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Parameter determination for hypoplastic model using an inverse analysis algorithm : a case study Northsea Sand
The hypoplastic model is an advanced constitutive model which can describe the mechanical behaviour of granular materials for a wide range of stress levels and soil densities. Niemunis and Herle (1997) improved the model performance in cyclic loading by introducing the intergranular strain stiffness. A series of valuable researches have been carried out in order to explain the role of each parameter. However, the individual roles of intergranular (small strain) parameters and the methods by which they can be estimated were rarely addressed. This paper introduces a methodology using both a parametric analysis and an automatic optimization algorithm to calibrate cyclic triaxial tests and to estimate the hypoplastic parameters, including the small strain ones. The materials being used in this study are sandy soils.
Climate-resilient roads in Paraguay : mapping the risks and advising adaptive mitigation measures
Transport infrastructure plays a crucial role in growth and development of economies and thriving communities. In Paraguay, the economy depends heavily on (agricultural) export; mainly through road network. Climate-related hazards such as extreme weather threaten the availability of the road infrastructure. Such hazards are expected to increase in the future with changing rainfall amounts and intensities, posing chance of higher frequency for events like precipitation induced floods and landslides. This can have a deleterious effect on transport infrastructure, such as road networks and railways, with large negative economic, social, environmental, and security aftermaths. In this paper, a case study from a World Bank funded pilot project is presented. In this project, Deltares and CSI Ingenieros have been working with the Government of Paraguay (GoP), through its Ministry of Transport and Communications (MOPC), on developing a strategy to assess climate change related risks on the road network and on how improve their resilience. The ROADAPT approach (Roads for today, adapted for tomorrow) was applied for assessing the risk and vulnerability of a part of the road network (pilot study area of over 300 km) and mitigation measures were suggested.
Revising the definition of fluid mud by establishing new protocols for rheological measurements
Fluid mud can be described as a mixture of water, organic matter and mainly cohesive mineral sediment that is usually found in estuaries and in rivers with low-intensity currents. It is in a transient state and can densify over time unless mixing (produced by mechanical and/or natural forces) prevents its gelling. Typically, fluid mud exhibits bulk densities between 1080 and 1200 kg/m3. It has a weak strength that, in low energetic conditions, develops over time forming a structured bed of considerably higher rigidity. The current definitions of fluid mud are based on the density of the sediment. These definitions are ambiguous since the proposed critical parameters do not account for the possible strength developments in fluid mud. We propose to use rheological properties for distinguishing the fluid mud layer from the suspension layer above and the consolidated mud layer underneath. The protocols involve the use of a rotational bob (Couette) rheometer that can perform oscillations, shear stress and shear rate controlled experiments. A number of natural mud samples were used for testing the protocols.
Combined subsidence phenomena in high-rise built urban areas : numerical study for Frankfurt am Main
In many megacities, excessive population growth and urban development have brought to heavy concentration of structural loads and marked increase of water demand leading to huge ground water extraction. This paper addresses the effects of both factors on ground settlement magnitude in areas where high-rise buildings prevail. For this purpose, referring to the case study of Frankfurt am Main (Germany), a numerical analysis of soil settlements under structural loads was performed for a selection of high-rise buildings resting on combined pile-raft foundations in overconsolidated clays. Then, at the scale of the single building, the contribution of groundwater withdrawals to the total predicted settlements was quantified via 2D-FEM model, thus highlighting the key role of pore pressure changes on settlement occurrence.
Overviewing geotechnical issues associated with levees and dams in Europe and USA
In ICOLD a working group has been working on levees since 2015, preparing both a levee situation overview of Europe and USA, and a comparison between dams and levees. In both resulting reports, levee characteristics, geometry, safety and technical standards, design rules, governance, management and knowledge gaps are discussed. Levee and dam engineers can learn from each other. Geotechnical issues are significantly featured. This paper will give an overview of levees in Europe and USA, with special focus on their geotechnical aspects, such as geometry, materials, subsoil, failure modes, design rules and safety standards. Also special attention will be given to site investigation and monitoring. In both levees and dams, understanding of the performance and of associated uncertainties is a challenge. In assessing safety, geotechnical issues like internal erosion and different types of instability are essential, especially in the initiation of failure and the breaching process. Given these common interests, cooperation between TC201 of ISSMGE and a recently established ICOLD Technical Committee on Levees is important and should be encouraged; this cooperation has already been initiated as some members are involved in both committees.
