14 Compaction of Soils ae 14.1. INTRODUCTION compaction means _pre Con Te ee Pees the soi parle close to each other by mechanial methods. Air during Poaiaition of eich mace a eee Space in the soil mass and, therefore, the mass density is increased. 0 improve its engineering properties. Compaction generally increases the shear strength of the soil, and hence Econ ain ane ee the subity and bearing capacity. It is also useful in reducing the ipaction is an entirely different i following basic differences reduction in the volume. t process than consolidation discussed in chapter 12. It is important to between the two processes, even though both the processes cause a 1) Consolidation i @) ae ar oe eae Process of reduction of volume under sustained, static loading; whereas Process of reduction of volume by mechanical means such as rolling, tamping and vibration. Q) Consolidation causes a reduction in volume of a saturated soil due to squeezing out of water from the soil; whereas in compaction, the volume of a £ . s © Partially saturated soil decreases because of ulsion of air from the voids at the unaltered water content (Fig. 14.1) 2 C ts IZ (a) COMPACTION (b) CONSOL!DATION Fig. 14.1 (3) Consolidation is a process which occurs in nature when the saturated soil deposits are subjected to ‘Static Toads caused by the weight of the buildings and other structures. In contrast, compaction is an artificial process which is done to increase the density (unit weight) of the soil to improve its properties before it is Put to any use. Compaction of soil is required for the construction of earth dams, canal embankments, highways. Tunways and in many other engineering applications. This chapter deals with various methods of compaction and their effects on the engineering properties of the soil. Various other methods of site improvement are also discussed. Stabilisation of soils is discussed in chapter 15, For ground improvement, see chapter 33DATION ENGINEERING sott, MBCI y tion tests ar compaction tests are se he field, COM : 142, STANDARD PROCTOR TEST emer ont regis ne 0H Coen andthe ra the amount of compaction andthe wet COMET TA peiween Me PN ned from the esis provide naximum me soil in the laboratory. The te Jey density | The water content at which the ™ ry done ot UN ary dtasily reaionships provided by the 16. Proctor (1938) used a standard mould ae ais now pelty of 1/30 cubic foot, The moukd had a detachable MS TS cach ayer 5 blows Sounds rammer el ah a height of 12 inches. Ac 6 $55 pounds rammer falling through a helgt ee... a enna Ch » specifications as in Standard pe Mes g720 (hart Vit) reconimends essay the same SPECINTTATE F149 mm diameter, 127.3 mm some minor modifications and metrfication, The mould recommes fe neight of 4.6 inches, movable collar of 2 inches OG eas given 25 blows of or and an effectiv yebes internal diamel J of 4 inches inl ne 4S On Cotter J-three (vgs brozed on. 4 Pins to form catch for collar 362m [535mm 1 —Mouid Isom Bese plate: Siar Rommer- (2) Fig, 142. Standard Proctor Test.) height and 1000 ml capacity [Fig. 14.2 (@)}. The mammer recommended is of 2.6 kg mass with a free drop of 310 mm and a face diameter of 50 mm. The soil is compacted in three layers. The mould is fixed to a detachable base plate. The collar is of 60 mm height. Ifthe percentage of soil retained on 4.75 mm sieve is more than 20%, a larger mould of internal diameter 150 mm, effective height of 127.3 mm and capacity 2250 ml is recommended. Procedure. About 3 kg of air-dried, pulverised soil passing 4.75 mm sieve is taken. Water is added to the soil to bring its water content to about 4% if the soil is coarse-grained and to about 8% if it 8 ined. The water content should be much less than the expected optimum water content (Table 14.1) The Soil is mixed thoroughly and covered with a wet cloth and left for maturing for about 15 10 30 minutes. ‘Table 14.1. Range of Optimum Water Content Sand Sandy silt or silty sand Silt Clay 6 to 10% 8 10 12% 12 0 16%. 14 to 20% a ‘The mould is cleaned, dried and greased lightly. The mass of the f mK ° empty mould with the base plate, bul without collar, is taken, The collar is then fitted to the mould. The mould P clceed nis oll! base and fied with fully matured soil to about one-third'its height. Mhe soil is compacted by 25 blows of the rammer, withCOMPACTION OF SOILS 11 of 310 mm, 2 Tee blows are ee “aie 21S required for the bigger mould of 2250 mi capacity is 56 instead ‘econd layet is placed, Phen uted over the surfase, The ee Jpefore the Ie mi face. The soil surface is scratched spatula! by 25 blows. Likewise, the tira ie leo about twothids Rg wi he ol and compact aga oie UI 10 te clr By "more Thon 9 ind Compacted. The third layer should project above the 199 ‘The collar is rotated to bre: peat cenoveds and the Solis tamer ia peu ie the soil in the mould and that in cotlar. The collar is then i top of the iid. E and the compacted soil is taken, and thus the mass of ies te mould. The niass of the mould, base plate xi] s computed from the mass of the ea sclon ane ‘SDmpacted soil is determined, The bulk density of the Represeniatve Soil samples are tase the volume of the mould. er ‘ he bottom, mi ‘i ter content. The dry density is, : fom, middle and top of the mould for determining the wat Sompvted from the bulk density and the water content. ‘ Bulk mass density, M © = 5 em/ml 4.1) sphere — muss OF compacted soil (gm), =, volume On Ce eM (my. Dry density, py = —2— 1 where w is the water content, wand, More water is added to the : ae intent by 2 10 3%. It is a r is added to the soil So as 10 increase tne water 00 2 fo 8%: It 3s thoroughly mixed and allowed to mature, The testis repeated and the dry snciyg te ‘waler content are determined. pet a A compaction curve is plotted between the water content as abscissa and the corresponding cry densitX.as ordinate (Fig. 14.3), It is observed that the dry density initially increases. with sq inorease in water content till the maximum density 95 is attained. With further increase in water content, ‘ fie dry density decreases. The water content corresponding 10 the maximum dry density is known as 1$0| the optimum water content (O.W.C.) or the optimum ‘moisture content (O.M.C.). ‘Ata water content lower than the optimum, the soil is rather stiff and has Iot of void spaces and, therefore, ‘the dry density is low. As the water content is increased, ‘he soil particles get lubricated and slip over each other, ‘ani move into