Shallow Foundations Research Articles

Behavior of strip footing rested on undrained clay using consistency limits-based constitutive law

The behavior of undrained clay was extensively studied by many earlier researchers. A lot of constitutive models were developed to describe the behavior of undrained clay based on its mechanical properties. The aim of this research is to present an innovative constitutive model for undrained clay based on its consistency limits and water content. The main concept of this model is to estimate the mechanical properties of clay using earlier correlations with consistency limits, then implement the estimated mechanical properties in a hyperbolic model and calibrate the hyperbolic parameters to match the failure criteria of the undrained clay. To verify the validity of the developed constitutive model, it was applied on a standard problem which is a strip footing rested on undrained clay layer, the results confirmed the ability of the model to simulate the nonlinear behavior of undrained clay up to ultimate condition. The main advantage of this constitutive model is the ability to capture the reduction of mechanical properties of clay with the increase in its water content, which makes it ideal to study the impact of seepage on shallow foundation.

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

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

Bearing Capacity Analysis of Shallow Foundations Supported on an Artificial Fill (Substation at Kashari, Tirana)

Bearing Capacity Analysis of Shallow Foundations Supported on an Artificial Fill (Substation at Kashari, Tirana)

Numerical investigation of the contribution of the soil-structure interaction effects to the seismic performance and the losses of RC buildings

Seismic vulnerability and loss analyses of buildings are usually estimated under the fixed-based condition, omitting the soil-structure interaction (SSI) effects. However, according to the literature and the seismic damage due to past events, mid-to high-rise buildings located on soft soils can present a worse seismic performance. This manuscript aims to investigate whether the SSI effects affect the seismic performance and the losses of reinforced concrete (RC) buildings. To do so, a real 5-storey RC building has been selected as the case study. It was built prior to restrictive Spanish seismic codes. The building was constructed over soft alluvial strata and it has a shallow foundation. The area is characterised by a moderate seismic hazard. Nonlinear static analysis (NLSA) and incremental dynamic analysis (IDA) have been performed to assess the seismic behaviour and the losses expected of the case study building. The calculations have been done in the OpenSees finite-element framework. The direct method has been used to model the SSI. The results have been obtained for the fixed-base and for the SSI models. The numerical outcomes have shown the remarkable effect of the SSI on the fragility and on the performance of these structures. It has been observed that the severe damage expected can be worsened by up to 38% if SSI is taken into account. Additionally, the soft-storey mechanism at the ground floor concentrates all the damage expected, showing that this is the most seismic vulnerable part of the building (owing to higher interstorey-drift ratios and peak floor acceleration values). The losses expected derived for structural and non-structural components have been 140% higher if the SSI is considered.

Analytical fragility curves for displacement-based scour assessment of masonry arch bridges

The vulnerability of masonry arch bridges to scouring is primarily attributed to their shallow foundations. There is a constant need to assess the structural safety and identify those masonry arch bridge geometries susceptible to scouring. The immediate structural effect of scouring is the mobilisation of the bridge foundation resulting in the formation of a collapse mechanism involving the bridge superstructure. There is a critical gap in the literature in the availability of simple quantitative assessment procedures applicable to a population of masonry arch bridges susceptible to scouring. In this context, a generalised assessment procedure, primarily dependent on the geometry, is presented, which identifies bridge geometries susceptible to scouring through the quantification of available safety margin. The possible in-plane foundation movements and associated collapse mechanisms are identified as a function of bridge typology and the nature of scouring. Displacement-based analysis procedures are formulated the first principles for each identified in-plane collapse mechanism, replicating the observed collapse behaviour of masonry arch bridges. Fragility curves are then presented for each collapse mechanism with performance levels prescribed based on deformation demand, giving the exceedance probability for a developed foundation movement.

Physical Model of Shallow Foundation under Dynamic Loads on Sands

Structures built on sands worldwide, with shallow foundations, have experienced damage and collapse during and after earthquakes. Two phenomena triggered the collapse: the liquefaction phenomenon and the P-Δ effects. However, current research and practice do not fully understand granular soil behavior during liquefaction and P-Δ effects, as proven by the sum of investigations on physical models, constitutive models, and laboratory testing proposals about these topics. A question appears at this point: what is the relationship between excitation frequency, displacement amplitude, and the triggering of overturning? To cope with this issue, the authors propose to create a physical 1-g model composed of a single-degree-of-freedom oscillator (SDOFO) capable of transmitting cyclic loadings to the soil in rocking vibration mode. The measurement methodology was based on computer vision using OpenCV by Python, which allowed the “free movement” of the SDOFO. The authors use computer vision as a suitable way to obtain displacements and times without sensors placed directly in the physical model. According to the results, it was possible to define an inversely non-linear relationship between frequency, displacement amplitude, and the total cycles required to reach overturning for different effective grain-size (D10).

