Land subsidence is a complicated phenomenon, relevant in the Holocene coastal-plain of the Netherlands, that can be triggered by many different mechanisms and components. To cope with the effects of land subsidence, detailed information on which mechanisms are causing subsidence and its variation over time and space are needed. Subsidence studies predominantly focus on grass and agricultural areas with organic soils above the groundwater level. In this study, subsidence is also evaluated for dikes and the urban environment. It is attempted to model subsidence behaviour of four different projects, grass plots within the Krimpenerwaard polder, locations along the N3 Dordrecht, an embankment constructed for the A5 Badhoevedorp and locations along the Markermeerdikes, and to verify these model results with subsidence measurements available. Existing one-dimensional models for different subsidence components are used in the evaluations. For grass and agricultural areas it is found that subsidence behaviour could be modelled and the results lie within the range of uncertainty of the subsidence measurements used. However, the equations used are often empirical and do not include all relevant influencing factors and couplings. Compression by degradation of organic material as a response to drainage of organic soil is the main subsidence component in these areas. Anaerobic degradation of organic material is also included in the modelling approach, a component that is often neglected in other subsidence studies. Two infrastructure related projects provided insight to subsidence components in the urban environment. Compression by loading is the main subsidence component relevant in this area type, and thus settlement models are suitable to approximate the subsidence behaviour. However, a slight underestimation of creep shows that the existence of a small additional subsidence component for a situation with soft soil layers pushed below the water table could not be excluded. Unravelling subsidence behaviour from dikes showed to be more complicated, where an interplay between different components is relevant. Based on the evaluation in this study compression by loading and compression by an oxidation or shrinkage component are indicated the main subsidence components. Many uncertainties and assumptions used in this evaluation influenced the results. For all area types disentangling subsidence into contributions of separate components based on a total measured subsidence signal causes large uncertainties, as modelled subsidence contributions for individual components could not be verified.

Mechanical dredging of a stiff clay results in clay lumps. Those clay lumps can be reused for the construction of land reclamation projects, and hereby economic and environmental value is generated. Placement of the clay lumps
in water result in a matrix of clay lumps and an interlump void space. The collapse of the interlump void space will cause large settlements and needs to be overcome before the site can be used for construction. Preloading is
an effective method to close the interlump voids. Stiff clays soften over time due to unloading and swelling. As a result, the strength and stiffness of the clay lumps decrease over time. The presence of discontinuities accelerates
the softening process. It was proposed by Leung et al. (2001) that the interlump void space closes under a reduced
preload of 25 kPa. The interlump void space closes under a reduced preload because the lumps soften over time.
The question rises if closure occurs within a normal construction timespan, i.e., 1 - 2 years, under this reduced
preload. In this study, a combined experimental and numerical approach is applied to determine the influence of soil
characteristics, softening and the presence of discontinuities on interlump void closure. The influence of softening due to chemical and hydro-mechanical swelling is tested by experimental swell-load tests on stiff overconsolidated
Boom clay samples. Additionally, the presence of discontinuities is studied by CT images, and a miniature clay fill test is performed to study the softening time and the rearrangement effect. Furthermore, a numerical study is performed in which the influence of specific soil characteristics on void closure was researched by a sensitivity analysis. By the experimental tests, it is shown that a pore water chemistry change alters the degree of swelling and its compressibility. Furthermore, fissures were identified in the sample material by CT images. The smallest microfissures could not be identified due to the resolution of the images. Consequently, it is impossible to estimate the effect of fissures on the hydraulic conductivity. Therefore, literature data was used to estimate the hydraulic conductivity and this was used as the input in the calculations. In the numerical study, it was shown that MPM could model the softening behaviour over time. The sensitivity analysis showed that the MPM model responds consistently to parameter sensitivity analyses. This leads to the conclusion that MPM can be used as a investigation tool to increase
the understanding of the influence of parameter variability on the final interlump void closure problem. The resulting strains of the numerical model comply with the theoretically calculated strains. It was expected
that the numerical strains were smaller than the experimentally determined strains, due to the presence of interlump voids in the numerical model. But, the numerical strains are larger than the experimental strains. In the sensitivity
analysis, it was found that the final strains and closure time are highly dependant on the soil characteristics. It is likely that the input of the MPM model differs compared to the true sample material and thus different strains result.
The time until the interlump void space closes was determined by a simplified geometry in MPM under a preload of 25 kPa. For an unfissured Boom clay, interlump closure takes place after approximately 16 years while for a
fissured Boom clay it only takes 2 months. Thus, closure of the highly simplified geometry takes place within a normal construction timespan for a fissured Boom clay. It must be kept in mind that the results are highly dependant
on the geometry, lump size and soil characteristics. Therefore, these results can not be generalized into an estimate of the interlump void closure time for any stiff lumpy clay fill. In conclusion, the feasibility of MPM was explored and it turned out to be a promising method to model the interlump void closure problem. Further studies are required to check if the model gives plausible results for more advanced constitutive soil models and geometries. If the results are positive, MPM can be used as a investigation tool to increase the understanding of the interlump void closure time for more refined geometries.

