How to write a geotextile specification.

State what the fabric must do.

Every geotextile spec begins with function attribution. A single line in the BoQ should declare which of the five functions the fabric is performing: reinforcement, separation, filtration, drainage, or protection (often also erosion control as a sub-case of filtration plus survivability). The right properties to specify follow from the function. Mixing functions in one line item (or omitting function attribution entirely) is the single most common cause of non-conforming delivery in Malaysian projects.

The property-by-property structure.

1. Polymer

Declare PET (polyester) or PP (polypropylene). The chemistry differs in creep, hydrolysis, and chemical resistance. Reinforcement-class fabrics are typically PET; filtration and separation are typically PP. A spec without polymer attribution leaves room for the cheapest polymer to be substituted, sometimes compromising design intent.

2. Fabric construction

Woven, nonwoven, or knitted. For reinforcement, woven (or composite). For filtration, separation, and protection, needle-punched nonwoven. Specify the construction; do not leave it open.

3. Mass per unit area (ASTM D5261, ISO 9864)

Grams per square metre (g/m² or gsm). MARV. Indicates robustness, used as a nominal sizing for nonwoven. Common targets: 200 gsm for typical separation, 300 gsm for harder placements, 400-800 gsm for protection above geomembrane. Mass alone does not specify performance, but it correlates with installation survivability.

4. Wide-width tensile (ASTM D4595, ISO 10319)

Force per metre width at 200 mm gauge length, both machine direction (MD) and cross-machine direction (CMD). MARV. The acceptance figure for reinforcement. For BS 8006 design, wide-width is the right test; grab tensile is for installation survivability checks, not for tensile design.

5. Grab tensile (ASTM D4632)

Force at break on a 100 mm specimen with 25 mm jaws. MARV. Used as an installation survivability index, especially in AASHTO M288 classes. Always cited in JKR-aligned specs.

6. Trapezoidal tear (ASTM D4533)

Tear propagation resistance. MARV. Used to verify that a cut or puncture does not propagate as a long tear under load.

7. CBR puncture / static puncture (ASTM D6241, ISO 12236)

Force to push a 50 mm CBR plunger through the fabric. MARV. Primary installation survivability metric. AASHTO M288 Class 1 requires 2750 N; Class 2 requires 2200 N; Class 3 requires 1650 N.

8. Apparent opening size, O95 (ASTM D4751, ISO 12956)

The 95th percentile particle size that can pass through the fabric. Typically expressed in millimetres or as a US sieve equivalent. Critical for filtration and erosion control. Do not specify just a maximum O95; specify a target range or a maximum O95 that satisfies the retention criterion against the protected soil grading.

9. Permittivity, ψ (ASTM D4491, ISO 11058)

Volumetric flow rate per unit area per unit head loss. Units of inverse seconds (s⁻¹). MARV. The permeability of the fabric cross-plane, normalised by thickness. Higher permittivity allows water through faster.

10. In-plane transmissivity, θ (ASTM D4716)

Volumetric flow per metre width per unit hydraulic gradient at design normal stress. Units of square metres per second (m²/s). MARV. Only relevant for drainage-function fabrics.

11. UV resistance (ASTM D4355)

Percentage of strength retained after 500 hours of xenon-arc UV exposure. Typical AASHTO M288 minimum: 50 percent retained. For longer outdoor exposure (e.g. erosion control before riprap), higher retention or UV-stabilised products are specified.

The statistical basis for acceptance.

MARV (Minimum Average Roll Value): the average value minus two standard deviations of the production lot. Approximately 97.5 percent of roll-level tests exceed the MARV. AASHTO M288 specifies all properties in MARV. This is the right basis for project acceptance because it bounds variation from below; if every roll meets MARV, the design is protected.

DV (Declared Value): the value declared by the manufacturer per product line, often aligned with EN ISO 9862 statistical sampling. Used in BS EN 13249-13257 alongside characteristic value.

Typical Value: the average of production tests. Useful for orientation but should not be the acceptance basis. Specifying a "typical" value in the BoQ leaves a 50 percent statistical chance that any individual roll fails the target.

Use MARV (or DV) in the spec acceptance column. Reserve typical for the explanatory text. The difference matters when test results are challenged on site.

