Delineating weak zones in limestone based on borehole drilling and electrical resistivity tomography

Abstract EN

This study is focused on imaging weak zones in the subsurface using borehole and geophysical datasets.

these weak zones are present within the Jhill limestone of the Miocene age across northern Karachi.

a total of forty-nine core samples were collected from eleven boreholes about 30 m deep within the study area.

the core analysis reveals the presence of cavities in fractured limestone at shallow and deep levels.

the lateral extension and thickness of these weak zones are well imaged by the electrical resistivity tomography (ERT) dataset.

the 2D tomographs of the six profiles show variability in the ground resistivity response.

the ERT profiles are interpreted using on-hand samples collected from boreholes.

these tomographs reveal relatively high resistivity values interpreted as intercalation of dry clay and marl beds within the limestone.

the medium resistivity values suggest the presence of clay and sand in highly fractured limestone or surficial dry features.

the low resistivity values are interpreted to be originated from the weak zones filled with lithologies having high moisture content within the limestone.

the collected core samples were analysed for geotechnical parameters.

the integration of borehole and ERT datasets delineated weak zones in the northern and central regions, which should be well-cemented to avoid any geohazard.