Bearing Capacity Of Circular Foundations Research Articles

Development of Z number-based fuzzy inference system to predict bearing capacity of circular foundations

Precise bearing capacity prediction of circular foundations is essential in civil engineering design and construction. The bearing capacity is affected by factors such as depth, density of soil, internal angle of friction, cohesion of soil, and foundation radius. In this paper, an innovative perspective on a fuzzy inference system (FIS) was proposed to predict bearing capacity. The uncertainty of fuzzy rules is eliminated by using Z-number theory. The effective parameters, i.e., depth, density of soil, internal angle of friction, cohesion of soil, and foundation radius were considered as inputs to the proposed model. To compare regression and FIS model with Z-based FIS, statistical indices such as the coefficient of determination (R2), root mean square error (RMSE), and variance account for (VAF) were employed. For training and testing Z-FIS, the R2 was (0.977 and 0.971), the RMSE was (1.645 and 1.745), and the VAF was (98.549% and 98.138), whereas for the FIS method, the values were (0.912 and 0.904), (5.962 and 6.76), and (90.12% and 88.49%). It should be mentioned that Z theory decreased the computational time by 89.28% (174.04 s to 18.65 s). The comparison of the statistical indicators of the presented models revealed the superiority of the Z-FIS model over the FIS. Notably, sensitivity analysis revealed that the most effective parameters on bearing capacity are internal angle of friction, depth, and soil density.

Horizontal bearing capacity factors for conical footings on clay

Many offshore foundations can be approximately treated as circular footings. There have been a number of studies in the past few decades on the vertical bearing capacity of circular foundations, however, limited work has been reported for buried footings under horizontal loading. This paper presents the results of a numerical investigation into the undrained bearing capacity of conical footings in clay for both uniform and linearly increasing shear strength profiles. In total 1296 three-dimensional finite element limit analyses were conducted to investigate the horizontal bearing capacity, considering the effects of embedment ratio, foundation–soil interface roughness, conical angle and soil strength heterogeneity. The effects of each of the above critical factors on the horizontal bearing capacity are presented and discussed. The bearing capacity factors in this study are summarized in design tables, providing new solutions to improve the current design practice for conical footings in clay soils.

Evaluation of the Performance of the Circular Foundation Surrounded by the Diaphragm Wall

Increasing the bearing capacity of shallow foundations is a significant challenge in the urban environment due to increased population growth. This paper presents the bearing capacity of circular foundations encircled by a diaphragm wall. In this study, the effects of diaphragm wall depth (0.5 D, D, 2 D) (D is the foundation diameter) of the foundation on the bearing capacity of the foundation are investigated. Varying relative densities of sand soil (loose, medium, and dense) are utilized. The results of the experimental tests show that the diaphragm wall possesses an influence upon the settlement and the foundation bearing capacity. Where, the capacity of bearing increased as the diaphragm wall depth increased. On the other side, increasing the depth leads to a decrease in the settlement ratio of about 57%. The results of experimental work also demonstrated that the best depth is between D and 2D for all types of relative densities

Failure Envelopes for Circular Foundations on Two-Layered Clay under Combined Loading

This study numerically investigates the undrained bearing capacity of circular foundations founded on a two-layered clay under combined loading of vertical, horizontal, and moment loads using three-dimensional finite-element analysis. Each clay layer has different thicknesses and shear strengths, and two types of foundation–subsoil interface are considered: an interface with (a) zero tensile capacity or (b) nonzero tensile capacity. Analysis results are presented in the form of normalized failure envelopes for a wide range of layer thicknesses and shear strength ratios. The presented normalized failure envelopes under combined loads with or without the interface tension can be considered as graphical solutions for circular foundations on a two-layered clay in offshore marine environments. Failure mechanisms under various combined loads provide further insights into foundation-layered soil interactions.