Severity-based survivability classes.

For separation under road sub-base

Class selection logic:

• Class 1: CBR less than 1, angular aggregate, drop height greater than 1 m, heavy track plant on thin first lift. Coastal reclamation, oil-and-gas yard platforms, mining haul.
• Class 2: CBR 1-3 (the typical Malaysian residual-soil case), normal placement. Plantation access roads, urban platforms, hillside development.
• Class 3: CBR greater than 3, rounded aggregate. Less common; only on firm dry sites.

For filtration under cover, around drainage

AOS and permittivity selection is separate (filter criteria, see geotextile design guide) and depends on the protected soil grading. Class selection is the survivability skeleton; AOS / permittivity is the function skeleton. Both are required.

European standards by application.

The BS EN 13249-13257 family applies geotextile property requirements to specific application sectors. Each standard sets out the characteristics required to be declared by the manufacturer for that sector. Useful when the project follows European specification practice (common on Singapore-influenced consultancies, multinational developers).

Malaysian government works spec.

JKR Standard Specifications for Roadworks and for Building Works reference geotextile properties in line with AASHTO M288. A JKR-aligned BoQ entry typically includes:

1. Function attribution (separation / filtration / reinforcement)
2. AASHTO M288 class (1, 2, or 3 with the relevant minimum properties)
3. MARV grab tensile (ASTM D4632), trapezoidal tear (D4533), CBR puncture (D6241)
4. MARV AOS (D4751) with retention check against protected soil
5. MARV permittivity (D4491)
6. Polymer declared (PP or PET)
7. UV resistance after 500 hours (D4355), minimum 50 percent retention
8. Manufacturer certificate of conformance with batch traceability
9. Roll size and packaging requirements (typical 5 m x 100 m or 5 m x 200 m)
10. Storage and installation handling requirements (UV exposure window, overlap, anchorage)

Submission to JKR Cawangan typically requires the consulting engineer's design report demonstrating the geotextile meets the project's hydraulic and tensile demands, supported by the manufacturer's published MARV or declared values.

Specifications that work in practice.

Example A, road separation

Item: Supply and install nonwoven geotextile for sub-base separation under bituminous pavement, Function: Separation, AASHTO M288 Class 2.

Properties (MARV):

• Polymer: Polypropylene (PP)
• Construction: Needle-punched nonwoven
• Mass per unit area: 250 g/m² (ASTM D5261)
• Grab tensile: minimum 1100 N (ASTM D4632)
• Trapezoidal tear: minimum 400 N (ASTM D4533)
• CBR puncture: minimum 2200 N (ASTM D6241)
• AOS (O95): maximum 0.22 mm (ASTM D4751)
• Permittivity: minimum 1.5 s⁻¹ (ASTM D4491)
• UV strength retention at 500 hr: minimum 50 percent (ASTM D4355)

Acceptance: Manufacturer certificate of conformance with batch number and tested MARV values. Roll-by-roll labelling. Installation per AASHTO M288 / JKR-SPJ Section 7.

Example B, filter wrap on perforated drain

Item: Supply nonwoven geotextile filter wrap on 100 mm perforated uPVC pipe in French drain. Function: Filtration.

Properties (MARV):

• Polymer: PP, needle-punched nonwoven
• Mass per unit area: 200 g/m² (ASTM D5261)
• AOS (O95): 0.10 to 0.20 mm (ASTM D4751), sized to retain protected residual soil
• Permittivity: minimum 1.5 s⁻¹ (ASTM D4491)
• Grab tensile: minimum 800 N (D4632)
• Gradient ratio: less than 3 against the project's protected soil (ASTM D5101)
• UV strength retention at 500 hr: minimum 50 percent (D4355)

Example C, basal reinforcement mat under highway embankment

Item: Supply and install high-strength woven geotextile as basal reinforcement under embankment on soft alluvial clay. Function: Reinforcement.

