Settlement Of Shallow Foundations Research Articles

Prediction of Gypseous Soil Settlement Using Artificial Neural Network (ANN)

Gypseous soil exhibits problematic geotechnical engineering properties as they expand, collapse, disperse, undergo excessive settlement, owns a distinct lack of strength, and it is soluble. Gypseous soil has a metastable structure, with dissolvable minerals with a minimal quantity of clay binding the particles together. When gypseous soil unsaturated, they are quite potent. When they are subjected to increased wetness, however, the excess water weakens or damages the bonds, resulting in shear failure and subsequent settlement. Estimating the settlement of shallow foundations on gypseous soils is a difficult topic that is still not fully understood. It is concluded that artificial neural network (ANN) is appeared to be viable solution since it has been successfully used in numerous prognosis applications in geotechnical engineering. In this research, the precipitation values of gypsum soil were predicted under the influence of the applied load using an artificial neural network. The study found that this model is very good in predicting precipitation and found a convergence between the real values and the predict values.

SSI effects on seismic settlements of shallow foundations on sand

The gradual extension of performance-based design in geotechnical engineering has focused the attention on the seismic performance of foundations, typically, in terms of settlement, tilt and bearing capacity degradation. The aim of the present paper is to explore the role of superstructure inertia on the performance of shallow foundations through a series of non-linear numerical analyses of structure-foundation-soil systems, performed with the Finite Difference Code FLAC3D. The NTUA-Sand constitutive model is used to simulate the nonlinear cyclic soil response. The parametric analyses focus upon the effect of key soil-structure interaction parameters, such as the frequency characteristics of the structure – foundation (SFS) system and that of the free-field soil profile, as well as, the structural and excitation properties. Initially, the nonlinear fundamental period of vibration of the SFS system is correlated to the above key parameters of the system and the seismic excitation. In the sequel, to isolate the SSI effects, settlements of SFS systems are compared with the respective settlements of equivalent foundation-soil systems (FS). Simplified relations are finally developed for the analytical calculation of SSI effects on foundation settlements, based on a multi-variable statistical analysis of the available numerical predictions.

Numerical Modelling Observations of Settlement for Pad Footings Supported on Soft Clay Soil

Settlement calculation is an important part in the design of shallow foundations resting on soft soils. The size of the foundation, the depth of the footings, and the rise in ground water level are thought to influence settlement and have been the subject of much research for many years. Thus, this study compared several pad footing sizes using numerical techniques as the basis. The first objective of this study was to analyse soil and pad footing settlement, and to determine the optimal size of footing that withstands excessive settlement due to variation in the water table and the depth of the foundation. Three footing embedment depths of 1.5, 2, and 3m with three water table positions, at the GL (0m), 1.5, and 3m with an applied foundation concentrated load of 440 kN using five footing models of 1.5mx1.5m, 2mx1.5m, 2 m x 2 m, 2.5x1.5m, and 2.5x1.5m pad footing with a uniform thickness of 0.5m were considered. In this study, a 3D Plaxis simulation is used for predicting the settlement of shallow foundations on soft clay soils. Settlement results were discovered at various water table positions and foundation depths. The study found that the 2.5x2m footing was deemed the best among the simulated foundations, and the 3m foundation embedment was considered the best at shallow depths due to less excessive settlement than the other tested foundations. The settlement had a significant impact on the size of the foundation and the depth of the footing. The depth of the water table has a small impact on the settlement. Parametric analysis is also being used to gain a better understanding of the behaviour of the elastic settlement of various shallow foundations. It is found that the footing area increases, settlement decreases and vice versa.

