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Computerized approach to bridge foundation inspection.

By the late 1980s, the Williamsburg Bridge in New York City was in a serious state of decay. Following an intense debate among city officials and engineering consultants, a decision was made to salvage the bridge by rehabilitating it in place. A conceptual plan was developed that broke down the rehabilitation process into four successive contracts with a total estimated construction cost of over $750 million.

The first contract addressed the rehabilitation of the main cables and suspension system and was successfully completed in May 1996. The remaining three contracts are based on the concept of slicing the bridge into three longitudinal sections - north roadways, south roadways, and transit line sections. The existing approach structures will be demolished and new approaches built, consisting of reinforced cast-in-place concrete piers with a composite steel girder and concrete deck. Also included is a complete redecking of the main and end spans on the bridge.

The second contract to be let, now 30 percent completed, was reconstruction of the south roadways. In constructing the new south roadway approaches, the corresponding foundation work consists of reinforced concrete footings installed over groups of bored-in piles. The plans for building the approaches call for over 830 bored-in piles that will be installed as pier, abutment, and retaining wall foundations.

Greenman-Pedersen, Inc. (GPI) was retained by the New York City Department of Transportation to provide Resident Engineering and Inspection (REI) Services for the south roadways reconstruction contract. Under this contract, GPI is responsible for ensuring that all of the foundations are installed in accordance with the contract plans and specifications. To accomplish this task, a computerized system was needed to keep track of the inspection, report on results, and make payment for the foundation work.

Keeping track of over $30 million worth of foundation work was a sizable task, since the specifications that governed the piling work were performance oriented. Only after the contractor submitted his piling design and installation methodology could the REI staff begin to develop a plan of action for documenting this work.

To make matters more complicated, it was discovered early on that a majority of the areas below the bridge, where the new pier footings would be installed, were contaminated with hazardous materials (lead and petroleum). Paint chips from the bridge's superstructure were flaking off, dropping to the ground, and leaching into the soil. After extensive testing, some areas were identified as having hazardous levels of lead that would require complex methods of handling and disposal.

By the time the contaminated soil conditions surfaced, and the contractor had submitted his pile design, it was clear that the inspectors assigned to the foundation work would need a great deal of background information about each piling location, and would have to record significant amounts of data to accurately track and quantify the work at hand. A simple method needed to be developed for documenting the ongoing work, while providing field inspectors with the information needed to accurately assess the contractor's means and methods. Moreover, a tracking and recording system was critical for ensuring site and worker safety.

Developing a System

The first step in developing a system to track the foundation work was to determine what information was needed by the inspectors to perform the work, and what data had to be collected during the construction process. The foundation work was broken down into three task groups. First, work was required to install temporary soil stabilization elements which included installation of H-piles with lagging, excavation of the footing, and installation of whalers.

The second task was the bored-in pile installation process, which included installation of seismic casings, drilling the piles, placing reinforcement, and grouting the piles while extracting the drill casing. The third consisted of erection of footing reinforcement steel and pouring the concrete footings. Once the work was grouped, it was easier to focus on the in formation being utilized by each group.

Figure 1 shows a flowchart that lists the information that was to be collected under each of the above groups of work. List development also depended upon the pay items used for the work and the method of payment for each of those items. Field inspectors worked with the contractor to identify the information and determine what contract information was required in the field to improve performance. It was agreed that the pay quantities to be used for the work would be taken from the dimensions and quantities shown on the approved shop drawings.

Essentially, the measurements were already determined for the purposes of payment. In case of a dispute, or if field conditions were not accurately shown on the shop drawings, the tracking system was designed to make use of both the shop drawings measurements and to collect field measured data.

Upon completion of this phase of the project it was decided that a database with links to graphic image displays of the work would be best suited for the task at hand. In addition, data input would be performed in the field as the work progressed, to minimize the additional work load on the field office staff.

Initially, readily available software systems were used to minimize the expense of adding new software. Due to incompatibility with database file structures, the team switched to Lotus Approach as the database engine, FieldNotes 4.0 was used for the field portion of the software.

A significant amount of shop drawing information had to be input to the various database fields and reviewed for accuracy, Despite the tedium of this process, it was essential at this stage to define the characteristics of each data field before building the databases. The few fields that were uncertain at the start were extremely difficult to integrate into the system at a later date.

As each database was created and all known information entered, the databases were linked to each other as out- lined in the flow model [ILLUSTRATION FOR FIGURE 1 OMITTED]. It was clear at this point that the choice of using a separate database containing the drilling logs was really going to pay off. With the system fully integrated, an inspector could create an unlimited number of drill log entries on each individual pile installed, This eliminated the chance that a pre-established number of entries was not enough, and it also eliminated numerous blank fields in each pile record if the inspector recorded less entries than anticipated. Using a separate database limited the size of the files and used a minimum amount of hard disk space on the notebook computer.

