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The micropiled raft (MPR) offers an efficient foundation system that combines the advantages of micropiles and piled rafts that can be used as primary foundation system or to enhance an existing raft foundation. In this paper, a finite element model (FEM) calibrated and verified with centrifuge tests was used to carry out a numerical investigation on the performance of MPR in clay. A total of 26 different cases were analyzed in this study to assess the behaviour of MPR in clay taking into account a number of factors that may influence its behaviour such as: the number of micropiles (MPs), the spacing to micropile diameter (S/D mp ), the raft thickness, and type of loading. The outcomes of this investigation should help in understanding the effect of these factors on the MPR axial stiffness, including; differential settlement; load sharing between the MPs and the raft; the raft bending moment and micropiles skin friction. Moreover, the ability of the Poulos-Davis-Randolph (PDR) method to evaluate the axial stiffness of a MPR for the preliminary design stage is examined. It was found that the MPR system can increase the tolerable bearing pressure by 100% compared to an isolated raft system. In addition, an adjustment factor (ω PR ) for PDR method was introduced to account for the raft flexibility. Equations were proposed in order to design MPR systems in terms of load sharing between micropiles and the raft. [ABSTRACT FROM AUTHOR]

The high-strain dynamic load test (HSDT) is a convenient and efficient method of assessing the compressive load capacity of piles. Although several numerical models are available to interpret the responses of open-ended pipe pipes (OEPPs) in the HSDT, these models cannot capture the motions of pile base soil or distinguish the difference in the external and internal soil resistance of the OEPPs. Thus, a novel fictitious-soil pile (FSP) model is developed in this study to analyze the responses of small-diameter OEPPs with soil plugs under high-strain impact loading. Apart from simulating the wave propagation in the base soil and slippage at the pile–soil interface, the proposed model also describes the sliding modes of the soil plug under dynamic load conditions (DLCs). The developed model was validated by comparing the calculated pile responses with those obtained from conventional numerical models as well as field measurements of a steel OEPP. Based on the proposed model, two sliding modes of the soil plug (bottom- and top-sliding) were found in the HSDT to be dependent on impact loading durations. The prediction of the OPEE load capacity from HSDTs could be affected by the soil sliding mode, which should be investigated in more detail in future research. [ABSTRACT FROM AUTHOR]

Existing numerical models for simulating the pile behaviours in high-strain dynamic load tests (DLTs) cannot account for the wave propagation in base soil. This paper proposes a nonlinear fictitious-soil pile (FSP) model to better simulate the base soil. The proposed model regards the base soil as a FSP with a cone angle extending from pile toe to bedrock, and simulates shaft resistance by improved Randolph model. The pile-soil system is discretized into a series of mass-nonlinear springs, and was solved based on the Newmark's β method. The proposed model was validated by comparing its predictions with those obtained from Randolph model and Smith model, as well as field measurements of driven and bored piles in different sites. Parametric study demonstrated that the calculated results were significantly affected by the discretization degree, FSP dimensions and soil nonlinearity. The displacement attenuation in base soil is nonlinear, and the impact energy is consumed rapidly near pile toe. Besides, large-diameter piles tend to have a larger affected zone, in which the wave phenomenon in base soil should be considered. Empirical formulas for soil affected zone and required pile displacements in DLTs were proposed to facilitate the practical application of FSP model. • A nonlinear fictitious-soil pile model for simulating pile base soil undergoing high-strain dynamic loading. • The wave propagation in base soil determines the extent of soil affected zone. • Validations from conventional models and field test measurements. • Sensitivity analysis of soil parameters. • Empirical formulas for the soil affected zone and required pile displacements in pile DLTs. [ABSTRACT FROM AUTHOR]

