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With Wednesday's signing of an executive order to channel federal funds to build a wall on the US-Mexico border, what started out as a highly controversial campaign promise of President Donald Trump is now on its way to become a reality.
Throughout his campaign, Trump pledged that on day one of his administration, he would "build an impenetrable, physical, tall, powerful, beautiful, southern border wall," and that Mexico would pay for the wall.
Trump has repeatedly said there are several ways to force Mexico to finance the wall, including measures such as imposing fees on the many billions of dollars in remittances that Mexican migrants in the US send home to their relatives in Mexico, cancelling visas for Mexican nationals and increasing visa fees.
White House spokespeople said on Thursday that Trump was considering to establish a 20% sales tax on imports from Mexico to fund the wall's construction. The announcement was met with an uproar from the Mexican authorities, but also from US lawmakers from both sides of the aisle. Mexican foreign minister Luis Videgaray reacted to the announcement by saying the proposed tax would ultimately hurt US consumers.
Although it is still unknown if the Trump administration will find a way to persuade Mexico to cover the expenses of building the wall, the administration is determined to start construction as soon as possible even if it means that US taxpayers will have to initially foot the bill.
But what exactly would it take to actually build the wall? BNamericas looks at some of the details of what the project would entail.
Size and location
The Mexico-US border is roughly 3,185km, more than half of it along the Colorado and Rio Grande rivers. At this length, the wall would literally become the largest infrastructure project undertaken in the US in recent years. Its construction would also face an array of challenges related to the geography of the terrain: much of the border crosses the desert, and some areas also cross a number of floodplains.
There are already about 700 miles of border wall or fence along the US-Mexico border, some of which were completed in compliance with the Secure Fence Act of 2006, which was passed during the George W. Bush's administration. Although the act mandated that the fence had to be double-layered, a lot of it was not built that way. As a consequence, it is not impossible to get through the existing fencing and, as such, it probably does not fit into the project that Trump envisions and would have to be replaced.
As for the wall's dimensions, in an article for news outlet National Memo, New York-based engineer Ali F. Rhuzkan said the wall "should reach about five feet (1.5 meters) underground to deter tunneling, and should terminate about 20 feet (6 meters) above grade to deter climbing."
In addition, according to an article in the MIT Technology Review, the wall would have to be one-foot-thick on average in order to have sufficient stability and be difficult to cut through.
Given that the intention of Trump is to build an "impenetrable" wall, the choice of the materials will be a very important one. Since he has stated that "a wall is better than fencing," the material of choice for the wall's future builders will probably be concrete.
According to Rhuzkan, there are two types of concrete that builders could choose from: cast-in place or pre-cast concrete. He said the second option would be the more suitable one for the wall given the high temperatures experienced near the border areas.
Taking into account the dimensions stated above, the estimated volume of concrete that the project would need (including the foundation, columns and wall panels) is around 12.5mn cubic yards, according to Rhuzkan. Other outlets, such as Concrete Construction magazine, put the figure as high as 31mn cubic yards, an amount that roughly equals 10% of the current annual consumption of concrete in the US.
In addition, the reinforcing steel needed to have the kind of barrier that Trump wants would probably be about 3% of the wall's total volume, according to estimates.
Although estimates for the wall's total price tag vary, US Senate leader Mitch McConnell said at a press conference on Thursday that the project would cost between US$12-15bn. Paul Ryan, speaker of the US House of Representatives, also attended the conference and said congress would initially going to finance the construction of the wall.
The MIT Technology Review article estimates the total project cost in the range of US$27-40bn. The concrete alone would cost around US$9bn (based on a 12.7mn cubic yard figure), while the steel reinforcement could cost around US$4.6bn. The rest of the investment would be used to cover labor-related costs.
The cost of labor would depend on many factors, such as the expenses related to transporting the concrete from the facilities where it will be pre-cast to the border areas where it will be used. Although temporary facilities could be set near some project sites in order to shorten transport times, as Rhuzkan points out, workers will need access to food and shelter facilities, as well as medical care, which are not easily available in every area of the border. Some of the largest expenses will probably be related to getting the materials, workers, and equipment transported to some of the project sites. The project may also involve building roads in inhospitable road-less areas where reaching the border is not an easy task.
The price tag would also depend on other factors such as the topography of the place of construction. Another factor to be considered is the fact that some of the land that straddles the border is private property or Native American territory. The government would have to acquire the land from private holders and this could prove financially costly and also pose legal challenges for the Trump administration.
Who will build it?
Although building the wall would no doubt represent a lucrative contract for any construction or engineering firm, working on such a controversial project could risk facing legal problems, boycotts and massive criticism on social media. According to an article published on specialized urban-issues website CityLab.com, some architect and builder associations might refrain from participating in the project based on ethics concerns.
CNN reported earlier this month that Trump's transition team was already in discussions with the US Army Corps of Engineers in regards to the planning of the wall. An act by congress could authorize the corps to take on the project. However, as CityLab.com states, the corps' usual practice is to hire a prime contractor to physically do the work.
To build the wall, a company would not only need to be knowledgeable of this kind of construction, but it would also have to have the capacity to deal with the challenging logistics that such a major project entails. According to CityLab.com, only a handful of architect and engineering firms would fit the profile.
How long will it take?
Estimates on the project duration also vary widely, ranging from five years to more than a decade depending on the financial resources available. Some experts, such as Mexican architecture firm Estudio 3.14 put the figure as high as 16 years.
The Washington Post spoke to a former estimator for one US construction firm, who said such a huge wall project would require at least 40,000 workers a year for at least four years – and the project would most likely take longer to complete.
Even Rick Perry, Trump's pick for energy secretary, said in an interview last year that building the wall would "take literally years. I don't care how good of a builder you are."
Before starting construction, the project's builders would need to carry out the relevant land survey studies for at least some months. In the meantime, the government would have to go through the process of acquiring land from private owners, which could take time depending on whether the landowners accept the offer or want to dispute the decision. The construction plans could also face legal action regarding environmental matters, which could delay the start of the works.
Experts consulted by fact-checking website PolitiFact said that although building the wall in a year can be possible, it would be highly unlikely given the large amount of money and workers it would require.
Building a wall on the border is a high priority for Trump, as he has stated time and time again, so his administration might already be looking at ways to fast-track the project. However, completing the wall will depend on many factors and the real cost and project duration of such an undertaking is very hard to predict.