Bearing Capacity Of Shallow Foundations Research Articles

Bearing capacity of foundations resting on rock masses subjected to Rayleigh waves

This study investigates the ultimate bearing capacity of shallow foundations resting on rock masses under earthquakes using upper-bound limit analysis. A modified pseudodynamic method (MPD) that considers the influence of Rayleigh waves is initially used to characterize the spatiotemporal variation in earthquake acceleration. The strength of rock masses is governed by the generalized Hoek‒Brown criterion and the plastic flow at failure is assumed to respect the associated flow rule. The generalized tangential technique is introduced to provide a linear approximation of the strength envelope for capturing the equivalent Mohr‒Coulomb strength parameters. The classic nonsymmetrical multi-block translational mechanism, which is capable of assessing a rock-foundation system under asymmetrical load, is reconstructed to portray the velocity discontinuity of the plastic failure region. Based upon the energy equilibrium theorem of the limit analysis, an analytical solution of seismic bearing capacity is derived and then formulated as a multivariate optimization problem. Comparisons show good agreement with the literature and validate the correctness and rationality of this work. Parametric study indicates that the seismic foundation capacity obtained by MPD tends to be conservative compared to the pseudostatic method with the same seismic coefficients, and that the period of a Rayleigh wave has only a slight effect on the bearing capacity. The failure region is more sensitive to the disturbance coefficient than it is to the other rock strength parameters.

Bearing Capacity of Shallow Foundations on Unsaturated Silty Soils

In general, the ultimate bearing capacity (UBC) of shallow foundations on unsaturated soils is characterized by the conventional shear strength (SS) parameters in which saturated theories are applied. However, in this case, it is clear that the foundations designed using the obtained values from the saturated cases not be economical. In recent years, procedures have been developed to estimate the UBC of foundations on unsaturated soils, that take into account drained and undrained loading conditions. However, these studies generally concentrate on sandy soils. The validity of the results proposed in the literature should be tested for other soils. Therefore, this paper includes a conventional direct shear box (DSB) test to determine the unsaturated SS of statically compacted silty soil, and a series of model tests were performed to determine the foundation’s UBC. In the experimental model setup, the UBC values of different types and sizes of model foundations on silty soil layers with a different soil saturation degrees (SSDs)/matric suctions (MSs) and different void ratio values were measured. In addition, the soil-water characteristic curves (SWCCs) and SS parameters of unsaturated silt were obtained. Using the experimental results, a new equation is proposed for the characterization of the UBC of shallow foundations on unsaturated silty soils. Using this equation, the UBC of unsaturated soils can be determined based on the results of unconfined compressive strength tests (UC) measured on unsaturated soil samples and based on the degree of saturation and the fitting parameter. The results indicate that the measured bearing capacity values obtained via the model footing test, shows a good consistency with those obtained by the proposed equation.

Nonisothermal Failure Envelopes of Strip Shallow Foundations Resting on Partially Saturated Clay Subjected to Combined Inclined and Eccentric Loadings

Shallow foundations are commonly resting on partially saturated soil and are very likely to be exposed to severe variations of temperature. The degree of saturation and matric suction will be changed at the elevated temperatures, thus resulting in different hydromechanical behavior and a considerable variation in the imposed suction stress. In this study, the effect of temperature increase on the ultimate bearing capacity of strip shallow foundations resting on partially saturated clay layer subjected to vertical (V)–horizontal (H)–moment (M) combined loading is examined through a set of finite-element limit analyses (FELA) adopting lower bound theorems and second-order cone programming (SOCP). The unified effective stress for partially saturated soils is first incorporated into the soil yield function, considering the significant effect of temperature variations on suction stress by means of the well-established previously developed nonisothermal soil–water retention curve (SWRC) model. The equilibrium equations corresponding to the combined loading are also incorporated into the FELA formulations to account for the effects of inclined and eccentric loadings. Accordingly, the failure loci of obliquely and eccentrically loaded shallow foundations are presented for a wide range of temperatures. It is shown that with an increase of the temperature in the underlying unsaturated clay, the suction stress within the soil medium significantly rises, and thus, the failure wedges as well as the failure loci for both eccentric and inclined loadings substantially expand at elevated temperatures, revealing the considerably greater bearing capacity of the strip footing. The contact pressure beneath the foundation in all loading scenarios increases with an increase in the temperature of the underlying clay. This trend is much less pronounced at higher angles of load inclination, while it is barely affected by the load eccentricity. In addition, with an increase in the induced temperature and consequently the suction stress within the partially saturated clay beneath the foundation, the failure wedge expands, thereby resulting in an overall increase in the bearing capacity of the shallow foundation against vertical–horizontal–moment combined loading.