Prediction of Residential Slab Foundation Movement Through a Finite Element-Based Deep Learning Algorithm

Deep learning networks were employed to predict the maximum differential deflection of stiffened and waffle rafts due to reactive soil movements, Δmax. Four deep learning networks were used to predict Δmax, these are (1) stiffened rafts on shrinking soil, (2) stiffened rafts on swelling soil, (3) waffle rafts on shrinking soil, and (4) waffle rafts on swelling soil. The deep learning models were used to create design lines, which showed that both soil and structural features strongly influence the stiffened rafts. In contrast, waffle rafts showed a strong dependence on soil features in shrinking soils and beam depth in swelling soils. This demonstrates that the finite element-based deep learning networks captured the effect of the embedment of the beams. The results of the deep learning models led to non-linear design curves, which are disparate from the suggested standard Australian design. These results suggest that increasing the value of beam depth can have a positive or negative impact on the global residential slab depending on the type of substructure and whether the founding reactive soil is shrinking or swelling. Global sensitivity analyses of the deep learning models showed that for stiffened rafts on shrinking soil, the slab length, slab width and active depth zone of reactive soil had the most significant influence on Δmax, whilst for stiffened rafts on swelling soil, the primary drivers are ground movement, beam depth, and slab width. The prediction of Δmax for waffle rafts on shrinking soil was driven by the surface characteristic and mound movements, and the active depth zone, whilst waffle rafts on swelling soil was driven by the beam depth. Overall, the finite element-based deep learning showed the capacity to estimate Δmax in both shrinking and swelling design scenarios for different types of residential footing systems to further understand the characteristic behaviour of shallow residential slab foundations on reactive soils leading to improved designs.

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.

Effect of structural inertia on liquefaction-induced settlements of shallow foundations

The majority of published research on the performance-based design of shallow foundations on liquefiable soil focuses on seismic settlement accumulation by neglecting soil-structure-interaction (SSI) effects. On the other hand, SSI effects prove dominant when the foundation soil is non-liquefiable. Thus, the aim of this paper is to investigate the dynamic response of structure-foundation-soil (SFS) systems by examining the role of structural inertia on the performance of shallow foundations on liquefied soil, through a series of 3D fully coupled nonlinear numerical analyses of SFS systems. As a first step, the nonlinear fundamental period of vibration of the SFS system is correlated to the key system and excitation parameters. Next, in order to isolate the effects of structural inertia, shear-induced seismic settlements of SFS systems in liquefied soil are compared with the respective settlements of conjugate foundation-soil (FS) systems that apply the same static contact pressure on the foundation soil. Finally, approximate relations are proposed for the effects of structural inertia on liquefaction-induced settlements of shallow foundations, based on a multivariable statistical analysis of the numerous parametric numerical estimates.

Development of an advanced constitutive model for spoil-structure interaction problems

Revitalisation options for mine spoil heaps is an important issue to consider when planning for post-mining land use. One option is the installation of wind turbines on the spoil heaps, which provide a sustainable energy source. This option poses challenges for foundation design due to the nature of the spoil material, which is usually highly heterogeneous due to the way spoils are deposited, and can contain high proportions of high-plasticity cohesive soils (clay). This paper presents results obtained using an advanced constitutive model that was developed to simulate cohesive mine spoil behaviour and presents model results for the prediction of foundation response under both monotonic and cyclic loading. The model is a modified version of the original isotropic bounding surface plasticity model that additionally involves a damaged-based plastic modulus in order to realistically represent soil strength degradation induced by cyclic action. The model is used for the simulation of shallow foundations for onshore wind turbines on a cohesive clay with a heterogeneous (linearly increasing) undrained shear strength (random spatial variability is not considered). Two different loading scenarios of a shallow strip foundation are considered in the paper: a pure moment-vertical loading (M-V), and a moment-horizontal-vertical loading (M-H-V). The effect of the adopted spoil-foundation interface type is also considered: (1) a fully-bonded interface and (2) a tensionless interface. Results demonstrate that, though the vertical bearing capacity is only slightly affected by the interface properties, the moment capacity is shown to be strongly influenced by the predefined contact conditions. For the footing system under M-H-V loading, a dominant footing uplift mechanism is obtained for light structures and the opposite holds for heavily loaded structures, where significant settlement accumulation occurs during cyclic loading. Based on the analysis, the moment bearing capacity of the footing system decreases as the slenderness ratio and/or the vertical safety factor increase, and the opposite mechanism is obtained as the strength heterogeneity degree increases.

