Bearing Capacity Of Circular Footings Research Articles

Machine learning techniques to predict the dimensionless bearing capacity of circular footing on layered sand under inclined loads

Machine learning techniques to predict the dimensionless bearing capacity of circular footing on layered sand under inclined loads

Application of Machine Learning to Predict the Dimensionless Bearing Capacity of Circular Footing on Layered Sand under Inclined Loads

Application of Machine Learning to Predict the Dimensionless Bearing Capacity of Circular Footing on Layered Sand under Inclined Loads

Numerical analysis of bearing capacity of circular footing reinforced with geogrid layers

Numerical analysis of bearing capacity of circular footing reinforced with geogrid layers

Scale effect on the behavior of circular footing on geogrid-reinforced sand using numerical analysis

ABSTRACT Using plate load test to evaluate the scale effects of shallow foundation bearing capacity on geogrid-reinforced sand is expensive because large boxes need to be built, and the devices to apply the loads to the reinforced soil are complex. Consequently, the finite element method is an alternative to investigate this phenomenon. In this study, a series of 3D axi-symmetry finite element models were developed to study the scale effect on the bearing capacity of circular footings resting on geogrid-reinforced sand. First, a 100 mm-diameter circular foundation supported by geogrid-reinforced sand was simulated in order to validate the finite element model with laboratory tests. Subsequently, different models were made by increasing the diameter of the foundation and the diameter of the geogrid in the same proportion. Modelling results indicated that as the foundation diameter increased, the bearing capacity of unreinforced and reinforced soil decreased. Likewise, the benefit obtained from the reinforcement was less when the model size was increased.

THE BEARING CAPACITY OF A CIRCULAR FOOTING ON GYPSEOUS SOIL BEFORE AND AFTER IMPROVEMENT

Bearing capacity of soil is an important factor in designing circular footing. It is directly related to foundation dimensions and consequently its performance. The calculations for obtaining the bearing capacity of a soil needs many varying parameters, for example soil type, depth of foundation, unit weight of soil, etc. In this work, the comparison between the values of bearing capacity of circular footing on gypseous soil before and after improvement determined by two different methods, the first method using compacted cement dust (Case1). The improvement were performed by making trench under the footing filled with compacted cement dust (at its optimum moisture content) at three depths [(Depth of trench, D =Width of trench, B =2 * the radius of footing R); (D=2B=4R) ; (D=3B=6R)], the trench had the same footing Dimensions, The second method is reinforcing gypseous soil with biaxial geogrids (Case2) have been shown to be an effective method for improving the ultimate bearing capacity of granular soils.

Numerical Implementation of a Stress-Anisotropy Model for Bearing Capacity Analysis of Circular Footings in Clays Prone to Destructuration

Research indicates the presence of in situ structure of soil skeleton in several natural deposits of clay. However, the effect of such in situ structure and its evolution during loading are rarely accounted for in solution of boundary value problems in geomechanics. This paper explores the effects of inherent soil structure and its degradation on bearing capacity of circular footings in structured clays. An advanced constitutive model that accounts for stress-induced anisotropy, soil structure, and their evolutions with loading is implemented within a finite element analysis (FEA) framework. FEA results demonstrate a significant increase in the bearing capacity of structured clay as compared to that in reconstituted clay. Nonetheless, such an enhancement in limit bearing capacity is subdued by destructuration of soil below the footing. A bearing capacity factor accounting for soil destructuration is proposed for inclusion in the limit bearing capacity calculation of circular footings on structured clay. Successful numerical predictions of results from an instrumented field load test on a footing resting on structured clay further substantiates the importance of considering soil destructuration in bearing capacity analysis.

Bearing capacity-relative density behavior of circular footings resting on geocell-reinforced sand

Geocell reinforcement (GR) improves load-deformation behavior of shallow foundations. A series of instrumented large-scale plate load tests was performed to ascertain such improvements and to correlate that to the relative density (Dr ) of geocell-reinforced sand (GRS). Variable effects on stiffness, bearing capacity (BC), load dispersion and strain-stress behaviors are discussed. The extensive tests made it possible to arrive at a simplified analytical procedure for predicting the BC of circular footings on GRS, taking into account probable shear failure mechanisms and monitored GR deformation. These results allowed the validation and generalization of the procedure reduced from an equivalent-layer BC model considering ‘confinement’ and ‘stress dispersion’ effects on the failure mechanism. Load dispersion angle and strains increase with increasing the sand Dr resulted in significant stress reduction below the GR. This was found most beneficial for the higher densities ranges. The proposed analytical approach can confidently be used for practical design purposes.

