Landslide Mitigation with Drainage Management
As engineers and geologists, we have observed over the years that most foundation
and hillside problems are either caused by water or aggravated by water.
In general, 1) the water will cause most clays to expand, 2) running water
will erode slopes, 3) saturation of the subsurface materials makes soil
and rock materials heavier and thereby affects the stability of slopes,
4) water decreases the strength of clays and some bedrock materials, and
5) water flowing through soil and bedrock materials exerts seepage forces
and therefore can contribute to a failure.
Water is an instrument of nature. It erodes gullies, swales, valleys, and
even formed the Grand Canyon. Landslides are caused by water, as are soil
or mud flows and, obviously, floods. All of these are natural on-going geologic
processes. The above-mentioned natural processes can adversely affect man-made
structures and, therefore, geologists and engineers must consider them and
design to minimize their effects.
The following recommendations and suggestions, when utilized, constitute
proper maintenance procedures that will improve drainage conditions and
increase slope stability:
- Maintain positive drainage at all times. All water should have a cleared
flow route away from buildings.
- Water should be drained into lined ditches or closed pipes that discharge
into appropriate facilities.
- Check roof drains, gutters and downspouts to be sure that they are clear.
Depending on their location, roofs can shed tremendous quantities of water
during a rainstorm. Without gutters or other adequate drainage facilities,
water falling from the eaves may collect against the foundation and/or basement
walls.
- Erosion on slopes should be corrected immediately and any flowing water
should be directed away from eroding areas.
- Water should not be allowed to flow over slopes. Large concentrations
can be particularly harmful.
- Water should not be permitted to pond or flow adjacent to a building's
foundation.
- Periodically check to verify that subsurface drains are not clogged.
- Correct any damage to the drainage system as soon as possible. Prompt
attention to minor problems may prevent them from growing into major problems.
- Remove any obstructions from surface drains. Make certain that all drain
elements are in good repair.
- Check for loose fill materials above and below your property, because
they can erode or slide during the rainy season.
- Do not over-irrigate landscaped areas. Sprinklers or water hoses should
not be left on longer than necessary and never overnight.
- Never connect roof drains to subsurface drains.
- Do not modify or obstruct any part of the existing drainage system without
professional advice from a registered civil engineer.
- Do not allow water to flow into or accumulate on areas above septic
tanks or leach fields.
- Do not compact earth behind walls or in trenches by flooding with water
(this is commonly called jetting).
- Do not place loose soils or fills on a slope.
In general, common sense and normal awareness are all that are needed
to prevent costly and sometimes serious damage. If damaging effects of drainage
are observed it is advisable to obtain the services of an engineering geologist
or a geotechnical engineer.
|
