15.RIVER PROTECTION



RIVER PROTECTION WORKS

1. GENERAL

River training and protection works shall include construction of guide bunds, guide walls, spurs, groynes, bank protection, flooring, cut-off walls, apron and approach embankment protection, as required for ensuring safety of the bridge structure and its approaches against damage due to flood/flowing water. Construction of various components shall conform to IRC: 89 and MoRTH Specifications or as directed by the Engineer.

2. GUIDE BUND

  1. This work shall consist of construction of embankment of guide bund in accordance with Clause 2502 of MoRTH Specifications or as directed by the Engineer.
  2. The provision of apron and toe protection and pitching/revetment on slopes, etc shall be as indicated in the Drawings and constructed in accordance with Clauses 2503 and 2504 of MoRTH Specifications.
  3. The alignment and layout of guide bund shall be as indicated in the Drawings or as approved by the Engineer.
  4. The construction of embankment for guide bund shall conform to provisions of Section 2100 of this Manual.
  5. Guide bunds shall be made of locally available materials. Trial pits shall be taken in borrow areas to examine suitability of soil for construction and also to decide the types of earth moving machinery to be used. No borrow pits should be dug on the river side of the guide bunds.
  6. Construction of guide bund shall be taken in hand along with the construction of the bridge and to complete the work of the guide bund in one working season.
  7. Sufficient area along the side of the guide bund shall be ready within one to two months of commencement of work, so that the placing of stones in the apron and in the slope pitching can be commenced.
  8. Earth work shall be completed within 80% of the working season and about 70% of the working season shall be available for laying apron and pitching.
  9. No portion of the guide bund should be left incomplete below high flood level before the onset of the monsoon.
  10. The methodology for transport of stones from the quarries to the site of work including the quantities of stone to be transported every day, mode of transport to be used (train, truck, ferry, boats), labour for loading, unloading and laying etc. shall be furnished by the Contractor for approval by the Engineer.
  11. Adequate reserve of stones should be maintained for major works as decided by the Engineer. The reserve stones shall be stacked away from the main channel of the river.
  12. Where the alignment of guide bund or the approach embankment crosses branch channel of the river, the branch channel shall be either diverted to the main channel of the river with the help of spurs, groynes etc. or closed by a properly designed closing dyke or closure bund, before taking up construction of guide bund.

3. APRON

This work shall consist of laying boulders directly or in wire crates on the bed of rivers for protection against scour. The detailed specifications and construction procedures are given under clause 2503 of MoRTH Specifications.

  1. The stones used in apron shall be sound, hard, durable and fairly regular in shape.
  2. Stones subjected to marked deterioration by water or weather shall not be used.
  3. Quarry stones having angular shapes shall be preferred to round boulders.
  4. The size of stones for boulder aprons shall conform to relevant clause of IRC: 89.
  5. Where the stones of required size are not economically available, cement concrete blocks in minimum M15 grade conforming to Section 3300 of this Manual or stones in wire crates shall be used.
  6. Requirements of wire crates and mattresses for apron shall be as per clause 2503 of MoRTH Specifications.

4. PITCHING/REVETMENT ON SLOPES

This work shall consist of covering the river side slopes of guide bunds, training works and road embankments with stone, boulders, cement concrete blocks or stones in wire crates over a layer of granular material which will act as a filter. The rear slopes, not subjected to direct attack of the river, may be protected by 300 mm to 600 mm thick cover of clayey or silty earth and turfing.

  1. The pitching shall be provided with stones of thickness and shape as indicated in the Drawings. The size and weight of stones shall conform to IRC: 89. No stone weighing less than 40 kg shall be used.
  2. The stones shall be obtained from quarries and shall be sound, hard, durable and fairly regular in shape. Round boulders shall not be allowed. Stones showing marked deterioration by water or weather shall not be accepted.
  3. Where the stones of required size are not economically available, cement concrete blocks in minimum M15 grade concrete conforming to Section 3300 of this Manual or stones in wire crates, shall be used.
  4. Geosynthetics, if used in pitching, shall conform to Section 2600 of this Manual.
  5. The material for the filter shall consist of coarse sand, gravel or stone. One or more layers of graded materials, to act as a filter medium, shall be provided underneath the pitching, to prevent loss of the embankment material and build up of uplift head on the pitching. The gradation of the filter material shall conform to IRC: 89 and MoRTH Specifications.
  6. Construction operations of pitching on slopes shall be carried out conforming to MoRTH Specifications.

