By: Rodney Garret
The Global Positioning System (GPS) is increasingly becoming the tool of choice for pinpointing specified locations on many construction projects, with causeways and bridge projects being no exception. Among GPS-technology applications showing to be cost effective on bridge-building projects is in determining the precise locations for driving piles. Likewise, GPS technology use saves in production time and labor when carrying out vibra cast-in-place columns (VCIPC) projects.
An example of these GPS technology practices can be found on the Rte. 52 Causeway Bridge Replacement Project that is between Somers Point and Ocean City, N.J. The existing causeway and the new causeway project are owned by the New Jersey Department of Transportation (NJDOT). It is estimated the completed project will cost $400 million, with Phase I (Contract A) now under way at a cost of $140 million. Funding for the project is shared between the state and federal agencies.
Somers Point and Ocean City are approximately 12 miles southwest of Atlantic City. Somers Point is northwest (inland) of Ocean City, with the 2-mile causeway going over various bodies of water and islands thus linking the two towns and their respective counties, Atlantic and Cape May. Ocean City is a popular summer resort town that features both sandy beaches and a boardwalk along the Atlantic Ocean.
Here is an overview of the project and why NJDOT finds it necessary to replace the 70-year-old causeway. Primarily, it is due to a combination of age and deterioration coupled with a substantial increase in marine and highway traffic. NJDOT said the traffic flow increase is responsible for too many vehicle accidents. A major reason for this increased traffic flow (and under-the-bridge marine traffic) is vacationers and weekenders visiting the seashore resort for summer recreational activities. Marine traffic disrupts the vehicle traffic flow because the only thoroughfares are at two bascule bridges in the causeway alignment. Actually, there are four concrete bridges within the causeway alignment but the other two are fixed.
At the Somers Point end of the causeway, there is a traffic circle that will be removed. Its removal is significant for it is one of 67 such traffic circles built in New Jersey during the 1920s and ’30s. As well known and celebrated as the New Jersey traffic circles are, there are only 37 left; this is mainly because more efficient traffic-flow road designs have replaced them.
Supporting cast-in-place
The prime contractor for Phase I is George Harms Construction Co. Inc., of Farmingdale. It is a mid-size construction company employing 200 people and completing over $50 million in construction projects each year. For this project, Harms will perform all construction activities in-house, as the company does on most of its construction projects.
The four existing bridges will be replaced with two new bridges. Phase I calls for building the low-clearance sections (there are high-clearance sections, too) of the two bridges. Both are fixed, continuous-span, bulb-T bridges, each featuring four 12-ft lanes with 8-ft outside shoulders and two 5-ft inside shoulders (for northbound and southbound, respectively). Additionally, there is a 10-ft-wide walkway for pedestrians and bicyclists.
Starting at Somers Point and pointing southeast toward Ocean City, Bridge I immediately ascends on a 5% grade for high clearance over the Ship Channel and Elbow Thorofare bodies of water and then descends on a -5% grade to reach Rainbow Island. The length of the bridge is 3,600 ft. On Rainbow Island, a new 1,600-ft roadway will link Bridge I to Bridge II. Along the roadway alignment on Rainbow Island the ground is being stabilized to meet load specifications.
Two methods are being used to increase the ground support at both bridge abutments on Rainbow Island and the new highway connecting them. One method is VCIPC and the other is surplus-load/wicking.
At the Bridge I abutment on Rainbow Island, where the roadway slopes at -4.3%, the VCIPC method is carried out by building deep-hole, cast-in-place concrete shafts (columns) to support the abutment. The shaft-placement patterns vary according to the geotechnical conditions.
At the end of the abutment, where the highway starts, the surplus-load/wicking ground stabilization is carried out. First, water-wick drains are installed in the ground and an overburden 14 ft high and slightly wider than the width of the highway is built. This temporary surplus load compacts the in situ ground beneath it amply so the compacted ground can support the combined weight of the new highway and the live weight created from vehicular traffic.
Wicking enables groundwater to escape readily during the compacting ground process that is brought about by the surplus load. This compacting action squeezes the groundwater from the soil, thus enabling the ground to densify and meet specification. Once the monitored overburden stops settling (several months later), it is removed to the specified sub-base grade and a crushed-stone base is installed in several lifts, followed by the paving.
