🛤️ CBR Bearing Ratio of Soil

Construction PN-EN 13286-47

Overview

STATUS (as of 02.11.2026). PN-EN 13286-47:2022-04 — English version (Polish title in the PKN catalogue: “Mieszanki niezwiązane i związane spoiwem hydraulicznym — Część 47: Metoda badania kalifornijskiego wskaźnika nośności, natychmiastowego wskaźnika nośności i pęcznienia liniowego”), published 21.04.2022, implements EN 13286-47:2021 [IDT]; it replaced PN-EN 13286-47:2012 (English version). The card has no withdrawal note — the standard is current. Compared with the 2012 edition, the 2021 edition revised Clause 10 (more information on the possible shapes of the force–penetration curve and their correction) and Annex A, which is normative.

SCOPE (clause 1). The standard specifies test methods for the laboratory determination of the California bearing ratio (CBR) and the immediate bearing index (IBI). The tests apply to that part of the mixture with grains up to 22.4 mm. When curing of the specimen includes immersion in water, the standard also covers the determination of vertical swelling before the CBR determination. The EN 13286 series concerns unbound and hydraulically bound mixtures; in PCA accreditation scopes, laboratories apply this part most often to soils, and also to aggregates and mixtures.

DEFINITIONS AND PRINCIPLE (clauses 3–4). CBR is a ratio characterising the bearing capacity of a mixture, determined immediately after compaction or after a period of curing; IBI is the immediate CBR test without surcharge. The relationship between force and penetration is determined when a cylindrical piston of a standard cross-sectional area is made to penetrate a specimen in a mould at a given rate; the ratio is the force on the piston at a given penetration expressed as a percentage of a reference force.

APPARATUS (clause 5). Proctor mould B with a spacer disc (if required) and rammer A or B according to EN 13286-2 (mould B: diameter (150.0 ± 1.0) mm, height (120.0 ± 1.0) mm, extension collar at least 50 mm high — Table 1 and 5.1 of that standard); a balance up to 30 kg accurate to ± 0.1 % of the mass weighed; apparatus for water content determination according to EN 1097-5. For soaking: a base plate perforated over at least 1 % of its surface, a perforated top plate in aluminium alloy with an adjustable stem for the gauge, a swell gauge accurate to 0.05 mm, a tank in which the mould can be submerged, and annular surcharge rings with a mass known to ± 100 g, an internal diameter of (53 ± 1) mm and an external diameter equal to the mould diameter minus 5 mm (half-annular segments permitted). For penetration: a cylindrical piston (50 ± 0.5) mm in diameter with a lower end of hardened steel and a machine with a capacity of at least 50 kN, pushing the piston at a rate of (1.27 ± 0.20) mm/min, with a force reading of 5 N or better.

SAMPLE AND COMPACTION (clauses 6–7). The mixture is sieved on a 22.4 mm sieve; about 7.5 kg is used for one test with water content determination, weighed so that the quantity used for the specimen can be established after compaction. The IBI of hydraulically bound mixtures is determined not later than 90 min after mixing, and where lime is used not sooner than 60 min. The mould with its extension collar is clamped to the base plate, filter paper is placed on the spacer disc and the assembly is set on a solid substrate; the mixture is compacted with Proctor or modified Proctor compactive effort according to EN 13286-2 (in mould B according to Table 5 of that standard: rammer A 2.5 kg, 3 layers of 56 blows, height of fall 305 mm, or rammer B 4.5 kg, 5 layers of 56 blows, 457 mm). Then the collar is removed, the mixture is trimmed flush with the top of the mould, holes are patched with smaller material and the mould with the specimen is weighed to the nearest 5 g; the water content is determined on the surplus mixture according to EN 1097-5. An immediate test (CBR or IBI) is carried out at once; otherwise the specimen is cured first.

CURING AND SOAKING (clause 8). Curing is storage for a specified time: without evaporation (mass loss not more than 2 % — e.g. in a cabinet with a humidity of at least 98 %, by waxing the ends of the specimen or by sealing the end caps of the mould with petroleum jelly, silicone or tape) at (20 ± 2) °C or another specified temperature, in full immersion in water, or first without evaporation and then in immersion; the type of curing, the average temperature and the duration are recorded. For soaking, the mould with the specimen is inverted onto a perforated plate with filter paper, filter paper, a perforated plate and — if so specified — surcharge rings are placed on top (according to the standard a 2 kg surcharge corresponds to 70 mm of overlying construction). The assembly is immersed in water at (20 ± 2) °C so that the water has access to the top and bottom, and after the initial reading it is soaked for at least 96 h at a constant water level; swelling is read where required to 0.05 mm, and the final swell is given as a percentage of the initial specimen height. After soaking the specimen drains for (15 ± 1) min, and then the mould with the specimen is weighed.

