Remediation of the Centenary College President's House

A week after the New Year 2015, a fire started in the over 125-year-old President’s House at Centenary College, Hackettstown, New Jersey. Large quantities of water were used to put out the fire on that freezing night. As a result, a roughly 22-foot diameter sinkhole opened near the back door, causing a fireman to fall into the collapse. Subsequently, approximately 11⁄2 to 2 cubic yards of pumpable, flowable fill was placed into the sinkhole throat. The house was a loss and demolished in the late spring of 2016, leaving the foundation in place. During long delays resulting from local zoning laws being somewhat different than they were in 1910 (when the house was moved to its present location), another sinkhole opened below the rear foundation wall and basement floor slab. Approval was granted to build a similar structure within the existing footprint of the historic home and the old foundation was removed in April 2016. To support the new structure in an area known for sinkhole formation, an exploratory grouting program was employed. 45 probe holes were drilled and grouted with 88.4 cubic yards of site-mixed, fluid grout. The subsurface conditions were erratic and difficult to model as the voids encountered were not large in size, nor very linear, but appeared to extend for distances beyond the house footprint. The new structure was completed in 2016. Introduction The President’s House was originally built as the Bright Stowe house in the “Millionaires Row” section of Morristown, NJ in 1890. It was dismantled and moved by rail to Hackettstown, NJ, to a lot across the street from the College. It was reconstructed in 1910 and subsequently purchased by the college in 1945. Under the college’s ownership, it housed five college presidents, but has been used for meetings, gatherings and housing guests more recently. It was gutted by fire in January 2015. The authors have been involved in a number of sinkholeand karst related projects for Centenary College (now Centenary University) in the past. Therefore, it was no surprise when we were called to inspect a sinkhole that formed adjacent to the President’s house as a result of the large quantities of water used in an attempt to extinguish a raging fire. A firefighter reportedly fell into the collapse as it formed. We were asked to inspect and remediate the sinkhole so that demolition work could safely begin on the house. During our inspection, we also noted two depressions in the rear yard that may have been sinkhole precursors. The valley in which the college is situated is a geologically complex portion of the Valley and Ridge physiographic province of northern NJ. There are a variety of sedimentary formations, many carbonate, with a glacially altered landscape. As in most Appalachian Karst landscapes, the bedrock has been highly tectonized, leaving the bedrock faulted, fractured and folded with varying bedding and fracture angles. Solutioning in this hard rock environment is usually slow and additional solutioning is likely not of concern during the economic lifetime of most structures. Therefore, karst remediation efforts are generally directed toward the existing conditions. The college campus is a little larger than a square mile in area and is mantled by residual and glacially derived soils atop at least three carbonate bedrock formations. In our previous experience at the campus and in the region, bedrock solutioning takes place along a complex set of bedding and fracture channels that, collectively, can account for significant overburden volume or grout losses. Often times, the channel system includes cavities of significant size, but their extent is extremely difficult to determine because of their usually complex shape. The President’s House is on the northwest side of the campus and is mapped as being underlain by Flanders Till Joseph A. Fischer Geoscience Services, 1741 Route 31, Clinton, New Jersey, 08809, USA, geoserv@hotmail.com Joseph J. Fischer Geoscience Services, 1741 Route 31, Clinton, New Jersey, 08809, USA, geoserv@hotmail.com Justin Terry Compaction Grouting Services, Inc., 375 Parkmount Road, Media, Pennsylvania, 19063, USA, jterry@cgsinc.net