8,131 research outputs found
Designing against pile-tip bearing capacity failure in liquefiable soil
No full textRecent experimental data has demonstrated that piles passing through liquefiable layers and bearing in dense sands can suffer extensive settlement and bearing capacity failure during earthquakes. An analytical solution for the pile tip bearing capacity in liquefied soil is proposed and validated against centrifuge test data from instrumented end-bearing piles. In these experiments, strong sinusoidal shaking was applied to examine the reduction in load capacity at the pile tip across the full range of excess pore pressures which may be encountered. This demonstrated that the liquefied bearing capacity may be determined by knowledge of the excess pore pressure ratio at pile tip level alone. A database of full-scale load tests on instrumented piles bearing in sandy soils is then used to empirically relate the reduction in base capacity to the minimum static safety factor (SSF) to be used in design to avoid punching failure
Design of plate and screw anchors in dense sand:failure mechanism, capacity and deformation
Full text linkPlate and screw anchors provide a significant uplift capacity and have multiple applications in both onshore and offshore geotechnical engineering. Uplift design methods are mostly based on semi-empirical approaches assuming a failure mechanism, a normal and a shear stress distribution at failure and empirical factors back-calculated against experimental data. However, these design methods are shown to under- or overpredict most of the existing larger scale experimental tests. Numerical FE simulations are undertaken to provide new insight into the failure mechanism and stress distribution which should be considered in anchor design in dense sand. Results show that a conical shallow wedge whose inclination to the vertical direction is equal to the dilation angle is a good approximation of the failure mechanism in sand. This shallow mechanism has been observed in each case for relative embedment ratios (depth/diameter) ranging from 1 to 9. However, the stress distribution varies non-linearly with depth, due to the soil deformability and progressive failure. A sharp peak of normal and shear stress can be identified close to the anchor edge, before a gradual decrease with increasing distance along the shear plane. The peak stress magnitude increases almost linearly with embedment depth at larger relative embedment ratios. Although further research is necessary, these results lay the basis for the development of a new generation of design criteria for determining anchor capacity at the ultimate limiting state
Effect of soil deformability on the failure mechanism of shallow plate or screw anchors in sand
Full text linkMost analytical approaches for the design of shallow plate and screw anchors in tension are based on the limit equilibrium of a rigid soil wedge for which a horizontal stress distribution acting on the failure plane is assumed. Finite element analysis for a wide range of soil properties was carried out to identify the shape of the failure mechanism and to study the stress distribution at failure. Results show that soil deformation modifies the stress field around the anchor and increases the uplift capacity. A semi-analytical approach is proposed to describe this stress distribution, based on peak friction angle.</p
Jonathan Ned Katz Author Event: The Daring Life and Dangerous Times of Eve Adam
No full text“The Daring Life and Dangerous Times of Eve Adams,” interview with author, Jonathan Ned Katz, moderated by Emily Weiner (WWU) and organized by Congregation Beth Israel
Optimisation of screw anchor lateral capacity in sand for offshore renewable energy applications
Full text linkScrew piles or screw anchors are a promising solution to anchor floating offshore renewable energy devices, such as wind turbines or tidal turbines. The installation generates limited noise (driven piles are noisy) and can be undertaken in all soil conditions. Although they are mainly used for their large uplift capacities, screw anchors can also be designed to provide significant lateral resistance. The optimisation of screw anchor design does not rely only on the geotechnical assessment of the uplift capacity based on soil strength, but also on operational (installation requirements) and structural (helix bending, core section stress, limiting steel plate thickness) constraints. This paper develops a methodology for the design optimisation of screw anchors under lateral loading in dense sand, incorporating all of these constraints, based on simplified analytical or semi-analytical approaches. The results show that it is possible to optimise the anchor design, maximising the anchor lateral capacity, whilst minimising the anchor weight. The maximum embedment depth and then the anchor capacity is mainly limited by the maximum torque available during installation and the short-pile to long-pile failure mechanism transition respectively
Contemporary Literature. Analysis of Jonathan Bazzi's novels
No full textopenDopo una breve panoramica della letteratura italiana degli ultimi vent’anni si analizzano i due romanzi di Jonathan Bazzi "Febbre" e "Corpi minori" dai punti di vista formale, stilistico e tematico. Si discute inoltre il rapporto tra social media, autofiction e autore; nel capitolo 4 si riporta l'intervista che Bazzi ci ha gentilmente concesso, in cui questi argomenti vengono ripresi.
