Screw piles are uniquely-shaped concrete piles with screw threads that have been widely used in various fields, including construction, structural design, and geotechnical engineering. Research on the dynamic characteristics of screw piles under vertical loads is limited compared with that investigating traditional circular piles. This report describes an analytical solution that has been developed to investigate the dynamic features of a screw pile under a longitudinal load while considering the cushion cap effect. The Laplace transform and Potential functions are applied to decouple the three-dimensional wave equations of the soil. The dynamic response of the screw pile is deduced using a modified impedance transfer function method. Finally, the cushion cap displacement and velocity in the frequency domain are determined by combining the initial conditions. The analytical solutions are compared with field-measured curves to validate the developed method. The results indicate that the soil around the pile can be regarded as a threedimensional continuous medium to simulate the radiation-damping effect as the wave propagates outward. The cushion cap reduces the screw pile damage caused by resonance, particularly in the low-frequency range. Considering the effects of vibrational loads, a screw pile should employ a large lightweight cushion cap, i.e., with the largest reasonable dimensions and with concrete materials that are as light as possible. The results of this study provide a theoretical basis for designing a dynamic foundation of a screw pile.

A novel slope stabilization technique was recently developed incorporating screw piles with vegetated flapped soilbags. These screw piles are subjected to lateral stress from soil slope and their deformation can be difficult to quantify, given the fluctuating pore-water pressure and heterogeneous soil conditions. This study proposes the use of in-situ spectral analysis of surface waves (SASW) test to estimate the small-strain soil stiffness which can then be factored to calculate the lateral deformation of the pile in finite element modelling based on prescribed pore-water pressure change. A case of bioengineered slope in Kanchanaburi province, Western Thailand was studied, involving field monitoring of pile head tilt, pore-water pressure, suction, and soil moisture over one year. The findings revealed pile head tilt of up to 0.2 degrees in response to rainfall and rise in pore-water pressure and soil moisture over one year period. A series of finite element modelling were performed using factored shear moduli from in-situ SASW test and the monitored pore-water pressure variation to reproduce the amount of pile head tilting as observed in the field during one year. It was revealed that by assuming operational shear modulus ranging between 0.0075 and 0.01 times small-strain soil stiffness, a satisfactory agreement was obtained between field measurement and analysis of pile movement. This findings provides a basis for further studies on performance of bioengineered slope utilizing screw piles. (c) 2025 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Upscaled screw piles have been proposed as anchors for offshore floating wind applications, but this upscaling can result in a significant increase in vertical installation forces. Previous studies have shown that the use of overflighting techniques during installation (installation advancement ratio, AR<1.0) can reduce or eliminate these forces and improve the capacity and stiffness of screw piles under monotonic tensile loading conditions. However, the impact of overflighting installation on the cyclic response of screw piles has not received adequate attention. To address this, a series of drained cyclic uplift tests in a geotechnical centrifuge were conducted. The tests involved different AR values during installation and varying one-way cyclic tensile loading amplitudes. The results revealed that reducing the installation AR can significantly decrease displacement accumulation and improve cyclic loading stiffness, resulting in a more stable cyclic response. The cyclic axial loading stiffness tends to stabilize or slightly decrease with cycling for stable cases, while unstable and metastable cases exhibit an initial reduction of loading stiffness followed by a stabilization or slow recovery. The postcyclic monotonic uplift tests also show that capacity degradation was predominately due to the displacement accumulation itself rather than any additional cyclic effects. The cyclic stability of the screw pile investigated was found to be comparable with straight-shafted and screw piles from previous studies and beneficial installation effects were maintained under cyclic loading. A predictive framework for displacement accumulation and capacity degradation is also presented and developed within this paper.

Screw piles have a greater bearing capacity than straight piles due to their larger helix. However, an excessively large helix can cause bending and reduce the soil bearing capacity. This study investigates the failure pattern and mechanical performance of screw pile helices through full-scale load tests and numerical analyses. The results revealed that the helix buckled at its connection to the shaft. Additionally, the geological characteristics of the soil in which the pile was located had a negligible effect on the mechanical properties of the helix. Furthermore, the shape of the anchor plate (flat or helical) had a negligible effect on the load-bearing properties of the pile or the mechanical properties of the anchor plate itself. To simplify the analysis, the screw pile helix was assumed to be a flat circular plate. For a uniformly loaded flat circular plate with fixed inner edges, the result of Roark's formula satisfactorily agreed with the measured maximum radial normal stress in the helix. Moreover, the value given by Roark's formula for a flat circular plate with simply supported inner edges agreed well with the measured helix deformation.

In northern Canada where permafrost is prevalent, a persistent shortage of accessible, affordable, and high-quality housing has been ongoing for decades. The design of foundations in permafrost presents unique engineering challenges due to permafrost soil mechanics and the effects of climate change. There is no specific design code for pile or shallow foundations in northern Canada. Consequently, the design process heavily relies on the experience of Arctic engineers. To clearly document the current practice and provide guidance to engineers or professionals, a comprehensive review of the practice in foundation design in the Arctic would be necessary. The main objective of this paper is to provide an overview of the common foundations in permafrost and the geotechnical considerations adopted for building on frozen soils. This study conducted a review of current practices in deep and shallow foundations used in northern Canada. The review summarized the current methods for estimating key factors, including the adfreeze strength, creep settlement, and frost heave, used in foundation design in permafrost. To understand the geotechnical considerations in foundation design, this study carried out interviews with several engineers or professionals experienced in designing foundations in permafrost; the findings and the interviewees' opinions were summarized. Lastly, in order to demonstrate the design methods obtained from the interviews and review, the paper presents two design examples where screw piles and steel pipe piles were designed to support a residential building in northern Canada, according to the current principles for adfreeze strength, long term creep settlement, and frost heave. The permafrost was assumed to be at -1.5 degrees C, and the design life span was assumed to be 50 years. The design examples suggested that for an axial load of 75 kN, a 12-m-long steel pipe pile or a 7-m-long screw pile would be needed.

With the rapid development across major cities, low-capacity screw piles are adopted by builders as a viable economical option in managing risk involving settlement in soft soil deposits. Although the required installation torque and the capacity of a screw pile can be correlated to the soil shearing resistance at the interface of its shaft and helical plates, the correlated ultimate capacity of the pile is specific only to undrained conditions. Therefore, if the water table fluctuates within the embedment length of the pile, the correlated ultimate strength is not valid. This poses a serious design concern in over-consolidated fills. Therefore, due to the uncertainty associated with the compressive capacity of installed screw piles in soft saturated deposits, it is advantageous to perform a static load test to verify the serviceability and ultimate loads. In this study, four static load tests were carried out on screw piles at four different construction sites in the city of Melbourne, to study the load transfer mechanism at various levels of axial loading and subsequent unloading/reloading stages. In one of the sites, the screw pile was equipped with miniature transducers to monitor the generated total stress and pore-water pressure during the installation and post-installation. The results of this study indicated that a static load test can accurately estimate the real bearing capacity of a screw pile which differs significantly from the design geotechnical strength calculated using theoretical equations. It was concluded that in the absence of a pile load test, it is rational to adopt a geotechnical reduction factor of 0.4 and neglect the skin friction capacity of the screw pile to provide a safe foundation design.