Subgrades and pavements - Geotechnical Investigation and Design Tables - page 160

•

Adding cement is just one of the means of acquiring additional strength.

•

Above 10% cement may be uneconomical, and other methods should be
considered.

•

The table presents a typical range, but amaterial specific testing programme should
be carried out to conform the most economical cement content.

13.13 Effect of cement soil stabilisation
•

The stabilisation of pavement layers is also used to produce higher strengths, and
minimise the pavement thickness.

•

These may be cement treated base (CTB) or cement treated sub bases (CTSB).

Table 13.13 Soil stabilisation (Lay, 1990; Ingles, 1987).

Stages Soil Modified soil Cemented soil Lean mix Concrete

Cement content for granular material 0% 5% 5% 15% < > >

Tensile strength

<

80 kPa

>

80 kPa

Failure mode Plastic--------------------------------------- Brittle

→

•

For each 1% cement added, an extra unconfined compressive strength of 500 kPa
to 1000 kPa may be achieved.

•

Shrinkage concerns for cement > 8%.

•

Tensile strength ∼ 10% Unconfined compressive strength.

13.14 Soil stabilisation with lime
•

Applicable mainly to high plasticity materials.

•

The table presents a typical range, but amaterial specific testing programme should
be carried out to conform the most economical lime content.

•

Use the lime demand test first, before testing for other material properties. With-
out this test, there would be uncertainty on the permanent nature of the lime
stabilisation.

Table 13.14 Typical lime content for various soil types (Ingles, 1987).

Soil type Lime requirement

Fine crushed rock 0.5%-1%

Well graded and poorly graded gravels GW, GP 0.5-2%

Silty and clayey gravels GM, GC,

Well graded and poorly graded sands SW, SP

Silty sands, clayey sands SM, SC 2%-4%

Sandy clay, silty clays, low plasticity inorganic clays and silts ML, CL, 4%-6%

Highly plastic inorganic silts MH

Highly plastic inorganic clays CH 5%-8%

Highly organic OL, OH, Pt Not recommended