The conceptual model of the rock-soil (and future shaft) interface was confirmed (so far not rejected) using data from investigation boreholes. The location of a depression in rock (a likely deformation zone) was indicated and confirmed using borehole data. Wave-washed deposits (upper part of the stratigraphy) and a lower water-bearing strata (soil) coinciding with the depression are key water-bearing features in soil. The likely deformation zone is expected to be a key water-bearing feature in rock. Grouting design (curtain- and blanket grouting) and sealing of soil (jet-grouting and sheet-pile walls) focus on sealing these features. The wells (infiltration) that are planned between the shaft and a contaminated site may, if needed, further reduce the effect of the construction on hydraulic head and flow. Changes that are of interest since they may also influence the mobility of a contamination. A low grouting pressure is used in rock adapting to a shallow depth (curtain grouting) and a possible horizontal connectivity. The steps of the observational method, as described by Peck (1969), were found very useful. Its focus on "the general nature, pattern and properties" and "a working hypothesis of behaviour" is of particular interest, highlighting the understanding of the system at hand.
Construction of infrastructures such as shafts and tunnels in a rock-soil interface, below the groundwater level and at a contaminated site, demand transdisciplinary collaboration (rock-, geotechnical- and environmental engineering as well as engineering geology and hydrogeology). A collaboration aiming at a relevant description of conditions as a basis for an understanding of behaviour and as a mean to provide an appropriate and site-specific design.
This paper presents a case study from an ongoing railway project integrating the above areas. Focus is on water control (hydraulic head and flow) using sealing (rock grouting, sheet-pile walls, jet-grouting), infiltration (adding water) and pumping (removing water). Simplified drawings of the shaft including technical measures (sealing), wells for observation and protective measures (wells) are shown in Figure 1. The description of geology and hydrogeology (the conceptualization) are presented and discussed in the framework of the observational method and Eurocode-7 [1].