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Due to the extreme sensitivity of the superconductive gravimeter GWR T020, based at Metsähovi Research Center in Kirkkonummi, Southern Finland, various local meteorological and hydrological changes influence or disturb its measurements. This study is part of a large research project which aims to identify the contribution of the local hydrology at Metsähovi to these gravimeter measurements. For this purpose a study is made to investigate the geological structure of the subsurface and the hydrological properties of the stratigraphic layers. In order to perform numerical calculations a digital model is made using digital modeling software. A field investigation is performed consisting of: • A literature study on hydro-geological setting in Southern Finland. • An extensive fieldwork consisting of bore holes, field observations and various field measurements (among others GPS, GPR, slug tests and monitoring of soil moisture with soil sensors). • Laboratory work to obtain necessary soil properties. Main property which was found is the grain size distribution. A large amount of data is gathered and processed in order to integrate the data into a structural model. A method is found to integrate a maximum amount of information into a model and by optimally using the understanding and knowledge of the geological setting. A model is constructed with several layers. The area can be characterized in two hydrogeological domains. One is the higher area where overburden is thin and only till covers the bedrock, the other is a lower area dominated by a low permeable silt and clay layer. The till is low permeable but is still found to infiltrate water considerably. The hydrological setting of Metsähovi is analyzed and theories of the hydrogeological processes which govern moisture changes in the area are investigated. Main focus is how these processes can be modeled with their governing laws and parameters. It is recommended to initially make a 1 dimensional model with software such as CoupManual.

Properties of soils are spatially variable and to describe the behaviour of soils as a response to loading, this variability appears crucial in giving the correct range of possible solutions for structure response. Because site investigation techniques only provide exact information at a limited part of the site, random field simulations are used to assess this variability over the full test site domain. The random fields use the spatial statistical characteristics that are derived from the site investigation, which in geotechnical application mainly consists of cone penetration tests (CPT’s). To reduce the range of possible solutions to be found for structure response analysis, the random fields can be conditioned by the actual CPT measurements. This report describes the conditioning of the random field in order to generate conditioned simulations of sand state fields. In order to derive the state parameter from the CPT tip resistance, the NorSand constitutive model is calibrated against the results of 55 triaxial tests of the test site. Different methods of calibration using triaxial test data are described and the results are discussed. 140 CPT’s of the test site are then transformed into state parameter profiles. The statistical characteristics of the profiles are determined to be used for the simulation of the spatially variable fields of sand state. The statistical characteristics of the profiles are used in the conditional simulation of the fields. A conditional simulation algorithm to generate realisations of spatially variable sand state fields is derived and demonstrated. Using unconditioned random fields, generated with the Local Average Subdivision (LAS) method, conditioned simulations of the field around the CPT profiles are generated in a post-processing algorithm. The algorithm uses the geometry-dependent property of the kriging estimation error for the exchange of noise terms between estimation fields. The specific properties of the kriging estimator are demonstrated to be suitable to be used for the conditioning. The decrease in uncertainty by the conditioning with respect to the unconditioned random fields is presented. This decrease in uncertainty is used to demonstrate that the effectiveness of the conditioning is a function of the number and location of conditioning points relative to the scales of fluctuation of the field. It is demonstrated that conditioning reduces the range of possible solutions for the simulation of sand state fields with respect to unconditioned fields. This reduction will lead to a smaller range of solutions to be found when the conditional simulations are used in structure response analysis, leading to less uncertainty in design. The conditional simulation is shown to produce fields that honour the initial distribution function, the correlation structure and the actual CPT profiles in the simulated fields. To demonstrate that conditional simulation can be applied on the test site, a stochastic characterisation of the test site is performed and conditional simulations of the state parameter fields are generated for a small part of the test site.

More than the half of the Netherlands is under the high level of sea and rivers. Therefore, evaluating the safety of dykes is primordial. A specific interest is given to peat dykes safety which suffer of a lack of knowledge which manifested recently by some peat dykes failures (Van Baars 2005). The behaviour of peat is also of interest in others countries, for assessing peat slope stability for instance (Long and Jennings 2006). Due to its high anisotropy and fibrosity, peat cannot be tested with any device in the laboratory. The direct simple shear test is routinely used since it can mimic several in situ conditions and provides conservative results for peat dyke stability evaluation. Furthermore, it does not show the inconvenience of triaxial testing with peat (Landva 1980). Larger samples than for usual testing are desirable to investigate the effect of fibres on tests results. The Direct simple shear testing devices remain imperfect since it is unable to provide additional shear stresses on the sides of the specimen. As consequence, non uniformities develop on all the faces of the specimen, in particular compression in the obtuse corners and tension in the acute corners. In practice, thin samples are used (height over diameter around 0,2 to 0,3) to limit the nonhomogeneities to the sides and leave the major part of the sample in an homogenous state of stress. Testing peat at low vertical stress, remains a challenge and necessities the development of adapted devices (Boylan and Long 2009). A series of tests has been performed on a wood and sedge peat with the Geonor device in order to compare the effect of two boundary conditions on tests results. The first one is a classical reinforced membrane (Bjerrum and Landva 1966) and the second is an unreinforced membrane enclosed in a stack of rings. The vertical stresses applied during the tests varied between 10kPa and 120kPa. The results show small differences when the Mohr Coulomb parameters are determined. The comparison is limited considering the variability of the material tested. A more accurate calibration of the stack of rings would be desirable. Some improvements are needed on the actual apparatus to test peat at low vertical stress. Removing the membrane between the soil and the rings would give more accuracy in the results. A direct simple shear prototype has been developed in order to test larger samples (with height over diameter ratio of 0.5) at low vertical stress. The effect of two innovative rough boundaries on the stress-strain homogeneity of the sample has been investigated. The sidewalls of the device are transparent and make possible a visual assessment of the deformation of the sample. The Particle Image Velocimetry analysis is also considered to assess the shear strain homogeneity in the sample. The results show an improving shear strain homogeneity and reduced tension forces in the acute corners. Slippage is also observed between the top cap and the sample and the normal load could not be measured. Further research is needed to validate the utility of this prototype. Stress-strain curves obtained from the three boundaries should be compared to quantify the improvement of rough boundaries. A finite element analysis of the prototype boundaries has been performed with two models (Mohr Coulomb and Soft Soil Creep model). The boundaries considered were perfectly rough at the top and bottom and perfectly smooth at the sides. The presence of strips and even more the presence of vanes increase the stress – strain homogeneity inside the sample with both models. Reliable stress – strain curves as measured in classical devices could not be obtained with such boundaries. Interfaces should be preferred to model more realistic conditions.