Structural Design of Pavement Thickness 241Example 8.2
A highway is envisaged to carry a traffic loading of 40 msa over its design
life. Interpret the necessary asphalt thickness for a wholly bituminous pave-
ment using the relevant chart from HD 26/01 (DoT, 2001).
Solution
From Fig. 8.7, the following required thicknesses can be deduced:
(1) For DBM/HRA base: 350 mm
(2) For DBM50 base: 310 mm
(3) For HDM base: 290 mm
(4) For HMB35 base: 280 mm.
Note: all thicknesses are rounded up to the nearest 10 mm in accordance with
the guidance from HD 26/01.
Example 8.3
A highway is envisaged to carry a traffic loading of 30 msa over its design
life. Interpret the necessary surfacing and lower base thicknesses for a flexi-
ble composite pavement using the relevant chart from HD 26/01.
Solution
From Fig. 8.8, the following information can be deduced.
The total asphalt layer required is 190 mm. Typically, this would be com-
posed of:
40 mm HRA wearing course (surface course), overlaying
50 mm basecourse (binder course), overlaying
100 mm roadbase (base).
For DBM/HRA base, required thickness is 350 mm
The lower base layer required on a granular subbase is:
250 mm of CBM3G base,or
200 mm of CBM3R or CBM4G,or
180 mm of CBM4R or CBM5G,or
150 mm of CBM5R.
Note: CBM 5, 4 and 3 are the highest quality cement bound materials,
usually prepared at a central plant from batched amounts of processed
crushed gravel or rock.
A very similar result is obtained from LR1132. If one examines Fig. 8.5
detailing required thicknesses for a concrete roadbase plus asphalt surfacing:
For a cumulative traffic figure of 30 msa:
Asphalt surfacing thickness =200 mm
Lean-mix concrete roadbase =250 mm.
which is within 10 mm of the overall thickness recommended by HD 26/01.