TUNNELS - Railway M11 Saronno-Malpensa
Detailed design concerns portion extracted from final design of T2 line between progressive km 30+726.37 and km 32+635.79, located in Castellanza municipality, Varese province. Design consists in two blind hole tunnels and eight wells. Blind hole tunnels are made up of two separate archways, an odd track of 1853.09 meters and an even track of 1853.09 m. Blind-hole galleries are made up of two separate arch. Odd track is lenght 1853.09 m and even track 1853.09 m. Cross section is circular type with external diameter of 8 m. Contractual documents and company foresaw EPB tunnelling system, but during integrative geognostic investigations of executive project this system was not judged suitable, as demonstrated by the detailed report on the choice of the mechanized excavation methodology drawn up by SGAI S.r.l.. SGAI S.r.l.proposed design that allowed use of EPB machine, solving criticalities through preconsolidation cap with cement based mixtures injections and a filling partial of the excavation chamber. Executive design was made on this choice. Main problem was low coverage in the passage below Olona river that required particular calculations and solutions, for tunnel and for stability of upper two bridges. This problem was resolved with jet injections grouting. Further interference was found with retaining works in "Via Italia". Finally, construction of eight wells. Two of which are located at tunnel extremity, constitute access to tunnels under construction and when work is completed are ventilation chambers, emergency exits and VVF entrances. Six wells intermediate have similar functions, important works dimensions, excavated to a depth of about 25-30 m.