Environmental Impact Assessment of Canal Irrigation Projects

 

1. General Description and Scope
   The work comprises providing and laying dry rubble pitching for embankment construction. This item includes quarrying or procuring selected rubble, transporting and depositing it as dry pitching, and constructing an inverted graded filter system. The system consists of a base layer of 20 cm of gravel (or metal aggregate) overlaid by a 20 cm layer of sand, with both layers serving as a stable and uniform base for the filter. Additionally, the work includes the provision and fixing of precast concrete header stone made with M15 grade concrete, along with hand packing, trimming, and dressing of slopes. All operations shall be executed in accordance with the project drawings and applicable standards for embankment and slope construction.

2. Material Requirements

• Rubble Pitching Material: The rubble used for pitching shall consist of durable, angular stones from approved sources. The selected material shall be free from deleterious substances, weathered, or contaminated particles that may compromise performance.
• Gravel/Metal Layer: The 20 cm layer of gravel or metal aggregate shall conform to the gradation requirements specified in ASTM C33 or IS 383, ensuring the material is well-graded, clean, and suitable for load distribution.
• Sand Layer: The 20 cm sand layer shall be a clean, natural fine aggregate conforming to ASTM C33 or IS 383, free from excessive fines and organic matter, to provide a uniform base for the filter.
• Precast Concrete Header Stone: The header stone elements shall be precast using M15 grade concrete, prepared in accordance with IS 456:2000. The precast units shall have the required dimensions and compressive strength, with quality assured through controlled production methods.

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3. Construction Methods
   The Contractor shall execute the work as follows:

• Material Procurement and Transport: Quarry or source the rubble, gravel, and sand from approved locations. Transport the materials to the site within a lead distance not exceeding project limits, using equipment that prevents contamination or segregation.
• Laying Dry Rubble Pitching: The rubble shall be placed in situ as a dry layer, ensuring proper alignment and uniform thickness. No binding agents shall be used.
• Construction of Inverted Graded Filter: Over the rubble pitching, a base layer of 20 cm of gravel/metal aggregate shall be spread uniformly. Immediately above this, a 20 cm layer of sand shall be laid, providing a graded filter that ensures proper drainage and stability.
• Fixing of Precast Header Stone: The precast header stone units shall be accurately positioned along the designated header line. They shall be fixed in place using methods prescribed by the Engineer (e.g., mechanical anchorage, grout, or adhesive) to ensure stability and alignment.
• Hand Packing, Trimming, and Dressing of Slopes: Following placement, each layer shall be hand-packed to eliminate voids and achieve close interlock. Slopes shall be trimmed and dressed to the required profile and finished to a neat appearance.
• Moisture Conditioning: Where required, water shall be applied uniformly to adjust the material moisture to the Optimum Moisture Content (OMC) as determined by standard Proctor tests (e.g., IS 2720 Part 3). This is to ensure that the compacted embankment achieves the specified dry density.

4. Quality Control and Testing

• Material Testing: Samples of gravel, sand, and rubble shall be tested for gradation, cleanliness, and physical properties in accordance with ASTM C33 or IS 383.
• Precast Concrete Verification: Precast header stone units shall be tested for compressive strength per IS 456:2000 to confirm conformity with the M15 grade.
• Field Density Tests: After compaction, the density of the constructed layers shall be verified using standard field density tests (e.g., nuclear density gauge or sand cone method) to ensure that the required percentage of maximum dry density is achieved.
• Inspection and Documentation: All work shall be inspected by the Engineer or designated representative. Test results and inspection records shall be maintained and made available for review.

5. Measurement and Payment

• Measurement: The quantity of work shall be measured based on the volume of material placed, the area and thickness of the embankment layers, and the number of precast header stone units fixed. Measurements shall be taken as per the contract documents and verified by the Engineer.
• Payment: Payment shall be made at the contract unit rates, inclusive of quarrying, transporting, laying of dry rubble pitching, spreading of graded layers, compaction, placement and fixing of header stone, and all ancillary operations such as hand packing, trimming, and slope dressing.

6. Compliance with Standards
   All materials and construction practices shall conform to relevant standards and specifications, including:

• ASTM C33 or IS 383 for aggregates and sand,
• IS 456:2000 for concrete (M15 mix for header stone), and
• IS 2720 Part 3 for compaction testing.
  Any additional project-specific or local regulatory requirements shall also be adhered to.

7. Safety and Environmental Considerations

• Safety: All operations shall be conducted following applicable safety regulations. Personnel shall use proper personal protective equipment (PPE) and machinery shall be operated by qualified operators.
• Environmental Protection: Measures shall be taken to minimize dust, control noise, and manage runoff. All waste and surplus materials shall be disposed of in accordance with environmental guidelines.
• Site Restoration: Borrow areas and transport routes shall be restored as required by project specifications, ensuring minimal environmental impact.