what does "to walk at grade" mean?
John was walking at grade and slipped on a patch of ice. When John slipped he did not fall to grade as he caught himself with his right hand [...]
In construction, grade has several potential meanings:
grade
Definitions (8)
The surface or level of the ground.
A classification of quality as, for instance, in lumber.
The existing or proposed ground level or elevation on a building site or around a building.
The slope or rate of incline or decline of a road, expressed as a percent.
A designation of a subfloor, either above grade, on grade, or below grade.
In plumbing, the slope of installed pipe, expressed in the fall in inches per foot length of pipe.
The classification of the durability of brick.
Any surface prepared to accept paving, conduit, or rails.
dictionaryofconstruction.com
The expressions walking at grade and fall to grade, clearly eliminate five definitions, and leave three possibilities to choose from:
grade
Definitions (8)
The surface or level of the ground.
The existing or proposed ground level or elevation on a building site or around a building.
Any surface prepared to accept paving, conduit, or rails.
All three of the remaining definitions are consistent with the the ODO definition of at grade:
North American On the same level:
Emphasis mine
On a construction site, the default meaning of grade is "existing ground level", unless otherwise specified. The most likely interpretation is:
John was walking at ground level and slipped on a patch of ice. When John slipped he did not fall to ground level as he caught himself with his right hand.
If the larger context provides information specifying another definition of grade, it is interpreted:
John was walking at a specified level and slipped on a patch of ice. When John slipped he did not fall to the specified level as he caught himself with his right hand.
We know from this account that John fell less than his own height at or near ground level.