Engineering Geology Research Focused on Dutch Environment Dominique Ngan-Tillard, lecturer/researcher Faculty of Civil Engineering and Geosciences, Department of Applied Earth Sciences, Engineering Geology Group Some of the results obtained in 1999 on the reduction of clay adherence on steel and data clustering are highlighted. Future research directions regarding the properties of clay materials and the improvement of 3D soil mass models using clustering techniques are briefly presented. A new research project entitled Tunnel Advance Monitoring Advisory System (TAMAS) is introduced. Reduction of clay adherence on steel- Results in 1999 Recently the TBM technology has been employed to excavate the Second Heinenoord tunnel. As not much experience was available on boring large diameter tunnels in the typical Dutch soils, some unexpected problems were encountered. One was the adherence of stiff clays to the interior of the TBM. In the near future, several tunnels will be built through other Dutch clay formations where similar problems can be expected. Several solutions are available to prevent adherence of clay inside a TBM but they are not always satisfactory. For example, polymers are sometimes used but with rather controversial results. Therefore, alternative solutions such as the use of electro- osmosis deserve to be considered. In 1998, it was decided to investigate in the laboratory the adherence of clay to forecast and eventually prevent problems to occur in the future. Efforts were put on understanding the fundamental aspects of clay adhesion and on elaborating adequate testing facilities and procedures to identify sticky clays as well as to quantify their stickiness. In 1999, tests were performed with a direct shear box, by shearing clay samples over a steel plate to gain a qualitative insight into the parameters that determine adhesive shear strength (Zimnik et al., 2000). It was found that the value of adhesive shear strength is depending on the mineral type; and for a given clay it increases with increasing contact time between clay and steel and increasing steel roughness. A range of critical roughness for which failure is a combination of sliding along the steel surface and through the clay has been identified. In 1999, the use of electro- osmosis (van Baalen et al., 2000) and polymers (Appel, 2000 and Piek, 2000) as a mean to reduce clay adherence were also examined. By applying an electric charge to the steel parts of a TBM, water can be transported through the clay by electro- osmosis to the interface between the clay and the steel. This creates a film of water at the clay-steel interface and therefore reduces the adherence. Because of this film, the clay can easily be removed by the hydraulic force of the slurry. To investigate the effect of electro-osmosis on clay adherence, laboratory tests were performed on four different clay soils using two test methods: the tilted plate and the direct shear box. It has been shown that both tests can be used to reveal the sensitivity of a clay soil to a reduction in the adherence by electro-osmosis. Apart from a so-called threshold potential below which little reduction in adherence was observed, the shear box test has been shown to permit also the determination of the shear stress drop due to electro-osmosis. Experiments were also conducted to investigate the influence of a polymer [SC50] on the behaviour of a slurry transporting clay lumps, the adherence of clay to steel and the stickiness of clay lumps to each other. The effects of parameters such as the soaking time of clay in polymer, the slurry concentration in bentonite and polymer, the pH of the slurry will be interpreted in Appel and Piek MSc thesis. Data clustering – Results in 1999 With respect to the uncertainties in the design of large infrastructure, those related to soil properties are among the most notorious. All geotechnical parameters show a spatial variation which is related to the soil geological background. As a result, stress-strain behaviours of soils around structures are difficult to predict. Data clustering techniques can help in the construction of a more reliable geotechnical model of the subsurface. Results of cluster analysis can be correlated to borehole descriptions and engineering properties determined in the laboratory. This leads to a better knowledge of the spatial variability of the geotechnical parameters since the rule of thumb in the Netherlands is to bore only one hole from which few cores are tested for 50 cpts. Data clustering has been applied in 1999 at NITG-TNO with some promising results to the Eem clay (Dankelman, 1999). A good match was obtained between the sequences shown by the cpt clusters and the lithostratigraphical facies of the Eem clay. As the performance of the clustering techniques is thought to be strongly depending on the degree of vertical