The box culvert construction
The type of culvert selection mainly depend on the site condition, where excavation of the existing structure have to consider. The width of the box culvert is smaller than the pipe culvert, prefer for box culvert. The box culvert can be constructed easily. The box culvert components identification are indicated below; Culvert base, Vertical walls, Deck Head walls or wing wall (Act as support to the box culvert - which are attached to the end of the culvert to reduce the erosion and inhibit seepage and aesthetic improvement). Culvert with head wall or wing wall type support selection for the site depends on the soil condition. Muddy soil which it is saturated with water, where commonly used the head wall type culvert. Haunch bar is to prevent the shear crack at the corner in the top and bottom of the vertical wall area, as shear force is maximum at the corners of the box culvert.
Site Investigation
A site investigation must be carried out at each proposed culvert site. The extent and complexity of the investigation will depend on the size, importance and cost of the proposed culvert, site conditions, the height of the embankment and the loading that will be imposed on the foundation material and on the culvert itself. Survey information should be sufficient to permit the culvert to be located in plan and profile, and should include relevant physical features.
Procedure for the box culvert construction.
After finishing excavation, the setting out works for the screened area have to do and screed was concreted with approved specific grade concrete (Normally G15 using at the assigned site). For an example; in chain age, G15 with 75 mm thick scree ding. Where screed gives a smooth surface and act as an impervious layer for the base of the culvert. Reinforcement works have to carry out by referring the approved drawings and at the bottom corner of cell box area, haunch bars and form works need to carry out before concreting and level checking by using levelling instrument and base concreting with G30 grade concrete. Before concreting, concrete area need to clean with water to remove the mud and dirties. After concrete hardened (Normally in a hot climate area road site, 15- 18 hours), form works are allowed to remove and curing have to provide. Like that, vertical walls have to construct and deck have to construct by referring to approved drawing at the top corner of cell box area, haunch bars need to provide. If head wall support culvert, after that head wall's 1st, 2nd and 3rd steps (number of steps varying in every design) were concreted with Grade 20 concrete and weep holes were provided according to the design. Finally, the parapet wall and guard stone were concreted.
Consideration
Jack supports need to provide for the form work to reject the loosest of the form work when concreting. There, Jack should provide for the joining of two boards. Curing is important after concrete hardened. 50D lapping and 50 mm cover are used in the site. Minimum 7 days curing was provided for the deck of the culvert to harden, and traffic was not allowed 28 days.
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