Experiments and modelling of horizontal loading tests on small-scale foundations in sand

The accurate prediction of settlements of shallow foundations under operational conditions is still an open issue for both scientists and engineers, in particular in the case of complex loading conditions (e.g. combined vertical and horizontal loads). The complexity of the soil mechanical response and the difficulty in managing a multiscale problem (ranging from the local scale of the soil representative elementary volume to the macro-scale of the structure) makes a rigorous modelling of such problems particularly demanding for standard numerical tools such as three-dimensional finite-element codes. In this perspective, the well-known macroelement approach may represent a valid simplified approach, capable of overcoming these limitations and allowing a comprehensive description of both serviceability limit state and ultimate limit state of such systems, particularly useful even for practitioners. In the paper, based on a small-scale 1g experimental campaign on a strip foundation, the effect of embedment is investigated over horizontal loading paths at a constant vertical load. In particular, relatively low vertical stress values are considered for the foundations, as it often happens in real structures under usual working conditions. A simple macroelement plastic model, based on a strain hardening law with non-associated flow rule is then proposed and validated over the available experimental data.

Settlement of Shallow Foundation in Dry Sand Under an Earthquake

Seismically induced settlement of buildings with shallow foundations resting on dry sand soils has resulted in severe damage in recent earthquakes. A multi-degree of freedom shaking table and a fixed container were manufactured and used to study the foundation settlement. Series of shaking experiments on the shallow foundation situated in a center of the container and atop of a dry sandy soil has been performed to identify the mechanisms involved to calculate the foundation settlement induced by earthquake shaking. In this research, the important factors are identified, including shaking intensity, the soil relative density, the degree of freedom and the building’s weight. Two relative densities (55 % and 80%) are used and three local magnitudes of earthquakes (5.8, 6.4, and 7.2) (Anza, Jalisco, and Guerrero) respectively with one and two degrees of freedom. The results of the shaking indicated that shallow foundation settlement on the dry sand increases with the increase of the local magnitude of earthquakes and maximum acceleration. In the case of Anza, the percentage decrease in the settlement between the relative density of 55% and 80% for systems (x and xy) is (47% and 42%) respectively. While in the case of Jalisco and Guerrero, the percentage decreases in their settlement and for the same systems is (11% and 57%), (36% and 36%) respectively. The degree of freedom has an impact on the foundation settlement; it is proportional to the degree of freedom. Also, the results show that the settlement decreases when the relative density of sand increases.

Stress-strain state of a borehole determined analytically using drilling-out as a technology of reducing differential settlement

The existing approaches for reducing the differential settlements of buildings and structures have their own advantages and disadvantages. Lowering of a building or part of it is one of the promising methods to reduce the differential settlements of shallow foundations resting upon weak silt-loam soils. The effect is achieved by drilling-out vertical boreholes in the immediate vicinity of the foundation from the minimal settlements. Method: Russian and foreign scientists have been involved in the development of calculation procedures for horizontal and inclined drilling-out of boreholes. It has been important to determine drilling parameters when using this technology and how soil characteristics and stress state of soils around the borehole influence the reduction of differential settlements. The paper discusses the influence of the strength characteristics of soils on the stress state of the soil massif around the borehole, as well as the influence of the borehole radius on the formed areas of limit state. The analytical solution is based on the well-known ratio used to determine the stress state around the borehole during pressure tests. Tangential and radial stresses are determined from this ratio; next, they are checked according to the condition of the strength law, and thus, the stress state around the borehole becomes evident. Result: The stress state of the soil around the boreholes has been calculated by the given method; it has made it possible to calculate the areas of soil destruction and determine the parameters of boreholes and their geometry depending on the purposes when regulating the settlements of slab foundations. It has been established that drilling behind the foundation contour in relation to drilling in the foundation contour makes it possible to increase the radius of the plastic deformation zone up to two times under the same soil conditions and well geometry.