Bearing capacity of surface circular footings on granular material under low gravity fields

Low gravity fields have been simulated through magnetic acceleration to conduct experimental study on bearing capacity of circular footings on a type of crushable planetary regolith simulant, which has comparable density and particle size distribution of lunar soil. The load–settlement responses of surface spread footings are obtained by investigating the relative density, footing size and gravity effects. Applying the hyperbolic asymptote method, normalised foundation stiffness and ultimate bearing capacity are obtained by curve fitting and predicted by power functions using multivariate nonlinear regression. The results show that the nonlinear gravity effect is not negligible, related to stress condition, soil dilatancy and mobilised friction angle. A cone penetration test (CPT)-based method for prediction of bearing capacity is proposed with correlations between ultimate bearing capacity of footings and shallow penetration stiffness of CPTs, avoiding the uncertainties of soil property estimations. Analyses of allowable bearing capacity and footing influence zone in consideration of footing size and gravity effects could therefore improve the design of shallow foundations on the Moon and Mars, and provide new understandings and potential implications to the bearing capacity of shallow foundations on crushable granular material in both terrestrial and extraterrestrial geotechnical engineering.

The bearing capacity of circular footings on sand with thin layer: An experimental study

Thin layers have substantial effects on the ultimate bearing capacity, despite their seeming insignificant. In this research, the effects of a thin layer on the ultimate bearing capacity of a circular footing on the sand bed are investigated by small-scale physical models. The investigations were carried out by varying the material type, thickness, and depth of the thin layer. The results indicate that the weak thin layer decreases both the ultimate bearing capacity and stiffness of the soil-footing system and the strong thin layer increases both the ultimate bearing capacity and the soil-footing system stiffness. The amount of this effect depends on the thickness, depth of deposition, and the material type of the thin layer. According to the results, the weak layer for the critical depth of 1B led to the most reduction in ultimate bearing capacity by 26% (from 183 kPa to 135 kPa), while no effects were observed at the depth of 2B. The strong layer is also for the state where this layer is just below the footing, had the highest increase in ultimate bearing capacity by 329% (from 183 kPa to 603 kPa), but at a depth of about 1.25B, it was ineffective.

Proposing two new metaheuristic algorithms of ALO-MLP and SHO-MLP in predicting bearing capacity of circular footing located on horizontal multilayer soil

In this study, for the issue of shallow circular footing’s bearing capacity (also shown as Fult), we used the merits of artificial neural network (ANN), while optimized it by two metaheuristic algorithms (i.e., ant lion optimization (ALO) and the spotted hyena optimizer (SHO)). Several studies demonstrated that ANNs have significant results in terms of predicting the soil’s bearing capacity. Nevertheless, most models of ANN learning consist of different disadvantages. Accordantly, we focused on the application of two hybrid models of ALO–MLP and SHO–MLP for predicting the Fult placed in layered soils. Moreover, we performed an Extensive Finite Element (FE) modeling on 16 sets of soil layer (soft soil placed onto stronger soil and vice versa) considering a database that consists of 703 testing and 2810 training datasets for preparing the training and testing datasets. The independent variables in terms of ALO and SHO algorithms have been optimized by taking into account a trial and error process. The input data layers consisted of (i) upper layer foundation/thickness width (h/B) ratio, (ii) bottom and topsoil layer properties (for example, six of the most important properties of soil), (iii) vertical settlement (s), (iv) footing width (B), where the main target was taken Fult. According to RMSE and R2, values of (0.996 and 0.034) and (0.994 and 0.044) are obtained for training dataset and values of (0.994 and 0.040) and (0.991 and 0.050) are found for the testing dataset of proposed SHO–MLP and ALO–MLP best-fit prediction network structures, respectively. This proves higher reliability of the proposed hybrid model of SHO–MLP in approximating shallow circular footing bearing capacity.

