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To arrest rockfall boulders, baffles are constructed as steel members affixed on top of a concrete footing. Existing designs aim to prevent any footing rotation and steel member bending. As such, existing baffle designs require massive reinforced concrete footings and complex bolt and weld connections. Such designs have limited constructability and result in complex failure mechanisms (i.e., tensile failure of concrete foundation at connections). In this paper, we introduce a new baffle design concept that optimizes the balance between steel member bending and footing rotation to enable a compact design. Full-scale pendulum experiments are conducted to evaluate the proposed easy-to-construct and design baffle under successive boulder impacts of 50 kJ. It is demonstrated that by considering the effects of steel member deflection and concrete foundation rotation, the maximum impact force on baffles is reduced by up to two times when compared with those on a rigid barrier and the failure modes are simplified to either overturning failure of the footing or buckling failure of the steel member. A ratio that defines the flexural capacity of the steel member to the overturning capacity of the shallow concrete foundation is proposed to control the failure mode. The optimized baffle configuration for an impact energy of 50 kJ, with minimum residual deflection, has a target capacity ratio of 2.0. • A capacity ratio (flexural capacity of steel member to overturning capacity of footing) is proposed for baffle design. • A new baffle design concept is proposed and evaluated using full-scale pendulum experiments. • A failure criterion based on baffle rotation is proposed considering the residual boulder velocity. [ABSTRACT FROM AUTHOR]

On 12 October 2013, the 24-storey high 'Space' building collapsed in Medellín, Colombia. The building had a reinforced concrete structure founded on large-diameter piles with enlarged bases. During and after construction the building exhibited structural problems and excessive settlements of some piles. Because of the evidence of structural damage, the building was evacuated on 11 October 2013, 1 day before the collapse. Isolated large-diameter piles excavated in a firm, high-plasticity saprolitic residual clay, supported building columns. Building collapse was triggered by a significant increase of the vertical load transmitted by some columns, which, in turn, is explained by widely different settlements experienced by neighbouring piles and the resulting loading transfer mechanisms. The first part of the paper presents the results of the field exploration and laboratory tests, as well as the structural and architectural layout, including the construction process and other forensic aspects that could influence the collapse of the structure. Afterwards, the joint structure–foundation–soil numerical model developed and its predictions are described. Matching the records of pile settlements, measured during construction and afterwards until building collapse, with model predictions allowed the validation of the model. The causes that triggered the collapse were identified and some other lessons were learned. [ABSTRACT FROM AUTHOR]

A design method for spread footings and pile caps is presented. The model is in principle based on the strut-and-tie concept, but with the strut dimensions defined by compatibility conditions and therefore not possible to manipulate by the designer. Due respect is paid to the size effect--that is, the decreasing strength with increasing member size--which seems to be disregarded by common strut-and-tie methods. Comparison with test results of column footings and four-pile caps in the literature demonstrates that brittle punching failure as well as yielding and brittle cracking failure can be predicted with very good accuracy. [ABSTRACT FROM AUTHOR]

Stone columns are a popular formof ground improvement that can be applied to a variety of foundation solutions involving soft soil deposits. Many design methods are based on an assumption that columns with a length-to-diameter ratio greater than 4 bulge uniformly along their length. This mode of deformation is not valid for small groups of columns in which interaction between individual columns and the footing gives rise to more complex behavior. The deformational behavior of stone columns at serviceability limit state is of utmost importance, because settlement rather than bearing capacity criteria are generally more onerous in soft soils. The results of some high-quality laboratory studies have been informative in this respect, but the extrapolation of results from small-scale tests comes with the caveats associated with single-gravity laboratory testing. The FEM, in combination with advanced constitutive models, can provide a link between the deformational behavior and settlement performance of discrete column groups at working stress levels. A series of analyses was conducted to examine the influence of key design parameters such as column length, spacing, and the number of columns. The influence of a stiff crust was also examined, because the reference soil profile adopted for these analyses was that of the well-characterized Bothkennar test site. The following three modes of deformation were identified by examining the distribution of stress and strain within columns and the surrounding soil: individual punching, block punching, and bulging. Individual and block punching developed in short or closely spaced columns, whereas block punching was more prevalent in larger groups. Bulging develops in long, widely spaced columns and generally occurs at the point of lowest lateral restraint. In addition, novel parameters referred to as compression and punching ratios were developed to validate the in-depth analysis and identify the principal design parameters that influence the behavior of small groups of stone columns. The results indicate that the mode of deformation is governed by column spacing and length rather than the number of columns. This finding is important, because it indicates that settlement design methods that are developed for large groups of columns are applicable to discrete groups at similar spacings and lengths. It was also observed that the influence of the stiff crust forces bulging to occur deeper and might have led authors in the past to suggest the existence of a critical length. [ABSTRACT FROM AUTHOR]

