Design Of Shallow Foundations Research Articles

Displacement-based design of soil–foundation–structure systems

In this paper a displacement-based design procedure is presented to rationally account for the effects of soil–foundation–structure interaction (SFSI) in the seismic design of shallow foundations. The non-linear deformations at the soil–foundation interface, such as foundation uplift, soil yield and soil–foundation shear deformation can dramatically alter the dynamic response of a building. The lack of consideration of the modifying factors of SFSI and an absence of procedures for controlling foundation and soil behaviour under seismic loads have resulted in inadequate designs for buildings sited on soft soil. A soil–foundation macro-element model was used to calibrate expressions to quantify the non-linear foundation rotational stiffness as well as the effects of foundation energy dissipation and soil–foundation shear deformation on the response of the soil–structure system. A series of concrete wall buildings were designed with the proposed design procedure and numerically assessed to validate the suitability of the design procedure. The simple hand calculation procedure presented here quantifies the modifying factors of SFSI in an intuitive and direct manner to allow engineers to design building–foundation systems with a clear understanding of their expected performance.

Soil inertial factors for seismic bearing capacity

Earthquake loadings can reduce the ultimate bearing capacity of shallow foundations due to the imposition of transient horizontal loads and moments arising from the inertia of the supported structure, inertial forces in the soil mass and strength reduction in the founding materials due to rapid cyclic loading. In this paper, the general bearing capacity equation is used to calculate the seismic bearing capacity of shallow foundations. To account for the effect of inertial forces in the soil mass, soil inertial factors for level and sloping ground are recommended and their significance to the seismic bearing capacity is assessed. This paper provides a straightforward method to calculate seismic bearing capacity for the seismic design of shallow foundations within the limitations of pseudo-static analysis.

Consideration of soil strata heterogeneity influence on differential foundation settlements of overpasses for high-speed railways

The implementation of projects for the construction of high-speed railways actualizes the search of effective approaches to accounting the influence of soil strata heterogeneity along the course of the track on differential foundation settlements of overpasses. Russian special technical conditions prescribe sufficiently stringent regulation limits of absolute values of overpasses' foundation soil settlements (20 mm for ballastless track) and angles of break in profile (the differential foundation soil settlement), which should not exceed 1 ‰ for ballastless track. These requirements make it necessary to develop the calculation method, which is based on the criterion of deformation. To ensure compliance of design solutions to the specified regulations it is appropriate to use the method of the predefined equated soil settlements for design of shallow foundations of overpasses for high-speed railways. Several features of application of this method are presented in this article.

Effective Design Solutions in the Design of Shallow Foundations

The article presents the main directions related to constructive solutions and methods of calculation of shallow foundations. The analysis of the method of calculation of these foundations Institute NIIOSP (Research, design and survey and design-technological Institute of foundations and underground structures N. M. Gersevanova) associated with the choice of the calculation scheme. To take into account the spatial stiffness of shallow foundations, it is proposed to use the numerical method of calculation. An example of a numerical method for calculating shallow foundations for the action of normal forces of frost heaving for a one-story building is given.

Combined rupture mechanisms in shallow foundations

Conventional ultimate limit state (ULS) shallow foundation design is typically based on a simplified analysis that fails to consider the possible existence of a combined structural and geotechnical failure, which is shown here to significantly affect the limit load. Neglecting this occurrence may lead to unsafe design, whereas a full analysis can be beneficial for the dimensioning. With the emphasis on separate serviceability limit state and ULS design in modern design codes such as Eurocode 7 (EN 1997-1, 2004 edition), this paper explores unsafe loading scenarios and the benefits to be gained from a rigorous ULS design based on combined failure. For the sake of simplicity, a long foundation slab subjected to three different loading conditions is analysed using elastic, elasto-plastic, and rigid-plastic methods, and the results compared for a range of foundation strengths and stiffnesses. It is found that the limit load may be significantly influenced by plastic hinges in the structure and for each load condition it is possible to derive a curve relating ultimate load to plastic bending moment representing the ultimate limit state of the foundation.

