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The paper describes load and resistance factor design (LRFD) calibration for the resistance factor used in the Stiffness Method internal stability soil failure limit state for geogrid mechanically stabilized earth (MSE) walls. The Stiffness Method was recently adopted in the current American Association of State Highway and Transportation Officials LRFD Bridge Design Specifications in the US, and will appear in the next edition of the Canadian Highway Bridge Design Code. The paper describes the details of the calibration of the soil failure limit state which is unique to the Stiffness Method. Calibration outcomes include consideration of the concept of level of understanding in the selection of nominal load and resistance values which is unique to LRFD foundation engineering practice in Canada. A practical conclusion from these calculations is that if product line-specific creep test data are available to estimate the reinforcement secant creep stiffness used for design, then a resistance factor of 1.0 is reasonable for US practice. If only minimum average roll value tensile strength data are available, then a value of 0.95 is recommended for US practice. For Canadian practice, the corresponding values for typical level of understanding are 0.90 and 0.85, respectively. [ABSTRACT FROM AUTHOR]

Helical piles are used extensively for low and medium rise developments and are a popular foundation solution in cases where resistance to significant uplift loads is required. The ability to re-use helical piles and recent interest in their use as foundations in offshore wind and solar energy applications has renewed interest in improving existing design methods. This paper presents the results from field investigations in medium dense and dense sand that examine effects on the axial tension and compression capacity of varying the helix pitch, shaft diameter, advancement ratio and shaft tip geometry. The results from the 20 pile tests conducted (many of which included instrumentation) indicate low sensitivity to a range of the investigated parameters and a strong correlation of the capacity to the cone penetration test resistance. A design method based on these findings is proposed for typical helical pile geometries and is shown to provide predictions that are generally within 10 to 15% of the axial capacities reported for 30 other well documented pile tests reported in the literature. The method, referred to as UWASP-22, incorporates a simple means of estimating the load-displacement response of a helical pile as well as a formulation enabling prediction of the installation torque which is a common quality control measure for helical piles. [ABSTRACT FROM AUTHOR]

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 νϕ′ = 0.15. Overall, the sliding resistance factors recommended here agree well with the resistance factors of ϕgu = 0.6 for cohesive soils and ϕgu = 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. [ABSTRACT FROM AUTHOR]

Wind turbines are typically designed based on fatigue and serviceability limit states, but still require an accurate assessment of bearing capacity. Overconsolidated clay deposits in Canada often have a thin layer of crust with a relatively high undrained shear strength developed from weathering, desiccation, and geochemical processes. However, existing design methods only assess the bearing capacity using effective area and inclination factor without consideration of surficial crusts. This paper studies the undrained VHMT (vertical, horizontal, moment, and torsional) failure envelope of circular foundations founded on a surficial crust underlain by a uniform soil with a zero-tension interface condition using finite element analysis. An analytical expression for the VHMT failure envelope is derived. [ABSTRACT FROM AUTHOR]

Although the geotechnical resistance factors at ultimate limit state (ULS) used for dynamic loading conditions should be different from those for static loading conditions, most current structural and geotechnical design codes do not specifically provide dynamic resistance factors. In this paper, the ULS reliability analysis of individual shallow foundations for drained and undrained soil conditions under seismic (pseudo-dynamic) and wind loads using the Random Finite Element Method is carried out using the provisions of the National Building Code of Canada. The geotechnical resistance factors required to achieve target maximum lifetime failure probabilities are estimated for a few major Canadian cities. The results indicate that the failure probability for drained soil conditions is slightly greater than that for undrained soil conditions. In addition, the results suggest that the dynamic resistance factors for foundation bearing capacity design at ULS are lower than those for static foundation design specified by the code. The current analysis can be used to guide the calibration of these geotechnical resistance factors. [ABSTRACT FROM AUTHOR]

The influence of combined loading on the response of monopiles used to support offshore wind turbines (OWTs) is investigated in this paper. In current practice, resistance of monopiles to vertical and lateral loading is considered separately. As OWT size has increased, the slenderness ratio (pile length, L, normalised by diameter, D) has decreased and foundations are tending towards intermediate footings with geometries between those of piles and shallow foundations. Whilst load interaction effects are not significant for slender piles, they are critical for shallow footings. Previous research on pile load interaction has resulted in conflicting findings, potentially arising from variations in boundary conditions and pile slenderness. In this study, monotonic lateral load tests were conducted in a geotechnical centrifuge on vertically loaded monopiles in dense sand. Results indicate that for piles with L/D = 5, increasing vertical loading improved pile initial stiffness and lateral capacity. A similar trend was observed for piles with L/D = 3, when vertical loading was below ≈45% of the pile's ultimate vertical capacity. For higher vertical loads considered, results tended towards the behaviour observed for shallow footings. Numerical analyses conducted show that changes in mean effective stress are potentially responsible for the observed behaviour. [ABSTRACT FROM AUTHOR]

