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

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%.