Study the geotechnical characteristic for the soil of wasit electrical station by using the downhole seismic velocity logging method

Abstract EN

The Downhole Seismic velocity logging (DS) was used for the first time in Iraq.

It is one of the bore hole seismic methods and it was conducted on January 25th 2010 in two drilled boreholes (WVT1 and WVT2) of 60 meters depth each.

These boreholes located in area which was selected to build an electrical generating station in Wasit governorate, Iraq.

The purpose of the survey is to know the geotechnical characteristics of the subsurface soil layers in that area.

The first arrival time, of the P-wave and S-wave, was measured for each meter downward till 59 meters for each well separately.

The picking of the first arrival times was done for the 118 seismic records (59 records for WVT1 and 59 records for WVT2).

At each depth the travel time of the first arrival for three components were measured.

These are P-wave, S-wave vertical and S-Wave horizontal (with 90o angles between them).

The picking was done using the Terraloc instrument software in addition to ReFlexw ver.

4 software and from the first arrival the P-wave and S-wave velocities were concluded which are related to the important geotechnical elastic constants of Poisson’s ratio, shear modulus, bulk modulus, and Young’s modulus.

By knowing the density (from the boreholes tests data) then the elastic–dynamic modulus and constants for the subsurface soil layers had been determined.

The measurement results for WVT1 and WVT2 plotted as curves (velocity verses depth) in addition to the borehole lithology (stratigraphic column).

The lithology, or the stratigraphic columns of the nearest boreholes (BH 126 and BH 137) were used to compare with the results of seismic measurements.

There was very good relation between the seismic results and the lithology However, it seems that the Vp and Vs curves show more details than the stratigraphic logs of these boreholes itself, also there was convergence between them and the results of the SPT test which were done in this area.