Fill specifications - Geotechnical Investigation and Design Tables - page 219

17.10 Rock revetments
•

Rock revetments can be selected rock armour, rip rap or stone pitching.

Table 17.10 Rock revetments (McConnell, 1998).

Revetment type Specification Porosity Thickness

Rip-Rap D 85 /D 15 2 to 2.5 35 to 40% 2 to 3 stones/rock sizes thick ∼

Rock armour D 85 /D 15 1.25 to 1.75 30 to 35% 2 rock sizes thick ∼

17.11 Durability
•

The degradable materials decompose when exposed to air, as they take on water.

•

Sedimentary rocks are the most common rock types, which degrade rapidly, such
as shales and mudstones.

•

Foliated Metamorphic rocks such as slate and phyllites are also degradable.

Table 17.11 Indicators of rock durability.

Test Strong and durable Weak and non durable - Soil like

Rock like behaviour in long term Soil like behaviour in the long term

Point load index 2 MPa 1 MPa ≥ <

Free swell

≤

3%

>

5%

Slake durability test 90 60 ≥ <

Jar slake test 6 2 ≥ <

Los angeles abrasion 25% 40%

< >

Weathering Fresh to slightly weathered Extremely weathered

RQD

>

50%

<

25%

•

Several of the above indicators should be in place before classed as a likely non
durable material.

17.12 Durability of pavements
•

The pavement material is usually obtained from crushed aggregate.

•

The wearing and base courses would have a higher durability requirements than
the sub base.

Table 17.12 Durability requirements for a pavement.

Parameter Wearing Base Sub base

course course

Upper Lower

Water absorption 2% 3% 4% 5%

< < < <

Aggregate crushing value

<

25%

<

30%

<

35%

<

40%

Los angeles abrasion 30% 35% 40% 45% < < < <

Sodium sulphate soundness 10% 15% 20% 25% Loss < < < <

Flakiness index

<

35

<

40

<

40

<

45

Ten percent fines (Wet) 150 kN 100 kN 75 kN 50 kN

> > > >

Wet/Dry strength variation

<

30%

<

40%

<

50%

<

50%