Ultimate Bearing Capacity Of Footings Research Articles

剛塑性有限要素法を用いた二層系粘性土地盤の直接基礎の支持力解析

The ultimate bearing capacity formulas of foundation and penetration foundation have been specified in the guideline published by Architectural Institute of Japan for design of building foundation. The rigid plastic finite element method was developed by Tamura and Ohtsuka and has been applied to estimate the ultimate bearing capacity of footing. The characteristic of this method is to employ limited soil constants in comparison with deformation analysis. It only uses the strength parameters as cohesion, c and friction angle, φ since it deals with the limit state directly by disregarding the deformation of building and ground. Through a series of rigid plastic finite element analyses, the comparison of ultimate bearing capacities of penetration foundation between the simulation results and the formula of Architectural Institute of Japan was conducted for two layered soil system of clay. The change in failure mode of ground was discussed with the geometrical ratio between the width of footing and the height of surface layer. The strength ratio of the surface and the second layers of ground was clearly shown to affect the formation of failure mode. The applicability of rigid plastic FEM was demonstrated to the assessment of ultimate bearing capacity of two layered clayey soil system.

Undrained Stability of Footings on Slopes

Solutions for the ultimate bearing capacity of footings on purely cohesive slopes are obtained by applying finite element upper and lower bound methods. In a footing-on-slope system, the ultimate bearing capacity of the footing may be governed by either foundation failure or global slope failure. The combination of these two factors makes the problem difficult to solve using traditional methods. The importance of a dimensionless strength ratio in determining the footing capacity is broadly discussed, and design charts are presented for a wide range of parameters. In addition, the effect of footing roughness and surface surcharge are briefly quantified.

Behavior of confined square and rectangular footings under eccentric-inclined load

This paper presents the results of laboratory model tests on the effect of soil confinement on the behavior of square and rectangular model footings resting on Ganga sand under eccentric - inclined load. Confining cells with different heights and widths have been used to confine the sand. The studied parameters include the cell height, cell width and the depth from base of footing to the top of the confining cell, load eccentricity and load inclination. The ultimate bearing capacity improvement due to the soil confinement is represented using a non-dimensional factor, called the bearing capacity ratio (BCR). The results indicate that the ultimate bearing capacity of footings can be appreciably increased by soil confinement under axial load as well under eccentric-inclined load. It has been observed that such confinement resists the lateral displacement of soil underneath the footing leading to a significant decrease in the vertical settlement and hence improving the ultimate bearing capacity. For small cell width, the cell-soil footing behaves as one unit (deep foundation), while this pattern of behavior was no longer observed with large cell width. The recommended cell heights, depths, and widths that give the maximum ultimate bearing capacity improvement are presented and discussed.

Ultimate bearing capacity of footings on coal ash

Coal ash is recognized as an alternative fill material to the conventional natural soils near a coal fired thermal power station where its large deposits are available. This paper presents experimental investigations on footings on coal ash subjected to loads. A series of laboratory model tests on varying sizes of footings were conducted. The conventional bearing capacity evaluation methods applied for natural soils do not consider progressive failure. These effects are explained based on the non-linear strength behavior of the granular soil and occurrence of progressive failure. The classical bearing capacity theory was applied in relation to the relative dilatancy of coal ash to describe this phenomenon. Few novel observations presented here show that the extent of progressive failure of ash fills is a compressed function of material characteristics of the ash, size and depth of footing and the settlement ratio.

Centrifuge Modeling of Rigid Square Footings on Weak Jointed Rock

Abstract Four series of centrifuge tests were performed using a model rock made from a mixture of sand, bentonite, cement, and water. Tests were conducted to determine the effect of horizontal and vertical discontinuities in the bedrock on the load settlement response of a rigid, shallow footing. A prototype footing, measuring 1 m × 1 m, was simulated in the study. Horizontal and vertical joints, in-filled with compressible material, were simulated by incorporating thin seams of styrofoam. Results from this study are compared to the commonly used methods used to predict the ultimate bearing capacity of footings on jointed rock mass. It is concluded that the existing methods to predict the bearing capacity are conservative for the range of design parameters studied in this research.

