Earthwork Study Notes

Earthwork Notes

Learning Objectives

  • Understand the basic components of a site plan.

  • Identify retaining walls, gabions, and earth reinforcement visually.

  • Recall the procedures for filling and backfilling.

Site Plans

  • Lot dimensions: Measured dimensions of the lot where construction takes place.

  • Building setbacks: Required distances from property lines to the structure.

  • Public Utility Easements (PUE): Areas designated for utilities, must remain unobstructed.

  • Building footprint: The outline of the structure at ground level.

  • Location of structure on lot: Positioning of the building within the lot.

  • Driveway location and width: Design and positioning of access points.

  • Topography: The arrangement of the natural and artificial physical features of an area (not shown in the current materials).

Retaining Walls - Purpose

  • Function:

    • Retaining walls are designed to hold back soil in areas where there is an abrupt change in ground elevation.

    • They must possess sufficient strength to withstand the forces exerted by the earth and any groundwater present.

Retaining Walls - Failures

  • Retaining walls are susceptible to several types of failures, including:

    • Horizontal sliding: Movement of the entire wall sideways due to pressure from the soil behind.

    • Overturning: When the wall tips or rotates due to an imbalance of forces, causing it to collapse.

    • Undermining: Erosion or washout occurs beneath the wall, leading to structural instability.

Retaining Walls - Construction Type

  • A visual representation of different construction methods may be required here for detailed analysis (not provided).

Foundation Requirements

  • Gabions:

    • Define gabions as a form of earth retention using corrosion-resistant wire baskets filled with cobble or boulder-sized rocks.

    • They are placed in layers to create sturdy walls that hold back soil and resist erosion.

Gabions

  • In addition to their primary function, gabions may also serve to combat erosion effectively by stabilizing loose ground and preventing soil degradation.

Earth Reinforcement

  • Definition:

    • Often referred to as "Mechanically Stabilized Earth (MSE)."

    • Involves placing reinforcing material between layers of fill or backfill, which is compacted accordingly.

  • Benefits:

    • The addition of reinforcement creates tensile strength in the soil, which aids in structural integrity.

    • It is frequently a more economical alternative compared to traditional retaining walls for soil stabilization.

Filling and Finish Grade

  • Filling:

    • A broad term that refers to any process of placing earth material, such as raising the existing grade of a site.

  • Backfilling:

    • Specifically pertains to replacing earth material back into trenches or excavated areas to restore the ground to its original or desired level.

  • Lifts:

    • Both filling and backfilling operations are performed in layers or “lifts.”

    • Lift thickness can typically range from 4 to 12 inches based on the compaction requirements.

Filling

  • Large open areas allow for the effective compaction of fill material using heavy construction equipment, ensuring stability and density of the earth used.

Filling and Proper Compaction

  • In constrained or confined spaces, the compaction of fill or backfill may necessitate the use of smaller, walk-behind equipment to ensure proper density and stability of the material.

Backfilling

  • Backfill operations often take place in trenches, where each layer, known as a "lift," is critically compacted to ensure firm ground structure and prevent settling or shifting over time.