Public comment – Draft IA Report (Marten Falls Community Access Road): basal reinforcement / “heavy geogrid” design basis

We are a manufacturer of high-tensile-strength geogrids and have reviewed the floating-road design described in the Draft Impact Assessment Report. The report states that the permeable rock embankment over peatland would be “supported with reinforcing material such as heavy geogrid” to help it settle without clogging. We respectfully submit that the geotechnical basis for this reinforcement is not characterized in the report, and that this matters both to structural safety and to the environmental claim that the floating road will maintain peatland hydrology. We request that the proponent clarify the following:

Function and terminology
1. “Heavy geogrid” is not a defined engineering term. What is the specified characteristic ultimate tensile strength (kN/m), polymer type, and structure (uniaxial / biaxial / triaxial) of the proposed reinforcement?
2. The report attributes a “prevent clogging / allow settlement” function to the geogrid. As clogging prevention is a separation/filtration function (a geotextile role) and geogrids primarily provide tensile reinforcement, can the proponent confirm which geosynthetic provides which function, and whether a separation geotextile is included in addition to the geogrid?

Reinforcement design basis
3. To which design standard will the basal reinforcement be designed (e.g., BS 8006-1:2010, FHWA geosynthetic design guidance, TAC/MTO muskeg practice)? The codes cited in the report (CSA S6:25, Ontario Roadside Design Manual, Structural Manual) do not govern geosynthetic basal reinforcement.
4. Is a single layer or multiple layers of reinforcement proposed, and on what basis (total required tensile capacity, load-transfer platform, bridging of variable peat)?
5. What tensile stiffness (secant modulus at 2–5% strain) and creep-reduced long-term design strength are specified, given that operation is described as indefinite/permanent?

Peat conditions and stability
6. What is the design peat depth and undrained shear strength profile along the route, and how variable is it?
7. Have the ultimate limit states required for embankments on soft soil been checked — overall rotational stability, foundation extrusion/squeezing, and lateral sliding of the fill over the reinforcement — and what factors of safety result?
8. For the lateral-sliding case specifically, what interface friction values are assumed between the open rockfill and the geogrid, and between the geogrid and the saturated peat?
9. What durability assessment supports the chosen polymer in acidic, anoxic peat over the design life (e.g., polyester hydrolysis, oxidation, installation damage)?

Link to the hydrology claim and monitoring
10. The report’s environmental case rests on the floating road maintaining peatland hydrology, yet several reviewers (ECCC, WCS Canada, and Indigenous groups) expressed uncertainty. Differential settlement is controlled by reinforcement stiffness — what differential-settlement limit has been adopted to protect hydrological function?
11. The draft conditions include environmental follow-up (water quality, air, caribou) but no geotechnical monitoring. Will a settlement/strain monitoring program (settlement plates, inclinometers, reinforcement strain) be added as a condition to verify the floating-road performance predictions?

We would be pleased to provide technical input on high-tensile basal reinforcement for floating embankments over peat.
 

Amirali Khanjani

Geotechnical Engineer, P. Eng.