Tunnel „T16“ precut protection- Construction of New Railway Section Kriva Palanka – Border with Republic of Bulgaria | Macedonia |
Precut protection for the tunnel
A challenging project we worked in the last couple of months is the precut protection for the tunnel „T16“ on the New Railway Section Kriva Palanka – Border with the Republic of Bulgaria, as Part of Corridor VIII.
A interesting fact about corridor VIII is that it’s crossing the Republic of Macedonia at a length of 309 km starting from Lin (border with the Republic of Albania) and ending at Deve Bair (border with the Republic of Bulgaria) and it is one of the ten trans – European corridors connecting the Adriatic and the Black sea.
This project of the new railway line between Kriva Palanka and the Bulgarian Border will enable the construction of an electrified single-track railway line for a nominal speed of 100km/h.
Section 3, involves 23.4 km of open track and it includes one station at Kriva Palanka and one-halt in Zidilovo. Along with section 3, there are 24 tunnels in a total length of about 9 km and 52 viaducts with a total length of about 5 km.
Our task included main foundation design of 19 objects (viaducts, bridges), foundation designs for railway station buildings Zidilivo and Kriva Palanka, protection design for tunnel precuts (5 tunnels).
As a basis for designs the extensive geotechnical investigation works were performed (Engineering-geological and hydrogeological mapping of the terrain, Schmidt hammer rebound value test, Investigation boreholes, Trial pits, Geophysical survey…) in order to define geotechnical units.
A Seventeen high vertical cut, from the level of the railway line to the existing terrain, needed to be protected.
The object is located in a seismic zone with a maximum earthquake intensity of VIII degrees, which is an important factor for the aseismic design of structures. Based on this, the excavation protection was designed to a horizontal peak ground acceleration of 0.25 g (gravity)
Challenges:
– Significant soil thickness (up to about 9.0 m from the surface of the existing terrain)
– Renovation required ensurement of the stability of the existing road to nearby houses
Decision:
– tunnel precut protection will be ensured by pile wall (diameter D = 800 mm with a spacing 1,20 m), installation of rock bolt of 9,0, 12,0 and 15 meters length with 2 x 5 cm thick shotcrete and drain tubes of 2,0 meters length
Pile wall analyses were performed using GEO5 – Sheeting Check software that enabled us to coordinate and solve this geotechnical challenge
