29.09.2015 Views

Engineering Geology

Engineering Geology - geomuseu

Engineering Geology - geomuseu

SHOW MORE
SHOW LESS
  • No tags were found...

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

E n g i n e e r i n g G e o l o g y<br />

Methods of Excavation: Digging<br />

The diggability of ground is of major importance in the selection of excavating equipment and<br />

depends principally upon the intact strength of the ground, its bulk density, bulking factor and natural<br />

water content. The latter influences the adhesion or stickiness of soils, especially clay soils.<br />

At present, there is no generally acceptable quantitative measure of diggability, assessment<br />

usually being made according to the experience of the operators. However, a fairly reliable<br />

indication can be obtained from similar excavations in the same materials in the area or the<br />

behaviour of the ground excavated in trial pits. Attempts have been made to evaluate the<br />

performance of excavating equipment in terms of seismic velocity (Fig. 9.4). It would appear<br />

that most earth-moving equipment operates best when the seismic velocity of the ground<br />

is less than 1000 m s -1 and will not function above approximately 1800 m s -1 .<br />

When material is excavated, it increases in bulk, this being brought about by the decrease that<br />

occurs in density per unit volume. Some examples of typical bulking in soils are given in Table 9.2.<br />

The bulking factor is important in relation to loading and removal of material from the working face.<br />

Groundwater and Excavation<br />

Groundwater frequently represents one of the most difficult problems during excavation, and<br />

its removal can prove costly. Not only does water make working conditions difficult, but piping,<br />

uplift pressures and flow of water into an excavation can lead to erosion and failure of the sides.<br />

Figure 9.4<br />

Seismic velocities for determining diggability.<br />

462

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!