Center the 1/8-inch panel of wood around a form, such as a metal arch. Bend the wood around the arch slowly until it presses against the arch all the way around. Clamp the wood into place on both sides of the arch.
Leave the wood in place on the arch for 24 hours so that the form takes hold. Remove the clamps from the wood and the form.
Apply wood glue to the outside of the wood with a paintbrush. Line the 1/8-inch wood panel up with one side of the first wood panel. Bend it around the form at the back of the first piece of wood. Clamp the second board in place with the first on both sides of the arch.
Continue adding layers to the curved wood, with glue between them until the wall piece reaches the thickness you desire. Cover the entire structure with polyurethane once it has been bent. Use these panels side-by-side to build the wall.
Dig a curved trench in the ground to the length and width where you want to build the curved wall.
Cut the rectangular wood pieces for the wall down to the lengths that you can fit into the curved sections of the trench. Fill in the spaces around these wood pieces with sand until the sand sits level with the wood.
Apply 1 inch of mortar to the top of the wood row and sand with a trowel. Place more pieces of cut wood on top of the mortar to create a second row. Add sand around the wood up to ground level. Add another 1-inch layer of mortar on top of the wood.
Build another row of the wall with wood pieces. Fill the spaces left between the pieces of wood with mortar to within 1 inch of the edges. Let the mortar dry for 24 hours.
Fill in the 1-inch spaces left on the outside of the mortar with wood filler. Stain the wood filler to match the wood used in the wall to create a uniform surface.