Development of Two Novel Hybrid Prediction Models Estimating Ultimate Bearing Capacity of the Shallow Circular Footing

In the present work, we employed artificial neural network (ANN) that is optimized with two hybrid models, namely imperialist competition algorithm (ICA) as well as particle swarm optimization (PSO) in the case of the problem of bearing capacity of shallow circular footing systems. Many types of research have shown that ANNs are valuable techniques for estimating the bearing capacity of the soils. However, most ANN training models have some drawbacks. This study aimed to focus on the application of two well-known hybrid ICA–ANN and PSO–ANN models to the estimation of bearing capacity of the circular footing lied in layered soils. In order to provide the training and testing datasets for the predictive network models, extensive finite element (FE) modelling (a database includes 2810 training datasets and 703 testing datasets) are performed on 16 soil layer sets (weaker soil rested on stronger soil and vice versa). Note that all the independent variables of ICA and PSO algorithms are optimized utilizing a trial and error method. The input includes upper layer thickness/foundation width (h/B) ratio, footing width (B), top and bottom soil layer properties (e.g., six of the most critical soil characteristics), vertical settlement of circular footing (s), where the output was taken ultimate bearing capacity of the circular footing (Fult). Based on coefficient of determination (R2) and Root Mean Square Error (RMSE), amounts of (0.979, 0.076) and (0.984, 0.066) predicted for training dataset and amounts of (0.978, 0.075) and (0.983, 0.066) indicated in the case of the testing dataset of proposed PSO–ANN and ICA–ANN models of prediction network, respectively. It demonstrates a higher reliability of the presented PSO–ANN model for predicting ultimate bearing capacity of circular footing located on double sandy layer soils.

Eccentrical behavior of square and circular footings resting on geogrid-reinforced sand

A simple approach to describe the centrically and eccentrically ultimate bearing capacity of circular and square footings resting on geogrid-reinforced sand is developed in this paper. To establish and evaluate this approach, a series experimental test for circular footing and square footing were considered as shallow foundation models. The proposed approach for eccentrical loading in unreinforced and reinforced conditions has been validated with Meyerhof’s Effective Width Concept, laboratory model tests, numerical analyses data and field tests on actual full scale reported in the literature review. It was revealed that the new method provides reasonable agreement of the ultimate bearing capacity. Also, the results show ultimate bearing capacity of circular footing decreases less with increment of load eccentricity in comparison of square footing in reinforced condition. Improvement Index investigated that reinforcement layers increased the ultimate bearing capacity in both loadings and their contributions increased with increasing the load eccentricity.

Bearing capacity on sand overlying clay: An analytical model for predicting post peak behaviour

New analytical models have recently been presented for evaluating the peak bearing capacity of circular footings penetrating sand-over-clay and the subsequent capacity once embedded in the underlying clay. However, in lieu of any analytical model, current methods of analysis use an inaccurate linear interpolation for the bearing capacity between the peak and the clay surface. This paper proposes an analytical model for calculating the bearing capacity of circular footings after the peak failure in sand-over-clay soils and before the footing enters the clay. Based on observations from visualisation experiments conducted in a geotechnical centrifuge, and consistent with the silo analysis approach used in predicting the peak capacity, the failure mechanism is a vertical frustum of sand progressively being forced into the underlying clay. Analysis of the capability of the new model to retrospectively simulate a database of 66 geotechnical centrifuge tests is provided. Motivation for improved prediction methods comes from the offshore mobile jack-up industry where concerns remain over the punch-through of large 20 m diameter spudcan footings in sand-over-clay. Accurate prediction of not just the peak bearing capacity but the subsequent load-displacement behaviour is required in order to assess the effectiveness of operational methods used to mitigate punch-through incidents.

Bearing capacity of circular footing supported on coir fiber-reinforced soil

A series of triaxial compression tests on sandy soils reinforced with varying percentages of coir fibers have been numerically simulated to observe its effect on the elastic properties and friction angle of the sand. Test results indicated that with increase in fiber content, the elastic properties and friction angle of soil improved significantly. Three dimensional numerical investigation has also been carried out to investigate the load settlement characteristics of a circular footing resting on fiber-reinforced sand using the properties obtained from the triaxial simulations. This study provides an insight into the effectiveness of addition of coir fibers in the sand of different strengths on the bearing capacity of circular footing.

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.

A Simplified Method for Prediction of Ultimate Bearing Capacity of Eccentrically Loaded Foundation on Geogrid Reinforced Sand Bed

This study aimed to develop reduction factors for eccentrical ultimate bearing capacity of circular and square footings resting on geogrid-reinforced sand. The process has been simplified with presenting non-dimensional charts for the various load eccentricities, the number of reinforcement layers and footing shape, which can be used by practicing engineers directly. To establish and evaluate this approach a series experimental tests for circular and square shallow footings was considered. Regarding square footing, different ratios of load eccentricity were considered; one-way and two-way. The proposed approach for eccentrical loading in unreinforced and reinforced condition has been validated with Meyerhof’s Effective Width Concept, laboratory model tests and numerical reported data in the literature review. Also, this solution is verified using the results of field tests on actual full scale reinforced soil foundations to study scale effects. New method provides reasonable agreement of the ultimate bearing capacity. Also, the results of laboratory tests conducted by the authors show that the ultimate bearing capacity of circular footing decreases less with increment of load eccentricity in comparison with square footing in reinforced condition. Improvement Index investigated that contribution of reinforcement layers in enhancing the ultimate bearing capacity increases with the load eccentricity. This behaviour followed with the proposed model. Also, finite element method (FEM) in a three-dimensional space is performed for verifying the laboratory tests and studying the stress–strain behaviour of reinforcement layers.