Bridge I’s high-clearance peaks (i.e., its ship passage clearance) over the ship channel at 55 ft. The horizontal clearance is 100 ft. Both clearances are more than sufficient for the biggest craft allowed to pass under the bridge. Further, the channel is deep and wide enough for accommodating ships that have relatively deep drafts.
Bridge II is similar in design to Bridge I except it is 5,900 ft long, with the final 1,200-ft section, which terminates in Ocean City, designed with a noticeable curve. The opposite end of the bridge starts on Rainbow Island with a low-clearance height passing over Rainbow Channel, continues over Garret’s Island, bridges Beach Thorofare (an intracoastal waterway) and terminates at the northwest end of Ocean City. Near the southwest end of Garret’s Island, the bridge ramps up at a 5% grade to feature similar pass-under clearances as found on Bridge I. The peaked clearance height is above the Beach Thorofare, and then the bridge descends on a -5.5% grade to terminate at the edge of Ocean City.
On Rainbow Island, VCIPC also is the method used to support the abutment at Bridge II. Instead of building a highway across the next island in the alignment, Garret’s Island, Bridge II will continue over it with a low-clearance configuration. All sections of both bridges are, except for the abutments, supported by piers set on piles.
Driving with GPS
Traditional surveying and layout methods have been circumvented while carrying out VCIPC by implementing a Leica Geosystems GPS 3-D system that is mounted on a Bauer BG 40 drilling rig fitted with a Bauer TR 17 vibration soil penetrator (VSP). VCIPC is a recent technology for North America as is the use of GPS technology to guide the drilling-rig operator to position precisely the VSP prior to commencing vibration soil penetration. The combination of these technologies is better known and more widely used in Europe.
Harms has the reputation for trying cutting-edge technology on its projects, providing its use can improve the quality of the company’s workmanship and likewise improve its productivity.
Tony Guerrieri, P.E., and a NJDOT supervising engineer on the project noted that Harms used advanced construction methods on his past construction projects.
“Harms is one of the bigger and better contractors in New Jersey. The company has been progressive in using new technology just as it is doing here by using GPS and VCIPC. The results in using these technologies here have been so far very good,” he said.
Taking the lead for Harms in applying the GPS 3-D technology is Jason Hardell, P.E., a project superintendent for this project. Hardell was convinced that using a GPS 3-D system in concert with the Bauer equipment would optimize the cost effectiveness in carrying out VCIPC.
Justin LaBarca, technical field representative for Atlantic Laser Specialists Inc., Matawan, N.J., which served as the local Leica Geosystems dealer, worked closely with Hardell to select the correct GPS components to build a system that would optimize the vibration soil penetration operation. Fortunately, the mast on the Bauer BG 40 is so designed that the Leica antenna can be installed atop with no offset compensation required when setting up the software program.
The GPS system supplied for this project included uniquely written third-party computer software for enabling the operator to see in real-time all penetrator-point positioning data on an onboard monitor that is installed inside the operator’s cab. A GX1230GG receiver (rover) also is installed inside and connected to the monitor. When not used for the vibration soil penetration operation, the GX1230GG is easily removed so it can be used as a rover.
The antenna, installed on the drilling rig’s mast, receives a signal sent from the GPS base station/antenna (with integrated GNSS/GPS) that is installed at the contractor’s field office about 1½ miles away.
Here are some advantages in using GPS for positioning the VSP compared with using the conventional survey and layout methods that include using stakes. Usually, three or more stakes are placed near and around the specified penetration spot. The stakes act as a guide for the drilling-rig operator to position the VSP point prior to commencing vibration soil penetration. Without stakes, the GPS method enables the operator to position the VSP point within ±1 in. of the wanted spot. The NJDOT specifications accept a tolerance of ±3 in.
More than 2,000 cast-in-place concrete columns will be built on this project using VCIPC. Avoiding conventional surveying and staking will eliminate 800 man-hours of a two-man crew’s time. These accrued hours are the result of the crew’s taking two to three hours each day to lay out and stake around each hole location prior to the day’s vibration soil penetration activities. Normally, the layout crew would have to start earlier in the morning before vibration soil penetration starts. This enables the crew to have some of the penetration locations laid out prior to vibration soil penetration, thus avoiding either activity from hindering the other.
