There are three main methods for connecting continuous filament geotextiles on-site: Overlapping, Sewing, and Thermal Welding.

1. Overlapping (Friction Joint)

This is the simplest method. Two geotextile sheets are overlapped and held in place by the weight of the overlying backfill material (soil, gravel, or aggregate).

• Overlap Width: A standard overlap of 30 cm (12 in) is typical. For soft subgrades, saturated conditions, or underwater placement, extend the overlap to 50–100 cm (20–40 in).

• Placement Rule: Always follow the direction of water flow and slope angle. Overlap the upstream (or higher elevation) panel over the downstream (or lower elevation) panel to prevent hydraulic lift or seam separation during backfilling.

2. Sewing (Mechanical Seaming)

Recommended for applications requiring high tensile load transfer, such as reinforced embankments, subgrade stabilization, and steep slopes.

• Execution: Joined using a portable industrial bag closer / handheld sewing machine. A double-stitched chain seam using high-strength UV-stabilized polyester or polypropylene thread is recommended for maximum joint efficiency.

• Requirement: Avoid sewing wet fabrics, as moisture reduces thread tension and seam consistency. Ensure full seam strength through field tension checks prior to backfilling.

3. Thermal Welding (Heat Bonded Seaming)

The strongest and most secure method, ideal for applications requiring high seam shear strength and displacement resistance, such as landfills, containment basins, and critical hydraulic structures.

• Execution: A hot-air welding gun melts the synthetic fibers at the interface, which are then roller-pressed together to form a monolithic bond upon cooling.

• Requirement: Hot-air welding must never be performed on wet or muddy geotextiles, or during rainfall. Moisture severely prevents thermal fusion, leading to seam delamination under stress.

Method Selection Matrix