Large scale triaxial compression tests on three peat samples from Eemdijk, the Netherlands
The fibrous nature of peat introduces complexity in describing its mechanical behavior. Large fibres have sizes in the same order of magnitude as the dimensions of conventional specimen for laboratory testing. Therefore, size effects are expected when analyzing conventionally sized laboratory tests on peats. This paper shows the results of three large triaxial tests conducted on peat and gives a comparison with previously obtained results. In undrained shearing the pore pressure builds up until the lateral effective stress is reduced to zero. When shearing continues a (semi) drained stress path is followed. The samples fails along clear sliding planes, which are usually not found in conventional sized tests. This behavior can be explained by sliding or rupture of the fibres, which is dominated by displacement rather than strain. Failure is found at an elongation of the diameter in the order of 3 to 5 cm, equivalent to previously obtained results. The mobilized fibre reinforce-ment is in the order of 10 to 15 kPa.
Impact of the Eemdijk full-scale test programme
Levees in the Netherlands have traditionally been constructed from soil. Climate change and land subsidence require heightening and/or reinforcing these existing levees. Traditional reinforcements demand additional space, which in some cases conflicts with existing buildings. Applying sheet pile walls in levees allows for strengthening while minimizing needed footprint. However, a validated design approach that complies with relevant regulations lacked. To enable validation, a full-scale field test programme has been performed near the town of Eemdijk (The Netherlands). This has resulted in better insight in the soil-structure interaction of the structurally reinforced levee, on soft soil, loaded by high water and uplift conditions. This paper describes the rationale behind the test setup and operation of the test programme in relation to the current design codes and guidelines. First the set of knowledge questions to be resolved is considered. These questions gave direction to the type of failure tests, the required instrumentation and the impact of conclusions.
De pycnosonde, een bijzonder instrument
De pycnosonde is een meetinstrument dat vanaf een meetvlet of oever in het water wordt afgevierd tot de gewenste diepte tot enkele tientallen meters. Tijdens het weer ophalen worden opeenvolgende watermonsters door luchtdruk beheerst, verzameld in een glazen buis en bovengekomen wordt de dichtheid als functie van de diepte van het watermonster afgelezen met gekleurde duikertjes, de zogenaamde pycno-duivels. Op deze manier kan in een korte tijd (ten hoogste enkele tientallen seconden) een dichtheidsprofiel van de gehele gestratificeerde waterverticaal als gevolg van saliniteit- en temperatuurverschillen worden verkregen. Het grote voordeel is dat de dynamiek van de snel veranderende profielen gedetailleerd in de tijd kan worden vastgelegd.
NCR-days 2019 (Utrecht, January 31 - February 1, 2019) - Land of rivers : book of abstracts
Bloemrijke sterke dijken
Grote delen van onze dijken bestaan uit zachte, groene bekledingen met verschillende plantensoorten. Het is belangrijk dat de zode, bestaande uit grassen en kruiden, beschikt over een goed ontwikkeld wortelsysteem. Daarmee draagt een goed doorwortelde zode bij aan de erosiebestendigheid van het talud tegen golfklappen, golfoverslag en stroming. De soortenrijkdom van de begroeiing draagt bij aan robuustheid en veerkracht, en kan zich goed handhaven zowel onder omstandigheden van grote droogte en van overvloedige neerslag. Ook draagt een bloemrijke dijk bij aan landschap, natuur en cultuurwaarden. Deze factsheet gaat in op het wat, waarom en hoe van bloemrijke dijken.