Study on the Influence of Groundwater Variation on the Bearing Capacity of Sandy Shallow Foundation

Groundwater variation has a significant effect on the bearing capacity of sandy shallow foundations. Groundwater and capillary water in the shallow foundation would result in the various water distributions in the soil mass. Therefore, there are three types of water conditions in the shallow foundation. They are the total saturated, capillary-water-effect zone and dry soil. In this study, a physical mode experimental was developed to investigate the effect of groundwater variation on the deformation behavior under different loading conditions. The effect of water level and fluctuation times were examined by a novel setup with a water-pressure control system. A total of 10 group model tests were carried out. The results indicated that the relationship between water level height and foundation bearing capacity is negatively correlated. In addition, the numerical analysis was carried out to investigate the effect of water-level change on the bearing capacity of the foundation. The bearing capacity of the foundation decreases as the water-level cycles increase. The increase in the fluctuation range of the water level will decrease the bearing capacity of the foundation. The outcome of this study would be helpful to predict the bearing capacity of shallow foundations due to the change of the water level.

A case study of resistance factors for bearing capacity of shallow foundations using plate load test data in Korea

ABSTRACT Ground conditions comprised of slightly or completely weathered rock are frequently encountered in design of bridge foundations in Korea. It is rather challenging to assess the accuracy of the common design methodologies for shallow foundations in these ground conditions as the foundation bearing capacity depends on the degree of weathering. This paper presents reliability-based derivation of resistance factors for the bearing capacity of shallow foundations on slightly and completely weathered rock using field plate load test data. More than 140 plate load tests were performed at 52 sites, 33 of which were considered to be of high quality and reliable. These high-quality tests were used to evaluate the uncertainties associated with the bearing capacity equations, and the resistance factors corresponding to current prescribed load factors. A reliability-based approach, with target annual failure probabilities of 1.0 × 10−3, 2.0 × 10−4, 1.0 × 10−4, was adopted to estimate the required resistance factors for different design equations. A Bayesian approach was adopted to facilitate quantification and propagation of statistical parameter uncertainty due to limited available data. The best estimates of the calibrated resistance factors range from 0.40 to about 0.47 for the considered target reliability levels, which is in good agreement with currently used values in Korea.

Analytical Method for Determining Bearing Capacity of Shallow Foundations on Unsaturated Soils

Analytical Method for Determining Bearing Capacity of Shallow Foundations on Unsaturated Soils

Efficient utilization of tire chip reinforced sand under footings subjected to purely inclined loads-an experimental and life cycle investigation.

The proper disposal of large stockpiles of tire wastes has become a major challenge today. Through this study, an attempt was made to effectively utilize the large chunk of tire wastes as a reinforcement for improving the bearing capacity of shallow foundations subjected to purely inclined loads. The study was accomplished in two phases. In the first phase, the tests were conducted on reinforced beds by varying the quantity of tire chips, the thickness of the reinforced zone, the inclination of loading, and the equivalent relative density of the reinforced zone. The bearing capacity ratio (BCR) was used as a factor to quantify the gains. It was observed that the optimum quantity and thickness of the reinforced zone were 20% by weight and 1B, respectively, where B is the width of the footing. Improvements were found significant at both loose and dense equivalent relative densities. The BCR values under inclined loads were higher than in central vertical loading conditions indicating that the technique is more useful in the latter. The study also compares the environmental impacts generated from tire chip and geogrid foundations in terms of various midpoint and endpoint impact categories using cradle-to-gate LCA. Midpoint environmental impacts have been shown in climate change, freshwater ecotoxicity, fossil depletion, ozone depletion, and water depletion, and endpoint impacts are represented in terms of damage to ecosystem quality, damage to human health, and damage to resources. The study found that foundation prepared with waste tire chips is less polluting to the environment compared to geogrid foundation. In addition to this, landfill of waste tires will be reduced by this technology which will further help in the reduction of the total environmental impact of the system. Henceforth, by adopting the current technology into construction practices, the large stockpiles of discarded tires can be disposed of in a sustainable way.

