2d Model Study on Slip Surface around Belled Anchor Pile under Uplift in Cohesionless Soil

The belled anchor pile has proficient application in the field of geotechnical engineering as because its enlarged base can bear more compressive loads and large volume of breakout soil within slip surface move upward under tension. The bell anchor pile can be used in case of on-land and off-shore structures where there is a threat to overturning of structures due to external tension loads. The previous researchers reported qualitative and quantitative estimation of uplift resistance of belled pile for both small scale laboratory model and full-scale field models. But 2D model studies only can interpret the variation in response of 3D models. Semi-cylindrical 2D model studies are conducted in present investigation to visualize the pattern of slip surface. Herein the 2D model studies are conducted for the ratio between thickness of shaft to bell thickness of (Ts/Tb) = 0.28, 0.32, 0.38 and 0.46 and all the models are tested for embedment depth ratio of 3, 4 and 5 having constant bell angle 45°. Total 12 numbers of tests are conducted in dry sand bed of density 15.6 kN/m 3 . The foundation bed is prepared with dyed sand maintaining 3 mm thickness of dyed sand and 18 mm dyed sand, and placed alternatively. A proving ring and dial gauges are attached with the models and a close contact of the models are kept with the side of perpex sheeted tank. Images are captured for soil deformation in case of all model tests. A void is formed underneath the base of pile and the slip surface is detected when the soil around the base collapsed to fill the voids. Here it is also observed that failure is indicated by the proving ring prior to the collapse of soil. The objective of the present paper is to investigate the nature of slip surface inside the soil and to evaluate the results on the basis of parametric study conducted in the experiments. The slip surface is indicated marking those points where nonlinearity or turning points are found in dyed layer as they are generating during uplifting. For all the bell pile it is seen that the failure initiates from the edge of belled portion of pile and move upward following a non linear path upto the ground level with a formation of heave irrespective of pile size and shape The failure points are plotted and the slope of nonlinearity is found out. It is observed that upto certain portion from the point of origin, the failure surface is close to the pile (i.e., slope of failure surface is less) and thereafter failure surface moves further away from the pile (i.e., slope of failure surface is more). The geometric configuration of belled anchor pile along with embedment 1 Deb_Tanaya1, Civil Engg. Deptt., Research scholar, NIT Agartala, Agartala, India, [email protected] 2 Pal_Sujit Kumar2, Civil Engg. Deptt, Associate Professor, NITAgartala, Agartala, India, [email protected] Tanaya Deb & Sujit Kumar Pal depth ratio and soil deformation around the pile should be taken care to design uplift resistant belled