Monopiles are the most commonly used foundation type for offshore wind turbine (OWT) structures and are characterized by relatively large geometric dimensions, compared with offshore pile foundations typically used in the oil and gas industries. To date, there are no established technical guidelines tailored for the design and analysis of OWT monopiles. This paper first identifies various intrinsic drawbacks involved with the existing design and analysis methodologies as applied to OWT monopiles. Next, a comprehensive experimental program of 1g repeated lateral load tests, performed on a scaled rigid monopile installed in dry sand beds, is presented to investigate its behavior under various loading scenarios. The experimental results provide insights into the various blurry issues in the existing literature related to monopile behavior under long-term repeated lateral loading. Lateral soil resistance profiles were determined from the measured pile bending strain data and found to be markedly dependent on the degree of the polynomial function used for curve-fitting of the bending strain data. Finally, an experimental model is presented for estimation of the pile's accumulated rotation, which takes into account various basic characteristics of the applied lateral load cycles. [ABSTRACT FROM AUTHOR]

Spudcans are typical foundations used in shallow to moderate-depth water oil and gas fields to support jack-up drilling units. Understanding the behaviour of spudcans under combined loadings is crucial to the overall response of the jack-up structure. This paper presents the development of a strain-hardening plasticity model for a spudcan footing on loose sand. Most of the model components are developed from direct centrifuge observations. The centrifuge tests were performed at an acceleration of 100 times that of the Earth's gravity on a model spudcan footing subjected to combined vertical, horizontal, and moment loads. All the experiments have been designed and conducted to allow the results to be interpreted with a strain-hardening plasticity framework. Combined loads were applied by using a novel apparatus, which enables independent vertical, horizontal, and rotational movements of the footing. Test results also revealed the existence of a three dimensional sliding surface that intersects with the conventional yield surface. This additional surface has been defined analytically. Retrospective simulation of the experimental data using the plasticity model confirms the model's capability for use in predicting the behaviour of larger spudcan applications offshore. [ABSTRACT FROM AUTHOR]

Foundations resting adjacent to the crest of a slope exhibit a smaller bearing capacity respect to the case of horizontal ground. In this paper the static and seismic values of the bearing capacity factor N γg for shallow strip foundations adjacent to slopes were evaluated using the method of characteristics, extended to the seismic case by means of the pseudo-static approach. N γg was evaluated for different values of the slope angle and, under seismic conditions, accounting only for the effect of horizontal and vertical inertia forces arising in the foundation soil. The results, for both smooth and rough foundations, are presented and checked against those obtained through finite element analyses. [ABSTRACT FROM AUTHOR]

The bearing capacity factor ( N γ ), correction factor ( K γ ), and failure mechanism of a strip footing with a rigid basement were investigated using UBFEM-RTME. The footing–sand interface and the sand-basement interface were assumed perfectly rough. The results are presented in terms of the variations of N γ and K γ with the friction angle, ϕ , and dimensionless thickness, h / b , of the sand. When h / b is smaller than dimensionless critical depth H cr / b , N γ and K γ increase with decreasing h / b or increasing ϕ and the mesh-like failure mechanism is found to confine within a small domain. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the dynamic interaction effect of closely spaced square foundations under machine vibration. Under a dynamic condition, a number of large-scale model tests were conducted in the field, which includes a wide range of study on the isolated as well as interacting footing response resting on the local soil available at Kanpur, India. The dynamic interaction of different combinations (size) of two-footing assemblies was investigated by inducing vertical harmonic load on one of the footings (active footing), while the other footing (passive footing) was loaded with static weight only. The active footing was excited with different magnitudes of dynamic loading and the response was recorded for both footings, placed at a different clear spacing ( S). The results are compiled and shown as the variation of displacement amplitude with frequency. The transmission ratio that predicts the effect of dynamic excitation of the active footing on the passive one is determined for the interacting footings and plotted with respect to frequency ratio. [ABSTRACT FROM AUTHOR]

Geosynthetic-reinforced soil (GRS) walls have been increasingly used to support bridge foundations as abutment walls. On the GRS abutment wall, large footing loads are applied adjacent to the wall facing. However, so far limited studies have been conducted to investigate the performance of GRS abutment walls subjected to static or dynamic loading. This study presents a series of model tests on the GRS walls to evaluate the effects of several influence factors, including the offset distance of a strip footing, the width of the strip footing, the length of geogrid reinforcement, and the connection mode between geogrid and facing, on the ultimate bearing capacities of the strip footings on the GRS walls. The settlements of the loading plate and the lateral displacements of the wall facing during loading were monitored. Thin colored sand layers were placed in the backfill sand to observe possible failure surfaces developing in the GRS walls. The experimental results showed that the footings on the GRS walls with 0.7H (H is the wall height) long reinforcement reached the maximum bearing capacities at the offset distances of 0.3 H and 0.4 H in the wall tests with mechanical and frictional connections, respectively. When the GRS walls had the geogrids with longer reinforcement length (2H), the ultimate bearing capacity increased with the offset distance of the footing and became constant when the offset was greater than 0.4H. It was observed that the failure surface started from the edge of the footing and exited from the facing of the wall. Based on the limit equilibrium analyses, under the footing loading, the slip surfaces by Spencer's two-part wedge method had a good agreement with those observed in the model tests. [ABSTRACT FROM AUTHOR]