Evaluation of Bearing Capacity of Shallow Foundation Resting on Cohesionless Soil Using Different Methods: A Case Study of Vizag City

The foundation is the part of a building that rests on the ground. The net safe bearing capacity (qns ) is a significant factor in foundation design. There are several ways published in previous studies to determine the net safe bearing capacity, however choosing the best method governs the stability of the structure when it is loaded beyond its capacity. The emphasis of this concern is investigated and presented in this paper by comparing the net safe bearing capacity of shallow foundations determined by three distinct approaches. Standard Penetration Test (SPT) on cohesion-less soil was carried out in several regions of Vizag to assess penetration resistance of the soil. The findings of this test were subjected to possible corrections, which eliminated the possibility of overestimating the resistance to penetration. Teng’s, Terzaghi’s, and the IS code approach were used to calculate net safe bearing capacity (qns ) using these test parameters. According to the final results of this study, the net safe bearing capacity of Terzaghi’s and IS code methods were 1.2 times and 2 times higher than the Teng’s method. As a result, the IS code method overstated the net safe bearing capacity by two folds, which may potentially cause the structure to fail and increase the structure’s economy. As a result of these findings, Teng’s method was reported to be the best approach for determining the net safe bearing capacity of cohesion-less soils.

Determining ultimate bearing capacity of shallow foundations by using multi expression programming (MEP)

This study presents an artificial intelligence approach, namely multi expression programming (MEP), for determining ultimate bearing capacity of shallow foundations on cohesionless soils. Five governing parameters (i.e., internal friction angle, soil unit weight, the length to width ratio of foundation, foundation depth and foundation width) were used as input variables to develop the MEP model. Through the determination of the optimal parameter setting of MEP, a group of expressions were proposed. Then, the MEP model was compared with linear multiple regression, non-linear multiple regression and several previous models, and three statistical indices (i.e., coefficient of determination (R2), root mean squared error (RMSE) and mean absolute error (MAE)) were employed to evaluate the prediction accuracy of these models. The results show that the proposed model has higher prediction precision than the other models, with higher R2 value and lower RMSE and MAE values. Additionally, a monotonicity analysis was performed to verify the correct relationship between ultimate bearing capacity and various factors. From the monotonicity analysis, the ultimate bearing capacity increases with the increase of internal friction angle (φ), soil unit weight (γ), foundation width (B) and foundation depth (D), whereas it decreases with the increase of the length to width ratio of foundation (L/B). Then, a sensitivity analysis was performed. Through the sensitivity analysis, the effect rank of the five input parameters on ultimate bearing capacity is φ>B >D >γ>L/B. Finally, a graphical user interface (GUI) of the MEP model is developed for practical application.

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

The Effect of the Water Table on the Bearing Capacity of a Shallow Foundation

Immersion is an important part of reservoir engineering investigation and evaluation. Determining the reasonable and effective burial depth of the critical immersion water table is one of the key scientific issues in the impact assessment of the bearing capacity of reservoir immersion foundations. In this study, basic physical and mechanical property tests were carried out on the soil in the typical immersion area of Xiaonanhai Hydropower Station, and the influence mechanism of saturation on the mechanical properties of building foundation soil and immersion on the bearing capacity of a shallow foundation was obtained. According to the test results, the influence depth of the rising groundwater level on the stability of the building foundation is analyzed, and a method to determine the critical depth of immersion groundwater in the reservoir is proposed. Taking the typical building foundation of Luohuang Town in the immersion area of Xiaonanhai Reservoir as an example, the validity of the critical water depth is further verified. The results show that the safety limit depth of the independent foundation affected by the rise of the water table increases with the increase of the width of the foundation and decreases with the increase of the buried depth of the foundation. Considering the safety limit depth, the critical depth of building immersion is 4.830 m, and without considering the safety limit depth, the critical depth of building immersion is 4.05 m. To a certain extent, it can reduce the impact of water table changes on the bearing capacity of shallow foundations.