The dynamic load test (DLT) is commonly applied for evaluating pile capacity due to its fast mobilization and cost savings compared to conventional static load test. This paper proposes a new DLT method, denoted multi-point method (MPM) to solve the empirical problems in existing dynamic methods. The proposed method involves measuring accelerations at multi points along the pile shaft, and assumes the soil resistance related to damping is zero at the zero-velocity moment of pile segment. Two-dimensional axisymmetric finite-element models (FEMs) were constructed to verify the method of calculating pile strain through acceleration measurements. A nonlinear discrete spring-dump numerical model was established to simulate the pile-soil system under static and dynamic condition, and subsequently to be used for validation of MPM and parameter analysis. The derived static curves by MPM, UPM, and modified UPM (M-UPM) were compared with theoretical static curves. Finally, laboratory model tests of DLT on pipe pile were conducted to verify the MPM. The results demonstrated the MPM is applicable for deriving the static curve of piles with various sizes. It also demonstrated the MPM is more accurate than other dynamic methods. As a direct method, MPM is more realistic as it eliminates the need to estimate a damping constant and it accounts for the pile elastic shortening. • Versatile dynamic method of direct analysis on pile compressive capacity. • Multi-point measurements to avoid subjective judgment. • Zero-velocity instant method to obtain static soil resistance. • Nonlinear discrete mass-spring numerical model for simulating pile-soil system. • Comparison of Small-scale laboratory SLT and DLT. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the seismic performance of moment-resisting frame steel buildings with multiple underground stories resting on shallow foundations. A parametric study that involved evaluating the nonlinear seismic response of five, ten and fifteen story moment-resisting frame steel buildings resting on flexible ground surface, and buildings having one, three and five underground stories was performed. The buildings were assumed to be founded on shallow foundations. Two site conditions were considered: soil class C and soil class E, corresponding to firm and soft soil deposits, respectively. Vancouver seismic hazard has been considered for this study. Synthetic earthquake records compatible with Vancouver uniform hazard spectrum (UHS), as specified by the National Building Code of Canada (NBCC) 2005, have been used as input motion. It was found that soil–structure interaction (SSI) can greatly affect the seismic performance of buildings in terms of the seismic storey shear and moment demand, and the deformations of their structural components. Although most building codes postulate that SSI effects generally decrease the force demand on buildings, but increase the deformation demand, it was found that, for some of the cases considered, SSI effects increased both the force and deformation demand on the buildings. The SSI effects generally depend on the stiffness of the foundation and the number of underground stories. SSI effects are significant for soft soil conditions and negligible for stiff soil conditions. It was also found that SSI effects are significant for buildings resting on flexible ground surface with no underground stories, and gradually decrease with the increase of the number of underground stories. [Copyright &y& Elsevier]

Abstract: This paper presents a new practical modeling approach, based on the beam-on-a-nonlinear Winkler foundation (BNWF) model, to simulate the 3D rocking, vertical and horizontal responses of shallow foundations using structural elements that are readily available in the element library of commercially available structural analysis programs. An assemblage of a moment-rotation hinge, shear hinge connected in series with an elastic frame member attached to the bottom end of ground story columns was proposed to model the response of the footing under combined action of vertical, horizontal and moment loading. To couple the responses of these hinges, two bounding surfaces equations were introduced and derived mathematically: a surface that defines the interaction between the rocking and vertical capacities of the footing along its width and length; and a surface that defines the interaction between the horizontal capacities of the footing along its width and length. Simple calculation steps to evaluate the geometric and mechanical properties of the proposed assemblage of structural elements are provided. The proposed modeling approach was verified using experimental results from large scale model foundations subjected to cyclic loading. Based on this study, it was found that the proposed assemblage can be reliably used in modeling the rocking and horizontal responses of shallow foundations under cyclic loading. [Copyright &y& Elsevier]

