When they reached the rock layer, Lu Yuan reached out and touched it. His hand touched a patch of water that was somewhat cold.
Lu Yuan knew that this was probably due to water seepage, which had caused the rock layer to become saturated with water.
Then Lu Yuan had Qiao Ke move the rope continuously toward the cut-off rock layer.
Upon arriving, Lu Yuan first shone a flashlight around the area, finding no gaps that the termites could easily burrow into.
However, Lu Yuan then discovered a place that looked different from the other rock layers.
The area was slightly whitish in color. Wearing protective gloves, Lu Yuan reached out and gently touched it, discovering that it was actually quite soft.
"Hmm? Soft? It looks like some protective material that the termites just secreted!"
Lu Yuan reached out and picked off a piece of the secretion, put it to his nose and smelled it. Immediately, a pungent smell came over him.
"Sour smell! It seems this stuff must be termite secretions!"
Then Lu Yuan put the collected sample into a box, and took out a stethoscope from his backpack and put it on.
With the side of the receiver pressed tightly against the rock layer, Lu Yuan listened quietly to the sounds coming from inside.
Because the rock layer was so thick, Lu Yuan couldn't hear any sounds coming from inside.
However, Lu Yuan had a feeling that the top should be hollow, so he asked Qiao Ke below, "How do you determine if the rock layer is hollow? Is there any good way?"
The other person thought for a moment and then said, "Listen with your stethoscope, then gently tap the rock layer with a hammer and see if there's an echo! If there's an echo, it means it's hollow inside; if there's no echo, it means it's solid!"
"Okay! I understand!"
So Lu Yuan took out a hammer from behind his back and gently tapped on the rock layer.
Immediately afterwards, an echo came from inside.
"Sure enough! It's hollow inside!"
Then, Lu Yuan guided the other party to move their position continuously. After probing several places, Lu Yuan would mark each place with spray paint after each probing.
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