Determination of design subgrade CBR

The CBR test is carried out on soaked specimens (for 4 days) and in accordance to CEN EN 13286-47 (2012). Samples are taken within the first 600 mm below formation level. The CBR value is determined at 90% of the maximum dry density determined by proctor (modified) compaction (see Section 1.4.7). When undisturbed samples are taken from naturally cemented soil material, where water table is low ( 1 m), the value of 90% changes to 95%. 

The design CBR is the value that is greater by 90% of the CBR values determined, for a project with design ESAL 1 x 10 , and by 75% of the CBR values, for a project with design ESAL 1 X 10 . 

Design CBR values greater than 20% are considered as being equal to 20%. 

The MAAT is the mean of all monthly average air temperatures. Its determination requires air (ambient) temperature data recorded over long periods, available at any central metrological office. 

For the needs of the methodology, a table is provided in the source containing the MAAT of most major cities in the Greek territory (Nikolaides 2005). The values were determined by utilising metrological data from 1965 to 1995. It is noted that the MAAT in the Greek territory was found to range from 13°C to 19°C. 

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