Construction Methodology of Embankment
This work deals with laying, spreading, and compacting embankment layers with approved materials as per clause 305 & 900 of MORT&H specification.
- End Dumper
- Motor Grader
- Water tanker with sprinkler
- Vibratory roller
- Survey kit
- Auto Level
- Levelling Staff
- Measuring tape etc.
The materials for the embankment shall be arranged from the approved source, including from roadway and drain excavation, borrow areas or other sources also it shall be meet the prescribed specifications as well as compliance with the different environment requirements in respect of excavation and borrow areas as stipulated, from time to time, by Ministry of Environment and Forest, Government of India and the local bodies, as applicable will be the sole responsibility of the Contractor.
As per clause 305.2 of MORT&H, the material to be used for the construction of the embankment shall be satisfying the following requirements.
- The particle size of the course material in the mixture of the earth shall not be more than 75mm.
- The physical requirement of the material shall be by clause 305.2.1 of MORT&H specification.
- The free swell Index of the material shall not be more than 50 per cent when tested as per IS: 2720 (Part – 40) 1977.
- The liquid limit of the material shall not be more than 50 per cent.
- The plasticity index shall be more than 25 per cent.
- Dry unit weight of the material shall not be less than 15.2 KN/Cum for Embankments up to 30 height not subjected to extensive flooding and not less than 16.0 KN/Cum for Embankments exceeding 3m height or embankment of any height subjected to long periods of inundation when tested as per IS: 2720 (Part – 8) 1983.
- Where the excavation reveals a combination of acceptable and unacceptable materials, the acceptable materials are excavated separately for use in permanent works without contamination by the unacceptable materials. The acceptable materials shall be stacked separately.
1. Setting Out:
After the site has been cleared as per clause 201, and C&G, the work will be set out true to lines, grades, slopes, curves and sections shown on the drawing.
2. Compacting Ground Supporting Embankment
The original ground is going to be levelled to facilitate placement of the primary layer of the embankment, scarified, mixed with water then compacted by rolling to achieve minimum dry density 95% as given in table 300-2 of MORT&H specification.
Where the ground supporting embankment is found to be unsuitable (material mentioned in clause 305.2.1.1 of MORT&H specification) or the original ground level material is having free swell index greater than 50% the same will be removed 500mm and will be replaced with approved material as per clause 305.3.4 of MORT&H specification.
3. Transporting of Material
The approved material from the roadway will be transported utilizing dumpers and dumped in the form of heaps as required.
4. Spreading Materials in Layers
Spreading of material shall be in layers, the compacted layers shall not be more than 250mm for vibratory roller and 200mm for 80-100 KN static roller and bringing to optimum moisture content by applying water from sufficient capacity of water tankers.
The moisture content of the material will be checked and extra moisture content required will be added before rolling.
The moisture content of each layer will be checked and it should be within the range of OMC +1% to OMC -2%. If the moisture content is found out of these limits the same will be brought within limits by addition of water or by aeration as the case may be.
The compaction will be done with the help of a vibratory roller of 8 to 10-ton static weight. Each layer will be thoroughly compacted to the densities specified in the specifications. Compaction will be carried out from lower edge to upper edge with 8 to 10-ton roller till to achieve the required compaction and no tyre or drum impression on the surface and compaction requirement as per table 300-2 of MORT&H and compaction procedure shall be as per clause 305.3.6 of MORT&H specification.
Field density tests will be carried out as per the frequency as specified in the specifications. Subsequent layers shall be placed only after the finished layer has been tested according to clause 903.2.2 of MORT&H.
If the required field density is not achieved, compaction will be continued till the required density is achieved.
Loose packets if any will be removed and replaced with an approved material.
The surface of the embankment at all times during construction shall be maintained at such a cross fall as will shed water and prevent ponding.
7. Embankment around structures
The material used for backfill shall not be an organic soil or highly plastic clay having a plasticity index and liquid limit more than 20 and 40 respectively. Around the structures, it may be impracticable to use conventional rollers. The compaction will be carried out by a small vibratory roller, plate compactor or power rammer.
The filling around culverts, bridges and other structures up to a distance of twice the height of the woad from the bottom of the abutment will be carried out independent of the work on the main embankment. The fill material will not be placed against any abutment or wing wall until the concrete or masonry has been in the position for 14 days. The fill material will be deposited in horizontal layers in loose thickness and compacted thoroughly to not less than 95% MDD (Maximum Dry Density).
8. Traffic Safety
Traffic safety measures shall be taken care of as per the safety plan where earthwork activities are in progress. All the vehicles will have red flags and reflective bands on the rear. Flagmen will be deployed where the crossing of the existing road is unsafe.
9. Quality Control
Quality control for the work shall be as per table 900-3 of MORT&H specification.
- Moisture content shall be checked before compaction preceding the work.
- The compacted surface shall be checked for field density at the frequency of 1 test per 3000sqm. The degree of compaction shall be as per clause 903.2.2 of MORT&H specification.
- The surface shall be checked for levels at as per MORT&H intervals longitudinally and transversely and shall be within the designed level.
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