Detection of underground utilities in the territory of old city buildings under asphalt concrete covering by GPR

The article presents the results of a search for underground utilities, in particular, sewer pipes, a well and a concrete tray with a cable line on an asphalted section of one of the streets of Yakutsk, Republic of Sakha (Yakutia) using the GPR. It is known that the search for communications using this method is a rather difficult task due to “air” interference and uneven properties of the surveyed soils. The GPR of the OKO-2 series (LogiS-Geotech group of companies, Russia) with an AB-250 antenna unit (center frequency 250 MHz) was used as a search device. GeoScan32 software was used to process GPR data; in the process of processing radargrams, bandpass and notch (bandstop) filters were used. Observation of the change in the signal delay time, their amplitude, as well as tracking the common-mode axes made it possible to identify various objects and boundaries in the soil thickness. It is noted that all radargrams are saturated with hyperbolas - reflections from local objects and from the intersections of various linear objects. Their presence is possibly associated with abandoned underground utilities, the skeletons of old buildings and other debris that has accumulated over the years of the city’s development. The position of underground utilities identified by georadar is confirmed by visual observation on the ground by subsidence of asphalt in the vicinity of the buried well and by hatches present on the surface.