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Geology of Urban Watersheds
Published in Daniel T. Rogers, Urban Watersheds, 2020
Stratigraphy is the study of rock layers or unconsolidated sediment and strata; particularly their ages, composition, and relationship with other layers (AGI 1962; Christopherson 2008). In geology, the term strata refers to the layers of rock or sediment with internally consistent characteristics that distinguishes it from contiguous layers (Krumbein and Sloss 1963). Each individual layer or stratum is generally one of a number of parallel and originally horizontal layers that were deposited by natural forces and lay one upon the other. Therefore, the study of stratigraphy of a particular area provides important clues concerning its geologic history. The origins of stratigraphy date back to Italy in the mid-1600s. A Danish anatomist named Nicolas Steno was studying shark teeth and noticed the similarity to fossils of shark teeth in Italy. He deduced that the fossils were remnants of past life. Based on his observations, he later deduced that deep rock layers in the Earth were older and that successive layers above gradually become younger. This was later expounded by Hutton and became known as the Principle of Superposition described below (Hongren 2004).
Geotechnical site investigations
Published in Alan J. Lutenegger, Soils and Geotechnology in Construction, 2019
Stratigraphy refers to the sequence of layering of the earth’s surface brought about by geologic activity over time. The principal objective of this part of a site investigation is essentially to determine the vertical and lateral extent of individual geologic layers (strata) or deposits at a site, insofar as they may impact design. How many layers are present at the site? How thick is each layer at a given location? What is the composition of each layer? Are the individual strata continuous over the site? These and other questions need to be answered. Normally, this will involve either direct test drilling in order to visually identify the different strata and materials. Alternatively, an in situ test that provides profiling, such as the Cone Penetrometer, may be used. Using the information obtained, stratigraphic cross sections around the site may be constructed in order to develop an understanding of any significant geologic controls on a project. The importance of regional and local geology cannot be emphasized enough, which means that it is important that geotechnical engineers have a strong understanding of geology and geologic processes.
Ground subsidence
Published in F.G. Bell, Geological Hazards, 1999
A site investigation for an important structure requires the exploration and sampling of all strata likely to be significantly affected by the structural loading. The location of subsurface voids due to mineral extraction is of prime importance in this context. In other words, an attempt should be made to determine the number and depth of mined horizons, the extraction ratio, the pattern of the layout, and the condition of the old room and pillar workings. The sequence and type of roof rocks may provide some clue as to whether void migration has taken place and if so, its possible extent. Of particular importance is the state of the old workings. Careful note should be taken of whether they are open, partially collapsed or collapsed, and the degree of fracturing and bed separation in the roof rocks should be recorded, if possible. This helps to provide an assessment of past and future collapse, which is obviously very important.
Force and deformation response analysis of dual structure slope excavation and support
Published in Geomatics, Natural Hazards and Risk, 2022
Xuhe Gao, Wei-ping Tian, Jiachun Li, Hongliang Qi, Zhipei Zhang, Shiyang Li
Stability analysis of dual-structure slopes often focuses on monitoring statistics or status analysis, without performing a verification of the simulation parameters used or a corresponding process analysis. Existing slope stability analysis methods and calculations are mainly dictated by geotechnical parameters, which have caused the determination of simulation parameters to be a contentious issue in this field. The current methods are to determine parameters through geotechnical tests, statistical data obtained from a large number of similar strata, or empirical data. However, these methods each have significant limitations. The parameters obtained by geotechnical testing often need to be revised as the testing conditions differ from the actual project conditions. The use of statistical data is only applicable to ordinary strata and requires the accumulation of significant amounts of engineering data. Finally, empirical data is convenient to use, but lacks rigor. Importantly, all three methods lack generalizability to slopes in special geological environments. In order to address these limitations, this paper uses deep displacement monitoring data and p value testing to verify the simulation parameters, and puts forward an analysis method for dual-structure slope excavation and reinforcement processes.