5. TOE PROTECTION

  1. A toe wall shall be provided at the junction of slope pitching and launching apron of a guide bund so as to prevent the slope pitching from sliding down.
  2. The toe wall shall be in dry rubble masonry (Un-coursed) conforming to MoRTH Specifications or in cement concrete of M15 grade.

6. RUBBLE STONE FLOORING

  1. Where specified, provide rigid flooring under culverts and extend for a minimum distance of 1.5 m on upstream side and 3.0 m on downstream side or as shown in Drawings.
  2. Excavate trench for laying foundation of bed protection and lay 300 mm thick cement concrete of M15 grade (Unless not specified in the Drawing), so as to commence paving work.
  3. There shall be no loose materials or pockets in the trench. The bed shall be compacted level and even. All concrete and other elements are laid in dry bed.
  4. Flooring is done with 150 mm flat stones/cement concrete block M15 grade thick, which are bedded on a 25 mm thick layer of 1:3 cement mortar. Fill the joints with cement mortar and finish neatly.
  5. Keep the top of flooring 300 mm below the lowest bed level and extend the flooring up to the line connecting the end of splayed wing walls on either side of the culvert/bridge.
  6. Adopt dry rubble stone where the velocity of flow is less than 1.5 m/sec by keeping the top of flooring 300 mm below the low bed level.
  7. Lay the rubble stones closely, breaking joints, and fill all joints with spalls of proper size, wedged in with rammers to ensure tight packing.
  8. Before laying the foundation and protection walls, the excavated trenches shall be inspected by the Engineer to ensure that:
  1. There are no loose pockets and unfilled depressions left in the trench.
  2. The soil at the founding level is properly compacted to true lines and levels so as to have even bedding.
  3. All concrete and other elements are laid in dry bed.

7. CURTAIN WALL AND FLEXIBLE APRON

  1. The rigid flooring shall be enclosed by curtain walls (Tied to the wing walls) with minimum depth below floor level of 2 m on upstream side and 2.5 m on downstream side.
  2. The curtain wall shall be in cement concrete M15 grade or stone masonry in cement mortar 1:3.
  3. Beyond curtain walls, flexible apron 1.0 m thick comprising loose stone boulders (Weighing not less than 40 kg) shall be provided for a minimum distance of 3.0 m on upstream side and 6.0 m on downstream side.
  4. The work of floor protection shall be simultaneously completed along with the work on bridge foundations.

8. QUALITY CONTROL

  1. The size and weight of stones for laying boulder apron and pitching on slopes shall conform to the requirement given in IRC: 89.
  2. The galvanising coating shall conform to IS: 4826 and that of annealed steel wire for wire crates shall conform to IS: 280.
  3. Size and weight of stones in apron/slope/flooring etc. shall be checked at quarry site before procurement.
  4. Wire crates (Size and mesh size) and cement concrete blocks (Weight and size) shall be checked before procurement.
  5. Gradation of filter media shall be checked for specifications in IRC: 89.
  6. The tests to be carried out during construction are indicated in table.

Sl.No.

Test/check

Frequency

1

Laying of filter granular material

Daily check for workmanship.

2

Laying boulders for

- Apron

- Pitching on slopes

- Toe protection

- Wire crates

 

Daily check for uniformity in

workmanship.

3

Mortar for joints

- Mix proportions (control on

quality of cement by weight)

- Consistency and water retentivity (IS: 2250)

- Compressive strength (IS:2250)

 

Each batch.

 

As required.

On a set of 3 cubes, where specified.

4

Laying of stones in flooring

Daily check for workmanship.

5

Curtain wall

Daily check for workmanship.

 RELATED CODES:

1.IRC:89:Guidelines for design and construction of river training and control works for road bridges.

2.IS:280:Mild steel wire for general engineering purposes.

3.IS:10751:Planning and design of guide banks for alluvial rivers –guidelines.

4.MoRTH:Specifications for Road and Bridge works (5th revision).

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