IS 15351:2008 and IS 7328:2020
BIS Guidelines for LDPE Geomembranes: Technical Specifications per IS 15351:2008 and IS 7328:2020
The Bureau of Indian Standards (BIS) provides comprehensive guidelines for low-density polyethylene (LDPE) geomembranes, primarily through IS 15351:2008, titled “Textiles – Laminated High Density Polyethylene (HDPE) Woven Fabric for Canal Lining – Specification,” and IS 7328:2020, titled “High Density Polyethylene Materials for Moulding and Extrusion – Specification.” These standards ensure the quality, performance, and durability of LDPE geomembranes, often laminated with HDPE woven fabrics or blended with linear low-density polyethylene (LLDPE), for lining applications such as ponds, reservoirs, and industrial effluent disposal systems. This overview details the material properties, manufacturing processes, installation guidelines, testing protocols, and certification requirements, tailored to meet the needs of civil engineers designing reliable containment systems.
Scope and Objectives of BIS Standards
IS 15351:2008 specifies requirements for laminated HDPE woven fabrics coated with LDPE or LDPE/LLDPE films, used as geomembranes for canal linings and similar applications. IS 7328:2020 complements this by defining the material properties of LDPE, LLDPE, and HDPE, including designation codes and performance characteristics. Together, these standards aim to:
Ensure Impermeability: Achieve hydraulic conductivity ≤ 10⁻¹⁰ cm/s to prevent seepage in water storage and effluent containment systems.
Enhance Durability: Provide resistance to chemical, biological, and UV degradation, ensuring a service life of 15–30 years.
Optimize Mechanical Performance: Deliver sufficient tensile strength, tear resistance, and puncture resistance to withstand installation and operational stresses.
Support Environmental Protection: Facilitate water conservation (e.g., 80–90% seepage reduction in canals) and safe containment of industrial effluents (e.g., pH 2–12).
Applications include:
Pond and Reservoir Linings: Reducing seepage losses by 85–95%, enhancing water storage efficiency.
Industrial Effluent Disposal: Containing aggressive effluents with high COD (>5,000 mg/L), protecting groundwater.
Canal Linings: Minimizing water loss in irrigation systems, saving 10–15% of water in large-scale projects.
Secondary Containment: Preventing leaks in storage tanks and industrial facilities.
Material Characteristics of LDPE Geomembranes
LDPE geomembranes, often laminated onto HDPE woven fabrics, are flexible, cost-effective materials with excellent elongation and chemical resistance. Key properties per IS 15351:2008 and IS 7328:2020 include:
Physical Properties:
Thickness: 0.25–1.0 mm for laminated films (per IS 13162 Part 3), with tolerances of ±10%.
Mass per Unit Area: 250–1,000 g/m² for laminated fabrics, balancing strength and flexibility (per IS 14715).
Density: 0.91–0.93 g/cm³ for LDPE/LLDPE films (per IS 13360 Part 5), ensuring low crystallinity for flexibility.
Surface Finish: Smooth or textured, with no pinholes, foreign matter, or delamination, ensuring uniform impermeability.
Mechanical Properties:
Tensile Strength: ≥ 10–25 kN/m for laminated fabrics (per IS 13326 Part 1), resisting installation stresses and soil loads.
Breaking Strength: ≥ 300–800 N for 50 mm width (per IS 1964), suitable for low-to-moderate load applications.
Tear Resistance: ≥ 100–250 N (per IS 14293), preventing propagation of tears during handling.
Puncture Resistance: ≥ 200–500 N (per IS 13162 Part 4), protecting against subgrade irregularities.
Elongation at Break: ≥ 500% for LDPE films, accommodating deformation without failure.
Hydraulic Properties:
Hydraulic Conductivity: ≤ 10⁻¹⁰ cm/s, ensuring effective containment under hydrostatic pressures up to 50 kPa.
Water Vapor Permeability: ≤ 0.5 g/m²/day (per IS 15909), minimizing moisture transmission in reservoir linings.
Durability:
Chemical Resistance: Stable in acidic and alkaline environments (pH 2–12), including industrial effluents with organic solvents.
UV Resistance: ≥ 60% strength retention after 1,000 hours of exposure (per IS 14324), suitable for temporary exposure during installation.
Environmental Stress Crack Resistance (ESCR): ≥ 300 hours (per IS 7328:2020), ensuring long-term performance in stressed conditions.
Service Life: 15–30 years, based on accelerated aging tests in aqueous and chemical environments.
Manufacturing and Quality Control
IS 15351:2008 and IS 7328:2020 mandate rigorous manufacturing processes to ensure consistent quality:
Production:
LDPE/LLDPE films are extruded and laminated onto HDPE woven fabrics (yarn denier ≥ 400, weave density ≥ 10 x 10 per 25 mm) using hot-melt or pressure lamination.
Films are produced with virgin resins containing ≤ 2.5% carbon black or UV stabilizers to enhance durability.
Rolls are manufactured in widths of 2–6 m and lengths up to 100 m, minimizing field seams.
Quality Control:
Manufacturers must adhere to IS/ISO 9001 quality management systems, with documented procedures for resin selection, lamination, and film adhesion.
In-process testing includes thickness, tensile strength, and pinhole detection at a frequency of one test per 500 m².
Lamination adhesion strength is verified (≥ 5 N/cm, per IS 15351 Annex A) to prevent delamination under shear or hydrostatic loads.
Installation Guidelines
Proper installation is critical to achieving the design performance of LDPE geomembranes. IS 15351:2008 recommends:
Site Preparation:
Prepare a smooth, compacted subgrade (≥ 90% Proctor density, per IS 2720 Part 8) free of sharp objects, rocks, or vegetation.
