Field works. Example 3.
Mapping of internal structure of stone-soil dam
Earthen and stone-soil dams using for forming artificially impounded body, embank (barrier) disposal of mine tailings and settler toxic waste.
Usually damage of dams related with narrow channel, in which wave move with breaking force. In future it leads to flooding (inundation) locate lower region. In 1990 – 2000 some disasters unfolded in Russian rivers.
It is necessary to control soil dams to avoid emergency situations. Hydrodynamic data were obtained from separate borehole. Information about the deep surface depression and pressure gradient into dam’s body describing possible zones of the more strong filtration. Often the boreholes are limited, so to obtain exhaustive information about all cross-hole space, it is necessary to apply geophysical remote sensing methods.
The geophysical methods on the base of ground-based measurements allow to get more continuous distribution of parameters, describing state damp. Among them the most informative are electrotomography, seismotomography, natural electrical field method.
Electrical tomography and seismic tomography data allow to detect the decompactification zones into dam’s body and current situation of building elements.
Natural electric field can be formed during ground water filtration through dam’s body.
The intensity of the field depends on the value hydraulic slope. The method allows to calculate the location of irregularity of flow filtration through dam’s body and on areas around.
Electrotomography data were processed with the use of ZondRes2d; seismotomography data were processed with the use of ZondST2d.
The figure illustrates the seismotomography results obtained along a dam. Seismic velocity distribution has 4 features: rapid change velocity value (Zone A and D); decreasing velocity zones (Zone B and C).
This zones can be loose soil or to be the centre of development filtration holes. The figure illustrates seismotomography (upper) and natural electrical field results in the area of dam. The arrows show on the more strong filtration in zones A and D.