Subgrades and pavements - Geotechnical Investigation and Design Tables - page 159

Table 13.10 Properties of mechanically stable gradings for pavements (adapted from Woolorton
(1947)).

Application % passing 75 % passing 425 micron % 2mm

>

micron Medium sand or less Gravel size

“Fine material''

Unstable in wet due to high volume change 50% 80% 0%

> >

Light traffic 40% to 20% 70% to 40% 0% to 40%

Heavy traffic wearing course 20% to 10% 40% to 20% 40% to 60%

Heavy traffic base course 15% to 10% 20% to 10% 60% to 70%

13.11 Soil stabilisation with additives
•

The main types of additives are lime, cement and bitumen.

Table 13.11 Soil stabilisation with additives.

Soil property Typical additive

% Passing 75 micron Atterberg

>

25% PI

<

10% Bitumen, cement

PI 10% Cement, lime >

25% PI 10% Cement

< <

PI

=

10-30% Lime, Cement, lime

+

bitumen

PI 30% Cement, lime cement > +

- Cement additive typically 5 to 10%, but can vary from 0.5 to 15%. Best suited
to Clayey Sands (SC).

- Lime additives typically 1.5% to 8%. Best suited to Silts and Clays.

- Bitumen additives typically 1 to 10%. Best suited to Clayey Gravels (GC).

13.12 Soil stabilisation with cement
•

If the subgrade has insufficient strength then stabilisation of the subgrade may be
required.

Table 13.12 Typical cement content for various soil types (Ingles, 1987).

Soil type Cement requirement

Fine crushed rock 0.5%-3%

Well graded and poorly graded gravels GW, GP 2%-4%

Silty and clayey gravels GM, GC,

Well graded sands SW

Poorly graded sand, silty sands, clayey sands SP, SM, SC 4%-6%

Sandy clay, silty clays ML, CL 6%-8%

Low plasticity inorganic clays and silts
Highly plastic inorganic clays and silts

MH, CH 8%-12%

Organic clays OL, OH 12%-15% (pre treatment with lime)

Highly organic Pt Not suitable