This paper presents the results of a field load test program used to investigate group effects on the pullout capacity of single-helix "deep" helical piles/anchors in sand. The high tensile capacity and silent installation of helical piles has given them serious consideration as an alternative to conventional deep foundations and anchors for offshore renewable energy structures. New offshore applications may consider the use of groups of helical piles to resist structural loads. Group interaction effects are known to occur in helical piles, but there is a scarcity of field data on groups in sands under tensile loading. This study involved the installation and load testing of single-helix 152 mm diameter round shaft piles and pile groups embedded in sand to depths of 12 and 18 helix diameters below the ground surface. The study was designed to explore the effects of close pile spacing, group configuration (i.e., number of piles), and soil strength (i.e., friction angle) as interpreted from cone penetration test (CPT) resistance. The results showed group efficiencies ranging from about 0.6 to 1.0 at a horizontal spacing of 2 to 3 times the helix diameter in sands with friction angles of about 39° to 44°. The data from this study may also be useful for validation of numerical models for analysis of helical pile group interactions. [ABSTRACT FROM AUTHOR]

Suction caissons supporting offshore wind turbines are exposed to great horizontal loading above the soil surface, which may lead to overturning failure of the caisson. This paper presents a modified three-dimensional failure mechanism to analyze the anti-overturning bearing capacity of suction caissons. The modified failure mechanism is composed of a meniscus-conical wedge with a meniscus shape at the soil surface and a scooped shape. The analytical solution to the anti-overturning bearing capacity of the suction caisson is deduced in terms of the limit equilibrium method, followed by a parametric study of the wedge depth ratio (c) to optimize the critical failure mechanism that satisfies both the force and moment equilibriums. Thus, the methodologies are relatively easy to implement in traditional spreadsheets, and the analyses tend to perform very quickly. The effects of gap formation at the rear side of the caisson, loading eccentricity, and adhesion factor at the caisson–soil interface on the anti-overturning bearing capacity are also investigated. Compared with the finite element limit analysis results, experimental data, and existing theoretical solutions, it is proved that the presented limit equilibrium analysis can satisfactorily predict the anti-overturning bearing capacity of suction caissons with low aspect ratios for offshore wind turbines in uniform and linearly increasing strength clays. [ABSTRACT FROM AUTHOR]

Estimating pile group efficiency for open-ended steel piles in small group arrangements is a challenging task for designers. This paper reports on the large-scale experimental campaign performed for the BorWin gamma offshore converter platform, which involved single piles and two-pile group systems on a scale of 1:10. The experimental works included installation, dynamic end-of-driving tests, dynamic restrike tests, and static load tests of a single pile and a pair of two-pile groups in densely compacted, artificially prepared homogeneous sand. The cone penetration test (CPT) profiles and the blow counts confirmed that the foundation systems are comparable to each other. The experimental results of the single pile system were compared with conventional design methods. Such comparison indicated that CPT-based methods and load-transfer methods are applicable at the considered model scale. The bearing capacity prediction obtained via the Case Pile Wave Analysis Program (CAPWAP) method is conservative with respect to the static capacity. A consistent setup effect can be detected by analyzing the complete dynamic loading session. The pile group efficiency for the given foundation system was found to be less than 1.0 at both very small and very large soil strains, while it equaled 1.0 at failure. [ABSTRACT FROM AUTHOR]

