Most Common Slope Stabilization Failures

Association of Construction and Development
May 30, 2012 — 1,347 views  

Let’s face it; the Earth is full of hills, valleys, gulches and slopes. Unless you're building on sand flats, you'll probably encounter some grading issues that need to be handled before construction begins. Proper slope stabilization strategies are essential for preventing erosion, landslides and serious damage. Here are several of the most common slope stabilization failures and how they can be avoided.

Sedimentary rock and sandstone pose certain dangers when excavated to form a slope. These rocks are prone to cracking and tumbling. This occurs when the rock's integrity is compromised by groundwater and fissures. Unfortunately, there's nothing builders can do to change the local geology. In many cases, consulting an engineering geologist is the best solution if the slope cannot be terraced to reduce the face or leveled to an incline less than 15 degrees.

Soil slumping is one of the most dreaded and most common slope stabilization failures. Soil nailing and rammed aggregate piers are two of the most successful methods for stabilizing slopes and preventing landslides. Soil nailing was introduced in France in the 1970s and has become the gold standard. Steel bars inserted at two-yard intervals can successfully stabilize slopes with an incline of 45 degrees. This popular method doesn’t require drilling. Rammed aggregate piers use a similar interior stabilization approach except compressed rock is inserted into deep wells. By tamping rock in layers, the aggregate forms pillars with undulating sides that prevent shifting. Erosion can be effectively prevented by installing landscaping as well.

Retaining wall failures are all too common, and the causes are preventable. When installed incorrectly, retaining walls merely hide mounds of unstable dirt. The width at the bottom of a retaining wall should equal half of the retaining wall's height. During periods of heavy rain, water collects behind retaining walls. It's imperative to fill the space between the wall and bedrock with free-draining aggregate. Drains should be installed in the wall or behind the facade. Soil and gravel must be thoroughly compacted. Geogrid mesh should be added after every three courses, and rebar can be installed for additional support.

Cutting and filling slopes to reduce the incline is the most effective and inexpensive stabilization method, but it isn't always practical. Slope stabilization failures are complicated by soil mechanics, faults, groundwater and strata layers that possess different characteristics, which are best understood by geologists.

Association of Construction and Development