1. General
This specification outlines the requirements for providing a turfing layer on the downstream (D/S) slope of the earthen dam. The work includes all necessary soil preparation, provision of a layer of selected soil, application of bio-organic manure, planting of grass turf, and subsequent watering and maintenance. The purpose is to prevent soil erosion and stabilize the slope.
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2. Materials
- Selected Soil: The soil used for turfing shall be fertile, loamy, and well-graded, free from stones, pebbles, roots, weeds, and other deleterious materials. It shall have a pH value suitable for healthy grass growth, typically between 6.0 and 7.5. The soil must be sourced from a location approved by the Engineer.
- Bio-Organic Manure: The manure shall be well-decomposed, mature, and free from seeds of weeds, harmful pathogens, and heavy metals. It shall be in a dry, friable condition and shall conform to the relevant standards for organic fertilizers. The contractor shall submit a sample of the manure for approval before use.
- Grass Turf: The grass turf shall be procured in healthy, fresh sods. It shall consist of a dense root system and a thick, continuous mat of a durable, deep-rooted grass species suitable for local climatic conditions (e.g., Bermuda grass, Zoysia grass). The sods shall be free from weeds, insects, or diseases. They must be laid on the same day they are cut or delivered.
3. Workmanship and Preparation
- Slope Preparation: The D/S slope shall be graded to the specified line and level. The surface shall be loosened to a depth of at least 150 mm to a rough finish to facilitate proper bonding of the new soil layer. All large stones, roots, and debris shall be removed.
- Soil and Manure Application: A layer of the selected soil, mixed with bio-organic manure in the ratio of 3:1 (by volume), shall be spread uniformly over the prepared slope. The compacted thickness of this layer shall be a minimum of 75 mm. The soil layer shall be lightly compacted to achieve a firm and uniform bed for the turfing.
- Laying of Turfing: The grass sods shall be laid carefully over the prepared soil bed, edge-to-edge, in continuous strips. Each sod must be firmly pressed down to ensure perfect contact with the soil underneath. Gaps between sods shall be avoided. Overlaps are not permitted. In case of any unavoidable gaps, they shall be filled with a similar mixture of soil and manure.
- Anchoring: On slopes steeper than 2H:1V, the turf sods shall be anchored to the ground using bamboo or wooden pegs. The pegs shall be driven through the sods at a spacing of approximately 500 mm in a staggered pattern, ensuring they are flush with the surface of the sod.
4. Curing and Maintenance
- Initial Watering: Immediately after laying, the entire turf area shall be thoroughly watered using a sprinkler or a fine spray to settle the sods and moisten the soil.
- Regular Watering: The turf shall be kept moist at all times for the first 15 days to promote root growth and establishment. Subsequently, watering frequency shall be reduced to twice a day for the next 30 days or as instructed by the Engineer, depending on weather conditions.
- Protection: The turfing shall be protected from foot traffic, grazing animals, and any other activity that may damage it until the grass is well-established. Any damaged patches shall be repaired promptly by removing the damaged sods and replacing them with new ones.
- Trimming: The grass shall be trimmed as needed to a height of approximately 50 mm once it has grown sufficiently.
5. Measurement and Payment
- Measurement: The measurement for turfing shall be in square meters (m2) of the finished and accepted work, measured on the surface area of the D/S slope. No separate measurement shall be made for the supply of soil, manure, grass sods, watering, or maintenance.
- Payment: The unit rate shall include the cost of all materials, labor, tools, equipment, and all operations required to complete the turfing, including initial site preparation, laying, watering, and a 30-day maintenance period. The payment shall be made only for the work that is completed satisfactorily and is approved by the Engineer.
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