Zakkende bodem voor beheerkosten een belangrijke factor: Mogelijkheden voor aanpassen van de Beheerkosten Openbare Ruimte (CROW publicatie 145)

Bij de aanleg én voor het beheer en onderhoud van gemeentelijke infrastructuur is de ondergrond een belangrijke kostenbepalende factor. Voor wegen speelt de draagkracht en vervorming van de bodem hierbij een belangrijke rol. Bijvoorbeeld een weg op een zandondergrond heeft minder intensief onderhoud nodig en heeft een langere levensduur dan op een klei- en veenondergrond. De onderhoudskosten, uitgedrukt in Euro per m2 per jaar, zijn op een zandondergrond dan ook aanmerkelijk lager dan op klei en veen. Voor veel gemeenten met een veenondergrond is de situatie ten aanzien van het onderhoud onbeheersbaar. Door een hoge zettingssnelheid bereikt de drooglegging eerder dan de kwaliteit van de verharding het interventieniveau. Daardoor is niet de kwaliteit van de verharding maatgevend voor de rehabilitatie (ook wel reconstructie genoemd), maar de drooglegging. Het onderhoud wordt hierdoor veelal budgetgestuurd, zodat de kwaliteitslijn in de tijd een dalend verloop heeft. Uiteindelijk resulteert dit in een ‘pappen en nathouden’ aanpak. De onbeheersbare situatie heeft diverse oorzaken, zoals het ontbreken van specifieke technische kaders voor het maken van keuzes of het tekort aan onderhoudsbudget. Dit rapport maakt onderdeel uit van het project “Duurzame Onderhouds Strategie voor voorzieningen op slappe bodem” (verder: DOS). Doel van het DOS project is het leveren van technische know-how voor de afweging van onderhoudsmaatregelen op basis van kosten en maatschappelijke factoren. De technische kaders worden daarmee ingevuld

Removal of both dissolved and particulate iron from groundwater

Iron is the primary source for discolouration problems in the drinking water distribution system. The removal of iron from groundwater is a common treatment step in the production of drinking water. Even when clear water meets the drinking water standards, the water quality in the distribution system can deteriorate due to settling of iron (hydroxide) particles or post-treatment flocculation of dissolved iron. Therefore it is important to remove dissolved and particulate iron to a large extent. This paper describes the study towards the current iron removal processes and experimental work towards improving removal of dissolved and particulate iron. The study was carried out at groundwater treatment plant Harderbroek, consisting of aeration, rapid sand filtration and tower aeration. The research contains two parts: 1) a particle fingerprint of the treatment, resulting in a quantification of particles breaking through the rapid sand filtration. 2) Small column experiments on the oxidation and filterability of iron. The fingerprint showed that operational events such as switching on/off of filters and backwashing have a significant impact on the volume concentration of particles breaking through the filter. A frequency plot of the different size ranges of particles indicates that mainly the filterability of the middle size ranges (2–7 ?m) of particles was influenced by switching a filter on/off. A backwash event mainly affects the bigger particle size ranges. The column experiments showed that in the cascade effluent the majority of the iron is dissolved iron(II), indicating that the oxidation of iron(II) to iron(III) is the rate determining step at Harderbroek, which is limited by pH. Dosing caustic soda resulted in a significant increase of the oxidation rate and improved the removal of iron(II) in the column. Crushed limestone filtration gave promising results, but the contact time applied was too short to completely oxidize iron(II).Civil Engineering and Geoscience

GNSS ambiguity resolution: Which subset to fix?

A key issue with GNSS carrier phase ambiguity resolution is that often the full set of ambiguities cannot be fixed fast and reliably. A possible strategy is then to resolve only a subset of ambiguities, one for which the probability of correct fixing, the so-called success rate, is sufficiently close to 1. However, a proper subset selection criterion is still lacking. This criterion should on the one hand guarantee an acceptably high success rate, and at the same time result in a significant performance improvement with respect to the remaining parameters, like the baseline parameters. The second requirement is important and has not yet been addressed in literature. As an extreme example consider the case where the float ambiguities are not correlated with the other float parameters. Ambiguity resolution would then be useless, since it will then not allow for an improvement of these other parameters. This indicates that resolving a subset of ambiguities (in the extreme example, an empty subset) may lead to the same, or almost same, performance improvement of the other parameters, notably the baseline solution. This contribution presents two approaches to subset selection, where both the requirements on success rate and performance improvement are taken into account. With this approach the user can set a threshold for the success rate to be obtained. It will be shown how much better the baseline solution will be after reliable fixing of the subset of ambiguities.Geoscience & Remote SensingCivil Engineering and Geoscience

Assessment of ionospheric corrections for PPP-RTK using regional ionosphere modeling (PPT)

Power Point PresentatieMathematical Geodesy and Positionin

SBW project werkelijke sterkte: Projectplan 2009

Het SBW programma heeft als doel onderzoek uit te voeren voor de nieuwe VTV 2011. Het SBW project getiteld werkelijke sterkte beoogt dit te realiseren voor het toetsspoor macrostabiliteit. Dit rapport beschrijft de planning van de werkzaamheden voor 2009 en geeft inzicht in de verwachte werkzaamheden in 2010. Thans is voorzien dat het project in 2010 wordt afgerond.SB

Assessment of ionospheric corrections for PPP-RTK using regional ionosphere modelling

Mathematical Geodesy and Positionin

Performance and thermoregulation of Dutch Olympic and Paralympic athletes exercising in the heat: Rationale and design of the Thermo Tokyo study: The journal Temperature toolbox

The environmental conditions during the Tokyo Olympic and Paralympic Games are expected to be challenging, which increases the risk for participating athletes to develop heat-related illnesses and experience performance loss. To allow safe and optimal exercise performance of Dutch elite athletes, the Thermo Tokyo study aimed to determine thermoregulatory responses and performance loss among elite athletes during exercise in the heat, and to identify personal, sports-related, and environmental factors that contribute to the magnitude of these outcomes. For this purpose, Dutch Olympic and Paralympic athletes performed two personalized incremental exercise tests in simulated control (15°C, relative humidity (RH) 50%) and Tokyo (32°C, RH 75%) conditions, during which exercise performance and (thermo)physiological parameters were obtained. Thereafter, athletes were invited for an additional visit to conduct anthropometric, dual-energy X-ray absorptiometry (DXA), and 3D scan measurements. Collected data also served as input for a thermophysiological computer simulation model to estimate the impact of a wider range of environmental conditions on thermoregulatory responses. Findings of this study can be used to inform elite athletes and their coaches on how heat impacts their individual (thermo)physiological responses and, based on these data, advise which personalized countermeasures (i.e. heat acclimation, cooling interventions, rehydration plan) can be taken to allow safe and maximal performance in the challenging environmental conditions of the Tokyo 2020 Olympic and Paralympic Games.Emerging MaterialsSustainable Design Engineerin