![]() Should the space be such that voids occur in the mix, the material will commonly show early signs of degradation and will be readily damaged by penetration of moisture. The volume of binder needs to be slightly greater than this volume, and hence a relatively high proportion of cement or lime may be required. ![]() The most important feature of sand for mortar manufacture is that the space between the aggregate particles must generally be about 30% by volume. Rock fines of similar grade can also be used. ![]() They are used in their natural form or processed by screening and washing. Sands for mortar production are excavated from sand and gravel pits in unconsolidated clastic deposits and are typically dominated by quartz. It is used as a jointing or surface-rendering material. Mortar consists of a fine aggregate with a binding agent. French, in Encyclopedia of Geology, 2005 Mortar This has been observed elsewhere, for example, in Florida, where several sinkholes formed following overabstraction of water ( Thornbush, 2017). In turn, the drop in the watertable may locally favor the development of sinkholes, such as those observed nearby Armala. This process may be further accentuated by a deficit in the solid load of the river, leading to river scouring and incision, which may locally endanger hydraulic structures like dams, culverts, and bridges and, more generally, induce changes in river morphology and eventually a lowering of the groundwater table. Mining also makes the land surface more unstable and may cause it to collapse. ![]() More specifically, they may cause bank erosion (undercutting, shallow landslides, collapses), thus, increasing the risk for adjacent settlements, especially when the river widens its active channel during the monsoon season. Although sand and gravel mining is allowing some poor families to make a living, such practices are also the cause of environmental deterioration (disappearance of aquatic life and habitat) and natural hazards. Many sand and gravel pits have been opened along the Seti Khola, particularly after the 2012 Seti Khola flood, because much debris was trapped in the upstream part of the sites where the flood current was constrained, such as Ramghat, or where the river could spread (meander loops) ( Fig. 12.18A and B). In recent decades, the rapid development of the city has dramatically increased the demand for construction materials. Further detailed body of work by Remke van Dam ( van Dam and Schlager, 2000 van Dam et al., 2002a, b, 2003) investigated the effects of iron minerals ( van Dam et al., 2002a), organic matter ( van Dam et al., 2002b), and determined that water content was the most significant control of dielectric properties in sediments ( van Dam et al., 2003). Field observations showed that GPR is able to image primary sedimentary structures, most likely due to changes in moisture content which were associated with changes in grain size where fine grained sediments have slightly higher water saturation than coarser grained sands and it was these minor changes in water that controlled the dielectric properties of the sediments ( Bristow et al., 1996). Some of the earlier GPR stratigraphic studies were conducted in sand and gravel pits where it was possible to ground truth the GPR profiles by comparison with exposed sections ( Bristow, 1994, 1995a Huggenberger, 1993 Jol et al., 2003) or excavated trenches ( Bristow et al., 1996). Bristow, in Treatise on Geomorphology, 2013 14.16.6 Radar Profiles as Cross-Sections and Ground Truth ![]()
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