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Structure Excavation [SPIG]

The Structure Excavation object calculates the volume of earth that needs to be removed to construct a foundation. It automatically generates excavation geometry from a selected footing and computes quantities based on the original ground surface.

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General

Foundation: Select the footing that defines the excavation boundary. The excavation extends from the footing bottom to the original ground surface. This is a required input.

Excavation Type: Determines the shape of excavation walls.

  • Vertical (0): Straight vertical walls from bottom to top

  • Sloped (1): Angled walls that widen toward the top for soil stability

Slope Ratio (H/V): The horizontal to vertical ratio for sloped excavation walls. Only shown when Excavation Type is set to Sloped. Common values include:

  • 1:1 (45 degrees)

  • 1.5:1 (gentle slope)

  • 2:1 (very gentle slope)

A ratio of 1.5 means 1.5 feet horizontal for every 1 foot vertical. Must be a positive value.

Boundary Offset Beyond Footing: Additional clearance distance beyond the footing edge in all directions. This provides working space around the footing for construction activities. Default is 12 inches. Must be non-negative.

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Top Elevation

Elevation Source: Method to define the original ground surface.

  • Elevation (0): Manual input of a single elevation value for flat ground

  • From DTM (1): Use a Digital Terrain Model for variable ground surface

Top Elevation: Manual elevation of the original ground surface. Only shown when Elevation Source is set to Elevation. This represents the existing ground surface before excavation.

Digital Terrain Model: Select a DTM object representing the existing ground. Only shown when Elevation Source is set to From DTM. The DTM must cover the excavation area.

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When using DTM mode, the excavation volume is computed as a precise prism volume between the DTM surface and the excavation bottom. This accounts for natural ground variations across the excavation area.

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Display

Show Excavation: Toggle to show or hide the excavation volume in the 3D view.

Opacity: Transparency of the 3D visualization. Range from 0 (fully transparent) to 1 (fully opaque). Default is 0.7.

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Quantities

All quantity fields are read-only computed values.

Excavation Volume: Total volume of earth to be removed. Calculated using:

  • DTM mode: Computed prism volume from terrainGrid function

  • Elevation mode (Vertical): Average Depth × Bottom Area

  • Elevation mode (Sloped): Frustum formula = (h/3) × (A_bottom + A_top + √(A_bottom × A_top))

Top Surface Area: Area of the original ground surface within the excavation boundary.

Bottom Surface Area: Area at the bottom of the excavation (at footing bottom elevation).

Min Excavation Depth: Minimum depth from ground to footing bottom. Particularly useful with DTM input to show the shallowest point.

Max Excavation Depth: Maximum depth from ground to footing bottom. Shows the deepest point of excavation.

Average Excavation Depth: Average depth of excavation across the area.

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Supported Foundation Types

Structure Excavation works with:

  • Custom Footing (OBPFoundation): Footing with point list or section-based geometry

  • Rectangular Footing (OBPFoundationRectangular): Standard rectangular footing

The excavation boundary is automatically derived from the footing polygon, offset outward by the specified boundary offset distance.

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