The use of the GPS is not limited to carrying out VCIPC. There are precast concrete piles to install using high-pressure water to jet them into the ground, so the GX1230GG receiver (rover) is used locating each pile’s correct position. As when using GPS for VCIPC, the elimination of staking when installing piles is a major time and labor saver.
There are a total of 77 cast-in-place concrete piers to be constructed to support the bridges on the Rte. 52 job. Typical spans run 140 ft. Each pier (station) necessitates installing six to 12 piles, depending on the geotechnical conditions encountered. Accordingly, there are more than 650 piles to be driven. At each pier station, one test pile is installed. The installation position is located with the GX1230GG, and the pile is water-jetted into the ground to within 7 to 10 ft of the minimum tip.
Using one of two Manitowoc lattice-boom crawler cranes, each fitted with a Pileco diesel hammer, the pile is driven to the wanted depth while it is monitored using a pile driving analyzer (PDA) for real-time readout, and later the PDA data is analyzed. Once the test pile capacity has been determined and approved, the remaining specified number of piles for that pier station is water-jet installed and then driven with a hammer.
SIDEBAR
GPS technology saves
The use of GPS technology for pinpointing pile placement and VCIPC will no doubt grow in popularity as contractors learn how much more efficient it is compared with the traditional layout work that includes installing stakes. There is more, however. There are favorable economic results to be enjoyed by the contractor who uses GPS technology. In fact, the contractor can readily justify the capital investment associated with GPS technology because it usually can be recaptured in less than a year.
At this project, the layout and stake-installation labor eliminated a total of six man-hours a day. Daily production of 12 to 15 columns is achieved using the Bauer BG 40 equipped with Leica GPS system and the Bauer TR 17 VSP (vibra-soil-penetrator). This includes penetrating the soil 70 ft and then backfilling the hole with pumped concrete. Most hole depths are 70 ft with a diameter of 18 in., except at the very bottom of the hole where the diameter is 24 in. This greater diameter at the bottom of the hole is achieved by slightly raising and lowering the VSP continuously.
Jason Hardell, P.E., a project superintendent for George Harms Construction Co., said a similar efficiency and time savings is experienced when spotting each of the locations required to install the 550 30-in. x 30-in. x 100-ft to 140-ft precast concrete piles. The only difference is, instead of the crane operator using a GPS 3-D system in his cab, as done when using the Bauer BG 40 drilling rig, a surveyor independently uses the GX1230GG portable receiver (rover) to lay out pinpoint locations for positioning and jetting in the piles.
All structural steel members are erected using a Leica Geosystems TBS 1200 Total Station system.
VCIPC—What is it?
VCIPC is a support system method that is on the cutting edge in North America. Its origin is in Europe, where it has been practiced for some time. The German company Bauer Maschinenbau GmbH has been promoting this method along with a potpourri of other ground improvement methods suitable for construction purposes.
Equipment Corp. of America (ECA) of Philadelphia is the supplier of Bauer and Pileco equipment to the contractor. The company is a specialist in pile and foundation construction equipment. ECA regional sales consultant Bruce Langan headed up a specialist team, including tech people from Bauer, to train the operator for efficiently carrying out VCIPC.
Harms management decided to use its Bauer BG 40 drilling rig with a TR 17 VSP for the VCIPC work because of efficient production. The company had the machine in the equipment fleet and it was used on other construction projects for stabilizing soil.
The thinking behind the VCIPC method is to transfer loads to deeper and more stable soils for a superior support system. It is a cost-effective method and functions much like traditional precast concrete piles. The columns do not depend greatly on the surrounding soils for support strength. However, one major difference is the cast-in-place concrete column has no steel reinforcement as some precast concrete piles can have.
The soils found on this project lend to the VCIPC method because they can be densified by the high-frequency vibrations originating from the Bauer TR 17 VSP as attached to the Bauer BG 40.
About The Author: Garrett is a freelance writer based in Bernville, Pa.
