Chen Hao stuffed the fuel rods into his pocket and turned to walk towards the lab. He had only taken two steps when Susan rushed out of the tunnel entrance and almost bumped into him.

“Something’s not right inside,” she said.

"What's wrong?" Chen Hao stopped. "Is the drill bit stuck in the rock again?"

“It’s not a machine problem.” Susan gasped for breath. “There are loose rocks falling from above, and one hit my helmet when I walked by just now.”

Chen Hao frowned: "Didn't it occasionally crumble before?"

“This time it’s different.” She shook her head. “There are more cracks, and they’re new. Carl said there are cracks in the sidewalls too.”

Chen Hao didn't say anything, stood there for two seconds, and then walked into the tunnel.

Nana was already inside, holding a scanner, its light scanning back and forth across the rock wall. Karl held up his flashlight, shining it into the passage on the left, the beam stopping on a narrow crevice running from top to bottom.

“Here,” he said, “it wasn’t here yesterday.”

Chen Hao looked closer and saw that the slit was big enough to fit his little finger, and it was wet.

"Leaking?" he asked.

Nana nodded: "The moisture content is 12 percent higher than yesterday. This layer of rock was not solid to begin with, and now it can't withstand the pressure at all."

"Then let's dig slower and be more careful, okay?" Chen Hao stroked his chin. "Anyway, we're using the laser sparingly, so the progress isn't fast to begin with."

“No.” Susan stood behind him. “Didn’t you see what’s above you? When I came in just now, a piece of stone the size of a fingernail fell down and landed right on my shoulder.”

Chen Hao looked up. The top was grayish-black, with several shallow lines crisscrossing it, like a dried-up riverbed.

“If we continue along this route for another 30 meters, we will most likely pass through a cavity.” Nana pulled up the projection map. “The original design did not consider the impact of groundwater, and the support density is insufficient. If we continue to excavate, the risk of collapse exceeds 70%.”

"Seventy percent?" Chen Hao grinned. "That means there's still a 30% chance it won't collapse? Let's take a gamble."

"It's a gamble with lives." Carl put down his flashlight. "Once it collapses, people will be buried inside. They can't be rescued from the outside, and they can't get out from inside."

The air suddenly felt heavy.

Chen Hao looked down at the toes of his shoes, then looked up at the crack. After a few seconds, he took out a fuel rod from his pocket, twirled it in his hand, and then put it back in his pocket.

“Alright,” he said. “Safety first. Otherwise, we’ll spend all that hard digging, only to find we can’t even find a place to collect someone’s body.”

Nana immediately opened the terminal and brought up the new solution interface.

“Three structural options are available,” she said. “The first is to install a steel frame along the entire section, which is the most stable, but there isn’t enough material. The second is to reinforce only certain areas, but the risks cannot be controlled. The third is to change the route, bypassing the high-risk area, and at the same time, to build spaced arches and cross supports, which saves materials and is also safe.”

"How much more will we have to dig if we take a detour?" Chen Hao asked.

"Seventeen meters."

"Seventeen meters?" He widened his eyes. "We can barely advance ten meters now, and you want me to go seventeen more?"

“But you can survive,” Nana said calmly. “The probability of death has been reduced to less than two percent.”

Chen Hao opened his mouth, but couldn't say anything. He turned to look at Karl, who shrugged: "I'll listen to you, but if I were her, I'd choose the one who lives."

“I’ll choose it too,” Susan said.

Chen Hao sighed, "Fine, let's go around in circles. We're not in a rush anyway, right? We even have to rely on burning plant-based fuel to keep going."

Nana began drawing a new blueprint. A curved line slowly took shape on the screen, and a bunch of data popped up next to it.

“The new solution requires 120 angle irons, 300 bolts, and 8 sealing plates,” she said. “Current inventory: 43 angle irons, 107 bolts, and 2 sealing plates.”

"More than halfway done," Chen Hao said with a wry smile. "Are we building a tunnel or an aircraft carrier?"

“If it were an aircraft carrier, we could salvage parts and make do,” Carl said. “But with this thing, you can’t skimp on anything. If even one support frame is missing, the whole section might not be able to hold up.”

"What about composite materials?" Susan suddenly asked. "Can we use waste plastics? There were dozens of bags of them piled up when we cleaned the warehouse last time."

“Yes,” Nana nodded. “After melting, it is injected into a fiber mesh to make a lightweight support plate that can bear up to 60% of the load of a steel frame. It is suitable for non-primary load-bearing areas.”

