Thickness determination of capping layer

The thickness of the capping layer is determined in terms of the design CBR of the subgrade. For simplicity, the methodology distinguishes two limiting CBR values and therefore only two capping layer thicknesses. In particular  

The abovementioned capping layer thicknesses are also shown in Table 13.10, aside from the recommended base/sub-base thickness. 

If the design subgrade CBR is lower than 3%, the value of CBR used to determine the asphalt layer thickness is taken as being equal to 3%. In all other cases, the design CBR is that determined from laboratory tests. 

The materials for capping layer may be selected granular material or cement- and lime-stabilised material, as those described in Section 10.3.1. Soil stabilisation is also recommended to be considered, when highly cohesive soil material is encountered. For details, see Section 10.3.2. 

The base and sub-base are dealt as one unified layer. The thickness of this layer can be 200, 300 or 400 mm, which simplifies construction works (base/sub-base is constructed in 100 mm thick layers). 

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