Experimental and Numerical Investigation of Lateral Loaded Flexible Hybrid Piles in Sand

This paper presents an innovative approach to shaping embedded retaining walls using hybrid piles with flexible shafts. The tests of the hybrid piles in sand confirmed that their displacement is 30-50% less compared to the standard piles at the same lateral load. The general concept of retaining walls with hybrid piles is described, assumptions are formulated and model tests, and full-scale tests and 3D FEM analyses are carried out to evaluate the response mechanism of hybrid piles in sand. It was confirmed that flexible hybrid piles interact with the soil in a different way than standard piles. Particular attention was paid to evaluation of pile displacements during the initial phase of increasing the lateral load up to H = 400 kN, M = 1600 kNm with M/H ratio = 4. It was found that changes in lateral stiffness of the hybrid pile increase with pile deflection in the range up to 50 mm. The long-term field tests showed that the hybrid piles L = 10 m, D = 1.2 m, slab overhang B = 1.2 m were stable for a period of eight months. Detailed 3D FE numerical analysis of the stress zones in front of the hybrid pile allowed new P-Y curves to be proposed for depths up to 2 m in the range of initial displacements. Simplified verification calculations using the modified p-y curves for hybrid piles with flexible shafts were carried out, and positive verification results were obtained for test piles in sand.