Culvert Fill [BC]

The Culvert Fill object defines the earth cover carried above a box culvert's top slab. It owns the single question every fill-driven load needs answered — how deep is the fill — and hands that depth, together with the fill soil unit weight and the soil-structure interaction factor, to Vertical Earth, Live Load Through Fill and Live Load Surcharge.

Fill is measured from the top of the culvert's top slab up to the top of fill. Where the top of fill sits is declared explicitly rather than guessed, so changing the roadway profile, the culvert elevation or the fill mode never silently changes the loads without the model showing it.

The object also draws the fill in the 3D view and reports its volume, weight and surface areas for quantity take-off. It does not apply any load itself — the earth pressure and live load objects do that.

General

Box Culvert: The culvert barrel this fill covers. Selecting it registers the fill on that culvert, which is how Vertical Earth, Live Load Through Fill and Live Load Surcharge find it without a second pick of their own — those objects select the Box Culvert Barrel and then read the fill through it. A value is required, and a culvert may carry only one fill; a second one is reported as an issue because the loads read the first and would silently ignore the rest.

Fill Extent Beyond Exterior Walls: How far the fill body extends sideways past the outside face of the exterior walls, measured transverse to the culvert axis. It affects the drawn solid and the reported quantities only — the loads are applied over the culvert's own top slab regardless. Leave it at 0 for a fill that stops at the barrel; increase it to include the fill placed against the walls in the take-off. Must not be negative.

Top Boundary

Top of Fill [Fill Depth/Elevation/Roadway Profile/DTM]: How the top of fill is defined. All four modes end at the same place — an elevation for the top of fill — and differ only in what that elevation is tied to.

• Fill Depth: a cover depth measured down from the top of fill to the top slab. The fill top moves with the culvert, so the cover stays constant when the barrel is raised or lowered.
• Elevation: an absolute elevation typed directly. The fill top stays put when the culvert moves, so the cover changes.
• Roadway Profile (default): the fill top follows the alignment's vertical profile. This is the usual case for a culvert under a road — the cover is whatever the road profile and the culvert elevation leave between them, and it updates automatically when either changes.
• DTM: the fill top is taken from a finished-grade digital terrain model, so the cover varies with the real surveyed surface.

Fill Depth Above Top Slab: The depth of cover from the top of the culvert's top slab up to the top of fill. Shown only when Top of Fill is set to Fill Depth, where a value is required. This is the depth the live load spread, the impact factor and the surcharge height all key off, so it should reflect the design cover rather than a nominal figure. Must not be negative.

Top of Fill Elevation: The elevation of the top of fill, entered directly. Shown only when Top of Fill is set to Elevation, where a value is required. Because it is fixed in space, raising or lowering the culvert changes the resulting cover.

Vertical Offset from Roadway Profile: A vertical shift applied to the alignment profile when Top of Fill is set to Roadway Profile. Shown only in that mode. Leave it at 0 to place the top of fill on the profile itself; use a negative value to put it below the profile, for example to allow for a pavement structure carried separately.

Finished Grade (DTM): The digital terrain model representing the finished ground surface above the culvert. Shown only when Top of Fill is set to DTM, where a selection is required. Use the finished graded surface rather than the original ground — the two differ wherever the road is built up on embankment.

Terrain Data: The clipped terrain solid between the top slab and the DTM, held on the object so that geometry, quantities and the 3D view can read it without re-reading the terrain on every recompute. Shown only when Top of Fill is set to DTM. It is not typed in: right-click the cell and choose Compute to populate it from the selected DTM. Until it is computed the cell reports an issue, and it should be recomputed whenever the culvert moves, the DTM changes, or the fill extent changes, because it is a stored snapshot rather than a live query.

Soil

Fill Soil Unit Weight: The unit weight of the fill material above the culvert. This is the single place the value is entered — Vertical Earth and Live Load Surcharge read it from here rather than each carrying their own copy, so the vertical earth pressure and the lateral surcharge cannot disagree about the same soil. It also converts the reported fill volume into a fill weight. Must be positive.

Display

Show Fill [No/Yes]: Whether the fill body is drawn in the 3D view. The drawn solid is for visual checking only and carries no weight of its own — the vertical earth load is applied by the Vertical Earth object, so hiding or showing the fill never changes any result.

Opacity: How opaque the fill body is drawn, from 0 (fully transparent) to 1 (fully opaque). The default is deliberately low so the culvert barrel stays visible through the fill.

Quantities

All quantity fields are read-only computed values. They may take a moment to refresh on recompute, and in DTM mode they follow the stored Terrain Data, so recompute that first if the terrain or the culvert has moved.

Fill Volume: Volume of the fill body above the top slab. In DTM mode this is the volume clipped against the terrain surface; otherwise it is the plan area of the fill footprint times the fill depth. (Read-only)

Fill Weight: Fill Volume multiplied by the Fill Soil Unit Weight. Useful as a sanity check against the total vertical earth load reported by the analysis. (Read-only)

Top Surface Area: Area of the top surface of the fill. In DTM mode this is the true surface area of the sloped terrain, which is why it can exceed the flat plan area beneath it. (Read-only)

Bottom Surface Area: Area of the fill's underside, where it bears on the culvert's top slab and the ground alongside it. (Read-only)

Average Fill Depth: Fill Volume divided by Bottom Surface Area — the mean cover over the footprint. In the non-DTM modes it equals the entered or derived fill depth; in DTM mode it summarises a cover that varies across the footprint. (Read-only)

IFC

Type: The IFC entity the fill is exported as.

Predefined Type [EMBANKMENT/BACKFILL/SUBGRADE/NOTDEFINED]: The IFC predefined type. The default, EMBANKMENT, describes fill placed as a road embankment over the culvert; use BACKFILL when the material is being modelled as backfill placed into an excavation.

Parent [SUBSTRUCTURE/SUPERSTRUCTURE/BRIDGE]: Where the fill is placed in the exported IFC hierarchy.