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A drainage geocomposite is an HDPE geonet core heat-bonded to geotextile filters on one or both sides, giving a lined system its in-plane flow path for leachate collection, leak detection, gas relief, and cover drainage. The property that matters is transmissivity under load per ASTM D4716, reduced to an allowable flow rate using the GRI-GC8 practice.
| Property | Test method | What is typically specified |
|---|---|---|
| Geonet core thickness | ASTM D5199 | Commonly 200 to 300 mil (5.0 to 7.6 mm) for biplanar cores; triplanar cores run thicker |
| Core polymer density | ASTM D1505 | 0.94 g/cc or higher (HDPE core) |
| Carbon black content | ASTM D4218 | 2.0 to 3.0 percent |
| Transmissivity | ASTM D4716 | Measured at the project's normal load, gradient, and boundary conditions; index values by product on the order of 1 x 10^-4 to 1 x 10^-3 m2/sec |
| Allowable flow rate | GRI-GC8 practice | Laboratory transmissivity reduced by factors for creep, intrusion, and clogging over the design life |
| Ply adhesion (geotextile to core) | ASTM D7005 | 1.0 lb/in minimum is a common specification value |
| Bonded geotextile properties | ASTM D4632 / D4751 / D4491 | Grab strength, apparent opening size, and permittivity per the geotextile specification |
| Application | What the geocomposite does |
|---|---|
| Landfill leachate collection | Carries leachate across the cell floor to collection pipes while protecting the geomembrane below |
| Leak detection layer | Forms the monitored gap between primary and secondary geomembranes in double-lined ponds and sumps |
| Landfill final cover drainage | Drains infiltration off the cap barrier layer to reduce head and improve veneer stability |
| Gas relief and venting | Provides a permeable path beneath barriers so gas and vapor reach collection or vent points instead of building pressure |
| Wall and slope drainage | Relieves hydrostatic pressure behind structures and lined slopes |
A drainage geocomposite pairs two functions in one factory-bonded product: an extruded HDPE geonet core that provides in-plane flow capacity, and nonwoven geotextiles heat-bonded to one or both faces that keep soil and waste out of the flow channels while letting liquid in. Single-sided composites place the bare core face against a geomembrane; double-sided composites are the default where soil sits on both sides.
Cores come in two geometries. Biplanar geonets, two sets of crossing strands, are the standard product for most collection and detection duty. Triplanar geonets add a central rib channeling flow in the machine direction, delivering higher transmissivity under high loads, and are specified on deep landfill floors and other high-stress, high-flow applications.
The number that sizes a geocomposite is transmissivity, the in-plane flow rate per unit width, measured per ASTM D4716. It is not a single number: transmissivity depends on the normal load squeezing the core, the hydraulic gradient, the boundary materials against each face, and how long the load has been applied. A value measured between steel plates at low load can be several times what the same product delivers between a geomembrane and soil under a full waste column.
Good specifications therefore name the test conditions: performance transmissivity per ASTM D4716 at the design normal stress, at the design gradient, with project-representative boundary conditions, seated for a specified duration. The GRI-GC8 practice then converts that laboratory value into an allowable flow rate by applying reduction factors for long-term creep of the core, geotextile intrusion into the flow channels, and chemical and biological clogging over the service life. A submittal that quotes only an index transmissivity without the reduction path has not answered the design question.
In landfill base liners, a geocomposite over the primary geomembrane collects leachate and conveys it to piping, keeping head on the liner within the regulatory limit. In double-lined ponds and sumps, a geocomposite forms the leak detection layer between primary and secondary geomembranes, where its job is to move any leakage to the monitoring sump fast enough to be measured against the action leakage rate.
On closures and caps, a geocomposite above the barrier layer drains infiltration off the cap, cutting the head that drives both leakage and veneer instability on the cover slopes. The same in-plane capacity works in reverse for gas: venting composites under building methane barriers and beneath covers give soil gas a designed path to collection or venting points, which is a barrier-side detail our methane mitigation installations rely on.
Geocomposite panels are deployed with the flow direction of the core aligned with the drainage path shown on the drawings, which matters for triplanar products in particular. Adjacent panels are joined by overlapping the cores or butting them and tying with plastic fasteners at the spacing the specification sets, then closing the geotextile flaps over the joint by shingling in the flow direction, with heat tacking or sewing where called out. White or contrasting fastener colors are standard practice so QA can see every tie.
The QA checkpoints mirror the product's two functions. For flow: core joints tied at spec spacing, no crushed or contaminated core, and no soil tracked into open channels. For filtration: geotextile flaps fully closed with no core exposed, repairs patched with bonded material rather than loose fabric, and no equipment traffic directly on the composite. Ply adhesion per ASTM D7005 is a manufacturing property, but delaminated corners found on delivery are a receiving inspection item, not a field repair.
A complete submittal pairs the manufacturer's data sheet for the named product with roll or lot certificates reporting core thickness per ASTM D5199, core density per ASTM D1505, carbon black content per ASTM D4218, ply adhesion per ASTM D7005, and the bonded geotextile's grab strength, apparent opening size, and permittivity per ASTM D4632, D4751, and D4491.
The performance centerpiece is the transmissivity report: ASTM D4716 data at the specified normal stress, gradient, boundary conditions, and seating time, plus the GRI-GC8 reduction-factor calculation showing the allowable flow rate meets the design requirement. The installation half covers panel layout, fastening and flap details, and repair procedures. If the project also involves the geomembrane and geotextiles around the composite, coordinating those submittals through one installer keeps the interface assumptions consistent.
Single and composite-lined cells, caps, and leachate ponds for MSW, hazardous, and coal-ash sites.
Send us your project specification and we will match materials, assemble submittal data, and scope the installation.