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The axisymetric failure mechanism of circular shallow foundations and pile foundations in non-cohesive soils Van Baars, Stefan in Computations and Materials in Civil Engineering (2017), 2(1), 1-15 In 1920 Prandtl published an analytical solution for the bearing capacity of a centric loaded strip footing on a weightless in-finite half-space, based on a so-called Prandtl-wedge failure mechanism ... [more ▼] In 1920 Prandtl published an analytical solution for the bearing capacity of a centric loaded strip footing on a weightless in-finite half-space, based on a so-called Prandtl-wedge failure mechanism. Reissner extended this solution for a surrounding surcharge and Keverling Buisman and Terzaghi for the soil weight. Meyerhof and other researchers presented correction factors for the shape of the shallow foundation, which would suggest that, the failure mechanism of circular shallow foundations, is related to the Prandtl-wedge failure mechanism. Meyerhof and Koppejan adapted this Prandtl-wedge failure mechanism also for pile foundations. The numerical calculations made in this article show that the Prandtl-wedge cannot be applied to circular shallow foundations and pile foundations in non-cohesive soils. The failure zone (plastic zone) below a loaded circular plate or pile tip, is far wider and deeper than the Prandtl-wedge. The calculations also show that there is, for these axisymmetric cases, failure both in and out of the standard x-y plane, but most of the failure is due to out-of-plane (tangential) failure. Therefore, this failure mechanism is different from the Prandtl-wedge failure mechanism. Also interesting are the circular and diagonal thin zones below the plate and around the pile tip, where there is no out-of-plane failure, although there is still in-plane failure. In these thin zones without out-of-plane failure, the tangential (out-of-plane) stresses are relatively high due to large shear strains, formed during previous shearing or sliding of the soil. [less ▲] Detailed reference viewed: 132 (4 UL)The influence of superposition and eccentric loading on the bearing capacity of shallow foundations Van Baars, Stefan in Computations and Materials in Civil Engineering (2016), 1(3), 121-131 In 1920 Prandtl published an analytical solution for the bearing capacity of a centric loaded strip footing on a weightless in-finite half-space. Reissner (1924) extended this solution for a surrounding ... [more ▼] In 1920 Prandtl published an analytical solution for the bearing capacity of a centric loaded strip footing on a weightless in-finite half-space. Reissner (1924) extended this solution for a surrounding surcharge and Keverling Buisman (1940) for the soil weight. Terzaghi (1943) wrote this as a superposition of three separate bearing capacity components for the cohesion, surcharge and soil-weight. The first question is to what ex-tent the currently used components are correct. The second question is to what extent the superposition is correct, because the failure mechanisms for these three components are not the same. A number of finite element calculations show that there is indeed an error, which is luckily not too large and leads to predictions on the safe side. Meyerhof (1953) extended the equation of Terzaghi with correction factors for the shape of the footing and the inclination of the load. For eccentric loading however, there are no correction factors. The common practice is to reduce the contact area of the foundation such that its centroid coincides with that of the load, which means that, the area of the foundation outside the effective area, is completely neglected. Therefore the third question is, if this reduction of the foundation area is an accurate method to describe the reduction of the bearing capacity due to eccentric loading. A number of finite element calculations show that this is indeed the case. [less ▲] Detailed reference viewed: 254 (7 UL) |
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