A hydrogeological approach for sustainable technical solutions in tunnel construction.

Abstract

Economic, environmental sustainability and management of climate changes are closely related to how we plan, build, and develop our society. The thesis aims to define and implement methodologies for providing technical solution (Hydrogeological Reference Conditions (HRCs)) prior to the construction and predict the requirement of cement grouting in underground tunnel construction (Grouting Domains). Performing grouting in rock tunnel is important to reduce the impact, effect and consequences that occur due to the water ingress through rock fractures. The suggested HRCs in a location south of Sweden are Crystalline bedrock (HRC1), Glacial till over bedrock (HRC2), Glaciofluvial deposits (HRC3), Wave-washed deposits, (HRC4), and Clay-covered areas (HRC5) each of which has specific stratigraphy from regional geological characteristics. The topographic map, quaternary deposit map, bedrock map, paleoshoreline map, soil depth map and geological history (sedimentology) were used for desktop study and the obtained result compared with the available borehole. Another focus on this thesis is to implement “grouting domains”, a hydrogeological description in Södertörn tunnel in Stockholm. The grouting domain follows demand assessed grouting to predict the requirement of grouting or no grouting. Grouting domains are classified into A, B and C, where each of which have specific standardized parameter limits and grouting classes. Water loss measurements and pressure built-up tests in core drilled boreholes are used for extraction of relevant hydrogeological data which in turn to the identification of domain classes. The prediction could provide information about the requirement of sounding boreholes and grouting boreholes. Moreover, the selection of effective hydraulic conductivity (Keff) in inleakage estimation is performed using K2D and K3D. Where K2D and K3D are upscaled hydraulic conductivities. The dimensionality of hydraulic conductivity (K2D or K3D) is identified based on the ratio of total section transmissivity (∑Ti) and full borehole transmissivity (Tfull). The weighing of the hydrogeological parameters helps to identify the dominant domain. Moreover, Class A presence sounding boreholes with no pre-grouting required while Class C requires pre-grouting. The prediction of specific domain classes could optimize the amount of grouting and deliberately helps to make better judgement for grouting prior to the execution.