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Engineering Geology

Engineering Geology - geomuseu

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Chapter 7<br />

Figure 7.13<br />

An electric penetrometer tip. (a) without friction sleeve, (b) with friction sleeve.<br />

level and clamped to the borehole casing or rigidly fixed to the ground. The maximum torque<br />

required for rotation is recorded. When the vane is rotated, the soil fails along a cylindrical<br />

surface defined by the edges of the vane as well as along the horizontal surfaces at the top<br />

and bottom of the blades. The shearing resistance is obtained from the following expression:<br />

M<br />

t = Ê<br />

2 3<br />

ˆ<br />

Ë Á DH D<br />

p<br />

2 + 6<br />

˜<br />

¯<br />

(7.3)<br />

where t is the shearing resistance, D and H are the diameter and height of the vane, respectively,<br />

and M is the torque. Tests in clays with high organic contents or with pockets of sand or silt are<br />

likely to produce erratic results. The results therefore should be related to borehole evidence.<br />

Loading tests can be carried out on loading plates in soils or rocks (Fig. 7.16a). However, just<br />

because the ground immediately beneath a plate is capable of carrying a heavy load without<br />

excessive settlement, this does not necessarily mean that the ground will carry the proposed<br />

337

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