Link points to Internet Archive / others. Not hosted by InfraLens. Details
IS 8763:1978 is the Indian Standard (BIS) for in-situ california bearing ratio (cbr) test for soils. This standard details the procedure for conducting the California Bearing Ratio (CBR) test on soils in-situ. It is used to determine the load-bearing capacity of subgrade soils for designing and evaluating pavements, roads, and airfields. The code specifies the apparatus, test procedure, data recording, and calculation methods.
Lays down the procedure for conducting the in-situ California Bearing Ratio (CBR) test on soils.
Overview
Status
Current
Usage level
Frequently Used
Domain
Geotechnical — Surveying and Geotechnical Investigation
! Ensure the reaction vehicle is significantly heavier than the maximum anticipated test load to prevent lifting, which invalidates the test.
! The test area must be leveled precisely to ensure the plunger is perpendicular and fully in contact with the soil before applying the initial seating load.
! If the load-penetration curve is initially concave, a correction must be applied by shifting the origin, as described in the standard.
Standard Test Method for CBR (California Bearing Ratio) of Soils in Place
Specifies the procedure for determining the in-place California Bearing Ratio of soil by using a portable hand-operated or vehicle-mounted loading apparatus.
BS 1377-9:1990British Standards Institution (BSI), United Kingdom
HighCurrent
Methods of test for soils for civil engineering purposes. In-situ tests
Clause 4.3 describes the determination of the California bearing ratio (in-situ), covering the apparatus and procedure for the test.
AS 1289.6.1.1:1998Standards Australia, Australia
HighCurrent
Methods of testing soils for engineering purposes - Method 6.1.1: Soil strength and consolidation tests - Determination of the California Bearing Ratio of a soil - Field in-place method
Provides a direct method for determining the in-situ CBR of soils for pavement design and evaluation.
Key Differences
≠The specified rate of plunger penetration in IS 8763 is 1.25 mm/min, whereas BS 1377-9 specifies 1.0 ± 0.2 mm/min and ASTM D4429 specifies a slightly faster rate of 1.3 mm/min (0.05 in./min).
≠IS 8763 requires a minimum surcharge mass of 4.5 kg. ASTM D4429 requires a similar minimum of 4.54 kg (10 lb), but BS 1377-9 specifies a higher minimum of 10 kg (two 5 kg rings).
≠The reaction load requirement in IS 8763 is specified with an example of a 7-tonne loaded truck. ASTM D4429 is more performance-based, requiring the reaction load to exceed the maximum test load by at least 4.5 kN (1000 lbf) without specifying the means.
≠IS 8763 suggests clearing a circular test area of about 450 mm diameter, while ASTM D4429 specifies a larger diameter of approximately 560 mm (22 in.) for test preparation.
Key Similarities
≈All standards use the same fundamental principle of measuring the load required for a standardized plunger to penetrate the soil at a controlled rate.
≈The dimensions of the penetration plunger are virtually identical across all standards, with a diameter of 50 mm (approx. 2 inches).
≈The procedure for calculating the CBR value as a percentage of standard loads at 2.5 mm and 5.0 mm penetrations is the same. The standard load values themselves are universally recognized and consistent.
≈All standards require the application of a small initial seating load (e.g., 4 kg in IS 8763, 4.54 kg/44 N in ASTM D4429) to ensure firm contact between the plunger and the soil surface before starting the test.
≈All standards include a procedure for correcting the stress-penetration curve if it is concave upwards, by adjusting the zero point to the tangent of the steepest part of the curve.
Parameter Comparison
Parameter
IS Value
International
Source
Plunger Diameter
50 mm
49.63 ± 0.13 mm (1.954 in.)
ASTM D4429-18
Rate of Penetration
1.25 mm/min
1.0 ± 0.2 mm/min
BS 1377-9:1990
Standard Load at 2.5 mm Penetration
1370 kgf (13.44 kN)
13.2 kN
BS 1377-9:1990
Standard Load at 5.0 mm Penetration
2055 kgf (20.15 kN)
20.0 kN
BS 1377-9:1990
Minimum Surcharge Mass
4.5 kg
10 kg
BS 1377-9:1990
Seating Load
4 kgf (approx. 40 N)
44 N (10 lbf)
ASTM D4429-18
Typical Load Readings Taken up to
12.5 mm penetration
7.5 mm penetration
BS 1377-9:1990
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Standard rate of penetration1.25 mm/min
Penetration plunger diameter50 mm
Penetration plunger length100 mm
Standard load for 2.5 mm penetration1370 kg
Standard load for 5.0 mm penetration2055 kg
Minimum reaction load/vehicle weight1000 kg heavier than max test load
Key Formulas
CBR (%) = (P_t / P_s) * 100 — Where P_t is the test load and P_s is the standard load for a given penetration.
Tables & Referenced Sections
Key Tables
Table 1 - Standard Loads
Key Clauses
Clause 3 - Apparatus
Clause 4 - Procedure
Clause 5 - Calculation and Plotting of Results
Clause 6 - Report
Frequently Asked Questions4
What is the standard rate of penetration for the test?+
The standard rate of penetration is 1.25 mm per minute (Clause 4.3).
What surcharge weight should be used?+
A surcharge weight of 10 kg should be used, which is equivalent to the effect of the pavement overlying the subgrade (Clause 4.2).
What happens if the CBR at 5.0 mm is greater than at 2.5 mm?+
If the CBR value at 5.0 mm penetration is higher, the test should be repeated. If the repeat test yields a similar result, the CBR value corresponding to 5.0 mm penetration is used (Clause 5.1).
What is the minimum distance between two test locations?+
The code does not specify a minimum distance, but general practice suggests spacing tests sufficiently far apart (e.g., 10-15m) to avoid influencing subsequent tests.