The design of shallow foundations has traditionally used a mixture of plasticity-based solutions to find the ultimate limit state and either a factor of safety on the plasticity solution or a linear elastic solution to attempt to design for the serviceability limit state. The serviceability limit state is intrinsically linked to the deformation mechanism that occurs beneath the shallow foundation in service. A better understanding of these soil movements can pave the way for more rational design approaches. In this paper, small-scale experimental work is used to show that the deformation mechanism beneath strip and circular foundations continuously changes as the footing is displaced. The mechanisms observed at intermediate settlements, noted to be typical design points, are best described by a mixture of solutions. Linear mixes of idealised fields were analysed using an upper bound approach to determine the load-displacement behaviour of each mix. The envelope of lowest upper bounds indicated that the optimal mix of fields changes depending on the footing settlement. At typical design points for shallow foundations mixtures dominated by ellipsoidal cavity expansion mechanisms were found to be optimal for both axisymmetric and plane strain cases. Comparison of theoretical and experimentally measured predictions indicated that using linear mixes of fields gives a good approximation to the true behaviour and may be used for settlement-based design approaches in the future. [ABSTRACT FROM AUTHOR]

Two geotechnical centrifuge tests were designed to elicit the influence of soil-foundation-structure interaction (SFSI) and structure-soil-structure interaction (SSSI) effects on the seismic demands of an inelastic frame structure founded on individual spread footings. Four experimental cases were considered: (1) SFSI of an individual inelastic frame structure (baseline case); (2) in-plane SSSI between the frame structure and a large elastic wall structure designed to respond predominately in a rocking mode; (3) anti-plane SSSI between the frame and wall structures; and (4) combined in-plane and anti-plane SSSI between the frame structure and two wall structures. Results from Cases 1, 2, and 4 are analyzed considering 13 demand parameters. The peak seismic demands from the baseline case are compared to the peak demands from the SSSI cases to elicit the impacts of building adjacency. The number of earthquake motions that resulted in increases or decreases in the seismic demands in the frame structure are tracked for the SSSI cases. For these tests, SSSI consistently results in increased peak foundation moment and foundation base shear demands, regardless of the geometric layout of the structures. These increases propagate throughout the superstructure, resulting in increases in moment, shear and curvature ductility demands in the structural components. SSSI effects are observed to be most significant for low-to-moderate intensity earthquake motions, suggesting that particular consideration should be given to the likelihood of SSSI for highly probable earthquakes. [ABSTRACT FROM AUTHOR]

Conventional bearing capacity analyses for shallow foundations placed on slopes use a modified set of bearing capacity factors based on soil properties, footing geometry, and slope configuration, but are restricted to purely cohesionless or purely cohesive soils. This approach is adequate for establishing bearing capacity on engineered fills with controlled foundation properties, yet does not adequately address design for bearing capacity on soils that have both cohesion and internal frictional resistance--a common scenario for native soils. This role becomes increasingly important in design for mechanically stabilized earth walls, which are often placed on slopes of native c'-φ' soils in which the bearing capacity can often be the critical design constraint. Prior approaches to bearing capacity on horizontal ground for c'-φ' soils utilize principles of limited state plasticity in their formulation, yet the most commonly applied bearing capacity approaches on slopes use semiempirical formulations that employ mutually exclusive soil strength parameters. In this work, results are attained using upper-bound limit state plasticity failure discretization scheme, known as discontinuity layout optimization (DLO), which uses nonassumptive failure geometry (under translational kinematics) in its formulation. The values presented demonstrate important components in consideration of bearing capacity for strip footings placed adjacent to slopes of c'-φ' soils, in particular, the relationship between soil strength properties, slope height to footing width ratio, slope angle, and critical collapse mechanism. A set of reduction coefficients that can be directly applied to the classical bearing capacity formulation is presented for ease of application. [ABSTRACT FROM AUTHOR]

This paper reports a set of centrifuge tests to investigate the increase in bearing capacity of a skirted circular foundation that results from preloading with consolidation. Results are compared with coupled numerical analyses using the modified Cam Clay model. Fundamental mechanisms are revealed from the stress paths followed during preloading and consolidation at the element level, accounting for both the change in mean normal effective stress and in the hardening parameter. A formulation is developed to predict the gain in bearing capacity as a function of the level of preloading applied on the foundation and the degree of consolidation achieved. The formulation provides good agreement with the centrifuge results. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the performance of two instrumented surface footings at the Bothkennar Clay research site in the UK. Footing A was loaded to failure over 4 days, reaching a net bearing capacity of = 138 kPa; footing B was loaded to 89 kPa, at an identical loading rate, and left to consolidate under maintained load for about 11 years. The preloaded footing was then loaded to failure over 3 days, reaching = 204 kPa. The increase in bearing capacity was significantly larger than that expected due to consolidation effects alone, and it is anticipated that the occurrence of creep and other ageing processes may have played a major role in the observed response. The complete loading history of the two footings is simulated by means of coupled axi-symmetric finite-element analyses in which the foundation soil is described using an elastic-viscoplastic model that mimics isotach viscosity. The ground profile and the model parameters are derived based on the extensive laboratory and field test data available in the literature. The numerical analyses are able to describe accurately the footings behaviour during first loading, the development of delayed settlement under maintained load and the increase in bearing capacity due to preloading. The paper emphasises various issues regarding the application of elastic-viscoplastic models to model boundary value problems in conditions close to failure. [ABSTRACT FROM AUTHOR]

