The increasing demand for sustainable and easily constructible housing has led to the exploration of alternative foundation systems for lightweight modular structures. This research investigates the feasibility of using short helical piles to support a lightweight wooden building, assessing its settlement behaviour and structural integrity over time. Unlike traditional deep pile foundations, short helical piles are designed to be easily installed, removed, and reused, offering both environmental and economic advantages. However, their application in soft soils raises concerns regarding excessive and differential settlement.

The main research question for this thesis is:
”What is the structural feasibility of a lightweight, modular wooden building design on short, screwed foundation piles that is expected to have large amount of settlement?”
To answer this question, a literature study was done in combination with a case study. The literature established the boundary conditions for the use of helical foundation piles and explores the expected capacity and settlement behaviour in soft soil. Afterwards, it focusses on aspects such as decay and modular systems of timber construction elements.
With the knowledge obtained from the literature, a case study was developed. To investigate the behaviour of a lightweight structure that is expected to settle, a numerical modelling approach is used, combining PLAXIS 2D and SCIA Engineer. PLAXIS 2D was used for simulating the settlement behaviour of the structure at multiple stages in time, while the effect of these settlements on the superstructure was analysed in SCIA Engineer. Different wall systems were investigated, focusing on the influence of the wall stiffness, varying pile capacities, and the impact of uneven loading. Time-dependent settlement effects were evaluated at time stages just after the completion of the construction and at three additional points further in time. This provides insight on the short-term and long-term behaviour of the structure. To prove that a structure of this typology is sufficient for housing, it is tested on total settlement (𝑈), differential rotations (𝛽), tilt (𝜔), and element capacity (𝜎).

The results of the calculations indicate that for a lightweight, timber structure placed on short helical piles large amount of settlement can be expected when positioned in soft soil. However, the settlements will not lead to a significant stress increase that causes failure of structural elements. A stiffer wall system has the ability to redistribute more force to the foundation piles at the most outer position. This reduces the differential settlement between piles, but also reduces the maximum total settlement of the wall. The resistance to deformations of the outer foundation piles is therefore more impactful with a stiffer superstructure. In general, the findings suggest that with careful consideration of settlement behaviour, short helical piles can be a viable foundation solution for supporting lightweight houses.

The early 20th century marked a period of significant infrastructural development in Europe, resulting in the construction of numerous bridges and structures that have lasted to the present day. Many of these foundations, often designed as piled rafts but analysed as pile groups, were constructed using simplistic methodologies. These methods neglected the interactions between the raft, soil, and piles. Despite advancements in geotechnical engineering, current standards like Eurocode 7 still rely on this outdated approach, potentially leading to unnecessarily conservative and expensive retrofitting solutions.

Recent research highlights the significant contribution of rafts to the overall bearing capacity of foundations, suggesting that current design standards may underestimate the capacity provided by rafts. This thesis investigates the behaviour of piled raft foundations compared to pile groups and rafts, utilizing both 3D finite element analysis with the SANISAND-MS constitutive model and centrifuge testing. Furthermore, it explores the feasibility of using a viscoelastic model to capture the cyclic behaviour of piled raft foundations. The study focuses on dry sand conditions and quasi-static cyclic loading to address questions regarding load-displacement behaviour, load and moment distribution, internal forces on piles, and the modelling of cyclic loading conditions.

The findings demonstrate the superior performance of piled rafts in terms of stiffness and resistance compared to pile groups and rafts. Specifically, the vertical resistance ratio (β_PR,V ) and combined resistance ratio (ξ_PR,V ) indicate that accounting for the raft nearly doubles the vertical resistance of the piled raft foundation and aligns closely with the combined resistance of the pile group and raft as separate foundations. In lateral loading, the horizontal resistance ratio (β_PR,H) and moment resistance ratio (β_PR,M ) suggest that the piled raft requires more horizontal load and moment to achieve the same displacement and rotation compared to the pile group alone. The raft contributes approximately 45% of the vertical load and 50% of the moment, reducing the axial load on individual piles by around 40%.

