Recently I received a call from a major national news source. They asked for help understanding what it would take to build “Trump’s Wall.” I’m an estimator, so I provided some realistic analysis of what it would take.
The border with Mexico is almost 2000 miles long. There is already about 700 miles of fence. This analysis makes an assumption it would be necessary to build only 1000 miles of wall. Also, this estimate is based on the type of wall you see along highways, precast concrete sound and site barrier wall. In reality it would need to be significantly more robust than the typical highway sound-barrier wall, and I’ve taken that into consideration in my estimate. So here goes.
(9-1-16 >>In some other recent articles I’ve read they have suggested a 40 foot high concrete wall. Well, I don’t think you can build a 40 foot high unsupported concrete wall (no bracing at sides) without getting into extremely massive volumes of materials. Such a high concrete wall would need to be much thicker at the base than at the top and the foundation to prevent overturning would need to be massive. Typical rule of thumb for foundation to prevent overturning is the foundation needs to be ~40% as wide as the height of the wall. The volume of concrete would be 4x to 5x what I’ve estimated for the wall I’ve defined here and the excavation, back fill and formwork would add considerable time to complete. Order of Magnitude I guess 40 to 50 million cubic yards of concrete for wall and foundation. I would roughly guess such a massive poured concrete foundation and wall, if it could even be built, would cost THREE TO FOUR TIMES what I’ve estimated here and would require substantially more labor and might take twice as long or more to build.)
This estimate is based on 8″ thick precast heavily reinforced concrete wall panels set between steel columns 12’0 on center. Even if the concrete could be chipped away, the reinforcing bars would prevent passage. Columns are set in 6’0 dia. x 10’0 deep column foundations. Between column foundations under the wall is a continuous footing to help resist overturning of the wall. The wall extends 25 feet above grade and 5 feet below grade. Bottom of concrete footing under the wall is 7’0 feet below grade. Bottom of column foundations is 15’0 below grade. The wall would be much higher than the approximate 12′ shown in the representative photo.
The foundations included here are based on up-sizing components from a known design for a 15′ high prison un-climbable open-mesh fence. Even with an open mesh fence design, to overcome wind load, column footings were 2″0″ dia x 8’0″ deep concrete post foundations set every 8′ apart. This solid wall 25′ high would have enormously greater wind loads and it is the foundation that must be designed to prevent overturning.
Just to get quickly to the end, I calculated the final cost of a 25′ high precast wall, foundations, excavation and access roads in the vicinity of $25 billion (in 2016 $), $10 million per mile or slightly less than $2,000 per lineal foot of wall. I’m fairly certain this estimate is somewhat low and the actual cost due to the many unknowns would be higher. At the end I’ve pointed out some of the issues that could generate unknown costs.
One huge factor is inflation. The cost 5 years from now could be 20%-25% greater than the cost today. If the wall takes 10+ years to build, the cost could be $30 to $35 billion.
This is a summary of some of the results from the estimate.
130,000 man-years, or 130,000 workers if it is to be built in 1 year. Or it would take 10,000 full-time workers 13 years to build this wall.
If 1,000 men worked on the wall 5 days a week 8 hours a day, it would take 130 years to build it. Therefore, I made the assumption the project would be broken into 50 segments each 20 miles long. That will require 700 men AT EACH SEGMENT concurrently to complete the wall in 4 years. That’s 35,000 men working for 4 years. That is 35,000 trades-worker jobs which does not include Architect, Engineering, Testing and General Contractors management personnel.
200 million square feet of precast concrete panels = 5.2 million cubic yards of concrete
5 million cubic yards of cast-in-place concrete foundations
Total cement to make the 10.2 million cubic yards of concrete = 2% of annual US cement production.
1.5 million tons of steel = 1.5% of annual US steel production.
25 million cubic yards of excavation required.
6 million cubic yards of that excavated earth must be hauled away and disposed since that volume will be replaced underground with concrete. That’s more than enough to completely fill the Superdome. Or, it’s enough to build a 20 foot wide earthen embankment 20 feet high and 100 miles long.
Delivering the Materials
250,000 truckloads of precast wall panels,
500,000 truckloads of ready mix concrete
50,000 truckloads of steel
200,000 truckloads to haul away excess excavated earth.