densely packed positions and the dry density is increased. However, at a water content more than the optimum, the additional water reduces the dry ‘deasly, a8 it occupies the space that might have been ‘cccupied by solid particles, as further explained in Sect. 30 - 195} Ua) moe \=—=Zero -cie void (100 Soturation tine 140 Dry density (am/mi) @ given water content, theoretical maximum GIy, (PA)icomax » 18 Odtained corresponding to the "condition when there are no air voids (ie. degree of saturation is equal to 100%). The theoretical maximum “dy density is alS0 known as saturated dry density (p_);q- In this condition, the soil becomes saturated by “wéection in air voids to zero but with no change in water content, The soil could also become saturated by ‘iiceasing the water content such that all air voids are filled: As we are interested in the dry density “Bien water content, the latter case is not relevant here, An-expression for the theoretical maximum density ‘eloped below. From the equations developed in chapter 2, the dry density (p,) is expressed as Fig. 143. Compaction Curve.(GINEERING poUNDATION sou. MECHANICS ANP Foun 360 GPw Pte Te Gow Ase = wG/S, ee curs when S = 100%. E ‘The theoretical maximum dry density 0 Gp. ltwG t may be mentioned that compaction methods never becomes fully saturated. Thus, the theoretical pevttated from Eq, 14.4 for any value of w if the value of G is cavimum dry density can be ploited along with the compaction cury®> oe ee igs, and. therefore, the soll aaotaiove atin 1a Can be js only bypet Le on tie Tine indicating the theoretical es shown in Fig, 143. It is also known in, For example, for S fs zero air void line or 100% saturation line, nace Likewise, the lines for other degrees of saturation, say 80%, 90% etc. can = 90%, Eg. 14.3 becomes - (145) Pa EanG70o0) ere) metimes more convenient sprees of saturatton, its Instead of drawing lines eomespenting vo diferent deuress 9° MONT ons developed ene. to draw lines corresponding to different percentage air vol (=n) G Pw T+wG (14.6) Pu For theoretical maximum density, 1, = 0. Therefore, Ge (PAineamax = Te wG (same as Eq. 14.4) ‘Thus, the zero-air void line and 100% saturation line are identical. i The lines for other percentages of air voids, such as 10%, 20% etc. can be drawn. For example, for 10% air voids, Eq. 14.6 gives py ea ee (147) Tew It may be noted that 10% air-void line and 90% saturation fine are not identical The water content at which the soil is compacted in the field is controlled by the value of the optinin water content determined by the laboratory compaction test. The amount fof compaction in the field should be | approximately. equal to thal in (he laboratory, The standard Proctor test described above is adequate to remesent the éompaction of fils behind retaining walls and in highways and earth dams where light rollers ire used. Th such eases, the optimum water content obtained from the standard Proctor test can be uscd 3s 2 srnirol efilerion, However, in situations where heavier compaction is required, for example in’ modem highways and tunwaysethe standard Proctor test does not represent the equivalent compaction in St Taborstory. For such conditions, the modified Proctor ‘est, as deseribed in the following section, is used {0 + represent the compaction in the field (See Chapter 30, Sect, 30.18 for the laboratory experiment). 14.3. MODIFIED PROCTOR TEST “The modified Proctor test was developed to represent heavier compaction than that in the standard Proctor test. The test is used to simulate the field conditions where heavy rollers are used. The (est was standardised by the American Association of State Highway Officials and is, therefore, also known os modified AASHO-test. The Indian Standard Codes » 2720 (Part VIII) gives the specifications for heavy compaction based on this test.COMPACTION OF SOILS Pimsriici Secs. 261 ; te rammer used iS Much heavier arg N¢ MOU Use is the same asi ‘ eb kg and the free drop is 450 mm. is A greater drop ces sina. standard Proctor etal Hoyerth Eompated in FN6 eGua layers, each ers ame 50 mm a ee re eae i, measured in kI/ny S. each layer is giver st Ps The soil | 8 erion i atained, 1 Lb Abou. 4.56 Uns Tee ee ee modified Prost in octor test, Thus, @ much be (Compactive effort i or percentage of ne Paco: ten = 2700 aA OS I ene imemal diameter, effective hergaed O78 4.75 mm sieve is more th ake aan Ye Mnired for each layer. The rest of tha ice ane Saat note an20 arene ‘mould of 150 mm ed fa ac et Ts fe of te orcea 1 ES : in the ae sows the compaction curve tar stel fifferent water contents and the eompaciion curve is drawn, Fig. 144 Modified Proctor test (curve No, 2). ‘The curve is higher than and to the jeft of that obtained from a standa maximum dry density but indard Proctor test (curve no. 1). The heavier compaction increases the 209 decreases the optimum water content. The percen- tage increase of the dry ve density is between 3 to 18% for most soils; the percen- fage increase is more for clayey soils than for the sandy soils Fig. 14.4 also shows the zero ait-void line. Tt may be | noted that the maximum dry density attained even in the ‘modified Proctor test is zs ower than the theoretical Bena density indi Woter content (*e)—e cated by the zero air-void Tine. The line of optimums shown in the figure joins the points indicating the maximum dry density. Tt is roughly parallel to the zero ait-void line. COMPACTION OF SANDS he compaction curves shown in Fig, 14.3 14.4 are obtained for soils which contain at me percentage of cohesive soils, In case of sandy soils, the effect of water content on ‘density is not well defined when the water Lis below the optimum value. There is a fering of the points on the compaction Generally, the dry density decreases with se in the water content in this range (Fig dry density decreases due to capillary pore water. The capillary tension resists ney of soil particles to take a dense state the volume increases. The phenomenon f nas the bulking of sand. The maximum epee Fe occurs at a water content of about 4 to ii further increase in the water conlent Fig 145. Campaction Curvee for Cohesiontess Sot Ua) Stendars proctor test Modes proctor test \ — tere oF vod tine Cs) es Dry density. (grind Fig. 14.4. Compaction Curves of Standard Proctor Test and Modified Proctor Test uN saturation Air ry Dey density tqm/ml) ——ee 32 coll, MECHANICS AND FOUNDATION ENGINEERING and take a closer the dry density increases as the