Compaction. Soil Compaction I. What is Consolidation. What is Compaction? Chapter 4 Dr. Talat A Bader

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1 Soil ompaction I hapte 4 alat ade ompaction Soil is used as a basic mateial fo constuction etaining walls, Highways, mbankments, amps ipots, ams, ikes, etc he advantages of using soil ae: 1 Is geneally available eveywhee 2 Is duable - it will last fo a long time Has a compaatively low cost What is ompaction? In most instances in civil engineeing and/o constuction pactice, wheneve soils ae impoted o excavated and eapplied, they ae compacted he tems compaction and consolidation may sound as though they descibe the same thing, but in eality they do not What is onsolidation When a Static loads ae applied to satuated soils, and ove a peiod of time the inceased stesses ae tansfeed to the soil skeleton, leading to a eduction in void atio epending on the pemeability of the soil and the magnitude of the dainage distance, this can be a vey time-consuming pocess ypically applies to existing, undistubed soil deposits that has appeciable amount of clay 1

2 ompaction - onsolidation Pinciples of ompaction ompaction means the emoval of ai-filled poosity onsolidation means the emoval of wate-filled poosity ompaction of soils is achieved by educing the volume of voids It is assumed that the compaction pocess does not decease the volume of the solids o soil gains uncompacted compacted uncompacted compacted Pinciples of ompaction he degee of compaction of a soil is measued by the dy unit weight of the skeleton he dy unit weight coelates with the degee of packing of the soil gains ecall that γ d = G s γ w /(1+e) he moe compacted a soil is: the smalle its void atio (e) will be the highe its dy unit weight (γ d ) will be What oes ompaction o? 1) Inceased Shea Stength his means that lage loads can be applied to compacted soils since they ae typically stonge 2) educed Pemeability his inhibits soils ability to absob wate, and theefoe educes the tendency to expand/shink and potentially liquefy ) educed ompessibility his also means that lage loads can be applied to compacted soils since they will poduce smalle settlements 4) ontol Swelling & Shinking ) educe iquefaction Potential 2

3 (Holtz and Kovacs, 1981; Head, 1992) Vaious ypes of compaction test Geneal ompaction Methods oase-gained soils Fine-gained soils ype of est S ight SM (lb) S Heavy SM (10lb) S Vibation hamme Mould One ite 4 in 6 in One ite 4 in 6 in Hamme mass (kg) to 41 op (mm) Vibation No of layes lows pe laye minute aboatoy Field Vibating hamme (S) Hand-opeated vibation plates Motoized vibatoy olles ubbe-tied equipment Fee-falling weight; dynamic compaction (low fequency vibation, 4~10 Hz) Vibation Falling weight and hammes Kneading compactos Static loading and pess Hand-opeated tampes Sheepsfoot olles ubbe-tied olles Kneading he Standad Pocto est Pocto in the ealy 190 s was building dams fo the old ueau of Watewoks and Supply in os ngeles, and he developed the pinciples of compaction in a seies of aticles in ngineeing News-ecod Vaiables of ompaction Pocto established that compaction is a function of fou vaiables: y density (ρ d ) o dy unit weight γ d Wate content w ompactive effot (enegy ) Soil type (gadation, pesence of clay mineals, etc)

4 he Standad Pocto est quipments Hamme Weight lb op Height h=12 Standad Pocto est o he soil is mixed with vaying amounts of wate to achieve diffeent wate contents o Fo each wate content,the soil is compacted by dopping a hamme 2 times onto the confined soil o he soil is in mold will be divided into thee lifts o ach ift is compacted 2 times o his is don 4-6 times fom dy-wet soil Volume 1/0 ft o 944 cm iamete 4 in o 1016 cm Height 484 in o1164cm soil 2 lows/aye aye o lift # aye o lift # 2 aye o lift # 1 Standad negy ompactive () applied to soil pe unit volume: (# blows/laye)*(# of layes)*(hamme weight)*(height of dop) = Volumeof mold (2blows/laye) * ( of layes) * ( lbs) * (10 ft) = (1/0)ft SP 12,7 / = ft lb ft y ensity (γ d ) esults fom Standad Pocto est Maximum dy unit weight Optimum wate content Wate ontent (w) Optionally, the unconfined compessive stength of the soil is also measued sample fom the mold 4