This paper presents the horizontal bearing characteristics of piles in coral sand and silica sand from comparative experimental studies. Six model piles with different diameters were tested. The horizontal bearing capacity, deformation characteristic, bending moment, p–y curve, change in soil horizontal pressure, as well as particle breakage behaviour of coral sand were investigated. The results show that, in the coral sand foundation, the horizontal bearing capacities of piles and the increments in soil horizontal pressures are obviously greater than those in silica sand. Accordingly, the lateral displacement, rotation of the pile head, bending moment, and corresponding distribution depth in coral sand are significantly smaller than those in silica sand. The p–y curves indicate that the horizontal stiffness of coral sand is greater than that of silica sand. Remarkably, the breakage behaviour of coral sand is mainly distributed in the range of 10 times the pile diameter depth and 5 times the pile diameter width on the side where the sand is squeezed by the pile. Furthermore, in coral sand, the influence of pile size is more pronounced, the squeezing force generated by the pile spreads further, and its influence range is larger compared to those in silica sand. [ABSTRACT FROM AUTHOR]

This paper describes an experimental study of the effects of sampling disturbance in an Australian natural soft clay and the consequences of different sample quality on the representativeness of soil parameters used in geotechnical designs. The paper is divided into three sections. Laboratory test results obtained from specimens retrieved using three different tube samplers as well as the Sherbrooke (block) sampler are first described. Then, the sample quality assessment, using available indices proposed for soft soils, is presented. It is shown that sample quality varies with the stress paths and boundary conditions applied in laboratory tests. Finally, mechanical soil properties derived from specimens retrieved using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice. [ABSTRACT FROM AUTHOR]

6.Databaseofloaddata Miyata and Bathurst (2019) developed a database of 113 measured steel grid loads (T max) from 11 instrumented steel grid walls constructed with cohesive-frictional soils and purely frictional soils. Reliability-based design and analysis for internal limit states of steel grid-reinforced mechanically stabilized earth walls. Thegeneralapproachdescribedin thispaperisanimportantcontributiontonext-generationanalysis and design using modern concepts of RBD for internal stability design of both steel and polymeric soil-reinforced MSE walls and is thus in alignment with the international movement towards RBD for geotechnical structures (e.g., Low and Phoon 2015;Phoon2017;PhoonandChing2015;ISSMGE2017). Allen et al. (2001, 2004) quantified the level of accuracy of the Simplified Method for steel MSE walls using bias statistics deduced from a large number of instrumented walls. 1.Introduction This paper is focused on reliability-based design (RBD) and analysis for tensile strength and pullout limit states of steel grid-reinforced mechanically stabilized earth (MSE) walls constructed with frictional soils and subjected to typical operational conditions. [Extracted from the article]

This paper describes a centrifuge study using novel penetrometer tests (T-bar and piezoball) and model foundation tests to explore through-life changes in the strength of a reconstituted natural carbonate silt. The test procedures include episodic cyclic loading, which involves intervals of pore pressure dissipation between cyclic packets. These loads and the associated remoulding and reconsolidation cause significant changes in the soil strength and foundation capacity. Soil strength changes from penetrometer tests differed by a factor of 15 from the fully remoulded strength to a limiting upper value after long-term cyclic loading and reconsolidation. For the model foundation tests, the foundation capacity of a surface foundation and a deep-embedded plate were studied. The soil strength interpreted from the measured foundation capacity varied by a factor of up to three due to episodes of loading and consolidation, with an associated order of magnitude increase in the coefficient of consolidation. The results show a remarkable rise in soil strength over the loading events and provide a potential link between changes in soil strength observed in penetrometer tests and the capacity of foundations, allowing the effects of cyclic loading and consolidation to be predicted. [ABSTRACT FROM AUTHOR]

This paper investigates the isolation efficacy of geocell-reinforced foundation beds infilled with different materials through a series of block resonance tests. The geocell made with a novel polymeric alloy (NPA) was used in the experimental investigation. In total, five different cases — namely, unreinforced, geocell-reinforced silty sand, geocell-reinforced sand, geocell-reinforced slag, and geocell-reinforced aggregate — were considered. Presence of the geocell has resulted in improvement of screening efficacy of the foundation bed regardless of the infill material. The displacement amplitude of the geocell-reinforced bed cases was reduced by 68%, 64%, 61%, and 59%, respectively, for aggregate, slag, sand, and silty sand infill cases as compared to the unreinforced condition. Maximum isolation efficiency was observed in the presence of aggregate, among the four different infill materials. In the presence of aggregate infill, the shear modulus of the foundation bed was improved by 150%. Similarly, the peak particle velocity and peak acceleration were reduced by 57% and 48%, respectively. Further, the efficacy of mass spring dashpot (MSD) analogy was studied in predicting the frequency–displacement response of different reinforced cases. From the analytical study, a significant improvement in damping ratio of the foundation bed was observed in the presence of geocell reinforcement. [ABSTRACT FROM AUTHOR]