meniscus is destroyed and the particles are able to shift ES ree packing, The maximum dry density occurs when the soil is fully saturated. If the water comet Ty oy beyond this point, the dry density again decreases, The coarse- grained soils do not adsor> wal ‘amenable 10 lubrication. These do not display a distinct optimum water content. rege: For sandy soils, the compaction curve is of Litle practical use. For such soils, the Folate SoM r discussed in chapter 3, is used as a criterion for measurement of compactness (or denseness). Tne ¢1¥ TAT of the sand is measured in the embankment and iis relative density 1s determined if the dry densits oosest and densest states are known, 145. JODHPUR MINI COMPACTOR TEST yea The Jodhpur Mini Compactor test was developed by Prof. Alam Singh (1965). small mould of Sn diameter 70.8 rim (cross. sectional area = 5000 mm?) effective heignt 60 mm and 2 capacity of 300ml is used. The rammer used is of 2.5 kg mass and is known as the dynaroie ramming tool (DRI). The mass secs down a stem through a height of 250 mm and falls over a foot of 40 mm diameter and 75 mm height 0 compacts the soil. The test 38 suitable for both fine-grained soils and coarse-grained soils (minus 4.75 mm siewe). The procedure for conducting the test is similar to that in the standard Pi compacted only in 2 layers. Euch layer is compacted by 15 blows of the dynam: distributed over the soil Surface. The compactive effort is approximately equal to that obtained in Proctor tes. It is claimed that the optimum water content and the dry density obiained in the test are almost ‘equal to that in the standard Proctor test, It is recommended that, for fine- grained soils, a fresh soil sample shall be taken for each lest after allowing a suitable maturing time. 14.6. HARVARD MINIATURE COMPACTION TEST In Harvard miniature compaction test, compaction is done by the kneading action of a cylindrical tamping foot of 0.5 inch (12.7 mm) diameter. The tamping foot operates through a pre-set compression spring to give the tamping force to a predetermined value, The mould used is of 1; inch (33.34 mm) diameter and of effective height of 2.816 inch (71.53 mm). The capacity of the mould is 1/456 cubic foot ( = 62.4 ml), ‘The number of layers, the tamping force and the number of tamps per layer are selected depending upon the type of the soil and the amount of compaction required. 14.7. ABBOT COMPACTION TEST In the Abbot compaction test, a metal cylinder (mould) of 5.2 em internal diameter and 40 cm effective height-is used, The cylinder is clamped to the base, The soil is taken in the cylinder and compacied by a 2.5 kg rammer having a circular face of 5 cm diameter. The rammer is lifted up and dropped inside the cylinder through Height of 35 cm above the base. FACTORS|AFFECTING COMPACTION 1 dry densityiof the soil is increased by compaction. The increase in the dry density depends upon the following factors : (1) Water Content. Ablow water content, the soil is stiff and offers more resistance to compaction. As the water content is increased) the soil particles get lubricated. The soil mass becomes more workable and the particles have closer packing, The,dry density of the soil increases with an increase in the water content till the optimum water content is reached, At that stage, the air voids attain approximately a constant volume. With further increase in water content)the air voids do not decrease, but the total voids (air plus water) inerease and the dry density decreases. Thus the higher dry density is achieved upto the optimum water content due to forcing air out from the Soil Voids. After the optimum water content is reached, it becomes more difficult to force air out and to further reduce the air voids. ‘The effect of water content on the dry density of the soil can also be explained with the help of electrical double layer theory (chapter 6). At low water content, the forces of attraction in the adsorbed water layer are roctor test, but the soil is jc ramming tool uniformly the standard . $eCOMPACTION OF SOILS 38 i there is more anger 208 Tesistance to geal double 1ye¢ expands ant tye MOVERS Of the panicle: As te wate content nee te ia ye ot of Cae Packed. This eee slide over jount of Compaction. As discmac) 1 UiShe dry density. jort is tO ee the maximum dey iui carlier, the effect of increasing the amount of compactive water conte han the optimum, the i, ant 10 decrease the optimum water content (BE: 144). Al s Soteat more than the optimum, the volte, °!,OF increased compaction is more predominant. At a water ‘compaction is not Significant, Me Of air voids becomes almost constant and the effect of increased It may be mentioned that the mari tive effort. For a certain inosine ater and smaller. Finally, a stage ig wea stan increase in the compactive “The line of optimums which (l eect . ip Zero-air void line. This line corresponds to air voids of about 5%. |. The dry density achieved de ee Gomum water content for cites neve! SePea%s upon the typeof sei. The maximum dry dent aid sr to higher dy deny then ne snow i Fi, 146, Ta general, corse gine sls ean be commroarse-prained eine our aiat fine- grained soils. With the addition of even a small quantity of fines a carry of fines is increased wo MUCH higher dry density forthe same compactive effor. However od ie pacity Ge to a value more than that required to fill the voids of the coarse-grained eel graded soil. 'y decreases. A well graded sand attains a much higher dry density than a dry density does not go on increasing with an increase in the is rane | compactive effort, the increase in the dry density becomes ae ted beyond which there is no further increase in the dry density Conese sols have high ai voids These sols asin a relively ower maximum dry denny Bee content ie G fo cits Such soils require more water than cohesionless soils and, therefore, the oe igh. Heavy clays of very hi it a ba imum water content. ry high plasticity have very low dry density and a very high (4) Method of Compaction. The dry density achieved depends not only upon the amount of compactive for but also on the method of compaction. For the same amouat of compactive effort, the dry density will ‘upon whether the method of compaction utilizes kneading action, dynamic action or static action. For igample, in Harvard Miniature compaction test, the soil is compacted by the kneading action, and, therefore, the 200 1.90 ! 