The drill bit was stuck two meters deep, as if it were being held firmly by something. Chen Hao and Karl each stood on one side, stepping on the support frame, and pulled upwards with all their might. The machine emitted a screeching sound, and sparks flew from the wires. Nana immediately cut off the power.
"Let's try again," Chen Hao said, panting. "I was almost at the bottom just now."
Susan squatted to the side, holding the black fibers she had just pulled from the soil. The sunlight shone on them, reflecting a dull light. She didn't speak, but simply put the sample into a sealed bag, then took a fresh clod of soil and rubbed it in her palm.
“The moisture level is still rising,” she said. “It’s 10 percent higher than it was an hour ago.”
Nana activated the ground-penetrating radar, expanding the scanning range to ten meters. A blurry, net-like structure appeared on the screen, resembling tree roots or a torn spider web, extending towards the main foundation of the wall.
“The cavities are connected,” she reported. “The deepest point is 4.1 meters, and the horizontal span exceeds 5 meters. Water seepage is rapidly expanding the internal space.”
Chen Hao stared at the screen for a long time before finally speaking: "So, what we're standing on isn't a piece of land, but an empty shell?"
“Currently, only the top 1.8 meters of clay remains as the supporting layer,” Nana said. “If no intervention is taken, a regional collapse will occur within seven days.”
Karl released the drill rig support and wiped his face: "Then what happened to the piles we drove before? Were they just stuck in tofu?"
No one laughed.
Chen Hao bent down, picked up a piece of gravel, and threw it into the crack. Several seconds passed before a dull thud was heard after the stone landed.
"This is a pretty deep hole." He looked up at Nana. "Does your team have any records of handling similar situations?"
Nana's eyelight flashed: "There are thirty-seven similar cases. Thirty of them used reinforced concrete backfilling, five used grouting reinforcement, and two chose to relocate the entire building."
“We can’t do the first two,” Susan chimed in. “We don’t have steel bars, cement pumps, or transportation equipment. The third… relocating the wall? We can’t even stand on our own two feet right now, let alone move a wall?”
"Then we'll just have to make do." Chen Hao patted the drill's casing. "Let's seal it with quick-drying cement for a few days and see how it goes."
“No.” Nana shook her head. “The existing material has a compressive strength of less than 3.5 MPa, while the load-bearing capacity of this area is required to be at least 6.2 MPa. Forcing it in will cause pressure concentration and will actually accelerate the breakage.”
So you're saying that filling it out is pointless?
"yes."
The scene quieted down. The wind blew from the north, stirring the scattered plastic sheets on the ground. A thin crack appeared at the edge of the fissure, and soil slowly slid down.
Carl suddenly asked, "Could it be that someone built something under here before?"
Susan held up the sealed bag: "This woven netting isn't a natural product. It's an engineering protective material used to prevent soil slippage. This indicates that foundation treatment was done here."
"So that means," Chen Hao slowly straightened up, "that someone dug it up, built on it, then it collapsed, and then nobody cared about it, and it just rotted here?"
“It’s highly likely.” Nana pulled up the database map. “Based on the degree of soil erosion, the underground structure was damaged in about three to five years. This doesn’t match the current construction cycle of the base.”
“You mean,” Carl continued, “that it wasn’t us who created it, but a pit left by someone before us?”
“To be precise,” Nana added, “it’s land that we’re currently using that was previously used for other engineering projects, and the cleanup efforts haven’t been completed.”
Chen Hao chuckled: "Goodness, we got a piece of land for free, but it turns out there are landmines buried underneath."
Susan frowned: "What's more troublesome is that the direction of the water flow is unknown. If the water source is external, such as an underground water vein or a leaking drainage pipe, simply sealing the surface won't work. The source must be cut off."
“But we don’t even know where the water came from,” Karl said, shrugging. “We can’t exactly turn the whole base upside down, can we?”
“We don’t need to turn everything over,” Nana said. “I can simulate the seepage path to narrow down the search area. But we need more borehole data to support this.”
"Drilling?" Chen Hao looked at the smoking drilling machine. "How many more runs can this broken machine last?"
"We'll drill two more holes at most," Carl said, checking the battery. "Provided the intervals are long enough, otherwise the motor will be ruined."
“Then let’s start drilling.” Chen Hao grabbed his toolbox. “The third hole will be offset by 1.5 meters as originally planned, and the fourth hole will be placed directly below the main fissure. We’ll dig as deep as we can.”
Susan recorded the coordinates. Nana recalibrated the sensor and secured the receiver to the bracket. Carl tightened the drill bit connection and applied a mixture of machine oil and fine sand.
The drilling rig was restarted.
Buzz—
The machine vibrated, and soil was stirred up. The first ten centimeters went smoothly, but the resistance increased after fifty centimeters. At one and a half meters, the drill bit started to wobble noticeably.
“Something’s not right.” Carl steadied himself on the fuselage. “The bottom isn’t level.”
Chen Hao leaned closer to look at the display screen: "The angle is off by seven degrees, adjust it quickly."
Susan gestured for the machine to stop: "Wait, the soil sample has changed color."
She used a small spoon to pick out a dark gray clump of mud, which contained more black fibers arranged neatly, like some kind of grid structure.