This paper presents and discusses the measured responses of single and grouped helical piles to strong ground motions during a large-scale shake table testing program. The effects of earthquake characteristics (i.e., intensity and frequency content) on the seismic performance of single and grouped helical piles are evaluated from the measured responses. In addition, the performance characteristics of helical pile groups are discussed in terms of the interaction between piles within a group and the contributions of vertical and lateral stiffness of individual piles to the rocking stiffness and the overall capacity of the pile group. Furthermore, the effect of pile head connection to the pile cap (fixed or pinned) on the pile group's response is evaluated and the responses of fixed pile groups (2-bolts connection) and pinned pile groups (1-bolt connection) are compared. Finally, the behaviour of a single pile and a pile within a group is compared in terms of their normalized responses. • Large-scale shake table testing of single and grouped helical piles subjected to different ground motions was conducted. • Responses of single piles increased exponentially with PGA, while a linear relation was observed for pile groups. • Resonance conditions significantly increased responses for both single and grouped helical piles. • Helices provided additional resistance and fixation to the piles, which resulted in an 80% contribution of rocking stiffness. • 1-bolt pile head connection provided fixation and should not be considered as pin connection. [ABSTRACT FROM AUTHOR]

Abstract: The helical pile is a foundation system used to support new residential and commercial buildings, and to stabilize repairs of existing structures. It also represents an attractive alternative to upgrade the seismic resistance of existing foundations. This paper is part of a comprehensive study to assess the seismic performance of foundations supported by helical piles. The paper presents an experimental study conducted to evaluate the seismic performance of the specialized connectors, linking the pile shaft to the concrete foundation, in the lateral direction. The paper also presents a simplified model that can be used to account for the connector behaviour while conducting seismic analysis of structures supported by helical piles. [Copyright &y& Elsevier]

Structures with inappropriate distributions of strength and stiffness have performed poorly in recent earthquakes, and most of the observed collapses have been related to some extent to configuration problems or a wrong conceptual design. Shear building models of multi-story structures are considered in this study and are subjected to a group of severe earthquakes. It is shown that the strength distribution patterns suggested by the seismic codes do not lead to a uniform distribution and minimum amount of ductility, drift, and damage. A new pattern is proposed that is a function of the period of the structure and the target ductility. An iterative approach is also developed to determine the design strength (and stiffness) pattern needed to achieve a prescribed ductility (or drift) distribution according to different dynamic characteristics of the structure and earthquake. Utilizing this approach, a performance-based design methodology is introduced. This approach is shown to be efficient in finding the optimum strength and stiffness distribution patterns and can also be used to determine the optimum stiffness distribution within buildings with hysteretic dampers, and thus can be used to devise efficient retrofitting schemes using hysteretic dampers. [Copyright &y& Elsevier]

The High Strain Dynamic Test (HSDT) offers an alternative approach to the conventional static load test for estimating the axial capacity of helical piles due to its faster implementation and potential cost savings. In this paper, a mathematical model developed by Clough & Penzien that simulates the force-time response at the top of a pile with uniform cross-section subjected to a hammer impact is evaluated for the HSDT setup. To verify the suitability of the model, the calculated force-time history from the mathematical model is compared with actual field data for driven and bored piles. The model is then used to explore the characteristics of hammer impact on helical piles with attention to estimating the impedance increase caused by the helices. Generally, helices offer additional end bearing resistance, thus increase the mechanical impedance of the pile. The obtained results demonstrate that it is necessary to account for the effect of helical plates in the analysis, especially for large diameter helical piles. Consequently, a method to approximate the increase in the pile impedance for a helical pile with single and double helices is developed using added soil mass model. [ABSTRACT FROM AUTHOR]

Two-dimensional (axi-symmetrical) dynamic finite element analyses were performed to simulate the static load tests (SLT) and High Strain Dynamic Load Tests (HSDT) conducted on helical piles to gain better understanding of their behaviour during the tests. The finite element models were verified using the results of two case histories involving SLT and HSDT on large diameter helical piles. The finite element models simulated the helical piles installed in both sand and clay soils and were used to characterize soil-pile interaction during the tests and to establish the derived static load-settlement curves for both types of soil. The verified numerical models were employed to perform a comprehensive parametric study to investigate the influence of various material and geometric aspects of the soil-pile-hammer system on the dynamic response of helical piles during axial impact loads. The results from the parametric study were used to formulate guidelines for the design of effective HSDT on helical piles as well as on driven piles. [ABSTRACT FROM AUTHOR]

