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APPENDIX 8: XERXES PRIMARY BACKFILL REQUIREMENTS B7.GENERAL number 6 of rounded stones,for example,20-55 percent of the sam- B1.1.The backfill material surrounding an underground storage ple(measured by weight)should pass through a 1/2-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 ment 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 B1.2.The Xerxes Installation Manual specifies that select rounded Xerxes'requirements but are not identified by a standard coarse stones or crushed stones are to be used as primary backfill material. aggregate size number.The supplier should be able to provide a B1.3.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. 62.4.1.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 then be compared B1.5.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 materi- shown in table Bl-1. als have no problems meeting the hardness requirement. B3,ROUNDED STONES 81.5.1.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 over time. mix of rounded particles,sizes between 1/8 inch and 3/4 inch. B2.ACCEPTABLE BACKFILL MATERIALS B3.2.The rounded stones must conform to the specifications of 82.1.Coarse aggregate is a technical tens for the material(rounded ASTM C 33,sizes 6,67 or 7. stones and crushed stones)that meets Xerxes'backfill size requirements. 83.3.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 gradation re- B2.3.TABLE 61-1 gives the standard sizes of coarse aggregate that quirements are larger than allowable crushed stones. meet Xerxes'backfill material specifications for rounded stones 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. 84,2.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 82.3.1.The percentages give an indication of the particle size distribu- about specifications. tion or gradation within a given aggregate size.With aggregate size TABLE B1-1 —Percent of Stones Passing Through Sieve by Sieve Size Rounded Stones 40, Crushed Stones ASTM C 33 #6 Stone #67 Stone #7 Stone ASTM C33 #7 Stone #8 Stone Size# Size# 1 inch o 1 inch ___ ___ Sieve [25 mm] 100 /0 100% --- 125 mm] Size 3/4 inch 3/4 inch [19 mm] 90-100% 90-100% 100% [19 mm] 100% --- 1/2 inch1/2 Inch [12.5 mm] 20-55% --- 90-100% 90-100% 100% [12.5 mm] 3/8 inch 0-15% 20-55% 40-70% 3/8 inch 40-70% 85-100% 19.5 mm] 19.5 mm] No.4 No.4 .0187 inch 0-5% 0-10% 0-15% .0187 inch 0-15% 10-30% 14.75 mm] [4.75 mm] No.8 No.8 .094 Inch --- 0-5% 0-5% .094 inch 0-5% 0-10% [2.38 mm] [2.38 mm] 28