A Comparative Study on the Interpretation Procedure of Field Tests for Measuring the Dynamic Impedance of a Surface Footing

ABSTRACT The paper analyses in detail and compares different interpretation procedures of snap-back and forced-vibration tests on a full-scale prototype founded on soft-soil, in order to assess their effectiveness for measuring the stiffness and damping of a shallow foundation under dynamic loads. Both properties were back-calculated through three alternative methods, i.e. through impedance functions computed in the frequency domain, or by interpreting force-displacement loops in terms of peak-to-peak amplitudes or of phase-shift. The damping was further calculated from the logarithmic decrement of free-vibration records. The resulting foundation stiffness and damping were observed to vary with the number of cycles and with the load frequency and amplitude. The comparison among the interpretation techniques revealed that the peak-to-peak approach fails when damping is high, because it neglects the delay between force and displacement.

Improvement of consolidation properties of clay soil using fine-grained construction and demolition waste

As urbanization spreads rapidly, more structures are being built, and more construction and demolition waste (CDW) is produced, occupying about 36–40% of the total solid waste generation in the world; hence, CDW has become a burden nowadays. Moreover, the construction of low-rise buildings on weak soil is always challenging and costly due to the soil's high compressibility and low bearing capacity. Sand or other granular materials are commonly used to improve the compressibility behavior and associated settlement, drainage, and shear strength of weak soil. The massive use of natural sand for construction purposes of different civil engineering structures have lessened their reserves in recent times, increasing their price and destroying the balance in the environment. Among the several methods of improving soil, this research uses fine-grained CDW to improve the geotechnical behavior of weak soil under study. The main objective of this research is to observe the changes in soil properties after mixing with CDW. Recycled waste mortar powder has been selected as CDW mixed in different percentages in the soil. In addition, CDW powder was inserted into soil mass as a circular powder column in triangular and square grid patterns as an alternative to the sand column. CDW in the soil samples improved consolidation settlement, and reduced settlement time and compression index. Increments in the pre-consolidation pressure, consolidation rate, and permeability of the clay-CDW mixtures were also remarkable. Soil improvement through reusing CDW is a sustainable way to solve problems in solid waste management and the soft soil settlement issue under a shallow foundation, ultimately reducing the environmental footprints, saving natural resources, and supporting the circular economy concept.

1-g physical modelling of shallow foundation treated with polypropylene-reinforced soil-cement columns in liquefiable soil

The fibre-reinforced soil-cement columns are used as remediation measure against earthquake induced soil-liquefaction associated large settlements in liquefiable loose surface layer of sand. This loose surface layer of sand was overlying on the non-liquefiable dense bottom layer of sand. 1-g physical modelling of shallow foundation was carried out using shaking table. There were four 1-g physical models constructed for testing and the two types of improvements were used such as adjacent and beneath the structure. First model was 1-g physical model constructed without improvement, and three models were constructed with the provision of polypropylene-reinforced soil-cement columns. In the first treated model the columns were installed in the wooden fixity plate and adjacent to the structure, the second treated model was improved with improvement installed upon the soil-cemented fixity plate and provided adjacent to the structure, and in the third treated model with improvement installed upon the wooden fixity plate and provided beneath the structure. The results obtained in case of untreated 1-g physical model concludes that the penetration of structure inside the soil and settlement of structure, both are up to unacceptable limits. The results of first treated 1-g physical model concludes that the penetration and settlement of structure both are unacceptable. The results of penetration and settlement of structure in the case of second treated 1-g physical model are achieved up-to acceptable limits. The most successful type of improvement against the liquefaction-induced penetration and settlement of structure was achieved in case of third treated 1-g physical model in which the values of settlement and penetration are negligible. It is concluded that the improvement installed upon wooden fixity plate and provided beneath the structure is relatively the most efficient remediation measure against the earthquake induced soil-liquefaction induced settlement of structure.

