Behaviour of circular footings confined by rigid base and geocell reinforcement
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ORIGINAL PAPER
Behaviour of circular footings confined by rigid base and geocell reinforcement Pezhman Fazeli Dehkordi 1 & Usama Farhan Abdul Karim 2 Received: 8 April 2020 / Accepted: 6 October 2020 # Saudi Society for Geosciences 2020
Abstract Soil in nature may exist in a stratified state. A possible condition is the case of a rigid layer underlying a weak sand stratum. In this instance, the bearing capacity of a shallow footing is affected by the lower rigid boundary. The treatment of thin soil layer by geocell reinforcement to raise the load carrying capacity of single shallow footing has been limited in the literature. Accordingly, rigid base and geocell reinforcement are investigated separately and in combination to study their influence on the behaviour and BC of shallow circular footings in dry sand bed. To capture that effect, different size rigid circular footings were tested on a bed in fully instrumented small- and large-scale laboratory installations. The ratio of sand layer thickness to footing diameter was changed considering optimum dimension and embedment depth for geocell mattress. The extensive laboratory part involved monitoring subgrade deformations, soil-geocell stresses and strains revealing the appropriate models for failure mechanisms in the presence of such confinements. Large increase in bearing capacity up to 225% and significant settlement reduction up to 66% are measured for the combined case. Base confinement less than three times the footing diameter in combination with the geocell mattress resulted in favourable higher design performance factors. New equations are proposed to estimate these factors for design and to extend classical formulations for footings strengthened by combined geocell-base confinement. A design performance factor is dependent on footing diameter, sand relative density and the ratio of layer thickness to footing diameter. As this ratio increases, this design factor decreases reaching a constant value at the critical depth. Keywords Bearing capacity and settlement . Geocell reinforcement . Circular footing . Rigid base . Footing size
Introduction First-generation bearing capacity (BC) equations (Terzaghi 1943) require some modifications for any boundary effects. In many practical situations, a thin sand layer is underlain by hard stratum such as bedrock. The presence of a stiff stratum within a certain depth beneath weak sand layer supported the footing base results in vertical confinement and can notably Responsible Editor: Zeynal Abiddin Erguler * Pezhman Fazeli Dehkordi [email protected] Usama Farhan Abdul Karim [email protected] 1
Department of Civil Engineering, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran
2
Faculty of Technology, University of Twente, Enschede, The Netherlands
affect the sand bearing pressure (Meyerhof 1974; Tournier and Milović 1977; Pfeifle and Das 1979; Brown et al. 2004; Cerato and Lutenegger 2006; Eid et al. 2009). On the other hand, using 3D honeycombed reinforcement such as geocell to stabilise loose
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