The IDF reports that it has destroyed some 80% of tunnels within the Philadelphi Corridor and that it can destroy the remaining 20%, if given the order from the government, within three weeks, according to Army Radio reporter Doron Kadosh.
As to the question of why tunnels running from Gaza to Egypt were all found to be sealed, Kadosh said the IDF believes that the tunnels were sealed by Hamas or by Egypt during or before the war.
The army believes the tunnels primarily served as a means for Hamas to build up an independent military industry inside the Gaza Strip during the tenure of Egyptian President Mohammas Morsi, who was a member of the Muslim Brotherhood, which is close in ideology to Hamas.
Once that phase was completed, Hamas relied primarily on the raw materials brought in through the Gaza border to create its current arsenal, which is spread out over dozens and even hundreds of locations throughout the Gaza Strip, both above and below ground.