METHODOLOGY FOR EMBANKMENT & SUBGRADE CONSTRUCTION

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METHODOLOGY FOR EMBANKMENT & SUBGRADE CONSTRUCTION
(Acceptance Criteria: Ref. sec. 305of MORT&H)

Scope:

This work consists of construction of embankment including subgrades; earthen shoulders, median and rock fill in embankment by mechanical means with approved materials from roadway excavation or borrow pits.

Equipment/ Machinery Requirement:

  1. Excavator
  2. Dumper
  3. Water tanker
  4. Motor grader
  5. Roller

Materials:

  1. These materials shall be free from logs, stumps, roots, rubbish or any other ingredient likely to affect the stability of the embankment and the sub grade. The materials that have LL less than 50%, Pl less than 25%, free swelling index less than 50% shall be used for embankment construction. The material, which is having lab MDD 15.2kN/cum, for filling in medians & embankment up to 3 meters height, MDD 16.0 kN/cum for Embankment Exceeding 3 meters height, and for subgrade & shoulders, the material having lab MDD 17.5kN/cum. The samples from the identified borrow areas shall be brought to site laboratory and tested for the above requirements.

Procedure for Embankment:

  1. Toe line will be marked as per clause 305.3.1 of MORTH to ensure proper rolling up to the edges of the toe line.
  2. The original ground shall be levelled, scarified, mixed with water and compacted to achieve 90% to 95% of laboratory MDD. When the soil of the original ground for embankment is not suitable the same shall be removed up to 500mm and compacted in layers not exceeding 250 mm to achieve the 95% of MDD.
  3. Approved material will be placed as per the calculated loose thickness, so that compacted thickness does not exceed 250 mm, in accordance to clause 305.3.5 of MoRT&H.
  4. All the roots / deleterious material will be removed if any manually.
  5. The dumped material will be spread over the entire width by means of dozers / graders to achieve specified slopes and grades.
  6. Required quantity of water will be sprinkled after calculating the
    difference
    Between OMC & NMC + 1% for evaporation losses. If any water logging is
    Observed dewatering will be carried out in accordance to clause305.3.2 of MORTH.
  7. Final grading will be done with motor grader to true line and levels.
  8. Moisture content will be checked before the rolling commences. (If the moisture is not in limits, the same will be brought to -2% to 1% range of OMC by adding or drying).
  9. The compaction shall be done with a vibratory roller of 80 to 100kN static weight. The rolling shall commence from the lower edge and proceed towards upper edge. Each pass of the roller shall overlap 1/3rd of the preceding pass.
  10. The compaction shall be done to achieve minimum of 95% of MDD.
  11. Field dry density will be carried out by sand replacement method and recorded in the format.
  12. During the period of construction arrangement of traffic shall be in accordance with MORT&H 112.

Procedure for Sub grade:

  1. EPC proposed to do sub-grade of 500 mm in Two layers for each 250mm compacted thickness.
  2. The approved material for subgrade shall be excavated at borrows areas / tippers. roadway excavation by excavators and hauled to site by The materials shall be spread in layers of uniform thickness up to 250mm required thickness for 1st layer and Subsequently 250mm required thickness for Top layer of subgrade portion respectively over the entire width by means of dozers/ graders to achieve specified slopes and grades.
  3. The moisture contents shall be checked for OMC and if it is less than required water may be added by sprinkling and if it is more than required, can be allowed to dry, by exposure to the sun.
  4. The moisture content of each layer shall be checked, and an allowance for evaporation losses of I% above to 2% below OMC shall be allowed and then compacted to achieve 97% of MDD for subgrade & shoulders and then successive layers shall be placed.
  5. Final grading will be done carefully as per required slope and level.
  6. The compaction shall be done with a vibratory roller of 80 to 100kN static weight. The rolling shall commence from the lower edge and proceed towards upper edge. Each pass of the roller shall overlap 1/3 rd of the preceding pass.
  7. The compaction shall be done to achieve minimum of 97% of MDD.
  8. Field dry density will be carried out by sand replacement method and recorded in the format.
  9. During the period of construction arrangement of traffic shall be in accordance with MoRT&H 112.

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