Obviously, these changes can be made and are made on a regular basis. Sometimes the solution to a desired flat area is to create a steep slope above and below the flat area. Sometimes the solution is to construct a retaining wall or two. Sometimes the solution is to remove the top of a hill and use that soil to fill a hollow.
I have frequently seen the constructed solution take the form of reshaping the land to create steep slopes on one or more sides of a site. This can be a very effective way to create privacy, by creating berms, or to create a flat central lawn. All to often I have seen this done, though, without the aid of a trained designer. In fact, many 'garden centers' and 'landscapers' offer grading services. Frequently these outlets have people who might know how to operate a backhoe or bulldozer, but do not have any design knowledge or training. Although some equipment operators have an inherent sense of how to form the soil, many do not. As a result, I have seen a good deal of disastrous consequences.
|Don't let this happen to you!|
All soils are made up of small particles of minerals - the result of the breaking down of rock that formed the site millions of years ago - and organic matter - the result of the breaking down of plants in very recent times. Soils are generally classified as sand, silt and clay (with a fourth classification of gravel that is not considered to be soil) based on the size of the particles that make up the soil. Sand is the largest of the particles and clay is the smallest. When these soils are built up to create a steep slope, they will naturally only stay at the steepness defined by their specific angle of repose. This angle is directed by the individual particle density, surface area of the particles, their shape and the coefficient of friction as they relate to the force of gravity that acts on them. Attempts to form a slope steeper than the angle of repose of the specific soil of a site will result in that soil reverting back to its natural angle. That angle becomes flatter when you add water to the mix because water reduces the coefficient of friction allowing the particles to slide past each other. For example, a dry sand has an angle of repose of 35 degrees, but a wet sand has an angle of repose of 25 degrees. That is why the contractor can walk away from a completed site and the disaster of slope failure will not occur until it rains.
Make sure you know who is designing your grades and how much training they have had. It is also helpful to get a soil analysis if a great deal of grading is being proposed. Clients that refuse to pay the 'extra' for a soil analysis often take the burden of failure on themselves and find that the 'extra' paid for that analysis might have been a wise investment. Don't let a lack of knowledge about your site and your soil cause you to be the next person facing disaster.