Laserfiche WebLink
80 SOIL MOfSTJRE ASVD GROUND WATER <br />' SI system of units hydraulic conductivity is in meters per day A derived unit of <br /> • <br /> "dons per day per square foot was used in the past it can be converted to feet <br />' per clay by dividing by 7 48 <br /> 4 3.3 PERM1=kB1LJTY OF SEDIMENTS <br />' Unconsoliaatea coarse-grained sediments represent some of the most <br /> prolific proauccrs of ground water Likewise, clays are often used for engineer- <br /> ing purposes, such as lining solid-waste disposal sites, because of their ex- <br />' tr2mely low ininnsic permeability There is obviously a wide-ranging continuum <br /> Of Pe meabwty values for unconsolidated sediments (Table 4 5) <br /> The intrinsic permeability is a function of the size of the pore opening <br />' The smaller the size of the sediment grains, the larger the surface area the water <br /> contacts (Figure 4 13) This increases the fractional resistance to flow, which <br /> reduces the tntruisic permeability For well-sorted sediments, the intrinsic <br /> Permeability is proportional to the a aw size of the sediment (25) <br />' For sand-sized alluvial deposits, several factors relating intrinsic perme- <br /> abalaty to grain size have been noted (26) These observations would Bold true <br /> for all sedimentary deposits, regardless of ongan of deposition <br />' 1 As the median grain size increases, so does permeability This is due <br /> to larger pore openings <br /> 2. Permeability will decrease for a given median diameter as the stan- <br /> dard deviation of particle size increases The increase in standard <br /> deviation indicates a more poorly sorted sample, so that the finer <br /> material can fill the voids between larger fragments <br /> 3 Coarser samples show a greater decrease in permeability with an <br /> increase in standard deviation than do fine samples <br /> 4, Unimodal (one dominant size) samples have a greater permeability <br /> 1 <br /> TABLE 4 5 Ranges of intrinsic permeabihties and hydraulic conductivi- <br /> ties for unconsolidated sediments <br />' Intrinsic Hydraulic <br /> Permeability Conductivity <br />' Material (darcys) (cm/sec) <br /> Clay 10-6-10_3 10""9-10_6 <br /> Sift, sandy silts, <br /> clayey sands, tall 10-3-10µ' 10-6--10-4 <br />' Silty sands, fine sands 10-2-1 10rt5-10-3 <br /> Well-sorted sands, <br /> glacial outwash 1 —102 10-3-10�' <br /> Weil-sorted gravel lo-101 10-z-1 <br /> 1 <br /> 1 _ <br />