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.
Highlights
This study was conducted to investigate the cause of cracks and subsoil collapse appeared recently at a residential area in Authal Center, Al Qassim Region, and Central Saudi Arabia
This study shows the results of mapping numerous cavities and distress which appeared and detected in Qassim area, Saudi Arabia
This study investigated the cause of cavity formation near surface and close to foundation level for a site of a school building in central parts of Saudi Arabia
Summary
This study was conducted to investigate the cause of cracks and subsoil collapse appeared recently at a residential area in Authal Center, Al Qassim Region, and Central Saudi Arabia. The area was reported to have unusual subsidence and near surface cavities. The cause of these faults and collapse was obviously not related to human activities and expected to be a natural phenomenon. Investigation program included geotechnical engineering and geological assessment. In addition to these methods, a 2D geophysical resistivity imaging system was used. Calcium carbonate (CaCO3) reacts with CO2 to form soluble calcium bicarbonate; Ca(HCO3). Calcium carbonate (CaCO3) reacts with CO2 to form soluble calcium bicarbonate; Ca(HCO3)2 This can cause solid material to reduce and wash away with water. CaO + SO2 → CaSO3 with oxidation of the CaSO3 gives CaSO4 or Ca SO4·N(H2 O)
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