If you want to move the earth, build a retaining wall—by the time you're done, you'll feel as though you've moved half the planet. Because a retaining wall is going to be in contact with the ground, make sure you use lumber that's rated for ground contact. Your best choice is a pressure-treated wood that has a rating of .40 or higher. Avoid railroad ties—they're heavy and soaked with creosote, which is messy and can harm plants.
There are 8 steps to completing this project:
Lay out the wall, excavate the soil behind it, and dig a trench 8 inches deep for the first course of timbers. Line the trench and excavation with landscape fabric, then add 2 or 3 inches of gravel and tamp it in place. Make sure the trench is level and flat.
Drill a 1/2-inch hole 6 to 12 inches from the end of each timber to hold the rebar stakes. If necessary, cut the last timber to fit with a chain saw. Treat cut ends with a preservative to keep them from rotting, and set the timbers in the trench. Any irregularity in the first course will show up in all the other courses. Use a level to make sure the timbers are level from end to end and from side to side. At corners, check for square with either a 3-4-5 triangle or with a framing square. Add or remove gravel and move the timbers as necessary.
Drive 42-inch lengths of #4 (1/2-inch) rebar through the holes in the ends of the timbers with a 6-pound sledgehammer. Mark the location of the rebar on the face of the timber so you'll know where they are when you fasten the next course. Offset the ends of the second course by at least 4 inches from the ends of the course below. Place the timbers so the front of the upper timber steps back 1/2 inch from the face of the lower timber.
Each row of timbers is fastened to the one below with 10-inch landscape spikes. Lay out holes for the spikes 6 to 12 inches from each end of the timbers and every 4 feet in between. Make sure the holes won't hit the rebar that holds the first row in place. Drill the holes with a 3/8-inch bit in an electric drill. Drive the spikes into the holes with a 3-pound sledgehammer. Mark the location of the spikes on the face of the timbers with chalk so you won't hit them when you drive the spikes for the next course.
Once you have nailed the second course in place, lay a thin bed of gravel on the ground behind it, sloping it 1 inch every 4 feet. Lay drainpipe on the gravel and against the wall. (If a sidewall turns uphill, lay the drainpipe before you put in the sidewall's second course.) Deadmen and tiebacks are installed on every other course to anchor the wall. They should be offset from the ones on lower courses. Fold the landscape fabric out of the way, cover the drainpipe with gravel, and dig trenches for the deadmen and tiebacks at 4-foot intervals. Make each trench large enough for a 4-foot tieback and a 3-foot deadman. Dig so the bottom of the trench is level with the top of the first course. Cut a hole in the landscape fabric for each deadman.
Cut the deadmen and tiebacks. Set one end of each tieback on the second course of timbers, the other end on the crosspiece. Make adjustments as needed to level and square the deadmen and tiebacks. Bore two 3/8-inch pilot holes through each tieback and deadman for a 10-inch landscape spike. Drive spikes into the holes, attaching the tiebacks to the deadmen and the wall. Lay the next course, offsetting the timber ends by at least 4 inches from the ones below. Position the timbers so the front edge of the upper course steps back from the lower course by 1/2 inch. Drill and spike as before.
Fill the trench with gravel to the top of each course as you lay it, and firmly pack down the gravel with a tamper. As you lay the timbers, the front of each course should step back from the front of the one below. Install deadman and tiebacks every other course. Spike the courses to each other. For the top course, drive a spike through the corner.
After installing the top course, fold the landscape fabric over the gravel and fill the remaining space with topsoil. Tamp it, fill any resulting low spots, and rake it smooth.
