Ali A. Al-Jazaairry and  Tahsin T. Sabbagh,  Performance of Axially Loaded Single Pile Embedded in Cohesive Soil with Cavities.   journal   = {International Journal of Geotechnical and Geological Engineering}, [online]. World Academy of Science, Engineering and Technology.
    June 2017, vol. 127(7). 635 - 639
    [viewed 01 April 2020]. Available from: https://publications.waset.org/pdf/10007574.