This paper describes a program of centrifuge model tests on the uplift behaviour of suction caisson foundations. The parameters considered were the loading rate, caisson diameter (D), soil strength profile, and type of footing (i.e., mono-caisson and tetra-caissons group). The loading responses were examined in terms of total uplift resistance, suction beneath the caisson lid, and the vertical displacements of the caisson and at the soil surface. There exists a critical uplift displacement, approximately 0.02D and 0.01D for the mono-caisson and the tetra-caissons groups, respectively, at which a turning point can be identified in the load–displacement curve. This was found to be attributed to the adhesion on the caisson–soil interface reaching a peak response and then dropping. Of interest is that the tetra-caissons group exhibits much greater normalized uplift resistance than the mono-caisson group before reaching an uplift displacement of about 0.02D, suggesting superiority of the former in term of serviceability. However, a reversed trend was observed at greater displacement, and accordingly an empirical model was derived to quantify the shadowing effect of caisson groups. Regarding the cyclic response, several cycles of large-amplitude loading are sufficient to reduce the ultimate bearing capacity of caisson(s) to below the self-weight of the inner soil plug(s), indicating a transition of failure mechanism. [ABSTRACT FROM AUTHOR]

The interaction between geosynthetics and soil is vital for the stability and the bearing capacity of geosynthetic-reinforced soil structures. This contact behavior between geosynthetics and granular soils has been extensively studied in the literature while there is scarcity of it related to geosynthetics and cohesive soils particularly with softening responses. This paper presents a strain-softening model of geobelt–clay interaction based on direct shear test results under two compaction degrees. A theoretical model for evaluating the pullout behavior of a geobelt is proposed by employing the strain-softening model verified by direct shear tests and a hyperbolic model capturing the stress–strain curves of a geobelt calibrated by uniaxial tensile tests. The proposed model is numerically solved and validated by pullout tests. A kind of sensor-enabled geobelt (SEGB) was adopted in all the aforementioned tests. Both test and numerical results show an overall softening trend in terms of front pull-out force versus displacement. Generally, the model proposed can give reasonably good agreement between calculations and test data during the whole pull-out range. Also, the strain distributions measured by SEGBs demonstrate the working process during the pullout tests, which makes SEGBs a potentially new choice for the strain measurements of in-soil geobelts. [ABSTRACT FROM AUTHOR]

This paper presents an efficient, practical, and automated strategy for deriving modified Cam clay parameters from undrained self-boring pressuremeter (SBPM) data. A mixed approach involving a parametric sweep and numerical optimization is used, with a focus on parameter groups that dominate the modified Cam clay response in undrained cavity expansion. The proposed technique is illustrated using data from SBPM tests carried out in soft estuarine clay. The resulting parameters are used to back-analyse large-scale foundation load tests and are shown to provide an excellent match to the measured foundation response. [ABSTRACT FROM AUTHOR]

Recently, tetrapod piled jacket (TPJ) foundations have shown considerable promise in offshore developments, due to the increases in power capacity and water depth for offshore wind turbines. This paper presents a set of centrifuge tests to look into the lateral loading behaviour of TPJ foundations in sand, with the overall load–displacement responses of the foundation as well as the soil resistance and internal forces on or within individual piles being examined carefully. Test results show that the back-row piles are more likely to be pulled out when the TPJ foundation is loaded laterally along the diagonal direction compared to when loaded along the orthogonal direction. The lateral soil resistance per unit length on the back-row pile(s) is approximately 60% of that on the front-row one(s) in the orthogonal loading case, and only about 40% in the diagonal loading case. Moreover, although the TPJ foundation is in its form a special case of pile groups, it is highlighted in the present study that the former case exhibits distinct loading behaviour from the latter case due to the typically large overturning moment encountered by the foundations for offshore wind turbines. Finally, the p-multipliers of the piles are demonstrated to be dependent on pile deflections, but independent on soil depths, and as a result, a modified pm model is proposed to provide guidance for the design of TPJ foundations in sand. [ABSTRACT FROM AUTHOR]

