Page 102 - Geotechnical Engineering Soil and Foundation Principles and Practice

Soils That Are Sediments
Soils That Are Sediments 97

4.3. Explain how one might identify the following from airphotos, and discuss
engineering features:
(a) Alluvial terrace composed of sand and gravel deposited by a braided
river.
(b) Peat bog.
(c) Terminal moraine.
(d) Esker.
(e) Stable sand dunes.
(f) Point bar and clay plug.
(g) Landslides.
(h) Alluvial fans.
(i) Talus.
4.4. Differentiate between a youthful stream, a braided stream, and a
meandering stream.
4.5. What confines a meander belt within a broad floodplain? Which are
most effective for containment, clay plugs or natural levees? Why? Draw a
cross-section showing a clay plug and associated point bar, backswamp
clay, and a natural levee.
4.6. Sketch a cross-section for a stream valley that has a succession of progres-
sively lower floodplain levels. What are these levels called? Which is the
oldest?
4.7. The transportation agent for sand dunes and for loess silt is the same, wind.
Which deposit do you expect to be closer to a source? Why?
4.8. What changes occur in loess with increasing distance from a source?
Explain the changes.
4.9. How do deposits from a braided stream differ from those from a
meandering stream? Make a list of deposits from a meandering stream.
4.10. Radiocarbon dating shows that Wisconsin-age loess in the United States
was deposited during the period between 29,000 to 14,000 ybp (years before
present). How does the average thickness accumulation per year of the
thickest loess deposits compare with the accumulation of dust alongside
a dusty road, measured to be as much as 2.5 mm/y (0.1 in./y)?
4.11. Suggest ways to keep sand dunes from encroaching on a housing
development.
4.12. The edge of a field of barchans 6 m high is located 2.4 km (1.1 miles) upwind
from an express highway. Estimate the time of arrival.
4.13. Would you expect to find any gravel terraces along the Mississippi River
floodplain? Why?
4.14. If you did find gravel terraces along the Mississippi River floodplain, would
they be loess covered? Why?
4.15. Which should give the better prediction of maximum scour depth that
might be anticipated during a flood, the deepest water depth in the river, or
the maximum clay thickness in a nearby oxbow? Why?

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