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Retaining walls provide an essential function whether that is to help prevent erosion, to support a home's foundation, or merely to improve a lot's aesthetic appeal.  Like all good walls, a retaining wall is intended to keep the good things in and the bad things out.  Regrettably, retaining walls are very seldom built correctly.  This is especially troubling in areas of the world such as North Texas that have expansive soils.  

Ideally a retaining wall should be both a wall and a drainage system, essentially a wall that fronts a French drain.  The wall itself should include drain ports and be built with reinforcement such as iron rebar.  The drain system should have gravel or rocks slightly above the level of the drain ports.  The rocks should be covered with a fabric membrane that will help prevent the drain system from silting up.  Then the fill dirt should be done in layers and compacted.  Ideally this should be done by hand.   If heavy equipment is used exclusively for this task, it is almost guaranteed that the life expectancy of the retaining wall will be dramatically shortened.  When the sod is installed, the level of the grade behind the wall should be at or slightly above the wall itself.  The goal is for all surface water to be shed by the wall and not to pool behind it.  Drains and good top drainage are vital to the performance of the wall.  The goal is to minimize the weight and mass of the water absorbed by the soil which is substantial especially with expansive soils.  

A few final thoughts about reinforcement and structural design.  A wall can be built that is very thick and strong, but if it is not anchored to something it wouldn't take much force to push it over.  Think of a sheet of plywood.  One sheet of plywood will not stand up by itself, but if you nail two, three, or four sheets of plywood together to form a "L" or a "U" or a box shape, each form is significantly stronger.  Asking a retaining wall that is just one "wall" to hold up against the pressures of time is asking it to do something it can't.  If the wall is built with corner walls and the corners are reinforced it has a much better chance of enduring.  In a masonry wall where there is little or no reinforcement, the corners are only as strong as the mortar which is guaranteed to crack and fail.  Obviously, adding reinforcement like rebar will greatly strengthen the corners.

And a final note about materials, if your retaining wall is structural and is supporting the soils that support your foundation, you should select the most durable materials available.  Cutting corners to save money on a structural retaining wall does not work.  The potential cost of a failing retaining wall and a failing foundation is too high a risk.  In my experience, railroad ties make a very poor material for a structural retaining wall.  These are almost never installed with enough reinforcement and almost always fail over time.  

Almost all retaining walls are built either missing one or more of these key components or are installed improperly or with unsuitable components.  It is no wonder that most older retaining walls fail in some fashion and need to be rebuilt.  

The retaining wall above has failed because it did not have a single drain opening.

It did have rebar as reinforcement, but the rebar should have been angled and tied  together on both sides of the corner.

This is a new retaining wall (installed less than a year ago).  It is already cracking because it has no drainage system.  Within a few years it will look just like the wall it replaced.

Here is a wall with both high and low drains.  Regretfully when it was built they did not excavate behind the wall and install gravel or rock.  The drains will help, but they could have been more effective.  The drains close to the ground were already silting up further reducing their effectiveness.

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