1.80 a ()Well-graded send E @Low-plosticity silt 5 @)Low-piasticity clay 2170 WHigh-plesticity clay z 3 > 160 6 1.50 1-40] woter content (“) ; Fig. 146. Compaction Curves for Different SoilsOU O———— savanna ATION SHANICS AND FOUR 36 SO}. MECHAN! cb an equa Kona tess in ie ‘compaction curve obtained is different from thot obtained from the other convent compoctive effort is applied. consequently, tbe lines of optinvis Differeot methods of compaction give their own compaction curves, Consed ing, otter mateciais, are also different oe () Admixture. The compaction characteristics of the soils are improved by as discussed io bitumen, known as admixtures. The most commonly used admixtures are lime, cement and ee ‘The dry density achieved depends upon the type and amount of admixtures. (49. EFFECT OF COMPACTION ON PROPERTIES OF SOILS é ace achieved by 2 ei Racrin Properties of soils are improved by compaction. The desirable propestios ty acinicss Proper selection of the soil type, the mode of placement and the method of compaction. compaction on various soil properties is discussed below. In the following discussions, the dry of ‘optimum means when the water content is less than the optimum, and the wet of optimum means when the water content is more than the optimum. (D) Soil structure. The water content at which the soil is compacted plays an important role in the engineering properties of the soil. Soils compacted at a water content less than the optimum water conteot generally have a flocculated structure, DISPERSED HIGH COMPAL TIME EFFORT CURVE a) FLOCCLLATED DISPERSED Low compactive EFPORT Cunve ORY DENSITY —_ regardless of the method of compaction, Soils compacted at a water content more than the optimum water content usually have a dispersed Structure if the compaction induces large shear strains and a flocculated structure if the shear strains are relatively small. , Jn Fig. 147, a point A on the dry side of the optimum, the water content is so low that the attractive forces are more predominant than the repulsive forces, This resulle in Hlocallaied struciuce. AS the water content 1s increased beyond the optimum, the repulsive forces increase and the particles get oriented into a tispersed structure. If the compactive effort is increased, there is a Corresponding increase in the orientation ot the particles and higher dry densities are obtained, as’ shown by the upper curve. @) Permeability. The permeability of a soil depends upon the size of voids, as discussed in chapter 8. he permexbility of a soil decreases with an increase in water content on the dry side of the optimum water ontent. There is an improved orientation of the particles and a corresponding reduction in the size of voids hich cause a deerease in permeability. The minimum Permeability occurs at or slightly above the optimum | WATER CONTENT (41) Fig. 147. Soil Simcaure in Compacted Soils. iproved orientation, If the compactive effor is increased, the Permeability of the soil decreases due to increased dry density d better orientation of particles, ) Swelling. Soil compacted dry of the optimum water content hhas high water deficiency and more dom orientation of particles, Consequenlly, it imbibes more water than the sample compacted wet of the imum, and has, therefore, more ‘swelling. (A) Pore water pressure, A sample compacted dry of the optimum has low water Content. The pore water sure developed for the soil Compacted dry of the optimum is therefore. less than that for the same soi pacted wet of the optimum. 5) Shrinkage. Soils compacted ‘dry of the optimum shrink less on drying compared with those acted wet of the optimum, The soils Compacied wet of the optimum shrink more because the sail ‘es in the dispersed structure have early parallel. orientation of particles and can Pack more efficiently.ne coMPACTION OF SOILS (6 Compressibility. The face, seqgnce t0 COMPTESSiC a ee one ion than the dis, However, the Compressibiti, . in the degree of saturates. f ioe inlvenced By the method of oe SOM ise dispersed structure with a conor : fe re) compressibility Toe ve lar 8 — rn re Oe wen Fe sie Sucl : (P) Stress-Strain relationshi; snd ot tn te re fhe 148). The modulus of elasticity for ihe ie compacted dry of the optimum ig fore high. Such soils have brittle failure wr dense sands Or over-consolidated claye, ipo sols compacted wet of the optimum have tively flatter stress-strain curve and a ‘compaction, ‘ed structure devel s loped on the dry side of the optimum offers: greater ; Persea structure on the wet side. Consequently, the soils on the dy SiGe | f the soi Soil depends upon a number of other factors, It increases with an ressibiity of sll compacted on ihe wel side of the ‘optimum she compaction is of kneading or impact type, it creates & % DEVIATOR STRESS—= e | AXIAL STRAIN — Fig. 148, Stress Strain Curves. nding lower value of the modulus of elasticity. The failure in this case occurs at a large strain and 1s of plastic 1¥Pe- Shear Strength. In Bike eos eee 8 given water conten, the sear strength of the soi reas with an imipeclve effor, the shear strength decreases legree of saturation is reached. With further increase in the mype the moulded water cont ases. The sheat strength of the compacted soils depends upon the Bee ee ills ond cbs lent, drainage conditions, the method of compaction, etc. The shear strength of the comps nd Clays at the moulded water content and at a water content when fully saturated are guie diferent, as discussed below. (@ Shear strength s moulded water content. ‘Two samples are compacted to the same dry density, one of the optimum and the othet wet of the optimum, and tested for shear strength. Fig. 14.9 shows the Mot-Coulomb failure envelopes. The soils compacted dry of the optimum have a higher shear strength at ‘pw strains. However, at large strains the culated structure for the soil on the dry sée is broken and the ultimate strength is qroximately equal for both the samples. On the wet wide, the shear strength is futher reduced if the compaction is. by tneading action. It causes a greater orientation (owards a dispersed structure than that by satic compaction methods. (6) Shear strength after saturation. Two samples are compacted to the same dry teasity, one dry of the optimum and the other Wil of the optimum, and then soaked in water, without any volume change, ‘0 have full ed dry of the optimum uch smaller than that Suration, The samples are then ‘tear strength, The samples compact e n 8 & b DRY SIDE g a = a ee WET SIDE NORMAL STRESS (©) —> Fig. 149. Failure Envelopes. show greater strength, However, the difference in prior to, saturation, The difference in the water ile strength of the two samples is m consequent pore water tension is greatly reduced after saturation. iciency of the two samples and theSL ——— pens _ HL, MECHA IND PDD EIN foribes wists 1 poet 0 gucmited Goniny saumation, the Otterenwe by sheng wf soe wo soaps Sn woniies costs, Ihe suenighe ConnnCled on the Wet side may exbital wren more iret ‘The denined sow seenysh 0 the \i10 wunnples Ia aimices eae, 1410, METHODS OF COMPACTION USED IN VHLD ee Pye age sar SonemalO OL GTi lero i eto wit Heer "es wel typ, the takin Oty deny required, and cocmunnle comesderd Carvers res ae Osclased Vow, Oer otk rr an soe ts DTaP, ‘ms Sicueed Iwler, 2995 tg (1) Tapers, 6 band-amermes taper (or rammer) conmieis of 1 tock of iron {or soe), stk in mine, inched 10 4 wooden tod, The tamper is Wicd for sbenn 0.9) m0 topped on the $0 Wo oe enced, ‘mechanical rammer is operated by comsresenn sit or yaswine power, I mou hice, 10 1H) kip, Muchancal imimens have been sed wih 1 mia of 10) ky in soma opi cate, 4 fa te rte oom wos cent to extng evcncn ox conte sca, sich x8 ences tapers ee rate etmentn where cer melhods of compacion cant be used, Onrog to very Sow cut, lannprers sie 06M ecomomnicah viene large quantities of wile ace ished, Vanipens ean be wed 98 ‘iis, 2) KeMors, Resets of different pes ae weed tor compaction of uss, The compaction Gepente pon the following, factors, ao oS Commer Presure, In genera, the compaction increases vith an inerecoe in the contact presouse, 4 smoothed roller, the coniact pressure depends upon the load per unit width and the diaaseser of ‘the roller, OH) Nuabser of pwsces, The compaction of 9 wih increases 9th an increase in the number of passes mite, Vaowever, beyond % certain limit, the increice in the denwity sith an inereave Sa the nuesber of rte In N01 appreciable, From economy comnideraion, the number of penwes 's generally restricted to 8 cexsonable Meni between 5 10 15, Wh) Sayer Whekavess, The compaction of 1 toll increanes with % decteave In the thickness of the Sayer. However, for coomomy consideration, the thickness is rarely keph Jess than 15 xn, 14 ‘pres of roller, The compaction depends upon the vpeed of the rollec, The speed should be 60 adjioned thal the maximurn effect Ss achieved, ‘Aye fh Maser (i) Smonth-—Whael Rollers, A wncoh—sibet roller yenetally consisis of sree wheels; two large ia’ In he Fer iid one smal wehee Sn the eons, A tandem type sencoth—vhee roller consists of only wo run, one jn the rear and one in the front, ‘The mass of 4 smiooth—wheel roller generally varies besween 2 1015 My These rollers are operated by interri\ combustion (Note, Senne subors expres 1000 ky ss de one tonne (11), As tonne 18 nok a standard ‘St unit, i is beter 10 expres 100) ky av 1 My), Smeoli-wice wiles ae usetul fox fnlbing operons ater compaction of fits and fox compacting wile Via comes of Wiysinays, ‘Thee ire non effective for compaction of deep layers of soll, resulting, Comnpricsion presoures Induced are low, Purther, these rollers als cause in deep layers due to non-uniform comnpactlon, ‘ieee rollers are wenerally uted 10 “seal” the surface of the fil at the end on day's Work to provide 4 smooth surtace 10 quickly drain off any rain water, 5 rollers une compressed air 10 develop the ftequired inflation rt ae ne the area of Contact wid the Inflation pressure. ‘The roller jenveraily coniats of 9 ‘i's i ty haloesuseful for la; Sometimes, the rolien are designed vo cross 4 Wied aaa tracked. This improves the ned 10 produce a wobble effect, duc to which a slightly weaving path is Manic of he soil. Poeumaticiyred rolles are generally provided with 2 1) Sheep tan pox. The box con be filled with Ballas o inerease the weight ofthe roles a flock of sheep on the news Phere i time before the advent of the rollers, it was usual practice to pass & of sheep-foot rolies, ly. ‘soil fill to cause its compaction. The same principle is used in the desig ‘The sheep-foot ‘i a oe Ta OF 8 low cru with ape eater ae an es eee Fhe dts are OnOlet oa ee eee ee ee ee Te eae aga, Te mn ca Se elas ple oct ee one al Bebo oe 8 sete propelled unit and a towed unit. As rolling i done, most of Te Ee a ae ie poles tie a eee Fey otic sol ‘The roller may sink into the soil if the contact pressure is more than the bearing, ae eee eacig re suited for compaction of cohesive soils, The rollers compact the soil by a 2 jeading action. When the roller is passed for the first time, the projections er eal ee ae ee ee cee haber tion of th This si . ALi ot be ioe 9p portion of the layer. This continually rising effect of the compaction s ‘The depth of layer that can besompacted depends upon the length of the rei projections and the weight of the roller. Small rollers can Compacilayers of 15 cm thickness, whereas heavy rollers can compact layers of 40 om thickness. In general, the thickess of the layer compacted is kept not more than 5 em greater than the Jength of the projection. @) Vibratory compactors. In vibrayry compactors, vibrations are induced in the soil during compaction. ‘The compactors are available in a variet. of forms. When the vibrator is mounted on a drum, it called 2 vibratory roller, These rollers are availnle both as pneumatic type and the smoothwheel type. In & smooth-wiseel type, 4 separate motor drives:n arrangement of eccentric weights to create high frequency, low ‘amplitude, up- and-down oscillations of thtrum. These rollers are suitable for compacting gramilar soils, with no fines, in layers upto 1 m thickness. Hever, if there is appreciable percentage of fines, the thickness tas to be reduced, In a pneumatic-tyred vibrato, compactor, a separate vibrating unit is attached to the whee! ane, The ballast box is suspended separately ft the axle so that it does not vibrate. These compaciors are fuitsble for compacting granular soils with thickts of layer of about 30 crn. ‘Another form of a vibratory compactor i8 a Vilating-plate compactor. In this system, there are a number of small plates, each plate is operated by a separalt vibrating unit. Hand- operated vibrating plates are also available. The effect of the vibrating plates is limites small depths. Their main use is to compact granular base courses for highways and runways where the thitress of layers is small. Vibratory compactors can compact the granular s0iito a very high maximum dry density. 