Grondgedachten

Civil Engineering and Geoscience

Nonlinearity in groundwater flow

Since 1856 when Darcy laid the basis for the calculation of the flow of water through sands, researchers have been interested in groundwater flow. Groundwater is essential for agriculture and water supply, but it also plays an important role when soil is used as a construction element, such as for dykes, roads and foundations. The mechanical behaviour of saturated or dry, fine graded or coarse soils are quite different. The theory of groundwater mechanics must be based on the system: water-soil-air. Up to now study has been restricted to mainly saturated and/or undeformable soil. In this thesis the contemporary theory is extended to compressible fluid flow in a semi-saturated deformable porous medium; a water-soil-air mixture, the air in which appears in the form of micro-bubbles. The pore water moves, whereas the soil itself deforms. It is assumed that this deformation behaviour is linear and free of rotations. From a fundamental reconsideration it is shown that the mechanical behaviour of this system can be formulated in a rather simple way taking into account various nonlinear effects. Convective terms and the variation of the permeability related to soil deformation are included. The validity of the formulation derived is discussed. A general solving procedure applying the Mellin transformation technique allows elucidation of the influence of these nonlinear terms on the basis of analytical solutions of some characteristic problems. In the phenomenon of groundwater flow so-called moving boundaries also occur. The free surface of natural groundwater, which actually varies, is such a boundary. This implies that the domain in which the process of porous flow is considered, changes (geometric nonlinearity). This aspect is explained. Transient phreatic porous flow problems can be solved by applying numerical models. In the discussion reference is made to the extensive literature. In conclusion, the following statements hold for nonlinear groundwater flow. In most practical cases the linear theory is sufficiently accurate, nonlinearity becomes manifest in a reduction of the area of influence, and time dependent porous flow problems can be explicitely solved applying a time step much larger than formerly assumed.Hydraulic EngineeringCivil Engineering and Geoscience

Een dijk in de branding

Het effect van golfkrachten op een dijklichaam.Asfaltbekledinge

Syllabus Grondwatermechanica CTwa3320

Civil Engineering and GeosciencesWaterbouwkund

An extension of Lauwerier’s Solution for heat flow in saturated porous media

One of the crucial topics in this century is sustainable energy. Since the sources of fossil fuels are limited and are going to be exhausted, there is a need to look for sustainable renewable energy. In this respect, the exploitation of geothermal energy from deep hot aquifers becomes opportune. Hence, insight is required in the heat balance of potential aquifer systems. Essential issues are convection, conduction and dispersion. Modeling such processes is affected by numerical errors when using computer models and by the complexity of analytical solutions. This article focuses on Lauwerier’s problem. As an extension, it is suggested that beside convection in the aquifer and conduction to adjacent layers also conduction in an aquifer can be considered in a simple way. For a characteristic situation, a comparison is made with the result of the numerical code COMSOL. This gives new insight in the possible misjudges of heat transport simulations due to numerical effects and in the applicability of models.Geo-EngineeringGeotechnologyCivil Engineering and Geoscience

Groundwater mechanics, flow and transport

Civil Engineering and GeosciencesHydraulic Engineerin

Computer aided evaluation of the reliability of a breakwater design

The risk~analysis offers a method to determine the probability that an important function of a structure is no longer fulfilled (failure or malfunctioning). This probability should be selected having in mind the minimization of the generalized cost of the structure and the maximization of its utility (Minimax). Comparison of the contribution of failure mechanisms to the total probability of failure of a design leads the way to rational improvement of a design and to further research directed towards the improvement of weak elements in the design. In a complex structure like a rubble mound breakwater with a crest wall, many events (accidents) can be distinguished which may lead directly or indirectly to failure of the structure. Hydraulic and geotechnical stability as well as material failure by fracture or loss of position, must be considered. Failure may start in the toe, near the berm, on the slope, at the crest or on the inside slope, and it may progress into total failure with time (accident sequence). Failure of the structure should be carefully defined. The choice of the definition will predispose the meaning of the calculated probability of failure. The more precise the definition the clearer the physical meaning and the better the insight presented through the failure probabilities. A clear and detailed definition can be achieved in a fault tree, which in a logical sequence states the possible causes leading to eventual failure. The CIAO project group limited the scope of work in this report to the following activities: * reviewing the reliability theory and risk analysis * indicating the simulation models available for the various failure mechanisms performing a case~study for a rubble mound breakwater, applying the risk~analysis to relevant failure mechanisms and calculating the probabilities of failure using a fault tree approach * evaluating results of the case~study. The underlying theory of the risk~analysis is only presented in outline. Much work is presently done to further develop applications [7,9,10], In essence it depends on the reader to which degree of sophistication he wants to formulate failure. The project group elaborated an existing design following the probability theory. It would ofcourse have been better to evaluate design alternatives, but this was not possible within the time available. The case study is the substantial part of the work of the project group. Again, it is only an illustration of how the risk~analysis can be applied, leaving the reader free to simplify or extend the method. The geometry of the rubble mound breakwater used in the case study and its composition are shown in Figure 1.2.1. Actually, it is an existing breakwater, the available information of which has been F.C. de Weger BV, missing data necessary for the study have been fancied as reasonably as possible. Therefore, the outcome of the study cannot be conceived in absolute sense reflecting the reliability of the existing breakwater

Twee watervoerende lagen met semi-doorlatende scheidings- en afdeklaag: Tijdsafhankelijke grondwaterstroming onder dijken ten behoeve van een peilbuizennet langs Nederlandse rivieren

In het kader van het onderzoek van een peilbuizennet langs de nederlandse rivieren, is er een studie uitgevoerd naar de effecten van een geinstalleerde bron in een twee-lagen systeem; een watervoerende zandlaag en een afdekkende klei- of veenlaag [2],[3]. In dit rapport wordt aan de hand van bovengenoemde studie, de vergelijkingen beschreven van twee watervoerende zandlagen, gescheiden en afgedekt door consoliderende klei- of veenlagen (zie figuur 1). Het verkregen stelsel differentiaalvergelijkingen wordt Laplace getransformeerd en opgelost. De terug transformatie in de tijd moet dan gebeuren m.b.v- de direkte methode [2]. Aangetoond wordt dat de oplossing reële wortels heeft, zowel vlaksymmetrisch als axiaal symmetrisch.TAW/EN