EXPERIMENTAL STUDY OF MODEL PILED RAFT FOUNDATION EMBEDDED WITHIN PARTIALLY SATURATED COHESIONLESS SOILS

This paper presents an experimental study conducted on model piled rafts in partially saturated sandy soil. The aim of the experimental program is to study the effect of matric suction on the load carrying capacity of piled rafts embedded within partially saturated sandy soil .The influence of number of piles are presented and discussed in this study. The piled raft is arranged in different configurations of piles (single, double and triple piled raft with spacing 3.5D c/c) with the same area ratio (raft area to the cross section area of piles) to avoid different contact pressure area and to show the effect of different piles number and its group action. The influence of matric suction (i.e., capillary stresses) in partially saturated zone is typically not taken into account in the conventional design of both shallow and deep foundations so that the present research study the determination and contribution of matric suction towards the load carrying capacity of piled raft. The experimental work consist of 3 models of footing single piled raft (8.3 x 5) cm, double piled (16.6 x 5) cm and triple piled raft (25 x 5) cm. All these models are loaded and tested under both of fully saturated condition (i.e., matric suction equals to 0kPa) and unsaturated conditions (i.e., matric suction value equals to 6kPa , 8kPa and 10kPa), which are achieved by predetermined lowering of water table. The relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil, water characteristic curve (SWCC) estimated by applying fitting methods through the program (SoilVision). The results of experimental work demonstrate that the load carrying capacity of piled raft increases with increasing all values of matric suction as the number of piles supporting the raft increases. And the matric suction has a significant influence on the load carrying capacity of all tested models. The increasing value of the ultimate bearing capacity for single, double and triple piled raft under unsaturated conditions is approximately (2.1-4.47), (2-4.44) and (1.5-3.54) times higher than that at saturated condition respectively

Seismic Bearing Capacity Factor Considering Composite Failure Mechanism

This article describes how the design of shallow foundation needs complete knowledge about bearing capacity. During earthquakes additional lateral force acts at the foundation bed which reduces the bearing capacity. Most of the literature present either the pseudo static analysis or assume a planar failure surface to estimate seismic bearing capacity factors. Here, a pseudo dynamic approach that considers the time dependent effect of earthquake loading is employed. A composite failure surface has been considered for a more realistic estimation of seismic bearing capacity. New expressions were formulated to arrive at the seismic bearing capacity factor, considering the forces acting on the failure wedge based on the limit equilibrium approach. The effect of soil friction angles and the seismic peak of horizontal ground accelerations on the seismic bearing capacity were studied using the proposed method. It was observed that present pseudo-dynamic analysis with a composite failure mechanism gives lower values of seismic bearing capacity factors when compared to pseud- static analysis.

A long term evaluation of circular mat foundations on clay deposits using fractional derivatives

This study proposes to use fractional derivatives to evaluate the long term performance of circular mat foundations overlying clays and also predict the associated ground settlement. Closed form solutions for the deflection and bending moment of foundations and the subsequent reaction of subgrade are obtained with the Mittag–Leffler function. Numerical examples are used to determine how the fractional order affects the time dependent properties of the foundation and ground settlement, and to simulate the case history of a large standpipe constructed over Tertiary sediments. New insights into design and prediction of shallow foundations and ground settlement are also discussed.

Advance in the penetrometer test formulation to estimate allowable pressure in granular soils

In this paper, we present a modification of the existing mathematical formulation used to obtain the allowable bearing pressure from dynamic penetration tests in order to extend its applicability to the design of shallow foundations. The conventional relationships adopted to obtain the allowable bearing pressure from penetrometer tests have a discontinuous gradient, and they are limited to a depth less than the footing width. The aim of this work was to find a relationship that permits the estimation of this pressure in cohesionless soils, from the results of dynamic probing super heavy tests, through a single non-piecewise and continuous relationship that remains valid up to depths several times the footing width. This equation was applied as part of the geomechanical characterization survey undertaken for the construction of an elevated helipad in the centre of the Iberian Peninsula. The survey results were considered satisfactory, and the construction was completed without structural problems.

Bearing Capacity of Shallow Foundations on Cohesionless Soils: A Random Forest Based Approach

Determining the ultimate bearing capacity (UBC) is vital for design of shallow foundations. Recently, soft computing methods (i.e. artificial neural networks and support vector machines) have been used for this purpose. In this paper, Random Forest (RF) is utilized as a tree-based ensemble classifier for predicting the UBC of shallow foundations on cohesionless soils. The inputs of model are width of footing (B), depth of footing (D), footing geometry (L/B), unit weight of sand (γ) and internal friction angle (ϕ). A set of 112 load tests data were used to calibrate and test the developed RF-based model. The used data set consists of 47 full-scale observations and 65 small-scale laboratory footing load tests. To demonstrate the efficiency of proposed RF-based model, the results are compared with some popular classical formulas that are most commonly used for determining the UBC. The results show the efficiency and capabilities of the proposed RF-based model as a practical tool in evaluating the UBC of shallow foundations in a fast and accurate way.

Algorithm for generation of stratigraphic profiles using cone penetration test data

Cone Penetration Test (CPT) data are often used directly in the design of shallow and deep foundations and many other applications. To produce more cost-effective designs, it is advantageous to use CPT data to establish stratigraphic profiles as well. Algorithms to generate a stratigraphic profile using data from an individual CPT sounding and a Soil Behavior Type (SBT) chart as inputs are presented. Two SBT charts from the literature were selected and modified to eliminate ambiguity in soil classification. Novel algorithms were developed for handling the occurrence of thin layers within a stratigraphic profile to account for the fact that the standard CPT cone cannot accurately sense layers with thickness below a certain limit and a representative cone resistance cannot be obtained if the layer is too thin. Likewise, the algorithms prevent the creation of a soil profile with adjacent layers of essentially the same soil by consolidating layers appropriately. The algorithms presented generate a design soil profile, produced using a precise classification based on soil type and state and by elimination of artificial layering, that can be more effectively used in design.

