This dissertation presents axial compressive load tests where the pile base and shaft resistances were measured with distributed fibre optic sensors. Two test sites were established: one at Amaliahaven in the port of Rotterdam, and another in Delft. At Amaliahaven, the performance of three different pile types was compared in very dense sand: driven precast, driven cast-in-situ and a screw displacement pile type known as a screw injection pile. The screw injection piles were further investigated in the medium dense sand of Delft, comparing screw injection piles installed with a removable casing to screw injection piles installed with sacrificial casings. With these tests, the influence of installation method on the axial pile capacity was examined, and the results were considered in the context of design methods which use the cone penetration test to predict the axial pile capacity.
The piles at Amaliahaven reached very high base and shaft resistances, up to 30 MPa and 600 kPa respectively. These values are nearly three times greater than limiting resistances in design standards, suggesting that limiting resistances lead to excessive conservatism in dense to very dense silica sands. On the contrary, the screw injection piles at Amaliahaven mobilised much lower base capacities than anticipated. This became the focal point for the tests at Delft, and likewise, the piles at Delft also mobilised much lower base capacities than forecasted.
The influence of different installation methods on the pile base resistance was then examined in a review of other instrumented load tests—a review extending beyond screw injection piles and to screw displacement piles overall. The analysis confirmed that the installation of a screw displacement pile leads to little soil improvement around the pile base. In other words, a screw displacement pile tends to mobilise base resistances comparable to a soil-replacing (bored) pile rather than a soil-displacing (driven) pile.
A larger database of both instrumented and uninstrumented test records was then used to consider the implications of these findings. To do so, the base, shaft, and total capacity of each pile was compared to design methods from Belgium, France, the Netherlands and the USA. These design methods tended to overestimate the pile base contribution yet underestimate the shaft contribution, especially at cone resistances greater than the limiting resistances. A best-fit to the measured base and shaft resistances gave the best agreement on average to the measured total capacity. Nevertheless, there is room for improvement with this new formulation, particularly for the shaft resistance of screw displacement piles with an enlarged displacement body.
From the findings in this dissertation, a series of adjustments have been proposed for the Dutch pile design standard NEN 9997-1. The tests presented in the dissertation are also the first set of pile tests to be incorporated into the Dutch national pile test database, with the findings also being used to refine and optimise quay wall design across the port of Rotterdam.

As offshore pile foundations increase in diameter and weight, the risk of uncontrolled and unsafe penetration events (pile run) also increases. Traditional approaches to evaluating this risk rely on static resistance to driving (SRD) formulations, equating the SRD to the effective weight of the pile. However, high penetration speeds during uncontrolled pile penetration can lead to a soil response much different to static conditions, particularly with regards to pore pressure dissipation around the pile. With this in mind, the paper proposes an analytical model for determining when uncontrolled penetration may occur and its extent. The model integrates novel SRD formulations with a penetration rate effect model, both of which are derived from cone penetration test (CPT) measurements. The model's predictions were then benchmarked against industry-standard methods using a database of self-weight penetration events in clays and sands of varying densities and strengths. The predicted self-weight penetrations compared well with field observations across the full range of soil conditions and gave a better performance compared to standard prediction methods. Furthermore, the results emphasise the critical role of soil volumetric behaviour during shearing and future research should clarify the influence of rapid penetration on the pile's shaft and base resistance.

The InPAD project investigated the axial capacity of different pile types in sand, including driven precast piles, screw displacement piles and driven cast-in-situ piles. This was done through several full-scale field tests and small-scale physical models, using state-of-the-art instrumentation to analyse the base and shaft response of each pile. This article shows some of the findings from the project and puts forward recommendations for the NEN 9997-1 pile design method.

