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APPENDIX B: XERXES PRIMARY BACKFILL REQUIREMENTS B1.GENERAL number 6 of rounded stones,for example,2055 percent of the sam- B1.1.The backfill material surrounding an underground storage ple(measured by weight)should pass through a 112-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. 82.4.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 ;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, a dirt,sand,large rocks,roots,organic materials,debris,ice and snow. 82.4.1. 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 a 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 B1-1. fa als have no problems meeting the hardness requirement. B3.ROUNDED STONES B1.5.1.Materials like soft limestone,sandstone,sea shells or shale 63.1.When using select rounded stones,the material is to be a .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 B2.1.Coarse aggregate is a technical term 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 48 sieve.See TABLEBI-1 for additional information Highway and Transportation Officials(AASHTO)have specifications about specifications. forstandard sizes of coarse aggregate. NOTE:Generally,rounded stones that meet the gradation re- B2.3.TABLE B1-1 gives the standard sizes of coarse aggregate that quirements are larger than allowable crushed stones. meet Xerxes'backfill material specifications for rounded stories and crushed stones.It identifies standard sieve sizes used to grade ag- 114,CRUSHED STONES gregate material.For each aggregate size,the amount of material 84.1.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. B4.2.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 B1-1 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 size.With aggregate size TABLE R1-1 —Percent of Stones Passing Through Sieve by Sieve Size Rounded Stones Crushed Stones ASTM C 33 ASTM C 33 Size# #6 Stone 4t67 Stone #7 Stone Size# #7 Stone #8 Stone 1 inch 100% 100 1 inch --- Sieve --- [25 mm] — — [25 mm] Size 3/4 inch 3/4 inch [19 mm] 90-100% 90-100% 100% [19 mm] 100% — 1/2 inch 20-55% --- 90-100% 1/2 Inch 90-100% 100% [12,5 mm] [12.5 mm] 3/8 inch 3/8 inch [9.5 mm] 0-15% 20--55% 40--70% [9.5 mm] 40-70% 85-100% k No.4 No.4 l' s .0187 inch 0-5% 0-10% 0-15% 0187 inch 0-150/0 10-30 [4.75 mm] [4.75 mm] No.8 No.8 .094 inch ---- 0-5% 0-5% .094 inch 0-5% 0-1011/0 [2.36 mm] [2.36 mm] 28 i? i