577 or equivalent)
Cable jointing compound
Acetone (commercial)
Spanner 6, 8, 10, 18, 24, 30 and 38
Allen key 2, 4 3.4.8 Screw driver (tip size 6 x 0.8 and 3 x 0.5 mm)
Phillips head screw driver (tip size 2 mm)
Hacksaw with 150 mm blades
Cable cutter
Wire stripper
Insulated pliers 165 mm
150 mm flat file
Toothbrush
wire brush
Cloth for cleaning (lint less)
Cello tape/Insulation tape
Micrometer depth gage 100 mm range
Digital indicator model EDI-54V
Digital multi-meter
Vibrating Wire Extensometer Installation Procedure
Refer to the above image and remove the cover (19) to take out the polythene bag that contains requisite quantity of reference buttons (15), link plates (16), sensor tightening nut (17), locknuts (18), M6 x 100 cheese head screw (24) and locking nuts (25).
Remove guide plate (7) with the help of a 4mm Allen Key and hollow bolts marked 1, 2 and 3 from flanged housing (5). Place the housing on the clean ground, ensuring that it is at least 1m away from the borehole. Loosen the other two hollow bolts slightly from holes marked V and G.
The next step in the vibrating wire extensometer installation procedure is to cut grout and air vent tubes (12 mm od x 10 mm id supplied in coil form) to the length that is required. In most cases, the lower end of the grout tube is placed at a level higher than the anchor which is the closest to the face of the borehole.
Make sure that the grout covers the anchor closest to the borehole mouth or is around 1 m from face of the borehole, whichever is closest. When you’re determining the length of the grout tube, remember than around 1.5m is of it is required to be outside the reference plate as it used to easily attach to the grout pump. Similarly, the air vent tube should project around 0.3 m is outside the reference plate.
Like we did for the grout covers, the lower end of the air vent tube should always be at a higher level than the lower end of the grout tube. When it is time to insert the last anchor in the borehole, make sure the lowest end of the grout tube is tied to the connecting rod with a cable tie.
NOTE: When installing with upward to the horizontally sloping borehole, make sure the grout tube is 2m longer than the specified depth of deepest anchor and taped around 100 mm below far end of the anchor. To prevent is from swinging loose, use a PVC tape and tape the grout tube at every 2m to the plastic tube of connecting ...[Continue Reading]
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