Measured and modeled gravity anomalies above the tunnel in clays - implication for errors in gravity interpretation
Abstract
We measured gravity anomaly above the tunnel excavated in clays. Technical parameters of the tunnel were known.
In order to obtain material parameters of clays the borehole was drilled in the study area. For calculation of gravity anomaly of the tunnel we used wet bulk densities of clays derived from laboratory measurements of drill core samples.
But the fit between observed and calculated gravity data were poor in this case. If we use for interpretation densities calculated from laboratory measurements we interpret the roof of the tunnel much deeper than it is in reality.
The reason is that the borehole clay samples do not retain natural moisture probably. Much better fit between observed and calculated gravity values we received when we used for modeling densities derived from gamma-gamma log.