The objective was to replace the Harrison Avenue Bridge in Scranton, Pennsylvania, which was built in 1922 and had outlived its usefulness. 3C Drilling, LLC was contracted to drill (7) 96” diameter piers ranging in depth from 35’-55’ deep. (10’-12’ overburden and 43’-45’ rock) One pier was for a test pile and then (3) piers on each side of Roaring Brook and Central Scranton Expressway.
Drilling was bid, anticipating an average of 2’-3’ of rock drilling per day, utilizing conventional augers and core barrels and a template set-up to drill (7) holes 24” diameter to tip elevation with a mono hammer and bit. Drilling commenced in December 2015. 3C augured down to top of rock, set casing and then grouted the template in place with low psi grout. It took three days to drill the (7) 24” diameter holes to tip, then switched back to conventional tools.
On day one, drilling went pretty much as planned using conventional tools. 3C drilled 20’, the next day 5’, then 4’, then 1’, then 3”, and then 9”. Needless to say, the daily production was unacceptable. 3C decided it was time to change tools and went to a Center Rock 58” LP Drill and were able to drill center out all the way to tip in four days. 3C then went back to conventional tools and drilled from 8’ to 49’ in seven days and could not advance any further.
They then went back in with Center Rock’s 58” LP Drill and literally worked it around the OD of pier and drilled wherever the hammers would fire. The first (2) piers took approximately seven weeks each to drill.
3C then made contact with Center Rock for a better solution. Richard Soppe recommended a full face 66”LP Drill for the pilot hole and a 96” x 66” LP hole-opener. When the new LP drilling tools arrived, the third shaft was started with a 68” diameter centralizer set on rock. Then the 66” LP Drill began drilling the hard rock. It was set-up with a 4’ long calyx basket and a ratchet attachment to operate on 3C’s R-625 Soilmec drill rig with standard telescoping kelly bar.
Penetration rate for this section averaged 15’– 25’ per day depending on hole depth. The 66” LP Drill was set aside and the 96”x 66” LP hole-opener was hooked up and drilling commenced. Because of the combined weight of the kelly bar, LP Drill, and cuttings the drilling had to be done in 1.5’ lifts. The 96” LP hole-opener penetration rate was 12’ – 20’ per day depending on hole-depth.
This was a very challenging project for all involved. The first (2) shafts: One 51’ and one 55’ took 14 weeks to complete even with the 24” relief holes and drilling out the center with Center Rock’s 58” LP Drill. The last (2) 55’ shafts on the first side took eight days to complete with Center Rock LP Drills. Second side production was (1) shaft at 51’-6” which took five days to complete, and (2) shafts at 35’ which took two days each.