Analysis of internal forces reveals that shaft resistance is relatively small. Larger moments are observed in edge piles under axial loading, indicating the deformability of the raft and suggesting a likelihood of failure in the edge piles due to moments. Under lateral loading, the tension piles quickly reach maximum tensile resistance, with moments continuing to increase, highlighting a high probability of failure in the edge piles due to moments.

The study also demonstrates that modelling the elastoplastic cyclic behaviour of piled rafts using a viscoelastic model with frequency-independent viscosity is feasible. While not fully capturing all aspects of foundation behaviour, this approach adequately replicates stiffness and damping characteristics, making it useful for seismic design using a pseudostatic approach.

These findings offer potential for more efficient foundation designs, improved retrofitting strategies for existing structures, and increased understanding of the foundation behaviour of piled raft systems.

Debris flows are extremely rapid gravity-driven mass movements of saturated sediment in concentrations between 60% to 80% by volume that move along steep channels, eroding and entraining material, typically terminating in a fan-shaped deposit. Debris flows are responsible for causing innumerable deaths and extensive damage across the world. The mobilisation of rainfall-triggered landslides is the primary cause of such flows. Estimating the debris flow travel distance or runout is essential for managing this hazard.

The conventional approach to debris flow runout analysis idealises the triggering of landslides across the source area into an instantaneous event. When this idealisation is done, a key characteristic of debris flows, their tendency to propagate in surges or waves, is overlooked. This study analyses the effect of accounting for surging on runout estimation by spatially and time-resolving debris flow events. A prime candidate for such a study is the Mocoa Debris Flow of 2017, a tragedy that involved 273 shallow landslides mobilising into a debris flow, resulting in the death of more than 300 people and the devastation of local infrastructure, Sarmiento et al. (2019). First, the landslide inventory was analysed to assess the scale of the disaster. Then, a novel method to spatially resolve events based on stream orders is implemented, after which a runout analysis is performed for different spatially resolved scenarios using a depth-averaged numerical model. Next, the timing and distribution of landslides are assessed based on a four-day storm period using a process-based landslide susceptibility model. This assessment determines the relative volume of each debris flow surge. The surges are then incorporated into a time-resolved runout analysis. The results of both the spatially and time-resolved runout analyses are compared. We find a marginal difference in the estimate of runout based on critical performance criteria, such as area coverage ratio, in favour of the spatially resolved analysis.

This study concludes that incorporating the phenomenon of surging caused by non-simultaneous landslide events does not improve the forensic analysis of the Mocoa Debris Flow runout. One of the main limitations of this study is the absence of data measured during the event to confirm the extent of surging due to non-simultaneous landslides. A possible avenue for future research would be varying the period of rainfall that is considered by reevaluating initial groundwater conditions.

This thesis investigates the soil-structure interaction and corresponding stability of pneumatic caisson foundations compared to monopile foundations for offshore wind turbines. The monopile foundation has been the industry standard for years, yet pneumatic caisson foundations are being investigated as a possible alternative. This research applies finite element analysis with the software Plaxis 3D to explore the monotonic and cyclic behaviour of the two foundation types, analysing important properties including soil deformation, energy dissipation, and cyclic stability.

The results of the monotonic behaviour analysis show that caissons are experiencing non-linear soil behaviour at lower forces than monopiles. However, their elastic capacity is sufficient to support the environmental loads, resulting in lower displacements under these loads. Monopiles exhibit greater flexibility, energy dissipation, and a tendency to increase soil stiffness over cycles. At the same time, caissons maintain structural stability with small permanent deformation and low energy dissipation, as demonstrated by cyclic loading tests. Pneumatic caissons demonstrate potential as viable alternatives to monopiles, as they offer increased initial rigidity and reduced displacements. Additionally, the pneumatic caisson foundation can provide a solution in environmentally sensitive areas because the pneumatic caissons can be installed with low noise and vibration impacts on the environment. As the load increases to its maximum capacity, the caisson shows a more abrupt failure compared to the monopile. Beyond the load tipping point, where the caisson shows non-linear behaviour, it undergoes significantly more deformations as force increases. The monopile shows a more gradual increase in deformations with an increase in force. As a result, the monopile shows a more gradual failure behaviour.