Mitigating the seismic settlement of foundations on sand by ground improvement techniques

Geotechnical design of shallow foundations on clean fine sands often requires provisions for earthquake-induced settlements. In this regard, there have been many investigations on the volume-change behaviour of fine sands during dynamic and cyclic loading, and different methods have been developed to estimate ground settlement. However, less attention has been given to the role of ground improvement in reducing earthquake-induced settlements. This paper focuses on Anzali sand, which is representative of most sands found in the northern Iran, a region subject to high seismic activity. This sand was studied with the aid of physical modelling in the laboratory, and three different soil stabilisation techniques were applied to improve its stiffness and strength against volume change. Investigations revealed that among these methods, the cement treatment technique has an appreciable effect on the mitigation of seismic settlement.

SoFA: A matlab‐based educational software for the shallow foundation analysis and design

ABSTRACTShallow Foundation Analysis (SoFA) software is a newly‐developed free stand‐alone program based on Matlab for the calculation of bearing capacity and settlements of shallow foundations. SoFA uses several well‐known formulas from the literature and design codes that are preferred in engineering practice and not complicated numerical methods. The main goal is to provide the end‐user (student, academic, or professional civil engineer) with a simple, useful, user‐friendly tool to perform preliminary assessment of foundation analysis. © 2017 Wiley Periodicals, Inc. Comput Appl Eng Educ 25:214–221, 2017; View this article online at wileyonlinelibrary.com/journal/cae; DOI 10.1002/cae.21791

Calculation of Presumed Bearing Capacity of Shallow Foundations According to the Principles of Eurocode 7

Various simplified design procedures can be found in the literature, intended for the design of shallow foundations of lower importance buildings and pre-dimensioning. In most cases, these design procedures are based on vaguely defined soil types and parameters, and are not compatible with Eurocode. The aim of this paper is to establish a „design procedure by prescriptive measures”, according to the guidelines of Eurocode 7. Within this framework, previous design procedures are reviewed and a new procedure is developed for the simplified calculation of the bearing capacity of shallow foundations, conforming to the principles and rules of Eurocode 7.

Effective usage of poker vibrator for compacting quarry dust: an application to ground improvement in shallow foundation design

Appropriate ground improvement is required to stabilize soil under shallow foundations when there is a high groundwater table or weak soil. In such situations, a granular material like sand or quarry dust is widely used in the construction industry as a filling material to achieve higher bearing strength and to minimize settlement underneath foundations. Quarry dust, which is a waste product of the crushing process, is more economical and environmentally friendly. According to existing studies, quarry dust can be easily compacted by providing a vibration effect and a poker vibrator is a practical approach that can be used to achieve high degrees of compaction in quarry dust. However, as this technique is still quite novel to the industry, the expected results, in terms of degree of compaction, cannot be guaranteed. This is basically due to inappropriate practice and lack of guidance in the application of poker vibration. It is therefore essential to eliminate inappropriate practice by carrying out laboratory experiments on optimum poker vibration application techniques. The aim of this study was to optimize the effectiveness of poker vibrator in shallow foundation design by studying various factors affecting it, including time of application, shape of the foundation, preferable layer thicknesses and patterns of application of poker vibrators. This was done by conducting a series of poker vibration compaction experiments in circular and square containers and then by assessing the variation of degree of compaction in each trial. According to the test results, the most effective period of compaction for poker vibration comes at around 30 s after the compaction commences and lasts up to around 10 s. Degrees of compaction (DOC) in both circular and square containers increase with increasing application points, because the higher the number of vibration points, the more the compaction process is enhanced. The application of vibrator at the middle gives a relatively higher DOC than application at corners, because the vibration of middle area affects a greater area in the quarry dust fill compared to vibrating from a corner. DOC reduces with increasing initial layer thickness, regardless of pattern, because reduction of the layer thickness causes the vibration applying dust thickness to be reduced, which causes more vibration to the dust in the entire layer. The best poker vibration application pattern was also investigated.