14,11, PLACEMENT WATER CONTENT 'As the methods used for compaction in the field are ¢l-rent from that for compaction in the laboratory, the optimum water content in the field may not be nectarily pe the same as in the laboratory. The laboratory value may be taken as @ rough guide for placement ser content in the field, The ideal placement tact content vinen the pneumatictyred rollers are used is 2PP-imatcly equal to the optimum water content % oblained from a standard Proctor test. The placement waler ‘nent when the sheep-foot rollers, smooth- heel rollers 4nd vibratory rollers are used, is of the order Of. optimum water content obtained in the modified Proctor test. : For important works, foll-scale test is conducted in the field \4erermine the placement water content,:ERING ANICS AND FOUNDATION ENGINEI xs soit, MECH in case of small, of mi ti pasecs: Somelt he standard ess of layer, mass and speed of roller and the number of passes. SOME TL oe an fa the thickness of Lay speed ee ae nimportant works, the placement water content is taken equal (0 the optimum Se 7 However, the field water content is sometimes kept intentionally different from ‘order t0 achieve or {6 improve a specific engineering property of the soil he floors, cohesive Soils in such To avoid targe expansions and swelling peessure under pavements and TNE Te ity ite resulting dry Gases are generlly compacted at a water content more than the optimum water @™TT cry dam ia also density less than the maximum dry density, The clayey soil in the imperviX® TT end, the highway Compxicied on the wet side of the optimum to reduct swelling pressure. OF U er than the optimum enrbapkmen's of cobesive soils are generoMly compacted at a waler conten! SOmeNM! O° Soa in the outer Sater conicnt in order to achieve bigh shear sirength and tow compressibility. LM neabiity and shells of earth dams is compacted dry of the optimum to oblain high Shear strength, Towispore prassure. a tent. For su o ee cartier, cohesionless soils do not exhibit a well- defined oplimam aoe et Aas soils, the maximum dry density is achfeved either in completely dry Condition eee ee the condition. In the field, completely saturated condition is preferred for practica! maximum compaction. ci ws Ie the water content of the sol in the borow ezea is tess than the required plsemen! Water One. water is sprinkled over the area. On the other hand, if it is more than the desired vali*, HEE/OUTICAI to decrence the borrow pit, spread and allowed to dry. However, in wet weather, it becomes Tl the water content and the work has to be stopped. 414.12. RELATIVE COMPACTION :, uf ‘The dry density achieved in the field is compared with the maximum ‘ty density obtained in the standard Procior test or that in the modified Pcoctor test. The ratio of the dry denity in the ficld to the maximum dry density is known as the relative compaction or percent compaction. Ths puin the field. 99 +(14.8) (Pa)max inthe laborator For cohesive soils, y density of the order of 95% of t& maximum dry density of the standard Proctor test (Le. 95% reilive compaction of the standard Procic’'¢st) can be achieved using a sheep-foot roller or 4 pneumatic-tyred rolles. However, if the soil is very heay Slay, only sheep-foot rollers are effective, For moderately cohesive soils, the dry density of the order of 9% of that in the modified Proctor test can be achieved using pneumatic tyred roller with an inflation pressur Of 600 KN/m* or more. For cohesioness soiis, the dry density of the order of 107 Ot even more of that in the modified Proctor ‘esl can be obtained using pneumatic-tyred rollers, vibratoryOllers and other vibratory equipment. 14.13, COMPACTION CONTROL ( The laboratory compaction tests give the optimum ater content and the maximum dry density. In the field, during the compaction of the soils, it is essential 1 Check the dry density and the water content in order ‘0 effect proper quality control. ‘The geotechnical *ineer has to ensure that the specified amoun 2? Compaction and the desired dry densities are achieve Compton control is done by measuring the density and the water content of the compacted soil ia be field. (1) Dry Density. The dry density is measur’ USing the methods discussed in chapter 2. The core-cutter ethod and the sand replacement method are ¢MOnly used, The nuclear methods are Occasionally used as se are non-destructive and requte no phys Of chemical processing ofthe soil and re very cence (2) Water Content, The oven-drying 40d Of tHe determination of the water content takes 24 nous Us mathod, though very accurate, cannot’ Used for Controlling construction, asthe soll layer an enc | sample was taken would be buried ¥ the time the water content is known. Therefore, the basic ulrement is that the method used be 4H that it gives quick results, In the field, the water content is i P ‘ve compaction =COMPAEHION OF SEL wenerally determined Using Ihe sund-buth method, alcobot aes eatbide tneihenl, wo dice ‘aad in hopler 2. The nuclear methoss ae i set inerwintily, The water conteni enn wlio be determined indirectly using a Poooter mbadle (let IW is plasticity needle), The Proctor needle consists of 4 tod {0 4 spriniloialed plunwer (Hig, 14,10), ‘The stem of the plunger i ie Heid the fesistanice in hewion, A sliding ring on the stem indicates the marian restate FecuRded during the lest, ‘The needie-shank has graduations to indicaie. the dopit Of penwiration, ‘The equipment is provided with a senes of neuile poinls OF different cross-sectional mess (0.25, 0.50, 1.0 and 2.5 em’) to obtain 4 Wide (Hue Of the penetration restelunce, For cohesive soils, the needle points of Inter erOss-séotona! areKe Are requited and for cofesionless soil, those of simile CTORS: Seellonal sreas ure used, ‘The necdle point used should be such that 18 nether (60 sal! for nceurate fnessurement nor too large. A nillable needle point is setocted and screwed to the needle stank. After the soll hs been compacted at yiven water content in the compaction test in ihe lnbormiory, the Proctor needle is forced 7.5 an into i at the rete of ebout 125 emisee. The méxiinum force used is found from the compression of the spring. From the koown ares of the needle point, the penetration resistance per wnt area 18 computed, A number of such Measurements are made in the Jsbonitory during the compaction test, and a calibration axve is obtained between the penetration resistance () and the water content, 2s shown in Fig. ee eaieneae oe. q J4l1, It 1s found tht for a given degree of compaction, the penetration decreases with 4n Increase in weter content. 