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Post-tensioning of box culverts


Pedestrian-cycling underpasses laid fast and easily thanks to the precast Box Culverts


 

COPREM has developed a post-tensioning system for box culverts of all sections that solves in a few hours the problem of crossing roads, highways and railways.

The new market needs require the speed of the intervention with the consequent reduction of environmental impact. These needs have pushed COPREM's technicians towards an innovative solution capable of realizing crossings with pedestrian-cycling tunnels and sewage pipes in a single night of work and interruption of road and rail traffic.



Costruzione condotta idraulica Autostrada A9

zero impact underpass for hydraulic pipeline for A9 highway
 


COPREM system of zero impact underpasses does not want to replace other systems already used, such as microtunnelling. It wants to be an alternative, as there are conditions in which push pipes cannot be used because the distance between the road surface and the structure is minimal - not guaranteeing the stability of the ground in the jacking zone.

The technique of post-tensioning has been used for years in pre-stressed structures, from bridges and buildings to civil construction above and below ground. In our case, post-tensioning has the function of connecting the box culverts together in order to give monolithicity to the structure during the lifting and positioning phase.

COPREM has already tested this technique with more than 300 crossings already in place. All the interventions have proved to have a very low environmental impact as they are generally scheduled at night. They have also created little inconvenience to traffic, proving to be reliable, fast and economically advantageous.

The box culverts for zero-impact underpasses are built with through-holes at the four corners so as to allow connection by special strands with variable section (depending on the needs of the project). The pulling force is calculated according to the lifting conditions of the assembled monolith and to the construction characteristics of the single box culverts, without generating breaks and cracks in the concrete.

 

realizzazione di sottopassi autostradali con scatolari in calcestruzzo post tensionati

Zero-impact underpass for sewer pipeline on A4 freeway​
 

Environmental impact is now an integral part of any project that professionals present to the Public Administration during the tender phase. The emission of pollutants from vehicular traffic is influenced by many factors, involving both the pollution produced by individual vehicles and the overall emission of the traffic flow passing on the road section.

Our system involves open excavation: the speed of laying makes this solution a success in case of roads with heavy traffic volume. The closure of the road is only temporary, for example at night and therefore with limited traffic, and has little environmental impact compared to the construction on site of the structure itself.

We have carried out interventions on freeways even with a weight of 160 tons (involving two cranes specialized in positioning) in the case of a monolith of 32 m formed by sixteen boxes of size 125x200 cm - thickness 25 cm. Another case is the one with a weight of 100 tons with six box culverts measuring 275x300 cm - thickness 25 cm for a total length of 12 m. The anchor sling bar to be positioned in correspondence of the upper slab on each side must be appropriately sized for the lifting of the monolith and is hooked to the box culverts by means of special hooks embedded in the box during production.

realizzazione di sottopassi autostradali con scatolari in calcestruzzo post-tensionati

Laying of the underpass for bicycle and pedestrian underpass on the A9 freeway​
 

There are numerous reports about the value of the post-tensioning technology used by COPREM. "Only about 20 hours compared to a job that otherwise would have involved closing the road for about three weeks," recalled Riccardo Riccardi, Councillor for Roads and Highways of the Friuli Venezia Giulia Region on the occasion of the laying of the bicycle-pedestrian underpass for the workers of Officine Danieli in Udine.


Stages of post-tensioning of concrete box culverts

There are a few special steps involved in the post-tensioning operation:

  1. Placement of the box culverts in a designated area on site
  2. Insertion of strands of a specific diameter at the four corners of the boxes
  3. Positioning of the appropriate drafting machines
  4. tensioning according to project specifications
  5. Placement of the specially sized sling bar


In the case of highway crossings, it may be necessary to divide the intervention into one phase for each roadway. In this case, after the first post-tensioning of the two monoliths carried out separately, a second post-tensioning is necessary to connect the two monoliths previously assembled. This operation is made possible thanks to a second hole at the corners of the box inside which the appropriate strand passes.

In the case of crossings of state and provincial roads without the necessary space to move the large monoliths, COPREM has developed a variant to allow the positioning in the excavation of individual boxes and then perform the operation of tensiong to give monolithicity to the entire structure.

COPREM technicians are always at the available to organizations and professionals to advise from the initial stage the best solution at the lowest possible cost.


Costruzione dell'attraversamento ciclo pedonale ferroviario Induno-Olona

bicycle and pedestrian crossing under the railway in Induno Olona (VA) ​



Costruzione del sottopasso carrabile a Tolentino.

bicycle and pedestrian subway to cross the railway in Tolentino (MC)

 
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