Geosynthetics
Anchorage is bought with depth, not just length. A grid a metre down does a third of the work of the same grid three metres down.
— kN/m
Anchorage the embedded length develops per metre of wall
Overburden is taken as dry soil weight times depth, so it ignores surcharge, sloping backfill and any water table — all three change the answer materially and belong in a full stability analysis. The interaction coefficient is not a soil property; it is a fitted result for one grid geometry in one backfill, and borrowing it from a datasheet for a different aperture or a different gradation is the usual source of an unsafe answer. Reinforced soil structures are governed by design codes and must be signed off by a qualified geotechnical engineer.
Geogrid Pullout Resistance & Soil Friction Coefficient — free, with the formula and a worked example, at Textile School.