This article presents the findings of an investigation that used finite-element analysis to determine the influence of a concrete footing's dimensions on its temperature development and cracking at early age. A three-dimensional finite-element model was used to predict temperatures in the footing and to assess cracking potential of the concrete. A parametric study consisting of 63 finite-element analyses was conducted on three different footing shapes: (1) a cubic shape, (2) a length:width:depth ratio of 4:4:1, and (3) a length:width:depth ratio of 4:2:1. Volume-to-surface area ratios () ranged from 0.33 to 4.0 m. The results showed that cracking potential does not depend on a footing's dimensions when its is 1.3 m or greater. Rectangular footings that have the same but different shapes (dimensional proportions) developed a similar maximum temperature, a similar maximum temperature differential, and a similar minimum crack index under the same insulation condition. Smaller footings allowed slightly higher maximum temperature differential before thermal cracking occurred. [ABSTRACT FROM AUTHOR]

Highly layered soils are prevalent in several areas of current offshore activity and in particular in emerging provinces and fields. However, no investigation has been carried out for spudcan penetration in stratified sediments with more than two layers. This paper reports centrifuge modelling of spudcan foundations penetrating through 3∼6 clay layers with interbedded stronger clay, silica sand and carbonate sand layers. The aim was to provide insight into the behaviour of spudcan foundations in stratified sediments comprising layers of different drainage conditions and mineralogy. The motivation for this paper emanated directly from the future needs identified by the recent revised version of ISO 19905-1. It was found that the downward soil deformation was extended into 3∼4 underlying layers of sand and clay with thickness ratios (/) less than 0·6. The limiting squeezing depth was 0·17∼0·18 when approaching stiff clay-moderate clay layers and 0·28 when approaching dense sand-stiff clay layers. These depths were enhanced (to 0·3∼0·35) by the soil plug trapped beneath the advancing spudcan. The values obtained using the ISO criteria either overestimated or underestimated these depths. Punch-through failure at a shallow penetration depth occurred with a load-spreading gradient of 1 (horizontal):3 (vertical) in silica sand and with a much smaller gradient of 1:7 in carbonate sand. In both sands, the spreading angle reduced with increasing depth of punch-through failure, and diminished quickly immediately after a failure. In contrast to ISO guidelines, the plug base, where the end bearing was mobilised, was located in one of the lower layers moved down with the advancing spudcan. For all cases, a soil plug developed at the base of the advancing spudcan, with the height of the plug accumulating through trapped clay and sand, regardless of their strength, from layers above and below the advancing spudcan. The height of a soil plug was reduced partly by soil backflow and squeezing out from contact with a strong layer. The observed soil failure mechanisms and corresponding penetration resistance profiles highlight uncertainties in ISO 19905-1. Guidelines are provided to improve the suggested punch-through and squeezing methods in ISO 19905-1. Implications for the bottom-up design approach proposed by ISO, and also a top-down design approach used by some practitioners, are discussed. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the behavior of an eccentrically loaded model ring footing resting on a compacted replaced layer of sand that overlies an extended layer of loose sand. Particular emphasis is placed on the potential benefits of reinforcing the replaced sand layer with geogrid reinforcement. Load configuration was designed to simulate ring footings under vertical loads and overturning moment caused by lateral loads. Several configurations of geogrid layers, number, and stiffness were used to study ring footings with different inner-to-outer-diameter ratios and load eccentricities. The effect of the depth and the relative density of the replaced sand layer was also investigated. Test results indicate that the behavior of an eccentrically loaded ring footing significantly improves with an increase in the depth and the relative density of the replaced compacted sand layer. However, the inclusion of soil reinforcement not only leads to a significant reduction in the depth of the replaced sand layer but also causes a considerable increase in the bearing capacities of the eccentrically loaded rings, leading to the cost-effective design of the footings. On the basis of the test results, the effects of different parameters are presented and discussed. [ABSTRACT FROM AUTHOR]

Lower-bound calculations based on the finite element method are used to determine the bearing capacity of a strip foundation subjected to a vertical, eccentric load on cohesionless soil with varying surcharges. The soil is assumed perfectly plastic following the Mohr-Coulomb failure criterion. The results are reported as tables and graphs showing the bearing capacity as a function of the eccentricity and surcharge. Normalised interaction diagrams in the vertical force versus moment plane have been produced. The results from the analysis are in reasonable agreement with existing methods for smaller eccentricities, whereas for greater eccentricities ( e > 0.25 B-0.3 B, where B is the width of the foundation), the lower-bound values in general - and especially for greater surcharges - are considerably smaller than the bearing capacities predicted by existing methods. For the special case of no surcharge, the results are in very good agreement with results obtained by the effective-width approach originally proposed by Meyerhof. [ABSTRACT FROM AUTHOR]

The article presents a study on pressure distribution in stone columns reinforced with crushed basalt in soft clay, under foundation loading and consolidation. A 60 millimeter (mm) in diameter footing was used to test the stresses on stone columns in a 300 mm diameter by 400 mm high clay samples under drained conditions and loading. Results show that the pressure distribution on the columns have shown complex behavior during loading and negative skin friction has developed after unloading.

