SCOPE :-
This method statement covers the construction of Minor Bridge at various location. It shall consist of furnishing and providing plain and reinforced concrete foundation placed in open excavation, Substructure and Superstructure in accordance with the drawings as per MORT&H Specifications & drawing.
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REFERENCES :-
Ministry of Road Transport and Highways specification.
Relevant drawings. IRC IS Codes and SP 13.
WORKING DRAWINGS :-
Working drawings, structural drawings and bar bending schedules will be submitted to the AE prior to start the work on site. After approval of the above submissions by the EPC/Concessionaire, the setting out of the structures shall be done.
MATERIAL:-
Shuttering and staging Material:-
Formwork shall be of steel with steel fixtures. Vertical and horizontal joints shall be sealed with foam type of material to prevent possible leakage of cement slurry during concreting. Formwork shall be erected on stay soldiers with the help of tie rods, props and pipes. Shuttering shall be leveled and aligned to the true lines.
Staging shall be designed with adequate safety margin to hold the load of the concrete. Scheme shall be submitted with the design calculations for the AE approval.
Reinforcement bars :-
Reinforcement bars shall be procured from the approved manufactures. Test certificate shall be obtained with each consignment.
On clearance of the consignment, bars shall be cut and bend to the size and shape as per approved bar bending schedule and tied on the site as per the relevant drawings and specifications.
CONCRETE MIX :-
Approved concrete mixes of the required compressive strength shall be used in the construction of various elements of the structure. The characteristics of constituents of the concrete mix shall conform to drawing, MORT&H, IS Codes & IRC Codes. Compliance of the constituents shall be controlled as per the above Codes and Specifications.
EQUIPMENT DETAILS:
Following equipments shall be deployed in the execution of this bridge:
- Excavators
- Dumpers
- Batching & Mixing Plant
- Transit Mixers
CONSTRUCTION SEQUENCE: –
a. Soil Exploration & confirmation of founding level.
b. Excavation of abutments & piers portion 300mm above the founding level.
c. Water table at founding level will be lowered by excavating pit near the foundation. The depth of pit will be 1 more below the founding level. Water pump will be installed at pit to pump water.
d. Construction of raft for all piers.
e. Construction of piers.
f. Annular/Backfilling of the completed stages of the piers up to required level.
g. Pedestal casting to erect staging as per the available staging system.
h. Excavation for abutments up to founding level.
i. Casting of raft for abutments.
j. Construction of abutments.
k. Staging arrangement for all spans.
I. Fixing bearing after casting of bearing pedestal after approval.
m. Fixing shuttering and formwork as per approved materials and setting out checking before placing of reinforcement for slab.
n. Pouring of slab and its arrangement inspected before the start of
pouring.
o. Back filing with filter media as per approval section and material.
p. Fixing of Strip Seal expansion joints with 40 mm joint width after approval of the same.
q. Construction of crash barriers and approach slabs.
r. Laying of Wearing coat.
CONSTRUCTION OPERATIONS: –
1. Setting out: After the site has been surveyed and OGL recorded the limits of excavation shall be set out to true lines, curves, slopes as per the drawings.
2. Excavation:
The excavation for founding levels of abutments and piers shall be done in two stages. Excavation up to 300 mm above the abutment founding levels shall be done in first stage to keep the founding level for abutments undisturbed, trimming the side slope to 1 horizontal and 1 vertical if required.
Excavation upto the Founding levels of piers shall be done in the second stage, trimming the sides slopes to 1.5 horizontal and 1.0 vertical if required or as per true size.
3. Lean Concrete: Lay out for the structure shall be done. Formwork of the required size and length shall be provided for laying and placing lean concrete over the approved excavated base.
4. Reinforcement Fixing: Rebar’s prepared to the shape and size as per approved bar bending schedule shall be fixed in position and tied using binding wire as per the requirement of the relevant drawings and got inspected. Bar shall be bent cold to the specified approved shape and dimensions using proper bar bender operated by hand or machine. Layers of the reinforcement shall be separated by spacer bars at approximately 1 meter. The maximum size of the spacer bar shall be 20mm or equal to maximum size of rebars or maximum size of aggregate, whichever is greater. Necessary stays cover blocks, metal chairs, spacers, metal hangers, supporting wires etc. shall be provided as per site requirements to fix the reinforcement firmly in its correct position.
5. Design, Erection & Removal of Form work: The design and erection of formwork shall be as per IRC-87 & conforming to MORTH section 1500. Convenient removal of the shutter without disturbing the concrete shall be ensured. Design shall be to facilitate proper and safe access to all parts of formwork.
Staging shall have cross bracing and diagonal bracing in both directions. Staging shall be provided on firm strata.
The inside surface of the forms shall be coated with approved release agent supplied by the reputed manufacturer to prevent adhesion of concrete to formwork. Application shall be strictly as per manufacturer’s instruction and shall not be allowed to come into contact with any reinforcement other embedment.
The formwork shall be removed in such a way that it does not cause damage to the concrete surface. Form work shall be lowered gradually and uniformly to prevent the concrete to take stress due to its own weight uniformly and gradually to avoid any shock or vibration.
6. Mixing, placing and compaction of Concrete:
(a) Concrete mixing:-
Concrete shall be mixed in approved proportions in batching and mixing plant or in a concrete mixer (clause 1708 of MORTH).
(b) Placing and compaction of concrete: –
Concrete shall be placed as near as possible to its final position so that no contamination, segregation, loss of its constituents material take place. It shall not be freely dropped into place from a height exceeding 1.5m. All formwork and reinforcement fixed shall be cleaned and made free from standing water and other unsuitable material, prior to concreting. Concrete shall be deposited in horizontal layers to a compacted depth of not more than 450 mm when internal vibrators are used.
CONSTRUCTION JOINTS: –
Construction joints shall be avoided as far as possible and in no case the location of the joints shall be changed or increased from those shown on drawings except with approval from Engineer. The joints shall be provided in a direction perpendicular to the member axis or as shown on Drawing.
PROTECTION AND CURING OF CONCRETE:-
Exposed surfaces of the concrete shall be kept continuously in a damp or wet condition by ponding or by covering with a layer of sacks, convas, hessian or similar materials and shall be kept constantly wet for a period of 14 days from the date of pouring concrete and as per clauses 1713 of MORT&H.
SAFETY: –
1. During construction of Bridge adequate safety & traffic sign shall be installed adjacent to the road shoulder to protect the ongoing work.
2. Bridge location shall be provided with visible safety & Road signs.
3. The Safety Officer shall make frequent patrols of construction site to ensure that the safety equipment’s and signs are operational at all time.
4. Other safety arrangement shall be as per approved safety manual.
FAQS
What is a minor bridge?
A minor bridge is a smaller structure built to span a gap or obstacle, typically carrying a road or pathway over a stream, drainage channel, or similar feature.
How is a minor bridge different from a major bridge?
Minor bridges are generally smaller in size and have a lower carrying capacity compared to major bridges. They are designed for lighter traffic loads and shorter spans.
What defines a major bridge?
A major bridge is a larger and more significant structure designed to carry heavy traffic loads and span longer distances, often over major water bodies, valleys, or other challenging terrains.
What is the length of a minor bridge?
The length of a minor bridge can vary significantly depending on factors such as the specific site conditions, the width of the obstacle it needs to span, and local design requirements. There isn’t a strict numerical definition for the length of a minor bridge as it can range from a few meters to several tens of meters. In general, minor bridges are smaller in scale compared to major bridges and are designed to handle lighter traffic loads over relatively short spans. The length is determined based on the needs of the particular location and the purpose of the bridge.