I have, but here in FL the ground is all sand, and not too hard to poke a hole in....Anybody install these things before? Or have any new ideas for me?
3-feet of 1-inch heavy wall pipe and a sledge hammmer. Drive in at each corner of the sign trailer leaning away from the sign at a 45* angle. Remove with an old-style bumper jack hooked to a chain wrapped around the pipe. Go look at any circus tent.
How about using studded T posts. They are available in different lengths and gauges. I've used them for pasture fencing.
They can be easily put in with a post pounder (your arms will get tired):
I also need to be conscious of having channel (large "spears") out each direction of the trailer in case of a vehicle collision.
In the end, I'll sink some stakes a good distance in the ground and at a good angle, cable it down and keep my fingers crossed.
I spoke with the county highway department manager and shoed him your pictures. He liked the smart use of barrels to protect the sign in the first picture. Here's what I learned:
1) He says whomever engineered your signs is an idiot. The trailer frames for that sign should have rectangular shapes at least 12x8 feet, plus the tongues, with the stabilizer jacks at the corners, not halfway up the tongue. Asked what he would do with such signs, he said he would weld square tubing in a diagonal pattern under the frame, similar to a hitch receiver, and slide in additional tubing with the jacks mounted to the ends, and secure with pins like a trailer hitch. Remove jack handles to make stealing parts difficult. Adjusting outrigger length would be as easy as drilling multiple holes in the outriggers. He recommended retro-reflective tape wrapped around the upper jack tubes. He also recommended installing a crossmember to prevent the spearing effect, and to allow weighting further out. Another idea he uses on signs that are going to be in position for a long period of time is to chain the trailer frame to stacks of old railroad crossties, which act as jacks, weight, and extended fulcrums. Old telephone poles serve the same purpose. Progressive lengths are used to level a sign.
2) Forget stakes. Highway departments do not appreciate their carefully engineered road beds and shoulders being subjected to poking and digging, which leads to erosion. Besides, the type of soils used as shoulders won't hold stakes, anyway, since they are nothing but unconsolidated sediments.
3) Jack extensions are simple: remove the foot, attach the foot to a piece of pipe the same outside diameter as the lower tube of the jack and long enough to reach the ground with the jack in the raised position, slip a slightly larger diameter pipe about 2 feet long over the extension, slip the extension in place under the jack, slide the 2-feet piece of pipe up until it hits the top tube on the jack, lower the jack until all is snug, put a muffler clamp on the extension tube to keep the 2-foot piece from sliding down. Ideally, the joint of the two smaller pipes is somewhere near the middle of the 2-foot pipe.
Now, from an engineering perspective, your 77ft^2 sign, when subjected to 90mph perpendicular wind, will generate about 3400 pounds of force. Figure at 14-feet tall, the center of force is 10.5 ft off the ground, which would apply 35,700ft/lbs of torgue to the ground directly below the sign. Fortunately, the miracle of mechanical advantage means you don't have to use 35,700 pounds of restraint. For instance, if there is a 10.5-foot spread between the fulcrum (downwind jacks) and load (upwind end of trailer), you'll only need 3400 pounds of mass to keep the sign upright. The shorter the distance between fulcrum and load, the more weight is necessary. The longer the distance, the more weight is necessary. Extend the fulcrum-to-load distance to 20 feet, you'll only need 1700 pounds of weight.
I hope all this info helps.
EDIT: Almost forgot. I broached the idea of using channel extensions bolted to the trailer frame, sloped down to avoid the spearing effect. A couple channel crossmembers could be bolted to the bottoms of the extensions to provide trays for ballast. We clamped up some channel he had sitting around to a flatbed trailer, and he liked the idea that the extension could be easily disassembled and loaded right on the trailer for transport. The angle the extension dropped could be adjusted for slopping ground.