Tech Sheet Detention • Retention • Water Quality A division of Porosity of Structural Backfill Tech She et # 1 November 2012 General: StormTech advises tha t a porosity of 40% is appropria te to use for the storage capaci ty o f str uct ural aggregate used in the bedding and embedmen t zones around St ormT ech chambers . This memo provides technical sup por t for the use of a porosity of 40%. The major points of t he memo are: • 40% po rosity is approp ria te for the clean , op en graded , angular aggregate material StormTech recommend s for foundation and embedment. • Most of the porosity data available is ba sed on a compacted condition. St ormTech requires compaction of the fou ndation (be dding) and allows dumped aggre gate embedment around the chambers. • Test da ta indicates that the average po rosity of all gradation s of the co mpacte d foundation is approxim ately 40%. The porosity of the dumped backfill in the embedment zone is ty pi call y grea ter than 40% and the cal culated weigh ted average porosity the refore exc eeds 40% for ty pi cal St ormT ech syst ems. • Porosity is protec ted from soils migration by a non-wove n geotex tile tha t surrou nds the en tire system. For some exf il tra tion syst em s, a draina ge ne t is subst ituted for the geotextile on the bottom of the bed. Terms: Porosity (n) is defined as the volume voids over the total volume expressed as a percent: n = (V v / V t) x 100%. Other terms commonly used to describe porosity include; “voids” and “void space”. A related term that should not be confused with porosity is void ratio (e) which is the volume of voids over the volume of solids expressed as a decimal: e = V v / V s. Compilation of Known Test Data: Sample Da ta S ource Porosity Bulk Densit y Test / Desc riptio n AASH TO # 4 Storm Tech lab 39 .9% 94 .3 lbs/f t 3 dumped, correc ted 1 AAS HTO # 57 St orm Tech lab 45 .4% 87 .2 lb s/f t 3 dumped, correc ted 1 AAS HTO # 4 St orm Tech lab 37 .4% 103.0 lb s/f t 3 jigged & t amped, c orr ected 1 AAS HTO # 57 St orm Tech lab 38 .7% 97 .7 lb s/f t 3 jigged & t amped, c orr ected 1 AASH TO # 57 NTH lab 50 - 51% tapped & agitated, dried 2 AASH TO # 57 NTH lab 50 - 52 % tapped & agitated , dried 2 AASH TO # 3 NTH lab 53 - 54% tapped & agitated, dried 2 -1 ½” Anders on E ng . Cons. 41 .9% 96 .8 lb s/f t3 dry rodded, C29 3 -1 ½” Anders on E ng . Cons. 35 .3% 101.7 lb s/f t3 dry rodded, C29 3 -1 ½” Anders on E ng . Cons. 37 .8% 98 .6 lb s/f t3 dry rodded, C29 3 -1 ½” Anders on E ng . Cons. 41 .3% 93 .6 lb s/f t3 dry rodded, C29 3 -1 ½” Anders on E ng . Cons. 38 .2% 98 .7 lb s/f t3 dry rodded, C29 3 -3/4” Ande rs on E ng . Cons. 38 .5% 100 .3 lb s/f t3 dry rodded, C29 3 -3 /4” Anderson E ng . Cons . 38 .9% 97 .9 bs/f t 3 dry rodded, C29 3 70 Inwood Road Suite 3 Rocky Hill, CT 06067 Toll Free 888-892-2694 Fax 866-328-8401 www.stormtech.com Page 2 of 2 Compilation of Known T es t Da ta: Tech She et # 1 Sample Da ta S ource Porosity Bulk Densit y Test / Desc riptio n AASHTO # 4 Universal Eng. Serv. 44.3% 78.6 lbs/ft 3 rodded C29 4 AASHTO # 57 Universal Eng. Serv. 43.2% 79.8 lbs/ft 3 rodded C29 4 AASHTO # 4 Universal Eng. Serv. 46.1% 70.8 lbs/ft 3 rodded C29 5 AASHTO # 57 Universal Eng. Serv. 42.8% 74.8 lbs/ft 3 rodded C29 5 -1 ½” Crushed Ro ck CTL T ho mpson TX 46% 90 .5 lb s/f t 3 rodded C29 6 -1” Crushed Rock CTL T hompson TX 45% 91 .6 lbs/f t 3 rodded C29 6 -1 ½ ” Crushed Conc CTL T hompson TX 48% 77 .1 lb s/f t 3 rodded C29 6 1Testing was conduct ed by StormTech in October, 2003 usin g aggregate fr om Connecticut . Water was used to fill voids and a correction factor that reduced porosi tie s by 3 to 16% was calcula ted and applied to correc t for wall eff ects of the t est container . 2Testing was conducted by NTH Consultants,Ltd. Exton, PA in December, 2002 for ADS. Thi s wa s dry test ing in acc ordance wi th the “Ci vil Engineering Re feren ce Manual, Sixt h Edition” by Michael R. Lindburg, PE. 3Testing was conducted by Anders on Engineering Consultants, Inc., Li ttle Rock, AR in Feb rua ry, 2000 f or 7 di fferen t aggregate s amples fr om f ou r s uppliers in Arkan sas. 4The material test ed wa s li me rock fr om cen tral Flo rida. Test in g wa s conducted by Universal Engineering Sciences in Orlando, F L in Novemb er, 2005. 5The material tested was recycled, crushed concrete from central Florida. Testing was condu ct ed by Univer sal Engineering S cience s in O rlando, F L in Novem ber , 2005. 6Tes ting was condu ct ed by CTL | T hompson T exas, LLC in A ugust, 2006. AS TM C2 9 is the “S tandard Tes t Me thod for Bulk Densi ty (Uni t Weight) and Voids in Aggregate” . Po rosity References: • “Urban Ru noff Quality Management” WEF MOP 23 / ASCE MOP 87. Table 5.1 2 li st s uniform s ized gravel at 40%. • “Controlling Urban Runoff: ” by Thoma s R. Schu eler, Jul y 19 87 de sc ribes storage volume of the void space in the tre nch at 40% of the excava ted trench volume. • “On-site Stormwater Management: Applications for Landscape and Engineering” Second E di tion by B ru ce F erguson and T homas Debo st ates t ha t open graded crushed st one has 40% void space. AADSDS 601601 NON-WNON-WOOVVEENN GGEOTEXTILEEOTEXTILE (OR(OR EQQUAL)UAL) AALLLL AAROUNDROUND CCLEAN,LEAN, CRRUUSSHED,HED, AANGULARNGULAR STTONEONE ADS “Terms and Conditions of Sale” are available on the ADS website, www.ads-pipe.com StormTech is a registered trademark of StormTech, Inc. Universal Engineering Sciences is a registered trademark of Universal Engineering Sciences. ©2012 Advanced Drainage Systems, Inc. ST TS1 11/12 70 Inwood Road Suite 3 Rocky Hill, CT 06067 Toll Free 888-892-2694 Fax 866-328-8401 www.stormtech.com.