A stiffened deep mixed (SDM) column can significantly increase the bearing capacity, reduce settlement, and enhance the slope stability of soft clays as compared with a conventional deep mixed (DM) column. This technique involves inserting plain concrete, reinforced concrete or a steel pile into the center of the DM column after the DM column is constructed. In this paper, a series of centrifugal modeling tests were conducted to investigate the performance of an SDM column-supported embankment over soft clay. A model embankment supported only by DM columns was constructed for comparison. Two ideal numerical models of column-reinforced soil under equal stress and equal strain conditions were established to explore the role the column played in accelerating soil consolidation. A parametric study was conducted to investigate the influence factors of the length of the core pile, column spacing, thickness of the underlying soil, modulus and thickness of the cushion, and modulus of the slab on the load transfer of the system, and some recommendations were proposed for its application. The load-transfer mechanism of an SDM column-supported embankment system with a slab was established based on the development of the volumetric strains and the principal stresses in the numerical models. [ABSTRACT FROM AUTHOR]

This paper summarizes 239 static load tests to evaluate the performance of four static design methods for axial resistance of driven piles in clay. The methods are ISO 19901-4:2016, SHANSEP, ICP-05, and NGI-05. The database is categorized into four groups depending on the load type (compression or uplift) and pile tip condition (open or closed end). The model uncertainty in resistance prediction is quantified as a ratio between measured and calculated resistance, which is called a model factor. The measured resistance is interpreted as a load producing a settlement level of 10% pile diameter. Database studies show that the four methods present a similar accuracy, where the mean and coefficient of variation (COV) of the model factor are around 1 and 0.3, respectively. The COV values are smaller than those for driven piles in sand available in literature. The model statistics determined from the database are applicable to a simplified or full probabilistic form of reliability-based design (RBD) of driven piles in clay. As an illustration, the resistance factors in load and resistance factor design (LRFD, a simplified form of RBD) are calibrated by Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Design implications of suction installation of bucket foundations are still not well understood. During suction installation, applied suction under the bucket lid results in seepage flow through the surrounding sand. Seepage flow plays a pivotal role in reducing the penetration resistance, allowing for full penetration despite the initial large soil resistance. However, loosening of the inside soil plug might be problematic when the soil approaches its failure stage, due to soil piping or extensive soil heave inside the bucket foundation. To better understand the interaction between the soil and bucket skirt during suction installation, this paper describes the results of medium-scale tests of bucket foundation installations in sand, comparing jacking and suction installations. Experimental measurements of the pore pressure around the bucket skirt are compared with the numerical simulation results, to validate the finite-element model and to enable analysis of the soil behavior around the skirt. [ABSTRACT FROM AUTHOR]

The paper presents a formulation for evaluating the effect of tunneling on existing buildings. The formulation involves the matrix condensation method to represent the response of a linear elastic building and macroelements to represent the nonlinear elastoplastic soil behavior. The formulation includes new features that allow interaction between macroelements, both through the soil continuum and the structure, to result in the final displacements of the foundations due to tunneling. One of the advantages of the formulation is its ability to incorporate a general input of a greenfield field displacement for the interaction analysis, allowing consideration of various tunneling scenarios. The formulation is evaluated by a comparison with a continuum-based solution obtained using the finite difference method. The formulation is then used to conduct a parametric analysis of tunneling–soil–superstructure interaction, considering three different approaches: (i) the suggested elastoplastic formulation, (ii) purely elastic analysis, and (iii) simplified analysis in which the foundations are forced to displace as a greenfield. It is shown that the vertical settlements of the foundations, due to tunneling, are the greatest when the first approach is considered. This is an outcome of the combined vertical and horizontal yielding, depicted in the formulation by the coupled yield function and plastic flow potential. Yet damage, which relates to differential settlement, appears to be smaller in the elastoplastic formulation. [ABSTRACT FROM AUTHOR]

Estimation of the bearing capacity of shallow foundations on layered soil profiles, such as a sand layer of finite thickness over clay, is mainly based on empirical models resulting from the interpretation of experimental test results. While it is generally accepted that such models may be applicable to soil properties and footing geometries outside the range tested experimentally, they offer limited insights on how the assumed failure mechanism affects their range of application. In particular, the contribution of the sand layer to the overall capacity is accounted for via simple considerations, which are valid only for a specific range of problem parameters. This paper addresses the estimation of the undrained bearing capacity of a rigid strip footing resting on the surface of a sand layer of finite thickness overlying clay, using finite element limit analysis (FELA). The rigorous upper and lower bound theorems of plasticity are employed to bracket the true bearing capacity of the footing, and identify the geometry of possible failure mechanisms. Insights gained from FELA simulations are used to develop a new simple bearing capacity model, which captures the variation in shear resistance from the sand layer with the dimensionless undrained strength of the clay layer. The proposed model provides results that are in close agreement with published experimental studies, and allows treating simple problems, such as the design of working platforms, without having to resort to numerical simulations. [ABSTRACT FROM AUTHOR]

