Question

 In a CBR test, the load sustained by a remoulded soil specimen at 5 mm penetration is 120 kg. The CBR value of the soil will be:
1. 9.2%
2. 7.3%
3. 5.84%
4. 2.4%

Answer 1

Correct Answer - Option 3 : 5.84%

Concept:

CBR test is strength test conducted on the soil by introducing surcharge load at the compaction rate of 1.25 mm per minute on a completely soaked soil sample passing through 20 mm sieve size.

\({\rm{CB}}{{\rm{R}}_{\rm{\delta }}} = \frac{{{{\rm{P}}_{\rm{\delta }}}{\rm{\;of\;soil}}}}{{{{\rm{P}}_{\rm{\delta }}}{\rm{\;of\;standard\;crushed\;aggregate}}}} \times 100\)

δ = displacement in mm

Pδ = Load corresponding to ‘δ’ settlement

Ps = Load for standard crushed aggregate:

 At 5 mm penetration Standard load Ps = 2055 kg

 At 2.5 mm penetration standard load Ps = 1370 kg

Calculation:

 Given,

 Sustained load at 5 mm penetration = 120 kg 

\(CBR = \;\frac{{{\rm{Load\;carried\;by\;specimen}}}}{{{\rm{load\;carried\;by\;standard\;specimen}}}} \times 100\)

At 5 mm penetration, \(CBR = \;\frac{{120}}{{2055}} \times 100 = 5.84\% \)