“This isn’t just a few scattered remnants,” she said. “It’s a large, laid-out anti-collapse layer, and…” she paused, “it’s been torn apart.”
Nana took the sample, and the camera quickly scanned it: "The fiber fracture surface is in a tensile state, indicating that the force direction is vertically downward. It is speculated that a large weight was subjected to above, causing the protective layer to break."
"So it collapsed under the weight?" Carl asked.
"It's more likely that it will leak first, then soften, and finally fail to bear the weight," Susan said. "Like a piece of cardboard that's been soaked and rotten, no matter how strong it is, it's useless."
The drilling rig continued to descend. At 1.8 meters, the resistance dropped sharply.
"It's empty," Chen Hao shouted.
The drill bit suddenly accelerated downwards, almost slipping from his grasp. He quickly shut it off and pulled out the drill rod. The end was covered in wet mud, with a small piece of broken black wire still attached.
Nana immediately initiated a radar rescan. After the image was updated, everyone's expression changed.
“The cavity is not just one layer,” she said. “It has now been confirmed that there are two layers of cavities, separated by collapsed soil. The upper layer has connected to surface cracks, and the lower layer is still expanding.”
"What about depth?" Chen Hao asked.
"4.3 meters. Close to the main foundation bearing layer of the wall."
"Damn it!" Chen Hao slammed his fist on the support frame. "Our walls are practically hollow from sitting on them!"
“Yes.” Nana nodded. “If a through collapse occurs, the entire 30-meter section of the north wall will tilt and cannot be repaired.”
Susan opened her notebook: "All the existing cement, metal piles, and tarpaulins combined aren't even enough for temporary support. We lack materials, equipment, and technology. Conventional methods won't work."
“Then that’s unconventional.” Chen Hao wiped his sweat. “You said there’s an alternative, tell me now.”
Nana's eyes flickered slightly: "Option 1: Use volcanic ash to react with alkaline substances to produce a concrete-like substance. We need to find natural alkali mines or industrial waste alkali, but there are no records locally."
"Next."
"Option 2: Reinforcement with wooden stakes and bamboo mesh. This option relies on a large amount of resilient plant materials, but the area has low vegetation coverage and no suitable resources."
"Next."
"Option 3: Segmented grouting. Waste plastic is melted and injected into the cavities, then cooled to form a sealed shell. The required materials can be recycled on-site, and high temperatures can be achieved using solar thermal energy."
“Plastic?” Carl frowned. “Isn’t it poisonous when it burns?”
“Keeping the temperature below 180 degrees Celsius can prevent the decomposition of harmful gases,” Nana said. “Under these conditions, polyethylene and polypropylene only soften and do not burn.”
“But we need to build a melting chamber,” Susan added. “It needs to be sealed, heat-resistant, and able to transport liquid plastic underground.”
“It can be done.” Chen Hao looked toward the warehouse. “Kitchen waste bins, old ventilation pipes, broken solar panel frames—take them all apart and weld a furnace.”
“Welding requires a protective gas atmosphere,” Carl cautioned. “We don’t have argon.”
“Then let’s use the old-fashioned method,” Chen Hao said. “Double layers of sheet metal, with asbestos insulation in the middle, charcoal for heating at the bottom, and a lid on top to control the temperature. It doesn’t have to be fancy, as long as it works.”
“The challenge is the transport,” Susan said. “How do you get the molten plastic into a four-meter-deep hole? By tilting it? It would cool down too quickly.”
"Use high-pressure air to push it," Chen Hao gestured. "Connect a tube, put one end into the hole, and pump air into the other end. As soon as the plastic goes in, it will be blown into place."
“It’s theoretically feasible,” Nana analyzed. “But we need to ensure the pipes are sealed and the grouting ports are distributed reasonably to avoid local accumulation.”
"Then let's start by drilling holes and laying pipes," Chen Hao decided. "Starting today, construction on the perimeter wall will be suspended. All manpower and resources should be prioritized to address potential foundation hazards."
“Are you sure?” Carl looked at him. “Once we stop, the alert system can’t be installed.”
“I know.” Chen Hao looked down at the crack. “If we don’t repair the ground now, we won’t even have a place to stand in the future.”
Susan put away her notebook: "I suggest we do a small-scale test first. Select a minor cavity, inject a small amount of melted plastic, and observe for three days to see if it is effectively sealed."
“Okay.” Chen Hao nodded. “Let’s try one hole first. If it succeeds, we can roll it out across the board. If it fails…” He smiled, “At worst, I can just go back to laying bricks.”
Carl began dismantling the drill rig support. Nana accessed the database and compiled a list of required materials. Susan took the samples to the lab tent, preparing for further analysis of the fiber composition.
Chen Hao stood at the edge of the crack, holding a piece of black woven netting in his hand. Sunlight shone on it, making the edges brittle, like paper that had been soaked for a long time.
He suddenly squatted down and put his hand into a small hole on the side of the crack. His fingertips touched something hard.
Upon pulling it out, it turned out to be a rusty metal plate with a broken plastic pipe pressing down on it.
There were a few blurry characters on the sign, covered by mud.
He wiped it with his sleeve.
Three crooked scratches are visible:
"Dangerous Zone"
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