Bearing capacity of three closely-spaced footings on sand

Num Anal Meth Geomechanics

2007

SUMMARYThe ultimate bearing capacity of a group of equally spaced multiple rough strip footings was determined due to the contribution of soil unit weight. The analysis was performed by using an upper bound theorem of limit analysis in combination with finite elements and linear programming. Along the interfaces of all the triangular elements, velocity discontinuities were considered. The value of was found to increase continuously with a decrease in S/B, where (i) is the ratio of the failure load of an interfering strip footing of a given width (B) to that of a single isolated strip footing having the same width and (ii) S is the clear spacing between any two adjacent footings. The effect of the variation of spacing on was found to be very extensive for small values of S/B; approaches infinity at S/B = 0. In all the cases, the velocity discontinuities were found to exist generally in a zone only around the footing edge.

Section: With the Theory Of Graham Et Al [9]supporting

confidence: 90%

Section: With Experimental Data Of Graham Et Al [9]mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultimate bearing capacity of equally spaced multiple strip footings on cohesionless soils without surcharge

Kouzer

Num Anal Meth Geomechanics

2007

“…The interference effect of two strip footings on their ultimate bearing capacity was studied theoretically by Stuart (1962) on the basis of the limit equilibrium method. For the problem of three closely spaced strip footings on sand, Graham et al (1984) have employed the method of characteristics so as to obtain the solution for determining the interference effect on the central footing (not the two outer footings). This theory was meant for obtaining the interference effect due to a number of strip footings, for instance the foundations of railway sleepers.…”

Section: Introductionmentioning

confidence: 99%

Upper bound limit analysis for finding interference effect of two nearby strip footings on sand

Ghosh

2007

Geotech Geol Eng

The ultimate bearing capacity of two closely spaced strip footings, placed on a cohesionless medium and loaded simultaneously to failure at the same magnitude of failure load, was determined by using an upper bound limit analysis. A logarithmic spiral radial shear zone, comprising of a number of triangular rigid blocks, was assumed to exist around each footing edge. The equations of the logarithmic spiral arcs were based on angles / L and / R rather than soil friction angle /; the values of / L and / R were gradually varied in between 0 and /. The ultimate bearing capacity was found to become maximum corresponding to a certain critical spacing between the footings. For spacing greater than the critical, the bearing capacity was found to decrease continuously with increase in the spacing. The extent of the spacing corresponding to which the ultimate bearing capacity becomes either maximum or equal to that of a single isolated footing increases with increase in /. The results compare reasonably well with the available theoretical and experimental data.

“…However, with respect to finding the interference effect on a group of multiple strip footings, for instance the foundations of railway sleepers, the study of Graham et al (1984) is perhaps the only available theory in literature; this theory is based on the method of characteristics. From this research investigation, it has been demonstrated that the ultimate bearing capacity of a group of multiple strip footings placed on sand increases continuously with decrease in spacing among the footings; the increase in the bearing capacity becomes quite extensive for very small spacing.…”

Section: Introductionmentioning

confidence: 99%

Interference of Multiple Strip Footings on Sand Using Small Scale Model Tests

Bhoi

2008

Geotech Geol Eng

By using small scale model tests, the interference effect on the vertical load-deformation behavior of a number of equally spaced strip footings, placed on the surface of dry sand, was investigated. At any stage, all the footings were assumed to (i) carry exactly equal magnitude of load, and (ii) settle to the same extent. No tilt of the footing was permitted. The effect of clear spacing (s) among footings on the results was explored. A new experimental setup was proposed in which only one footing needs to be employed rather than a number of footings. The bearing capacity increases continuously with decrease in spacing among the footings. The interference effect becomes further prominent with increase in soil friction angle. In contrast to an increase in the bearing capacity, with decrease in spacing of footings, an increase in the footing settlement associated with the ultimate state of shear failure was observed. The present experimental observations were similar to those predicted by the available theory, based on the method of characteristics. As compared to the theory, the present experimental data, however, indicates much greater effect of interference especially for larger spacing among footings.