11 Pa.C.S. § 12206: Certain surface supports not to be removed.

It shall be unlawful for an individual, partnership, association or corporation to dig, mine, remove or carry away the coal, rock, earth or other minerals or materials forming the natural support of the surface beneath the streets and places of a city to an extent and in a manner as to remove the necessary support of the surface, without having first placed or constructed an artificial permanent support sufficient to uphold and preserve the stability of the surfaces of the streets and places.