It happens a fair bit up here at my place in townsvill. Both teh ground and concrete slabs expell air as the rain water flows through them. Never had an major subsudence or anything from it and i live on very expansive clay soils.
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lexDyscis luRe!!
Scientific knowledge is always tentative and subject to revision. The entire history of science is littered with discarded theories once thought to be incontrovertible truths. Prof David Deming