IE Circular No. 81-08, Foundation Materials

                                                          SSINS No.: 6830  
                                                          Accession No.:   
                                                          IEC 81-08        

                               UNITED STATES 
                           WASHINGTON, D.C, 20555 

                                May 29, 1981 


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 
                         erosion controls 
     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. 

                                                            IEC 81-08     
                                                            May 29, 1981  
                                                            Page 2 of 3   

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 
     not performed. 

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. 

                                                            IEC 81-08     
                                                            May 29, 1981  
                                                            Page 3 of 3   

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. 

Recently issued IE Circulars 


Page Last Reviewed/Updated Tuesday, September 01, 2015