Si individuano alcune differenze che i testi mostrano rispetto alla letteratura moderna, e gli aspetti che hanno in comune con quella contemporanea; nel fare questo si accennano quindi alcune caratteristiche della società che li ha prodotti.The paper starts off with a brief overview of the contemporary Italian literature; then the reader is guided through an analysis of Jonathan Bazzi's novels, "Febbre" ("Fever") and "Corpi minori" ("Minor bodies"), both translated in English and published by Scribe. The relationship between author, autofiction and social media will also be discussed; in chapter four the reader will find the interview Bazzi kindly granted us
Using discrete element method (DEM) to create a cone penetration test (CPT)-based method to estimate the installation requirements of rotary-installed piles in sand
Full text linkDeep foundations may be used in a range of soil types where significant foundation resistance is required, but their installation is often associated with disturbance due to noise and vibration. Greater restrictions on use in urban and offshore environments is now commonplace. Screw piles and rotary-jacked straight-shafted piles are two potential methods of silent piling that could be used as alternative foundation solutions, but the effects of certain geometric and installation properties such as installation pitch, i.e., the ratio between vertical displacement and rotation, on the required installation torque and force in sand are not well understood. In this paper, the effects of installation pitch and base geometry on the installation requirements of a straight-shafted pile are simulated in three dimensions using the discrete element method (DEM). The installation requirements of straight-shafted piles into sand have been validated against centrifuge testing in three different relative densities. The DEM shows reductions in installation force can be achieved by increasing the installation pitch or including a conical tip. An existing cone penetration test (CPT)-based prediction method for installation requirements has been improved to include the effects of installation pitch and base geometry for rotary-installed piles in sand.</p
Screw pile design optimisation under tension in sand
Full text linkMany applications in offshore engineering, such as floating or jacket-founded wind turbines or wave energy converters, require a significant uplift capacity of their foundations to be kept in place. Straight-shafted or suction piles in sands have a limited uplift capacity as they resist by friction only. In contrast, screw piles or screw anchors are a promising solution which provides a similar capacity to plate anchors and does not generate disturbance for marine mammals (e.g. from pile driving operations). The optimisation of the screw pile design does not rely only on the geotechnical assessment of the uplift capacity based on soil strength, but also on operational (installation requirements) and structural (helix bending, core section stress, limiting steel plate thick-ness) constraints. This paper develops a methodology for the design optimisation of screw piles under pure ten-sion in sand, incorporating all of these constraints, based on simplified analytical or semi-analytical approaches. The results show that the uplift capacity provided by an optimised screw pile is able to meet the needs of the offshore industry, across a range of soil densities and different applications (jacket foundation pile or tension leg platform anchor), providing that adequate installation plant could be dev
Optimised design of screw anchors in tension in sand for renewable energy applications
Full text linkThe offshore deployment of floating offshore structures such as wind turbines or wave energy converters is expected to strongly increase during the next decade, to face the appetite for green energy sources. The growing size of these structures’ dimensions, inducing very large mooring forces, makes the anchoring solution adopted a critical issue for the commercial success of floating marine energy farms. The upscaling of the screw anchor technology from onshore to the offshore environment has been recently proposed as an efficient way of providing a large tension capacity while their installation generates far less noise and vibrations than impact pile driving. Most of recent studies on screw anchors have focused on separated geotechnical problems such as their uplift capacity or installation requirements. This paper incorporates within a single procedure geotechnical and structural constraints to calculate the optimal anchor geometry able to maximise the uplift capacity available. Performance envelopes for screw anchors have been derived in a parametric study, covering a broad range of soil conditions as well as in a case study, representative of offshore conditions. Results show that single screw anchors are more efficient (e.g. shorter and lighter) than driven piles to sustain tension loading. The results presented in this study support the applicability of screw anchors to be used as part of the mooring system for wave energy converters. However, tension requirements for tension-leg platform wind turbines would probably require the use of group of anchors.</p
Anchor geotechnics for floating offshore wind: Current technologies and future innovations
Full text linkA rapid expansion of the anchor market is required to meet the increasing demand for floating offshore wind. This paper, which is aimed at a broad readership within and beyond geotechnical engineering, summarises the current state-of-the-art and discusses future developments of anchor types and geotechnical design methods.Current anchor technologies are presented via comparative analytical assessments of performance across a range of practical scales and seabed conditions. This analysis demonstrates the relative merits and performance of different anchor types, using simplified cost-performance indicators for each anchor technology. An example outcome is the large differences in anchor efficiency (capacity per unit weight), that are linked to the different ways anchors achieve their holding capacity.Potential improvements in the performance-cost response for each anchor type, through future enhancements, are then explored. These enhancements are categorised as (1) unlocking higher anchor performance through improved design methods with a better understanding of the geotechnical response, (2) upscaling or (3) commoditising of the anchor type, by making larger versions or enabling more efficient mass production and installation, or (4) invention of new anchor technologies. Finally, findings of the different sections are summarised within a single table to enable a quick selection of anchoring solutions
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