In this study, the dynamic responses of a single pile in liquefiable sand under bidirectional loading are investigated using fully coupled three-dimensional nonlinear finite element analyses. A multi-surface plasticity model is adopted to simulate the liquefiable sand behaviour. The analysis procedures elaborate the bidirectional shaking patterns of 2-D linear, circular, and oval shape simultaneously. Results reveal that compared to the unidirectional loading, the bidirectional loading reduces the soil liquefaction resistance and increases the depth of liquefied soil layer. The results also showed that the phase difference between orthogonal components of base excitation and the frequency content of the input motion have a significant impact on the dynamic responses of soil and pile. In addition, an increase in the phase difference reduces the excess pore water pressure and the thickness of liquefied layer, and delays the liquefaction occurrence. Moreover, the maximum pile bending moment and its location correspond to the dominance of either inertia or kinematic interaction forces, which are primarily influenced by the frequency content of input motion. • Dynamic response of single pile embedded in liquefiable sand is investigated through a 3D nonlinear finite element model. • Seismic performance of soil-pile systems under unidirectional and bidirectional loadings is studied. • Soil-pile response is remarkably influenced by the pattern of bidirectional loading and its frequency content. • The frequency content of input motion has a decisive effect on the maximum pile bending moment. [ABSTRACT FROM AUTHOR]

Oil sands drill cuttings waste represents one of the most difficult challenges for the oil sands mining sector. Reducing the amount oil sands drill cutting waste sent to landfill offers one of the best solutions for waste management. The present work offers an innovative solution for the recycle and reuse of treated oil sands drill cuttings waste (TOSW) in grout manufacture. In this study, the physical, chemical and mineralogical characteristics of the treated oil sands drill cuttings waste were investigated. Fresh and hardened properties for grouts incorporating the treated solid drill cuttings waste were evaluated. The results show that incorporating up to 20% of the treated solid drill cuttings waste as a partially replacement of cement will not adversely affect the properties of the grout. Leaching tests evidenced the reduction in the release of heavy metals from the tested mixtures compared to that of the raw waste indicating successful stabilization/solidification of such waste in the grout. [ABSTRACT FROM AUTHOR]

The isolation of vibrations from the surroundings is one of the important problems in the design of machine foundations. The use of open trenches, infilled trenches, single and multiple pile rows have been widely studied. In this paper, the vibration screening efficiency of an inclined secant micro-pile wall positioned as an active vibration barrier is investigated. The study is performed using three-dimensional time domain finite element analyses. Various parameters such as barrier depth, inclination, barrier distance and load excitation frequency were studied. The results show that inclined secant micro-pile walls are a viable vibration isolation option for a multitude of vibration problems. It is shown that varying barrier inclination angle from 90° to 120° improved vibration isolation performance as high as 44% relative to the vertical barrier for the active isolation case. The effectiveness of the barrier increases as its depth increases and also as the excitation frequency increases. The orientation of the inclined barrier towards or against vibration source is shown to be a fundamental design consideration. [ABSTRACT FROM AUTHOR]

Abstract: Several studies have shown that the lateral response of concentrically-braced frames is dominated by the inelastic behavior of the bracing members. However, the overall performance of the entire frame depends on the frame configuration including its connections. In this study, the hysteretic characteristics of modular steel-braced frames under reversed cyclic loading are evaluated. The design and construction of the test specimen accounted for the unique detailing requirements of these frames. A regular concentrically-braced frame with similar physical characteristics was also tested for comparison. Both test specimens consisted of a one-storey X-braced system with tubular brace cross-section. This paper describes the behavior characteristics and provides a detailed comparison of the two systems to assess the strength, stiffness, inelastic force and deformation, and energy dissipation characteristics of the modular system. An analytical model capable of capturing the effect of the system’s unique detailing requirements is proposed and validated using the test results. [Copyright &y& Elsevier]

