RESEARCH PAPER Interference effect of two nearby strip footings on layered soil: theory of elasticity approach Priyanka Ghosh • Anirudh Sharma Received: 22 October 2009 / Accepted: 21 May 2010 / Published online: 14 July 2010 Ó Springer-Verlag 2010 Abstract In recent times, rapid urbanisation coupled with scarcity of land forces several structures to come up ever closer to each other, which may sometime cause severe damage to the structures from both strength and service- ability point of view, and therefore, a need is felt to devise simplified methods to capture the effect of footing inter- ference. In the present study, an attempt has been made to model the settlement behaviour of two strip footings placed in close spacing on layered soil deposit consisting of a strong top layer underlying a weak bottom layer. Theory of elasticity is employed to derive the governing differential equations and subsequently solved by the finite difference method. The perfectly rough strip footings are considered to be resting on the surface of two-layer soil system, and the soil is assumed to behave as linear elastic material under a range of static foundation load. The effect of various parameters such as the elastic moduli and thickness of two layers, clear spacing between the footings and footing load on the settlement behaviour of closely spaced footings has been determined. The variation of vertical normal stress at the interface of two different soil layers as well as at the base of the failure domain also forms an important part of this study. The results are presented in terms of settlement ratio (n d ), and their variation is obtained with the change in clear spacing between two footings. The present theoretical investigation indicates that the settlement of closely spaced footings is found to be higher than that of single isolated footing, which further reduces with increase in the spacing between the footings. Keywords Bearing capacity  Elasticity  Interference effect  Layered soil  Strip footing List of symbols B Width of footing E Elastic modulus E 1 , E 2 Elastic moduli for top and bottom soil layers, respectively E m Elastic modulus for middle soil layer in case of three-layer deposit G Shear modulus of soil G 1 , G 2 Shear moduli for top and bottom soil layers, respectively H Total thickness of soil stratum H 1 , H 2 Thicknesses of top and bottom soil layers, respectively H m Thicknesses of middle soil layer in case of three- layer deposit S Clear spacing between two footings i Subscript representing space domain along x-direction j Subscript representing space domain along z-direction q Applied load intensity on footing u Displacement along x-direction w Displacement along z-direction x Horizontal co-ordinate axis z Vertical co-ordinate axis d v Vertical settlement of single isolated footing m Poisson’s ratio r xx Normal stress in x-direction r zz Normal stress in z-direction s xz Shear stress on xz plane n d Settlement ratio P. Ghosh (&)  A. Sharma Department of Civil Engineering, Indian Institute of Technology, Kanpur, Kanpur 208 016, India e-mail: priyog@iitk.ac.in 123 Acta Geotechnica (2010) 5:189–198 DOI 10.1007/s11440-010-0123-2