140} ethnic?) & 8 Penetration cesistenc. 2 s 3 8 10 C3 8 WISER CONTENT (+45) —— Fly, 14.11. Calibration Curve for Penetration resistance R. To determine the waler content of the compacted soil in the field, the soil is compacted in the standard Paction mould in the field in the same manner as was used during the calibration of the needle. The “raion resistance of the compacted soil is measured, The moisture content is then obtained fore) the ration curve, This method of the determination of the water content is quite rapid and reliable for fine-grained soils. Fri anne Rot give accurate results for cohesionless soils and for soils having a large percentage of ls and stone pieces. : VIBROFLOTATION METHOD Drofcration is used for compacting thick deposits of loos, sandy soils upto 30 m depth, A vibcofet 4 of 4 eYlindcical ‘ube; shout 2m diameter, fitted with water jels atthe top and the bottom. It conan1g AND HOUNDATION HNODNR EIN, wo), MICHANIC v0 4 totaling eccenurle mae wists develops 1 Horizontal vibratory menion, ‘The vlbxoF1ot Is sunk Into the Jocee ‘oll uphe the desired depth uetny. the lower water Jet (Pig. 14.12 (ay), Ax Wier comes Out Of the Jel, ih crenten 1 ‘momentary quick condivion ahead of the vibroflol duc io which ihe shear sirengih of he voll Is reduced, ‘The Vibrotlot scitiea due 1 sis own mon, When the desired depth pas been reached, the vibrator J6 slivated, The wibroflot then vibrites \aterslly and causes the compaction of ie soll In the horizontal direction 10 4 radius of HbOUL 1.5, m, ‘The water from the lower bs enough £0 caery the sind poured ut the top 10 ite bottom of the hole (Fig. 14.12 (b)]> Ebene the vibroflt Is slowly ralsed 10 ihe suctiee, Addilonal sand fs continually dropped ace tenho, around the vibroflot, By raising the vibrotiot In wtages and simultancously buekf! Ning, I he woil is compacted (Pig, 14.12 (¢)). ‘The spacing of the holes ts usually kept between 210 3:m on a gid pattern, The ae Bis ena Inder) achleved for the sandy sols 6.70% or more, Th sof, cobealve sols, vibcotlotaton no let, tx cohesive soils, it can be wed to form # sand pile to reinforce the deposit and to accelerate consolidation and thus Improve its engineering propertics, 1415, TERRA PROBE METHOD ‘Terra probe method in many respects Js simile to the vibrofolalion method, The terta probe consuls o Wich ceciaay bppe, about 75 em diameter, Is provided with a vibratory pile delve, ‘The vbtatory pile drive het ccivated gives vertical vibrations to the terea probe and tk goes down, tler teaching the deoken depth, ihe terra probe is gradually rived upward while the vibxodiiverconlinuen 0 Operate, Thus, the soi within and around tbe terra probe ts denuified, ihe terra probe method has been aucceasfully ued upto depth of 20 m, ‘The Spacing of the holes \ I aly Kept about 1.5 m. Saturated soll conditlons ure Ideal for the success of Ihe methoel For the sitew where the water lable is deep, water Jets ae fled 10 te lemma probe 10 asst the Penetration and densification of the wll. Is conslderably faster than the vibcof However, the method 18 leas effective than Phy. 14.12, Vibroftotnton, Jet ts transferred to the top jet and the preamure Is reduced wo that ft is jug achieved is also lower, 14,16. COMPACTION BY POUNDING pounding method hay also been Fecently used, ‘The mais 300 the felght are welected depending upon ihe crane available ‘ind the depth of the soil deposit. A #10 pattern {6 selected for the Pounding locations, At each location, 5 to 10 Poundings areINEERING, COMPACTION OF sous deposits as well. The depth (D) in met to 1 iat’ following relation, ‘*P (P) in metes upto which the method js effective’ eum be determined Da cM peu Wine ca eatcient ©. 0.0.75), i = mass (Wig), Him bean OF op (m) ct i eeeists {he pounding method, eare shall be taken that harmful vibrations are not transferred to the ee es, ils Of influence (R) in metees beyond which oo barTul vibrelogs ere anc | ‘can be determined from the relation, aa Rs BovN (1419) Where M = mis (nd = bei ok op, 1412. COMPACTION BY EXPLosivES is just Sand whlch i followed by densiicaion, th paralydauraetl tolbnee ces Fe) Pee po tiny action a proven! tne soipag eesti eng) Clee ten ator) | effective for patally ssuanted a of the ‘The depth upto which the blast i effective is Umi fo BS of about 1 0 patrdipiscea'in a tandommtanoe cea el sly | _hould be compactes using ine conventional meihats ty conor . For nie The TUBS Usually consist of boot 60% dysamilé and 30% special gusta dynamite. and and tnmmonite. The charges are placed ai woxhids ie thickeess of the stratum tees ere Je #xolasire points kep bervcen 3 to 8m, Tre fo ve bla are gest cop The radius of influence (R) of compaction can be determined wsing the relation Sof | R= M/C) (14.11) iver where Kraus of influence (m), Af = mass of barge (kg), C cosiat ( = 0.08 for 6 dys) ee —_*A4.A8. PRECOMPRESSION | os saused in chapter 12, precompresson improves the properties of the cobesive soll. In this method, is | _Be Soil is preloaded before the application of the design loads. reloading causes setloneas tetas weeny ere | _Ghnsinction begins The preload is georally i he fom of earth il which lt i pace for slong ine SS £0 a {0 induce the required setiement. After the required compression has been achieved, ne pret Fnac tor tothe construction, A monitorieg syslem consisting of Stent plates and piezouiets moy a be used t0 check the progress of settlement, 5 “he recompression method is effective for compiction of sills, clays, organic sols and Sanitary land f cer gare brclond must be carefully selected Sos nol to cause shear failures inthe sll. The sablty ot the Soll deposit under preload should be checked, Sufficient soil dala should be collected to predict tne ste ana magnitude of the settlement. Sometimes, vertieal sand drains are used to decrease the tine of ettlemars ¢ | 1419, COMPACTION PILES 4 4 Cobesionless soils can be densified by consincting compaction piles./A Gapped, pipe pile is driven into 1 tie sol, The soll surrounding the pile is compacied due to vibrations caused dung driving The pile he } | __tiacled und the hole formed is backfilled wilh sand. Ths the compaction pile is formed. (Por nove dec, | | see chapter 25.) | 1420, SurrapiLery OF VARIOUS METHODS OF COMPACTION ‘The suitability criteria of various methods of compaction can be summarised as under: (1) Cohesiontess Soils only, Smooth-wheel rollers are suitable for compacting layers of small thicknessee a = oH iat naa] ~— _ 1p FOUNDATION ENGINEERING xi - sol. MECHANICS 26110 178 = Fy (05 % 2.6779) or 80.1% = 2.67 or $ = 0.801 261 x19. 