Xai-Xai IDP – TRANSPORTATION PLANNING AND ROADS
TYPICAL PAVEMENT DESIGN CROSS SECTION
Double seal surfacing
19mm and 8,5 mm stone
Base course: Sand + 6% cement
150 mm thick
Sub-base course: CBR > 45%
200 mm thick
Sub-grade Compaction 95% CBR > 30%
200 mm thick
In situ processing
The pavement design for local roads should be based on a design for brick paving. A lightly cemented base may be required for structural strength, on a selected sub base.
4.3.2 Construction and Construction Materials
Construction cost was obtained from the provincial roads department. The rates are based on current internal rehabilitation rates and may be conservative for a large contract where economy of scale comes to play. However, the risk to a contractor may result in high rates. The cost estimate of USD $470,900 for the 3.37 km of Praia Velha internal roads gives a cost per km of US$ 141,157, which can be rounded off to US$150,000 per km.
The available material for road construction is sand. The soil consists of red and white sands. Both types are very fine (up to 25% of the material is finer than 75 micron). The plasticity index of the material is in the order of 10, indicating no cohesion. It is prone to wind and water erosion if exposed and is highly permeable.
The dunes consist of either white sand or red sand. The latter has some cohesion (Plasticity Index of 7 to 12) and generally has a higher California Bearing Ratio than the white sand. Borrow pits are located along the district road between the town and the beach. By utilising the existing borrow pits, the environmental impact is reduced and provision can be made to finish off the borrow pits in an orderly manner. At present, some of the borrow pits are used as rubbish dumps.
There is a total absence of local alternative construction materials. Coarse aggregate for seals and concrete aggregate must be transported in from Maputo and is very expensive. Bitumen is available as by-product from fuel refinery, though transport cost may be significant.
The use of paving bricks made for local sand and cement must be investigated as a means of retaining income in the local community. Variations in colour and texture can be used to enhance the appearances and link with urban design elements.