Viaduct ReplacementWith ECA Drilling Rigs

The inTernaTional deep foundaTions and marine consTrucTion magazine

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mar/apr 2016Volume 32, issue 2

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JOB STORY

A BAUER BG 18 H Rotary Drilling Rig sits wedged between an earthen embankment,

a shotcrete-covered bridge abutment, a maze of rusty steel trestles, and the un-derside of a historic railroad viaduct in Swarthmore, Pa. on a glacial January morn-ing. The rig, working in a low overhead configuration, was supported by a BAUER BG 20 H, both of which prime contractor Walsh Construc-tion of Chicago rented from the nearby Aldan, Pa. office of Equipment Corporation of America (ECA).

ReBUiLding A HiSTORic ViAdUcT

This high-profile $89.9-million Southeastern Pennsylvania Transporta-tion Authority (SEPTA) project requires the complete replacement of the 925-foot-long, 100-foot-high Crum Creek Viaduct. The structure Walsh is replacing, built in 1895, underwent repairs in 1983 but was in dire need of replacement to safely carry SEPTA’s passengers on the Media/Elwyn commuter rail line. The original bridge

on this site was a pre-Civil War era, five-span timber arch truss bridge on masonry piers. It was owned by the Philadelphia, Baltimore & Washington Railroad (PW&B RR) and later acquired by the Pennsylvania Railroad.

Walsh began construction on the substructure in Sum-mer 2015 and is working ag-gressively toward an etched in stone deadline of Summer 2017. Despite the variety of

construction processes in-volved, drilling the founda-tions for new footings, piers, and abutments was the key to the project.

nO ORdinARY SiTe cOndiTiOnS, nO ORdinARY dRiLLing RigS

Walsh and ECA began dis-cussing the project in March 2015 at The International Foundations Congress &

Equipment Exposition (IF-CEE). ECA’s Aldan Branch Manager Tim Dutton and Engineering Sales Manager Gordian Ulrich walked the site in April with Walsh Su-perintendent Richie Vance to determine which drilling rigs would work best on this challenging site.

It was ultimately deter-mined that Walsh would rent the BG 18 H and BG 20 H Premium Line Drilling

By Brian M. Fraley, Fraley AEC Solutions

ecA dRiLLing RigS A PeRfecT fiT fOR ViAdUcT RePLAcemenTSwarthmore, PA

The BAUER BG 18 H Rotary Drilling Rig works in low overhead configuration to install drilled shafts near the Crum Creek Viaduct west abutment with limited overhead clearance. Walsh rented the BG 18 H and BG 20 H from Equipment Corporation of America to install eight 20- to 58-foot-deep, 36-inch-diameter drilled shafts at each pier and 12 at each abutment.

pilebuck.com | Vol.32 No.2 2016 | pile buck magazine 25

Rigs because they were light enough to navigate rough terrain with adequate hydraulic output to core through hard rock of up to 25,000 psi. The low head-room capability of the BG 18 H was determined to be opti-mal for drilling in work areas with height restrictions.

ECA delivered both drill-ing rigs in June 2015. The BG 20 H, part of the Aldan location’s existing rental fleet, worked on site through Christmas. ECA coordinated manufacturing and delivery of the BG 18 H with BAUER Maschinen and imported the rig from Schrobenhausen, Germany. Its unique ability to work in both low overhead and standard configuration kept the BG 18 H on site until February 2016. ECA brought

in an operator from BAUER to assist with training, but all on-site service and reconfiguration of the BG 18 H was handled by its own technicians in Aldan.

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 op-posed 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 4 emission standards, and are heavier machines with greater hy-draulic output.

fOUndATiOn WORk SeTS THe PAce

Walsh is tasked with building a new viaduct beneath the original struc-ture before demolition can commence. The keystone of the project is foundation work for the substructure, which includes two abut-ments and four sets of piers. Walsh used the BG

18 H and BG 20 H Drilling Rigs to install eight 20- to 58-foot-deep, 36-inch-diameter drilled shafts at each pier and 12 at each abutment.

Vance indicated in Janu-ary 2016 that drilling was a week and a half behind schedule primarily due to unexpectedly hard rock and environmental permit-ting delays, but he was

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Walsh Construction is replacing the 925-foot-long, 100-foot-high Crum Creek Viaduct in Swarthmore, Pa.

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JOB STORYconfident 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 says, as a SEPTA railcar rattles across the viaduct behind him. “De-pending on how that goes, it’s almost how the whole job goes.”

