This can be done with a bar hole
or hammer drill either before or after the coring process.
Subsequent bar hole
surveys indicated a major underground gas accumulation of about 270 feet by 170 feet and peripheral gas accumulation of about 380 feet by 220 feet (Figure 2).
If no opening (12 inches x 12 inches opening) exists in the asphalt or pavement near the service rise, a CGI reading performed in conjunction with a bar hole
placed near the riser is necessary.
Record bar hole readings, manipulate data, and use diagnostic tools to analyze gas concentrations.
Each bar hole, for example, is assigned one of ten symbols depending on its latest reading.
Then, as the search progresses, they can compare the pattern of a single bar hole over time to determine effects of repair or adjustment.
The operator can direct a steady flow of air down the bar hole or a quick burst if needed.
After the surface hole has been created, the sinker drill is retracted and swung out of the way so the auger can be fed directly into the bar hole.
A bar hole 5- to 6-ft deep can be drilled in a single pass with the use of the standard 5-ft auger and a 3-ft extension.
Ergonomic tommy bar holes
make assembly easy and eyebolts are included for nut models over 30 kg.
Bar holes suggest the tower could be secured against attackers.
Inside the porch is a 12th Century Norman doorway, again with bar holes.