> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/box-culvert-workflow/loading-bc/vertical-earth-bc.md).

# Vertical Earth \[BC]

Vertical Earth applies the weight of the fill above the culvert as a uniform downward pressure on the top slab, following AASHTO LRFD 12.11.2.2:

`EV = F_e · γ_s · H`

where `H` is the fill depth over the top slab, `γ_s` the fill unit weight, and `F_e` the soil-structure interaction factor for an embankment installation (12.11.2.2.1), taken as `min(1 + 0.20·H/B_c, 1.15)` with `B_c` the culvert's outside width. `F_e` accounts for the fill column over a relatively rigid culvert attracting more than its own weight as the softer soil beside it settles further.

## General

**Box Culvert:** The culvert barrel this load is applied to. A selection is required. The pressure is applied over the barrel's top slab.

**Stage:** The construction stage this load is activated in. Leave it empty for a model that is not staged.

**Fill Data From \[Inputs/Culvert Fill]:** Where the fill depth and unit weight come from. *Inputs* takes them from the two fields below. *Culvert Fill* takes them from the Culvert Fill registered on the selected barrel, so the cover and the soil weight cannot drift apart from the ones the other fill-driven loads use. The Culvert Fill is not picked here — it is found through the culvert — and choosing this option when the culvert carries no fill is reported as an issue rather than silently falling back.

**Fill Depth Above Top Slab:** The cover depth over the top slab. Shown only when Fill Data From is set to Inputs, where a value is required. Must not be negative.

**Fill Soil Unit Weight:** Unit weight of the fill above the culvert. Shown only when Fill Data From is set to Inputs, where a value is required. Must be positive.


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