Study on Behaviour of Two Adjacent Strip Footings on Unreinforced/Reinforced Granular Bed Overlying Clay with Voids

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ORIGINAL PAPER

Study on Behaviour of Two Adjacent Strip Footings on Unreinforced/Reinforced Granular Bed Overlying Clay with Voids S. Anaswara

. R. Shivashankar

Received: 8 February 2020 / Accepted: 30 September 2020  Springer Nature Switzerland AG 2020

Abstract This paper numerically studies the behaviour of two adjacent strip footings on unreinforced and reinforced granular bed (RGB) overlying clay having voids. The influence of different parameters such as granular bed thickness, length of reinforcement/s, number of layers of reinforcement, presence of void/s beneath the footing/s in the weak soil, on the behaviour of footings are carried out in this study. It is found that there is a certain optimum spacing between the two adjacent strip footings at which the footing/s carry the maximum load. The voids could be formed in weak soil due to various reasons and the presence of voids may affect the performance of footings. Such voids tend to reduce the load carrying capacity of the footing/s. However, providing a RGB over weak soil can be used as an effective method to maintain the good performance of footings, even when voids could be formed in future. Keywords Interference effect  Adjacent strip footings  Bearing capacity  Layered soil  Void

S. Anaswara (&)  R. Shivashankar Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal, Karnataka 575025, India e-mail: [email protected]; [email protected] R. Shivashankar e-mail: [email protected]; [email protected]

1 Introduction Due to rapid urbanisation and scarcity of lands, buildings or structures are often closely spaced. The foundation of the same building or adjacent buildings could be closely placed. This leads to the phenomenon of ‘Interference’. Numerous studies have been conducted on the interference effect on footings, but most of the studies are done on homogeneous soils, especially cohesionless medium (Stuart 1962; Das and Larbi-cherif 1983; Kumar and Saran 2003; Kumar and Ghosh 2007; Ghazavi and Lavasan 2008; Kumar and Bhoi 2009; Lavasan and Ghazavi 2012; Lavasan et al. 2017). Quite often low-lying areas with clayey soil (or weak soil) are provided with granular fill (granular bed) on top. This granular fill (Granular Bed (GB)) serves two purposes such as raising the ground level to the nearby road level and secondly it increases the allowable load on to the filled-up ground from the superstructure. Adding reinforcement in the fill, i.e. providing a reinforced granular bed (RGB) will further enhance the load bearing capacity and reduce the settlements. The weak soil could contain voids. Voids could be formed prior to or after the construction. Voids could be formed in weak soil strata due to various reasons such as due to water leakage from the water supplying lines or sewer lines and erosion of soil, animal burrows etc. In this study, medium dense sand overlying soft

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clay with or without void are being considered. Th