Micropiles are have been effectively used in many ground improvement applications to increase the bearing capacity and reduce settlement, particularly in strengthening existing foundations. This paper presents the results of laboratory model tests on the behavior of a square footing supported on micropiles. The parameters varied in the study include micropile diameter, length, spacing between the micropiles and distance of micropile from the edge of the footing. Bearing capacity of unreinforced and reinforced footings is determined and bearing capacity improvement factor and settlement reduction factors are evaluated. The results are then analyzed to study the effect of each parameter. The improvement of bearing capacity is noticed when the diameter and length of micropile increases and spacing between the micropiles and distance of micropile from edge of footing decreases. [ABSTRACT FROM AUTHOR]

In this study, a number of model tests were conducted to study the interference effect of two near-by strip footings on dry, cohesionless, layered soil. The single as well as two-layer foundation bed was prepared by using Ennore sand. Two different widths (75 and 50 mm) of model footing were employed in the study. To study the interference effect between two footings, first, the bearing capacity of single isolated footing was obtained and later on, that of closely spaced footings was determined. The experimental study indicates that the bearing capacity of single footing on the layered deposit decreases with increase in D/B, where D and B are the depth of top weak layer and width of footing, respectively. The effect of centre to centre spacing (S) between two footings, on their bearing capacity and settlement at failure is mainly focused in this paper. The settlement behavior of closely spaced footings is found to follow the same trend as the bearing capacity. The results are presented in terms of efficiency factors (ξγ, ξδ) and their variation was obtained with the change in S. The present experimental observations are generally found in good agreement to those theoretical and experimental results available in the literature. [ABSTRACT FROM AUTHOR]

Abstract: Shallow footings are subjected to lateral forces induced by earthquake movements, wind loads, water wave pressure, lateral earth pressure, and transmitting power cables. In some structures such as water front structure, earth retaining structure and transmitting power structures, the lateral forces acting on the footings may be dominant. There has been little work studying the performance of skirted footings subjected to lateral loads. Twelve loading tests were performed on small scale circular skirted footing to shed some light on the performance of skirted footings when subjected to lateral loads. The effects of skirt length and the relative density of sand on the performance of the footing were investigated through laboratory testing program. Also a comparative experimental study between ultimate horizontal loads attained by skirted and unskirted footings with the same properties was conducted. From the accomplished laboratory tests it was found that the skirts changed the failure mode of circular shallow footings from sliding mechanism into rotational mechanism. Also the skirts attached to footings increased appreciably the ultimate horizontal capacity of shallow footings. [Copyright &y& Elsevier]

Abstract: The paper presents a laboratory study of the effect of geosynthetic reinforcement on the cumulative settlement of repeatedly loaded rectangular model footings placed on reinforced sand. Repeated load tests were carried out with different initial monotonic load levels to simulate structures in which live loads change slowly and repeatedly such as petroleum tanks and ship repair tracks. Three series of tests were carried out. Tests of series 1 were performed to determine the ultimate monotonic bearing capacity. Tests of series 2 were performed on unreinforced sand under vertical repeated loads. Tests of series 3 were performed to study the effect of sand reinforcement on the footing response under the same loads. The studied parameters include the initial monotonic load levels, the number of load cycles, and the relative density of sand along with geosynthetic parameters including size and number of layers. Both the ultimate bearing load and the cumulative settlement were obtained and analyzed. [Copyright &y& Elsevier]

Granular materials underneath footings are subjected to static and dynamic loads. As a result of these loads particle crushing may occur depending on the strength of the soil particles. Since particle crushing reduces the shear strength of a granular material and produces settlements, the performance of an engineering structure supported on a crushable soil can be compromised due to granular crushing. This paper presents the results of two DEM (Discrete Element Method) simulations intended to compare the effect of crushing on the bearing capacity of a simulated dense granular material. Also, a comparison with the theoretical bearing capacity is presented. Even though the two simulations considered the same idealized material, crushing was allowed only in one simulation. Particle crushing was possible by replacing the particle fulfilling a predefined failure criterion with a group of smaller particles. It was found that the ultimate bearing capacity of the material was strongly reduced as a consequence of only a moderate amount of crushing. This paper also presents the visualization of the failure mechanisms involved in the two analyzed cases. [ABSTRACT FROM AUTHOR]

