Pittsburgh Post-Gazette (TNS) by Anya Litvak
Pittsburgh-based engineer Richard Gray provided two fundamental ideas in a brief history of sinkholes and troughs, which are formations that can occur when a portion of an abandoned coal mine collapses:
In a 2020 edition of the book Surface Subsidence Engineering, Gray stated that it is impossible to foresee when ancient, abandoned voids—many of which were produced during a coal mining boom in the early 1900s—will reveal themselves at the surface. According to estimates, millions of homes and structures are situated on top of Pennsylvania’s dubious status as the state with the greatest inventory of abandoned mines.
It’s strange what seems to have happened to Elizabeth Pollard, 64, whose body was found in a pit 30 feet deep.
However, sinkholes aren’t. Simply put, they are usually far shallower than that.
In Pennsylvania, a number of mines were destabilized and abandoned. In addition to offering mine subsidence insurance, the state provides a website where residents may determine whether the coal beneath their houses has been hollowed out.
The top of a sinkhole in the town of Marguerite, Pennsylvania, where a lady vanished, is depicted in this Tuesday, Dec. 3, 2024, photo from the Pennsylvania State Police. (AP, file; Pennsylvania State Police)AP
The answer is probably going to be yes in a large portion of southwest Pennsylvania.
Small pick-axe digs gave way to the more industrial room and pillar method of coal extraction in Pennsylvania in the 1800s. In this process, the coal seam would be carved out in some places but left intact in others, allowing pillars to support the mine’s ceiling.
According to Gray, this meant that between 60 and 70 percent of the coal was still underground. Coal operators sought to extract more of the commodity that was driving Pittsburgh’s steel boom by the turn of the 19th century. Smaller pillars were found in newer mines, and some businesses had started retreat mining, in which the roof collapsed because the pillars were mined as they were leaving.
More work to be done
The sinkhole in Unity Township originated at the room and pillar Marguerite Mine, which was closed in the 1950s. Overburden, or the layers of rock and soil above the coal seam, was present at the scene of Pollard’s death for roughly 20 feet.
According to study, sinkholes typically occur where the overburden is less than 50 feet.
According to Joe Bonetti, a geologist and project manager at Howard Concrete Pumping Co. Inc., located in Cecil, they are usually not very deep. They are created when a pillar gives way or a mine ceiling collapses.
Since the 1980s, he has been stabilizing mines by using grout to fill in the holes left by abandoned mines and stop them from sinking. He claimed that in recent decades, there has been a significant increase in awareness of the issue.
Pennsylvania claims to have restored 91,000 acres as part of its ongoing efforts to address the issue of abandoned mines. However, roughly twice that much, according to the state, still need attention.
Although Bonetti claimed to have completed hundreds, if not thousands, of projects, he would not consider himself an expert in sinkhole prediction.
He stated that no one is. You may say that it’s likely to occur. You cannot claim that it will occur tomorrow.
Call the DEP’s environmental program manager, Roger Rummel, at 814-472-1800 or send an email to [email protected] if you notice a hole in your backyard.
Telltale indications are present.
According to Doug Clark, a geotechnical engineer and principal at Civil & Environmental Consultants, an engineering firm based in the Moon, mine subsidence is typically rather rapid rather than gradual like soil settlement.
Building changes brought on by mining subsidence may show up as foundation cracks or doors that suddenly jam or fail to close.
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