Influence of Water Table On Bearing Capacity of Adjacent Strip Footings On Sand Exhibiting Anisotropy

It is possible that many footings become inundated due to a rising water table or flooding at some stage during their structural life. The effect of water table on the ultimate bearing capacity of footings on anisotropic soils has not get received much attention. The purpose of this investigation therefore was to study the effect of water table on the ultimate bearing capacity of adjacent strip footings on Toyoura sand possessing anisotropy in the angle of internal friction using the method of characteristics. It was found that the influence of water table on the shape of stability lines is considerable and is negligible for the location of maximum pressure for both isolated and interfering footings. The results show that due to the effect of water table, the ultimate bearing capacity can be reduced by 38% for Toyoura sand. The study also revealed that the influence of anisotropy in the angle of internal friction for Toyoura sand on the ultimate bearing capacity of adjacent footings for a given depth of water table was considerable.

Bearing capacity of foundations on a weak sand layer overlying a strong deposit

The ultimate bearing capacity of footings resting on subsoils consisting of a weak sand layer overlying a strong deposit has been investigated. Based on model tests of strip and circular footings in a loose or compact sand layer overlying a dense sand deposit, the classical equation of bearing capacity of footings on homogeneous sand was extended to cover cases of these footings in layered sands where the upper layer is the weaker. The theory compared well with the available model test results. Design charts are presented.

Experimental evaluation of bearing capacity of footings subjected to inclined loads

The ultimate bearing capacity of footings subjected to axially inclined loads was investigated experimentally by conducting tests on model strip and circular footings on homogeneous sand and clay. The results were analyzed to determine the inclination factors, depth factors, and shape factors incorporated in the general bearing capacity equation for shallow foundations. These values are compared with the recommended values given in the Canadian Foundation Engineering Manual.

Foundations on Strong Sand Overlying Weak Sand

The ultimate bearing capacity of footings on subsoil consisting of a strong sand layer overlying a weak sand deposit was investigated. A theory was developed and then results predicted. These predictions compared well with test data on model strip and circular footings resting on dense sand overlying loose, as well as, compact sand. Design charts are presented for use in practical application. Based on these charts, a procedure to determine the ultimate bearing capacity of a strip and circular footings on a strong sand layer overlying a weak sand deposit is described.

Ultimate bearing capacity of foundations on layered soils under inclined load

The ultimate bearing capacity of footings resting on subsoils consisting of two layers has been investigated for the cases of a dense or stiff layer overlying a weak deposit, and a loose or soft layer overlying a firm deposit. The analyses of different modes of soil failure are compared with the results of model tests on circular and strip footings on layered sand and clay soils.

Strip footing on weak clay stabilized with a granular trench or pile

There are many field situations where at least a moderate increase in the bearing capacity in weak clays is desired. One of the solutions for such situations is stabilization by installing a granular pile or stone column using empirical designs. The plane strain version of a granular pile is a granular trench. In the present investigation a failure mechanism is postulated for the granular trench and analytical expressions are derived for the ultimate bearing capacity of footings on such stabilized soils. Bearing capacity factors are presented for various combinations of the parameters considered. From the present study it has been reaffirmed that a granular trench significantly reinforces weak clay deposits.

Ultimate Bearing Capacity of Footings on Sand Layer Overlying Clay

The ultimate bearing capacity of footings resting on subsoils consisting of two layers has been investigated for the cases of dense sand on soft clay and loose sand on stiff clay. The analyses of different modes of soil failure are compared with the results of model tests on circular and strip footings and some field observations of foundation failures.

Penetration Tests and Bearing Capacity of Cohesionless Soils

From comparison between standard (dynamic) and static penetration resistances on number of sites, simple approximate correlation has been obtained to estimate relative density and angle of internal friction; proposed relationships applied to determine ultimate bearing capacity of footings and point resistance and skin friction of piles; results compared with field loading tests on plates and piles.