Efficiency of different methods to predict settlement of shallow foundation in cohesionless soil

During the last decades, many methods have been developed to predict the settlement of shallow foundations on cohesionless soils based on the results of SPT. However, such prediction methods with the required degree of accuracy and consistency have not yet been developed. The current study is an attempt to evaluate the performance of some of these methods and obtain the most efficient one. This goal has been performed by evaluating and ranking eight common methods. These methods are Terzaghi and peck, Meyerhof 1, Bowles (1986), Parry, Schultze and Sherif, Meyerhof 2, Burland and Burbidge and Anagnostopoulos et al.. A total number of 189 cases published in the literature were adopted to carry out the ranking analysis of the selected methods. The concept of rank analysis depends in general on four approaches. These approaches are Nash-Sutcliffe efficiency, arithmetic average & standard deviation, accumulative probability analysis, and Log-Normal distribution of the ratio between the predicted and measured settlement. The results of the analysis revealed that the Anagnostopoulos et al. method have got the first rank with a rank index of 6 while Terzaghi and peck have achieved the last rank with rank index of 27. Therefore, Anagnostopoulos et al. method can be used to estimate the settlement of shallow foundations based on the results of SPT with high confidence.

Empirical Relationships Between the Elastic Settlement of Rigid Rectangular Foundations and the Settlement of the Respective Flexible Foundations

The problem of settlement of shallow foundations is among the most important ones in classical soil mechanics. And while for the settlement of flexible foundations elastic solutions are widely used, for rigid rectangular foundations where the actual contact pressure distribution is still unknown, the problem is approximated either analytically assuming a contact pressure distribution or semi‐empirically combining the theory of elasticity with experimental and/or numerical results. A third and often attractive choice is the use of simple empirical relationships or relevant tabulated values relating the elastic settlement of rigid foundations (ρR) with the settlement of the respective flexible foundations (e.g. at the center, ρCe). Reviewing the relathionships of this third approach, the author revealed serious lack of consesous between the various sources; for example, according to the literature, ρR ranges between 68 and 125% of ρCe, the time when it is well-known that ρR < ρCe. In this paper, comparison of the settlement of 210 rigid foundation cases derived from 3D elastic finite element analysis, with the settlement of the respective flexible foundations derived from the theory of elasticity, led to simple empirical relationships between ρR and ρCe as well as between ρR and ρAv (ρAv = average settlement of the flexible foundation) with coefficient of determination (R2) almost unity. The analysis showed that these relationships are largely independent of the aspect ratio of foundations and the thickness and Poisson’s ratio (ν) of the compressible medium, although separate relationships are given for ν = 0.5, slightly increasing R2. Finally, a correction factor for foundation rigidity is given exploting the known linear relationship that exists between the relative stiffness factor of foundations and settlement.

Calculation of Shallow Foundation Settlement Taking into Account Lateral Expansion of Soil

Nowadays the prediction of the settlement of shallow foundation is almost carried out by using the result of the oedometer test, in which the lateral expansion of soil mass is excluded. Geotechnical engineering software, such as Plaxis, Geostudio, Flac, Midas-GTS-NX, etc, are capable of solving most geotechnical problems, taking into account the lateral expansion of soil mass. The comparison between the result procured when using the classically analytical method and the result obtained with the help of the geotechnical engineering software show us an enormous divergence. It can be explained by the difference in approaches of solving the question between numerical method and analytical method, in which the effect of lateral expansion of soil mass is neglected. Therefore, the authors suggest a method to improve the prediction of settlement basing on the studies of Russian scientists in the 1960s, taking into account the effect of lateral expansion of soil mass below the shallow foundation. The result of the article can be considered to predict the long-term, short-term settlement as well as the settlement at any moment of soil consolidation with the acceptable difference when comparing with the results given from the nowaday geotechnical engineering software.