Undrained capacity of circular shallow foundations under combined VHMT loading

Wind turbine (WT) foundations are generally subjected to large combined vertical, horizontal, moment, and torsional (VHMT) loads. The available investigations of the ultimate limit states of WT foundations focus predominately on unlimited-tension soil-foundation interfaces that are more appropriate for offshore settings. However, the interfaces for onshore WT foundations are generally unable to resist tensile loads. To address this omission, a zero-tension interface is used to investigate the VHMT failure envelope of circular shallow foundations under undrained soil conditions using finite element analysis. The effects of soil strength heterogeneity and foundation embedment were investigated. The results show that torsional loads reduce the VHM bearing capacity of circular foundations. The foundation embedment is also found to significantly increase the foundation bearing capacity. A full 4-D analytical expression for the VHMT failure envelope has been proposed based on the calculated failure envelopes.

Prediction of ultimate bearing capacity of circular foundation on sand layer of limited thickness using artificial neural network

ABSTRACT The present study focuses on the development of an Artificial Neural Network (ANN) model equation to estimate the average ultimate load of shallow circular foundation on a sand layer of limited thickness underlain by a rigid rough base subjected to an eccentrically inclined load. The model is developed using the 260 number of data points obtained from extensive laboratory model tests. The input parameters considered are depth of embedment (Df /B) of the foundation, thickness of the sand layer to diameter of foundation ratio (H/B), eccentricity ratio (e/B), and load inclination to friction angle ratio (α/ϕ) to estimate the reduction factor RF as output. The RF is the ratio of the ultimate eccentrically inclined load on a sand layer of limited thickness to the ultimate eccentrically inclined load on a sand layer, which is extending to a great depth. Importance of input parameters, which reflect the output, is studied using Pearson’s correlation and Spearman’s rank correlation. The sensitivity analyses are carried out using Variable Perturbation methods and Weight methods. It has been professing that H/B ratio is the most important input parameter.

Bearing Capacity of Circular Foundation on Sand Layer of Limited Thickness Underlain by Rigid Rough Base Subjected to Eccentrically Inclined Load

Abstract Laboratory model test results for the ultimate bearing capacity of a shallow rough circular surface foundation over a sand layer of limited thickness underlain by a rigid rough base subjected to an eccentrically inclined load have been presented. The sand layer for tests was prepared at a relative density (Dr) of 69 % using five different thicknesses, H. Tests were conducted at H/B values of 0.3, 0.5, 1, 2, and 3 (B = diameter of foundation). The load eccentricity ratio e/B varied from 0 to 0.15, and the load inclination with the vertical (α) was changed from 0° to 20° in 5° increment. Based on the model test result, a reduction factor has been proposed that can be used to estimate the ultimate eccentrically inclined load per unit area of the foundation supported by a sand layer of limited thickness, from the ultimate bearing capacity of a foundation on a sand layer extending to a great depth under an eccentrically inclined load.

Depth factors for undrained bearing capacity of circular footing by numerical approach

The undrained vertical bearing capacity of embedded foundation has been extensively studied using analytical and numerical methods. Through comparing the results of a circular embedded foundation in the literature, a significant difference between the bearing capacity factors and depth factors is observed. Based on the previous research findings, numerical computations using FLAC code are carried out in this study to evaluate the undrained bearing capacity of circular foundations with embedment ratios up to five for different base and side foundation roughness conditions. Unlike the foundation base, the roughness of the foundation side has a significant effect on the bearing capacity. The comparison of the present results with numerical studies available in the literature shows that the discrepancy is related to the procedures used to simulate the foundation side interface conditions and to the estimation of the bearing capacity.

Bearing Capacity of Circular Footing on Sand Deposit

Bearing capacity and settlement are two important parameters in geotechnical engineering. The bearing capacity of circular foundations on sandy soils is important to geotechnical practicing engineers. Design of foundations includes soil parameters and bearing capacity of foundation. This paper presents the results of laboratory experimental model tests of circular footings supported on sand deposit under static load. The finite element software Abaqus is used to compare the results. The effects of the relative density of the sand (30%, 50%, and 70%) and the diameter of circular footing (75 mm and 100 mm) are investigated. It can be concluded that the experimental test results fit quite well with the results of numerical method.

