Pratt Industries Retention Basin Sinkhole Remediation

What do you do when you have an ongoing problem that just isn’t getting fixed? You call on someone you know can fix it!

This was the case for an emi client in Macungie, who had unsuccessfully used other firms in the past to mitigate the problem.

“This client uses us for their landscape maintenance and snow removal,” says emi’s Bob Marks. “We have built a level of trust that when they have a problem, they know they can turn to emi. They wanted us to come in and find a more permanent solution.”

This time around, water had started draining into a sinkhole of a retention basin, opening it up and making the problem much worse: the sinkhole ultimately drained hundreds of thousands of gallons of water from the adjacent pond.

We had to come in with a large excavator and start digging down to hopefully find the crack in the bedrock, which is what was allowing the ground to erode. We worked with an engineering firm who helped us coordinate checking the compaction level. And then we’d dig deeper into the softer areas. We finally found the area that we believed to be the cause of the sinkhole.

To test the theory, we brought in a tanker truck and flushed the hole with 4,000 gallons of water. Then we waited and watched to see where the water was draining from, which identified the crack in the bedrock.

Once we identified the area, our team came back the next day and pumped three truckloads of flowable fill, a thin concrete, to create a cap over the hole and fill any voids in the bedrock. This had to sit overnight while we let it cure.

When excavating, the team uncovered another previous attempt at a repair. There was black landscaping fabric on one side of the hole. This fabric was roughly 10’ below grade and had stone layered on top.

Now that may have worked to some degree at some point, but it hadn’t solved the problem. So, being the perfectionists we are, we removed the fabric and did it the right way.

But, back to the dig. Mother Nature wasn’t exactly cooperative at this point. The work was being done at the end of November, and she decided to add a half-inch of rain overnight. Not only did this complicate the repairs, but it also ruined about 300 yards of soil we were hoping to backfill the area with once the job was complete.

But there’s always a silver lining!

Because this area is a retention basin, there was a lot of water in the hole and the surrounding area as a result. Fortunately, it showed us immediately that the concrete had closed the hole because it was holding water!

Our team went to work to finish the job: we pumped the standing water out, brought in replacement fill, compacted it, and mixed in Bentonite.

Once Bentonite gets wet for the first time, it swells up, and that created a secondary cap. So we are more confident that this fix is a permanent one.

We were able to get the basin back to grade and seeded all the disturbed areas. The entire project took six days from start to finish, but finally, the sinkhole is no longer an issue for the client.

If you’re looking for a project done right, look no further than emi! Our team of experts can help with commercial landscape projects large and small.