An Investigation on the Settlement of Shallow Foundations Resting on Cross-Anisotropic Soil Deposits

Natural soil deposition process results in formation of anisotropic planes with different properties along different directions, and hence, such natural deposits possess inherent anisotropy. On the other hand, an estimate of the elastic settlement of surface foundations placed on such anisotropic deposits is very important. In this research, the effect of anisotropy (in fact, cross-anisotropy) on the elastic settlement of shallow foundations resting on anisotropic granular soils, often sands, has been investigated. The most important properties in this work, in addition to the geometry of the footing, are the soil modulus of elasticity, Poisson’s ratio and the ratio of these moduli along anisotropic planes in a cross-anisotropic medium. The governing equations of deformation in such media are first presented. Then, the elastic settlement of shallow foundations resting on such media has been estimated using the finite difference method, and then, some influence factors are presented. The factors are useful in estimating the elastic settlement of shallow foundations on cross-anisotropic soils, when the soil properties along two perpendicular directions are known. A series of design charts are provided in non-dimensional form so as to avail their practical use in a general form.

Accounting for shallow foundation settlement in the analysis and design of multi-storey frame buildings: Development of a new software package

In this work we explain a new methodology that have been utilized in a new software package (program) to take into account the influence of foundation settlements in the analysis and design of 3D reinforced concrete frame buildings. We present the solution using a new load pattern in the program, named SETTLEMENT. Firstly, the program analyzes and calculates the displacements in the ground joints of the structure according to several methods of the prediction of the settlement of shallow foundations. Secondly, the program assigns these displacements in the ground joints and analyzes the structure under the influence of these displacements only, calculates the internal forces and the deformed shape of the structure, and stores these values within the results data of the SETTLEMENT load pattern. The program is based on finite elements method. It provides a drawing environment (3D view, plan view, elevation view) with tools to create the model and to perform the structural analysis and design.

Evaluation of settlement of shallow foundations laid on unsaturated soils

The study presents an experimental and numerical study on an unsaturated, non-plastic and poorly graded sand, originated from Fortaleza-CE, Brazil. The numerical analyses used the Finite Element Method (FEM), were performed using the UNSTRUCT software to simulate the curve stress versus strain, considering the effect of suction on soil stiffness. Characterization and determination of the retention curve were performed through filter paper tests, which were used to determine the stress versus strain curve in a double-oedometer test. Suction was considered constant along the entire test. From the numerical analyses done with UNSTRUCT software presented satisfactory results, especially in the presence of suction profiles, that show the variation of suction along of the depth. It can be concluded that higher suction values (and soil stiffness) generate lower settlements.

CALCULATION OF VERTICAL DEFORMATIONS OF THE FOUNDATIONS ON THE SOFT SOIL IMPROVED BY GEOTEXTILE ENCASED STONE COLUMNS

The article provides information on research in the field of improving weak clay bases by installing vertical soil piles in a shell of geosynthetic materials (geotextile encased stone columns). This method has proven to be effective for strengthening the foundations of large areal objects in certain soil conditions, but has not become widespread as a method for improving the foundations of building foundations, which, among other things, is due to the lack of simple engineering methods for calculating the improvement parameters. The article presents an engineering technique for determining the settlement of shallow foundations on a weak clay base which is improved by the geotextile encased stone columns. The technique is based on considering the elementary cell of the improved foundation for which the pressure distribution in the weak soil and the improvement element is determined by the iterative enumeration process. This distribution should ensure equality of the vertical deformations of the improvement element and the soft soil, which should be the same due to the stiffness of the foundation of the building or structure. The calculation of the deformations of a geotextile encased stone columns is carried out by solving the Lamé problem and the deformations of soft soil by standard methods presented in the regulatory literature. Comparison of the calculation results by the proposed method with the data of numerical modeling in an axisymmetric setting is presented. In the numerical modeling of the soil, the Mohr-Coulomb elastic-plastic model was used. Geosynthetic reinforcement was modeled using a special element that only accepts tensile stresses. The rigidity of the foundation of the base is taken to be infinitely large. The analysis of the presented simulation results showed good convergence of the calculations with the data of experimental studies and the data of numerical simulation using the finite element method.

