The sleepy idea of constructing a tunnel across the Strait of Gibraltar between Morocco and Spain is being relaunched, according to to 'El Pueblo de Ceuta', a Ceuta publication. As reported, the new management of the SECEGSA (a Spanish committee for promoting the fixed link - The Moroccans have SNED on their turn for the same purpase) have visited the mayor of Tarifa on the Spanish coast.

The fixed link plans across the Strait of Gibraltar are not new. A tunnel had been proposed as early as in 1930 but the enthusiasm died reportedly when a survey concluded that the technology was not there to tunnel under the Mediterranean sea.

As recently as in 2009, a feasibility report has been proposed to EU. And that was it really. Since then, it is a back burner, reminded by events like dthe SECEGSA visit to Tarifa mayor.

Technically, a tunnel across the Strait of Tunnel is considered more complex than that of the Channel tunnel between UK and France. Mainly because of the depth of the sea and the geology of the area -severe earthquake area- and is deemed as less stable than that under the English Channel.  The presence of two deep Quaternary clay channels makes it a difficult place for tunnelling.

If built, the tunnel would be "38,67 kilometers long with 27,75 kilometers under the water, with a maximum depth of 475 meters and a slope of 3%". Over the depth: It would be deeper than any tunnel built so far. The deepest tunnel now is Norway's Ryfylke Tunnel, is 291 meters below sea level. Another one Rogfast,  (under construction) will be deeper than Ryfylke but still would be shallower than the Strait of Gibraltar tunnel: 392 meters.

'El Pueblo de Ceuta' says a study conducted by the University of Zurich in collaboration with Herrenknecht concluded that designing and manufacturing a TBM which could bore the tunnel is feasable.

https://elpueblodeceuta.es/art/53827/secegsa-relanza-el-estudio-del-enlace-entre-espana-y-marruecos-por-un-tunel-en-el-estrecho-de-gibraltar