Ensure subgrade CBR ≥ 3% or place a nonwoven geotextile (≥ 150 g/m²) to protect against punctures.
Grade slopes to ≤ 1V:4H for canal linings to maintain geomembrane stability.
Geomembrane Placement:
Unroll geomembranes with minimal wrinkles, aligning panels parallel to the canal or pond axis to reduce seam length.
Overlap panels by 100–200 mm for heat sealing or adhesive bonding, ensuring continuous impermeability.
Deploy during low-wind conditions (< 15 km/h) to prevent uplift or misalignment.
Seaming:
Use hot-air welding, solvent bonding, or adhesive tapes, achieving shear strength ≥ 80% of parent material (per IS 15910).
Test seams non-destructively (e.g., visual inspection, pressure testing) at 100% coverage and destructively (e.g., peel tests) at one sample per 200 m of seam.
Anchoring:
Secure geomembranes in anchor trenches (depth ≥ 400 mm, width ≥ 800 mm) filled with compacted backfill (≥ 85% Proctor density).
Use sandbags or soil cover (≥ 200 mm) to prevent wind uplift during installation.
Cover Placement:
Place protective layers (e.g., geotextiles, soil cover ≥ 150 mm) immediately after seaming to prevent UV degradation and mechanical damage.
Use low-ground-pressure equipment (contact pressure < 40 kPa) to avoid geomembrane stress.
Testing and Conformity
IS 15351:2008 and IS 7328:2020 require rigorous testing to verify compliance:
Laboratory Testing (in BIS-approved labs):
Mechanical Tests: Tensile strength, breaking strength, tear resistance, puncture resistance (per IS 13326, IS 1964, IS 14293, IS 131 fungerar62).
Hydraulic Tests: Hydraulic conductivity, water vapor permeability (per IS 15909).
Durability Tests: UV resistance, ESCR, chemical stability (per IS 14324, IS 7328).
Field Testing:
Inspect for pinholes, tears, or delamination during placement, repairing defects with patches (minimum 200 mm overlap).
Perform seam integrity tests (e.g., peel strength ≥ 4 N/cm) at a frequency of one test per 200 m of seam.
Sampling frequency: One roll test per 2,000 m² for thickness and mechanical properties.
Grouping Guidelines:
Testing a sample of the highest thickness (e.g., 1.0 mm) within a group covers all lower thicknesses (e.g., 0.25–0.75 mm) for BIS licensing, streamlining certification.
Conformance:
Non-compliant geomembranes (e.g., tensile strength < 90% of specified value) must be rejected or repaired to maintain impermeability.
Labeling and BIS Certification
Labeling Requirements:
Each roll must bear the BIS Standard Mark (ISI Mark), indicating compliance with IS 15351:2008.
Labels include manufacturer name, BIS License number (CM/L-XXXXXXXX), batch number, thickness, roll dimensions, and BIS website (www.bis.gov.in), marked indelibly every 1 m along the roll edge.
BIS Quality Control Order (QCO):
Mandates that LDPE geomembranes conform to IS 15351:2008 and carry the BIS Standard Mark for sale in India.
Non-compliance results in penalties under the BIS Act, 2016.
Certification Process:
Manufacturers apply through the BIS portal, submitting resin specifications, production records, and quality control plans.
BIS conducts factory inspections to verify compliance with IS/ISO 9001 and IS 15351:2008.
Samples are tested in BIS-recognized laboratories, with certification granted within 30 days under simplified procedures (Option 2) for MSMEs.
Licensing Efficiency:
Option 2 streamlines licensing for domestic manufacturers, processing applications within 30 days, including factory audits and sample testing.
Applications and Performance Benefits
LDPE geomembranes per IS 15351:2008 deliver significant benefits:
Pond and Reservoir Linings: Achieve 85–95% seepage reduction, increasing water storage capacity by 10–20% in small-to-medium reservoirs.
Industrial Effluent Disposal: Contain effluents with high salinity or organic content, protecting groundwater and reducing remediation costs by 30–50%.
Canal Linings: Enhance irrigation efficiency, saving 10–15% of water in systems with flows > 5 m³/s.
Cost-Effectiveness: Offer lower material costs (20–30% less than HDPE geomembranes) while maintaining adequate performance for low-to-moderate load applications.
Practical Implications for Civil Engineers
Adherence to IS 15351:2008 and IS 7328:2020 ensures LDPE geomembranes meet stringent performance criteria, delivering reliable, cost-effective lining solutions. Engineers should:
Conduct site-specific assessments (e.g., subgrade stability, effluent chemistry) to select appropriate film thickness and lamination type.
Verify seam quality through field testing to prevent leakage, which can increase maintenance costs by 40–60%.
Train installation crews on proper handling and seaming techniques to avoid errors, such as pinholes or weak bonds, which can reduce impermeability by 15–25%.
Integrate geotechnical data (e.g., subgrade CBR, soil gradation) to optimize protective layers and anchorage systems.
By leveraging these BIS standards, civil engineers can design lining systems that comply with regulatory requirements, ensuring environmental protection, water conservation, and client satisfaction through enhanced durability and performance.
Complementary BIS Standards
IS 15910:2010 – Geosynthetics – Guidelines for Seaming of Geomembranes:
Provides procedures for heat sealing and adhesive bonding, ensuring seam integrity.
IS 13360:1992 – Plastics – Methods of Testing:
Governs density, tensile, and ESCR testing, supporting IS 7328:2020 requirements.
IS 2720 (Various Parts):
Guides subgrade preparation and testing (e.g., Proctor density, CBR) for installation readiness.
IS 14715:2000 – Geotextiles – Methods of Test:
Supports testing of laminated fabrics for mass per unit area and mechanical properties.