Bearing capacity of strip footings on jointed rock mass

Rock masses are non-homogenous, discontinuous media composed of rock material and naturally occurring discontinuities such as joints, fractures and bedding planes. Due to the presence of the geological discontinuities such as joints, faults and bedding planes, the compressive strength and modulus of elasticity of jointed rock mass are significantly reduced and the measurement of the strength behaviour of these jointed rock masses below the foundation becomes a challenging task. Previous researches have dealt with the bearing capacity of strip footings on the jointed rock mass for concentric, eccentric, inclined loading, separately. But, very limited work has been carried out for determining the bearing capacity of footings on jointed rock mass under eccentric-inclined loading together. In this study, the behaviour of rock masses under the pressure of strip footing has been investigated. To make the problem, more realistic, eccentric-inclined load was applied on the strip footing resting on horizontal jointed rock mass. A parametric study has also been carried out to develop some non-dimensional correlation between different parameters including GSI, e/B ratio, inclination, bearing capacity, etc. Three-dimensional analysis has been carried out by the finite element method using PLAXIS 3D software. Modified Hoek–Brown criteria was used to simulate the behaviour of rock mass and elastic behaviour of foundation was taken into the consideration for analysis. From the results, it can be concluded that the bearing capacity values drop as the eccentricity of the load increases. This indicates that as the eccentricity of the load increases, the bearing capacity of jointed rock mass diminishes. The bearing capacity value decreases with increasing loading inclination with respect to vertical. In the current study, non-dimensional correlations have been developed using data from non-linear elasto-plastic FEA to forecast footing’ bearing capacity, settlement and tilt of shallow foundation. These connections rely on the inclination of the load as well as the eccentricity to breadth ratio. The results obtained from the non-dimensional correlations holds goods on comparing the results obtained from the FEM analysis.

Performance of Rocking Shallow Foundations and the Evolution of Beam-on-Nonlinear-Winkler Foundation Modeling

The nonlinear behavior of shallow bridge and building foundations under large-amplitude seismic loading is an important aspect of performance-based earthquake engineering. Soil yielding beneath foundations can be an effective energy dissipation mechanism; however, this yielding may lead to excessive permanent deformations. The research and engineering community has established decades of model testing and analytical modeling to understand foundation nonlinearity and uplift. Physical model testing provides insight into the mechanisms at work in rocking, shallow foundations, while analytical modeling and simulation are validated against these experiment results such that modeling recommendations can be applied in practice. This body of work led to the current design procedures in industry, such that the benefits and consequences of foundations allowed to rock under seismic events can be understood and implemented in practice generally for design of proposed structures, as well as retrofit of existing structures. While there are various established analytical modeling approaches, this paper presents a summary of both the elastic and nonlinear Winkler analytical modeling approaches used to approximate observations from experiment, the status of codified design procedures incorporating rocking, and includes speculation on the future of research and design in this field.

Effect of Foundation Shape on Settlement by Numerical Method

Five prototypes arranged in three different soil conditions is presented to find out the load-settlement relationship of soil and foundation. For creating three types of condition two types of managed soils are stiff clay and soft clay. The five prototypes used here represent the condition of shallow foundation. Prototypes area being same for cases has the shape of Triangular, Square, Rectangular, Pentagonal and Hexagonal. The load-settlement behavior has been found out plan-wise using Plaxis 3D software. Geotechnical engineering software which uses finite element method and Mohr-Coulomb failure criterion following mathematical differential equational problems. Plaxis 3D software uses the properties of soil cohesion, angle of internal friction, Elasticity modulus and unit weight, elasticity modulus of the foundation to settle a relation for the interaction between soil and foundation. Load-settlement behavior for the five prototypes as tried to be found out by Plaxis 3D has represented the immediate settlement of soil on which the prototypes have been rested. The graphs also help to understand the difference in the bearing capacity and settlement for the five prototypes, each of which acted as foundations. Pressure bulb is an effect of vertical pressure which differs from shape to shape of foundation. It directly affects the intensity of pressure and the intensity of pressure affects the settlement. The bearing capacity also affects the settlement. A triangular foundation has the best bearing capacity as its settlement is the lowest. But as a triangular shaped foundation is not practically used and not ideal it is not used for structural work. This study shows that square or rectangular foundation is best for a structure due to higher bearing capacity and lesser settlement compared to the same of pentagonal and hexagonal shaped foundation. But if comparison is done between square and rectangular shaped foundation, square is the best.

