IACMAG 2011 – Melbourne, Australia, 9–11 May 2011 Response of single pile in cohesive soil under lateral load V.S. Phanikanth Department of Civil Engineering, IIT Bombay, Mumbai – 400076, India; Architecture and Civil Engineering Division, Bhabha Atomic Research Centre, Mumbai – 400085, India D. Choudhury Department of Civil Engineering, IIT Bombay, Mumbai – 400076, India G.R. Reddy Structural and Seismic Engineering Section, Homi Bhabha National Institute, Reactor Safety Division, Hall – 7, Bhabha Atomic Research Centre, Mumbai – 400085, India Abstract In addition to vertical loads, mostly pile foundations need to be designed also for horizontal loads which are coming from wind/earthquake/wave loads etc. In this paper, behavior of single piles in cohesive soils subjected to horizontal loads are analyzed by using modulus of subgrade reaction approach with finite difference technique. MATLAB computer program is developed for the analysis of both free headed and fixed headed piles with floating tip. Soft, medium and stiff normally consolidated clay soils are used for parametric studies to evaluate the influence of surrounding soils on bending moment and deflection profile of both rigid and flexible piles. Pile response is found to be affected significantly for change in soil type. Pile deflection is increased by about 170–238% for change of soil from medium to stiff clay. The present results are validated with benchmark problems available in literature. 1 INTRODUCTION Pile foundations are required to be designed for lat- eral loading in addition to the vertical loads due to wind/seismic loads and in case of horizontal forces due to the impact of ships during berthing and wave action. In the design of such pile foundations, not only the ultimate loads shall be worked out to arrive at the safe loads but also the deflections need to be worked out to ensure that serviceable limits are sat- isfied. For short piles, based on earth pressure the- ory, Hansen (1961) had developed a method to estimate the ultimate lateral resistance of rigid piles. Using two forms of varying modulus with depth, Matlock and Reese (1960) had given a generalized iterative solution for rigid and flexible piles sub- jected to lateral loads. For layered soil system, using different constant moduli of subgrade reaction, Davisson and Gill (1963) studied the case of a later- ally loaded pile. Generalized solutions for laterally loaded pile in elasto-plastic soil have been proposed by Reddy and Valsangkar (1970). An elasto-plastic model was used by Madhav et al. (1971) for obtain- ing the response of laterally loaded piles. Using earth pressure theory, Broms (1964a, b) proposed the so- lutions for pile deflections for both short and long piles. Broms (1964a, b) method for computing ground surface deflections of rigid and flexible, with fixed and free head piles was based on Terzaghi’s (1955) modulus of subgrade reaction approach. A state-of-the-art discussion on soil modulus and ulti- mate soil resistance for laterally loaded piles were given by Jamilokowski and Garassino (1977). Algebraic expressions for pile head displacement and rotation for flexible piles subjected to lateral loads was given by Randolph (1981). Karthigeyan et al. (2006) have investigated the influence of verti- cal load on the lateral response of piles. Yang and Jeremic (2002) carried out a finite element study on the behaviour of a single pile in elastic-plastic soils for single as well as double layer for both sand and clays and generated p-y curves. Zamri et al. (2009) have carried out the lateral load behavior under combined vertical and lateral loads considering vari- ation of different water table at different elevations. Recently Phanikanth et al. (2010a) have studied the behavior of single piles in cohesioness soils for free headed piles with floating tip. Also Phanikanth et al. (2010b) have investigated the behavior of single piles in cohesionless soils for fixed head piles with floating tip. Analysis of pile during earthquake is more complex and the state-of-the-art on such prob- lems was presented by Choudhury et al. (2009). In the present study, behavior of single piles in cohe- sive soils for various soil types under lateral loading for various soils is attempted. Both fixed head and free headed piles were analysed under floating tip condition. Parametric studies are carried out on the