Numerical Investigation Into the Behavior of Circular Pad Shallow Foundations Supported by Geogrid Reinforced Sand

This study seeks to widen the pool of knowledge on the use and characteristics of geosynthetics, specifically in the area of circular foundations supported by geosynthetic reinforced sand. The main objective of the work was to increase the awareness of circular foundation systems and thus increase the accuracy of current laboratory methods. Also, compare the results with that of previous papers on the subject and to provide new model curves to estimate the bearing capacity of circular foundations. In this respect, the foundation and the soil underneath was modeled using four nots isoparameters finite element aid, while, for geogrid reinforcement, the four nots one-dimentional finite element model was used. The sand behavior was based on demolition elasto-plastic drucker- prager criteria and for the reinforcement the linear criteria was used. The paper investigates the effects of the reinforcement placing properties, soil properties, reinforcement properties, and the geometric properties of circular foundations. The results showed that; the bearing capacity ratio at a settlement level for geogrid reinforced sand is effected considerably by parameters such as: reinforcement placement, reinforcement layers, reinforcement strength, geometric properties of circular foundations, and effects of using granular soils. Based on the results achieved, a number of design curves have been developed to assist with the estimation (design) of field bearing capacity of shallow foundations supported by geogrid reinforced soil. Keeping in mind the settlement limitations in real space, the curves have been developed for normal settlement levels up to a settlement ratio of 2.5%.

Undrained bearing capacity factors for conical footings on clay

INTRODUCTION The bearing capacity of circular foundations on undrained clay is of fundamental importance in many geotechnical problems. In particular there are a number of designs of offshore foundations where the foundation can be treated approximately as a large circular footing, for instance some gravity bases, the spudcan foundations of jack-up units, and the more recently developed caisson foundations. In most cases the footing is not placed at the ground surface, and it is important to take into account the depth of embedment. Furthermore, the base of a spudcan is generally not flat, but approximates a shallow cone. For foundations on soft clays, the effect of the increase of strength of the soil with depth needs to be taken into account, and this is particularly important for large foundations. The purpose of this note is to present calculations of bearing capacity factors for shallow circular foundations, accounting for embedment, cone angle, rate of increase of strength with depth, and surface roughness of the foundation. The results have widespread application, particularly in the offshore industry. The soil is assumed to be rigid-plastic, with yield determined by the Tresca condition with an undrained strength su. The method of characteristics is used for the bearing capacity calculation, as described by Shield (1955), Eason & Shield (1960), Houlsby (1982) and Houlsby & Wroth (1982a) for application to undrained axisymmetric problems. Some previous results have been published for this problem using similar numerical techniques (e.g. Houlsby & Wroth, 1982b; Salencon & Matar, 1982; Houlsby & Wroth, 1983; Tani & Craig, 1995; Martin, 2001), but the study presented here involves a much more comprehensive coverage of the parameters. Where comparisons can be made with the previous solutions, the factors differ by up to about 0·5%, which gives some indication of the level of accuracy attainable with this numerical technique. Exceptionally, the rough footing results given by Tani & Craig (1995) are higher by up to about 5%, but this may be due to a problem with their numerical integration procedures (see Martin & Randolph, 2001).

Numerical studies of the bearing capacity of shallow foundations on cohesive soil subjected to combined loading

This paper presents the results of three-dimensional finite-element analyses of circular foundations on the surface of homogeneous, purely cohesive soil. The foundations were assumed to adhere fully to the soil, and compressive, tensile and shear stresses may develop at the interface between the footing and the soil. The predicted ultimate response of the foundations to combined vertical, moment and horizontal loading was compared with other available theoretical predictions. A three-dimensional failure locus is presented for these foundations, based on the numerical predictions. An equation that approximates the shape of the failure locus is also suggested, and this provides a convenient means of calculating the bearing capacity of circular foundations on a uniform clay and subjected to combined loading.