This study utilises parallel discrete element method (DEM) simulations of cone penetration tests (CPTs) and pile load tests to investigate the application of direct CPT-based methods for predicting the base capacity of bored piles in layered soils. To reduce boundary effects, a coupled DEM-finite difference method (FDM) model is constructed to simulate pile load tests. The study focuses on the scale effect of pile diameter on the correction factor αb and the effectiveness of existing qc averaging methods in layered soils. Two pile diameters and three soil layering conditions, featuring a single silt layer interbedded within sand at varying depths, are considered in the simulations. Results show that both soil layering and pile displacement influence the scale effect. At small settlements (s) up to 0.3 times the pile diameter (D), the scale effect is insignificant, except when a soft layer is directly above the pile tip. At larger settlements, particularly when s > 0.5D, piles with smaller diameters show more pronounced reductions in base resistance due to a weak layer closely beneath the tip. Among the four methods evaluated, the BD-18 qc averaging method produces more consistent αb values across various soil profiles and pile diameters. Microscopic analysis reveals that soils above the tip contribute less to the pile base resistance at s/D = 0.1 than to the cone tip resistance. Additionally, the strength mobilisation levels of soils in most soil layering conditions appear similar at s/D = 0.1, supporting the proposal of a constant αb value in direct CPT-based methods.

Amsterdam is renowned for its picturesque canals, lined by tall, narrow buildings on either side. Hundreds of kilometres of quay walls support these canals, all founded on long, slender timber piles. Yet many of these quay walls are falling into disrepair and the remaining lifespan of these quay walls is often unknown. Consequently, an extensive amount of research and pilot projects are ongoing, investigating how these walls can be upgraded without intruding on the urban environment. Press-in piling presents an excellent alternative to conventional piling techniques because of its effectiveness in tight working spaces, generating low noise and vibrations as it does so. However, Amsterdam poses some unique geotechnical challenges. Built on marshland, soft clay and peat deposits are widespread throughout. Underlying these deposits are dense sands, the primary load-bearing layer for piled foundations. Understanding how piles behave in these sands is therefore vital, particularly in the case of piles with low embedment depths or in areas where there are thin weak zones in the vicinity of the pile tip. With the growth of press-in piling in the Netherlands, this paper presents some of the opportunities and challenges facing press-in piling, with a particular focus on how the Cone Penetration Test can be used to improve pile design and installation forecasting.

Recent advancements in fibre optic sensing have increased the range of monitoring techniques available for measuring the axial response of full-scale piles. For instance, distributed fibre optic sensing gives a continuous measurement of normal force with depth in a pile, meaning the shaft resistance of a pile can be accurately quantified in each soil layer. Other fibre optic sensing methods, such as Fibre Bragg Gratings, have been shown to provide accurate and robust high-frequency measurements of pile installation. With these improved measurement techniques, detailed insights can be obtained into not just the geotechnical response of the pile, but also the structural response. Presented in this paper is some first-hand fibre optic data collected from axial load tests on piles founded in dense to very dense sand, ranging from driven piles to screw displacement piles. Using fibre optic sensing, key insights could be gained into both the structural and geotechnical response of these piles at large base and shaft resistances, facilitating changes to CPT-based pile design methods at a site-specific and nationwide level.

This report presents the execution and results of axial pile load tests on screw injection piles in the south of Delft in 2022. Two types of screw injection piles were tested: a screw injection pile with the steel casing removed (SI, Fundex pile) and a screw injection pile with the casing remaining in-situ (Sic, Tubexpile).The tests were carried out with the guidance of NPR 7201 (NPR 7201, 2017) and NEN 9997-1 (NEN, 2017), with each pile loaded under compression to a pile base displacement of 20%. During this process, strains were measured along the entire pile length, giving comprehensive insights into the pile base and shaft response.

This document provides a factual summary of the results for dissemination to the NPR 7201 advisory committee, with the primary aim of fully detailing of the test methodology and execution, along with the underlying dataset. Minimal interpretation of these results is presented in this report and has instead been published in the following publications:

• Duffy, K.J., Gavin K.G., Korff, M., de Lange, D.A. (2024) Base resistance of screw displacement piles in sand. Journal of Geotechnical and Geoenvironmental Engineering, 150(8), https://doi-org.tudelft.idm.oclc.org/10.1061/JGGEFK.GTENG

• Kevin Duffy (2025) Axial capacity of piles in sand: A field investigation using distributed fibre optic sensing. [Doctoral dissertation, Delft University of Technology]. (to be published)

The data from the tests is publicly available on the 4TU.ResearchData repository under doi: 10.4121/78720ecb-daf4-4676-b5f4-281e93e4388a (Static load tests on screw injection piles with distributed fibre optic sensors in Delft).

