Real Estate Journal — Pennsylvania — February 13 - 26, 2015 — 7C


M id A tlantic

P ennsylvania By John T Pusey, Jr., Earth Engineering, Inc. Understanding and managing your risks with sinkholes


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 excava- tion method. Conversely, stabilization 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 geotechni- cal engineering firm such as Earth Engineering to evaluate the sinkhole activ- ity, cost based options for repair can be presented to the owner to reduce the risk for future sinkhole activity. The most challenging as- pect of a property owner is deciding how much money to spend to reduce that risk. It is important to realize however, that risk for sinkhole can never be completely eliminated. Any

property underlain by carbon- ate bedrock will always have some inherent risk for sink- hole development. If you have sinkhole activity on your property, the profes- sionals at Earth Engineering Incorporated would be pleased to put our many years of ex- tensive experience in sinkhole consulting to work for you. John T Pusey, Jr. is as- sistant director of field operations at Earth Engi- neering, Inc. in East Nor- riton, PA. The firm has specific exper- tise in geotechnical investiga- tion, design, and consulting. n

The grouting method typically involves installing hollow steel casing an and around the sink- hole 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 surround- ing the sinkhole. Generally speaking, the excavation and replacement method is less expensive than a subsurface grouting operation but it might not be the best alternative in many situations. A qualified geotechnical engineer or geolo- gist should be on site to direct and document the chosen sta- bilization operation.

he discovery of a sink- hole on a homeowner or developers property

often leads to panic by the owner. De- ciding what to do, who to call, and maybe most importantly, trying to fig- ure out the

John T Pusey, Jr.

cost to repair can be chal- lenging. In my fifteen years of experience at Earth Engi- neering Incorporated, I have heard the panic in people’s voices when they call the office to report 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 typically of Limestone or Dolomite. In southeastern Pennsylvania, a relatively thin swath of car- bonate bedrock extends from Lancaster County through cen- tral Chester County and termi- nates in southernMontgomery County. Areas underlain by carbonate bedrock generally form a valley in between more weather-resistant rock types, such as the Great Valley situ- ated along the Route 202 cor- ridor between Malvern and King of Prussia, PA. Sinkholes are commonly dis- covered after grading activities have occurred on new construc- tion projects or where a concen- tration 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 depression on the ground surface. Once the sur- face depression is identified, the area should be cordoned off before the remaining 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 grouting operation. In general, the exca- vation and replacement tech- nique involves excavating the soft/loose overburden soil asso- ciated with the sinkhole activ- ity and replacing the area with a combination of quarried ag- gregates, geotextile fabric and compacted fine grained soils.

Celebrating over 20 years of Engineering Excellence!


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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