A practical method to evaluate failure envelopes of shallow foundations considering soil strain softening and rate effects

This paper presents a practical method to evaluate the development of failure envelopes of coastal and offshore shallow foundations after the action of multi-directional cyclic loading considering soil degradation. This is realised by implementing a soil strain softening and rate model into a finite element package and using a combined approach of load controlled geometrically nonlinear finite element analysis and displacement controlled small strain finite element analysis. The gradual evolution of soil strain softening and rate effects are monitored and utilised to update the shear strength during the analysis under multi-directional cyclic loading. The failure envelope is then investigated based on the updated shear strength field of the soil. After introducing the approach and demonstrating with an example, a systematic study is presented to explore the effects of soil strain softening and rate parameters, soil stiffness index and period of cyclic loading on load carrying capacity of coastal and offshore shallow foundations. The results show that soil degradation should be taken into account in design of coastal and offshore shallow foundations because it is detrimental to the capacity of shallow foundations. Results of the parametric analyses have shown that soil sensitivity, relative ductility and the stiffness index have more influence on capacity of shallow foundations subjected to undrained cyclic preloading than strain rate parameter and the period of cyclic loading.

On a unified theory for reliability-based geotechnical design

Some theoretical models have been developed over the years by the authors dealing with reliability-based design of geotechnical systems. A comparison reveals that these models follow the same form which can be used to develop a unified reliability-based model, which includes the effects of spatial variability, site understanding, and failure consequence severity. This paper describes the unified model and applies it to four geotechnical problems to determine resistance and consequence factors to be used in design. The problems considered are the ultimate and serviceability limit state design of shallow foundations and ultimate and serviceability limit state design of deep foundations.

LABORATORY FOOTING TEST ON PARTIALLY SATURATED SANDY SOIL

Conventional analysis and design of shallow foundation are based on the assumption that the soil is under fully saturated condition. However, shallow foundations are typically constructed near the ground surface where the soil is under partially saturated condition. Therefore, more research to investigate the behaviour of shallow foundation in unsaturated soil is very essential in order to aid engineers in making good analysis and design. This paper presents a series of laboratory footing tests conducted on unsaturated sandy soil. A specially designed test tank was fabricated for the test. Square footings of two different sizes (100 mm x 100 mm and 150 mm x150 mm) were used and loaded on Rawang sand which has residual suction value of 10 kPa. The measured values of matric suction of the soil in the test tank were in the range of 0 to 30 kPa. Based on the results, it was observed that bearing capacities of shallow foundation under fully saturated condition were the lowest compared to soil under unsaturated conditions. The highest values were measured at matric suction equals to residual suction (i.e 10 kPa). Furthermore, the relationship between the bearing capacities of shallow foundation with the matric suction was observed to be non-linear.

REASONING ON IMPLEMENTATION OF FROST PROTECTED SHALLOW FOUNDATIONS

Implementation of frost protected shallow foundations (with insulation) in frost susceptible soils in the areas of the Baltic region is an item under discussion. A design method recommended by EN ISO 13793 has been applied. The design base is the EN 1997-1 which includes conditions and valid climatic data for the localities in the Republic of Latvia. The study contains the results of external air temperature data processing from the last 70 years, and consequently a determination of a freezing index value, and moreover pointing out the variation depending on the reference period taken. Results of temperature data processing for decades of winter seasons testify that quite distinctive frost protection levels may be defined for shallow foundation design parameters depending on the number of frost seasons sampled. The specific design results were obtained for eccentrically loaded columnar spread foundations of an unheated building insulated to reduce heat loss from the soil below the foundations keeping the subgrade soil unfrozen. As a result of the research the conclusion about the benefits expected has been presented, based on the comparison of concrete consumption and soil excavation volumes from different localities in Latvia. It has been concluded that the cost effectiveness of heated foundations correlates closely with the type of frost-heaving soil. Use of frost protected shallow foundations in clayey soils leads to an increase of ground volume to be excavated and filled back, and concrete consumption for foundations decreases. In silty sand soils, if the required foundation depth is less than some definite level, both reductions may be achieved by shifting the ground, and in concrete consumption as well.

Settlement predictions of footings on sands using probabilistic analysis

The design of footings on sands is often controlled by settlement rather than bearing capacity. Therefore, settlement predictions are essential in the design of shallow foundations. However, predicted settlements of footings are highly dependent on the chosen elastic modulus and the used method. This paper presents the use of probabilistic analysis to evaluate the variability of predicted settlements of footings on sands, focusing on the load curve (predicted settlements) characterization. Three methodologies, the first- and second-order second-moment (FOSM and SOSM), and Monte Carlo simulation (MCS), for calculating the mean and variance of the estimated settlements through Schmertmann (1970)'s equation, are presented and discussed. The soil beneath the footing is treated as an uncorrelated layered material, so the total settlement and variance are found by adding up the increments of the layers. The deformability modulus (ESi) is considered as the only independent random variable. As an example of application, a hypothetical case of a typical subsoil in the state of Espirito Santo, southeast of Brazil, is evaluated. The results indicate that there is a significant similarity between the SOSM and MCS methods, while the FOSM method underestimates the results due to the non-consideration of the high-order terms in Taylor's series. The contribution of the knowledge of the uncertainties in settlement prediction can provide a safer design.