Page 101 - Geotechnical Engineering Soil and Foundation Principles and Practice

Soils That Are Sediments
96 Geotechnical Engineering

Surcharging can be beneficial but remains an uncertain remedy because of gradual
disintegration or decay of components in the fill. Another method of treatment is
to repeatedly drop a large weight using a crane, a process called deep dynamic
compaction. Driven piles can be used as foundation elements, but even this can be
difficult if the fill contains structural elements such as concrete rubble that also
makes the fill difficult to investigate by drilling.

4.10.2 Clues
Fill soil is out of place—that is, it does not fit a natural order. This requires an
appreciation for the natural order, which is a reason for emphasis in this and the
next chapter. Fill soil does not follow the dictates or conditions imposed by
geology or by weathering. Fill soil is a mix. A common evidence for fill is a buried
layer of topsoil that under normal circumstances would be on top.

Other critical evidence is bits of glass, concrete, brick fragments, bones, coal ashes,
lumber, bedsprings, soup cans, etc. Such clues to landfill must be recorded in boring
logs and soil reports, which are legal records and can be subject to subpoena.

Fill containing organic material or garbage can generate methane and if allowed
to accumulate inside a building can cause an explosion. Buildings should be
separated from such fill with a plastic liner and/or ventilation system.

Landfills that include toxic or radioactive wastes add another dimension to the
problem, and are addressed by specialists in geoenvironmental engineering.

The failure to recognize random fill and take it into account in design almost
inevitably leads to future difficulties.

4.11 SUMMARY

Most geotechnical problems are not the result of mathematical errors or use of the
wrong formulas, although such errors obviously must be avoided. Some problems
result from poor or inappropriate construction practices, but most derive from
an inadequate appreciation for the soil, its properties, and its variability.
A geotechnical engineer learns to have a critical eye in order to see problems
before they happen.

Problems
4.1. Explain how the weight of a continental glacier can affect properties of the
underlying soil deposits. How may this relate to allowable foundation
pressure to minimize settlement?
4.2. How can a continental glacier move so far on such a low slope angle?

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