A foundation system may involve more than a single footing with an arrangement such that the footings are sufficiently closely spaced that adjacent footings interact. Vertical, horizontal, and moment capacity of multifooting foundation systems are potentially dependent on footing interaction, and in particular overturning capacity can be significantly enhanced by the structural rigidity of a multifooting foundation system. There is no established procedure for the calculation of bearing capacity of a shallow foundation system comprising cojoined footings and ad hoc approaches may simply involve summing the ultimate limit states of the individual footings as if they acted independently; neglecting additional capacity of the system available from the kinematic constraint provided by the structural connection between the footings. Plane strain finite-element analyses have been carried out to investigate the undrained ultimate limit states under general loading of skirted two-footing foundation systems at various normalized spacing compared to a single skirted footing of equal bearing area and embedment ratio. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents data obtained from a series of laboratory plate load tests performed on geogrid-reinforced sand beds. Fine, medium and coarse sands were used as test sand beds. Circular geogrids of diameter 120mm were used as reinforcement layers. Improvement in load–settlement response was studied. The test sand beds were compacted to a relative density of 50%. A surface footing plate of diameter 60mm was used as the shallow foundation. It was found that the horizontal geogrid reinforcement improved the load–settlement response. The applied load for a deformation of 0.5mm in the case of geogrid-reinforced fine sand, medium sand and coarse sand was, respectively, 83N, 44N and 87N, whereas it was 63N, 38N and 47N when the sands were unreinforced. Load–settlement response was found to improve further with increase in number of geogrid layers and with decrease in spacing between them. Load improvement ratio (LIR), defined as the ratio of load for a given settlement in geogrid-reinforced case to that for the same settlement in unreinforced case, increased with number of geogrids (n) for all sands, but the improvement was significant in the case of coarse sand. [Copyright &y& Elsevier]

The response of skirted foundations to combined vertical, horizontal and moment loading is important for the design of offshore installations. The vertical skirts beneath the footing interact with the soil and increase the foundation capacity, compared with a surface footing. Previous researchers have assumed that the soil within the skirts remains rigid during undrained loading, but this assumption has not been investigated rigorously. A series of plane-strain finite element analyses has been conducted to investigate directly how the skirt geometry affects the undrained strip foundation capacity under combined horizontal-moment loading and the mechanisms occurring at failure. Conditions of both uniform and non-uniform undrained strength soil have been considered. The results show that deformation of the soil between external skirts can lead to significantly less foundation capacity than that of an equivalent solid embedded foundation. Hence the specific geometry of the foundation must be considered in design. In addition, the failure envelopes for skirted foundations with different embedment ratios differed significantly. This makes general recommendations for failure envelope shapes problematical. Finally, significant increases in foundation bearing capacity may be achieved by adding an intermediate skirt to the foundation, which results in a foundation capacity that is almost equal to that of a solid embedded foundation. [ABSTRACT FROM AUTHOR]

This paper describes a series of centrifuge model tests investigating the vertical bearing capacity of flat and conical circular foundations on sand, which are representative of the spudcan foundations of offshore jack-up units. It is found that at shallow embedment the bearing capacity factor, Nγ, mobilised by a conical footing is significantly lower—by a factor of up to 2—than that for a flat footing. Plasticity solutions indicate that this discrepancy cannot be attributed to the theoretical differences in Nγ that arise from the roughness and geometry of the cone: these theoretical differences are minor (<10%). Instead, it is proposed that in dense sand the pre-shearing induced by the conical shape of the footing leads to a form of progressive failure, so a lower operative friction angle is applicable to conical foundations than for flat footings. Since accurate solutions for Nγ exist, the key uncertainty in the prediction of bearing capacity is the appropriate friction angle, which is affected by this progressive failure mechanism. A backanalysis that incorporates Bolton's stress-dilatancy correlations in an iterative calculation for bearing capacity is introduced, using recently published definitive values of Nγ. This framework is calibrated using centrifuge model test data. The progressive failure mechanism is captured in a simple fashion by varying Bolton's m parameter, which controls the dilatant contribution to peak strength. This back-analysis is used to create simple charts that illustrate the effects of stress level, density and progressive failure on the operative friction angle and Nγ. These charts are compared with existing guidance for spudcan bearing capacity. [ABSTRACT FROM AUTHOR]

A moment connection of concrete-filled fibre reinforced polymer (FRP) tubes (CFFTs) to concrete footing is explored. The CFFTs are directly embedded into the footings to develop their full moment capacity, in lieu of using mechanical connections, dowel reinforcing bars, or posttensioning methods. CFFT specimens of 219 mm diameter (D) were embedded into footings, at various depths, ranging from 0.3D to 1.5D. The CFFT cantilevered specimens were then laterally loaded to failure. The objective was to establish the critical embedment length, which was found to be 0.73D. Shorter embedment lengths resulted in a bond failure associated with excessive slip, where the full flexural strength of CFFTs was not reached. Specimens with the critical or longer embedment lengths have achieved flexural tension failure of the CFFT, just outside the footing. Ancillary push-through tests were also carried out using CFFT stubs embedded into concrete footings, throughout the full thickness of the footing, and tested under concentric compression loads. The objective was to establish the bond strength between the GFRP tube and concrete footing, which was found to be 0.75 MPa. The bond strength and critical embedment length will vary from case to case. As such, the parameters affecting their values have been identified. [ABSTRACT FROM AUTHOR]

