**SUMMARY**

This article will describe the calculations used for CBR Test per BS standard.

**SOLUTION**

**LOAD [L]**

Recorded during test or manually entered by user.

**PENETRATION [P]**

Recorded during test or manually entered by user.

**CORRECTED LOAD [CL]**

CL = L- initial load + top cap weight.

**CORRECTED PENETRATION [CP]**

CP = P - initial displacement

**CBR PERCENTAGE [CBR]**

**PENETRATION INDEXES [PI]** = 2 mm, 2.5 mm, 4 mm, 5 mm, 6 mm, and 8 mm.

CBR Values are calculated at closest CP to PI.

**DIVISION VALUES [DV] per BS **=

11.5 @ 2 mm, 13.2 @ 13.2 mm, 17.6 @ 4 mm, 20 @ 5 mm, 22 @ 6 mm, and 26.3 @ 8 mm.

DV values are in units kN.

CBR @ PI = CL [kN] / DV * 100

**CORRECTED CBR PERCENTAGE [CCBR]**

Same as CBR but adjusted by correction line drawn.

From the correction line we get the correction lines **Slope [S]**, **Y-Int [B]**, and **Corr [C]**.

Next, we need to determine the displacement offset of the line. This is found with the line equation when y is zero.

**CORRECTION LINE PENETRATION CORRECTION VALUE [C]**

C = -B / S. This is derived from y = mx +b and we are solving for x.

The closest matching P value for the PI is adjusted with C yielding the Adjusted Penetration value.

**ADJUSTED PENETRATION [AP]**

AP = CP + C

Finally, we determine where the AP value intersects with the curve. A vertical line is used to determine intersection. This will yield the **ADJUSTED LOAD [AL]** value.

CCBR = AL / DV

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