When purchasing a site, what level of due diligence is warranted? Most sophisticated buyers know a Phase I Environmental Site Assessment and evaluation of potential soil contamination is a must. But what about the physical properties of the soils? Are they suitable for support of your development, or will unfavorable soil conditions increase foundation construction costs significantly?
At Pioneer, we are experts in performing geotechnical investigations in order to analyze site conditions that can make or break a development’s foundation budget. With our knowledge of area geology, we are often able to anticipate site conditions and scope the ideal level of investigation needed, from single-family residential developments to mid-rise structures.
The fact is at many properties, particularly in long-urbanized areas such as Chicago, we find adverse soil conditions that directly affect the prospective foundation design and budget. Once these conditions are known, a plan to address the issues in the most economical way can then be developed. Common unfavorable site conditions include deep fill materials from former basements/developments, soft or loose materials at the proposed footing depth, high groundwater tables, and deep layers of organic materials that decompose and cause settlement over time. Sometimes the solution is as easy as undercutting the unsuitable soils and replacing them with structural fill, while other times “push piles” or “helical anchors” are more economical and recommended instead.
Deep foundations, such as drilled shafts, that are ideal for support of heavier building loads can be difficult or more expensive to install depending on the site’s soil profile. Occasionally, granular layers are encountered deep within the typical silty clay layers, causing groundwater to flow into the shaft excavations. Other times, soil profiles can vary significantly throughout the site, affecting the depth of the drilled shafts and cost of construction. For example, this year Pioneer performed a geotechnical investigation where the bearing soil varied by a depth of 15 feet over a distance of a mere 50 feet. While unusual, the developers were made aware of the site’s challenges and the foundation was successfully installed with meticulous planning, site inspections, and the confidence of knowing what soils to expect from the geotechnical report.
At Pioneer, we are committed to providing our clients with the site-specific knowledge required to make an informed decision prior to purchasing a property. While it may be tempting to skip the up-front cost of a geotechnical investigation during due diligence, it is well worth the expense to be aware of the site’s specific soil properties and to proceed with confidence knowing the suitability of the soils for foundation support and construction.