8B — July 25 - August 14, 2014 — Owners, Developers & Managers — M id A tlantic
Real Estate Journal
www.marejournal.com
A rchitects & E ngineers By John T. Pusey, Jr., Earth Engineering Understanding and managing your risks with sinkholes
T
he discovery of a sink- hole on a homeowner or developers proper-
when they call the office to re- port the presence of the earth swallowing feature on their property. If the sinkhole is simply filled back in with soil or concrete without any other modifications, the probability for re-occurrence is almost a certainty. True geologic sinkholes form in areas underlain by carbon- ate bedrock composed typi- cally of Limestone or Dolomite. In southeastern Pennsylvania, a relatively thin swath of car- bonate bedrock extends from Lancaster County through central Chester County and terminates in southern Mont-
gomery County. Areas under- lain by carbonate bedrock gen- erally form a valley in between more weather-resistant rock types, such as the Great Valley situated along the Route 202 corridor between Malvern and King of Prussia, PA. Sinkholes are commonly discovered after grading ac- tivities have occurred on new construction projects or where a concentration of stormwater flow has been occurring over time. One of the most common observable indications that a sinkhole is about to form is the presence of circular depres- sion on the ground surface.
Once the surface depression is identified, the area should be cordoned off before the re- maining ground falls into the open void. The two most commonly utilized methods for repair of sinkholes are 1.) An excavation and replacement operation and 2.) a subsurface grout- ing operation. Overall, the excavation and replacement technique involves excavating the soft/loose overburden soil associated with the sinkhole activity and replacing the area with a combination of quarried aggregates, geotextile fabric and compacted fine grained
Celebrating over 20 years of Engineering Excellence soils. The grouting method typically involves installing hollow steel casing around the sinkhole and pumping a fluid grout mix into the subsurface to fill in the voids at the soil/ bedrock interface as well as densifying the overburden soils surrounding the sink- hole. Generally speaking, the excavation and replacement method is cheaper than a subsurface grouting operation but might not be the best al- ternative in many situations. A qualified geotechnical engi- neer or geologist should be on site to direct and document the chosen stabilization operation. The method for repair of the sinkhole feature should be based on the risks associ- ated with the given location in addition to its practicality. If a sinkhole forms below an existing or proposed build- ing, the subsurface grouting method would most likely be the preferred option since this approach is expected to further reduce the potential for sinkhole re-occurrence compared to the excavation method. Conversely, stabiliza- tion of a sinkhole utilizing the excavation and replacement method below a parking lot or road may be just as effective as grouting for the long term stability of the area. By involving a geotechnical engineering firm to evaluate the sinkhole activity, cost based options for repair can be presented to the owner to reduce the risk for fu- ture sinkhole activity. The most challenging aspect of a property owner is deciding how much money to spend to reduce that risk. It is impor- tant to realize however, that risk for sinkhole can never be completely eliminated. Any property underlain by carbonate bedrock will always maintain some inherent risk for sinkhole development. If you have sinkhole ac- tivity on your property, the professionals at Earth Engi- neering Incorporated would be pleased to put our many years of extensive experience in sinkhole consulting to work for you. John T. Pusey is the as- sistant director of field op- erations at Earth Engineer- ing Incorporated in East Norriton, PA. Pusey has monitored the successful stabilization of numerous sinkholes throughout PA. n
ty often leads to panic by the owner . D e c i d i n g what to do, who to call, and maybe most impor- tantly, trying to figure out
John Pusey, Jr.
how much it is going to cost to fix can be challenging. In my fifteen years of experi- ence at Earth Engineering Incorporated, I have heard the panic in people’s voices
Celebrating over 20 years of Engineering Excellence!
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Subsurface Investigations • Construction Inspection and Testing Geotechnical Design & Analysis • Environmental Site Assessments and Remediation • Clean Fill Testing • Carbonate Site Assessments Stormwater Infiltration Testing • Laboratory Soils Testing www.earthengineering.com Corporate Headquarters: 610-277-0880 • Lehigh Valley: 610-967-4540 Central PA: 717-697-5701 • South Jersey: 856-768-1001
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