SOiL cOndiTiOnS? iT’S cOmPLicATed

Project Geologist Bill Bradfield of Schnabel Engi-neering’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 says, noting that meta-morphic rock in this region can be highly variable over short distances.

The site contained primarily Schist, but production was hampered when crews hit Amphibo-lite. This extremely hard metamorphic rock was prevalent near the western abutment and the Crum Creek channel.

Bradfield recalls watch-ing production drastically improving from as little as two feet per day with an auger to a foot an hour using the BAUER roller bit core barrel, which is recognized as a respectable rate of pro-duction 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 confirms Brad-field’s observations, noting that the production increase was mainly due to the switch from conventional tooling to the BAUER roller bit core barrel. “With con-ventional tools they were getting two to three feet per day,” he recalls, pointing to an extracted four-foot Amphibolite core. “When the roller bit core barrel was running in optimal condi-tions 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

says, 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 pri-marily 36-inch augers, core barrels, drilling buckets, and roller bit core barrels. There were a few 42-inch tools for overburden areas where the rock was not immediately below the surface.

SiTe AcceSS, LOW OVeRHeAd, STeeP SLOPeS & ViBRATiOn mOniTORing

The topography surround-ing the viaduct is compli-cated by steep inclines, wetlands, the meandering Crum Creek, and a narrow,

snake-like access road, all encapsulated within a densely wooded area that happens to be a designated arboretum. This challenging terrain dictated not only the selection of rigs, but also the site preparation.

One of Walsh’s main chal-lenges; however, was drilling foundations in hard rock beneath the viaduct with limited headroom near the east and west abutments. Watching the BG 18 H drilling below the farthest western span of the viaduct, makes it clear why its unique low headroom capabilities were essential. The rattling tip of the mast is within mere inches of the steel girders. The BG 18 H worked in standard configuration from late June through early October and was then recon-figured to low headroom.

Site Geologist Bill Bradfield of Schnabel Engineering measures the depth of a

recently drilled shaft beneath the viaduct.

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JOB STORYVance says the height

restricted areas were more severe than expected because the viaduct eleva-tions Walsh was initially given did not account for drilling nuances. He indi-cates that maneuvers such as putting the drilling rig in crowd force, or pulling up a full bucket can require up to eight inches of additional overhead space.

One of SEPTA’s key con-cerns was ensuring that its commuter trains could con-tinue to pass safely across the existing viaduct during construction. Every pier and tower on the viaduct has a sensor to monitor for vibra-tion. There are also four inclinometers in each slope to measure movement.

cUSTOm cASing dRiVe AdAPTeR RedUceS WASTe & cOST

ECA designed and fabricated a custom casing drive adapter for Walsh to facilitate overburden drill-ing. Dutton watches as the operator of the BG 18 lowers the mast, inserts the adapter into J-shaped notches in the casing, and begins to seam-lessly drill it into the soil from the cab of the rig.

“We fabricated that at the Aldan shop,” he says, as the casing descends into the soil. “You need some-thing to transfer the torque against, so Walsh cut those j-shaped notches in the top of the casing.”

Vance says this innovation reduced costs and elimi-nated wasted material. “We pulled a lot of the casings out as we drilled shafts so we saved a lot,” he says.

BRidging THe gAP BeTWeen UTiLiTY & AeSTHeTicS

Walsh has demonstrated considerable environmental sensitivity throughout the project because of active involvement by neighbor-ing Swarthmore College. Although 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 Emi-nent Domain. In addition to obtaining permitting from multiple agencies, the con-tractor will have to rebuild

wetlands, replace up to 6,000 trees and shrubs, and reconstruct a Stonehenge-esque circular formation of Wissahickon Schist slabs dubbed “Crumhenge” by locals.

SEPTA will shut down service for roughly 10 weeks during Summer 2016 to allow Walsh to install new girders, bridge deck, and cat-enary towers. Rail cars will travel over the new viaduct by Labor Day 2016. Walsh will conclude the project by Summer 2017 with demoli-tion of the existing struc-ture, removal of the access road, and restoration of the

site to original condition.As SEPTA passengers,

college students, and lo-cal residents admire the towering modern viaduct that has replaced the rusty, outdated structure that once straddled this area of natural beauty, the critical foundation work performed by two drilling rigs with custom tooling will remain unknown. The folks at Walsh, ECA, and BAUER; however, will relish their role in providing safe pas-sage for mass transit pas-sengers and improving the aesthetics of a critical piece of infrastructure.

ECA designed and fabricated a custom casing drive adapter to facilitate the drilling of overburden. It reduced costs and eliminated wasted material by

allowing Walsh to easily remove and install casings during the drilling process.