Full-scale axial load tests were performed on five screw injection piles founded in medium-dense to dense sand at a site in Delft, the Netherlands. Each pile was instrumented with distributed fiber-optic sensors along its full length, giving detailed insights into the shaft and base response under compression loading. The paper focuses on the pile base response and combines the test results with a newly compiled database of instrumented load tests on screw displacement piles in sand. Given the range of screw displacement piles on the market, the influence of different installation methods and pile geometries on the base resistance can be assessed through the database. In summary, the analysis showed that all screw displacement pile types tended to mobilize base capacities similar to bored or nondisplacement piles. Despite high variability in the database, no significant trend with pile geometry, such as length or diameter, was evident.

Three driven precast, four driven cast-in-situ, and four screw injection piles were installed and tested in dense to very dense sand at a site in the Netherlands. Each pile was instrumented with two types of fiber optic sensors and tested under axial compression. Through these tests, a comparison could be made of how different installation methods influence the pile base and shaft response. For example, large residual base stresses were measured in the driven precast piles after installation. Of the three pile types tested, the driven precast piles also reached the highest base stresses, mobilizing their full base resistance at comparatively low displacements. The base response of the driven cast-in-situ piles was also like that of a driven precast pile with residual stresses excluded. In contrast, the screw injection piles mobilized much lower ultimate base resistances and with a much lower stiffness. In terms of shaft resistance, the precast piles showed friction fatigue effects in line with existing models, but this effect was not evident for the driven cast-in-situ or screw injection piles. Finally, shaft and base resistances measured in the dense to very dense sand layers were greater than limiting resistances prescribed in several design standards. By taking this into consideration in design standards, the results would help reduce some of the overconservatism present in design and consequently reduce the financial and environmental cost of pile manufacturing and installation.

Currently, the offshore renewables industry uses a range of foundation systems originally developed for the oil and gas sector. However, innovative foundation measures still need to be developed for offshore renewables because of key differences in scale, loading conditions and the geographical areas in which renewable developments are deployed. Furthermore, the large-scale of offshore wind developments means there is often significant uncertainty regarding the ground conditions between site investigation points. With this in mind, this paper explores the potential use of press-in pile technology for offshore renewable development. Firstly the paper looks at how press-in piling data can be used to inform and ground-truth soil models during pile installation, as well as informing the in-service behaviour of a structure. The paper then describes a number of innovations that may allow for reduced costs and environmental impacts of offshore foundations.

Geotechnical structures are often partially embedded, if not fully embedded, making it challenging to assess the remaining lifetime and reusability of a foundation. In-situ monitoring offers a solution. By attaching different types of sensors to a foundation, the foundation’s response and reliability can be assessed at various stages of a structure’s life cycle. To illustrate this, an example of a “smart quay wall” is taken from the Port of Rotterdam. During the design phase, fully instrumented pile tests showed that the design could be optimised, leading to substantial financial and carbon emission savings. During construction, movements and forces in the quay wall were closely monitored and were used to validate a numerical model, thus providing a reliable tool at later stages during the quay wall’s lifetime when reuse or readaptation of the quay wall is being considered. Lastly, ongoing measurements during the operational phase of the quay wall have shown a large amount of residual capacity, particularly when compared to the pile load tests.

Understanding the geological and geotechnical characteristics of the shallow subsurface is crucial for engineering decisions in densely populated regions like the Netherlands. Urban areas are for a large part built on a complex stack of sand, clay, silt, gravel and organics that were deposited over the last hundreds of thousands of years under gradually subsiding tectonic conditions. One of these units, a fluvially deposited sand known as the Kreftenheye Formation, is widespread across the western part of the country and is vital for foundation design and groundwater dynamics. The Kreftenheye Formation is therefore well described by geotechnical and geological tests, yet integrating both types of data has rarely been done on a nationwide scale.

This paper focuses on 76 pairs of Cone Penetration Tests and boreholes that include Kreftenheye, out of a full database of nearly 200 pairs from TNO - Geological Survey of the Netherlands, generally reaching depths up to 40 meters. The study reveals significant spatial variations and depositional patterns within the Kreftenheye Formation, illustrating how overlying or interlayered flood plain or soft channel lag sediments influences the response of the CPT. Furthermore, CPT response and borehole samples have helped with making geological distinctions between the upper, Weichselian part of the Kreftenheye Formation and the lower Saalian part, showing how integrating both datasets can give both geological and geotechnical insights.

