“The Efficiency of Belled Piles in Multi-Layers Soils Subjected to Axial Compression and Pullout Loads: Review”. Journal of Engineering 29, no. 09 (September 1, 2023): 166–183. Accessed July 3, 2024. https://joe.uobaghdad.edu.iq/index.php/main/article/view/1739.