Page 122 • March 23, 2016 • www.constructionequipmentguide.com • CONSTRUCTION EQUIPMENT GUIDE
Premium Line Rigs Offer More Crowd Force, Greater Output RIGS from page 8
These Premium Line rigs offer some additional benefits over Bauer’s Value Line that were ideally suited for the Crum Creek Viaduct project. The main difference between the two is that the Premium Line features a crowd cable system with a winch as opposed to the crowd cylinder system on the Value Line. The Premium Line rigs, as a result, deliver more crowd force. They also comply with the latest Tier IV emission standards, and are heavier machines with greater hydraulic output. Foundation Work Sets the Pace Walsh is tasked with building a new viaduct beneath the original structure before demolition can commence. The keystone of the project is foundation work for the substructure, which includes two abutments and four sets of piers. Walsh used the BG 18 H and BG 20 H Drilling Rigs to install eight 20- to 58-ft. (6 to 17.6 m) deep, 36-in. (91.4 cm) diameter drilled shafts at each pier and 12 at each abutment. Vance indicated in January 2016 that drilling was a week and a half behind schedule primarily due to unexpectedly hard rock and environmental permitting delays, but he was confident that Walsh would be back on track shortly. Despite the unforeseen challenges, Vance was satisfied with the drilling production rate. “Drilling is make or break,” he said, as a SEPTA railcar rattles across the viaduct behind him. “Depending on how that goes, it’s almost how the whole job goes.” Soil Conditions? It’s Complicated Project Geologist Bill Bradfield of Schnabel Engineering’s West Chester, Pa. office describes the Crum Creek site as “interesting.” “We ran the full gamut of drilling conditions within the span of this bridge,” he said, noting that metamorphic rock in this region can be highly variable over short distances. The site contained primarily Schist, but production was hampered when crews hit Amphibolite. This extremely hard metamorphic rock was prevalent near the western abutment and the Crum Creek channel. Bradfield recalled watching production drastically improving from as little as 2 ft. (.6 m) per day with an auger to 1 ft. (.3 m) an hour using the Bauer roller bit core barrel, which is recognized as a respectable rate of production in hard rock. Walsh initially tried a cluster drill but had no luck keeping the tool straight. The switch to roller bit core barrels also quieted drilling chatter and reduced the strain on the drilling rigs.
Roller Bit Core Barrel Keeps Production Rolling Dutton confirmed Bradfield’s observations, noting that the production increase was mainly due to the switch from conventional tooling to the Bauer roller bit core barrel. “With conventional tools they were getting two to three feet per day,” he recalled, pointing to an extracted Amphibolite core. “When the roller bit core barrel was running in optimal conditions they were getting a foot an hour in some really hard rock.” Conventional drilling tools could not stand alone on this site, according to Dutton. “This is the beast here that did a lot of the hard rock drilling,” he said, pointing to a Bauer roller bit core barrel. Walsh initially considered down-the-hole and hammer drills, but ultimately decided the core barrel was the right tool for the job. Walsh purchased 10 tools from ECA, including primarily 36-in. augers, core barrels, drilling buckets, and roller bit core barrels. There were a few 42-in. (106 cm) tools for overburden areas where the rock was not immediately below the surface.
operator of the BG 18 lowered the mast, inserted the adapter into Jshaped notches in the casing, and began to seamlessly drill it into the soil from the cab of the rig. “We fabricated that at the Aldan shop,” he said, as the casing descends into the soil. “You need something to transfer the torque against, so Walsh cut those j-shaped notches in the top of the casing.” Vance said this innovation reduced costs and eliminated wasted material. “We pulled a lot of the casings out as we drilled shafts so we saved a lot.”
Bridging the Gap Between Utility & Aesthetics Walsh has demonstrated considECA designed and fabricated a custom casing drive erable environmental sensitivity adapter to facilitate the drilling of overburden. It reduced costs and eliminated wasted material by throughout the project because of allowing Walsh to easily remove and install casings active involvement by neighboring Swarthmore College. Although during the drilling process. SEPTA had the right-of-way available for the viaduct, it negotiated with the college to use a necessary adjacent piece of land instead of using eminent domain. In addition to obtaining permitting from multiple agencies, the contractor will have to rebuild wetlands, replace up to 6,000 trees and shrubs, and reconSite Access, Low Overhead, struct a Stonehenge-esque circular Steep Slopes & Vibration formation of Wissahickon Schist Monitoring slabs dubbed “Crumhenge” by The topography surrounding the locals. viaduct is complicated by steep SEPTA will shut down service for inclines, wetlands, the meandering roughly 10 weeks during summer Crum Creek and a narrow, snake-like 2016 to allow Walsh to install new access road, all encapsulated within a girders, bridge deck and catenary densely wooded area that happens to towers. Rail cars will travel over the be a designated arboretum. This chalnew viaduct by Labor Day 2016. lenging terrain dictated not only the selection of rigs, but also the site Site Geologist Bill Bradfield of Schnabel Engineering Walsh will conclude the project by measures the depth of a recently drilled shaft beneath summer 2017 with demolition of the preparation. existing structure, removal of the One of Walsh’s main challenges, the viaduct. access road and restoration of the however, was drilling foundations in hard rock beneath the viaduct with limited drilling rig in crowd force, or pulling up a site to original condition. As SEPTA passengers, college students headroom near the east and west abutments. full bucket can require up to 8 in. (20 cm) of and local residents admire the towering Watching the BG 18 H drilling below the additional overhead space. One of SEPTA’s key concerns was ensur- modern viaduct that has replaced the rusty, farthest western span of the viaduct, makes it clear why its unique low headroom capabil- ing that its commuter trains could continue outdated structure that once straddled this ities were essential. The rattling tip of the to pass safely across the existing viaduct dur- area of natural beauty, the critical foundation mast is within mere inches of the steel gird- ing construction. Every pier and tower on the work performed by two drilling rigs with ers. The BG 18 H worked in standard con- viaduct has a sensor to monitor for vibration. custom tooling will remain unknown. The figuration from late June through early There are also four inclinometers in each folks at Walsh, ECA and Bauer, however, will relish their role in providing safe pasOctober and was then reconfigured to low slope to measure movement. sage for mass transit passengers and improvheadroom. Custom Casing Drive Adapter ing the aesthetics of a critical piece of infraVance said the height restricted areas were Reduces Waste & Cost structure. more severe than expected because the ECA designed and fabricated a custom (This story also can be found on viaduct elevations Walsh was initially given did not account for drilling nuances. He indi- casing drive adapter for Walsh to facilitate Construction Equipment Guide’s Web site at cated that maneuvers such as putting the overburden drilling. Dutton watched as the www.constructionequipmentguide.com.)