EM 1110-2-1100 (Part III)
30 Apr 02
(b) Where they are present at coastal engineering projects, such organic sediments must be considered.
Pile foundations bearing significant loads must penetrate the organic material. It may be required to remove
the compressible sediment before construction.
(3) Sand and gravel.
(a) Ocean beaches of the world consist of sand and some gravel. The typical temperate zone ocean beach
is made of quartz sand whose median diameter D50 is in the range 0.15 # D50 # 0.40 mm. In colder latitudes
where geologically recent glacial action has affected sediment supply and the wave climate is more severe,
the composition of the beach material becomes more varied and size tends to increase. See, for example,
Figure 89 of Davies (1980). In these glacier-affected latitudes, sand grains include silicate and oxide
compositions (heavy minerals) as noticeable components along with the quartz, and coarse pebbles (gravel
or "shingle") may locally dominate the sediment.
(b) In tropical latitudes, quartz beach sand may give way to calcium carbonate sand produced from shelly
organisms, algae, or coral. See, for example, Figure 92 of Davies (1980) derived from earlier work of Hayes.
Carbonate sands differ from quartz sand in two important ways: carbonates are chemically more active than
quartz, making carbonate grains subject to local cementation or sometimes dissolution, and individual
carbonate grains are structurally weaker than single quartz grains so that they may be crushed by traffic and
often have sharper edges.
(c) Oolites are a particular variety of carbonate sands locally abundant in the Bahamas and other
semi-tropical lands. Oolites are sands whose grains are ellipsoidal in shape, consisting of thin smooth
concretionary layers of calcium carbonate. There is a very large literature on this subject, mainly by
geologists; section 13.3 of Blatt, Middleton, and Murray (1980) is a good starting point.
(d) Beaches in bays and estuaries often differ from ocean beaches at the same latitudes. Often the beach
material along interior shores is coarser and much more limited in volume than along ocean shores, possibly
because limited wave action on interior waters has not eroded enough material to produce extensive sand
beaches.
(4) Cobbles, boulders, and bedrock. Glaciated lands, tectonically active areas, and hilly or mountainous
shorelines often have shores with abundant cobbles, boulders, and bedrock. Such shores result from enhanced
supplies of rock produced by glaciers, by stream erosion of mountainous terrain, or by enhanced wave erosion
at the downwind end of long fetches.
III-1-6. References
Allen 1970
Allen, J. R. L. 1970. "The Avalanching of Granular Solids on Dune and Similar Slopes," Journal of
Geology, Vol 78, pp 326-351.
American Society for Testing Materials 1994
American Society for Testing Materials. 1994. Volume 04.08, Soil and Rock (1): D420 D4914, American
Society for Testing and Materials, Philadelphia, PA.
Bagnold 1963
Bagnold, R. A. 1963. "Beach and Nearshore Processes; Part I: Mechanics of Marine Sedimentation," The
Sea: Ideas and Observations, M. N. Hill, ed., Interscience, New York, Vol 3, pp 507-528.
Coastal Sediment Properties
III-1-33
Previous Page
