IE Circular No. 81-08, Foundation Materials
SSINS No.: 6830
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C, 20555
May 29, 1981
IE Circular No. 81-08: FOUNDATION MATERIALS
Description of Circumstances:
Insufficient compaction of foundation and backfill materials during the
construction of nuclear plants has resulted in excessive settlement of plant
structures at a number of sites.
At the Midland Plant, Units 1 and 2, insufficiently compacted backfill was
discovered as a result of excessive settlement of the diesel generator
building. The results of extensive subsurface investigations subsequent to
settlement of the diesel generator building identified that fill materials
beneath portions of the auxiliary building, feedwater isolation valve pits,
essential service water intake structure, borated water storage tanks, and
plant area utilities were not compacted to specification requirements.
Other specific nuclear power plant sites and identified problems are listed
to illustrate the extent of the problem.
North Anna Service water pumphouse settlement
Summer Service water pumphouse settlement
Shearon Harris Inadequate moisture control in fill material
Cherokee Inadequate field density control and soils tests
Hatch Inadequate QC procedures and fill placement
Vogtle Inadequate compaction, groundwater, and soil
South Texas Inadequate QC procedures and inspection
The above problems necessitated extensive remedial work; for example,
removal of large quantities of fill material, underpinning structures,
surcharging foundation materials, project delays, extensive reanalysis, and,
in some cases technical specification requirements pertaining to settlement
monitoring during plant operation.
The causes of insufficient compaction were investigated by NRC,
licensees/construction permit holders, contractors and architect-engineering
firms. Based on these investigations, the various contributing causes were
found to include the following:
1. Soil selection, fill, and compaction activities were not accomplished
under the direction of a qualified geotechnical engineer.
May 29, 1981
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2. Compaction equipment was not qualified to achieve the required
compaction using the material specified, lift thickness, moisture
control, equipment speed, or number of equipment passes.
3. Procedures for control of soil testing were not adequate to assure
correct soil identification, selection of laboratory standards, and
control of field density tests.
4. Relative density and percent compaction test results fell outside the
theoretical limits, indicating an unrealistic comparison of laboratory
and field density tests.
5. Soils inspections did not verify controls specified in construction
6. Quality assurance audits did not identify the procedural inadequacies
or the cause of repetitive nonconforming conditions.
7. Design requirements were not properly translated into construction
8. Design change notices were not issued to reflect changes of
construction specification requirements.
9. Settlement calculations based on actual design bases (i.e. , load
intensity, index of soil compressibility, and type of foundation) were
Recommended Action for Construction Permit Holders:
1. For those facilities with ongoing soils work activities, verify that
quality assurance and quality control measures including procedures,
test results, inspection personnel and audits are implemented to assure
that the causes identified above do not exist for the soils work in
progress or planned.
2. For those facilities with completed soils work activities that have a
settlement monitoring program in effect, verify that the measured
settlement values are within the projected values. In the event the
measured settlement values exceed projected values, it is recommended
that an investigation to determine the cause be initiated. In those
cases, an evaluation which includes soil borings may be in order.
3. For those facilities with completed soils work activities that do not
have an ongoing settlement monitoring program, verify that the quality
assurance and quality control measures described in item 1 above were
in, effect during construction.
May 29, 1981
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Although no specific response is required by this circular, soil compaction
construction deficiencies identified and corrective actions initiated as a
result of the actions recommended may be reportable in accordance with the
requirements of 10 CFR 50.55e.
If you need additional information regarding this matter, contact the
Director of the appropriate Regional office.
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