Properties (MARV):

• Polymer: Polyester (PET) high-tenacity yarn, woven
• Wide-width tensile (MD): minimum 200 kN/m (ASTM D4595 / ISO 10319)
• Wide-width tensile (CMD): minimum 50 kN/m
• Strain at maximum tensile (MD): less than or equal to 10 percent
• Long-term design tensile T_d (after reduction factors per BS 8006 / ISO 13431): demonstrated by manufacturer datasheet to meet project design demand of 115 kN/m
• Junction efficiency: greater than 90 percent
• Mass per unit area: minimum 400 g/m² (ASTM D5261)
• CBR puncture: minimum 5000 N (ASTM D6241)

Installation: Roll-out in machine direction across embankment width, overlap 1.0 m or prayer-seam stitched to manufacturer's published seam efficiency. First lift granular fill 300 mm minimum, end-dump from anchored side, no tracked plant turns on bare fabric.

Example D, protection cushion above geomembrane in landfill cap

Item: Supply and install nonwoven geotextile as protective cushion above HDPE geomembrane in landfill cap. Function: Protection.

Properties (MARV):

• Polymer: PP needle-punched nonwoven
• Mass per unit area: 600 g/m² (ASTM D5261)
• CBR puncture: minimum 4000 N (ASTM D6241)
• Grab tensile: minimum 2000 N (D4632)
• Trapezoidal tear: minimum 800 N (D4533)

Compatibility: Compatible with HDPE geomembrane per GRI-GT12. Manufacturer to confirm puncture protection adequacy for the design drainage aggregate gradation.

And how to prevent them.

Error 1, specifying mass without AOS or permittivity

A BoQ entry that says "supply nonwoven geotextile 200 gsm" is functionally incomplete. Two different 200 gsm fabrics can have AOS values that differ by 2 to 3 times, and permittivity values that differ by 5 to 10 times. If the function is filtration, the spec should set AOS and permittivity targets in addition to mass.

Prevention: Always cite AOS and permittivity for filtration-function fabrics.

Error 2, specifying AASHTO M288 class without AOS check

AASHTO M288 Class 2 separation gives a generic AOS maximum (0.43 mm). For a soil with 50 percent fines, this is too coarse and the fabric will allow fines to pump up. The class is a survivability spec, not a filter spec.

Prevention: Apply the M288 class for survivability and add a project-specific AOS limit based on the protected soil grading.

Error 3, specifying ultimate tensile without design tensile framework

A BoQ entry that says "supply HSR 200 kN/m" without reference to reduction factors and design tensile (T_d) leaves the design at risk. The product complies with T_ult of 200 kN/m, but the long-term design tensile is 60-80 percent lower after RF_ID, RF_CR, RF_CH, RF_W. If the design demand was 100 kN/m, the project gets a 200 kN/m product when 400 kN/m was actually needed.

Prevention: Specify both T_ult MARV and T_d demand. Require manufacturer datasheet to evidence T_d at the project design life and conditions.

Error 4, mixing PET and PP in the same line item

PET and PP differ in creep, chemical resistance, and cost. Specifying "polyester or polypropylene" in the same line item allows substitution that compromises design intent.

Prevention: Declare polymer in every line item. Where multiple polymers are acceptable, write separate line items with separate property sets.

Error 5, accepting "typical" values rather than MARV

Acceptance against typical values means roughly half of delivered rolls statistically fail the target. On QA disputes, the supplier can show typical values met while individual rolls failed.

Prevention: Specify MARV (or declared values per EN ISO 9862) in the acceptance column. Require certificate of conformance with batch-level test results, not just typical.

Performance-based spec, then named equivalents.

For most Malaysian projects, performance-based specification (function + properties + standards) is preferred over brand-named specification. Performance-based specs allow competitive procurement, are defensible under public procurement rules, and protect the design intent regardless of supplier.

Where a specific product is mandated by the consultant (because of compatibility with adjacent geosynthetics, prior installed-base, or design liability considerations), an "or approved equivalent" clause around a named product is conventional. The equivalent must be demonstrated by:

• Manufacturer datasheet with MARV / declared values meeting or exceeding the named product
• Independent test reports from an accredited laboratory (ISO 17025 typically)
• Track record on comparable Malaysian or regional projects
• Certificate of conformance and batch traceability process

STRATA Geosystems products supplied through Starwall Sdn Bhd in Malaysia are accepted on JKR and private-developer projects. Datasheets are available on request for spec writing.

What to cite in the spec.

Spec writers and QSs usually ask:

Continue on design and product detail.