GTSM at Hsinchu Region, Taiwan
Big Hill (BMMT)
Big Hill was the first Taiwan instrument since the original 2003 site installs. This site uses the first of the large scale production components and as a result required less technical input in the field during the installation.
This site is the only site to include a seismometer in this array of instruments.
The BMMT borehole is 200.7m deep. However, the best rock for the deployment was at a depth of 199.7m and above. To ensure the GTSM strainmeter was correctly located, the hole was filled with river stones (small stones). This brought the base of the hole up 1m.
One issue during this process was whether there would be sufficient non-shrink grout to fill the base of the hole containing the river stones, as well as surrounding the entire instrument. The following calculations were made:
Volume of the Hole (1m Empty)
= pi r2h
= 3.1416 x 0.0752 x 1
Volume of the Cement Baler (total)
= 3.1416 x 0.0425 x 5.25
Volume Instrument (total)
= 3.1416 x 0.0502 x 2.3
Volume Instrument (measurement section only)
= 3.1416 x 0.0502 x 1.7
Now, assuming that the section filled with rock is 1m and 20% of that volume will require cement, the volume lost in the bottom of the hole would be:
= 17.67 x 20%
So, with 3.5L gone to be base of the hole we now had 26.3L remaining. For each meter of hole, that has the instrument in it, the volume of cement required is 17.7 L/m - 7.8 L/m = 10L/m. So, with 26L remaining, we would be capable of filling the hole to 2.6m, since our instrument is only 2.3m long, we can safely say that the instrument would be fully submerged in grout.
Backfill with small river gravel is not generally used. The preferred method is to dump a calculated bailer load for the uplift required, wait overnight for the cement to cure and then proceed with a normal deployment. The exercise was performed here for training.