Bearing Capacity Of Steel Pipe Piles In Expansive Soils

Abstract

The objective of this research is to study the performance of steel pipe piles in expansive soil media focusing on the bearing capacity of the piles. The research is composed of series of laboratory and field experiments. Model experiments on small diameter short steel pipe piles were conducted using expansive soil from Khartoum. To study their behavior in this type of soil, static pile load tests were conducted on the model piles to study the effect of plugging on bearing capacity of the piles. The unplugged pile measured about 63% of the total capacity of the plugged pile having the same diameter and length. It is useful to note that the model studies on piles showed that the bearing capacity of steel pipe piles in plugged condition dropped by 8% due to wetting of the surrounding soil. Also wetting reduced the total capacity of concrete pile by 46%. The steel pile – soil interface strength and adhesion were studied in the laboratory. The tests showed that the adhesion factor is 0.48 for moisture content values less than or equal the plastic limit of the soil. The adhesion factor increased with increasing moisture content beyond the plastic limit. A case - study was given in this thesis. Field and laboratory tests data for foundations and soils were collected from a construction site in Adar field in the Upper Nile State. Piles of different diameters were driven in very stiff to hard swelling soil media. Driving records and plug lengths were collected from Asawer Petroleum Company. The results of these tests were analyzed to study the effects of pile diameter on the plugging of the pipe piles. It was found that the plugging length of the piles increased linearly with increasing the pile diameter. Also the driving records were analyzed to study the effects of diameter on the driving resistance of the piles. It was found that the small diameter piles offered lower resistance for driving compared to the large diameter piles.