Curt Peterson 2013-02-01 02:41:26
What Are Expansive Soils? My office frequently receives calls from people who have concerns about expansive soils. Many of these calls are from people who are purchasing a home or recently purchased a home in an area where expansive soils may exist. After speaking with many of these individuals, I have learned is that there is a vast amount of misleading and in some cases, erroneous information about expansive soils. For example, if you type “Expansive soils” into Google, numerous websites will appear which show major problems associated with expansive soil movement including diagrams of buildings tilting, cracks in foundations, large drywall cracks, etc. This search also lists various articles about the damaging effects of expansive soil movement across the United States. These articles are quite ominous and can cause concern to anyone. One article referenced in my Google search comes from the website Wikipedia, which provides the following definition for expansive clay: “Expansive Clay is clay that is prone to large volume changes that are directly related to changes in water content”. The first words that jump out to most people would be “large volume changes.” Such a definition implies that if expansive soils are present beneath a home and experience a change in water content, “large volume changes” will occur and cause damage to their home. This definition in conjunction with the various articles and diagrams shown on the Internet can cause fear to almost anyone. In fact, I have spoken to homeowners that were so concerned after doing such a search on the Internet, they were convinced that the walls of the home were going to buckle and their roof was going to eventually collapse. The question is whether this definition and diagrams are correct and are expansive soils this problematic? To answer this question, I will first give a more accurate definition of expansive soils. Expansive soils are soils that can experience volume changes due to changes in water content. The amount of volume change varies and is dependent on several important factors including the percentage of clay within the soil, the clay mineralogy, the density of the soil, the thickness of the expansive soil layer, the confining pressure, and the availability of moisture. The key point to this definition is that the amount of volume change is dependent upon numerous factors. In fact, when you combine most of these factors, most expansive soils in Arizona will usually have a low or moderate expansion potential and will not yield “large volume changes” as defined by Wikipedia. The amount of volume change can be as low as 1/16-inch or even lower which is imperceptible and will not cause damage to a home. I have personally visited thousands of homes in Arizona that are located in areas of expansive soils and there were no signs of any soil movement or damage to the home. Based upon my experience, this is typically the norm, rather than the exception. Furthermore, when expansive soil movement does occur, it is usually the result of poor drainage conditions around the perimeter of the home which allows moisture to migrate beneath the foundation and wet the underlying soils. When these poor drainage conditions are corrected, the movement typically stops. There are areas in Arizona where the soil characteristics are such that higher levels of expansive soil movement can occur. I have personally worked on projects where the expansive soils heaved more than 6-inches at the ground surface and caused significant damage to the supported structures. In these instances, very aggressive repairs were required to stabilize the structure; however, these instances are very uncommon and are the exception, rather than the rule. Unfortunately, these instances seem to get the most attention and are the ones that appear to be the most documented on the Internet. In summary, expansive soils are clayey soils that can sometimes be problematic, but in most cases in Arizona, the expansion potential is usually low to moderate and will not result in the damaging affects which are portrayed all over the Internet. If expansive soil movement does occur, the most common method to alleviate the expansive soil movement is to establish positive drainage around the structure. If you have a client that has concerns about expansive soils, or you would like to know more about this topic, please contact my office for more information. Lunch presentations can also be provided upon request. Curt Peterson is the founding engineer of Peterson Geotechnical Group, a forensic geotechnical engineering consulting firm. He holds a bachelor’s and master’s degree in civil and geotechnical engineering and has observed thousands of structures throughout his career. As principal engineer and with over 16 years’ experience in the field of engineering each project is given the upmost attention with focus on accurate analysis and meeting the client’s deadlines. The firm provides expert services including deposition and trial testimony and mediation attendance on construction defect lawsuits. For more information call (480)-219-0014 or visit the website, www.pgg-eng.com
Published by Target Market Media . View All Articles.
This page can be found at http://digitaleditions.walsworthprintgroup.com/article/GEOTECHNICAL+ENGINEERING/1301999/144944/article.html.