Beneath the Surface

Nov. 1, 2000
Subsurface analysis takes the guesswork out of a building project and can save time and money.

Subsurface analysis takes the guesswork out of a building project and can save time and money.

Educators and administrators constantly are on the hunt for ways to save time and money on facilities, from institutional master planning through routine maintenance. No single solution will prevent every problem, but subsurface exploration can save administrators time and money throughout the life of a building.

Subsurface conditions include the types of natural soil or rock, remaining foundations of pre-existing structures, and various type of fills deposited in the site. These elements have the potential to dramatically alter a project's scope, including site selection, site preparation and structural system design. If schools and universities don't deal properly with these conditions, they may face significant maintenance and renovation problems.

Administrators need to become intimately familiar with the subsurface conditions of the site on which they are planning to construct their next building project.

Geotechnical Engineering 101 For administrators unfamiliar with subsurface exploration, here's a short course:

- Preliminary sitework: Subsurface exploration begins as engineers view the site. They assess the grades and slopes and determine if the site has been modified. The depth and location of drilling also is defined.

- Drilling: Engineers drill into the soil in areas that will support the building and paved areas surrounding the building to gather relevant samples. The depth and diameter of drilling varies according to site-specific conditions and the type of building project that is planned.

- Laboratory testing: Engineers analyze the strength, moisture, density and other characteristics of the soil samples.

- Geotechnical report: Engineers provide project team members with a technical report of project needs, lab test results, a description of the site and subsurface conditions, and an engineering analysis. The report also includes guidelines for site preparation, types of and placement for fill materials, as well as structural design recommendations. In some cases, the report may recommend further engineering analysis.

- Site preparation and construction monitoring: During these phases, geotechnical engineers verify that fill placement, structural systems and geotechnical-related issues are accomplished as designed.

Verifying strategic plans By gaining an intimate familiarity with subsurface conditions, schools can evaluate whether a site is suitable. This underscores the importance of involving geotechnical experts from the inception of a building project.

In one case, a geotechnical engineering consulting firm was drilling on a site and found rubble fill - including pieces of parking lot asphalt - 10 feet below the surface rubble. The firm advised the client not to move forward with the project because the settlement potential could have led to disastrous results for the building.

Cost-effective design Empowering architects with information about subsurface conditions during design phases allows them to plan the building's structure most efficiently. Geotechnical reports include recommendations for structural design so that systems are not over- or under-designed.

Knowing subsurface conditions facilitates accurate bidding as well. By noting subsurface conditions, architects can include site preparation needs in bidding documents. If subsurface conditions are not known and the contractor discovers unsuitable materials during site preparation, delays occur and significant costs may result. The contractor is likely to charge premium rates to make the necessary site modifications.

More unforeseen costs could result if subsurface findings reveal that the building's foundation design is not feasible. With smaller jobs, that could render an entire project unworkable.

Monitoring construction During construction, monitoring is important to verify that planning and design decisions are being executed. This is especially important with academic projects, which typically are awarded to the low bidder. Consider a few examples.

- When excavating a footing, it is important to remove all loose material in the excavation. If all of the material is not removed, settlement is likely to occur, and problems will result.

- With floor slabs, it is important to ensure that the fill supporting the slab is placed properly and that the slab is poured according to construction specifications. Faulty construction may lead to cracked slabs.

- With steel framing, it is important that the frame is properly bolted and welded. Improper connections can lead to potential roof problems.

- For asphalt, if it is not placed with proper temperature or equipment, the paving will not perform well; it will crack and break up over time.

Ongoing maintenance Structural problems that arise following occupancy frequently are caused by settlement resulting from improper design, inadequate construction techniques, matured vegetation roots, long-term weather conditions or other factors.

The problems generally stem from two areas. First, foundation and structural systems that are improperly designed or constructed may settle, and as a result are damaged. As they crack or tilt, the integrity of the structural system is compromised, requiring re-construction.

Second, damage to the building systems can result from settling foundations. Facade systems, roofing systems, windows and interior finishes can be damaged because of the cracking, as well as from water and weather damage.

To avoid these problems and save on repair time and budgets, school officials should understand subsurface conditions.

No guesswork Without an understanding of subsurface conditions, some decisions become guesswork and can result in added project costs at multiple levels: over-designed structural systems, design changes, delays in construction and problems later in the project lifecycle. Get beneath the surface of your building project and you can get on top of costs and in control of project scheduling. You'll construct a better building in the process.

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