Bearing Capacity of Square Footing Resting on Layered Soil

The bearing capacity of layered soil studies was carried out with various approaches such as experimental, theoretical, numerical, and combination of them. This work is focused on the settlement and bearing capacity of shallow foundations subjected to the vertical load placed on the surface of layered soils. The experimental part was performed by manufacturing soil cubic container (570 mm x 570 mm x 570 mm). A model square footing of width 60 mm was placed at the surface of the soil bed. The relative density of sand was constant at 60%, and the clay was prepared with a density of 19.2 (kN/m3) and water content of 14.6%. PLAXIS 3D FEM was used to simulate the experimental tests and performing a parametric study. The results showed that there was a good agreement between experimental work and corresponding numerical results. The value of the bearing capacity was obtained from load-settlement curve. The bearing capacity of layered soil showed higher value for footing resting on clay over sand soil. It was found that an increase in the ultimate bearing capacity regarding the clay over sand with increasing in first layer thickness ratio; while, a decrease has been indicated for the sand over clay. The critical depth was found at H = (2-3m), and the failure pattern was not unique for layered soil.

Numerical analysis of liquefaction-induced differential settlement of shallow foundations on an island slope

Seismic differential settlement of shallow foundations on an island slope with a liquefiable sand stratum can significantly reduce the foundation's bearing capacity. Now, most studies focused on the settlement of foundation, while few efforts have provided a description of the differential settlement of foundation. In this study, we therefore adopted an approach using three-dimensional (3D) nonlinear finite element (FE) simulation. A special case that the water table located at the interface between the liquefiable sand layer and the clay layer was employed in this model. A series of parametric studies involving soil properties, surcharge load, foundation location, and the typical shaking characteristics of earthquake events were conducted to identify their impact on liquefaction-induced differential settlement. Generally, a more permeable sand stratum and a larger cohesion of the upper clay stratum were found effective at decreasing differential settlement. A foundation's length/width ratio also played an important role in reducing differential settlement and, when the distance of the foundation from the crest of an island slope reached a critical value, the differential settlement tends towards a steady value. Heavily-loaded shallow foundations resulted in more differential settlement, leading to a reduction in their seismic bearing capacity. The peak ground acceleration and Arias intensity of an earthquake had a significant effect as well. In addition, some preliminary design considerations for shallow foundation under the earthquakes were proposed. Overall, the numerical results offer some valuable references to improve the design and construction of foundations on an island slope under the seismic loadings.

Numerical and theoretical analyses of settlements of strip shallow foundations on normally consolidated clays under partially drained conditions

In the geotechnical community, the macroelement approach nowadays is largely considered to be a successful theoretical tool for solving soil–structure interaction problems. This approach is based on the definition of a generalised constitutive law putting in relation a small number of suitably defined generalised stress/strain variables. The macroelement formulations proposed in the literature take into consideration either drained or undrained cases, but disregard the hydro-mechanical coupling. In this paper, the authors intend to generalise the theory by introducing a new formulation for shallow foundations overpassing this limitation and capable of accounting for the influence of loading rate on the system response. To conceive and to calibrate the model, the authors numerically analysed the case of a shallow foundation positioned on a normally consolidated clayey soil stratum whose mechanical behaviour is reproduced by means of the modified Cam Clay model. Finally, the approach is discussed critically from the perspective of its use as a design tool according to approaches based on the ultimate limit state and displacement.

Investigation of the behavior of shallow machine foundation resting on a saturated layered sandy soil subjected to a dynamic load

In liquefying soils, Shallow foundations may experience an increase in settlement and displacement due to dynamic loading. Therefore, the machine footing may settle and tilt excessively. In this paper, the settlement of shallow foundation and inner displacement on liquefiable of unreinforced and reinforced saturated multi-layered sandy soils (medium-dense sand MD) will be studied. The relative density of the first and second layers is 50% and 85% corresponding to medium sand soil and dense sand soil respectively. The tests have been carried out on 20 models. The amplitudes of the applied harmonic load are 0.25, 1 and 2 tons with frequencies of 0.5, 1 and 2 Hz. The used foundation was with dimension 200*200*20 mm and the geogrid was used as reinforcement material. For each amplitude and frequency of load, the sand models were tested without and with reinforcement in various configurations (0.5B, 1B using single reinforcement layer and 0.5B, 1B using double reinforcement layers) where B is the square footing width. The results showed the high susceptibility for liquefaction and its potential which increased with increasing amplitude load and amplitude frequency. Also, the surface settlement and displacement were increased in the first layer and reduced with increasing relative density. The results also showed the high effect of reinforcement material and its configuration and number of layers by maintaining the little settlement values when fixing other parameters.

