North Tube of Nazzano Tunnel is WidenedThe widening of the Nazzano northbound tunnel on the Orte-Fiano Romano section of highway A1 Milan-Naples, a few kilometres north of Rome, ended on 17th November, 2005. The opening of the third lane was celebrated on 7th December, 2005 in the presence of minister for infrastructure and transport Pietro Lunardi, officials from ANAS, the public road administration, Autostrade per l'Italia, the concessionaire, and the companies involved in the project. The widening works have been achieved for the first time in the world without closing the tunnel to traffic thanks to the utilisation of an innovative, special technology.The expanded tunnel carries three lanes per direction, emergency lanes and pavements. The method employed for widening the cross section made it possible to continue operation of the tunnel throughout all the widening works, thereby enabling a daily traffic over 60,000 vehicles, whereof 15,000 trucks and coaches. Since the first days of January, technicians and workers have started work for the third lane in the second southbound tunnel. The second tunnel will also remain open while widening works are under way. Visit www.autostrade.itThe widening of the tunnel was planned by Milan-based Rocksoil, who designed and developed the innovative technology used at Nazzano. Visit www.rocksoil.com/tec_costruzione_allargamento.html. A JV formed by COSSI Costruzioni and Pacchiosi Drill won a EUR37.5 million contract and the works have been done completely by COSSI Costruzioni. Work supervision has been awarded to Stone SpA. The widening works and construction of the third lane in the first tunnel started on 25th July, 2002 and had a real duration of nearly 34 months, working 24 hours seven days a week. Visit www.cossi.comThe Nazzano tunnel is formed by two 337 m-long tubes (one per direction). It is therefore a short tunnel but it requires massive investment to improve safety. The tunnel crosses a hilly section of the highway at a pass. It is a bottleneck that obliged technicians to widen the two dual-lane roadways and expand each section to 14.6 m to carry three lanes and an emergency lane, so as to increase traffic capacity. The dual carriageway prior to the widening was as follows: four 3.75 m-wide lanes; two 3.5 m-wide inner lanes (or two 2.5 m shoulders); and central reservation ranging from 3 to 15 metres at the portals. After widening, the dual carriageway will carry four 3.75 m lanes; two 3.5 m lanes; two 3 m emergency lanes; and a central reservation with variable width (minimum 2.3 m). Each of the two carriageways will therefore be 11 m in width (3.5 m for the outer passing lane, 3.75 m for the central lane and 3.75 m for the slow lane) separated by a minimum central reservation of 2.3 m, adjacent to a 3 m lane dedicated to emergencies.The innovative technology used for the widening works of the tunnel has been invented by Prof. Pietro Lunardi, while the patent is the ownership of Gruppo Autostrade. The expansion of the section had to be achieved without traffic interruption whilst performing the works, without using temporary linings and without having recourse to a diversion, even temporary. The widening of the Nazzano tunnel without interrupting traffic is characterised mainly by the placement of a final lining formed by prefabricated segments, of various transversal dimensions and one metre of length, placed using the so-called 'active vault' at very short distance from the widened face, thus permitting to excavate, support and line definitively the widened tunnel. The employment of passive reinforcement techniques is therefore avoided, such as shotcreting and steel arches.The soil in the area crossed by the Nazzano tunnel belongs to the Plio-Pleistocene marine series. The ground is characterised in majority by thin sediments and granulometry, but the material tends to coarsen upward. The lithology is composed of sands with slight to moderate alluvium content alternating with slightly sandy to clayey alluvium, rare intercalated silty clay and sometimes lenses and/or paleo-canals of gravels, more or less important in fine sandy matrix.The enlargement of the Nazzano tunnel represents the most complex part of the highway upgrading on the 40 km Orte-Fiano Romano section. The precutting technology already exists for tunnelling of new tunnels still not in operation. Working with traffic kept flowing in the tunnel has been possible with a steel protection shell placed inside the profile to then cut slots into the face using the mechanical precutting method and subsequently support with concrete to form a shell above the old tunnel crown. Then the ground is excavated to expand the existing cross section up to the new concrete shell and finally reinforced-concrete prefabricated segments are erected, which shape the new widened roof and walls of the tunnel. 6,327 segments have been placed in the Nazzano tunnel, representing a total weight of more than 30,000 tonnes.The arched steel structure is both equipped with the precutting equipment and, in the upper part, the erector that places the final lining of prefabricated concrete segments. All the machinery used to perform the work is operated and moves above or behind the protection shell.The technology originates in the construction of 21.5 m-wide x 16 m-high Baldi degli Ubaldi station on Line A of the Rome metro. First of all, a 60 m-long steel traffic protection shell has been installed inside the tunnel. The steel protection shell moves as driving the widening face progresses. The construction method is implemented in three main stages detailed hereafter.Stage 1 consists in using the precutting method. This is a cutting blade looking like a giant chain saw blade, mounted on a arched steel structure and moving on a slide to cut the ground along the contour of the widened cross section. Fibre-reinforced shotcrete is then poured into the 35 cm-thick 5.5 m-deep cut. This shapes a shotcreted vault.During Stage 2, the ground beneath the just shaped vault is excavated and the old lining is demolished in steps of 600 mm to 1.5 m. The worksite operates two Cat 320 B excavators equipped with rotary cutters working from the sidewalls on either side of the steel protection. Two Cat wheeled loaders 966F and 950E are used for mucking-out. Visit www.cat.comStage 3 is the placement of the reinforced-concrete prefabricated segmental lining, at about 5 m from the working face, to form the new roof and walls of the expanded tunnel. To make the vault self-supporting, two flat jacks apply a compressive strength in the key segment to ensure a perfect bonding between the vault and the extrados and prevent any deformation in the surrounding ground. More info on the project and pictures of the worksite here.Slow setting epoxy resin is applied on the upper and lower ends of the segments and on the edge to be placed in contact with the segments of the previous ring. The segment erector places first the lower segments and then the upper ones until the arch is completed with the key segment at the roof. Then, mortar is injected behind the segments to fill the voids. The pressure jack in the key segment is then activated to bring the segments into firm contact with each other and immediately produce the confinement pressure required on the ground around the tunnel according to the active vault principle.The foundation structure or invert can be built either by simply joining the lining of the new widened tunnel to the invert of the old tunnel or a brand new invert is cast. Read E-News Weekly 46/2002.Not only the new technology designed by Gruppo Autostrade will be used at Nazzano but also to widen another tunnel on highway A14 near Porto San Giorgio. 03/06.