“Then let’s use it,” Susan said. “I’ll handle it. First, sort the waste and pick out the meltable parts.”

“Drainage also needs to be done,” Carl added. “Since the problem is seepage, we can’t just rely on reinforcement. I’ll dig a shallow ditch around the perimeter to divert the water and reduce erosion of the rock.”

"Let's do it both ways," Chen Hao decided. "You two take charge of these things, get started on what you can do first. Nana, continue working on the blueprints, and I'll see where else we can find some materials."

He emerged from the tunnel; the sun was already setting. The wind whipped sand against his face.

Back in the command tent, he pulled out an old map and spread it on the table. He traced his finger along the southeast direction.

“Here.” He pointed. “An abandoned industrial area. I’ve never been in there before; there might be warehouses.”

Nana walked over and glanced at it: "According to early reconnaissance records, temporary storage units were once deployed in this area, but they were not registered for disposal. There is a 68% probability that there are underground storage rooms."

"Sixty-eight is better than zero," Chen Hao said. "We'll set off tomorrow morning and try our luck."

“I’ll go,” Carl said. “The terrain over there is complicated; it’s not easy for one person to walk there.”

“Count me in.” Susan looked up. “I’ll go too, and see if there are any more usable plant materials.”

“Then you stay here.” Chen Hao pointed at Nana. “The base can’t be left unattended. Besides, you have to keep an eye on the fuel optimization process. If there are any problems with the new process, you’ll have to adjust the parameters.”

Nana nodded: "I can provide route suggestions and structural analysis support remotely."

"Then it's settled." Chen Hao stood up and stretched. "Get a good night's sleep tonight and set off early tomorrow. Hopefully, it won't be a wasted trip, otherwise we'll have to rely on this damn stick to grow legs and come help us."

He tossed and turned on his folding bed at night, unable to sleep. His mind was filled with images of cracks, fuel rods, and red dots on a map.

At four in the morning, he got up and walked to the warehouse in the dark.

Carl was already taking inventory of the equipment. His flashlight beam illuminated a pile of angle iron, bolts, rope, and tool bags.

"You're up so early?" Karl asked without looking up.

"I can't sleep well," Chen Hao said, leaning against the doorframe. "I always feel like some rock is going to fall."

"Once we've established proper support, it won't happen again."

"I hope so." Chen Hao walked in, picked up a piece of angle iron and weighed it in his hand. "It would be great if there were more of these."

“You couldn’t move any more,” Carl laughed. “With your size, if you gained another five pounds, you’d be stuck in the tunnel.”

"Get lost." Chen Hao put the angle iron back. "This is called being well-off, understand? Ancient emperors all looked like this."

“Then order the stones not to collapse.” Karl zipped up his backpack. “For the sake of the emperor.”

After they finished laughing, the atmosphere relaxed a bit.

Just as dawn broke, Susan arrived. She carried a canvas bag containing sampling tools and protective gloves.

Nana checked the communication equipment one last time and sent the exploration route to their handheld terminals.

“Signal coverage is limited,” she said. “Voice calls may drop beyond two kilometers. We recommend manually sending your location every half hour.”

"Roger that." Karl slung his large bag over his shoulder. "Let's go."

The three walked out of the base gate and headed southeast.

Chen Hao glanced back at the tunnel entrance. Piles of waste plastic bags, brought back the previous night, were at the entrance; Susan hadn't even started processing the materials she planned to use for the support panels.

He felt in his pocket; the fuel rods were still there.

After walking for a while, Karl suddenly stopped.

“Wait a minute,” he said. “I remember there was an old substation over there, and there seemed to be a maintenance manhole cover next to it. If it wasn’t buried, there might be cable trays underneath, and we could take some metal strips from them.”

"Why didn't you say so sooner?" Chen Hao glared at him.

“I just remembered,” Carl said, scratching his head. “I only recognized it when I passed by.”

"Then what are we waiting for?" Susan had already turned to the side of the road. "Let's go take a look."

They turned a corner and headed towards a section of collapsed wall.

Behind the wall, a green tin box, rusted black, was half-hidden. Next to it, a crack in the ground revealed a corner of a concrete manhole cover.

Carl crouched down and used his hands to remove the loose soil.

“It’s true,” he said. “It’s not completely sealed off.”

He took a crowbar out of his bag and inserted it into the gap.

Press down hard.

The manhole cover is loose.