When purchasing a home on a hillside, it is important to have an evaluation of the site. This would include having an expert walk the site to identify any soil and/or foundation related risks. Problems such as unstable slopes or expansive soils can be identified and dealt with more efficiently initially rather than later after the problem has manifested.

Erosion:
Hillsides have several common soil related issues that include erosion, slope failure, and slope seepage. Erosion is the disintegration / transportation of earth and rock materials by water, wind and ice. If a slope doesn’t have good landscape coverage, the slope will experience erosion. Erosion of a slope can be a result of pipe breaks, over-watering and rain. Unfortunately, pipe breaks will have to be dealt with as they occur.

Concentrated water flows on unprotected soil areas are what typically cause erosion. As a result, transported sediment can fill up your drainage swales (open surface drainage structures that are cut into the ground surface in the shape of “V” that are often, but not always, lined with concrete grout) and substantially disrupt the flow of water creating additional erosion problems. Hence, drainage swales need to be vigorously maintained. In the long term, a good landscaper should be consulted to help identify risks and/or problems and then develop a plan to eliminate those problems.

Surficial Slump: There are several types of slope failures but the most common type is a surficial slump or a “pop-out”. “Surficial” is a geologic term that means lying in or on a surface, specifically the surface of the Earth. Hence slope failures that occur close to or at the surface are typically called surficial failure. These types of failures are usually a result of saturated soils. Landslides typically move on a slide plane that is often deeper and related to geologic structure. These failures are generally shallow and oval shaped occurring in weak soil that has been inundated by prolonged heavy rainfalls and in some instances over-irrigation. The debris from surficial slumps usually ends up a few feet from its’ original location leaving a nearly a vertical scarp (A geologic term describing the near vertical face of exposed soil at the top of where a slide occurred, meaning the slide mass is now down slope some distance from its origin leaving behind a fresh exposure of underlying soil, the scarp face) below. The most common factors contributing to surficial slumping is, slope steepness, soil strength and the introduction of water.

Seepage:
Another problem common to slopes is seepage. In most cases this is a nuisance problem but it can manifest into health and safety hazards. Slope seepage is defined as a periodic to constant weeping of moisture, most commonly at the toe of a slope. This problem seems top be commonly overlooked in the development stages. But if the seepage is left unattended it could begin to pond and cause other problems such as, algae growth, expansion of soils that can raise streets and structures. The main source of seepage is typically improper irrigation, rainfall and pipe leaks.

Moisture Intrusion:
Interior moisture intrusion is often a result of the same problems that cause erosion and slope seepage such as poor landscaping, improper drainage and pipe leaks. Generally, interior moisture intrusion enters into the living space as a vapor through the concrete slab that can condense under flooring materials causing warping, mildew growth and other problems. In many cases the moisture intrusion is associated with construction defects such as poor quality of concrete, which usually means the concrete is more porous resulting in a greater volume of pathways for the moisture vapor.

There are solutions to all of these problems but only after they are identified and the causes are diagnosed.
A professional geotechnical engineer has the expertise and experience to determine the causes and will recommend appropriate corrective actions. The key is to identify at-risk areas as soon as possible and take action before the ground starts to move or the water damage is done.