A Crosstie Retaining Wall

Image Gallery The finished product: an effective, attractive crosstie retaining wall. MOTHER EARTH NEWS STAFF

Dirt is not exempt from the law of gravity. It seeks, and in time will reach, the lowest level. But it is possible to resist its will. A retaining wall allows you to turn a useless (for landscaping purposes) slope into a terraced, flat area. And perhaps the easiest way to build such a wall is with used railroad crossties.

As you know, ties are 6" X 8" X 8' (more or less) chunks of pine, redwood, or oak treated with wood preservatives (usually creosote but sometimes also pentachlorophenol). These nasty chemicals make the difference between a few years and several decades of life span for wood that's in contact with the ground. We wish there were some economical alternative to crossties. But, at this time, inherently decay-resistant woods and lumber treated with the less toxic chromated copper arsenate cost a minimum of twice what used railroad ties run (about $8 each in our area). So, for now, we're forced to recommend crossties for this purpose, but with some reluctance and the following precautions: Never use railroad ties near edible plants or in areas where children play, never burn the trimmings from these treated timbers, and always wear gloves when handling them.

ELEMENTARY SOIL MECHANICS

You don't have to search far to find an example of a wall where someone underestimated or misunderstood the forces that soil can exert. Tilted, bulging, or tipped retaining walls can be found just about anywhere there are hills and construction. In some cases, designing a sound retaining wall can become a very complex task-one definitely best left to an engineer. But we can simplify the job if your situation allows you to follow several guidelines: [1] The ground at the top of the wall should be approximately level for a distance equal to at least 1-1/2 times the wall's height; [2] most of the runof uphill from the wall should be routed away from the wall; [3] the fill behind the wall shouldn't consist of expansive clay; [4] the wall should rest on hardpan, rock, or thoroughly consolidated fill; and [5] the wall should be no more than six feet high.

On its own, a crosstie wall doesn't usually have enough strength to resist the slipping and overturning forces exerted by the weight of the retained earth. For a two-course wall, the weight of the ties themselves is sufficient to resist these forces, as long as they're spiked together (and into undisturbed soil) with 1/2" X 18" reinforcing rod every four feet. But as further courses are added, members running perpendicular to the wall and back into the fill (commonly called deadmen) are needed to keep the wall upright. (For example, the overturning force on a six-foot wall is equal to more than 10 times the weight of the ties themselves.)