RESULT. The ratio is the force on the piston at a given penetration as a percentage of the reference force (clause 4). According to the description of the method in the help of a geotechnical testing program citing ČSN EN 13286-47, the reference forces are 13.2 kN at a penetration of 2.5 mm and 20 kN at a penetration of 5 mm. Clause 10 of the standard describes the possible shapes of the force–penetration curve and their correction, and normative Annex A — a convex upward curve, a curve with an inflexion point at a penetration below 7.5 mm and a concave upward curve with an inflexion point above 7.5 mm.

WHAT WE DO NOT GIVE HERE. The penetration procedure itself (clause 9: seating of the piston, preliminary force, reading intervals), the rule for selecting and rounding the result, the method of correcting the curve (clause 10, Annex A) or the content of the test report (clause 11) — the available text of the standard ends at 8.3.9; the reference forces are given from a secondary source. Nor do we give “typical” CBR values for soil types or requirements for road subgrades — the description has no source for them.

Method principle

A piston (50 ± 0.5) mm in diameter is pushed at a rate of (1.27 ± 0.20) mm/min into a specimen of the mixture compacted by the Proctor method in mould B — immediately after compaction (immediate test; IBI — without surcharge) or after curing, including after at least 96 h of soaking in water with swelling measurement. The force–penetration relationship is recorded; the CBR or IBI is the force at a given penetration expressed as a percentage of the reference force (according to a secondary source: 13.2 kN at 2.5 mm and 20 kN at 5 mm).

Applications

• Laboratory determination of the bearing capacity of unbound and hydraulically bound mixtures — CBR and IBI (scope of the standard)
• Soils, aggregates and mixtures — test objects to which laboratories apply this standard in PCA accreditation scopes
• CBR after curing in immersion with measurement of the vertical swelling of the specimen
• IBI of hydraulically bound mixtures — not later than 90 min after mixing (with lime not sooner than 60 min)

Key parameters

Standard

Standard number

PN-EN 13286-47:2022-04

Title (PL)

Mieszanki niezwiązane i związane spoiwem hydraulicznym — Część 47: Metoda badania kalifornijskiego wskaźnika nośności, natychmiastowego wskaźnika nośności i pęcznienia liniowego

Title (EN)

Unbound and hydraulically bound mixtures — Part 47: Test method for the determination of California bearing ratio, immediate bearing index and linear swelling

Step-by-step procedure

1. Laboratory sample

   Sieve the mixture on a 22.4 mm sieve; weigh accurately about 7.5 kg for one test with water content determination, so that the quantity used for the specimen can be established after compaction (clause 6).

2. Compaction

   Clamp mould B with its extension collar to the base plate, insert the spacer disc (if required) and filter paper; set the assembly on a solid substrate, e.g. concrete. Compact the mixture with Proctor compactive effort (2.5 kg rammer, 3 layers of 56 blows) or modified Proctor effort (4.5 kg rammer, 5 layers of 56 blows) according to EN 13286-2 (7.1).

3. Trimming and weighing

   Remove the collar, trim the mixture flush with the top of the mould (check with a straightedge), patch holes with smaller material; remove the plate and spacer disc, weigh the mould with the specimen to the nearest 5 g. Determine the water content of the surplus mixture according to EN 1097-5 (7.2, 7.3, 7.5).

4. Immediate test or curing

   Immediate test (CBR or IBI) — proceed directly to penetration; IBI of hydraulically bound mixtures not later than 90 min after mixing, with lime not sooner than 60 min. Otherwise cure the specimen (clause 6, 7.4).

5. Curing

   Without evaporation (mass loss not more than 2 %; e.g. a cabinet with a humidity of at least 98 %, wax or sealed end caps) at (20 ± 2) °C or another specified temperature, in full immersion, or first without evaporation and then in immersion. Record the type of curing, the average temperature and the duration (8.1–8.2).

6. Soaking with swelling measurement

   Invert the mould onto a perforated plate with filter paper, place filter paper, a perforated plate and — if specified — surcharge rings on the specimen. Immerse in water at (20 ± 2) °C with access of water to the top and bottom, mount the gauge and take the initial reading; soak for at least 96 h at a constant water level, reading the swelling where required to 0.05 mm (8.3.1–8.3.6).

   🌡 Temperature: 20 ± 2 °C

7. End of soaking

   Read the final swell and give it as a percentage of the initial specimen height; remove the gauge, take out the assembly, allow (15 ± 1) min for draining, remove the surcharges and plates, weigh the mould with the specimen (8.3.7–8.3.9).

8. Penetration and result

   Push the 50 mm piston at a rate of (1.27 ± 0.20) mm/min, recording the force–penetration relationship; the ratio is the force at a given penetration as a percentage of the reference force, with curve correction according to clause 10 and Annex A. The procedure of clauses 9–10 is outside the available text (clause 4, 5.3).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The available text of the standard contains no safety requirements — rules for working with the loading machine, rammer and mould with specimen are set by the laboratory on the basis of a risk assessment

Frequently asked questions