The "bump at the end of the bridge" is the most visible grading failure on highway projects. It is caused by differential settlement between the rigid bridge deck and the flexible approach embankment — and it is preventable with proper compaction documentation and settlement monitoring. Bridge approach grading is held to a higher documentation standard than standard road embankment because the consequences of poor documentation are visible to the public for decades.
What documentation is required for bridge approach grading?
Bridge approach grading documentation requires five categories of records: (1) embankment fill records documenting material source, lift thickness, compaction test results, and post-compaction elevation for each lift from subgrade to finish grade; (2) settlement monitoring records showing embankment settlement readings from benchmarks installed in the approach fill at regular intervals (typically weekly during construction, then monthly until the approach slab is poured); (3) approach slab subgrade verification survey on a 5-ft grid confirming the subgrade is within ±0.05 ft of design before the slab pour is authorized; (4) approach slab QC records including concrete testing, rebar inspection, and placement records; and (5) post-construction elevation shots at the bridge deck approach end, approach slab midpoint, and end of approach slab to document the as-built profile before traffic opening.
Bridge approach embankments are typically specified with more stringent compaction requirements than standard road embankment. AASHTO and state DOT specifications commonly require 98% Standard Proctor (AASHTO T99) for the top 4 feet of approach embankment, compared to 95% for standard embankment.
Required documentation for each lift of approach embankment:
| Document | Required Content | Submitted To |
|---|---|---|
| Material source record | Borrow pit location, material description, Proctor test for each material type | Engineer of record |
| Lift placement record | Lift number, date placed, material type, loose lift thickness, location limits | Daily report |
| Compaction test log | Test location (station + offset), measured dry density, moisture content, % Proctor, pass/fail | Resident engineer |
| Post-compaction elevation | 25-ft grid shots after each lift, before next lift is placed | Retained in project file |
| Settlement monitoring | Weekly readings from embankment benchmarks; total settlement to date | Bridge engineer; triggers approach slab authorization |
The settlement monitoring program is what separates bridge approach embankment documentation from standard road embankment documentation. The purpose is to demonstrate that primary settlement has occurred and the embankment has stabilized before the rigid approach slab is poured.
A typical settlement monitoring program includes:
The authorization from the bridge engineer is a critical hold point. Proceeding to pour the approach slab without it exposes the contractor to responsibility for any future bump that develops.
After the settlement wait period, the final step before approach slab forming is a subgrade elevation survey on a 5-ft grid across the entire slab footprint. This tight grid is required because any high spot in the subgrade will reduce slab thickness below the specified minimum — a structural issue on a slab that spans over a compressible embankment.
Any point more than 0.05 ft above design subgrade must be cut down before the form is set. Low spots (more than 0.10 ft below design) should be filled and recompacted. Document all corrections and perform a final survey before authorizing the form crew to begin.
After traffic opening, conduct a profile survey of the approach zone to document the as-built condition. This survey includes:
This post-opening survey is the baseline for any future warranty or smoothness claims. If the approach develops a bump after opening, comparing the post-opening survey to subsequent surveys shows when the settlement occurred and by how much. Without the post-opening baseline, any settlement after opening is undocumented — and the contractor has no evidence of the condition at the time of acceptance.
Sitemark captures embankment lift records, settlement readings, subgrade surveys, and post-construction profiles in one package — giving you the documentation trail that bridge engineers and DOT inspectors require. Start free.
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