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FAO-PAP/RAC-MICOA

TRANSPORTATION PLANNING AND ROADS - Xai-Xai IDP

be in the road reserve, while sewerage (if provided) was assumed to run mid block. A typical cross section is shown in Figure 1 that follows.

Figure 1

TYPICAL CROSS SECTION

CUT

1,5m

3m

3m

1,5m

FILL

SIDE

ROADWAY

SIDE

SLOPE

SLOPE

SHOULDER

SHOULDER

Drainage

The sandy dune material drains very quickly and the existing district road between the town and the beach has not drainage culverts under the roadway. Natural depressions serve as sumps for storm water runoff. This approach was also adopted where possible. The detail design must review the drainage approach based on better information on the material and natural ground levels.

Design speed

The design speeds on the distributor and collector roads were taken as 60 km/h as these roads serve short distance traffic in a coastal resort setting. The design speeds on local roads were taken as 40 km/h.

Gradients

The high dunes dictate that either steep gradients or deep cuts and high fill is constructed. As the sand lacks cohesion and is prone to wind erosion after denudation, the design option of steep gradients (maximum 15% for short sections) was chosen for the route determination. The final design must review this option when more accurate surveys and geotechnical information are available.

Pavement design

The local pavement design for district roads consists of formed and compacted sub grade, 200mm selected sub-base, 150mm cemented base and double bitumen seal (see Figure 2 below). This pavement design should be the basis of the detail pavement design for distributor and collector roads, as the local road maintenance teams are geared to maintain these roads. The structural requirement in terms of traffic loading may reduce some layer thickness to 150mm.

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