Anyone who provides, reviews, or specifies soil special inspections is aware of the soil special inspections required by the International Building Code (IBC), Chapter 17, Section 1705.6 and Table 1705.6. The code-required special inspections listed in Table 1705.6 are vital to achieving the designed bearing capacity of the in-place soils and limiting potential settlement. IBC Chapter 18 lists additional soils special inspections that are just as important as those in IBC Section 1705.6.
The narrative of IBC Chapters 17 and 18 is clear on the issue of fill placement: During fill placement, the special inspector shall verify that proper materials and procedures are used in accordance with the provisions of the approved geotechnical report. IBC Section 1804.6 requires that the geotechnical report be developed in accordance with the IBC. Section 1803 requires that a host of soil field and laboratory tests, prior to and during earthwork operations, be performed by a special inspector to permit a reasonable (and satisfactory) prediction of the load-bearing capacity of the fill material.
It is important to note that the code requires that compacted fill beneath the building be placed and tested in accordance with the recommendations of the approved geotechnical report. The code also requires the geotechnical Engineer-of-Record to include the test method(s) used to determine the dry density (in place) of the compacted fill in their report. The most often-cited test method directed by project geotechnical engineers to determine (soil) field density is ASTM D 6938, “Standard Test Method for Density of Soil and Soil-Aggregates in Place by Nuclear Methods (Shallow Depth).” These density tests must be performed in strict accordance with the requirements of ASTM D 6938 to be accurate and valid. Common errors in D 6938 testing that could negatively impact test results are:
- Improper surface preparation of the area to be tested with the nuclear gauge
- Failure to use or improper application of standardization tests on a reference block (daily)
- Failure to calibrate for different soil types/moisture (wrong lab proctor value)
- Failure to properly correct for rock content (+ ¾ inch material)
Bottom Line: Strictly follow ASTM guidelines when performing soil tests to achieve accuracy.
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IBC Chapter 18, Section 1804.6 Compacted Fill Material
Where shallow foundations will bear on compacted fill material, the compacted fill shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803. (Note that the CODE invokes the geotechnical report and the provisions of the report and thereby makes those geotechnical report provisions enforceable as CODE.)
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For more information or further enthusiastic discourse on topics of CODE, please contact Alan Tuck at: [email protected] or 540.344.7939.
