vous ne donnez aucun contexte... Et vous posez deux questions distinctes . Il serait tonnat que "heading" signifie la même chose dans les deux cas

Excavation de tunnels? "Heading machine" c'est un tunnelier
"Heading" avec "sloping hole", c'est plutôt une galerie pilote pour forage d'un tunnel

"Tunnel-Technology - Mining and Blasting
http://miningandblasting.files.wordpress.com/2009/09/tunnel-...‎
"Tunnel Construction: Soft Ground and Hard Rock
Workers generally use two basic techniques to advance a tunnel. In the full-face method,
they excavate the entire diameter of the tunnel at the same time. This is most suitabletunnels passing through strong ground or for building smaller tunnels. The second
technique is the top-heading-and-bench method. In this technique, workers dig a smaller
tunnel known as a heading. Once the top heading has advanced some distance intofor
the rock, workers begin excavating immediately below the floor of the top heading; this isbench. One advantage of the top-heading-and-bench method is that engineers can use the heading tunnel to gauge the stability of the rock before moving forward with the project."


"TUNNELLING MACHINES
www.tehnoplaza.ru/http://.../Tunnelling, Mining and Special...‎
Tunnelling, Mining and Special Machines ... The tunnel heading machines by TEREX|Schaeff-ITC are .... Especially the heading with tunnel shields often re-."

"The continuous measurement of the position of the tunnel heading machine by a total station guarantees accurate drilling.

La mesure continue de la position du tunnelier par un tachéomètre garantit un percement précis."
http://leica-geosystems.com