5 y Unit Weight he compacted soil is emoved fom the mold and its dy density (o dy unit weight) is measued γ d = γ ω 1 V M g d γ m γ + m ω Whee Mg γm = V =y Unit weight =ulk ensity =Wate ontent =otal Soil Volume =otal Wet Soil Mass =Gavitational cceleation Wate ole in ompaction Pocess Wate lubicates the soil gains so that they slide moe easily ove each othe and can thus achieve a moe densely packed aangement little bit of wate facilitates compaction too much wate inhibits compaction ensity (Mg/m ) y Unit Weight ensity as ompacted Incease of ensity due to compaction ensity when compacted dy ensity when compacted y + mass of wate added Incease of density due to mass of wate added Modified Pocto est Was developed duing Wold Wa II y the US my ops of ngineeing Fo a bette epesentation of the compaction equied fo aifield to suppot heavy aicaft Wate content w (%)

6 Modified Pocto est Same as the Standad Pocto est with the following exceptions: ffect of negy on ompaction 2 > 1 he soil is compacted in five layes Hamme weight is 10 bs o 44 Kg op height h is 18 inches o 472cm hen the amount of negy is calculated emembe Standad Pocto negy SP = 12,7 ft lb / ft y ensity (γ d ) Modified = 2 soil # # 4 # # 2 # 1 (2blows/laye) * ( of layes)* (10 lbs) * (10 ft) MP = (1/0)ft MP = 6,20 ft lb / ft MP 6,20 ft lb / ft = = 4 12,7 ft lb / ft SP Wate ontent (w) Standad = 1 ompaison-summay Standad Pocto est Modified Pocto est ommon ompaction uves ncounteed in Pactice Mold size: 1/0 ft 12 in height of dop lb hamme layes 2 blows/laye negy 12,7 ft lb/ft y ensity (γ d ) Mold size: 1/0 ft 18 in height of dop 10 lb hamme layes 2 blows/laye negy 6,20 ft lb/ft Modified = 2 Standad = 1 Wate ontent (w) y unit weight γ d ell-shaped ouble-peaked One & one-half peaks Odd-shaped Wate content (w) 6

7 Holtz and Kovacs, 1981 y density ( Mg / m ) ine of optimums Zeo-i-Void egee of Satuation egee of Satuation 60% 80% Modified Pocto Standad Pocto 100% "Zeo i Voids" Wate content w (%) Points fom the ZV cuve can be calculated fom: γ dy = G s γ ω / 1+ e ZV:he cuve epesents the fully satuated condition (S=100%) ZV cannot be eached by compaction ine of Optimum: line dawn though the peak points of seveal compaction cuves at diffeent compactive effots fo the same soil will be almost paallel to a 100 % S cuve ntapped i: is the distance between the wet side of the compaction cuve and the line of 100% satuation y density ( Mg / m ) Zeo-i-Void egee of Satuation egee of Satuation 60% 80% Modified Pocto Standad Pocto 100% "Zeo i Voids" Wate content w (%) he quation fo the ZV cuves with diffeent degee of satuation is : ρws ρws ρd = = ρw S w + S w + ρs Gs You can deive the equation by youself, Hint ρs ρd = 1+ e Se = wg ack s Holtz and Kovacs, 1981 elow w omc y of Optimum s the wate content inceases, the paticles develop lage and lage wate films aound them, which tend to lubicate the paticles and make them easie to be moved about and eoiented into a dense configuation Hamme Impact i expelled fom the soil upon impact in quantities lage than the volume of wate added esults-xplanation y ensity (γ d ) t w omc he density is at the maximum, and it does not incease any futhe y Side OM y side Wet Side Wate ontent (w) scaping ai ntapped ai Wet side bove w omc Wet of Optimum Wate stats to eplace soil paticles in the mold, and since ρ w <<ρ s the dy density stats to decease Hamme Impact Moistue cannot escape unde impact of the hamme Instead, the entapped ai is enegized and lifts the soil in the egion aound the hamme Holtz and Kovacs, 1981; as, 1998 ffects of Soil ypes on ompaction he soil type-that is, gain-size distibution, shape of the soil gains, specific gavity of soil solids, and amount and type of clay mineals pesent y density (Mg / m ) Zeo ai voids, S= 100 % Wate content w (%) 8 7 NO Soil textue and Plasticity data esciption Well gaded loamy sand Well gaded sandy loam Med gaded sandy loam ean sandy silty clay ean silty clay oessial silt Heavy clay Pooly gaded sand Sand Silt lay NP PI NP NP NP 7

