Geosynthetics

Does your project require geosynthetic seaming or welding? The decision to use a seam is based on the following:
The weakness of the subgrade
The cost of the extra geotextile overlap versus the costs of seaming and installing large, fabricated panels
The feasibility of on-site sewing or welding
The reality of installing the geotextile or geomembrane panels at the jobsite

Soil CBR will determine if overlapping or sewing is the correct option. We offers these general guidelines for sewing versus overlapping:
Soil CBR > 3 Minimum overlaps of 0.3 - 0.45 meters
Soil CBR 1-3 Minimum overlaps of 0.6 - 1.00 meters
Soil CBR < 0.5 Must be sewn

Seam type can also be defined by the number of rows of stitching. Typically, one or two rows of stitching are used. Hand held sewing machines sew only a single row of stitches. It is difficult to hand-sew two parallel rows of stitches. In this case, a second row of stitching is really nothing more than a safety mechanism. More sophisticated equipment used in shops can result in significantly higher seam strengths than those made by hand held machines in the field.

Seam location is also important. Seams in nonwoven geotextiles should be sewn 1 to 2 inches from the edge. Woven geotextiles often have finished edges, or selvege. As such, woven geotextile seams should be sewn 1-1.5 inches from the edge of the fabric. If a woven has no selvege, the geotextile should be folded and the seam sewn within this area.

With most geotextiles, a 60-90% seam efficiency is typical.
Welded seams can be an option for geotextiles. These technologies use a heated wedge and pressure rollers to provide a thermal fusion seam. BPR technology seals against a base of suspended tensioned geotextile, compacted sub-soil or an external seaming board. OPR technology seals against two opposing rollers. The BPR is a preferred method since it permits welding on rough, uneven surfaces. Also, OPR requires both layers to be raised as they pass through the rollers. This can create equipment jams, material stretching and other mechanical issues. Wedge welding creates seams strengths comparable to, or better than, sewn seams.

Construction Quality Assurance (CQA) is a system that provides the owner and permitting agency assurance that the project was constructed as specified in the design. Construction quality assurance includes inspectors, verifications, audits, and evaluations of materials and workmanship necessary to determine and document the quality of the constructed project.

Construction Quality Control (CQC) refers to measures taken by the installer or contractor to determine compliance with the requirements for materials and workmanship as stated in the plans and specifications for the project. CQC is normally performed by the geosynthetics installer, or by the earthwork contractor, and is necessary to achieve quality in construction.

Construction QA/QC for Geosynthetic Installations focuses on the installation of geomembranes, geotextiles, geocomposites, geogrids, and/or geosynthetic clay liners. Special emphasis is given to establishing standard operating procedures for field inspections, documentation of tests and visual observations, and implementation of CQA plans.

CQA/CQA is applicable to all phases of geosynthetics manufacturing and installation:
Manufacturing – Geosynthetic materials are tested as part of the manufacturing process to ensure that the materials meet project requirements. Sometimes two rounds of tests are performed: one set of tests by the manufacturer and a second round by a third-party laboratory. The Engineer should review and approve the Manufacturer and third-party test results prior to the material being shipped to the site.

Delivery and storage – Once the materials are shipped to the site, they are inspected for quality and to ensure that the roll numbers that were delivered match the roll numbers that were tested and storage of the materials are within project requirements and standards.

Construction – Observations and testing are performed to ensure that the materials are installed and seamed together in accordance with project requirements. Any defects that are observed are patched and repaired. We recommend conducting third-party Construction Quality Assurance in addition to the Installer's CQC program to further ensure compliance with project requirements.

Post-Construction – An Electric Leak Location (ELL) survey can be conducted after construction to evaluate the integrity of a geomembrane and ensure that construction activities did not damage the barrier component of the liner system.