Effect of footing shape and load eccentricity on behavior of geosynthetic reinforced sand bed

This paper presents the results from a laboratory modeling tests and numerical studies carried out on circular and square footings assuming the same plan area that rests on geosynthetic reinforced sand bed. The effects of the depth of the first and second layers of reinforcement, number of reinforcement layers on bearing capacity of the footings in central and eccentral loadings are investigated. The results indicated that in unreinforced condition, the ultimate bearing capacity is almost equal for both of the footings; but with reinforcing and increasing the number of reinforcement layers the ultimate bearing capacity of circular footing increased in a higher rate compared to square footing in both central and eccentrial loadings. The beneficial effect of a geosynthetic inclusion is largely dependent on the shape of footings. Also, by increasing the number of reinforcement layers, the tilt of circular footing decreased more than square footing. The SR (settlement reduction) of the reinforced condition shows that settlement at ultimate bearing capacity is heavily dependent on load eccentricity and is not significantly different from that for the unreinforced one. Also, close match between the experimental and numerical load-settlement curves and trend lines shown that the modeling approach utilized in this study can be reasonably adapted for reinforced soil applications.

A Modern Approach to Estimate the Bearing Capacity of Layered Soil

This study is concerned with the bearing capacity of circularfootings on a granular fill layer above a soft clay soil. Theresults of an extensive series of laboratory and field tests wereused to define an empirical equation. This is generally doneby estimating the dependent variable (e.g. bearing capacity)based on the independent variables (e.g. granular fill layerthickness, soil and footing parameters and settlement ratio).A logarithmic model has been developed by using regressionanalysis to estimate the bearing capacity of a circular footingresting on granular fill at any settlement ratio, using allpossible regression techniques based on 342 field test data, toselect the significant subset of the predictors. The results indicatethat the logarithmic model serves a simple and reliabletool to predict the bearing capacity of circular footings placedon a granular fill with different thicknesses above a soft claysoil. And also, the validity of the developed formulation wasverified with different plate load test results from literature.

Model Uncertainty of Eurocode 7 Approach for Bearing Capacity of Circular Footings on Dense Sand

This paper presents a critical evaluation of the model factor M = qu,m/qu,c for Eurocode 7 calculating the bearing capacity of circular footings on dense sand, where qu,m = measured capacity and qu,c = Eurocode 7 calculated capacity. Regression analysis is required to remove the dependency of M on the input parameters. Because the input parameters cannot be varied systematically in load tests, previous studies showed that finite-element limit analysis (FELA) can be used as an alternative to load tests for regression. This is further verified from the model factor MFELA = qu,m/qu,FELA with a mean of 1 and a coefficient of variation (cov) of 0.1, where qu,FELA = FELA predicted capacity. A correction factor (Ms = qu,FELA/qu,c) is next defined, which can be decomposed as a product of a systematic part f and a residual part η (i.e., Ms = fη), which is modeled as a lognormal random variable with mean = 1 and cov = 0.11. Finally, a new model factor (M′ = qu,m/q′u,c = qu,m/fqu,c) is defined. The model statistics of M′ = ηMFELA can be obtained from those of η and MFELA, where mean = 1 and cov = 0.11. This is consistent with the results (mean = 1.02 and cov = 0.15) characterized using the load-test database directly, because M′ no longer depends on the input parameters.

Reply to Discussion on “Bearing capacity of circular footings over rock mass by using axisymmetric quasi lower bound finite element limit analysis” [Comput. Geotech. 70 (2015) 138–149

A discussion has been provided for the comments raised by the discusser (Clausen, 2015) [1] on the article recently published by the authors (Chakraborty and Kumar, 2015). The effect of exponent α for values of GSI approximately smaller than 30 becomes more critical. On the other hand, for greater values of GSI, the results obtained by the authors earlier remain primarily independent of α and can be easily used.