CBR test

The properties required to be determined depend on the requirements of the national specification. In general, it is required to determine the compressive strength after 28 days, tested in compliance with CEN EN 13286-41 (2003), or when required, the immediate bearing index, tested in compliance with CEN EN 13286-47 (2012). The latter is almost the same as the CBR test. 

The design CBR of the subgrade is determined by executing CBR tests in the laboratory, over a range of conditions to reproduce, as far as possible, the conditions of moisture content and density, which are likely to be experienced during construction and in the completed pavement. 

The CBR test is carried out on soaked specimens (for 4 days) and in accordance to CEN EN 13286-47 (2012). Samples are taken within the first 600 mm below formation level. The CBR value is determined at 90% of the maximum dry density determined by proctor (modified) compaction (see Section 1.4.7). When undisturbed samples are taken from naturally cemented soil material, where water table is low (>1 m), the value of 90% changes to 95%. 

The second test, BSENISO 12236 Static Puncture Test (California Bearing Ratio (CBR) Test) is referred to a large-size puncture test and appropriate to the situation of aggregate consolidation. It is also commonly referred to as the CBR test, because it is based on the ASTM D1883 CBR test performed by measuring the pressure required to penetrate a soil sample with a plunger. 

Figure 8.10 shows a schematic of the CBR test for a geotexthe. The specimen is clamped between the serrated surfaces of two steel rings. A plunger of 50 mm diameter is advanced at a constant rate onto the centre of the specimen and perpendicular to it. The push-through force, and push-through displacement are recorded and a force-displacement curve plotted. 

As the proportion of reclaimed fibres rises, stamping force (static puncture strength, CBR test) declines. The reason is the same as with maximum tensile strength. 

EN ISO 12236 1996 Geotextiles and Geotextile-related products - Static Puncture Test (CBR-Test)... 

R-value and Cahfornia Bearing Ratio (CBR) tests are performed to determine subgrade modulus and evaluate the pavement support characteristics of the in situ or fill sods. 

The CBR test is generally used for pavement design. The pavement contractor will usually re-compact the top layer of the fill prior to the installation of the pavement. The influence depth of such a test is very... 

Plate loading test, CBR test All soils Stiffness Carried out a the surface of a reclamation area... 

Puncture resistance (puncture index test) ASTM D4833 Replaced by CBR test ... 

The CBR test specifies a method to determine puncture resistance by measuring the force required to push a flat-ended plunger through geosynthetics clamped between two steel rings. Maximum push-through force and displacement at maximum force are measured. The test is applicable to most types of GTXs (Table 7.8 and Fig. 7.15). 

In the past, the puncture index test was also used for GTX. This test is similar to the static puncture test (CBR) but a different plunger (0 8 mm) is used and the specimen is smaller. CBR tests have replaced the puncture index test because the CBR test gives more consistent results than the small puncture index test. 

Note that this procedure is controlled by soil CBR as measured using ASTM D4429, Bearing Ratio of Soils In-Place, which should be performed on the wettest, weakest soil condition anticipated during construction, or a saturated, soaked laboratory CBR test (ASTM D1883) for predicting the performance of soils that will likely be wet during construction. 

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