1.78 (=n) G pw O=m XG Noes Pa Te WG 7 + 0.15 * 1, = 0.066 oF 6.6% iw 26110 = 1.91 g/ml Cadiiconae = Te wE 7 1 + 0.15 x 2 0.713 ui 178 + 5 PROBLEMS: ‘A. Numerical .d by compaction cength was prepared by compaction ig 14d. A cylindrical specimen of a cohesive soil of 10 em diameter and 20 em | a Terhune 8 ty dersity ‘a mould Ifthe wet mass ofthe specimen was 3.25 kg and its water comtent WAS °° y and the void rao op amraton, (Ane. 1.80 gai 050; 8) If the specific gravity of the particles was 2.70, find the degre ‘sample of soil 142. ‘The following are the results of a standard compaction test performed on 7 Water Content (%) ag 4S 146 115 19. ‘Mass of wet soil (kg) 17, 1.89 2.03 199 am sg gravity OF soil grains was 2.65, make necesary If the volume of the mould used was 950 c.c. and the specifi oo eee calculations and plot the water content-dry density curve a1 Pees cca, erica aoe fAns. 15%; 1.83 em/mi} 143. An earthen embankment of 10° m* volume is to be constructed with a soll having & BecratiolO 0.80 afer ‘compaction. There ate three borrow pits marked A, B and C, having soils with wyoid ratics of 0.90, 1.50 ang 1.80, respectively. The cost of excavation and transporting the soil is Rs. 0.25, Rs. 0 28 and Rs. 0.18 per m respectively. Calculate the volume of soil to be excavated from each pit. Which borrow bit is the mos | economical ? (G = 2.65). [Ans. 1.055 x 10° 1.389 x 10; 1.555 x 10° m, 4) B. Descriptive and Objective Type 14.4, Differentiate between consolidation and compaction. Give examples. | 145, Describe Standard Proctor test and the modified Proctor test. How would you decide the type of the test to be conducted in the laboratory ? 14.6. What is a compaction curve ? Give its salient features. What is a zero-air void line ? 14.7, What are the factors that affect compaction ? Discuss in brief. 14.8. What is the effect of compaction on the engineering properties of the soll ? How would you decide wheter the soil should be compacted the dry of optimum or the wet of optimum ? 14.9. What are the different methods of compaction adopted in the field? How would you select the type of roller to be used? 14,10. Write short notes on @ Placement water content (©) Compaction control (©) Vibroflotation (/) Compaction by pounding (g) Precompression (hy Compaction by explosives 14.11, Write whether the following statement are correct or not, : (a) Compaction occurs under a susiained, static load on a saturaied sol. (b) The theoretical maximum dry density can be attained in the laboratory. (r) The zero-air void line and 100% saturation Tine ate identical a mnd_obtain the optimum (b) Relative compaction (@ Terra probe“us COMPACTION OF SOILS (@) As the compaction is increased, th eased, the optimum water content increases {6) The modern Bighvays and runways fave compaction equa (ota ataned In tana Posts IS (P Vibroflotation is effective for highly cohesive soil (g) The Proctor needle can be used to determine the dry density achieved in the field. (i The relative compaction is the same as the relative den oo pe Pneumatic-tyred rollers can be used for both cohesionless and ct Gp The water content of the sil inthe fel is alvays ke al 6 x03) a soils compacted dry of the optimum have higher modulus of elasticity, () The core in an earth dam is generally compacted wet side of the optimum. (im) The permeability of the soil decreases by compaction. (2) The Jodnpur mini-compactor test gives lower dry density than the Standard Proctor test. (0) In the Todhpw. .>¥:.-compacas, "et, kneading action takes place {@) The number of passes made by a roller is generally more than ten (g) The shear strength of a soil always increases with an increase in compaction. () In pneumatic tyres, the contact pressure depends upon the inflation pressure (s) The thickness of the layer during compaction is Kept about 10 em. (9 The smooth-wheel rollers can be used for compaction of deep fils. johesive soils. jum water content. than those on the wet side, [Ans. True, (6), @, 9, Dy (es . Multiple Choice Questions 1, Pheumatie-tyred rollers are useful for compacting (a) Cohesive soils (b) Cohesionless soils (© Both (a) and (b) (@) For soils in confined space 2, Vibratory rollers are best suited for compacting (@ Coarse sand and gravels, () Silts (© Clays (2) organic soils 3, Precompression method is useful for compacting (@) Silts (b) Clays, (6) Organic soils (a) All the above 4, The line of optimums generally corresponds to percentage air voids of about (@) zero percent (b) 5 percent (©) 10 percent (d) 20 percent 55. The range of optimum water contents for the standard proctor test for clayey soils is (a) 6 10 10% () 80 12% (o) 12 to 15% (d) 14 w 20% 6. Soil compacted dry of the optimum as compared to that wet of the optimum {@) has less permeability (B) swells less (0) shrinks Tess (a) has less resistance to compression 4, For a Standard Compaction test, the mass of hammer and the drop of hammer are as follows : @ 26 kg and 450 mm (6) 2.60 kg and 310 mm (0) 48 kg and 310 mm (d) 4.89 kg. and 450 mm 8, Sclect the correct statement (@ Relative compaction is the same as relat (b) Vibratory rollers are effective in the cas (6) ‘Zero air yoid line’ and 100% saturation line tive density © of highly cohesive soils re identical fAns. 1, (©, 2 (a), 3. @), 4B, 5. @, 6. ©), 7. @, 8. (ONSer miners waneity _Naanonerupr ee et oe wa th ae ov Ajenedt ee "7 é ae a ae : 4 wy Brera realy qos) ‘ Cod) “ene Fig- Qeq denvit{ive moietune conten? (r) erro Ast two gece oh wand. 4E ) abarotorg compaction twat’ ee eine a Be Standard Pradr at MdaiR2d)/Pracdor Soe eB Vest top D fs eoden TS: 2€20 = Fan? %,19%0| Ts, 2590- Panr 2 . 1988 Apne Most o& tee oppl’s: |Heovien lood > Ape ones ee ql. ae apmas tone.) Ante AU cote Sone Pl een of} aan loo mP ? Selched cad | ae Dh ef harmal 276 ke ie > he of Ral of | Zio rm 450 mr. mm D>2 J wt Pe wot = | | Zs i ee aenpoctve #! ae behavior ok eomnpackad 4h Comparinan of aphaumss se oe ida. ae opium <4 Propuat | Corepaction a : io D) Strueiune a rFarticle axva mgprnent Water da ® hancg. ' Op oie a mare tandem rq) “deo ia mer. Jad ) Penman by > compress aty Wek ida 4 mat im lew stress Ta | Shroxgth Gheor) 4 Unavainad ' Droinod + | Org wide reuch Wi jor side womerhak Wok. | | J