This is far from a complete list of materials, because in addition to building the wall, in some places you first need to build a road. Assume about 500 miles of road. You can’t get 1,000,000 truckloads of 30-40 tons each, cranes, excavators and auger drills to a construction site without at least building a compacted gravel road to get there.
Adds 2 million cubic yards of stone for construction equipment road.
Adds 100,000 truckloads of stone
1,100,000 truckloads at 50 locations over 4 years is = 20 deliveries per day of 30 to 40 tons each at each of the 50 locations. That works out to 40 truck bypasses per day coming and going, so 30 ton trucks go by (some community) every 12 minutes at every one of 50 locations every workday for 4 years. It is very likely that heavy truck traffic will destroy many if not all the town roads used to access the 50 construction sites. The cost to repair/replace those existing roads is NOT included here, but I suspect it would be in the hundreds of millions.
Energy cost just to produce 1.5 mil tons of steel is enough to power 250,000 homes for 1 year. Energy to produce both steel and concrete probably more than doubles that number.
The money spent is enough to build 70,000 new homes or 500 new high schools.
Gasoline just for all truck deliveries is near 5 million gallons.
The concrete and steel materials gross to 2% of annual US cement production and 1.5% of annual US steel production, but that represents close to 3% of steel used in construction. About half of all US steel goes into your refrigerators, cars, etc., the other half goes into construction. The materials demand has far more affect than you might think on disrupting normal construction flow. Since it is all localized in one area of the country, the far southwest border, it could potentially represent 20% and 30% of the construction materials capacity in that area of the country, straining the capacity in that area and disrupting the normal volume of construction there for years. This would be detrimental to the rest of the construction industry growth in that area for that period.
This does not address the fact that manufacturing facilities to produce and fabricate the steel and deliver concrete needed at each of the 50 work sites ideally should be spread along this 1000-mile corridor, which is very unlikely. In fact, I suspect it more likely that some locations will not be in close proximity to a materials source, the result either driving cost up or extending duration beyond 4 years, or both. It could require building process plants along the path, for instance, ready-mix concrete batch plants and steel fabrication yards.
The time necessary for land acquisition, design, permitting, environmental study, mass material procurement, construction process planning and mobilization would be many months before construction begins. Although labor availability and the number of sites determines construction duration, 4 years would be a reasonable estimate for construction ONLY IF the 35,000 trades-workers needed can be mobilized simultaneously to 50 job sites, but that is not likely. The 4 years of construction starts when planning, design and permitting are complete. That might take 6 to 12 months.
Construction is experiencing what may be the tightest labor market in over 20 years. Since there are few if any available workers to shift to these new job site locations, we would need to assume much of this work is supported by creating nearly 35,000 new jobs. Several serious problems arise.
In this localized area of the country, that could potentially be 2% to 4% expansion of the construction workforce. The maximum historical rate of annual workforce expansion is 5% nationwide. Normal annual jobs growth is 3% to 4%. If one project were absorbing 100% of the jobs growth in an entire region, there would be no workers available for any other construction activity growth for several years.
Such an expansion would be extremely difficult to implement that quickly. The mobilization of 35,000 workers could take a very long time from initial ramping up to full employment, therefore extending the duration to complete the job. Many of these workers would be inexperienced adding further to the project duration. So reaching completion of this work would probably take much longer than 4 years. Adding time for planning and more time for ramping up labor, it could be 6 years.
Ramping up then down will soften the blow as the jobs begin to disappear at project completion. It could be pretty hard to generate enough new volume of work to keep all those men working. It will take new volume of $5 billion to $6 billion a year to keep all these workers working.
This brief analysis of cost and constructability does not begin to address issues such as, how would a wall be built anywhere along the 1,000 miles of the Rio Grande river, the border between Texas and Mexico, the 4th largest river in the United States. Assuming such a wall must be built on US soil, a wall would then completely cut off river access from the United States? Or, how would a wall be built through the hundreds of miles of national parks and national wildlife refuges along the border without disrupting natural wildlife migration flow? And, how would it be designed along its 1,000 mile corridor to accommodate drainage across a solid impervious barrier? It seems impractical or at the very least massively environmentally disruptive.
You can see, the logistics would be enormous, impediments loom, adjacent communities would be adversely impacted, the cost is probably far more than the $25 billion estimated and it seems highly unlikely this could ever be completed during the course of a single president’s term.