Inspection actual condition of dam’s soil using seismotomography and electrotomography
The investigation of subsurface condition of a dam was carried out by non-destructive geophysical method. To solve this problem have been done electrotomography and seismotomography for two profiles. Interpretation seismotomography and electrotomography were processed with the use of ZondST2d and ZondRes2d.
Geoelectric model of one of the profiles.
Resistivity values of near-surface section are 140 — 1000 Ωm corresponds to loose soil of different composition. Sands and gravels of underlying layer have a high resistivity values from 400 Ωm to 1000 Ωm; the clayey soil has resistivity values between 140 Ωm and 400 Ωm.
Zones of near-surface section are reflected by high resistivity values because of the dryness condition of the soil. Deeper, the resistivity decrease to 60 – 300 Ωm. Mark out three low-resistivity zones at a depth of 10 – 20 m. This zones coincide with low-velocity zones. Most probably, geophysical anomalies are associated with the clayey soil (morainal clay sand or loamy soil). Apparently, clayey soil doesn’t increase the permeable dam’s embankment base.
Velocity model with contours of low-resistivity zones.
In common, distribution of velocities is layered. Velocity increases with the depth. That depends on density increasing because of adding geostatic load. The least velocity values (from 0.4 to 1.0 km/s) correspond to dry soils. The greatest velocity values (4.4 km/s) detected below 5 m in northeastern part of the profile. These values interpreted as bedrock. Distribution of velocities is layered, but in some places velocity values are low.