Spatially variable soils affecting geotechnical strip foundation design

Natural soil variability is a well-known issue in geotechnical design, although not frequently managed in practice. When subsoil must be characterized in terms of mechanical properties for infrastructure design, random finite element method (RFEM) can be effectively adopted for shallow foundation design to gain a twofold purpose: (1) understanding how much the bearing capacity is affected by the spatial variability structure of soils, and (2) optimisation of the foundation dimension (i.e. width B ). The present study focuses on calculating the bearing capacity of shallow foundations by RFEM in terms of undrained and drained conditions. The spatial variability structure of soil is characterized by the autocorrelation function and the scale of fluctuation ( δ ). The latter has been derived by geostatistical tools such as the ordinary Kriging (OK) approach based on 182 cone penetration tests (CPTs) performed in the alluvial plain in Bologna Province, Italy. Results show that the increase of the B / δ ratio not only reduces the bearing capacity uncertainty but also increases its mean value under drained conditions. Conversely, under the undrained condition, the autocorrelation function strongly affects the mean values of bearing capacity. Therefore, the authors advise caution when selecting the autocorrelation function model for describing the soil spatial variability structure and point out that undrained conditions are more affected by soil variability compared to the drained ones. • RFEM is able to consider the soil variability structure in strip foundation design. • Bearing capacity mean value is affected by soil spatial variability. • Bearing capacity is affected by autocorrelation function model. • Coefficient of variation COV reduces as the foundation size increases. • Both drained and undrained soil conditions show similar COV reduction.

Effective Hybrid Soft Computing Approach for Optimum Design of Shallow Foundations

In this study, an effective intelligent system based on artificial neural networks (ANNs) and a modified rat swarm optimizer (MRSO) was developed to predict the ultimate bearing capacity of shallow foundations and their optimum design using the predicted bearing capacity value. To provide the neural network with adequate training and testing data, an extensive literature review was used to compile a database comprising 97 datasets retrieved from load tests both on large-scale and smaller-scale sized footings. To refine the network architecture, several trial and error experiments were performed using various numbers of neurons in the hidden layer. Accordingly, the optimal architecture of the ANN was 5 × 10 × 1. The performance and prediction capacity of the developed model were appraised using the root mean square error (RMSE) and correlation coefficient (R). According to the obtained results, the ANN model with a RMSE value equal to 0.0249 and R value equal to 0.9908 was a reliable, simple and valid computational model for estimating the load bearing capacity of footings. The developed ANN model was applied to a case study of spread footing optimization, and the results revealed that the proposed model is competent to provide better optimal solutions and to outperform traditional existing methods.

Experimental study on eccentrically loaded rectangular footing on sand for embedded condition to enhance serviceability of structures

After the introduction of Terzaghi’s theory in the field of geotechnical engineering regarding ultimate bearing capacity of shallow foundation, work has also been conducted in both experimental and theoretical in this field. But most of the studies were related to only vertically apply central loading on the footing. It is important to know durability of structure and the effect of various types of loading on bearing capacity of footing. At that point of time there was no study conducted regarding inclined loading and eccentrically loading on the footing. But later came the theory of Meyerhof in 1953 who suggested an empirical procedure regarding the estimation of ultimate (maximum) bearing capacity of shallow foundation for the eccentric loading condition. In the present experimental work, the sample tests have been computed to evaluate the maximum bearing capacity of shallow foundation for embedded condition in rectangular footing. Various test is carried out on sample footing of size 18 × 24 cm. The tests is carried out on dense sand. The relative density (Dr) of dense sand sustained during the test is 62.780 %. The eccentricity ratio is varied from 0 to 0.166 and depth is varied from 4.5 cm to 18 cm starting from 4.5 cm (0.25B). Maximum capacity of bearing has been computed for eccentric loading condition and enhancement in structural models was determined.

Perbandingan Nilai Daya Dukung Fondasi Dangkal Menurut Metode Terzaghi Dan Meyerhof

In every building, a foundation is needed as a strong and sturdy building foundation. The foundation aims to support the building and pass the load on the building above it to a layer of soil that is strong enough to have a bearing capacity. To calculate the carrying capacity of the soil, there are many formulas that can be used. The results of each of these formulas produce different carrying capacity values. The purpose of this study is to calculate and analyze the bearing capacity of shallow foundations from the results of hand boring with the Terzaghi and Meyerhof methods. The results showed that the carrying capacity of the shallow foundation soil in the Terzaghi method was smaller than that of the Meyerhof method. The value of the terzaghi method is 353,443 KN /m2, while the Meyerhof method has increased by 70,094%, with a value of 601,185 KN /m2.

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.