8 (inceasing) ensity ypical ompaction uve fo ohesionless Sands & Sandy Gavel i dy bulking omplete satuation (inceasing) Wate content he low density that is obtained at low wate content is due to capillay Foces esisting aangements of the sand gains Wate & ompaction emembe what is the ffect Inceasing the wate content at which soil is compacted: Inceases the likelihood of obtaining dispesed soil stuctue with educed shea stengths Inceases the poe pessue in the soil, deceasing the shot tem shea stength ambe and Whitman, 1979 Wate ole in ompaction Pocess Wate lubicates the soil gains so that they slide moe easily ove each othe and can thus achieve a moe densely packed aangement little bit of wate facilitates compaction too much wate inhibits compaction y ensity Stuctue of ompacted lay Flocculated Stuctue o Honeycomb Stuctue o andom Intemediate stuctue High ompactive ffot ow ompactive ffot Wate ontent ispesed Stuctue o paallel 8

9 Fom ambe and Whitman, 1979 ffect of Stength Samples (Kaolinite) compacted dy of optimum tend to be moe igid and stonge than samples compacted wet of optimum y unit weight (kn/m ) Molding wate content (%) eviation stess (kn/m 2 ) egee of satuation=100% xial Stain (%) egee of Paticle Oientation Paal 20 andom Molding wate content (%) Holtz and Kovacs, 1981 Unsoaked (%) y density (lb/ft ) ffect of Stength (con) blows / laye 26 blows / laye 12 blows / laye 06 blows / laye 1 20 Wate content (%) 2 10 lb hamme 18 dop (modified pocto) he (alifonia beaing atio) = esistance equied to penetate a -in 2 piston into the compacted specimen/ esistance equied to penetate the same depth into a standad sample of cushed stone geate compactive effot poduces a geate fo the dy of optimum Howeve, the is actually less fo the wet of optimum fo the highe compaction enegies (ovecompaction) Fom ambe and Whitman, 1979; Holtz and Kovacs, Pemeability 10 9 ensity ffect of ompaction on pemeability Wate content Pemeability at constant compactive effot deceases with inceasing wate content and eaches a minimum at about the optimum If compactive effot is inceased, the pemeability deceases because the void atio deceases Fom ambe and Whitman, 1979; Holtz and Kovacs, 1981 Void atio, e ffect of ompessibility y compacted o undistubed sample Wet compacted o emolded sample 0 Pessue, natual scale ow pessue consolidation Void atio, e y compacted o undistubed sample Wet compacted o emolded sample ebound fo both samples 0 Pessue, log scale High-pessue consolidation ompessibility of compacted clays is function of stess level ow stess level: lay compacted wet of optimum ae moe compessible High stess level: he opposite is tue 9

10 Holtz and Kovacs, 1981 ffect of Swelling Swelling of compacted clays is geate fo those compacted dy of optimum hey have a elatively geate deficiency of wate and theefoe have a geate tendency to adsob wate and thus swell moe Highe Swelling Potential y ensity (γ d ) y Side OM Wet Side Wate ontent (w) Highe Shinkage Potential y density ( Mg / m ) ompaction and Shinkage y of OM Wet of optimum optimum Kneading Vibatoy Static S = 100% Molding wate content (%) samples compacted wet of optimum have the highest shinkage egend Kneading compaction Vibatoy compaction Static compaction Popeties ngineeing Popeties Summay y side Wet side Stuctue Moe andom Moe oiented (paallel) Pemeability Moe pemeable ompessibility Moe compessible in high pessue ange Moe compessible in low pessue ange Swelling Stength Swell moe, highe wate deficiency Highe *Shinkage moe 10