Uniaxial hysteretic spring models for static and dynamic analyses of self-centering rocking shallow foundations

Self-centering rocking shallow foundations have been proved to be a potential alternative to conventional foundations that provide superstructures with “fixed-base” constraints. Through appropriate design of foundations to undergo controlled rocking motions, they serve as “seismic fuses” (associated with a rocking isolation mechanism) which enable their supporting structures to remain even undamaged during intense shaking events without compromising the overall resilience of the soil–structure interaction (SSI) system. Recent progress in rocking shallow foundations has heightened the need for simple and efficient models in seismic design and evaluation of structures with rocking isolation. To this end, the paper proposes uniaxial hysteretic rocking spring models to enrich modeling of rocking-dominated foundation response in engineering practice. Two types of models are developed, including a bilinear hysteretic model (BHM) and a smooth hysteretic model (SHM). These models are defined by dimensionless backbone curves and recentering ratio based hysteretic rules obtained by performing monotonic and cyclic push-over analyses using a nonlinear hysteretic Winkler foundation (NHWF). The current implementation is based on square or strip footings on saturated clay foundations. Using the developed models, seismic performance of practical SSI systems consisting of rigid shear walls or deformable bridge piers on rocking shallow foundations are examined.

Calibration of resistance factors for design of shallow foundations against sliding

The design of shallow foundations typically proceeds by using the load and resistance factor design (LRFD) methodology to avoid various limit states with some probability. This paper looks at the sliding limit state of shallow foundations, and the sliding resistance factors required for the LRFD approach are estimated using reliability analyses of surface strip foundations. Cohesive and frictional soils are separately studied under wind loading conditions. Monte Carlo simulations are used to estimate the sliding failure probability of foundation designs on cohesive soils, and an analytical method is developed for frictional soils. The results indicate the existence of a “worst case” correlation length for cohesive soils, and the sliding resistance factor required to achieve target maximum lifetime failure probabilities is around 0.4–0.65 for moderate soil variability. For frictional soils, the required sliding resistance factor is about 0.5–0.85 for ν ϕ′ = 0.15. Overall, the sliding resistance factors recommended here agree well with the resistance factors of ϕ gu = 0.6 for cohesive soils and ϕ gu = 0.8 for frictional soils stipulated by geotechnical LRFD code provisions in Canada. The analyses can be used to estimate the reliability of current designs and can also aid the calibration of geotechnical design codes.

Effects of Heavy Rainfall on Shallow Foundations in Bukit Timah Granite in Singapore

The increase in rainfall intensities due to climate change affect the entire globe. In particular, Singapore suffers from floods and rising of coastlines. Notably, in the Bukit Timah Region in Singapore, floods are getting more intense, and the region houses multitudes of low-rise constructions with shallow foundations. Damages ranging from physical, in terms of motor vehicle and property damages, to intangible losses such as major traffic delays in both private and public transit were caused by the floods. Few studies have been carried out in Singapore in terms of shallow foundations’ response to rainfall events. When rainfall infiltrates into the soil, the bearing capacity and soil stiffness are affected by the change in matric suction. Thus, the impact of heavy rainfall on shallow foundations in Bukit Timah Granite is investigated numerically using SIGMA/W. Fully coupled flow-deformation analysis with unsaturated soil characteristics, e.g., the Soil Water Characteristic Curve (SWCC) and unsaturated permeability functions, were conducted. A range of rainfall intensities, rainfall durations, and applied loadings were investigated to produce a load–settlement curve that was compared against a semi-empirical model to yield reasonable results. The studies showed that the change in matric suction is affected by the rainfall duration, rainfall intensity, initial groundwater conditions, and hydraulic properties of soil, which in turn affects the settlement response heavily. The bearing capacity is evaluated using graphical methods via the load–settlement response curves, and it was found that the reduction in matric suction heavily reduces the bearing capacity of the soil. Combined with the unsaturated residual soils and transient analyses, the discoveries give insight into the assessment of shallow foundations subjected to water infiltration.

Field Test Study on Vertical Bearing Characteristics of Coal Rock

Coal rock is rarely used as the foundation bearing strata. For buildings located on coal rock, it is a reasonable and feasible way to obtain the vertical bearing characteristics of coal rock through field tests. Three plate load tests and two bi-directional load tests were carried out, and the design parameters of the vertical bearing capacity of the shallow foundation and the deep foundation were obtained, respectively. The plate load test results show that the pressure–settlement curve of coal rock is a steep-drop-type, and the deformation modulus decreases with the increase of the pressure. The bi-directional load test results show that the unit tip resistance-displacement curve of coal rock is a steep-drop-type, and the load transfer function of the unit tip resistance is an ideal elastic–plastic curve, and the displacement value corresponding to the ultimate bearing capacity is about 1% of the pile diameter. The load transfer function of the unit side resistance of coal rock is a hyperbolic curve. The equivalent pile top load–settlement curve obtained according to the load transfer functions of the unit tip resistance and the unit side resistance is consistent with the equivalent conversion results of the bi-directional load test method.