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Groundwater Problems for Excavations in Soils
Published in Pat M. Cashman, Martin Preene, Groundwater Lowering in Construction, 2020
It is important to realize that for geotechnical purposes, the distinction between soils and rocks is based on the behaviour of a stratum, not its origin or its age alone. In groundwater control design, materials would be classified as a geotechnical soil if groundwater flow is intergranular and if the material can become readily disturbed or eroded under the action of groundwater flow in an excavation. So for example, in the United Kingdom, the Thanet Sand Formation (Menkiti et al., 2015) typically behaves as an uncemented sand and is analysed as a soil despite being part of the bedrock or ‘solid’ geology below London (the Thanet Sand Formation is more than 23 million years old). The underlying Chalk Group is analysed as rock because of the more cemented nature of the dominant limestones and marls; groundwater flow is mainly via fractures (Preene and Roberts, 2017).
Inversion tectonics in the Sorgenfrei–Tornquist Zone: insight from new marine seismic data at the Bornholm Gat, SW Baltic Sea
Published in GFF, 2022
Yaocen Pan, Elisabeth Seidel, Christopher Juhlin, Christian Hübscher, Daniel Sopher
The 2D seismic profiles used in this study are located in the Swedish territory of the Bornholm Gat region, with generally northeast-southwest and northwest-southeast trends. We present four profiles from the BalTec cruise MSM52 and two additional vintage OPAB (Swedish Oil Prospecting Company) profiles. The longest profile BGR-254c is transverse to the STZ with a length of ∼120 km. The Post-Permian seismo-stratigraphy framework in this study is based on Erlström et al. (1997), Sopher et al. (2016) and Al Hseinat & Hübscher (2017). We traced prominent horizons including the base Cretaceous Unconformity (BCU), the base Chalk Group BCG and the glacially eroded base Pleistocene Unconformity (BPU). The identification of the Chalk Group is adopted from previous studies in adjacent areas of the Danish Basin (Esmerode et al., 2007; Hübscher et al., 2019; Lykke-Andersen & Surlyk, 2004), with six major horizons; the base Campanian (BCA), the base late Maastrichtian (BLM), the internal lower Maastrichtian (ILM) and the internal upper Maastrichtian (IUM) (Fig. 4). Based on seismic facies, reflector continuity and bounded unconformities, the high-resolution seismic profiles allow us to map the well-defined Upper Cretaceous horizons for the entire study area. The Chalk Group has been sub-divided into five seismic units between the BCG and the BPU (Fig. 4). Deposits of Turonian-Santonian age make up Unit 1, the Campanian Unit 2 and the Maastrichtian-Danian is classified into units from Unit 3 to Unit 5. In the Hanö Bay Basin, precise well-ties were hampered by low-quality synthetic seismic sections due to borehole washout and large spacing between the seismic profiles. The sonic and density logs, as well as lithological information, from the exploration wells H-1 and H-4 provide additional stratigraphic constrains for the sandy intervals adjacent to the STZ (Fig. 5). Above the prominent seismic marker of the Top Cambrian, the BCG can be recognized by a distinct upward increase in sonic velocity, which corresponds to a transition in the seismic data from a lower less reflective portion to an upper more reflective portion. The age assignment of Santonian intra-chalk horizons can only be made tentatively.