Capacity Of Shallow Footings Research Articles

Rotational capacity of shallow footings and its implication on SSI analyses

Rotational capacity of shallow footings and its implication on SSI analyses

Bearing Capacity of Shallow Footing on Compacted Dune Sand Underlain Iraqi Collapsible Soil

Bearing Capacity of Shallow Footing on Compacted Dune Sand Underlain Iraqi Collapsible Soil

Bearing Capacity of Shallow Footing on Compacted Filling Dune Sand Over Reinforced Gypseous Soil

Existence of these soils, sometimes with high gypsum content, caused difficult problems to the buildings and strategic projects due to dissolution and leaching of gypsum by the action of waterflow through soil mass. In this research, a new technique is adopted to investigate the performance of replacement and geosynthetic reinforcement materials to improve the gypseous soil behavior through experimential set up manufactured loaclally specially for this work. A series of tests were carried out using steel container (600*600*500) mm. A square footing (100*100) mm was placed at the center of the top surface of the bed soil. The results showed that the most effective thickness for the dune sand layer with geotextile at the interface, within the tested range, was found to be almost equal to the width of foundation. Therefore, under this depth, the soil was reinforced with geogrid and geotextile. It can be shown that (Collapse Settlement Reduction Factor) increases to (72%) when using two layers of geogrid and one layer of geotextile under depth of replacement equal to the width of footing. In addition, the results showed that the bearing capacity increases to (1.5-2.0) time under concentric loads and (2.5-3) under eccentric loads after replacement and reinforcement of gypseous soil

Bearing capacity of Skirt circular footing on sand

Skirts are used to improve the bearing capacity of shallow footings on sandy soil by constraining the soil beneath and containing the plastic flow of soil. They are used as an alternative to deep foundations in soils with low strength at the surface. As there has been available little work studying the performance of skirted foundation, we are performing eighteen laboratory experiments on circular steel footings of different diameters and different skirt lengths. The aim of these experiments is to shed some lights on the effects of skirts on the bearing capacity of shallow footings. The effects of skirt length and the relative density of sand on the ultimate load attained were investigated. From the accomplished laboratory tests, it was found that skirts improve appreciably the sustainability of shallow footings to applied load as they increase the ultimate load of shallow footings by some up to 6.25 times for the current study conditions and variables. The performance of skirted footing depends upon the relative density of sand and on the skirt length to footing diameter ratio. Skirts are more beneficial in case of footings on loose sand than in case of medium and dense sand.

Horizontal capacity of skirted circular shallow footings on sand

Shallow footings are subjected to lateral forces induced by earthquake movements, wind loads, water wave pressure, lateral earth pressure, and transmitting power cables. In some structures such as water front structure, earth retaining structure and transmitting power structures, the lateral forces acting on the footings may be dominant. There has been little work studying the performance of skirted footings subjected to lateral loads. Twelve loading tests were performed on small scale circular skirted footing to shed some light on the performance of skirted footings when subjected to lateral loads. The effects of skirt length and the relative density of sand on the performance of the footing were investigated through laboratory testing program. Also a comparative experimental study between ultimate horizontal loads attained by skirted and unskirted footings with the same properties was conducted. From the accomplished laboratory tests it was found that the skirts changed the failure mode of circular shallow footings from sliding mechanism into rotational mechanism. Also the skirts attached to footings increased appreciably the ultimate horizontal capacity of shallow footings.

Influence of Matric Suction on the Results of Plate Load Tests Performed on a Lateritic Soil Deposit

Abstract This paper evaluates the influence of soil matric suction on the results of plate load tests conducted in an unsaturated, lateritic soil deposit at a depth of 1.5 m. Soil suction was monitored during the tests with tensiometers installed at the bottom of the testing pit. Field test results show that small increases in matric suction lead to substantial increases in bearing capacity of the soil-plate system. In situ experimental loading-collapse (LC) and suction increase (SI) yield surfaces are proposed for the soil investigated. Changes in matric sucion were observed to significantly influence settlement response, particularly for high levels of surcharge load. The rate of settlement shows a non-linear decreasing trend with increasing soil matric suction.