As a type of shallow foundation, a mudmat serves as the seabed support structure for subsea wells, pipeline manifolds, and pipeline terminations. The shallow foundations are usually designed with perforations to facilitate installation and removal, but the influence of these perforations has not been fully understood. This paper presents a method to analyze the bearing capacities of both two-dimensional (2D) and three-dimensional (3D) perforated shallow foundations using finite element analysis. The soil was idealized as a Tresca material, with the undrained strength increasing linearly with depth. The outcome indicates that perforations have nonnegligible effects on the bearing capacity of shallow foundations. The bearing capacity decreases with increasing perforation ratio, R, and the degree of reduction increases with the increase of the dimensionless ratio kB/Suo, where k is the shear strength gradient, B is the width of the foundation, and Suo is the shear strength at the mudline. For 2D shallow foundations, there exists a critical perforation ratio, Rc; when the perforation ratio is lower than the critical perforation ratio, the perforated foundation does not lose its bearing capacity. For 3D shallow foundations, the bearing capacity decreases directly with the increase of perforation ratio, R. [ABSTRACT FROM AUTHOR]

This paper thoroughly investigates the bearing capacity of strip footings on sand under combined loading by using a lower-bound limit analysis in conjunction with finite elements and second-order cone programming (SOCP). Two analyses were performed: one using a constant friction angle and the other using a variable friction angle. The analyses with a constant friction angle were used to calibrate the existing results, including the classical solutions commonly used in foundation design practice and other numerical or experimental solutions. The analyses with a variable friction angle allow us to investigate the effect of footing width B on the bearing capacity of strip footings. An iteration computational procedure is employed to account for the dependency of the friction angle on the stress level. According to the numerical results, it is found that the bearing capacity factor Nγ for eccentrically or obliquely loaded strip footings linearly decreases with the increase of B on a log-log scale, where the range 0.3-5 m of footing width was considered in this paper. In addition, it is found that the footing width has a negligible effect on the shape and size of the normalized failure envelopes. [ABSTRACT FROM AUTHOR]

Mechanical behaviour of the soil around a jacked pile changes significantly during pile installation and subsequent consolidation. Hence, an axially loaded jacked pile exhibits apparent time-dependent bearing performance after pile installation. This paper presents a semi-analytical approach to predict the time-dependent bearing performance of an axially loaded jacked pile in saturated clay strata. The effects of pile installation and subsequent consolidation on the changes in mechanical properties of the surrounding soil are modeled by the cavity expansion theory and the radial consolidation theory, respectively. An exponential function-based load-transfer ( t- z) curve is employed to describe the nonlinear behaviour of the pile-soil interface during pile loading. The evolutions of the three-dimensional strength and shear modulus of the surrounding soil are subsequently incorporated into the two model parameters of the proposed t- z curve to capture the time-dependent pile-soil interaction behaviour. The time-dependent elastic response of the soil outside the pile-soil interface is also considered in the proposed approach. With the proposed load-transfer curve, an incremental algorithm and a corresponding computational code are developed for assessing the time-dependent load-settlement response of a jacked pile. To verify the proposed semi-analytical approach, predictions of the time-dependent load-settlement curves are compared with the measured values from pile tests at two sites. The good agreement shows that the time-dependent bearing performance can be reasonably predicted by the proposed approach. [ABSTRACT FROM AUTHOR]

This paper presents an application of a method that will be implemented in the embedded data collector (EDC) system in the near future, to estimate the capacity of driven piles with a combined solid and voided cross section. Data from accelerometers and strain gauges located in the solid sections at both the top and the bottom of a pile are used to independently estimate the pile's skin friction and tip resistance. Wave propagation along the pile is modeled as a one-dimensional wave equation, with a nonuniform cross section and with nonlinear static skin friction and viscous-damping soil resistances acting along multiple segments of the pile. The static skin friction is extracted by least-squares fitting of computed particle velocities with measured data at both the top and the bottom of the pile. The pile tip is modeled as a nonlinear single degree of freedom with viscous damping. Static tip resistance (nonlinear stiffness-displacement relationship) is extracted by least-squares fitting of the predicted total force and energy with the measured tip data. The new EDC method was applied to four combined solid-voided cross section driven piles with capacities varying from 2800 to 6700 kN. The results of the data evaluated with the new EDC method are consistent with those from the static load tests to within 15%. [ABSTRACT FROM AUTHOR]

