NGL stands for Natural Grade Level, and FGL stands for Finished Grade Level, both terms commonly used in construction and civil engineering.
Here's a breakdown:
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Natural Grade Level (NGL): This refers to the existing, undisturbed ground surface before any construction or landscaping activities begin. It represents the natural topography of the site.
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Finished Grade Level (FGL): This refers to the final, designed elevation of the ground surface after all construction and landscaping work is completed. This is the intended level of the ground after grading, filling, and any other modifications.
The reference provided highlights the importance of these levels in foundation design:
Minimum depth of foundation for all structures shall be from the Finished Grade Level (FGL) where cutting has been done and shall be from the Natural Grade Level (NGL) where filling has been done at respective location, for achieving the required FGL.
In essence, the foundation's depth is determined relative to the FGL in areas where the ground has been cut away. However, in areas where the ground has been built up (filled), the foundation's depth is determined relative to the original NGL. This ensures adequate foundation support regardless of whether the final grade is achieved through excavation or filling. This is important for soil compaction considerations, as filled ground may not provide the same load-bearing capacity as undisturbed natural ground.
