Tree grille and frame installation

Box out area to suit outside dimensions of sub-frame - grille + 35mm = frame ± 3mm.
Ensure the depth around edge has a minimum of 100mm of concrete under the angle or outer frame.
Compact sub-soil base for firm bed for concrete strip and infill with concrete (a 3:2:1 mix is advised, sulphate resisting if necessary) around the edge. Reinforce if loading requires it.
Assemble outer frame and bed frame fixings in concrete foundation. Bed in angle frame ensuring top is level and at a height to suit the surfacing.
Ensure fixings used to join angle frames are tight and pulled up to maximum torque. Re-check level.
When concrete strip has set sufficiently to hold angle frame, check tightness of inner support frame fixing bolts, ensuring they are tightened up to maximum torque to achieve optimum frame rigidity and allow concrete strip to fully cure (allow minimum 24 hrs).
Fit tree grilles, ensure that anti-vandal bolts are fitted and the nuts are applied finger tight. Sufficient space for operative's arms should be left below the grille for anti-vandal bolt fitment.
Infill with pea gravel ensuring that the area under the inner aperture is compacted firm and free from voids and that the anti-vandal bolts are obscured from view.