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Building Design and Construction Handbook - Merritt - Ventech!

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TABLE 6.21 Site Improvement Methods<br />

Method Technique Principles Suitable soils Remarks<br />

Remove <strong>and</strong> replace Excavate weak or undesirable Any<br />

Limited depth <strong>and</strong> area where<br />

material <strong>and</strong> replace with<br />

cost-effective; generally � 30<br />

better soils<br />

ft<br />

Soil replacement<br />

methods<br />

Displacement<br />

Overload weak soils so that<br />

they shear <strong>and</strong> are displaced<br />

Very soft<br />

Problems with mud-waves <strong>and</strong><br />

trapped compressible soil<br />

by stronger fill<br />

under the embankment;<br />

highly dependent on specific<br />

site<br />

Trenching<br />

Allows water drainage<br />

Soft, fine-grained soils Effective depth up to 10 ft;<br />

<strong>and</strong> hydraulic fills<br />

speed dependent on soil <strong>and</strong><br />

trench spacing; resulting<br />

desiccated crust can improve<br />

site mobility<br />

Precompression<br />

Loads applied prior to<br />

Normally consolidated Generally economical; long time<br />

construction to allow soil<br />

fine-grained soil,<br />

may be needed to obtain<br />

Water removal<br />

methods<br />

consolidation<br />

organic soil, fills<br />

consolidation; effective depth<br />

only limited by ability to<br />

achieve needed stresses<br />

Precompression with Shortens drainage path to speed Same as above<br />

More costly; effective depth<br />

vertical drains<br />

consolidation<br />

usually limited to �100 ft<br />

Electro-osmosis<br />

Electric current causes water to Normally consolidated Expensive; relatively fast;<br />

flow to cathode<br />

silts <strong>and</strong> silty clay<br />

usable in confined area; not<br />

usable in conductive soils;<br />

best for small areas<br />

6.111

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