Site Investigation - Elements of Soil Mechanics - page 159

Table 6.2 Guidance values for depth (z a ) of investigation points.

Foundation type Depth criteria *

Shallow foundations for high-rise and civil
engineering projects

The greater of:
z a ≥ 6 m;
z a ≥ 3.0 b f
(b f = see Fig. 6.1)

Raft foundation z a ≥ 1.5 b B

(b B = see Fig. 6.1)

Linear structures: roads and airfields z a ≥ 2 m

Linear structures: canals and pipelines The greater of:

z a ≥ 2 m;
z a ≥ 1.5 b Ah
(b Ah = see Fig 6.1)

Pile foundations z a ≥ 5 m;

z a ≥ 1.0 b g
z a ≥ 3.0 D F
(b g , D F = see Fig 6.1)

* The depths are measured from the reference levels shown in Fig 6.1 .

z a

B f

z a

b B

(a) Shallow foundation. (b) Raft foundation.

b Ah

z a

z a

z a

(c) Roads and trenches.

D F

b g
(d) Piles and pile groups.

Fig. 6.1 Depth (z a ) of investigation points for various structures.