Hamas executed dozens of diggers responsible for its extensive tunnel system  in past weeks, fearing the workers would reveal the site locations to Israel, a  report on the Mako website’s army blog said.
The tunnelers, many of whom constructed the tunnels  over the course of months, would dig for 8-12 hours a day, and received a  monthly wage of $150-$300, according to the blog.
Sources in Gaza told the website that Hamas took a  series of precautions to prevent information from reaching Israel. The terror  organization would reportedly blindfold the excavators en route to the sites and  back, to prevent them from recognizing the locations. The tunnels were strictly  supervised by Hamas members, and civilians were kept far from the sites.
M., a former tunnel digger and Israeli collaborator,  told the website that Hamas would strip search the workers to ensure they had no  recording devices or cameras hidden on them.
“The people we met had their faces covered; no one  knew them by their real names, it was all codes and first names. They didn’t  want to take the risk that some of the diggers were collaborating with Israel,” he said.
A tunnel entrance, within a  civilian home, found by Golani soldiers in the northern Gaza Strip (photo  credit: IDF Spokesperson’s Unit/ Flash 90)
After the tunnels were completed, dozens were  reportedly executed to prevent intelligence leaks to Israel.
“Anyone they suspected might transfer information to  Israel on the tunnels was killed by the military wing,” a different source said. “They were very cruel.”
In 2012, a Journal of Palestine Studies article  claimed 160 Palestinian children were killed while working on Hamas’s tunnel  system.
The digging of tunnels began four years ago and has  demanded 40 percent of Hamas’s budget, The Times of Israel has learned.
Tunnel diggers have been using electric or pneumatic  jackhammers, advancing 4-5 meters a day. The tunnels found were reportedly  mostly dug 18-25 meters (60-82 feet) underground, though one was discovered at a  depth of 35 meters (115 feet).
 “That’s like a 10-story building underground,” one expert said.
Digging requires engineering and geological expertise,  with tunnels usually dug through sandy soil, their roof supported by a more  durable level of clay. As they are dug, the tunnels are reinforced by concrete  panels, manufactured locally in workshops adjacent to each tunnel. These  workshops have also been targeted by the IDF throughout its  military operation.
Elhanan Miller contributed to this  report.