Site Investigation

(Geotechnical Studies)Lecture 2

Site Investigation

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Investigation Program

- Desk study- Site reconnaissance - Subsurface exploration

- Areal photographs-Geological and topographical maps- Hydrological information- Any previous information on the site

Desk study

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Walk over survey

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Subsurface exploration

Planning

- Determine depth of investigation

- Determine extent of investigation

These depends on type and extension of the project .

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Depth

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Depth

.Spacing

Spacing

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Methods

A- Test pits

- Constructed by excavation of

the ground

- Max depth is less than 5 m

- Provide good inspection and good

- Obtain good samples

- Problem of disturbance of ground

- Problem of ground water

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B- Boring

By drilling a hole into the ground using special motorized equipment .Boring enable the engineer to - identify subsurface condition,

- Perform insitu tests

- Obtain samples for tests in the laboratory

There are mainly Three widely used boring methodsa) Auguring (continuous flight auger)

b) Wash boring

c) Rock rotary drilling

a) Continuous flight auger Continuous flight augers are available in diameters 76 to 305 mm

They either solid or hollow stem

Can go to depths up to 70 m

Can keep sides of borehole

Sampling and tests can be done

Good for cohesionless soils

Required power to drive

The flights of the auger brings

Loose soils to the top

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b) Wash boring

Casing is required and ,the method is fast but only wash samples can be obtained

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Rotary drilling

Drilling bit required water or

air for cooling and remove chops

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Sampling

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Degree of disturbance

Uiop[

Thin walled tube

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