Reinforcing levees with traditional methods is becoming more difficult in the Netherlands. Often there is a lack of space near the levee or it is desired that the landscape is maintained. Because of this, alternative methods for reinforcing levees are still sought after (CUR-commissie C141, 2007). In this study, the technical feasibility of a possible alternative reinforcement method for regional flood defences is studied: mass stabilisation. Mass stabilisation is a soil improvement technique with which soft soils are mixed with a binder on site and in-place to create a stronger soil layer (Forsman et al., 2015). It is presumed that mass stabilisation requires no extra space at the levee, does not affect the landscape and requires little transportation of materials. For determining the technical feasibility of applying mass stabilisation for reinforcing regional flood defences, three criteria have been examined. First, the ability of mass stabilisation to solve a stability deficit at levees was examined using two-dimensional stability analyses. Secondly, the achievability of the required effective strength parameters in compliance with Dutch standards was examined in the laboratory. Thirdly, the practicability of mass stabilisation at levees was examined using two-dimensional stability analyses. Although the results of this thesis have shown that mass stabilisation is a technically feasible technique for reinforcing regional flood defences, further studies will be required before a definitive conclusion can be drawn. It is therefore recommended that additional analyses into the practicability are carried out and that the relationship of the properties and the variability thereof between soils stabilised in the laboratory and the field is studied.

Around 55% of The Netherlands is protected by flood defences like dikes. Flood defences must meet requirements which are based on an allowed flood probability. Safety assessments are performed to check whether flood defences meet these requirements. Uncertainties are explicitly included in safety assessments. Uncertainty in soil behaviour is one of the major contributors to failure probability of dikes. Therefore reduction of this uncertainty in soil behaviour leads to potential savings in reinforcement costs. One of the uncertainties in soil behaviour is the effect of aging on the behaviour of soft clays in compression. Compression behaviour of clay is strongly dependent on the transition from overconsolidated to normal consolidated soil behaviour. This transition phase in plain-strain conditions is indicated by the yield stress. The development of the yield stress due to aging is described by isotach models in terms of creep strains and stiffness parameters. Examples of isotach models are the abc-model and PLAXIS’ Soft Soil Creep model (SSC-model). According to those isotach models, a yield stress induced by aging is similar to a yield stress induced by unloading. This study verifies the development of the yield stress predicted by abc-models based on K0-CRS tests. The test material is remoulded, highly organic, silty clay with a liquid limit of 165% and a plastic limit of 56% (OVP-clay). The determination of the abc-parameters is not straightforward. The value for the creep parameter is easily overestimated due to a slow decrease in excess pore water pressure during a constant stress phase, resulting in stress-dependent strains instead of creep strains. The b-parameter is affected by the gradual transition from overconsolidated to normal consolidated behaviour and by the development of structure during aging. The development of structure is not included in the isotach models and could result in a higher yield stress than predicted by the isotach models. The possible increase of the yield stress due to the development of soil structure is not visible in the test results, but the performed tests indicate softening behaviour after aging phases. The SSC-model simulates no increase in lateral stress during aging. Some studies present data showing that the lateral stresses increase under a constant effective stress in time. Unfortunately, the development of lateral stresses cannot be quantified based on the performed tests due to stick and slip behaviour in the K0-ring during laboratory testing. Based on the test can be concluded that a minimum yield stress in time can be predicted based on isotach models. An important note is that a yield stress is always obtained with respect to a certain isotach which is dependent on the loading rate and the creep parameter. The shift of the yield stress from the imposed isotach to the reference isotach is often significant in laboratory tests, but not taken into account. Effects of development of structure during aging should be further investigated: it influences the behaviour of the soil in compression and affects the yield stress determination.

In this study, the assessment of the KIJK dike follows the new guidelines given by POV-M 2018 using PLAXIS. The macrostability assessment and design of the dike is examined for two cases. In the first case the dike is assessed based on the in-situ conditions (Green dike) whereas in the second case a cantilever sheet pile wall is used in the design (Blue dike) to strengthen the dike. Prior to the analysis the interpretation of the available laboratory data that were executed according to the new protocol (WBI 2017) and the parameter determination of the necessary input parameters of the considered constitutive models (SHANSEP NGI-ADP, Hardening Soil, Soft Soil models) is established. The undrained shear strength (su) of the SHANSEP NGI-ADP model is based on the SHANSEP concept and the normalised su (S (NC, OC)) and the strength increase exponent (m) parameters are needed. For the HS and the SS models the effective strength parameters φ and c are required.
The FoS is determined with the use of the strength reduction method. Moreover, the CSSM framework is coupled with the SHANSEP (Stress History and Normalized Soil Engineering Properties) concept enabling the incorporation of the effect of stress history and the stress path characterizing the undrained shear strength in the design. The CSSM framework is applied in the design by determining the strength parameters of clays from an axial strain level equal to 25% under triaxial compression whereas for peats at 40% shear strain level under direct simple shearing conditions. In this study the strength parameters were additionally determined from the service conditions strain levels which are the 2% and 5% strain levels for clays and peats, respectively. The necessary strength parameters for the constitutive models are determined in the considered strain levels exposing their influence for both clays and peats. Moreover, the study includes the examination of the constitutive models at a single element level conducted in the Soil Test facility available in PLAXIS. When it comes to the design analysis, it was found that the SHANSEP NGI-ADP model fits properly the su determined from a cone penetration test. The HS and SS models based on the effective strength parameters may result in an undrained shear strength profile which deviates from the su that the soils exhibits in the field.
The study points out that both the strain level dependency of the strength parameters and the selection of the constitutive model at critical loading influence the results in terms of the developed failure plane and the FoS, especially in the case of Green dikes. The study also elaborates the response of the models in regard to the design requirements for the calculation of displacements and the structural forces. Finally, this study answers the knowledge gap regarding how the strain level influences the strength of the examined soils and how this should be translated in the design along with the explanation on the effects of the selected constitutive model on the results.

