Earthworks Notes

Introduction to Earthworks

  • Earthwork refers to the process of moving a portion of the earth's surface from one location to another, including transforming the earth's material into a new desired shape and physical condition.
  • It involves excavation, hauling, and placing earth materials.

Importance of Earthworks

  • Measurement of earth materials in the field.
  • Computation of the volume of such material.
  • Determination of the most economical method of performing such work.

Terminologies on the State of Earth Materials

  • Bank Measure: Volume of earth in its natural state.
  • Loose Measure: Volume of earth in the vehicle.
  • Compacted Measure: Volume of earth after compaction.
  • The state of the earth material is determined by its "swell and shrinkage" properties.

Classification of Materials

  • Common Excavation/Rock Excavation: Refers to soil; excavated material.
  • Common Borrow: Refers to the soil found outside the roadway and brought into the roadway if there's not enough material in the roadway excavation to provide for the embankment.
  • Waste: Materials excavated and thrown away, which are no longer necessary to form embankments.

Terminologies

  • Cut: Earthwork which is excavated, or is to be excavated.
  • Fill: Excavation which is placed in embankment, or is to be placed in embankment.

Earthworks Contracting

  1. The contractor bids a lump sum for the work, handling the materials as he sees fit.
  2. The contractor is paid per cubic yard for excavation (includes excavation, hauling, and placing of embankment).
    • Payment is normally either for cut and not for fill or for fill and not for cut. To pay for both would be paying for the same earth twice.
    • Highway work - for cut, Dam work - for fill.

Earthworks Contracting Considerations

  • The cost of hauling a unit volume of earth over a long distance can easily become greater than the cost of excavation, so it is often practical to pay a contractor for excavating and hauling earth.

Area and Volume Determination

Area Determination (Cross Sections)

  • Profiles of the earth are taken at right angles to the centerline of an engineering project (such as a highway, canal, dam, or railroad).
  • Taken to obtain volume measurement/estimate earthworks.
  • Usually taken at each full station and breaks in the ground along the centerline (Assumption: change in the earth's surface from one cross-section to the next is uniform).

Cross Section Types and Area Calculation

  • Level Section:
    • Area =c(b+sc)= c(b+sc)
  • Three-Level Section:
    • Area =c(d<em>l+d</em>r)2+b(h<em>l+h</em>r)4= \frac{c(d<em>l+d</em>r)}{2} + \frac{b(h<em>l+h</em>r)}{4}
  • Five-Level Section:
    • Area =cb+f<em>ld</em>l+f<em>rd</em>r2= \frac{cb+f<em>ld</em>l+f<em>rd</em>r}{2}
  • Irregular Section:
    • Area is found by triangles, coordinates, or planimeter.