Page 94 - RoadCem Manual - PCT BV

Figure 4.45 Car in clay soil area.
Insight into the bearing strength of the soil and/or sub-base can be obtained by visual inspection. In areas where the ground is relatively soft (in soaked conditions) there is a typically bad bearing strength. Figure 4.45 shows an example.
The bearing strength can also be qualitatively determined on the basis of the of the grain size and its distribution. The grain size is the main factor determining the bearing strength of a soil and/or sub base. Typical bearing strength values for different soil sub-bases under soaked conditions are given in table 4.7. With dry conditions higher values can be reached for the bearing strength but these are not representative since we use the worst possible scenario in the design criteria for the pavement foundation!
Rocks
Gravel
Sand
Clay
Peat (fine fraction with high organic content)
400
400 100 - 150 25 - 75 5 - 15
Table 4.7 bearing strength for different soils.
Soil sort
Bearing strength Edyn [MPa]
The California Bearing Ration (CBR) is a parameter that is developed to measure (estimate) soil/sub base bearing strength (Methodology for measuring of CBR is given in the appendix). When the CBR value is known then the following formula can be used to get an indication for the soil/sub base bearing strength.
Edyn = 10 * CBR
Determination of a number of required measurements (in-situ)
The bearing strength of soil/sub base varies spatially and should therefore be determined/estimated at a number of different and characteristic points along the road.
94