The presence of a thin soft clay layer inside a bed of sand may significantly reduce the bearing capacity of the sand layer, imposing a risk of punch-through failure. In this paper, finite element (FE) simulations are reported using a hardening soil (HS) model for sand. The FE model has been verified against centrifuge tests involving loose and dense sand layers overlying clay soil. The effects of sand stiffness, foundation roughness, sand friction angle, undrained clay strength, clay strength nonhomogeneity, and sand and clay layer geometries on the foundation peak capacities have been studied. Punch-through failure is initiated with an inclined sand plug being sheared and pushed into the underlying soft clay. During punch-through, the clay layer fails due to significant radial squeezing. Existing analytical models do not capture the combined failure mechanism of sand shearing and clay radial squeezing. A new analytical model is developed to estimate the peak punch-through capacity of a spudcan in sand with an interbedded clay layer, showing improved performance over the current industry guidelines. [ABSTRACT FROM AUTHOR]

Spudcan punch-through during installation and preloading process is one of the key concerns for the jack-up industry. This incident occurs in layered deposits, with new design approaches for spudcan penetration in sand-over-clay deposits reported recently. This paper reports a novel design approach for spudcan penetration in stiff-over-soft clay deposits. Large-deformation finite element (LDFE) analyses were carried out using the Coupled Eulerian-Lagrangian (CEL) approach. The clay was modelled using the extended elastic - perfectly plastic Tresca soil model allowing strain softening and rate dependency of the undrained shear strength. A detailed parametric study was undertaken, varying the strength ratio between bottom and top soil layers, the thickness of the top layer relative to the spudcan diameter, and degree of nonhomogeneity of the bottom layer. Existing data from centrifuge model tests were first used to validate the LDFE results, and then the measured and computed datasets were used to develop the formulas in the proposed design approach. The approach accounts for the soil plug in the bottom layer, and the corresponding additional resistance. Where there is the potential for punch-through, the approach provides estimations of the depth and bearing capacity at punch-through, the bearing capacity at the stiff-soft layer interface, and the bearing capacity in the bottom layer. Comparison shows that the punch-through method suggested in ISO standard 19905-1 provides a conservative estimate of the bearing capacity at punch-through, with guidelines provided to improve the method. [ABSTRACT FROM AUTHOR]

Due to its complex honeycomb structure, the numerical modeling of the geocell has always been a big challenge. Generally, the equivalent composite approach is used to model the geocells. In the equivalent composite approach, the geocell-soil composite is treated as the soil layer with improved strength and stiffness values. Though this approach is very simple, it is unrealistic to model the geocells as the soil layer. This paper presents a more realistic approach of modeling the geocells in three-dimensional (3D) framework by considering the actual curvature of the geocell pocket. A square footing resting on geocell reinforced soft clay bed was modeled using the 'fast Lagrangian analysis of continua in 3D' (FLAC3D) finite difference package. Three different material models, namely modified Cam-clay, Mohr-Coulomb, and linear elastic were used to simulate the behaviour of foundation soil, infill soil and the geocell, respectively. It was found that the geocells distribute the load laterally to the wider area below the footing as compared to the unreinforced case. More than 50% reduction in the stress was observed in the clay bed in the presence of geocells. In addition to geocells, two other cases, namely, only geogrid and geocell with additional basal geogrid cases were also simulated. The numerical model was systematically validated with the results of the physical model tests. Using the validated numerical model, parametric studies were conducted to evaluate the influence of various geocell properties on the performance of reinforced clay beds. [ABSTRACT FROM AUTHOR]

This paper reports advanced three-dimensional large-deformation finite element analyses investigating the effect of the padeye offset on the behaviour of plate anchors. The analyses varied the normalized padeye offset from 0 to 0.5 and identified two counterbalancing effects on the anchor bearing capacity induced by the padeye offset. These are the change in anchor inclination with respect to the direction of loading (detrimental due to the reduction of bearing area) and the reduction of loss of embedment (beneficial, as the anchor mobilizes stronger soil). The results provide insights to optimize the design of plate anchors. The underlying concepts also have applications for other types of anchors. [ABSTRACT FROM AUTHOR]

