Considerations on an embedded pile’s effective length in an analytical calculation according to the commentary on the STN 73 1002 standard

The analytical model for calculating the bearing capacity of a pile, presented in the commentary to STN 73 1002 – Pile Foundations, gives a recommendation to reduce the pile’s length in the calculation of the shaft resistance. The recommendation is based on Caquot-Kérisel’s theory. Especially in the case of embedded piles, reducing a pile’s length in the calculation can cause the shaft friction of the embedded pile to be neglected, and the calculated resistance of the pile is thus significantly lower. The results of instrumented static load tests of embedded piles were analysed. The main aim of the study was to verify the validity of reducing the pile’s length in the analytical calculation of the shaft resistance. The results of the static load tests analysed did not show any reduction in the shaft friction on the embedded part of the pile. In the form of a parametric study, the effect of reducing the pile’s length in the calculation of shaft friction was analysed for different dimensions of embedded piles

Calculation of soil volume loss caused by drilling of anchors

Accurate prediction of ground settlements related to deep supported excavations or foundation works are key in risk assessments of vulnerability of neighboring assets. Several studies show that rotary percussive duplex drilling of casings for tieback anchors and piles can cause substantial local soil volume loss (cavities) around the casings resulting in ground settlements. This paper presents FE back-analysis of a well-documented deep supported excavation in soft clay to investigate the influence from such soil volume loss on the surrounding ground. The analysis demonstrates a simple approach to estimate potential installation effects from overburden drilling by modelling volume loss in specified soil clusters. The method can be implemented in early-planning risk assessments in building projects to assess influence areas and suitability of drilling methods.Calculation of soil volume loss caused by drilling of anchorspublishedVersio

Numerical Investigation of Dynamic Pipe-Soil Interaction on Electrokinetic-Treated Soft Clay Soil

© 2019 American Society of Civil Engineers. Researchers have underscored the importance for a pipeline to safeguard against adverse effects resulting from its displacement in the vertical, axial, and lateral directions because of the low shear strength of the soil. The seabed may sometimes consist of soft or very soft clay soil with high water content and low shear strength. Dissipation of the water content from the soil void increases its effective stress, with a resultant increase in the soil shear strength. The electrokinetic (EK) concept has been applied to increase soil bearing capacity with barely any study conducted on its possible application on pipe-soil interaction. The need to explore more options merits further research. The EK process for the pipe-soil interaction consists of two main stages: the electroosmotic consolidation process and dynamic analyses of the pipe-soil interaction. The present study numerically investigated the impact of EK-treated soil on pipe-soil interaction over the non-EK process. The results of dynamic pipe-soil interaction on EK-treated soil when compared with non-EK-treated soil indicate a significant increase in the force required to displace a pipeline

Numerical and Experimental Analysis of Seismic Soil Pile Structure Interaction

The fundamental design of the piles is finished by static analysis, but particularly in seismically dynamic locales, the last configuration requires dynamic study. Dynamic soil-pile-structure interaction analyses require the stress-strain conduct of soils under dynamic loading conditions. The material nonlinearity can be addressed by comparable linear or completely nonlinear strategies. The correlation of these methodologies in the free-field site reaction analyses has been concentrated in recent years. In any case, the impacts on the soil-pile-structure interaction analyses have not been illustrated. In this study, a well-known centrifuge test was demonstrated and analyzed in the frequency domain (ACS SASSI) and in the time-domain (FLAC 3D) for equivalent-linear and fully nonlinear methods, respectively. The soil space was displayed with solid components in the projects, while the structural beam elements were utilized for the pile and the superstructure. The scaled speed acceleration time history of the Kobe earthquake was applied to the lower part of the soil-pile-structure model, and the acceleration-time histories were acquired at the ground surface and the superstructure. The outcomes obtained from the ACS SASSI and the FLAC 3D were compared with the centrifuge test. As per the outcomes, the peak ground and the superstructure accelerations were close to the experimental outcomes; however, the periods at the peak spectral accelerations were slightly different from the test results. The difference is more pronounced in SASSI than in FLAC, which may be attributed to the solution methods. Apart from the solution methods, the difference might be the inability to fully simulate the complex centrifuge test

Seismic Performance of Steel Helical Piles

Recent earthquakes have highlighted the need for safe and efficient construction of earthquake resilient structures. Meanwhile, helical piles are gaining popularity as a foundation for new structures and retrofitting solution for existing deficient foundations due to their immense advantages over conventional driven pile alternatives. In addition, helical pile foundations performed well in recent earthquakes, proving they can be a suitable foundation option in seismic regions. The objective of this thesis is to evaluate the seismic performance of helical piles by conducting full-scale shaking table tests and nonlinear three-dimensional numerical modeling using the computer program ABAQUS/Standard. The experimental setup involved installing ten steel piles with different configurations and pile head masses in dry sand enclosed in a laminar shear box mounted on the NEES/UCSD Large High Performance Outdoor Shake Table. The loading scheme consisted of white noise and two earthquake time histories with varying intensity and frequency content. The performance of different moment curve fitting techniques used for reduction of shake table experimental data are compared. The experimental results are presented in terms of natural frequency and response of the test piles. The effects of the loading intensity and frequency and the pile’s geometrical configuration and installation method were evaluated. The dynamic numerical model constructed accounted properly for the test boundary conditions, employing tied vertical boundaries. In addition, the nonlinear behavior of the soil during the strong ground motion was simulated by considering a strain-dependent shear modulus and applying Masing’s loading-unloading rules by the overlay method to account for the soil non linearity more realistically. The numerical model was verified employing the full-scale experimental results, then was used to conduct a limited parametric study that investigated the effect of pile stiffness and the location of helix on its lateral response. The experimental results show that the natural frequency of the driven pile was slightly higher than that of the helical piles. However, the response of the helical pile was close to that of the driven pile, which illustrates the ability of helical piles to perform as good as conventional piles under seismic loading

A sensitivity study on the mechanical properties of interface elements adopted in finite element analyses to simulate the interaction between soil and laterally loaded piles

An increasing number of offshore energy structures have been built recently on driven piles, ranging from jack- et piles with typical length-to-diameter (L/D) ratios of 10-40 to monopiles with far lower L/D ratios. The load-displacement behaviour of these foundations can be investigated by means of Finite Element (FE) analyses, for instance following the design methodology developed by the PISA Joint Industry Project (JIP). A challenging aspect of the modelling, for piles loaded either axially or laterally, is the simulation of the behaviour at the soil-pile interface with the adoption of suitable formulations for the interface elements and with representative mechanical properties. This paper presents a sensitivity study conducted on both the elastic and plastic properties of interface elements adopted in FE analyses of laterally loaded piles driven in chalk. The study benefited from the extensive field and laboratory test results collected during the ALPACA JIP and the corresponding pile tests. The aim of the paper is to provide guidance for numerical modelling on the selection of the most appropriate mechanical properties of interface elements to be used in the analyses of soil-pile interaction under lateral loading