I looked up the French fortifications at the Nivelle and the redoubt you mentioned was in a line of four, from west to east being the St Ignace, Signals, Louis XIV, and Madelaine redoubts. The St Ignace redoubt fell first, which compromised the position and signaled the eventual collapse of Clausel's second line. If you have access to Nick Lipscombe's Peninsular Atlas (page 335), the map showing the positions of the four redoubts is excellent and it shows a line of abatis covering the Louis XIV and Madeleins redoubts, but not the Signals redoubt.

Unfortunately, I don't have either a schematic or picture of the redoubts.