Rammed earth is where you use bulldozers to scrape dirt into piles. In theory, large piles could be created to be about 60-100 feet high, consisting of unstable soft soil, so that if anyone tried to climb it or tunnel in, a portion of the pile would just cave in on them, endangering their health and requiring a large amount of time, tools and labor to penetrate the wall. Currently, there aren't any bulldozers that by themselves could pull this off, but the cost of making such a vehicle versus the load of work each of them could do would by my estimate run the total price tag of the border from west California to east Texas to about $100 million(assuming you allowed each vehicle one year to complete its portion of the wall). What are the drawbacks or is it even possible?
Seeing how the government now spends about 100 million to do about 15 miles of freeway , and that is only about 1 ft high, I think your cost estimate is grossly underestimated. Rammed earth is not that unstable (or else they wouldn't allow it for building houses) and is labor intensive to make. It is a mixture of clay and sand so that it sticks together and you need a high hydraulic pressure to extrude it. Even at 20 feet high it would be extremely labor intensive and expensive for those distances. A concrete wall 6 inches thick and made like &sound walls& would be very difficult to penetrate , but would cost a lot. But it would be far cheaper than rammed earth. Making the wall high would actually help someone to tunnel into it. The added height would spread the tensile load over a greater distance (like how you can make arches out of brick and the weight above the arch helps spread the load between the arch supports) Plus with any determination, you can just drop a hose into the Rio Grande and use a pressure washer and dig a nice little hole into the wall,, enough to crawl thru and the chances of collapse are pretty slim. Rammed earth is only cheap if you have lots of time and your labor is free or very cheap.
A wall/fence along the border would be massively expensive and would not be particularly effective unless you patrolled it rather heavily. What made the Berlin Wall effective was the massive staff of soldiery along every inch of it. The US Mexico border is enormous and that kind of manpower would be a crippling expense. A wall/fence without massive manpower is not very effective. The triple layer fencing proposed in most proposals is trivially easy to get over, under, or break through. So unless you have enforcement/surveillance on the spot, you are only slowing people down. And the cost/benefit of that just isn't there. Especially since recent studies show that, contrary to social conservative myth, immigrants, even illegals, are economically positive in their impact, less likely to consume social welfare benefits, and likely to contribute substantial taxes. What's more, many illegals come here legally and simply overstay their visas, or sneak through at legitimate crossings. Fences/walls do nothing for that. The only thing that actually slowed the wave of illegals was the slowdown of the economy. This is, like drugs, a demand driven problem. Enforcement simply sin't a quality solution in and of itself.
Putting aside the question of whether we should build a border fence, I'd have to say no to this method. Rain would cause the loose soil to spread out and compact over time. Plus even though it would take time and effort, assuming the people didn't want to wait for the wall to naturally collapse someone would take the time and effort to dig through the wall. You'd dig a bit, let the wall settle, dig some more and continue until you break though. Probably an entrepeneuring immigrant smuggler would be the first to do so, but that's just speculation on my part.
100 feet = 30 meters might do the job better than a puny fence with 10,000 volt pulses and booby traps. Rainfall is rare along most of this border, so maybe. Lets build a short section to see how many get across by going over the top. How about free beer and food, but no pay for riflemen who like to shoot the aliens who reach the top, or bore though? With the riflemen and the 10,000 volt pulses, 20 feet = 6 meters might be sufficient. Likely there is no good solution to illegal immigrants. Listening devices would hear the digging, so we could be ready to arrest as soon as they emerged. I suspect your 100 million dollars is way low. One million meters long, with a cross sectional area of 1000 square meters is 1000 million cubic meters of soil. One dollar per cubic meter may be reasonable to ram the dirt to a height of 30 meters = 100 feet, so ten times your estimate for that height. Besides the deprecation on the bulldozers, you need fuel, repairs and pay the bulldozer drivers for hazardos work, so one dollar per cubic meter is optimistic. A cubic meter is about 1.5 cubic yards. Neil
