WALL BUILD TESTS ENGINEERING

Michael D. Engelhardt, professor of structural engineering at the University of Texas at Austin.

Steel is also malleable. Engelhardt said that a small hydraulic arm (similar to the “Jaws of Life” used to pry open a crumpled car) could easily be used to make an opening in such a wall: “The equipment is small (could likely fit in a backpack), inexpensive, widely available and can generate many tons of force.”

“Steel can rust really quickly,” said Curtis Patterson, a structural engineer based in San Diego who visited the prototypes with a team of Times journalists. He pointed to several rust spots that had already appeared on one of the prototypes, less than a month after construction.

But some envision the mixed-material walls as having more technological capabilities. They might be called smart walls: walls that incorporate radar, acoustics and other types of surveillance embedded in the infrastructure. One of the contractors bidding on the wall is ELTA North America, an Israeli defense contractor that specializes in radar and communication equipment.

“My sense is they will select multiple awards for these types of infrastructure,” said Jayson Ahern, a former acting commissioner of Customs and Border Protection who was involved in the construction of a border fence during the George W. Bush administration. “Some will be for technology, some for when they just need a wall.”

Opaque or transparent?

David Aguilar, a former deputy commissioner of Customs and Border Protection, said that with concerns over officer safety, it is critical that border patrol agents have good situational awareness: “It can be done visually or it could be done with technology, but in a high-activity area, it is difficult to discern legal activity versus illegal. In urban areas, you’re going to need that transparency. In terms of attempted intrusion, you want to see people coming toward the border so that they can respond.”

Michael Evangelista-ysasaga, the chief executive of Penna Group, which has contracted with the government before but whose prototype bid was rejected, said: “A see-through border wall allows them to know when they are facing threats on the other side, which Border Patrol has long preferred on their wish list. They didn’t want a solid wall. Going through was never the real threat. The real threat is going over or under.”

‘Big’ and ‘beautiful’?

Trump campaigned on a “big, fat, beautiful wall,” so it’s unsurprising that looks play a role in the border wall guidelines. The official proposal request says that the U.s.-facing side of the wall should be “aesthetically pleasing.”

But standing in front of the prototypes, Patterson winced when he considered the aesthetics of a potential wall. “I don’t know if there’s a way to make these beautiful — unless you get murals painted on them,” he said with a chuckle. “You want something that blends in, that you wouldn’t be offended to look at from your backyard. Some of the steel looks like something you’d find in a prison. The brick facade is more like something you’d see on a freeway.”

The only wall that actually has a brick facade is a prototype from Texas Sterling Construction. But in keeping with the guidelines, the pattern appears only on the U.s.-facing side. What Mexico gets to see is a bare concrete wall lined with barbed wire.

It turns out that barbed wire presents its own problems. Evangelista-ysasaga said that his company often uses razor wire in prisons and that animals routinely get stuck. For humans, hair and clothing could get tangled in it. Having such wire along the border would be “really inhumane,” he said. “You’re going to read about a whole family dead on a Sunday morning. It’s going to be a human rights nightmare in the international world.”

Precast or filled on-site?

The engineers and contractors agree that concrete walls aren’t the most complicated of structures to deal with. For them, the big question is: Do you make walls on-site or precast them?

Lengthy wall segments in very remote regions can make pouring concrete on-site expensive and logistically difficult.

Most experts thought that precasting — making the concrete panels elsewhere and then shipping them to the border — was the most practical choice. “Rather than build from Point A to Point B, the wall route could be divided into segments, say 100 miles apart,” said Daniel Abrams, a professor of structural engineering at the University of Illinois at Urbana-champaign.

Tube or no tube?

Border patrol officials have repeatedly said that they want to construct a wall that would be effectively impossible to scale — that it should be “physically imposing,” measure between 18 and 30 feet high and include “anti-climbing features.”

Many of the contractors added a rounded tube at the top of their prototypes; they believe it will make it far less likely that anyone could reach the top. “It makes it impossible to straddle or use to get a rope ladder across because there is nothing to hook onto,” Deputy Chief Patrol Agent Roy D. Villareal said.

The prototype is also supposed to prevent tunneling at least 6 feet underground. Both rudimentary and sophisticated tunnels, primarily used to bring drugs into the United States, have been a persistent problem in the San Diego area. Border Patrol officials would not provide any details about what the barriers looked like below the surface, saying only that many went “well beyond” the 6-foot minimum.

Up to environmental challenges?

There are several environmental concerns the government must also consider, including water flows, earthquake fault lines and wildlife along the border.

“The hydrologic flows are also critically important, so a solid wall is going to be useless — it cannot be applied and should not be applied in some areas,” Aguilar said.

Patterson, who routinely considers fault lines in the structures he designs in San Diego, said that the lighter the wall is, “the better off it will be during an earthquake.”

During construction of the current 650-mile border fence mandated by the 2006 Secure Fence Act, Ahern said that every mile of the southern border had to be carefully inspected. Officials had to assess potential environmental threats to the wall like monsoons and earthquakes as well as potential threats the wall posed to the environment like wildlife.

“It’s one thing to do a 30-by-30 prototype in California, but it’s a whole different story when you’re in the other 1,900 miles of the border,” he said.

And then there’s the bill

Nearly every expert we spoke to said the cost of a wall could be insurmountable: Congress has not authorized any funding, and Mexican officials have insisted their country will not pay. Cost estimates have varied widely, but an internal report from the Department of Homeland Security pegged it at $21.6 billion.

“It’s not like buying 100 cars, where you have a fixed price,” Ahern said. “There’s an awful lot of wild cards that people won’t actually know about until they get into the field. Clearly that was our experience before. A wall is not a single solution. It is one element of border security.”

There may be no future for any of these walls. And because they sit in a remote industrial section near the border, they are unlikely to become roadside attractions. If nothing else, they stand, for now, as emblems of the administration’s ambitions.