Determination of bearing capacity of shallow foundations without using superposition approximation

The Terzaghi superposition assumption has been widely used to determine the bearing capacity of shallow footings. Although this assumption always errs on the safe side, a rigorous procedure to calculate the bearing capacity is still of engineering value. This paper presents such a procedure that is free from errors as a result of the superposition assumption. It demonstrates that the ultimate bearing capacity can be precisely expressed by the Terzaghi equation, except that the bearing capacity factor Nγis dependent upon the surcharge ratio. A recently developed numerical method, i.e., the critical slip field method, is used to calculate the modification coefficient for modifying Nγ. It is found that this modification coefficient increases with the surcharge ratio at small values of surcharge ratio and then remains constant for large values of surcharge ratio. However, the errors invoked by the superposition assumption do not exceed 10%. On the basis of numerical calculations, a simple closed-form expression of the modification coefficient is proposed that yields the theoretically rigorous ultimate bearing capacity. In the later part of the paper, errors in bearing capacity calculations owing to the use of conventional procedures are analyzed. It is concluded that the continued use of conventional procedures is justified, but the inherent errors should not be neglected in assessing the performance of shallow foundations.Key words: shallow foundation, strip footing, ultimate bearing capacity, critical slip field.

Effective width rule in calculations of bearing capacity of shallow footings

The classical solution to the bearing capacity problem predicts the limit load on symmetrically loaded shallow strip footings. A useful hypothesis was suggested by Meyerhof to account for eccentricity of loading, in which the footing width is reduced by twice-the-eccentricity to its ‘effective’ size. This hypothesis sometimes has been criticized as being overconservative. This paper examines Meyerhof’s suggestion and presents the bearing capacity of eccentrically loaded footings calculated using the kinematic approach of limit analysis. It is found that the effective width rule yields a bearing capacity equivalent to that calculated based on the assumption that the footing is smooth. For more realistic footing models and for cohesive soils the effective width rule is a reasonable account of eccentricity in bearing capacity calculations. Only for significant bonding at the soil-footing interface and for large eccentricities does the effective width rule become overly conservative. For cohesionless soils, however, the effective width rule may overestimate the best upper bound. This overestimation increases with an increase in eccentricity. ©

Influence of relative density and stress level on the bearing capacity of sands

AbstractA finite element approach is presented to determine the bearing capacity of shallow footings on silica sand deposits. The approach can take into account the effects of relative density and stress level on the shear strength of granular soil and is applicable to a fairly large effective stress range. The strength of sand is characterized by a non‐linear Mohr–Coulomb criterion which depends on maximum and critical friction angles, widely used parameters in engineering practice. The results of analysis indicate that this approach yields reliable predictions of bearing capacity and, in particular, it can model the volumetric behaviour of the soil at failure.

Inclination Factors for Bearing Capacity of Shallow Footings

An investigation is made of the inclination factors for estimating the ultimate bearing capacity of shallow strip footings under central load inclined in the direction of footing length. The corresponding theoretical inclination factors are found to be generally larger than the previous factors for a load inclined in the direction of the footing width. The theoretical values of the present inclination factors are compared with some experimental results of model footings on clay and sand.

Bearing capacity of shallow footing, sand over clay. Technical note : Kraft L M; Helfrich S C Can Geotech J, V20, N1, Feb 1983, P182–185

Bearing capacity of shallow footing, sand over clay. Technical note : Kraft L M; Helfrich S C Can Geotech J, V20, N1, Feb 1983, P182–185

Bearing capacity of shallow footing, sand over clay

Measured results of full-scale and model bearing capacity tests are compared with predictions from projected area methods and with a more rigorous method developed by Hanna. The results of the comparisons for these 27 cases support the procedure developed by Hanna. The ratio of predicted to observed bearing capacity was 0.99, and the standard deviation was 0.23.

Effect of strength anisotrophy on bearing capacity of shallow footing in a dense sand : Oda, M; Koishikawa, I Soils Found, V19, N3, Sept 1979, P15–28

Effect of strength anisotrophy on bearing capacity of shallow footing in a dense sand : Oda, M; Koishikawa, I Soils Found, V19, N3, Sept 1979, P15–28

Effect of Strength Anisotropy on Bearing Capacity of Shallow Footing in a Dense Sand

Stress components in an anisotropic soil is analyzed on the assumption that it behaves like an anisotropic-rigid-plastic material. Numerical solutions by the stress characteristics indicate that the bearing capacity factor Nγ by self-weight is easily over-estimated about 40%∼50% when the effect of the strength anisotropy of sandy soils is neglected. The bearing capacity tests by means of a small testing box also support the possibility of the over-estimation. The ultimate bearing capacity is maximum when a strip footing is penetrated perpendicular to the bedding plane, while when a strip footing is penetrated parallel to the bedding plane, the bearing capacity becomes minimum. The ratio of the maximum to the minimum is 1.6 for dense Toyoura sand. In spite of the remarkable effect of the strength anisotropy on the bearing capacity, the residual bearing capacity is constant without any effect of the strength anisotropy. On the basis of the qualitative accordance between the experimental results and the anisotropic-rigid-plastic solutions taking account of the effect of the mean pressure, it can be said that the so-called scale effect of Nγ is mainly caused by the decrease of mobilized angle φ with the increase of the mean pressure.