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APPENDIX C: XERXES SPLIT BACKFILL INSTRUCTIONS Cf.GENERAL C2.5.Secondary backfill must be compacted to achieve a mini- C1.1.Use select rounded or crushed stones for primary backfill mum of 85 percent standard proctor density. material as specified in the Xerxes Installation Manual in effect at C2.5.1.Do not use rammer-type compactors over the top of the time of installation,and the Xerxes APPENDIX B(and supplement), tank. Primary Backfill Requirements. C2.5.2.Some tank owners may require sample testing and written C2.SPLIT BACKRLL INSTALLATION reports to verify the compaction of the backfill. C2.1.Use the primary backfill material vertically up to at least 75 C2.6.Material must be installed in 12-inch to 24-inch lifts compat- percent of the tank diameter.See FIGURE Cl-1. ible with the compaction equipment used. C2.2.Follow the instructions in SECTION 6 of the Installation C2.7.In some conditions,frost heave may be encountered when Manual on the placement of this backfill material. using secondary backfill.Therefore,consider any problems that C2.3.Install a layer of geotextile fitter fabric over the entire surface may occur. of the primary backfill material.See SECTION 9 for more informs- C2.8.Specifications for secondary backfill material and com- tion about geotextile fitter fabric. paction above the filter fabric layer may be determined by the re- C2.3.1.All joints in the fitter fabric should be ovedapped a mini- quirements of the piping,surface slab or roadway. mum of 12 inches. C2.9.Refer to applicable codes or standards for base course and C2.3.2.Geotextile fabric must overlap onto the tank and excava- subbase course material and compaction requirements. tion surface a minimum of 12 inches. C2.10.The following are examples of acceptable secondary back- C2.3.3.Installations with unstable soil may require that the fabric fill material: line the entire excavation.See SECTION 9 for specific information C2.10.1.clean native backfill about using geotextile filter fabric in unstable-soil conditions. C2.10.2.coarse send or gravel C2.4.Clean native backfill may be used as secondary backfill ma- C2.11.One hundred percent(100%)of all backfill material must terial above the geotextile fabric to subgrade. pass through a 1-inch sieve. C2.4.1.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 any time during installation. FIGURE G1-1 —Split Backfill Installation Grade or subgrade Secondary backfill Y material III IIII IIII Filter fabric with a III minimum of 12" overlaps IIII III IIII -III IIII ith IIII =III IIII= IIII IIII (-III 75% of tank diameter Primary backfill IIII y -IIII 11 =III material IIII= = 12" bedding Jill=Jill=Jill = Jill = Jill- IIII-IIII - III 29