Practical challenges in the caisson’s production, transportation, and installation need to be overcome. For the production of the big caisson structures, specialised production facilities are required with direct access to the sea. Due to the caisson dimensions used in this thesis, it is too heavy to float and must be transferred using large cranes and barges or semi-submersible vessels. Although this study did not look into it, dimension optimisation or the use of different materials to construct the caisson might save money on transport, particularly if the caisson can float. In order to install the caisson at the correct depth, water must be pumped into its hollow chamber to produce enough downward force to counteract buoyant forces and wall friction.

In summary, the pneumatic caisson foundation offers a viable alternative with advantages in terms of stiffness and lower displacements compared to monopiles. Pneumatic caissons are a promising foundation solution for offshore wind turbines. However, the economic feasibility of the pneumatic caisson method in the offshore environment remains to be examined.

Earthquakes have long posed challenges to geotechnical engineers, as serious destruction or harm can be caused at the surface. Especially cyclic liquefaction, the fluid-like behavior of soil under cyclic loading, is a phenomenon that has been extensively studied yet still needs more research. Two criteria are widely used to assess the potential of soils to liquefy, based on either the cone resistance qc or the shear wave velocity Vs. In practice, using liquefaction potential assessment criteria based on qc and Vs tends to lead to different outcomes. Because of this, the question arises what exactly contributes to the difference between the two. It is unclear whether potential differences can be attributed solely to differences in testing methods or whether the tested material primarily plays a role. The main question this research tries to answer is therefore: Can potential differences between results from qc-based and Vs-based liquefaction potential criteria be traced back to the intrinsic properties of the granular material?

Based on existing literature, fundamental principles behind liquefaction potential assessment criteria are investigated. These fundamental principles trace back to the physical meaning behind the parameters qc and Vs. Subsequently, data is gathered on four different types of sand: a rounded quartz sand, a compressible, angular carbonate, and two types of angular volcanic sand. This data originates from seismic cone penetration tests (SCPT), an invasive test measuring both qc and Vs. Based on four criteria, by Youd et al. (2001), Boulanger and Idriss (2014) (qc-based), Andrus and Stokoe (2000) and Kayen et al. (2013) (Vs-based), the resistance of the different sand types against liquefaction is determined in the form of the cyclic resistance ratio (CRR). Factors including compaction and aging are included in the analysis. Differences between different sand types are then interpreted considering the intrinsic properties of the granular material, like density, mineralogy, particle size and shape, gathered from existing laboratory data. Also, existing correlations between qc and Vs as well as new proposed ones are analyzed.

The fundamental difference between qc and Vs is that they represent behavior on opposite sides of the strain spectrum. Where qc is a large-strain parameter, Vs describes the soil’s behavior at very small strains. The results of the data analysis show large differences in qc and Vs across all sands, with carbonate sand showing low cone resistances while having high shear wave velocities. Both parameters appear to correlate better in quartz sand and the type 2 volcanic sand. This translates well to the corresponding CRR. Compaction affects both parameters, but seems to have a bigger impact on the qc than on the Vs, as well as the corresponding CRR. Ageing was analyzed over a two-year period, yielding a larger relative increase in Vs over qc. Based on literature, it is suggested that the CRR based on Vs represents the resistance of a soil against initial deformation, therefore the triggering of liquefaction. On the other hand, the CRR based on qc is more a reflection of the soil’s resistance against large strains, in other words, the extent of the consequences of the liquefaction event. In crushable soils, the qc appears to yield low values as the particles around the cone are crushed.

When considering how dependent the CRR is on the method used, it can be concluded that, when there is a good correlation between cone resistance and shear wave velocity, the CRR is to a small extent dependent on the type of liquefaction assessment method. However, when this correlation weakens, the corresponding CRR tends to deviate accordingly. Furthermore, it seems that the different liquefaction potential assessment methods are material dependent, and mainly the mineralogy and particle shape play a role. qc is mainly affected by soil mineralogy, as in carbonate sands particle crushing plays a big role. This can partly be accounted for with a Carbonate Correction Factor. Vs is significantly affected by particle shape and mineralogy. Mineralogy determines the cementation potential in a sand. qc-based criteria tend to be more material dependent than Vs-based criteria. Other factors that influence a correlation between qc-based and Vs-based liquefaction potential criteria are the compaction status (increasing the qc-based CRR more than the Vs-based CRR) and aging (increasing the Vs-based CRR more than the qc-based CRR). It is concluded that the intrinsic properties of the soil’s grains can explain to some extent its behavior when subjected to small or large strains, therefore explaining its resistance against liquefaction.