Since most of the existing port infrastructure needs to be upgraded or replaced in the coming decades, the Port of Rotterdam Authority invests in sustainable and future proof design solutions. Together with their partners, they aim to reduce the port’s CO₂ emissions by 50% in 2030 and intend to achieve a zero carbon footprint by 2050. The effective use of new and existing materials is crucial to reach these goals. However, the actual capacity of port infrastructure is generally not precisely known, given that no failures have been observed in practice and the existing berthing facilities are performing very well. In order to derive insight into the reserve capacity of these structures, unique full-scale field tests have been conducted on flexible dolphins, foundation piles and anchor piles. This paper presents the technical, commercial and environmental results of recent pile load tests performed in the port of Rotterdam. The tests have led to a significant reduction of CO2 emissions associated with manufacturing and installing foundations, as well as reducing installation risks. Furthermore, a higher reliability level was obtained using less materials. This paper shows that in spite of the cost of performing full-scale field tests, the verification of the actual capacity of foundation piles is crucial to improve the carbon footprint of port infrastructure.

This paper describes axial load tests on three full-scale driven precast piles in the Netherlands. The piles were founded in dense to very dense river-deposited sands, a soil that is widespread across the Dutch North Sea sector. The deposit is characterised by cone penetration test (CPT) tip resistances of up to 90 MPa and offers a detailed insight into pile response in realistic offshore conditions. Each test pile was incrementally loaded to failure under compression, while fibre optic sensors measured the changing deformation of the pile. The analysis and interpretation of the load test data focussed on how the three slender piles behaved at large shaft and base resistances. Notably, the piles mobilised base and shaft resistances greater than currently prescribed limiting resistances in design standards, thereby highlighting some overconservatism present when designing piles in dense sand.

Stresses generated from pile installation are a critical component in understanding pile behaviour. These are known as residual stresses and in Delft, the Netherlands, the response of three driven precast piles founded in sand was measured using distributed fibre optic sensing as part of a series of full-scale static load tests. The instrumentation set-up and analysis is discussed in this paper, highlighting the uncertainties with developing an appropriate residual stress distribution and in particular, how instrumentation selection, positioning and calibration can influence the interpretation of the residual stress profiles. The resulting profiles shows a substantial development of residual stress in the pile, an important consideration to take into account when preparing and analysing full-scale load tests on driven precast piles.

Large areas of the Netherlands are dominated by deep, soft soil deposits, posing a challenge to engineers with respect to the design of axially loaded foundations. The design of these foundations is primarily based on methods which use cone penetration test (CPT) parameters, such as that outlined in the Dutch national standard NEN 9997-1. A recent update to this standard included revised reduction factors for the pile base resistance. However, it is believed that this update is overly conservative in certain design situations, leading to increasing cost, environmental impact and difficulty of installation. As a result, a national research project was initiated to enhance the understanding of pile-soil interaction effects and their influence on pile design methods. As part of this project, a series of large-scale field tests on fully instrumented piles in dense sand has been executed and are being analysed with a view to refining the national standards and contribute to the existing knowledgebase on piles worldwide. This paper shall provide an overview of two pile test sites that have been developed as part of the programme, along with the design of the testing programme and an overview of the results.

This study examines how cone penetration test (CPT) parameters, such as cone tip resistance and friction sleeve resistance, can be used to assess the compressibility of fine-grained soils across the Netherlands based on a database of 286 paired CPTs and oedometer tests from across the country. This is done with the aim of refining and simplifying the parameterisation of the Koppejan consolidation coefficients, a procedure which can yield significant error and is prone to misinterpretation. It was found that there is significant potential
in using gradient boosting methods to obtain a relationship between the CPT parameters and the Koppejan parameters, with further investigation required into the noise within the dataset and the acquisition of additional high-quality samples. The use of such methods will offer a means of reducing the influence of human error or misinterpretation on the prediction of settlement and provide further confidence in the use of machine learning methods in engineering practice