TITLE:
Evaluation of Cavity Formation and the Use of Cut-off Wall to Reduce the Risk of Washing Subsurface Fine Material
AUTHORS:
Fouzan Alfouzan, Muawia A Dafalla, Akeel Alharbi
KEYWORDS:
Collapse; Cavities; Electrical Resistivity; Sarah Formation; Geotechnical Methods
JOURNAL NAME:
Open Journal of Geology,
Vol.3 No.2B,
October
22,
2013
ABSTRACT:
This study shows the results of mapping numerous
cavities and distress which appeared and detected in Qassim area, Saudi Arabia.
This phenomenon was observed near a school building and residential area and
became a serious risk to occupants and residents. The survey was carried out
applying geotechnical techniques which included advancing rotary boreholes to
depths of 23 m to 30 m with sampling and testing. The evaluation process also
included resistivity imaging profiles using 2D electrical resistivity
measurements. Results obtained from this research showed a thick top layer of
silty clayey sand soil rich of gypsum and carbonate presenting a hazardous and
high-risk soil type. The percentage of fines that are likely to be washed out
as a result of chemical disintegration and exposure to significant hydraulic gradient
was of great concern. Assessment was made using combined geotechnical and
geophysical approach in addition to chemical tests. Based on the data collected
and analysis of test results a practical solution was suggested to solve this
problem. The use of “cut-off wall” in order to reduce the level of subsurface
scour and cajuvity formation were found appropriate. The depth of the cut off
wall was determined based on the subsurface geological profile. Advantages of
this approach and concerns need to be considered in adopting typical solutions that are
presented.