# A collapsible soil sub-grade sample was tested using Standard California Bearing Ratio apparatus, and the observations are given below: Sl. No Load Penetration 1 60.55 kg 2.5 mm 2. 80.55 kg 5.0 mm Taking the standard assumptions regarding the load penetration curve, the CBR value of the sample will be taken as

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ESE Civil 2016 Paper 2: Official Paper
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1. 39%
2. 40%
3. 4.4%
4. 5.5%

Option 3 : 4.4%
Free
ST 1: Building Material and Concrete Technology
16847
20 Questions 20 Marks 12 Mins

## Detailed Solution

Concept:

CBR test is a strength test conducted on the soil by introducing a 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\

For standard aggregate at 2.5 mm penetration, Load is 1370 kg

For standard aggregate at 5 mm penetration, Load is 2055 kg

Calculation:

Given:

 Sl. No Load Penetration 1 60.55 kg 2.5 mm 2. 80.55 kg 5.0 mm

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

At 2.5 mm penetration, $$CBR = \;\frac{{60.5}}{{1370}} \times 100 = 4.4\%$$

At 5 mm penetration, $$CBR = \;\frac{{80.55}}{{2055}} \times 100 = 3.9\%$$

CBR is the maximum of the above two ratios i.e. 4.4%