c) Based on design SARs a pavement engineer has determined the cumulative damage

Question

c) Based on design SARs a pavement engineer has determined the cumulative damage factor for different distress modes as follows: DSAR5 = 6.78E+06 DSAR7 = 1.04E+07 DSAR125.27E+07 Subgrade rutting: Selected fill: N = 2.83E+11 N 3.87E+12 -> -> -> CDF = 3.67E-05 CDF = 1.1 CDF = 1.3 Cemented material fatigue: N 3.44E+07 The engineer suggested that although failed, did not fail by a significant amount and hence is ok. (i) Is this a valid conclusion? (ii) What would you recommend (no calculation needed)? ii) What is the impact if your recommendation is adopted? (3.0 marks) (1.5 marks) (0.5 marks)

Explanation / Answer

(i)CumulativeDamageFactor(CDF)isthesumof damage factors over all the loadings

– Pavement reaches its design life when CDF = 1.0

– If CDF < 1.0, then pavement has excess capacity, & CDF gives proportion of life consumed

– If CDF > 1.0, then pavement could fail early!

Since CDF is already 1.1 for Selected fill and 1.3 for Cemented material fatigue which shows that the pavement can fail anytime, hence it is not OK.

(ii) The selected fill needs to be replaced with another fill with a lesser value of CDF

(iii) If te CDF value reduces with the new fill, the pavement will be safer.

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