google for "artificial tunnel" engineering. I translate this stuff all the time.

see site below and search for 'artificial tunnel'.
It is the part usually in a box structure made of reinforced concrete which often leads to a natural tunnel, ie, one built into a mountain or under the ground as in a metro line. The artificial tunnel is often a connector from the road to the actual tunnel.

The twin-tube tunnel of Serra Rotonda is part of the macro-lot 3 part 1 of the new route of the A3 contracted to GLF Spa. The site of the tunnel is located in the Basilicata region in proximity to the town of Lauria. The north tube measures 3,725.50 metres, plus a 135,86 metre manmade section at the north portal and a 7.10 metre manmade section at the south portal. The south tube has a total length of 3,740.00 metres plus a 128,65 manmade section at the north portal and a 7.10 metre manmade section at the south portal. - See more at: http://www.indeco.it/en/job-applications/tunneling/1370-a3-h...

La Galleria Serra Rotonda

La galleria a due canne Serra Rotonda fa parte del macro lotto 3 parte 1 del nuovo tracciato dell’A3 realizzato dall’impresa GLF Spa. L’opera si trova nella regione Basilicata in corrispondenza del comune di Lauria. La canna nord ha una lunghezza di 3.725,50 metri, a cui si aggiungono un tratto di 135,86 metri in artificiale al portale nord ed un tratto in artificiale al portale sud di 7,10 metri. La canna sud ha invece una lunghezza complessiva di 3.740 metri a cui si aggiunge un tratto di 128,65 metri in artificiale al portale nord, ed uno di 7,10 metri al portale sud.

- See more at: http://www.indeco.it/it/component/content/article/37-it-it/a...

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Note added at 2 hrs (2015-05-18 20:53:26 GMT)
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Here they talk about: plus sections.
Both breakers and drilling and blasting were employed as they offered more suitable methodology for the conditions on the Serra Rotonda tunnel job site. The twin-tube Serra Rotonda Tunnel is located in Basilicata near the town of Lauria and forms part of the new A3 section contracted to GLF Spa. The north tube measures 3.7255km, plus sections measuring 150m and 7.1m at the north and south portals respectively. The south tube measures a total of 3.74km, plus 146.6m and 7.1m sections at the north portal and south portals respectively. Conventional excavation methods with breakers and blasting were selected due to the geological profile and also because in the south direction both tubes would lead out onto a viaduct under construction, ruling out the option of a TBM.

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Note added at 2 hrs (2015-05-18 20:54:07 GMT)
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http://www.worldhighways.com/categories/road-highway-structu...

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Note added at 3 hrs (2015-05-18 22:18:59 GMT)
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Here they talk about: "artificial tunnel":
https://books.google.co.uk/books?id=UoDvqSd4yp8C&pg=PA493&lp...
https://books.google.it/books?id=X06yp7GohfkC&pg=PA493&lpg=P...

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Note added at 3 hrs (2015-05-18 22:19:52 GMT)
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So, what does "in artificiale" mean after all???