Onshore bearing capacity methods have conventionally been used to predict the penetration of offshore jackup spudcans into the seabed. However, the Brinch Hansen depth factor has a step change in value at the point at which the lateral dimension of a footing equals its embedment. For soft clay seabeds, where penetrations can be greater than the spudcan diameter, the step produces a spurious, unrealistic prediction of punchthrough. A small modification is proposed to the depth factor to avoid this. Some consistent modifications are proposed for several related calculations. [ABSTRACT FROM AUTHOR]

Reinforcement slip in footings and beam-column joint regions can make a significant contribution to the total lateral displacement of a reinforced concrete structure. In this paper, a model for the prediction of lateral deformation of a column due to reinforcement slip in the anchorage zone is presented. The model employs a stepped bond stress along the embedded length of the reinforcing bar that allows for efficient computation of displacements due to slip. A method for computing slip when a reinforcing bar is stressed to its unloaded end and a corresponding failure criterion are presented. Procedures for calculating slip in hooked bars are also outlined. The proposed model is compared with five other commonly-used models found in the literature against three independent sets of test data. Considering its simplicity and computational efficiency, the proposed model predicts slip displacements reasonably well. [ABSTRACT FROM AUTHOR]

The purpose of this study was to critically examine insitu test methods as a means for predicting settlement of shallow foundations. Accordingly, a 1.8 m(6 ft) diameter concrete footing was statically load tested. Prior to construction, insitu [standard penetration test (SPT), cone penetration test (CPT), dilatometer (DMT), and pressuremeter (PMT)] and laboratory tests were performed to determine engineering properties of the soil. Predictions of the footing settlement were made by traditional as well as finite element methods. The results of the static load test showed settlements were over predicted by all methods. However, the traditional methods provided reasonable settlement estimates using either SPT-N or back computed CPT(N) as input. Finite element analyses using either DMT or CPT derived input parameters provided reasonable settlement estimates. Finite element analyses using SPT or PMT derived input parameters provided poor settlement estimates. The Mohr–Coulomb (elastoplastic) model, accounting for overconsolidation, provided better estimates than the hardening soil (hyperbolic-cap) model for all insitu test derived parameters. [ABSTRACT FROM AUTHOR]

Textbooks and university courses teach elasticity and plasticity as separate methods for analysing the stiffness and strength of a shallow foundation. The behaviour of real soil is neither linear elastic nor perfectly plastic. In this paper, two simple techniques for incorporating nonlinearity in routine design have been validated using finite element (FE) analysis. These two techniques—Atkinson's method and the mobilisable strength design (MSD) approach—assume that the responses of an individual soil element and the boundary value problem being considered are self-similar. Using this assumption, the soil element response can be scaled to predict the response of the boundary value problem. Atkinson's method is based on elasticity whereas MSD uses plasticity. Non-linearity has been captured in the FE analysis using a power law soil model. This approach uses minimal parameters, but is shown to capture accurately the undrained stress-strain response of typical clays under monotonic loading. Comparison with elastic and plastic solutions showed that the FE analysis was accurate to within < 5% at the elastic and plastic extremes of the loading range. The responses of the soil and the boundary value problem are shown to be sufficiently self-similar up to two-thirds of the failure load for the foundation response to be predicted simply by a linear scaling of the soil response. Previously reported scaling factors for vertical loading are confirmed, and new factors for horizontal and moment loading are derived. These results show that, for this particular boundary value problem, soil non-linearity can be captured with sufficient accuracy for routine design, without recourse to sophisticated numerical analysis. These self-similarity methods are simple enough to be taught to undergraduates, and could be incorporated in textbooks alongside the core sections on elasticity and plasticity, providing guidance on the application of these techniques to real non-linear soil. [ABSTRACT FROM AUTHOR]

The interaction of vertical, horizontal and moment (VHM) loads acting on a shallow foundation is complex, and it is becoming increasingly popular to represent ultimate limit states under general VHM loading as failure envelopes in three-dimensional load space. General loading is of particular interest offshore, where harsh environmental conditions lead to large horizontal and moment foundation loads. Shallow foundations with peripheral skirts that penetrate into the seabed are used to resist large lateral and overturning forces. During undrained loading, tensile resistance can be mobilised on the underside of the base plate by suctions developed within the skirt compartment. This paper presents failure envelopes and kinematic mechanisms for undrained ultimate limit states of circular skirted foundations in uniform and heterogeneous deposits under general VHM loading based on finite element results. An approximating method is proposed that permits accurate prediction of ultimate limit states under a full range of general loading. [ABSTRACT FROM AUTHOR]

Bearing capacity calculations are an important part of the design of foundations. Many of the terms in the bearing capacity equation, as it is used today in practice, are empirical. Shape factors could not be derived in the past because three-dimensional bearing capacity computations could not be performed with any degree of accuracy. Likewise, depth factors could not be determined because rigorous analyses of foundations embedded in the ground were not possible. In this paper, the bearing capacity of strip, square, circular and rectangular foundations in sand are determined for frictional soils following an associated flow rule using finite-element limit analysis. The results of the analyses are used to propose values of the shape and depth factors for calculation of the bearing capacity of foundations in sands using the traditional bearing capacity equation. The traditional bearing capacity equation is based on the assumption that effects of shape and depth can be considered separately for soil self-weight and surcharge (embedment) terms. This assumption is not realistic, so a different form of the bearing capacity equation is also proposed that does not rely on it. [ABSTRACT FROM AUTHOR]

