Using vertical electrical sounding in building sites investigation : a case study in south of Baghdad, Iraq

الملخص EN

Vertical Electrical Sounding is used for engineering purposes at Al-Jadiriya area, within Baghdad University site .Two different electrical resistivity techniques were applied using Schlumberger array.

These are the vertical electrical sounding (VES) and cross vertical electrical sounding (CVES) technique.

The measurements of VES were carried out at 38 points distributed as much as possible to cover the area.

Three main layers were delineated; these are the top soil, unsaturated layer of clayey sand or silty sand and saturated layer of sand to clayey sand and sand mixed with gravel at some places.

The resistivity of the top soil varies from 11 – 600 ohm.m, and thickness ranges from 0.7 – 2.8 m.

The unsaturated layer has resistivity values varying from 46 – 320 ohm.m, and thickness ranging from 2.0 – 7.2 m.

The resistivity of the saturated layer varies from 11 – 60 ohm.m, and thickness ranges from 4.6 – 13.8 m.

There are also lenses in some places within the layers, 1.2 – 2.45 m.

thick, which have high resistivity 800 – 900 ohm.m or low resistivity 9.6 – 29 ohm.m that may represent fill material and clay lenses respectively.

The average depth of the groundwater surface ranges between 5 – 8 m.

The measurements of CVES were taken along two perpendicular directions around fixed central point, at 5 points.

The results are presented as radial graphs to show the variation of resistivity with direction; these graphs show that the sediments are heterogeneous in their vertical and horizontal distribution; especially for the top soil.

Finally, it is concluded that three major causes of failures prevail in the buildings in Baghdad University.

The first cause is the lateral inhomogeneity of the subsurface sediments.

The second is the presence of lenses, and the third is the variation in the groundwater level.

These failures may cause many engineering problems such as cracks in the foundation and walls of buildings.