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APPENDIX D Split Backfill Guidelines L GENERAL 2.5.Secondary backfill must be compacted to achieve a minimum I.I.Use select rounded or crushed stones for primary backfill material of 85 percent standard proctor density. as specified in the Installation Manual in effect at time of installation, 2.5.1.Do not use rammer-type compactors over the top of the tank. and Appendix C,Primary Backfill Requirements. 2.5.2.Some tank owners may require sample testing and written 2.SPLIT BACKFILL INSTALLATION reports to verify the compaction of the backfill. 2.1.Use the primary backfill material vertically up to at least 75 percent 2.6.Material must be installed in 12-inch[30-cm]to 24-inch[60-cm] of the tank diameter.See Figure D-1. lifts compatible with the compaction equipment used. 2.2.Follow the instructions in section 5 of the Installation Manual on 2.7.In some conditions,frost heave may be encountered when using the placement of this backfill material. secondary backfill.Therefore,consider any frost-related problems that 2.3.Install a layer of geotextile fabric over the entire surface of the may occur. primary backfill material.See section 1 for more information about 2.8.Specifications for secondary backfill material and compaction geotextile filter fabric. above the geotextile fabric layer may be determined by the requirements 2.3.1.All joints in the geotextile fabric should be overlapped of the piping,surface slab or roadway. a minimum of 12 inches[30 cm]. 2.9.Referto applicable codes orstandards for base course 2.3.2.Geotextile fabric must overlap onto the tank and excavation and sub-base course material and compaction requirements. surface a minimum of 12 inches[30 cm]. 2.10.The following are examples of acceptable secondary 2.3.3.Installations with unstable soil may require that the fabric line backfill material: the entire excavation.See section 1 forspecific information about using • clean native backfill geotextile or fabric in unstable in-situ(native)soil conditions. • coarse sand or gravel 2.4.Clean native backfill may be used as secondary backfill material 2.11.100%of all backfill material must pass through a 1-inch sieve. above the geotextile fabric to subgrade. 2.4.1.Secondary backfill material must be clean,free-flowing, and free of large rocks,roots,organic materials,debris,ice and snow.Backfill material shall not be frozen or contain lumps of frozen material at anytime during installation. Figure D-1 Grade or Subgrade Secondary Backfill Material - —IIIII =IIIII IIIII= Filter Fabric With A IIIII= —IIIII Filter Fabric With A Minimum of 12"Overlaps =IIIII IIIII= Minimum of 12"Overlaps IIIII= __ Primary Backfill Material — IIIII IIIII-II II=IIIII =IIIII IIIII- 75%of Tank IIIII—III III—IIIII Diameter —IIIII IIIII IIIII-IIII =—_ 12"Bedding =IIIII- —_—_—_—_— IIIII=IIIII-IIIII=IIIII-IIIII—IIIII=IIIII-IIIII=IIIII -11 II-IIIII= I - IIII=� III-IIIII—IIIII=IIIII= 44