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Upstream constructed tailings dams – A review of the basics
Published in A.A. Balkema, Tailings and Mine Waste 2000, 2022
To demonstrate whether a static liquefaction trigger exists for a given tailings facility, a generic slope configuration(s) and probable stress loading paths for the tailings deposit should first be appreciated. Figure 3 presents such a generic slope. The value of “S” is often termed the slope of the tailings facility (or as the horizontal component in H:V ratios). Both compression and extension stress path triaxial data and simple shear data on the tailings are required to do a specific evaluation. From this data, at least conceptually, the “collapse surface” can be approximately located within the lines of phase transformation (steady state) as shown on Figure 4. In practice, it is often difficult to establish a collapse surface in compressive loading. The lines of phase transformation are identical in either compressive or extensive stress space. However, this isotropy is not evident with the collapse surface that is steeper in compressive loading than in extension. This anisotropy is largely due to fabric/grain imbrication (almost always preferential to the horizontal plane) and increases with grain angularity and elongation; two characteristics common to ground mill tailings. The imbrication, due mainly to the hydraulic deposition processes, results in elongated grains being aligned preferentially in horizontal to sub-horizontal layers. Typically, this horizontal plane is normal to the maximum principle stress resulting in additional cross-plane anisotropy in triaxial loading conditions.
Effects of irregular particle shapes on the sediment movement and transport rate in gravel-bed channels
Published in Wim Uijttewaal, Mário J. Franca, Daniel Valero, Victor Chavarrias, Clàudia Ylla Arbós, Ralph Schielen, Alessandra Crosato, River Flow 2020, 2020
Takatoshi Atsumi, Shoji Fukuoka
Figure 9 shows the pick-up volume at t = 0 ~ 100 s, x = 10 ~ 11 m in Case1 ~ Case4. The ratio of the pick-up volume in each case is almost the same distributions as the transported volume of gravel particles shown in Figure 4, the particle shape is a prominent effect in the pick-up process and river-bed structure. One of the hydro-geological phenomena characterizing non-spherical particles is the imbrication of the gravel-bed surface. Figure 10 shows the arrangement of particles on the river-bed surface before and after experiment. The imbrication is often seen at the bed surface in gravel rivers after floods where gravel’s longest axis is directed toward the streamwise direction and slightly vertically upward. The imbrication takes a stable posture by directing the contact force to the upstream direction (Figure 11). In Case1 ~ Case3, the imbrication was clearly formed on the gravel bed. In addition, in Case1 ~ Case3, a group of clusters composed of several gravel particles are formed. Figure 12 shows the clusters formed in Case1. A group of gravel enclosed by circles is clusters. The cluster has a stable structure in a group against stream forces. Unless particles moving from the upstream collide with clusters, the cluster kept stable.
Groundwater
Published in Stephen A. Thompson, Hydrology for Water Management, 2017
Alluvial deposits are usually anisotropic. Anisotropy means that K is different in different directions within the material. For example, hydraulic conductivity in the vertical direction Kz may be ten to twenty times smaller than in the downstream direction Kx. When K is the same in all directions the aquifer is said to be isotropic. One cause of anisotropy is imbrication of the sediments. Individual particles are not spherical, and when they are deposited they preferentially lay on their flat side slightly overlapping particles in the direction of flow (Fig. 8.7). This overlapping orientation of sediments is imbrication. Another cause of anisotropy is layering of sediments with different K values. When K is different at different locations within an aquifer, the aquifer is heterogeneous. When K is the same throughout the aquifer it is homogeneous. Example 8.2 demonstrates the calculation of average K values for a layered anisotropic aquifer.
Lateral, longitudinal, and temporal variation in trench-slope basin fill: examples from the Neogene Akitio sub-basin, Hikurangi Margin, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2022
Adam D. McArthur, Julien Bailleul, Frank Chanier, Alan Clare, William D. McCaffrey
Observations: Comprised of matrix (LF2) and clast supported polymict conglomerates (LF3), with rare mudstones (LF1 and LF6), and subordinate thick-bedded lenticular sandstones (LF13) (Figure 7). Clasts are dominantly comprised of older lithologies (e.g. Cretaceous to Paleogene Whangai [Figure 7A and C] or Weber [Figure 7D] formations) and range from pebbles (Figure 7B) to rafts tens of metres long (Figure 7C–D). Rare intraformational clasts also occur, but are typically <5% of any deposit. Some conglomerates may be monomict (LF4) (Figure 7A). These form packages at least tens of metres thick, but given only erosional remnants are preserved they may have formed considerably thicker intervals, as seen in the coastal exposures (Claussmann et al. 2021). This association is found on both margins of the Akitio Sub-basin (Figure 5), such as on the western margin near Pongaroa (Figure 7D) and the northern end of the basin (Figure 5), on the eastern margin near Ware Ware (Figure 4 – base of Coast Road section) and in the Pakowhai River (Figure 4). Similar successions are found at the base of other outcropping basins on the margin (Claussmann et al. 2021). Rare imbrications in conglomerates and traction structures in sandstones indicate transport away from the adjacent basin margin. In places this assemblage is seen to grade laterally and interfinger with Lower Miocene turbidites (Delteil et al. 2006).