The crack in the Gotthard Road Tunnel that appeared on Sunday - leading to its closure - has been confirmed as caused by "redistribution of tension" within the rock above the structure.
Bern ruled out any reason linked to the ageing of the tunnel.
Part of the false ceiling had already suffered similar damage in 1985 - just five years after the tunnel opened.
Swiss Transport Minister Albert Rösti expects the tunnel to be open again by the end of the week at the latest.
Heat to stay for now
The heatwave alert has been extended until Thursday, with temperatures set to climb as high as 37 degrees in some areas.
Growing anger over World Cup red card
The Swiss team's manager, Murat Yakin has called Breel Embolo's red card 'unacceptable', as anger builds over the refereeing of Switzerland's World Cup quarter-final loss to Argentina.
Fire damages trees in the Jardin Anglais
A fire tore through part of Geneva's Jardin Anglais on Saturday morning, gutting several trees and damaging a lakeside building used by the Mouettes ferry service.
Cows sweltering in the heat
The heat is now hitting the country's dairy herds, with cows producing less milk as they burn extra energy to stay cool.
Lake Geneva nudists fight for their lake section
A hidden stretch of Lake Geneva shoreline has become the focus of a long-running battle over public nudity.
Holiday makers seek more than the sun
Nearly half of Swiss holidaymakers are choosing to learn a new skill on their summer break rather than simply lie on a beach.
