Lately I have been Studying The Book of Tiana for my age. Here is the information that is relevant to the Excavators, (diggers)
The Excavators are described in The Book of Tiana as being snake-like in appearance, with large, brutal-looking drill bits on the front. They are a long, segmented craft, self-contained and able to withstand massive collapses within the rock around them. At the head of the craft is the Guild Master's cabin and the chart room. Moving back from that point, one would come across the equipment room, the crew quarters, the refectory (kitchen/dining), the bathing quarters, the sample storage room, and finally the research room, which was located in the tail of the craft. Everything in all of the rooms in the craft was locked and secured, in the event of a sudden shift or jolt.
Two of these machines were used to carve the D'ni Path from the Southern Gate toward the Surface during the expedition to make contact with the people of Earth. This was not the first time these machines had been used; they were used for thousands of years prior for the excavation of new tunnels and caverns for habitation and mining.
During excavation, the two craft worked in shifts, one performing the actual digging and the other acting as a shelter to the rest of the crew. The excavator that was involved in the digging would be positioned in front of the rock it was supposed to channel through, with the other out of the way of most of the flying debris. Only when everything was in place did the digger begin its work, boring straight into the rock, lashing the sides of the tunnel it made with the tail of the craft, making it easier to remove the remaining material once the Nara casing of the tunnel had been put into place.
One of the four great D'ni Digging Machines, originally built in 6430 DE for the broadening of the Rudenna Passage, along with its contemporary, Rock-Biter. Together, they finished off the walls of the Shaft excavated by Grinder and Old Stone Tooth, then cut the steps that would spiral up the shaft itself. At the time of that excavation, it was 3,000 years old.
One of the four great D'ni Digging Machines. Its age is undocumented, unlike its three older siblings, but it was present at the opening of the Tijali Mines, 1800 years prior to the excavation of the Shaft. Grinder is not only the youngest, but also the largest and loudest of the four diggers, built especially for the opening of new mines. Together with Old Stone Tooth, it drilled straight up toward the surface, digging out the bulk of the Great Shaft.
Old Stone Tooth
Stone Tooth was the oldest of the four remaining great D'ni Digging Machines, and built to eventually replace Stone Eater in 5359 DE. It was used in numerous projects, including the construction of the Uran District, an unfinished tunnel between the City and Ae'Gura, and the Great Shaft. At the time of the excavation of the Great Shaft, it was 4,000 years old. With the help of Grinder - another digger - Old Stone Tooth was responsible for the primary excavation of the Great Shaft. The machine itself was described as being almost mantis-like in its appearance, and was obviously very noisy when in operation.
One of the four great D'ni Digging Machines, this one built for the broadening of the Rudenna Passage. At the time of the excavation of the Great Shaft, it was 3,000 years old. Together with its companion digger, Burrower, Rock-Biter was responsible for finishing the excavations of the Shaft by smoothing out the walls and cutting the steps that would spiral around the edge.
Nara is the hardest of all D'ni stones. It was created in 5307 DE by the Guilds of Miners and Stone Masons in a joint development project. It requires the use of fusion-compounding technology, which was invented in 4826 DE by a member of the Guild of Stone Masons accepted under the policies of King Demath, who required all Guilds to admit a certain percentage of qualified students even if they were unable to afford the cost of attendance.
Nara is described in The Book of Tiana as being dark gray-green in color, and 200 times as dense as the rock from which it is forged. The DRC research journal on King Me'emen, however, presents a slightly more specific description of the material, which is also slightly different. It is described by the DRC as being a metallic gray stone, with thirty times the density of steel.
Although Nara is widely considered by the D'ni to be indestructible (as such, it was often used for such purposes as locks, shoring up tunnels, etc.). However, it is not without its flaws. Sirrus, in his bid to escape his prison, discovered a sonic frequency which would disrupt the material on a molecular level, causing it to shatter like glass. In this way, he was able to destroy the Linking Cell in Haven protecting the link back to Tomahna and earn his escape.