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A coarse sand barrier as an alternative preventive measure against backward erosion piping
Backward erosion piping is an important failure mode concerning the stability of levees along the main rivers of the Netherlands. The threat has strongly increased because of the expected effects of climate change and tightened assessment rules including higher safety demands and adapted calculation models. In order to prevent the development of a continuous pipe in a sand layer underneath an impervious levee, a barrier made of much coarser sand can be placed in the course of the growing path. Due to the larger grain size of the barrier particles, increasing erosion resistance, and the relatively high permeability in comparison with the surrounding material reducing the load on the barrier, the levee can withstand a larger head drop, resulting in a much higher safety level for the levee. As it does not take up any extra space and may be relatively easy to install, the use of a coarse sand barrier could be a good alternative to conventional prevention measures. To determine the strength of different barrier materials and to get a better insight in the principal mode of action and the scale effects, experiments at different scales have been performed. The research shows that a coarse sand barrier is a highly effective piping inhibiting measure. This paper presents two large-scale experiments that have been carried out in the Delta Flume facility of Deltares.
Modelling rainfall-induced landslides with the material point method : the Fei Tsui Road case
Rainfall-induced landslides seriously affect the safety of residents and properties in the surrounding area. In particular, landslides exhibit large mobilized volume with very large displacement. For this reason, the numerical modeling of a landslide is a challenging problem, as it requires a good pre-failure and post-failure description after large deformations process. For this reason, a dynamic fully coupled model using material point method is proposed to describe the landslide failure problem from the triggering phase until the complete runout. The Fei Tsui Road landslide in Hong Kong is used as a case study for the validation of this numerical tool.
Numerical simulation of impact driven offshore monopiles using the material point method
Impact driven monopiles are widely used in the construction of offshore wind turbines. The pile installation leads to soil disturbance in the vicinity of piles, which might affect their bearing capacity. A good understanding of the effect of pile installation on the bearing capacity of piles will lead to significant cost re-duction in the construction of wind parks. However, due to the limitations in the common numerical methods (e.g. the finite element method) the effect of pile installation is not considered because it involves complex large deformation analyses, which are problematic. In this study, the Material Point Method (MPM) is used to simulate the installation of a real monopile, driven in the North Sea, to demonstrate the capability of MPM to simulate the installation of monopiles using results of the field test.
Simulation of a mini slump test using a visco-hypoplastic constitutive model in an MPM code
Tailings dams are some of the largest earth structures geotechnical engineers construct. These embankments are often built with steep slopes using the coarse fraction of the tailings thereby saving on cost. To keep such impoundments standing is one of the most challenging tasks in mine waste management. This paper presents a procedure that can be used to model the behaviour of the material stored by these dams. The constitutive model proposed by Niemunis et al. has been implemented in a UMAT subroutine with the explicit integration method proposed by Fellin and Ostermann. This model is able to describe the behaviour of soft soil because it includes the simulation of the viscous behaviour that is characteristic for these types of very soft, unstructured soils. The procedure explained in this paper is a first simulation of the behaviour of these materials through a visco-hypoplastic constitutive model implemented in a MPM code.
Evaluation of mechanical properties of cement treated soils with different plasticity
This study examines the compression and strength properties of cement treated clays with various plasticity index. Clay samples with different plasticity were obtained by mixing kaolin and montmorillonite at different ratios. Clay blends were treated with cement in percentages of 3, 6 and 9 % in terms of the dry mass of clay blends and the amount of water content for each clay blend was set to the optimum water content. Besides, a group of cement free specimens were prepared for comparison reasons. All specimens were cured for 7, 28 and 90 days in a humidity-controlled room at a constant temperature. After curing, specimens were subjected to unconfined compression, ultrasonic pulse velocity tests.
Eemdijk full-scale field test programme : ground dike and sheet pile dike failure test
Dikes in the Netherlands have traditionally been constructed with soil. Climate change and subsidence requires heightening and or reinforcing these existing dikes. Traditional reinforcements demand additional space, which in some cases conflicts with existing buildings. Applying sheet pile walls in dikes allows for strengthening while minimizing the increase in footprint. However, a validated design approach that complies with relevant regulations lacks. To enable the validation of a proposed design approach, a full-scale field test programme (Eemdijkproef) was performed near the town of Eemdijk, The Netherlands. It consisted of a step wise approach: 1) sheet pile pullover tests, 2) ground dike stability test, 3) sheet pile dike stability test. All tests were loaded until failure occurred. The two similar test dikes were constructed at full scale (5m high, 25m wide, 60m long). In one dike an 18m long sheet pile wall was installed. This paper presents the test setup, monitoring, measurements and first findings. The test program provides better insight in the soil-structure interaction of the reinforced dike, on soft soil, under high water and uplift conditions. Ultimately this will lead to a validated design approach for sheet pile walls in dikes.
Pressure drop in vertical pipes of sand boils
Backward erosion piping is a threat for relatively impermeable dikes that are founded on a sandy, more permeable subsoil. Groundwater flow concentrates on the boundary between the impermeable layer and the sand and may cause erosion of the sand grains. The driving force is the head difference over the dike. If the sand on which the dike is founded is overlain by a relatively impermeable layer of clay or peat, backward erosion piping is only possible if there is also a vertical flow through a defect in that impermeable layer. The head loss in the vertical defect is of importance since it reduces the head loss over the horizontal pipe. Up to now, a rule of thumb is used to determine this vertical head loss. From a theoretical perspective, the head loss depends on the flow velocity in the vertical pipe and can be between 0*d and 1*d (with d the thickness of the impermeable layer). A calculation model is presented in this paper to relate the head loss in the defect to the groundwater flow towards the defect.