The XiTRACK three-dimensional track reinforcement technique has been very successful in overcoming difficult, long-standing track problems on the railway. This success led to the specification of the technique for use at Deep Wharf level crossing, Purfleet. This was the first time that the technique had been used to reinforce the track structure at a level crossing. The main technical challenge was the application of the technique to stabilise the track over very poor ground, namely the very soft alluvial soils present at the site. A review of other proposed methods, such as concrete foundations and/or piles, illustrated the cost-effectiveness of the reinforcement method: in particular, the rapid installation of the system (the polymer cured within 15 s) minimised track downtime and thus enabled considerable cost savings to be achieved. The design process adopted was used to predict track behaviour before and after treatment, which enabled the design of the most appropriate polymer rheology and polymer distribution and loading levels to achieve optimum performance and ensure that the technique worked. This paper describes the work performed at Purfleet using the technique, including measured acceleration time histories before and after treatment. [ABSTRACT FROM AUTHOR]

Abstract  This paper focuses on the effective utilization of pond ash, as foundation medium. A series of laboratory model tests have been carried out using square, rectangular and strip footings on pond ash. The effects of dry density, degree of saturation of pond ash, size and shape of footing on ultimate bearing capacity of shallow foundations are presented in this paper. Local shear failure of a square footing on pond ash at 37% moisture content (optimum moisture content) is observed up to the values of dry density 11.20 kN/m3 and general shear failure takes place at the values of dry density 11.48 kN/m3 and 11.70 kN/m3. Effects of degree of saturation on ultimate bearing capacity were studied. Experimental results show that degree of saturation significantly affects the ultimate bearing capacity of strip footing. The effect of footing length to width ratio (L/B), on increase in ultimate bearing capacity of pond ash, is insignificant for L/B ≥ 10 in case of rectangular footings. The effects of size of footing on ultimate bearing capacity for all shapes of footings viz., square, rectangular and strip footings are highlighted. [ABSTRACT FROM AUTHOR]

There is no established procedure for the calculation of bearing capacity of a shallow foundation system comprising cojoined footings. Ad hoc approaches are relied on and may simply involve summing the ultimate limit states of the individual footings as if they acted independently; neglecting additional capacity of the system available from the kinematic constraint provided by the structural connection between the footings. In this study, the undrained capacity under general loading of rigidly connected two-footing systems at various separations has been investigated with finite-element analyses. Results are presented in terms of ultimate limit states under pure vertical (V), horizontal (H), and moment (M) loading, and failure envelopes defining limiting load states under combined VH, VM, HM, and VHM loads. Kinematic failure mechanisms observed in the finite-element analyses are presented and in cases used to provide the basis for upper bound solutions. [ABSTRACT FROM AUTHOR]

The effect of interface friction angle (δ) between the footing and underlying soil mass on the bearing capacity factor Nγ was examined by using the upper bound limit analysis, finite elements, and linear programming. The analysis was carried out by employing velocity discontinuities along all the interfaces of the chosen triangular elements. The development of the plastic strains within elements was incorporated by using an associated flow rule. It was clearly noted that an increase in δ leads to a continuous increase in Nγ. With δ=[lowercase_phi_synonym], the magnitude of Nγ becomes almost the same as that for a perfectly rough foundation, that is, when no slippage takes place between the footing and underlying soil mass. The size of the plastic zones increases with increase in δ and [lowercase_phi_synonym]. The obtained values of Nγ, for perfectly smooth and perfectly rough footings, compare quite favorably with those reported in literature. The study demonstrates that in the case when δ is smaller than [lowercase_phi_synonym], the assumption of a perfectly rough footing will lead to an unsafe prediction of the ultimate bearing capacity. [ABSTRACT FROM AUTHOR]

The effect of interface friction angle (δ) between the footing and underlying soil mass on the bearing capacity factor Nγ was examined by using the upper bound limit analysis, finite elements, and linear programming. The analysis was carried out by employing velocity discontinuities along all the interfaces of the chosen triangular elements. The development of the plastic strains within elements was incorporated by using an associated flow rule. It was clearly noted that an increase in δ leads to a continuous increase in Nγ. With δ=[lowercase_phi_synonym], the magnitude of Nγ becomes almost the same as that for a perfectly rough foundation, that is, when no slippage takes place between the footing and underlying soil mass. The size of the plastic zones increases with increase in δ and [lowercase_phi_synonym]. The obtained values of Nγ, for perfectly smooth and perfectly rough footings, compare quite favorably with those reported in literature. The study demonstrates that in the case when δ is smaller than [lowercase_phi_synonym], the assumption of a perfectly rough footing will lead to an unsafe prediction of the ultimate bearing capacity. [ABSTRACT FROM AUTHOR]