Effect of Load Eccentricity on the Bearing Capacity of Strip Footings on Rock Masses

Document Type : Research Article

Authors

Geotechnical Engineering Group, Amirkabir University of Technology, Garmsar Campus, Garmsar, Iran

Abstract

In general, the effect of load eccentricity should be considered in determining the ultimate bearing capacity of foundations. In the present study, the upper bound method of limit analysis was used to propose an equation for determining the bearing capacity of rock masses subjected to the load of a strip footing. The Hoek-Brown failure criterion was used for the rock mass and the footing load was assumed to be exerted eccentrically to the rock mass. The maximum eccentricity value was limited to 1/6 of the footing width to keep the whole footing base in contact with the underneath ground and not result in lifting the footing. Extensive parametric analyses were performed to investigate the effect of the footing width and the rock mass properties on the bearing capacity of rock masses subjected to the eccentric loads. The results show that increasing the load eccentricity from zero to 1/12 and 1/6 of the footing width results in 20% to 40% reduction in the bearing capacity of rock masses, respectively. Also, for all considered eccentricities, the effect of the rock mass unit weight and the footing width and also the Hoek-Brown parameters σci and mi on the bearing capacity were reduced by increasing GSI. Increasing the unit weight of the rock mass from 20 kN/m3 to 25 kN/m3 results in increasing the bearing capacity between zero and 15%. Also, by increasing the footing width from 1 to 5 meters, the bearing capacity increases between 13% and 46%.

Keywords

Main Subjects


[1] G. Meyerhof, The ultimate bearing capacity of foudations, Geotechnique, 2(4) (1951) 301-332.
[2] G. Meyerhof, The bearing capacity of foundations under eccentric and inclined loads, in:  Proc. of 3rd ICSMFE, 1953, pp. 440-445.
[3] O. Sargazi, E. Seyedi Hosseininia, Bearing capacity of ring footings on cohesionless soil under eccentric load, Computers and Geotechnics, 92 (2017) 169-178.
[4] M. Jao, F. Ahmed, G. Muninarayana, M.C. Wang, Stability of eccentrically loaded footings on slopes, Geomechanics and Geoengineering, 3(2) (2008) 107-111.
[5] B.M. Das, Bearing Capacity of Eccentrically Loaded Surface Footings on Sand, Soils and Foundations, 21(1) (1981) 115-119.
[6] M. Foundoukos, R. Jardine, The effect of eccentric loading on the bearing capacity of shallow foundations, in:  BGA International Conference on Foundations: Innovations, observations, design and practice: Proceedings of the international conference organised by British Geotechnical Association and held in Dundee, Scotland on 2–5th September 2003, Thomas Telford Publishing, 2003, pp. 297-305.
[7] S. Saran, R.K. Agarwal, Bearing Capacity of Eccentrically Obliquely Loaded Footing, Journal of Geotechnical Engineering, 117 (1991) 1669-1690.
[8] R.N. Behera, C. Patra, Ultimate Bearing Capacity Prediction of Eccentrically Inclined Loaded Strip Footings, Geotechnical and Geological Engineering, 36(5) (2018) 3029-3080.
[9] M. Imani, A. Fahimifar, M. Sharifzadeh, Effects of Joint Spacing on Static Bearing Capacity of Rock Foundations in the Case of Punching Failure, Amirkabir Journal of Science & Research (Civil & Environmental Engineering), 46(2) (2015) 91-100. (in Persian)
[10] Z. Saada, S. Maghous, D. Garnier, Bearing capacity of shallow foundations on rocks obeying a modified Hoek–Brown failure criterion, Computers and Geotechnics, 35(2) (2008) 144-154.
[11] A. Serrano, C. Olalla, Allowable bearing capacity of rock foundations using a non-linear failure criterium, in:  International journal of rock mechanics and mining sciences & geomechanics abstracts, Elsevier, 1996, pp. 327-345.
[12] S. Shamloo, M. Imani, The Effect of Linearization of Hoek-Brown Criterion on the Bearing Capacity of Rock Masses using the Upper Bound Method of Limit Analysis, Amirkabir Journal of Civil Engineering, 54(4) (2022) 1341-1360. (in Persian)
[13] X.-L. Yang, J.-H. Yin, Upper bound solution for ultimate bearing capacity with a modified Hoek–Brown failure criterion, International Journal of Rock Mechanics and Mining Sciences, 42(4) (2005) 550-560.
[14] A. Alencar, R. Galindo, S. Melentijevic, Influence of the groundwater level on the bearing capacity of shallow foundations on the rock mass, Bulletin of Engineering Geology and the Environment, 80 (2021) 6769-6779.
[15] M. Imani, A. Fahimifar, M. Sharifzadeh, Upper bound solution for the bearing capacity of submerged jointed rock foundations, Rock mechanics and rock engineering, 45 (2012) 639-646.
[16] A.H. Javid, A. Fahimifar, M. Imani, Numerical investigation on the bearing capacity of two interfering strip footings resting on a rock mass, Computers and Geotechnics, 69 (2015) 514-528.
[17] A. Javid, A. Fahimifar, M. Imani, Numerical studies on the bearing capacity of two interfering strip footings based on Hoek–brown materials, in:  13th ISRM International Congress of Rock Mechanics, OnePetro, 2015.
[18] S. Shamloo, M. Imani, Upper bound solution for the bearing capacity of two adjacent footings on rock masses, Computers and Geotechnics, 129 (2021) 103855.
[19] H. AlKhafaji, M. Imani, A. Fahimifar, Ultimate bearing capacity of rock mass foundations subjected to seepage forces using modified Hoek–Brown criterion, Rock Mechanics and Rock Engineering, 53 (2020) 251-268.
[20] H. AlKhafaji, M. Imani, A. Fahimifar, Three-Dimensional Bearing Capacity Analysis of Rock Foundations Subjected to the Loads of Gravity Dams, Case Study: Shafaroud Dam, AUT Journal of Civil Engineering, 5(2) (2021) 257-268.
[21] M. Imani, R. Aali, Effects of embedment depth of foundations on ultimate bearing capacity of rock masses, Geotechnical and Geological Engineering, 38 (2020) 6511-6528.
[22] S. Shamloo, M. Imani, Upper bound solution for the bearing capacity of rock masses considering the embedment depth, Ocean Engineering, 218 (2020) 108169.
[23] S. Keawsawasvong, C. Thongchom, S. Likitlersuang, Bearing capacity of strip footing on Hoek-Brown rock mass subjected to eccentric and inclined loading, Transportation Infrastructure Geotechnology, 8 (2021) 189-202.
[24] H. Yousefian, M. Fatehi Marji, H. Soltanian, A. Abdollahipour, Y. Pourmazaheri, Wellbore trajectory optimization of an Iranian oilfield based on mud pressure and failure zone, Journal of Mining and Environment, 11(1) (2020) 193-220.
[25] H.A. Lazemi, M.F. Marji, A.Y. Bafghi, K. Goshtasbi, Rock failure analysis of the broken zone around a circular opening, Archives of Mining Sciences, 58(1) (2013).
[26] W.-F. Chen, Limit analysis and soil plasticity, J. Ross publishing, 2007.
[27] N. Mao, T. Al-Bittar, A.-H. Soubra, Probabilistic analysis and design of strip foundations resting on rocks obeying Hoek–Brown failure criterion, International Journal of Rock Mechanics and Mining Sciences, 49 (2012) 45-58.
[28] M. Mansouri, M. Imani, A. Fahimifar, Ultimate bearing capacity of rock masses under square and rectangular footings, Computers and Geotechnics, 111 (2019) 1-9.