Bearing Capacity of Footings on Rock Masses Using Flow Laws

The influence of the non-associative flow law on the bearing capacity of shallow foundations on rock masses is, in general, a subject that is not discussed in the field of rock mechanics. The calculation methods of bearing capacity usually do not define which flow law is adopted and, in some methods, the associative flow rule is assumed without knowing how that hypothesis influences the bearing capacity of the rock mass. In this paper, the study of the influence of the dilatancy angle on the bearing capacity of shallow foundations on rock masses is presented. The variation of the bearing capacity with the associative flow law and the non-associative flow law with zero dilatancy angle is studied using the finite difference method and by considering the influence of the self-weight of rock material. The calculations confirm the great influence of the flow law on the bearing capacity and a correction coefficient is proposed, which makes it possible to estimate the variation of the bearing capacity of the rock mass in terms of the function of the flow law for the hypothesis of weightless rock masses.

Investigating the Effect of Geological Heterogeneity of Strata on the Bearing Capacity of Shallow Foundations Using Markov Random Field

Geological heterogeneity is a result of the natural deposit process of strata with a highly irregular and uncertain distribution of soil mass in the real world. However, compared with the effect of inherent spatial variability of soil properties on geostructures, the effect of geological heterogeneity has received less attention so far. In view of this limitation, this paper adopts a Markov random field model to stochastically simulate the geological heterogeneity for assessing the bearing capacity of a shallow foundation with quantified uncertainty. By mapping the generated stratigraphic realizations in the commercial software FLAC3D version 7.0, an ensemble of numerical models is generated. Computational results show that geological heterogeneity has a significant influence on the estimated capacities. Information entropy is used to characterize the geological uncertainty. It is not surprising that the increase of boreholes could reduce the average information entropy, and thus reduce the standard deviation of bearing capacities. But the effect of increasing the borehole numbers on the uncertainty reduction exhibits a clear nonlinear form with a potential to select an optimal borehole number. Results from the proposed stochastic analysis provide a range of calculated capacities, which can be used to mitigate the risk of insufficient bearing capacity.

An attempt to apply the kinematic method of rigid solids in the study of bearing capacity of shallow foundations

Abstract In the geotechnical engineering field, shallow foundations are frequently needed to ensure good fieldwork stability. They are also intended to permanently and uniformly transmit all load pressure on the seating floor. However, numerous mechanical constraints, such as bearing capacity of foundations, durability, stability, design of shallow foundations, lead, unfortunately, to a serious realization challenge. Finding an adequate solution presents the main goal and effort of both scholars and professionals. Indeed, the corresponding drawback is observed through the high number of reported damages that occurred in the structure of foundations and the punching failure. The failure mechanisms of shallow foundations, verified in full size or on scale models, show “sliding surfaces” and rigid (solid) blocks, which can be described with the kinematic method of rigid solids. The main objective of this study is the application of the kinematic method of rigid solids in the study of the stability of shallow foundations with respect to punching, the purpose of which is to determine the bearing capacity factors Nc, N γ, and the passive earth pressure coefficient Kp of foundations. In this context, two mechanical models have been proposed with 5 and 7 rigid solids, and a program developed via the MathCAD environment is applied to check the validity of the two previous models. The kinematic method of rigid solids gives results very close and comparable with that of Caquot/Kerisel for the factors of the bearing capacity and passive earth pressure coefficient - the ratio Kp - according to the five- and seven-solid model.

An iterative algorithm for random upper bound kinematical analysis

Abstract A new approach for stochastic upper bound kinematical analyses is described. The study proposes an iterative algorithm that uses the Vanmarcke spatial averaging and kinematical failure mechanisms. The iterative procedure ensures the consistency between failure geometry and covariance matrix, which influences the quality of the results. The proposed algorithm can be applied to bearing capacity evaluation or slope stability problems. The iterative algorithm is used in the study to analyse the three-dimensional undrained bearing capacity of shallow foundations and the bearing capacity of the foundation for two-layered soil, in both cases, the soil strength spatial variability is included. Moreover, the obtained results are compared with those provided by the algorithm, based on the constant covariance matrix. The study shows that both approaches provide similar results for a variety of foundation shapes and scale of fluctuation values. Therefore, the simplified algorithm can be used for purposes that require high computational efficiency and for practical applications. The achieved efficiency using a constant covariance matrix for one realisation of a three-dimensional bearing capacity problem that includes the soil strength spatial variability results in about 0.5 seconds for a standard notebook. The numerical example presented in the study indicates the importance of the iterative algorithm for further development of the failure mechanism application in probabilistic analyses. Moreover, because the iterative algorithm is based on the upper bound theorem, it could be utilised as a reference for other methods for spatially variable soil.