Site Grading Design Calculator

ASCE 38-02 (Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data) for existing-grade / design-grade identification. ADAAG 504/505 (Americans with Disabilities Act / Architectural Barriers Act Accessibility Guidelines) for accessible-route cross-slope limits — pavement max 2.0%, accessible parking aisles max 2.0%. AASHTO Green Book 6th Ed. Tables 3-34 (crest vertical curves, stopping sight distance) and 3-35 (sag vertical curves, headlight sight distance) for K-min values. Average-end-area method per AASHTO §3.4 for cut/fill earthwork volumes.

Existing grade (natural ground) is the elevation measured during a topographic survey (ASCE 38-02 quality level A/B/C/D). Design grade (proposed finished surface) is the engineered target elevation after cut/fill. Sites are graded by removing soil where ground > design (cut / spoil) or importing fill where design > ground (fill). The calculator interpolates design grade between adjacent known points and reports per-station cut/fill.

Surface class drives the limits. ADA-accessible pavement is 1.0–2.0% (ADAAG 504/505). Standard landscape is 1.0% minimum (drainage) up to 12% maximum. Swales 0.5% minimum. Longitudinal road grade 0.5–8% per AASHTO Green Book Table 3-1. The calculator returns ok=true when the input is within [min, max] and a recommendation text otherwise.

The K value is curve length / algebraic grade difference (K = L / A) in metres per %. AASHTO Green Book prescribes minimum K for design speed — for crest curves, it ensures stopping sight distance (Table 3-34); for sag curves, headlight sight distance (Table 3-35). At 80 km/h design speed, K-crest is 30 m/% and K-sag is 21 m/%. A 4% algebraic grade difference therefore needs ≥ 120 m crest curve length.

Average-end-area method per AASHTO §3.4 — V_segment = (A₁ + A₂)/2 × L, where A₁ and A₂ are the cut (or fill) cross-section area at each end of the segment, and L is the segment length. Cut occurs where ground > design; fill where design > ground. Corridor width is applied uniformly. Total cut vs. total fill drives the balance verdict: balanced, waste (surplus cut), or borrow (deficit fill).

For typical site-civil subdivisions and roadways the design corridor is constant. For complex horizontal curves where the actual width varies, the average-end-area approach still gives a defensible AASHTO-endorsed estimate. For tapered corridors, divide the alignment into segments of constant width and run the calculator per segment.