Site investigation - Geotechnical Investigation and Design Tables - page 12

1.13 Sample size
•

The sample size should reflect the intent of the test and the sample structure.

•

Because the soil structure can be unknown (local experience guides these deci-
sions), then prudent to phase the investigations as suggested in Table 1.1.

Table 1.13 Specimen size (Rowe, 1972).

Clay type Macro-fabric Mass, permeability, km/s Parameter Specimen size (mm)

Non fissured None 10 − 10 C u ,C 37

sensitivity 5 m v ,c v 76 <

High pedal, silt, 10 − 9 to 10 − 6 C u , 100-250

sand layers, C 37

inclusions, m v 75

organic veins. c v 250

Sand layers 2mm 10 − 6 to 10 − 5 C 37

>

at 0.2 m spacing. m v, c v 75

<

Sensitivity 5 Cemented with C u , 50-250

>

any above. C ,

m v, c v

Fissured Plain fissures 10 − 10 C u , 250

C , 100

m v, c v 75

Silt or sand fissures 10 − 9 to 10 − 6 C u , 250

C , 100

m v, c v 75

Jointed Open joints 100

Pre-existing slip C r , 150 or remoulded r

1.14 Quality of site investigation
•

The quality of an investigation is primarily dependent on the experience and
ability of the drilling personnel, supervising geotechnical engineer, and ade-
quacy of the plant being used. This is not necessarily evident in a cost only
consideration.

•

The Table below therefore represents only the secondary factors upon which to
judge the quality of an investigation.

•

A good investigation would have at least 40% of the influencing factors
shown, ie does not necessarily contain all the factors as this is project and site
dependent.

•

An equal ranking has been provided although some factors are of greater
importance than others in the Table. This is however project specific.

•

The table can be expanded to include other factors such a local experience, prior
knowledge of project/site, experience with such projects, etc.