Tunnel construction projects in the western part of the Netherlands are typically built in soft, heterogeneous ground conditions with low stiffness and high groundwater tables. The tunnelling technique used is the ‘slurry shield’ method, which uses a tunnel-boring machine (TBM). The TBM consists of a steel cylinder with a cutting wheel at the front. At the face of the TBM, called bore front, a pressurised slurry is used as face support. The aim of a static tunnel face stability assessment is to determine the horizontal effective stress and pore water pressure acting at the tunnel face both during boring and a standstill. While the pore water pressure distribution along the tunnel is clear, the estimation of the horizontal effective stress distribution is difficult. At the moment many calculation models have been developed to calculate the latter, but none ever made it into a standard. The first part of this thesis consists of a comparative study between the Ruse-Vermeer (2002), Jancsecz-Steiner model (1984) and DIN4126+4085-model (2008). A theoretical background analysis has been performed for each model; by using a case study analysis, the effect of the models’ differences on the minimum support pressures has been determined. Thereafter, this theoretical analysis has shifted to a more ‘practical’ project analysis by including external aspects like project aspects, soil conditions and contract requirements. From the practical project analysis it resulted that at the entrance zones, the soil cover is limited and thus additional surcharge is required. The placement of this additional surcharge lead to consolidation in the subsoil which can subsequently influences the static face stability assessment. Within this research a model is proposed in order to incorporate a one-dimensional vertical consolidation analysis within face stability assessment. During tunnelling a continuous process of slurry penetration and excavation takes place and therefore, the interaction between the support fluid, advancement of the TBM and the soil needs to be taken into account. The combination of these two time-dependent effects can possibly lead to the build-up of excess pore pressures in front of the tunnel face which has a high influence on the minimum support pressure. The second part of this research investigates the possibility to include the time dependent effect of slurry infiltration and excavation within a face stability assessment e.g. transient face stability assessment. The last part of this research is based on the role of slurry TBM parameters on ground deformations. Due to overcutting and the tapered shape of the TBM, a joint (annulus) is present between the TBM and the soil formation. In this research it is assumed that the annulus is hydraulically connected to the face. This means that the annulus is pressurized with bentonite slurry originating from the face. Due to the slurry pressure gradient and hydraulic connection with the annulus, not at each location the exact geostatic stress can be reached and ground deformations will inevitably take place.

Four kilometers west of the Norwegian island Fedje, mercury, leaking from the U-864 wreck, has highly polluted a seabed area of approximately 40 000 m2. The bow section of the wreck is located on a stability critical slope of 15 degrees. In 2016, Van Oord used a flexible fall pipe system to install a counter fill to stabilize the wreck and simultaneously cap a portion of the contaminated area. In the future, the Norwegian government plans to cap the complete area to prevent further dispersion of mercury. This research aims to gain more knowledge about the spreading of sediments during such an operation occurring under realistic hydrodynamic conditions. A more complete understanding of the process will allow for better risk assessment of future capping operations. To this end, the unique data set gathered during the counter fill project has been analyzed.

In order to predict extreme flow events, the bottom currents are decomposed. By decomposing the erratic velocity signal, tidal (25 %) and inter-tidal residual current (38 %) components are identified and understood. However, the driving force for the remaining intra-tidal part, which contains the highest current anomaly events, cannot be identified. Evidence is found for the occurrence of internal waves providing a possible explanation. Due to a lack of data, a quantitative prediction cannot be made. Consequently, the exact maximum currents at the site are unpredictable, but stayed below 0.4 m/s during the project.

During the installation work, high turbidity clouds have been measured. The origin is investigated by analyzing the particle size distribution and the mercury concentration of sediment samples; said samples are drawn from the capping material, the installed capping layer and sediment traps placed around the wreck. The findings indicate that the clouds are caused by a loss of clean material and are not from the contaminated seabed. This is supported by modeling the dispersal of clean particles from the flexible fall pipe. The promising results regarding the use of a flexible fall pipe for capping layer installation are not only applicable for the U-864 area but also for other polluted offshore areas.