09-SUB STRUCTURES



SUB STRUCTURES (BRIDGES)

1. GENERAL

This part consists of construction of substructures for bridges and culverts in accordance with the details shown in the Drawing and conforming to the specifications or as directed by the Engineer.

  1. A method statement for construction shall be submitted by the Contractor for the approval of the Engineer well in advance of the commencement of the substructure work.
  2. The method statement shall include:
  1. Sources of materials.
  2. Design, erection and removal of form work.
  3. Production, transportation, laying and curing of concrete.
  4. Personnel employed for execution and supervision.
  5. Tests and sampling procedures.
  6. Equipment details.
  7. Quality management system to be adopted as per this Manual.
  8. Safety measures.
  9. Any other relevant information.
  1. Arrangements for execution under water wherever necessary, shall be included in the method statement.
  2. Dimensions, lines and levels shall be set out and checked with respect to permanent reference lines and permanent bench mark so that the substructure is constructed in accordance with the Drawings.

2. MATERIALS

The basic materials shall comply with respective sections of this Manual.

3. REQUIREMENTS/WORKMANSHIP

3.1 Abutment and piers

The work shall be strictly in accordance with the Drawings or as directed by the Engineer.

  1. For concrete piers and abutments, horizontal construction joints shall be avoided as far as possible, by arranging the concrete pour in one single operation.
  2. Where construction joints are unavoidable, they shall be prepared in accordance with the relevant provisions or as directed by the Engineer.
  3. No vertical construction joints shall be permitted. Construction joints shall not be permitted in splash zones.
  4. In case of tall piers and abutments, use of slip-form shall be preferred. The design, erection and raising of slip-form shall be subjected to special specifications which shall be furnished by the Contractor. The concrete shall also be subjected to additional specifications as necessary. All specifications and arrangements for use of slip form and placing of concrete therein shall be subjected to the approval of the Engineer.
  5. The top surface of foundation/well cap/pile cap over which new concrete is to be laid, shall be scraped with wire brush and all loose materials removed.
  6. In case reinforcing bars projecting from foundations are found coated with cement slurry, the same shall be removed by tapping, hammering or wire  brushing. Care shall be taken to remove all loose materials around reinforcements. Just before commencing masonry or concrete work, the surface shall be thoroughly wetted.
  7. In case of solid (non-spill through type) abutments and hollow concrete piers, weep holes as shown in the Drawings or as directed by the Engineer, shall be provided in conformity with relevant specifications.
  8. The surface finish shall be smooth, except on the earth face of abutments which shall be rough finished.
  9. In case of abutments likely to experience considerable movement on account of earth pressure from backfill of approaches and settlement of foundations, the construction of the abutment shall be followed by filling up of embankment in layers to the full height to allow for the anticipated movement during construction. Casting of superstructure resting on the abutment shall be taken up only thereafter.

3.2 Abutment cap and pier cap

  1. The locations and levels of pier cap, abutment cap, pedestals and bolts for fixing bearings shall be checked carefully to ensure correct alignment in accordance with the Drawings.
  2. The surface of cap shall be finished smooth and shall have a slope for draining off water as shown in the Drawings or as directed by the Engineer.
  3. The surface on which bearings are to be placed shall be prepared as indicated in the Drawing.

3.3 Dirt wall, return/wing walls

  1. In case of cantilever return/wing walls, no construction joint shall be permitted. The dirt wall and cantilever return/wing wall shall be cast in one operation.
  2. For gravity type masonry and concrete return/wing wall, the surface of foundations shall be prepared in the same manner as that prescribed for construction of abutment. No horizontal construction joint shall be provided.
  3. Vertical construction joint may be provided, if shown in the Drawing or as directed by the Engineer.
  4. Vertical expansion gap of 20 mm shall be provided in return wall/wing wall at every 10 metre intervals or as directed by the Engineer. The 20 mm gaps shall be filled with suitable type of asphaltic/bituminous board, so as to prevent embankment material from coming out.
  5. For masonry/concrete return/wing walls, weep holes shall be provided as prescribed for abutments or as shown in the Drawing.
  6. The finish of the surface on the earth side shall be rough while that of the front face shall be smooth.

4.  TOLERANCES

Table:  Permissible tolerance for substructures

Sl.

No.

Item

Permissible  limits

1

Variation in cross-sectional dimensions.

+10 mm/-5 mm

2

Misplacement from specified position in plan.

10 mm

3

Variation of levels at top.

±10 mm

4

Variation of reduced levels of bearing areas.

±5 mm

5

Variation from plumb over full height.

±10 mm

 

6

Surface unevenness measured with 3m

straight edge for all surfaces except bearing areas.

5 mm

7

Surface unevenness measured with 3m  straight edge for  bearing areas.

3 mm

5.  SAMPLING AND TESTING

The materials and work shall be tested in accordance with the relevant sections of this Manual and shall meet the prescribed standards of acceptance.

RELATED CODES:

1.IRC: 78:-Standard specification and code of practice for road bridges: Foundations and substructures.

2.MoRTH:-Specifications for road and bridge works (5th revision)

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