Vacuum consolidation trials to validate strength increase of peaty subsoil for dike stability
There is an increasing demand in the Netherlands for innovative solutions to increase the (macro) slope stability of dikes. This is mainly caused by new insights into the calculations method, increased safety regulations with climate change related higher design water levels, limited working space and a large amount of interfaces. Vacuum consolidation techniques have proven their efficiency in infrastructural and reclamation projects to reduce residual settlements. However, the technique has not been used with the sole intention to increase the soil strength in dike design before. It can have important advantages over traditional solutions. This paper presents the factual data and findings of vacuum consolidation trials performed on the Markermeerdijken project in Schardam, the Netherlands. Two trial areas were set up using different vacuum consolidations systems to consolidate the peaty subsoil: a traditional vacuum system and the Beaudrain-S system. The trials were performed to validate the (undrained) shear strength increase of the peaty subsoil. Several in situ tests and lab tests on subsoil samples were performed before and after consolidation such as DSS, Triaxial and (spherical) CPT testing. Before installation of the equipment only a limited working platform of relatively lightweight flugsand was applied to research solely the effects of the vacuum pressure on the strength increase. During the trials vacuum pressures were measured in the soil and in the drains using piezometers. Additionally, settlements were measured during consolidation as well as swelling after consolidation. For both areas a total pumping time of 13 weeks was applied and settlements up to 1.5m were measured under vacuum pressures of up to 70KPa. The laboratory test results of subsoil samples showed a considerable increase in undrained shear strength, corresponding to theoretical models.
Adaptieve lange termijn strategie voor de drinkwatervoorziening in de Provincie Flevoland
De Provincie Flevoland en drinkwaterbedrijf Vitens streven een duurzame drinkwatervoorziening na, die voldoet aan de wettelijke kwaliteitseisen en die voldoende water levert. De drinkwatervoorziening maakt zoveel mogelijke gebruik van langdurende bronnen die zo min mogelijk bloot worden gesteld aan externe risico’s en die aanvaardbare effecten heeft op de omgeving. De onzekerheid qua drinkwatervraag en ruimtelijke ontwikkelingen en het belang van een betrouwbare drinkwatervoorziening vragen om een veerkrachtige drinkwaterinfrastructuur. Veerkracht wordt bereikt enerzijds door robuuste bronnen in te zetten en een robuuste infrastructuur aan te leggen, anderzijds door flexibiliteit in te bouwen om in te kunnen spelen op onzekerheden. Deze verkenning levert, uitgaande van deze ambitie een eerste versie op van een adaptieve strategie voor de lange termijn drinkwatervoorziening in de provincie Flevoland. De strategie is adaptief, omdat in de strategie expliciet rekening wordt gehouden met onzekerheden op de lange termijn, in dit geval ontwikkelingen in de drinkwatervraag in de provincie Flevoland. Met behulp van een monitorings- en signaleringsysteem worden periodiek ontwikkelingen gemeten en indien nodig wordt de strategie aangepast.
Indicatoren voor de kwaliteit van habitattype H1110 in PMR-NCV
Van 2009-2013 vond de eerste fase plaats van de monitoring van de effecten van de natuurcompensatie in de Voordelta, in verband met de Tweede Maasvlakte (MV2). Eén van de effecten van de aanwezigheid van MV2 was het verlies van areaal van habitattype H1110 ("Permanent met zeewater van geringe diepte overstroomde zandbanken"). Als compensatiemaatregel is een bodembeschermingsgebied in een deel van de Voordelta ingesteld, waar boomkorvisserij met wekkerkettingen door schepen met een vermogen van meer dan 260 pk (boomkorvisserij op platvis) is uitgesloten. Het doel van de maatregel is een verbetering van de kwaliteit van het habitattype H111O. In de doelen van het monitoring- en evaluatieprogramma voor de natuurcompensatie (MEP-NCV) uitgevoerd van 2009 tot en met 2013 is voor de kwaliteit van habitattype H1110 sterk de nadruk gelegd op biomassa van bodemdieren als primaire parameter. Dit rapport heeft als doel na te gaan welke alternatieve indicatoren beschikbaar en geschikt zijn om de effecten van de compensatiemaatregel op de kwaliteit van H1110 te beschrijven. Uitgaande van de profielbeschrijving van dit habitattype, en een inventarisatie van beschikbare indicatoren is aan de hand van een aantal criteria een evaluatie opgesteld van de geschiktheid van de beschikbare indicatoren voor toepassing in PMR-NCV kader. Een voorstel wordt gedaan voor een aantal kwalitatieve en kwantitatieve indicatoren, met de kanttekening dat voor alle indicatoren geldt dat het verband tussen het voorkomen en intensiteit van boomkorvisserij op platvis en de respons van de indicatoren niet hard onderbouwd is. Het verdient daarom aanbeveling de indicatoren in samenhang te beschouwen middels deskundigenoordeel en het totaal van de resultaten te toetsen op plausibiliteit van de relatie met visserij.