ABSTRACT
Deep foundations such as piles are adopted in case of weak soil or when the type of soil in the site is not able to resist the external loadings from superstructure or collapsible soil. Therefore, using pile to resist the load as friction resistance or construct pile to reach the hard layer passing the weak soil.
Gypseuos soil is defined as that soil which contains calcium sulphates in sufficient quantity Such soil make big problems in the super-structure in case of becoming wet due to the dissolving of pypum salts that causes large settlements and sudden failure because of decrease in strength capacity of the soil.
One of the most significant piles foundations is Franki pile that is used in cases of need for high capacity, cast in situ and cost-wise where granular soil types of external loads that the pile can sustain such as compression and tension on the design of pile and on the real behavior of soil-structure interaction.
This study focuses on studying the behavior of a single bored Franki pile in gypseous soils in dry and soaking conditions to examine the effect of increasing the diameter bulbous base on the ultimate bearing capacity of pile where the increments ratio of bulb diameter to shaft diameter of pile 
in the three samples of gypseous soil with three different gypsum contents (S1=30%, S2=46%, S3=66%) and comparing the results with normal pile with a shaft diameter (d=1cm).
The study also studies the effect of slenderness ratio (L/d) (20, and 25) on pile with highest bearing resistance in dry and soaking conditions. The soaking time term is 24 hours.
The test results illustrate that the load bearing of pile increases with increasing 
in S1, S2 and S3 for dry and soaking conditions. Increasing the slenderness ratio (L/d) (20, 25) led to increasing pile load bearing for highest load bearing 
. The highest reduction due to the presence of water in pile bearing load is for pile with 
in three samples of soil (85.3% for S1, 88% for S2 and 89.1%) respectively.
