Petty's Run - Capital Park

Crack Gauge Monitoring

In November 2008, the City of Asbury Park requested that our client, Madison Marquette Realty Services, install crack gauges on the reinforced concrete piles that support the Convention Hall in order to learn if there is active movement. With this direction, S. Harris & Co. conducted a survey of the piles in order to obtain a general layout and understand the level of deterioration. The piers that were farther east were most damaged, as these piers were at one time fully submerged in the Atlantic Ocean. Over time, the hostile saline environment eroded many of the thirty-inch diameter piers down to half their size. In the early 1970s, a seawall was constructed to the east of the building and a jetty to the north, to prevent the water from breaking on the piers. The jetty and seawall prevent most water from reaching the piers, but there are several instances during the year where waves extend past the seawall.

Although we do not have foundation plans from the buildings inception in 1929, we believe that the piers were constructed utilizing driven steel, closed-ended casing piles that were then backfilled with concrete. The columns directly above the piers were then connected to the piers with reinforcement steel. Due to the level of deterioration, we were able to view the reinforcement steel cages inset within the concrete. In order to identify which piers should receive monitoring, we prepared construction documents indicating twenty-two locations to install crack gauges. We felt that this number was adequate for the 120 pier foundations.

The gauges were inexpensive and fairly easy to obtain. We purchased our gauges online from Humboldt Manufacturing Company for $17 apiece, at http://www.humboldtmfg.com/. The crack monitor gauge that we specified, the H-2936, is simple and accurate for monitoring and charting movement of cracks and joints in concrete and masonry structures. The gauge consists of two independent pieces of plastic that overlap with a grid. As the crack separates, the gauge moves further apart, taking the grid along for the ride. Movement is indicated by crosshairs on a grid and is recorded by periodically copying the crosshair positions onto an accompanying chart.

Procedure
All twenty-two gauges were installed in approximately one hour. All loose material and debris were cleaned off of the piers to achieve a clean mounting surface. The gauges were mounted onto the concrete piers, which were then drilled with screws for attachment. A non-metallic, non-shrink, grout was squirted into the gap between the front face of the concrete pier and the back side of the gauge in order to create a flush mountable surface. Once the epoxy set up, the tape binding the two pieces of the crack gauge was cut so that both sides were free to move as the crack expands and contracts.

Conclusion
Although movement may be indicated by the crosshairs on the gauge, it may not necessarily yield useful results as to the condition of the building foundation. Structural damage to the foundation due to corrosion is mainly noticeable in the form of the prevalent concrete spalling or the failure of elements. Consequently, this is the first step in a series of investigations to learn if the piers are truly geotechnically adequate.

Ultimately, research and field exploration will have to be implemented by a geostructural engineer. We were able to measure the circumference and diameter of the piers, but more in depth exploring will have to be conducted in order to determine the length. Also, the piers must be evaluated to determine the loading capacity. Analysis must be conducted to learn if underpinning or reinforcement is necessary. If they are inadequate for the proposed loads, there are several ways to increase their loading capacity without losing building fabric.