Down the Rabbit (Sink) Hole

 · 
May 3, 2024
 · 
3 min read
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You’re probably aware of sinkholes, but they may not impact your life until you learn that 202 in King of Prussia is temporarily closed again for an emergency sinkhole repair. What exactly are they? Why do they occur? And how do we fix or prevent them from occurring?

A sinkhole is a cavity in the ground that forms when soil moves to another, deeper cavity further below the surface. They can be as deep as a couple of feet, to the largest recorded that stretched 1,000 feet down. The underlying cavity is deep within the bedrock, which is typically limestone or carbonate rock. Some sinkholes occur naturally as soil migrates into a lower cavity by infiltrating groundwater, often the result of gravity or earthquakes. However, a vast majority are manmade and can happen during construction.

Most of these cavities, stable for thousands of years, are disturbed when we trigger a movement below. During land development, natural drainage paths can change, land is dewatered, drinking wells and drainage pipes can leak, or the overall vibration from construction causes significant changes. Also, when manmade cavities like drainage pipes, underground structures, or tunnels aren’t installed or constructed properly, soil can migrate into these voids and create a sinkhole.

So, how do we fix them? Look for the cause, such as a water leak, and cut off the source to be sure the sinkhole doesn’t become worse or happen again. Next, find the throat, which is the void where the soil above travels into the cavity below. This can be difficult when it’s small relative to the size of the cavity or so deep that digging it out is impossible. To plug the hole, we typically use flowable fill (a very wet cement/sand mixture) or a stone filter wrapped in fabric. Every hole is a bit different, and the method of fixing them varies.

How do we prevent them? This is a difficult question to answer when the natural responses would be, “Don’t build or develop near land with known sinkholes,” or “Do a better job inspecting and installing underground utilities.” These suggestions are valid but not always practical. Therefore, we developed standard practices for reducing the risk of sinkholes. We define sinkhole-prone areas using GIS databases and geologic maps. We perform thorough subsurface investigations for due diligence and implement engineered safeguards like avoiding the use of infiltration basins or requiring watertight pipe connections, just to name a few.

Many sinkholes start as a small hole at the surface, and seem harmless, but they can grow to massive sizes virtually overnight and cause extensive amounts of damage to infrastructure. Therefore, while we can’t prevent all sinkholes, our awareness combined with quick action and effective repairs can prevent catastrophic issues and avoid huge financial impacts.

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Howell 
West Chester

1250 Wrights Lane
West Chester, PA 19380

Phone: 610-918-9002
Fax: 610-918-9003

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Mechanicsburg

5020 Ritter Road #203 Mechanicsburg, PA 17055

Terrain
A Howell Company

53 Old Solomons Island Rd. Suite I
Annapolis, MD 21401

Phone: 410-266-1160

ePhase
A Howell Company

1250 Wrights Lane
West Chester, PA 19380

Phone: 610-692-7007

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