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Dynamic Compaction
Published in James Fern, Alexander Rohe, Kenichi Soga, Eduardo Alonso, The Material Point Method for Geotechnical Engineering, 2019
James Fern, Alexander Rohe, Kenichi Soga, Eduardo Alonso
The compaction process is carried out multiple times until an entire region reaches the desired density. However, this is difficult to achieve. Once a point, or location, is sufficiently compacted, the procedure is repeated at another point. This sequential process spans a grid of compaction points over the whole site. It is common to use several grids, referred to as phases, as they are completed one after each other starting with a coarse grid with bigger spacing between the compaction points and closing the gaps with finer grids. Compacting neighbouring points leads to interactions between them and this can cause loosening at already-compacted points. This can be prevented by filling the craters with additional material, which is again compacted until the crater is closed. The compaction of water-saturated soils is especially challenging as the pore-water pressure might prevent the soil from compacting. Drains can be applied in such cases to accelerate the consolidation process but, due to the impulse load induced by the pounder, a big amount of the kinetic energy dissipates in displacement and not compaction. This chapter presents a case study of dynamic compaction and compares the numerical predictions with experimental data.
Ground improvement
Published in Alan J. Lutenegger, Soils and Geotechnology in Construction, 2019
The process is repeated a number of times at the same location until the desired ground improvement is achieved, as shown in Figure 8.15. Drop heights range from 50 to 100 ft. and drop weights range from 10 to 30 tons. Although the process has traditionally been used around the world to densify loose, coarse-grained soils, other types of loose materials have been densified with DDC, including collapsible loess, municipal waste, uncontrolled fill, mixed clayey and silty sand, and peaty clay. The craters are usually filled with granular material, and there may be an “ironing pass” to smooth out the surface by using the drop weight at a lower height, or a vibratory roller may be used.
Dating the Acraman asteroid impact, South Australia: the case for deep drilling the ‘hot shock’ zone of the central uplift
Published in Australian Journal of Earth Sciences, 2021
Acraman is named after Lake Acraman, a late Quaternary 20 km-diameter salina placed eccentrically within the near-circular, ∼30 km-diameter Acraman depression in the Gawler Ranges (Figure 2). The depression marks the present extent of disrupted bedrock, with the level of erosion now being several kilometres below the transient crater floor. Williams (1994) deduced a transient crater diameter of ∼40 km from the extent of disrupted bedrock and the erosion history of Acraman. The fault-bounded Yardea corridor at ∼90 km-diameter marks the inferred line of the collapse-crater rim. The full structure is located almost entirely in the 1592 ± 3 Ma Yardea Dacite of the Mesoproterozoic Gawler Range Volcanics (Fanning et al., 1988). This flat-lying continental suite of mainly acid lavas and ash flows has an exposed thickness of up to 1 km and a total thickness of ∼4 km, and now covers >30 000 km2, with outlying remnants indicating that the suite was once much more extensive (Creaser & White, 1991; Pankhurst et al., 2010).
Study on the machining of Al–SiC functionally graded metal matrix composite using die-sinking EDM
Published in Particulate Science and Technology, 2019
M. Uthayakumar, K. Vinoth Babu, S. Thirumalai Kumaran, S. Suresh Kumar, J. T. Winowlin Jappes, T. P. D. Rajan
The SEM image in Figure 9 indicates the surface morphology of the machined surface conducted at the optimum condition. The surface appears with a mechanism of erosion of bulk material due to high spark. The crater formation is clearly observed due to erosion mechanism. The dimension of the crater depends upon the pulse/spark time. Along with the profile of crater, the material has undergone the susceptibility of micro arc oxidation. This is due to the plasma spark produced at a regular interval. The intensity of the spark will decide the metal loss, erosion, and crater formation. The high energy of the arc consumed during machining will increase the crater diameter, produce maximum surface irregularity, heat affected zone, and the surface appears with maximum ridges and grooves.
Effect of explosive cratering on embankment dams
Published in International Journal of Geotechnical Engineering, 2018
George Afriyie, Abass Braimah, Mohammad T. Rayhani
With the global increase in terrorism and the likely damaging effects of a dam breach, the vulnerability of dams to explosion effects is of utmost importance. Although no terrorist attacks have been successful in breaching dam infrastructure, the literature shows many attempts to attack dam infrastructure with explosives; for example, Chingaza Dam in Columbia and Bhakra Dam in India (Braimah et al.2012). In the light of recent increases in global terrorism and use of improvised explosive devices, dams appear to be attractive targets due to the capacity to adversely impact downstream communities and to attract media attention. Dam failures have been widely covered in the media and literature, and highlight their causes as well as associated widespread destruction (MacDonald and Langridge-Monopolis 1984; Kennard and Bromhead 2000; Muhunthan and Schofield 2000; Shepherd 2003; Braimah and Contestabile 2007; Graham 2009; De et al.2013). Dams are primarily concrete or earthen structures and depending on the mode of lateral load resistance can be gravity or compressive arch structures. Concrete gravity dams are least likely to be affected by explosives (Braimah et al.2012). Embankment dams, on the other hand, are generally earth-fill or rock-fill dams and are more susceptible to explosion cratering. The explosion crater can lead to overtopping and subsequent erosion of the dam. The level of damage caused by an explosive device on an embankment dam depends on the type and amount of explosive as well as the placement of the device relative to the dam cross-section. Knowledge of explosives effects on embankment dams is essential in assessing the vulnerability of dams to explosion attacks.