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Symptoms - Terrain

The big attraction to the hillside is the view, which leaves one breathless in most cases. But with the view comes the unknown stability factor. What soils are the hillside built on? What soils are at the base of the hillside? What soils are on the crest of the hillside? All of these are factors for looming danger.

Every day we hear of a landslide somewhere, especially where the terrain lends itself to mountains, escarpments, canyons, etc.

A landslide is a general term used to describe the downwards movement of organic materials, soils, and rocks created by pressure of weight to the upper portion of an escarpment that results in a gravitational flow towards the bottom of that slope. Normally, it is because of glacial sediments that build up over the years and the natural elements that erode the land and cause this type of activity which is very common.

There are three distinct physical events occur during a landslide; the initial slope failure, the subsequent transport, and the final deposition of the materials. This activity can be caused by one or some of the following:

• Undercutting of a slope by water causing erosion
• Human activity too close to the slope
• Shock or Vibration caused by mining, construction or nature
• Loading of additional weight to the upper portion of a slope

Landslides may result directly or indirectly from the activities of people undercutting a slope or constructing new structures, or adding additional materials on top of a slope. People are one of the major causes of slope instability by changing the landscape or clear cutting or benching when it is not necessary. Vegetation that is on that hillside is there to absorb moisture in the soil and strengthen the integrity of the hill itself with a complex root system that binds the slope together.

Most escarpments have a natural creep to them. They move with a gravitation pull towards the bottom which is a slow process of a fraction of an inch per year. This can be sped up to a rate of feet per second caused by the eco system being disturbed by human hands or nature itself in the form of waves, streams, rivers, rain, ice, or snow.

Populated areas and transportation routes are exposed to a great variety of landslides that not only cause property damage, injury and death. They also affect water supplies, fisheries, sewage disposal systems, forests, dams, and roadways for years after an event has occurred.

Most landslides are preventable but happen because:

• At the top of a slope, fill is placed to extend the some of the building lots
• At the bottom of a slope, the slope had been cut back to extend the building lots
• Erosion has occurred to the slope caused by heavy rainfalls, and moisture
• Homes were constructed too close to the crest at the top of the slope, and homes were constructed too close to the base of the slope well within the unstable zone of that slope
• Storm runoff is handled by open man made or natural ditches at the base of the slope
• Minor groundwater or springs seep at various locations and elevations along the escarpment
• Fill is pushed over the crest of the natural slope to extend a lot area and has been altered so that it is standing at a much steeper angle than the original natural angle to the slope
• Development behind the crest of the slope has affected the natural run off routes

In urban areas, loss prevention can be accomplished by:

• Removal of existing debris placed over the crest and not allowing new debris to be placed there
• Vegetation should be controlled
• All storm drainage from residences should be connected to a storm sewer and not allowed to flow freely across the property to the slope
• Any existing abandoned septic tanks and systems should be removed and the cavities filled and compacted with non-organic material
• All homes should have their drainpipes checked twice a year and maintained in a good working order
• No structures, fill or other activities should take place within a recommended distance to the crest
• Existing ground streams should be controlled and redirected safely away from unstable areas
• Flood control channels should be developed for heavy rains
• All buildings should not encroach on the toe of the upper slope
• All retaining walls and other structures should have proper drainage systems installed at their base

Another method of preventing loss is benching which is a relatively new process as we see it today. Benching got its start back in the forties and fifties in the form of placing large steps of some degree into the embankment. Benching is a form of using the landscape as a retaining wall. It is typically made of concrete or interlocking blocks, and built to keep a bank of sand or soil in its place.

At the top of a hillside do not construct anything for a distance from the edge that is within half the height of the hillside. For example, if the hillside is 250' vertical height, stay away from the edge 125' and don't disturb anything.

This rule is easier said than done, as are the loss prevention strategies, so here is another major cause for sinking foundations. Once a landslide has occurred, then you are definitely in recovery mode and this may not be the usual signs of foundation cracks or sinking.