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APPENDIX B: XERXES PRIMARY BACKFILL REQUIREMENTS Bt.GENERAL number 6 of rounded stones,for example,20-55 percent of the sam- 61.1.The backfill material surrounding an underground storage de(measured by weight)should pass through a 1P2-inch sieve.And, tank(UST)is a critical part of a proper tank installation.This docu- with aggregate size number 7 of crushed stones,0-15 percent of the mem gives guidelines for choosing the primary backfill material to sample(measured by weight)should pass through a No.4 sieve. use when installing Xerxes fiberglass tanks. B2.4.Some material suppliers may produce materials that meet B7.2.The Xerxes Installation Manual specifies that select rounded Xerxes'requirements but are not identified by a standard coarse stones a crushed stones are to be used as primary backfill material. aggregate size number.The supplier should be able to provide a 131.3.Primary backfill material is to be clean,free-flowing,and free of specification that identifies the size or gradation of the material. dirt,sand,large rocks,roots,organic materials,debris,ice and snow. B2.4.1.If the material supplier is unable to supply a gradation re- B1.4.No backfill material shall be frozen or contain lumps of port,an independent testing laboratory can perform a sieve analy- frozen material at any time during placement. sis on a sample of the material according to the ASTM C 136 testing specifications.The test results can than be compared B7.5.Another important characteristic of good backfill material is against the size requirements for rounded or crushed stones hardness or stability when exposed to water or loads.Most mater- shown in table B74. als have no problems meeting the hardness requirement. B3 ROUNDED STONES B1.5.1.Materials like soft limestone,sandstone,sea shells or shale B3.1.When using select rounded stones,the material is to be a should not be used as backfill because they break down overtime. mix of rounded particles,sizes between 1/8 inch and 3/4 inch. B2.ACCEPTABLE BACIMLL MATERIALS B3.2.The rounded stones must conform to the specifications of B2.1.Coarse aggregate is a technical term for the material(rounded ASTM C 33,sizes 6,67 or 7. stores and crushed stones)that meets Xerxes'backfill size requirements. B3.3.No more than 5 percent(by weight)of the backfill may pass B2.2.ASTM International and The American Association of State through a#8 sieve.See TABLE B1-1 for additional information Highway and Transportation Officials(AASHTO)have specifications about specifications. for standard sizes of coarse aggregate. NOTE:Generally,rounded stones that meet the predation re- B2.3.TABLE B1-1 gives the standard sizes of coarse aggregate that quirements are larger than allowable crushed stones. meat Xerxes'backfill material specifications for rounded stares and crushed stones.It identifies standard sieve sizes used to grade ag- 54•CRUSHED STONES gregate material.For each aggregate size,the amount of material B4.1.When using crushed stones,the material is to be a mix of finer than each laboratory sieve(square openings)is given as a angular particles,sizes between 1/8 inch and 1/2 inch. percentage of the total weight of the sample. 134.2.The crushed stones must conform to the specifications of NOTE:ASTM uses size numbers 6,67,7 and 8 to describe spe- ASTM C 33,sizes 7 or 8. cific gradation profiles for materials that pass through a series of B4.3.No more than 5 percent(by weight)of the backfill may pass sieves.Do not confuse these gradation profiles with sieve sizes. through a#8 sieve.See TABLE B7-1 for additional information B2.3.1.The percentages give an indication of the particle size distribu- about specifications. tion or gradation within a given aggregate sae.With aggregate size TABLE B1-1 —Percent of Stones Passing Through Sieve by Sieve Size Rounded Stones Crushed Stones ASTM C 33 #6 Stone #67 Stone #7 Stone ASTM C 33 #7 Stone #8 Stone Size# Size# 1 inch 1 inch $I@Ve [25 mm] 100% 100 Size 3/4 Inch 90-100% 90-100% 100% 3/4 inch 100% --- 119 mm] [79 mm] 1/2 2 Inch 20-55% --- 90-100% [72�] 90-100% 100% 9SImm]nch 0-15% 20-55% 40-70% 3/br�] 40-70% 85-100% No.4 No.4 .0187 inch 0-5% 0-10% 0-15% .01871nch 0-15% 10-30% [4.75 mm] [4.75 mm] No.8 No.B .094 inch --- 0-5% 0-5% .0941nch 0_5% 0-10% [2.38 mm] [238 mm] 28