Construction Methodology of Box Culvert

Box Culvert is a reinforced concrete structure used as drainage under the road work. In other words, It is a small structure of less than 6m span between faces of abutments. On the other hand, minor bridge, if the length of the span is greater than 6m.

BC Span

Fig.1 Box Culvert Span

The above figure shows the section span of the culvert.

It is a rigid frame structure and simple in construction. So, It is Suitable for non-perennial streams where scrub depth is not significant but the soil is weak. However, due to the strength of the concrete floor, water direction can be changed when a large amount of water is expected.

The scope of work shall consist of furnishing and providing plain and reinforced concrete placed into a required shape as per drawing.

MACHINERY

  1. Excavator
  2. Generator
  3. Tippers
  4. Concrete Batching Plant
  5. Transit Mixers
  6. Concrete Pump
  7. Plate and needle vibrators
  8. Water tanker
  9. Shuttering Plates
  10. Survey kit etc.,
BC Plan

Fig. 2 – Box Culvert Plan

The above figure shows the general plan of the culvert.

PROCEDURE

Centerline Fixing

Firstly, The place where the culvert exists shall be located and the centre line shall be marked with the help of Total station or electronic theodolite.

The located culvert must be either perpendicular or with some skew to the road alignment according to the direction of the flow. for example, 30 degrees to the road alignment.

Setting Out

Reference points have to fix on both sides of the culvert in both traffic and normal to the direction.

Temporary benchmark shall be located near the culvert. After that, it should be checked regularly w.r.t to the permanent benchmark.

The limits of excavation shall be marked on the original ground to the line and length as per drawing.

Original Ground Levels

The original ground level (hereinafter called the “OGL”) shall be taken on the centerline and either side of the centerline of the culvert location to the required width and length as per the drawing. However, the number of rows to be taken is depending on the width of the culvert.

OGL’s shall be taken throughout the length of the culvert including a flexible apron.

The length of the culvert varies from the culvert to culvert depending on proposed road levels and bed levels of the channels.

BC Section

Fig.3 – Box Culvert Section

Excavation

Most importantly,  before staring of excavation, proper barricading along with reflective marking with cautionary signboards shall be provided.

Dumpers or tippers will help in loading excavated material by removing with help of an excavator. The excavated portion shall be cleaned off if any slush, and it should be dressed properly.

Sand Filling

Fine to coarse sand shall be laid to the required length, width and thickness. However, the sand should be compacted properly with plate vibrators.

Levelling Course

The shuttering shall be thoroughly cleaned, aligned and marked to the required thickness. The transit mixer will transport concrete mix from batching plant to the site. After that, It shall be laid on the wet sand and compacted properly with plate vibrators.

Abutment Footings

Skin reinforcement shall be tied with reference to the centerline of the culvert and shuttering is placed with a proper cover to the skin reinforcement. The gap between the shutters has to fill properly. After that, the Concrete mix shall be laid layer by layer and compacted properly with needle vibrators.

Proper care shall be taken while placing concrete in a skew portion of the second lift to not develop any honeycombs.

Abutment Walls

The alignment of shuttering has to place properly. Further, Additional supports shall be given to skew a portion of abutment walls. Proper cover shall be maintained to the skin reinforcement.

Weep holes shall be provided at an interval of 1m c/c.

After completing all arrangements, concrete mix shall be places layer by layer without disturbing the weep holes with proper compaction by using needle vibrators. Therefore, the same method shall be followed for further lifts.

Construction joints shall be as per clause 1710 of MORT&H specification.

Dirt Wall

While constructing a dirt wall proper slope shall be maintained and top levels shall be fixed. After that, the designed concrete mix shall be laid with proper compaction.

Bed Block

Reinforcement shall be tied and slope should be maintained by providing steps at a uniform distance. Shutter plates shall be arranged properly and marking shall be done to the required depth. After that, the designed concrete mix shall be laid with proper compaction.

Top Slab

By fixing the bottom level of the top slab, bottom shutters of the top slab to be placed on designed vertical posts and gaps between shutters shall be packed carefully.

Care shall be taken while placing the formwork in position to withstand the lateral loads coming onto the top slab.

After fixing the reinforcement in position concrete of specified grade shall be laid to the required thickness with proper vibration. Proper care shall be taken while placing the concrete to not develop any horizontal or vertical joints.

Curing shall be done for 14 days by providing hessian cloth as per clause 1731 of MORT&H specification for foundation and substructure.

Moreover, the Date of casting shall be noted on each lift to monitor the curing.

Wing / Return Wall

The work may be started along with the construction of the vent or individually depending upon the site condition. The same procedure shall be followed for excavation, sand filling and levelling coarse like as vent for both wings and returns to the required line and level.

Approved concrete of specified grades shall be laid for levelling coarse and further lifts. Proper care shall be taken while pouring and vibrating the concrete in the skew portion.

Expansion Joints

Expansion joints of specified thickness shall be maintained in between return/wing wall and abutment walls and also placed at the periphery of the cross-section at the proposed centre line.

Backfilling & Filter Media

Filter media should be laid behind the return/wing walls as per specification. For backfilling selected material should be laid behind the abutment walls to the top of the embankment as per specifications and it should be compacted properly.

Uses

  1. Allows water from upstream to downstream.
  2. Serves as utility tunnels
  3. Serves as escape tunnels and Portals.
  4. Using precast concrete blocks offers a cost-effective solution.
  5. Precast concrete culverts can provide economical storage of stormwater.
  6. maintenance cost is minimum. Therefore, It is mostly used.
  7. The bottom slab of the box culvert reduces pressure on the soil.

In conclusion, A culvert may act as a bridge for traffic to pass on it. most importantly, They are mostly found in a natural flow of water and serves the purpose of a bridge or a current flow controller. As a result, Based on factors like hydraulic, roadway height and other conditions, Culvert will be designed. Above all, this is the general procedure for the construction of a culvert.

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Also Read: What is Formwork (Centering & Shuttering) in construction?

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