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Thin-layer detection from the cone resistance rate of change
Published in Guido Gottardi, Laura Tonni, Cone Penetration Testing 2022, 2022
H.B. Hammer, S. Nordal, J.-S. L’Heureux, H. Skrede
The near-continuous measurements of CPTU parameters cone resistance (qc, qt), pore pressure (u2) and skin friction (fs) provide great details of the subsurface. The combined response of these parameters can be used for characterization of materials for thick homogenous sediments. Close to layer interfaces and in thin layers the measurements may be significantly influenced by multiple materials simultaneously. Accurate characterization and interpretation of geotechnical parameters of thin layers requires correction of these effects, which in turn depends on the layer thicknesses. It is therefore important to obtain detailed information of the layer interfaces. The u2 parameter may not provide accurate measurement of the thickness of such thin clay layers (Hird et al. 2003, van der Linden et al. 2018, Hammer et al. in press).
Reactive (Oxygen) Gas Barrier and Zone Technologies
Published in Ravi Naidu, Volker Birke, Permeable Reactive Barrier, 2018
Ronald Giese, Frank Ingolf Engelmann, Dietrich Swaboda, Uli Uhlig, Ludwig Luckner
RGBZ are ideally applied in horizontal multiple-layered sediment formations of nonuniform fine- to coarse-grained sands and fine gravels. Depths to 50 m below the ground surface are accessible without the use of heavy drilling techniques. Enclosed finer texture lenses or thin layers do not limit the application of RGBZ, as they are typically not continuously shaped and contain weak zones of gas-available threshold pressures. A time scale of 1–3 years is required to complete a stable formation of a gas PRB. The horizontal scale needed for a gas storage domain depends on the geological structure. In the direction of groundwater flow, it is typically in the same order of magnitude as the saturated thickness of the aquifer. Stimulation of intrinsic microorganisms can be achieved when a suitable environment is established (redox, pH) and dominant electron acceptors or donors for the biodegradation of groundwater soluble contaminants are supplied. Variable zones of redox potential can be induced by sequential reactors (Figure 10.1) or rate controlled and time-variable gas injections. Products of precipitation reactions (e.g., iron or manganese oxidation or pH-induced instability of carbonate) do not put the long-term operation of the RGBZ at risk. The well-known effects of bypassing or channelling groundwater flow due to gas clogging can also be monitored and controlled.
Earth Systems and Cycles
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Sediments of all sorts are deposited on dry land, in lakes or streams, or on ocean bottoms. As gravity deposits new sediment on top of old sediment, thick sedimentary layers, up to thousands of meters thick, may form. Silt, sand, mud, gravel, soil, and biogenic debris such as seashells on a beach are some more common constituents. However, the nature of a sediment depends on the original parent material and on climatic factors, including temperature and precipitation, and on biological activity. Landscape and topography, too, affect the thickness and nature of sedimentary layers. The deposits remain sediments until they are consolidated and lithify (harden), at which point they become sedimentary rocks.
Stability analysis of two-layered non-homogeneous slopes
Published in International Journal of Geotechnical Engineering, 2021
Dooradarshi Chatterjee, A. Murali Krishna
For the second combination analyses, with the bottom layer fixed as soil-1, the results are presented in Table 4. The factor of safety changed from 1.594 to 1.591, when soil-2 is the top layer for its thickness (h) changed from 0.4D to 0.6D. As soil-2 is a shallow failure soil having its critical failure surface within the slope face itself, variation of soil-2 thickness from 0.4D to 0.6D did not affect the stability. On the other hand, with soil-3 as the top layer, the safety factors reduced from 1.705 to 1.593 for variation of soil-3 thickness from 0.4D to 0.6D. Soil-3 being a base failure type soil, for 0.4D thickness case, the critical slip surface was intersected by soil-1 beyond 0.4D depth and thus FOS value is higher. As the soft soil (soil-3) in the top layer thickness is gradually increasing, the stability of the slope is diminishing as the slip surface encounters soil material of lower shear strength, i.e. less resistance to sliding. Finite element results also show a slight decrease of SRF values from 1.64 to 1.51.
The influence of diagenetic heterogeneity on tight-reservoir properties in the Upper Triassic Yanchang Formation, Southeastern Ordos Basin, China
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Li Wang, Jianguo Zhang, Zaixing Jiang, Chao Han, Danting Luo, Yidan Zhang
Sandstone at a distance less than 0.5 m away from the sandstone-mudstone contacts has a higher content of carbonate cements (Figure 11a). Porosity and permeability at the edges of sandstones (<0.5 m) were less than 4% and 0.01 mD, respectively. Sandstones at a distance further than 0.5 m from the lithological contact have a lower and relatively stable content of carbonate cements, and consequently have higher porosity and permeability (Figure 11b). Thin sandstone layers were generally highly cemented by carbonate cements, meaning the reservoir quality of those sandstone layers was the poorest. When layer thickness was less than 1.5 m, the porosity had a positive correlation with the thickness of the sandstone layer. As layer thickness increased, the porosity kept stable relatively (Figure 11c). Samples from sandstone layers with a thickness of less than 1.5 m had lower reservoir qualities (porosity <4%, permeability <0.01 mD). When the thickness of tight sandstones was greater than 3 m, the porosity was greater than 6% and remained stable.