A three-dimensional method of analysis is presented for the seismic response of structures constructed on pile foundations. An analysis is formulated in the time domain and the effects of material nonlinearity of soil on the seismic response are investigated. A subsystem model consisting of a structure subsystem and a pile-foundation subsystem is used. Seismic response of the system is found using a successive-coupling incremental solution scheme. Both subsystems are assumed to be coupled at each time step. Material nonlinearity is accounted for by incorporating an advanced plasticity-based soil model, HiSS, in the finite element formulation. Both single piles and pile groups are considered and the effects of kinematic and inertial interaction on seismic response are investigated while considering harmonic and transient excitations. It is seen that nonlinearity significantly affects seismic response of pile foundations as well as that of structures. Effects of nonlinearity on response are dependent on the frequency of excitation with nonlinearity causing an increase in response at low frequencies of excitation. [Copyright &y& Elsevier]

Large fixed vertical offshore wind turbine (OWT) tower structures are typically used to transfer complex loads to the foundations from a combination of wind, waves, and self-weight. These loads must be accommodated within a very small rotation envelope and natural frequency bands to allow the turbines to operate effectively. These challenging loading conditions and strict operational requirements can lead to extremely costly foundation designs. Several foundation options are available to support these turbines, with monopiles currently accounting for 80% of the installed capacity with routinely used diameters of 5–8 m and depths of penetration of 30–80 m. To limit monopile diameters and penetration depths, an improved monopile design: the 'hybrid foundation' comprising a plate and centrally located pile, is proposed as an alternative to monopiles. A series of scaled physical model centrifuge tests were conducted to investigate the benefits of the hybrid foundation system and compare its behavior with the typically used monopiles. This type of foundation system can enhance the performance of an OWT since the turbines are subjected to high lateral loads and overturning moments. Centrifuge modeling has been used to investigate the lateral capacity and stiffness of the foundations under lateral monotonic and cyclic loading conditions. Two models were tested: a standard monopile (MP) and a hybrid foundation (HF). Lateral loads were applied with eccentricity for both models to replicate prototype (field) conditions. Models were tested at 50g in over-consolidated clay beds. These soil samples were prepared using inflight consolidation and subjected to a sand surcharge, to increase the shear strength in the zone of influence of the model foundations. Monotonic lateral loading results indicated that the addition of a plate improves the relative lateral ultimate capacity, whilst enabling a reduction of monopile penetration depth and diameter for similar capacities. Specifically, similar capacity/stiffness was realized for the HF system compared to the MP. One-way cyclic lateral loading indicated both the HF and the MP had a shakedown response under fatigue loading of up to 10000 cycles, which indicates the potential use of this novel system for future developments. • HF offered a similar capacity to MP although with a smaller and shorter monopile size. • Damage accumulation relationships are proposed describing the rotation evolution versus the number of cycles for various loading magnitudes. • Under cyclic lateral loading, the HF continued to record increased rotations; however, at decaying rates. • The rotation magnitude increased with the increase of cyclic loading ratio ζ. [ABSTRACT FROM AUTHOR]

Controlled Low-Strength Materials (CLSM) is a self compacted self-leveling cementitious material with compressive strength of 8.3 MPa or less. It is used as an alternative of soil backfill materials in geotechnical and infrastructure applications. This study investigates the effects of incorporating Treated Oil Sand Wastes (TOSW) as a partial replacement of sand or fly ash on fresh and hardened properties of CLSM. In addition, the environmental impact of the proposed new mixtures was evaluated. The results show that CLSM mixtures incorporating TOSW had satisfied the limits and requirements of ACI committee 229 for CLSM with no environmental hazards. The incorporation of TOSW has increased the flowability of all mixtures and consequently reduced the water demand to reach the required flowability which consequently increased the compressive strength of mixtures containing TOSW and flyash. Replacing flyash with TOSW on the other hand, reduced the strength of CLSM slightly, but the strength remains within CLSM acceptable range of strength. In addition, this produced a more re-excavatable mixture, adequate for applications that may require future re-excavation. This successful incorporation of TOSW in CLSM mixture will provide a safe recycling method for oil sand wastes while reducing the environmental footprint of both construction and oil sand industry. [ABSTRACT FROM AUTHOR]