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Building Design and Construction Handbook - Merritt - Ventech!

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SOIL MECHANICS AND FOUNDATIONS 6.13<br />

TABLE 6.4 Use, Capabilities, <strong>and</strong> Limitations of Test Pits <strong>and</strong> Trenches<br />

Exploration method General use Capabilities Limitations<br />

H<strong>and</strong>-excavated test<br />

pits<br />

Backhoe-excavated<br />

test pits <strong>and</strong><br />

trenches<br />

Bulk sampling, insitu<br />

testing, visual<br />

inspection<br />

Bulk sampling, insitu<br />

testing, visual<br />

inspection,<br />

excavation rates,<br />

depth of bedrock<br />

<strong>and</strong> groundwater<br />

Dozer cuts Bedrock<br />

characteristics,<br />

depth of bedrock<br />

<strong>and</strong> groundwater<br />

level, rippability,<br />

increase depth<br />

capability of<br />

backhoe, level<br />

area for other<br />

exploration<br />

equipment<br />

Trenches for fault<br />

investigations<br />

Source: NAVFAC DM-7.1, 1982.<br />

Evaluation of<br />

presence <strong>and</strong><br />

activity of faulting<br />

<strong>and</strong> sometimes<br />

l<strong>and</strong>slide features<br />

Provides data in<br />

inaccessible areas,<br />

less mechanical<br />

disturbance of<br />

surrounding<br />

ground<br />

Fast, economical,<br />

generally less than<br />

4.6 m (15 ft)<br />

deep, can be up to<br />

9 m (30 ft) deep<br />

Relatively low cost,<br />

exposures for<br />

geologic mapping<br />

Definitive location of<br />

faulting,<br />

subsurface<br />

observation up to<br />

9 m (30 ft) deep<br />

Expensive, timeconsuming,<br />

limited to depths<br />

above<br />

groundwater level<br />

Equipment access,<br />

generally limited<br />

to depths above<br />

groundwater level,<br />

limited<br />

undisturbed<br />

sampling<br />

Exploration limited<br />

to depth above the<br />

groundwater table<br />

Costly, timeconsuming,<br />

requires shoring,<br />

only useful where<br />

dateable materials<br />

are present, depth<br />

limited to zone<br />

above the<br />

groundwater level<br />

to meet exact specifications, such as those stated by ASTM D 1587-94 (1998). The<br />

Shelby tube shown in Fig. 6.1 has an inside diameter of 6.35 cm (2.5 in).<br />

Many localities have developed samplers that have proven successful with local<br />

soil conditions. For example, in southern California, a common type of sampler is<br />

the California Sampler, which is a split-spoon type sampler that contains removable<br />

internal rings, 2.54 cm (1 in) in height. Figure 6.1 shows the California Sampler<br />

in an open condition, with the individual rings exposed. The California Sampler<br />

has a 7.6-cm (3.0 in) outside diameter <strong>and</strong> a 6.35-cm (2.50-in) inside diameter.<br />

This sturdy sampler, which is considered to be a thick-walled sampler, has proven<br />

successful in sampling hard <strong>and</strong> desiccated soil <strong>and</strong> soft sedimentary rock common<br />

in southern California.<br />

Three types of soil samples can be recovered from borings:

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