An evolutionary hybrid optimization of MARS model in predicting settlement of shallow foundations on sandy soils

This study is attempted to propose a new hybrid artificial intelligence model called integrative genetic algorithm with multivariate adaptive regression splines (GA-MARS) for settlement prediction of shallow foundations on sandy soils. In this hybrid model, the evolution algorithm – Genetic Algorithm (GA) was used to search and optimize the hyperparameters of multivariate adaptive regression splines (MARS). For this purpose, a total of 180 experimental data were collected and analyzed from available researches with five-input variables including the bread of foundation (B), length to width (L/B), embedment ratio (Df/B), foundation net applied pressure (qnet), and average SPT blow count (NSPT). In further analysis, a new explicit formulation was derived from MARS and its accuracy was compared with four available formulae. The attained results indicated that the proposed GA-MARS model exhibited a more robust and better performance than the available methods.

Seismic settlement of a strip foundation resting on a dry sand

Seismic settlement of shallow foundations constructed in seismic active areas should be considered for a reasonable estimation of the total settlement. However, the trend of the seismic settlement of shallow foundation constructed on a sandy soil is not clearly understood and it is estimated by designer using simple analytical methods. These methods do not consider the effect of the soil–structure interaction. This research, therefore, reports the results of 105 robust finite element models developed to investigate the seismic settlement of a shallow foundation constructed on a dry sand. The influence of the load applied on the foundation, relative density of sand, foundation embedment, peak ground acceleration of the earthquake shake, thickness of the sandy soil, and the dominant frequency of the earthquake shake have been examined to provide a comprehensive understanding of the parameters influencing the seismic settlement. The results of the analyses showed that increasing the load applied on the foundation or the peak ground acceleration remarkably increases the seismic settlement, while increasing the embedment depth remarkably reduces the seismic settlement. In addition, the relationship between the thickness of the sandy layer and the seismic settlement is found to be very complex and noticeably influenced by the relative density of the sand. More importantly, it was found that the seismic settlement dramatically increases when the dominant frequency of the earthquake approaches the natural frequency of the system. Thus, all these parameters are important and should be considered by designers for a reasonable estimation of the seismic settlement. The conclusions drawn from this paper will aid the development of a good analytical method in future, and the results reported in this paper also provide useful and novel database to designers and practitioners.

Application of soft computing techniques for shallow foundation reliability in geotechnical engineering

This research focuses on the application of three soft computing techniques including Minimax Probability Machine Regression (MPMR), Particle Swarm Optimization based Artificial Neural Network (ANN-PSO) and Particle Swarm Optimization based Adaptive Network Fuzzy Inference System (ANFIS-PSO) to study the shallow foundation reliability based on settlement criteria. Soil is a heterogeneous medium and the involvement of its attributes for geotechnical behaviour in soil-foundation system makes the prediction of settlement of shallow a complex engineering problem. This study explores the feasibility of soft computing techniques against the deterministic approach. The settlement of shallow foundation depends on the parameters γ (unit weight), e0 (void ratio) and CC (compression index). These soil parameters are taken as input variables while the settlement of shallow foundation as output. To assess the performance of models, different performance indices i.e. RMSE, VAF, R2, Bias Factor, MAPE, LMI, U95, RSR, NS, RPD, etc. were used. From the analysis of results, it was found that MPMR model outperformed PSO-ANFIS and PSO-ANN. Therefore, MPMR can be used as a reliable soft computing technique for non-linear problems for settlement of shallow foundations on soils.