The capacity of dynamically installed anchors in soft normally consolidated clay was examined experimentally through a series of field tests on a 1:20 reduced-scale anchor. The anchors were installed through free fall in water, achieving tip embedment of 1.5-2.6 times the anchor length, before being loaded under undrained conditions at various load inclinations. Vertical anchor capacities were between 2.4 and 4.1 times the anchor dry weight and were satisfactorily predicted using the American Petroleum Institute approach for driven piles. Anchor capacity under inclined loading increased as the load inclination approached horizontal; the field data indicated this increase to be up to 30% for the minimum achievable inclination of about 20° to the horizontal. Corresponding large-deformation finite element analyses showed a similar response, with the maximum capacity occurring at a load inclination between 30° and 45° to the horizontal. The finite element results demonstrate that, for the anchor geometry considered, an inclined load at the anchor padeye could be decomposed into ultimate vertical and moment loading at the anchor centroid. The establishment of a vertical and moment loading yield envelope for the geometry investigated forms the basis of a simple design procedure presented in the paper. [ABSTRACT FROM AUTHOR]

The design of shallow foundations is dominated by issues of settlement rather than bearing capacity per se. The ability to predict the settlement of foundations at a given factor of safety is hence of key importance in design. In this paper, the energy method for a linear-elastic, perfectly plastic method utilizing the von Mises' yield criterion with associated flow developed and reported by McMahon et al. in 2013 is extended to consider the nonlinear behaviour of soil. The energy method is used to investigate the load-settlement behaviour of shallow foundations by utilizing an ellipsoidal cavity-expansion mechanism and deformation fields within the boundaries of the classical Hill and Prandtl mechanisms. An elastic mechanism obtained from an analysis in ABAQUS was also investigated using this energy method. The upper-bound approach demonstrates that the cavity-expansion mechanism produces a better solution at small values of settlement, whereas at greater settlements the Prandtl mechanism is shown to produce a more optimal upper-bound solution. [ABSTRACT FROM AUTHOR]

In this paper, the effect of spatial correlation of standard penetration test (SPT) data on the bearing capacity of driven piles in sand is analyzed. First, the direct approach for using SPT data to determine the bearing capacity of piles in sand is used to derive the expressions for probabilistic prediction of pile bearing capacity by considering the spatial correlation of the SPT data. To analyze the relationship between the probability of failure and the factor of safety, a procedure based on the advanced first-order, second-moment (FOSM) method is used. Then parametric studies are conducted on the spatial correlation between the spatial average of SPT numbers over the pile length, NLV, and the spatial average of SPT numbers over an interval near the pile base , NbV, and its effect on the bearing capacity of piles. The results indicate that it is important to consider the spatial correlation between NLV and NbV in the probabilistic prediction of pile bearing capacity. Ignoring this spatial correlation will underestimate the probability of failure and lead to unsafe design. Finally, three tested piles are analyzed to demonstrate the probabilistic analysis of piles by considering the spatial correlation of SPT data and the procedure for probabilistic analysis of pile bearing capacity is summarized. [ABSTRACT FROM AUTHOR]

'Spudcan' foundations for mobile drilling rigs continue to exhibit a high failure rate in the offshore oil and gas industry. The more frequent use of larger jack-ups in highly stratified regions, such as the Sunda Shelf in Southeast Asia, contributes to this concerning increase in 'punch-through' incidents, which can lead to buckling of a leg or even toppling of the rig. An industry practice known as 'perforation drilling' is sometimes used to mitigate the punch-through risk in layered clays, extracting soil from the upper strong layer before the jack-up is installed. This paper reports results from centrifuge model tests exploring the efficiency of perforation drilling. The soil conditions tested simulate offshore strength profiles that have reported punch-through failures. An experimental method for 'drilling' sites in an enhanced gravity centrifuge environment was developed and the installation responses of model spudcan foundations penetrating through multi-layered clays with interbedded stiff layers were recorded. The experimental results show that the removal of soil inside the spudcan perimeter, with an area of 9% perforated, eliminated rapid leg run and severe punch-through on the two- and four-layer seabed profiles tested. This confirms the effectiveness of perforation drilling and indicates how the offshore drilling plan may be optimized. [ABSTRACT FROM AUTHOR]