Geotextiles work in conjunction with other civil engineering, road construction, drainage, erosion control, ground stabilization, and a host of other activities. The geotextile is generally selected based on the properties you need to care for, such as tensile strength, permeability, U.V. resistance, puncture resistance and the like.
Of course, there are many such properties, but CBR puncture strength is one of the most vital mechanical properties. It reflects the degree to which the geotextile fabric will resist a concentrated load during the placing of the fabric and its lifespan.
Without an understanding of CBR puncture strength, contractors, engineers, and the project owner may fail to select the right geotextile fabric for hostile applications, leading to premature failure of the material in use.
What does CBR puncture strength mean?Simply put, CBR puncture strength reflects the manner in which the geotextile fabric resists the penetration of a standard plunger given the set conditions.
CBR is short for California Bearing Ratio, the name of the machine used to do the CBR test. In the test, a circular steel piston is driven towards a geotextile sample until puncture occurs, the force of the blow required is recorded as the CBR puncture strength. The readout is in kilonewtons (kN).
The higher the CBR, the better able the geotextile samples are to withstand damage from sharp aggregates, rocks, construction equipment and concentrated loads.
Why is CBR puncture strength important?It is not uncommon to place materials in less-than-perfect conditions for installation in construction. The fabric may be placed directly on subgrade surfaces that cling sharp stones and gravel.Aggregate is then spread over the top of geotextile layer and significant pressure/force may be applied at localized contact points.
An inadequate CBR means that the geotextiles may tear andThis can compromise the entire system.
A geotextile with good CBR puncture strength can help:
- Protect against installation damage
- Maintain separation between soil layers
- Preserve filtration performance
- Improve long-term durability
- Lower maintenance costs
- Extend project service life
That is why, puncture resistance is so important in infrastructure works where heavy loads are expected.
How is CBR puncture strength tested?
The test may be caried out in accordance with standards set out in international norm, for example EN ISO 12236.
During testing, the geotextile sample is tightly clamped in a circular fixture.Approximately a steel plunger of about 50mm in diameter .The plunger applies force to the geotextile at a designated rate of speed. The maximum force representing the puncture force is recorded.
The final result may be different depending upon the: - fibre type;
- fabric construction;
- weight of the material;
- means of manufacture;
- thickness of the geotextile.
The final result means that two geotextiles that use different materials and manufacturing processes may have a very different puncture strength
Typical CBR Values for Different Geotextiles
Not all geotextiles fabrics are the same with regard to puncture resistance. Non-Woven Geotextile
Traditional needlepunched non-woven geotextile is very good with puncture due to the thickness and three-dimensional structure of the fabric.Continuous Filament Non-Woven Geotextiles
These are generally much the same and have very high CBR values, and yet still maintain a good filtration property. These products generally go into:
Roads, Rail, Landfill, Drainage, Coastal works, Woven Geotextile
Woven fabrics generally have very high tensile strength, but less puncture strength than non-woven to an equivalent weight. High performance woven fabrics do have very good puncture strength though and are useful in reinforcement applications. Heat Bonded Geotextile
Heat bonded geotextiles have a less rough surface and are thinner than traditional needle-punched products, thus their CBR puncture strength may not be so great but may have other useful properties with regard to filtration and dimensional stability. Relationship between CBR strength and Tensile strength.
Many buyers naïvely assume that the strength in terms of tensile strength then equates to the CBR strength, this is a fallacy.performance characteristics.
Tensile strength measures how much force is needed to pull it to pieces.
CBR puncture strength measures how much force is needed to push into it locally.
A woven geotextile might have a very high tensile strength, and only a moderate puncture strength – this would still be a very useful product by the way. A thick non-woven geotextile that has been made by needle-punching can gain a good level of puncture strength at the expense of a somewhat lower tensile strength. We should test for both things.
Factors Affecting CBR puncture strength:
What, precisely goes to make up the puncture performance, well likely contenders are: - fibre material.Fibres have an enormous bearing on behaviour. Knowing a little about the basic properties will assist us in our evaluator capabilities.
- Fabric mass per unit area. Naturally, heavier geotextiles are more likely to succeed to do a better job than light because of being capable of absorbing concentrated loads better.
- Manufacturing process. A needle-punched technology, for instance, makes for more fibres that will “clump” together, and perhaps make for a weighte and “heavier” thing, whilst a continuous filament manufacturing (which produces) make fibres that are closely bonded to each other, thus able to absorb the impression put upon it as the load goes down.
thickness of fabric. It’s like, stick a stubby pencil through such and such thick cardboard, it may not go “in all the way,” but it will on light cardboard.
the use of heavy non-woven geotextiles does on the whole concerns tough ground conditions made mention of, but they do seem to be mandatory in landfill use.
Applications where high puncture CBR values are required:
The above is obviously right, but where radially very heavy loads are applied, exotic materials might well be called for, as:Road above crushed stone layers and in intimate contact with aggregate (including the construction traffic);Railways – for it is the dynamic repeated loading from trains, and that rail devising that requires the stability of the tracks be maintained. That, means strong puncturing in geotextiles too;as with landfillrock armouring, and riprap;can we tell the difference between the two?
How best might one specify a CBR puncture strength?
Everyone has a different CBR, which is quite stunning if you give credence to the facts, a well the same with the geotextile for, no single universal CBR applies for infitismal application. Rather it depends on the characteristic of the soil conditions, size of aggregate etc, methods of construction, the degree traffic is persistent, and more besides. Impose a facility emitting large angular aggregates and the geotextiles will have to be of greater puncture quality value for appointed jobs, than if it was using say, a fine granulate, for example. It’s best always to consult the engineering specification and see what they “say,” before proceeding to go out glopping at random, who a designer I mean. CBR puncture strength is a significant factor but performance criterion of geotextile fabrics though; it indicates the resistance to “local penetration,” from rocks, and so on, as you know.