variation shown by the geological formations under study, trials have been carried out with the Boom clay of the Westerschelde tunnel area with the objective of revealing the lateral extent of its layering. Research plan for 2000 Reduction of clay adherence to steel. In 2000, attention will be paid on understanding how much capillary stresses and differential fluid pressures are responsible for problems of adherence encountered in excavation machines. As the limitations of the direct shear box have been underlined in 1999, further testing will be carried out with a ring shear box equipped with a pore pressure transducer at the steel/clay interface. Data clustering. The sensitivity of the cluster results to the selected clustering procedure will be examined. The correlation between the cpt clusters and the laboratory results will be thoroughly investigated for the Eem clay and the Boom clay. The preliminary models based on data clustering will be validated using extra sets of cpts. New techniques will also be tested within the TU-Delft engineering geology group to couple the cpt clusters to borehole descriptions and laboratory results. Tunnel Advance Monitoring Advisory System (TAMAS). When using TBMs to construct new underground space below urban areas, ground movement due to the boring process is unavoidable but it has to remain below a certain threshold to avoid damage to the surrounding infrastructure. With the concept of TAMAS, adverse effects caused by tunneling will be minimized by monitoring the boring parameters together with their impact on the tunnel vicinity and subsequently by tuning the boring parameters accordingly. A knowledge-based expert system will suggest the optimal boring parameters for an a-priori model of the subsurface and its infrastructure. These will be checked by a prediction module with respect to the sensitivity of the tunnel surroundings and the production rate for example. The predicted parameters will be translated in real time into machine instructions with which a portion of the tunnel will be excavated. The response of the tunnel surroundings will be monitored and an evaluation module will compare forecasts and observations. In case of discrepancies, a knowledge-based expert system will suggest modifications of the a-priori model of the tunnel environment to obtain a better match and improve the quality of the next set of predictions. To develop the crucial modules of TAMAS, which are the knowledge-based expert system, the prediction module and the evaluation module, the use of a combination of neural networks and fuzzy logic is proposed. Publications in 1999 Baalen, L. van, A. Zimnik, P. Verhoef & D. Ngan-Tillard, Applicability of electro-osmosis to reduce clay adherence in a TBM, International Conference on Geotechnical & Geological Engineering, 19-24.11.2000, Melbourne, Australia, accepted. Drijkoningen G., D. Ngan-Tillard & G. Swinnen, Imaging the subsurface by using a TBM as seismic source; feasibility study and validation tests, AFTES International conference, Underground works: Ambitions and Reality, 25-28.10.1999, Paris, France, pp.43-47, 1999. Kuntz M., G.Viggiani, P.Besuelle, J.Desrues & D. Ngan-Tillard, Experimental observation of strain localization and rupture in rocks, 13 p., to be submitted. Swinnen G., G.Drijkoningen, D.Ngan-Tillard & J.T. Fokkema, Tunnel boring machine as seismic shear-wave source, 24th General assembly of the European Geophysical Society (EGS), Session SE 48, Den Haag, The Netherlands, 19- 23.04.1999, p.163, 1999. Zimnik A., L. Van Baalen, P. Verhoef & D. Ngan-Tillard, The adherence of clay to to steel surfaces, International Conference on Geotechnical & Geological Engineering, 19-24.11.2000, Melbourne, Australia, accepted. Supervised MSc thesis in 1999 Appel P., The influence of polymers on clay/water mixtures, memoirs of the Centre of Engineering Geology in The Netherlands, to be written in 2000. Baalen, L. van, Reduction of clay adherence by electro-osmosis, memoirs of the Centre of Engineering Geology in The Netherlands, No. 189, 1999. Dankelman, J., Geomechanische analyse van de eemklei in het bekken van Amsterdam in relatie tot de geologische facies, NITG 99-48-A, 1999. Kemp, C., Bepalen in Situ doorlatendheid met de doorlatendheidssonde, Kwantificeren heterogeniteit, memoirs of the Centre of Engineering Geology in The Netherlands, No 185, 1999. Piek, A., The effect of polymers and bentonite on the (adhesive) shear strength of clay lumps, memoirs of the Centre of Engineering Geology in The Netherlands, to be written in 2000. Wibbens, G., Data clustering applied to the Boom clay of the Westerschelde tunnel area, memoirs of the Centre of Engineering Geology in The Netherlands, to be written in 2000. Zimnik A., The adherence of clay to steel surfaces, memoirs of the Centre of Engineering Geology in The Netherlands, No. 187, 1999.