Questions remain around the use of the laboratory data that was gathered in the study, as testing samples are never from exactly the same location as the in-situ tests. This raises the issue on how representative the intrinsic particle properties are relative to the SCPTs used. The choice to limit the study to only the cyclic resistance ratio CRR is also discussed, as a safety analysis requires also the cyclic stress ratio CSR to get to a factor of safety, and the methods to determine susceptibility to liquefaction triggering that are evaluated in this thesis also differ in the procedure to determine the CSR. This study can therefore not be used for quantifying safety on site, but serves merely as a comparison of different liquefaction potential assessment methods, relative to each other. Finally, the legitimacy of the time-dependent increase in Vs is questioned with respect to liquefaction during an earthquake event, as the microstructure that was built up over time can be destroyed by the large imposed strains.

With the continued growth of the offshore sector and plans for new wind farm developments, shallow marine environments are becoming key areas for the renewable energy projects. As a result, the likelihood of encountering glauconitic sands is growing, posing challenges to the offshore wind infrastructure. Glauconite, or glauconitic sand, also known as ‘greensand’, refers to a soil containing peloidal sand-sized grains primarily comprised of mineral glauconite, an iron- and potassium-rich 2:1 interlayer-deficient mica. The tendency of glauconite to transform from sand to fine-grained soil with shearing creates uncertainties in site characterization and negatively impacts pile drivability to targeted depths. This thesis examines shearing behavior of glauconitic sands at soil-pile interface using two samples of Belgian glauconitic sands. With the final goal being the derivation of reliable interface shear strength parameters, the study aims to develop test procedures capable of capturing the transition of glauconitic sands from their natural uncrushed state to a reworked degraded condition, simulating the effects of shear-induced particle breakage during pile installation. To achieve this, a systematic experimental program was completed in two phases. The first part focused on glauconitic sands in their natural state and the second aimed to assess the degraded soil. Comprehensive material characterization, including geotechnical index tests, mineralogical analyses, and soil-steel interface direct shear tests under various conditions, was carried out to support each phase. The findings link the interface shear behavior and strength of glauconitic sands to their intrinsic properties, identify limitations in current experimental procedures, and offer recommendations for future research. New insights are provided into the behavior of Belgian glauconitic sands with the relatively low glauconite content and varying crushability potential. Interface roughness, shear rate, and normal stress effects are considered.

Large-diameter monopiles serve as foundations for offshore wind turbines (OWT), and the diameters are now up to 10 meters. These monopiles exhibit lower embedded length-to-diameter (L/D) ratios compared to the conventional monopile that is widely employed in offshore oil and gas platforms. They undergo rotation when subjected to lateral loading like rigid or semi-rigid bodies. This distinct geometry necessitates a different approach to describe the soil reaction that is induced when a lateral load is applied. Previous research introduced a 1D model incorporating four soil spring components to represent four aspects of soil reaction namely lateral soil reaction, distributed moment, base shear force, and base moment. However, questions have arisen regarding the contributions of base components, specifically the base shear force and base moment, to maintaining monopile stability. In response, a series of monotonic loading tests on monopiles in dry sand is conducted to assess the contributions of base shear force and base moment to monopile stability. Following this assessment of base components, parametric analyses are carried out to investigate the effect of pile diameter (D), the L/D ratio, load eccentricity (e), and sand relative density on monopile responses under cyclic and monotonic lateral loading. In this study, the SANISAND-MS material model is employed within 3D Finite Element (FE) software to model ratcheting during cyclic lateral loading. Finally, an investigation is conducted with the aim of constructing a 0D model to represent base shear force and base displacement responses under both monotonic and cyclic lateral loading.