With the databases completed, images were selected to be used with the graphical information system. As a base drawing, the footing layout plan from the contract drawings was used. Fortunately, the drawings were received in electronic format from the designer and simply modified to suit the project needs.

Temporary piles, lagging outlines, and individual footing piles were added to the original layout drawing using a CADD package. Computer images of temporary and permanent pile layouts were recreated for each footing type, based upon sketches taken from the approved shop drawings.

The graphic elements on these drawings were then separated into different layers of the drawing; temporary piles and lagging on one layer, permanent footings on a second, permanent piles on a third, and the rest of the graphics on a fourth layer. By separating the images onto layers the staff could later link these elements to their respective databases.

Two other key graphical elements were also selected. Soil profiles were taken from boring logs adjacent to each footing row, and profile sketches were made of each pile showing tip elevations, cutoff elevations, and other essential pile information. A VisualBasic program was used with AccuSoft to scan the images into the computer and divide them into separate image files to be used as illustrations for reference in FieldNotes 4.0. The images were finally linked to each database and user friendly input screens were developed for the GIS to tie it all together.

The result of this work was a program that starts by displaying the base drawing of the footing plan for the bridge. For the temporary H-pile and lagging work, the inspector clicks on the lagging outline and an information screen pops up that displays critical temporary piling data. From this screen the inspector can move to input screens for H-pile installation and field measurements for excavating simply by clicking on the folder tabs at the top of the screen.

When inspecting the permanent pile installation, the inspector simply clicks on the individual pile being installed and a general information/input screen pops up. This screen prompts the inspector for relevant data and also displays a graphical image of the pile configuration. By clicking on the folder tabs, the inspector can input information about each phase office pile installation or view a soil profile for the work area at hand.

When the actual drilling is taking place, the inspector clicks on the "Drilling" folder tab, which launches a new database that is set up as a drilling log. This log can be launched to either enter new data or review previously entered logs.

After the piling work is completed, the pile cap will be installed. Again, the inspector simply clicks on the outline of the pile cap and another information/input screen pops up. This screen is similar to those with folders for different facets of the work and graphical displays of the pile cap.

By linking all of the above operations to one footing layout plan, the inspector can record necessary inspection data and rapidly switch from one work operation to another. After recording data in the field, the information is downloaded to an office computer where it is organized and printed out for payment and progress reporting.

Implementing the System

After several months of review, the system was installed onto a Fujitsu Stylistic 500 notebook computer for use in the field. It was critical at this point to identify any problems before beginning a field trial. Again, the piling inspectors reviewed the program and commented on its capabilities. Finally, the GIS staff made modifications based on these comments.

One critical element brought out during the review is noteworthy. During system design, one of the facts overlooked was that all the input screens required pen writing to input field measurements and data. At first, the writing method appeared sufficient, but it was then realized that the computer often incorrectly interpreted the inspector's handwritten numbers and letters.

Fortunately, the GIS staff was able to install a pop-up scaled down keyboard that could be accessed by clicking on an icon. This keyboard allowed for rapid, accurate data entry in the field and would also allow modifications to previously entered data. In addition to the keyboard, several pull down menus for input fields that had restricted options were also added.

By the time the piling operations re-started in Spring 1996, the new computer tracking system was ready to be implemented. Initially, only one notebook computer was sent to the field as a test, with excellent results. The initial response to the amount of information displayed and the simple data entry was extremely positive. For one, entering the data directly into the computer was easier and less time-consuming than taking notes during the operations and later rewriting them into an inspection report.

The system eliminates the repetitive manipulation that takes place when a completely non-computerized system is used. By making computer entries in the field, the process of tracking, reporting, and paying for the piling work is much more efficient.

The system proved its effectiveness when a new piling subcontractor was retained by the prime contractor and design alterations were executed. Modifications were easily made on the entry screen. This made the transition easier by allowing the piling inspectors to call up information at specific locations. With a click of the pen, the information was at their fingertips.

As the Williamsburg Bridge project demonstrates, data systems can effectively replace the "trunk" full of documents inspectors typically rely on, and organize them into key graphical information easily displayed on a pen-based notebook computer. On the horizon there exists a job where after inspecting a $150-million project, one compact disc and a few boxes of non-computerized paperwork are turned over to the owner instead of today's final close-out package consisting of hundreds of boxes of miscellaneous record.
COPYRIGHT 1996 Hanley-Wood, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1996 Gale, Cengage Learning. All rights reserved.

 
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Author:Brindley, Peter V.; Trapani, Philip B.; Deacutis, Francine
Publication:Public Works
Date:Nov 1, 1996
Words:2059
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