Physical Properties of Soils and Compaction

Transcription

1 Soil Mechanic Phyical Propertie of Soil and Compaction page 1 Content of thi chapter : CHAPITRE 2. PHYSICAL PROPERTIES OF SOILS AND COMPACTION UNITS BASIC DEFINITIONS AND TERMINOLOGY OIDS RATIO AND POROSITY DEGREE OF SATURATION UNIT EIGHTS SPECIFIC GRAITY ATER (OR MOISTURE) CONTENT EXERCISES COMPACTION PURPOSE OF COMPACTION COMPACTION TEST EFFECTS OF SOIL TYPE FIELD SPECIFICATIONS EXERCISES...10 Chapitre 2. Phyical Propertie of Soil and Compaction 2.1 Unit For mot engineering application the following unit are ued: Length metre Ma tonne (1 tonne 10 3 kg) Denity 1 (ma/unit volume) t/m 3 eight kilonewton (kn) Stre MegaPacal (MPa) 1 MPa 1 N/mm 2 Unit eight 2 kn/m 3 To ufficient accuracy the denity of water ρ w i given by ρ w 1 tonne/m 3 In mot application it i not the ma that i important, but the force due to the ma, and the weight,, i related to the ma, M, by the relation M g where: g 9.81 m/ 2 i the acceleration due to gravity. In oil mechanic calculation, for implicity, one may ue g10m/². Hence the unit weight of water, γ w 9.81 º10 kn/m 3 1 Mae volumique.attention : denity denité (En Françai : rapport de la mae volumique du corp à une mae volumique de référence. Donc denité e traduit par : relative denity ou pecific gravity) 2 Poid volumique

2 Soil Mechanic Phyical Propertie of Soil and Compaction page Baic Definition And Terminology Soil i formed by the diintegration of rock under the action of variou force of nature uch a water, wind, frot, temperature change and gravity. It may thu be conidered to conit of a network of olid particle which encloe void 3 or pore. The void may be filled with water or air or both. Soil i thu a three phae material which conit of olid particle which make up the oil keleton void which may be : full of water if the oil i aturated, full of air if the oil i dry, partially aturated a hown in Figure 2.1. olume Air eight ater Solid Figure 2.1: Air, ater and Solid phae in a typical oil oid Ratio and Poroity Uing volume i not very convenient in mot calculation. An alternative meaure that i ued i the void ratio 4, e. Thi i defined a the ratio of the volume of void, v to the volume of olid,, that i e v A related quantity i the poroity, n, which i defined a ratio of the volume of void to the total volume. n v T Degree of Saturation 3 vide 4 Indice de vide

3 Soil Mechanic Phyical Propertie of Soil and Compaction page 3 The degree of aturation, S, ha an important influence on the oil behaviour. It i defined a the ratio of the volume of water to the volume of void : S w v Unit eight Several unit weight are ued in Soil Mechanic. Thee are the bulk, aturated and dry unit weight. The bulk unit weight 5 i imply defined a the weight per unit volume γ bulk T T hen all the void are filled with water the bulk unit weight i identical to the aturated unit weight, γ at, and when all the void are filled with air the bulk unit weight i identical with the dry unit weight 6, γ dry. T Specific Gravity Another frequently ued quantity i the Specific Gravity of the oil, G, which i defined by : G Denity of Soil ρ γ Denity of ater ρ γ γ w w w It i often found that the pecific gravity of the material making up the oil particle are cloe to the value for quartz, that i G 2.65 For all the common oil forming mineral 2.5 < G < 2.8 A pycnometer i hown in Fig It i ued in the determination of the pecific gravity of the olid particle in the field. In the laboratory, a 1 litre jar i ued together with a mechanical haker. The procedure for either method i, however, the ame : The ma of the empty pycnometer (m1) i found uing a balance. A ample of the oven-dried oil i placed inide and the combined ma (m2) i found. Fig Poid volumique apparent 6 Poid volumique ec

4 Soil Mechanic Phyical Propertie of Soil and Compaction page 4 ater i added to the oil which i agitated to remove all air pocket. and when the pycnometer i full up, it ma (m3) i meaured. Finally the pycnometer i emptied. cleaned and filled with water and it new ma (m4) found. S S m1 m2 m3 m4 Exercie 1. Demontrate that the pecific gravity can be calculated by the formula : m2 m1 G ( m4 m1) ( m3 m2) 2. A pycnometer having a ma of 620 g wa ued to determine the pecific gravity of an ovendried ample of oil. If the ma of the oil ample wa 980 g and the ma of the pycnometer with the ample and filled up with water wa 2112 g. determine the pecific gravity of the oil particle. The ma of the pycnometer when filled with water only wa 1495 g ater (or moiture) content The water content 7, w, i a very ueful quantity and it i imple to meaure. It i defined a the ratio of the weight of water to the weight of olid material. That value can be greater than 1 (100%) in the cae of peat (600%!). w w (x 100 if expreed in %) Example howing the tandard method of determining the water content : 3. A moit 8 ample of oil in a bottle had a ma of g and the bottle, when empty, had a ma of 14.2 g. After drying in an oven 24 hour, the bottle and oil ample had a ma of g. Find the water content of the oil Exercie 4. An unditurbed pecimen of clay i taken from a ampling tube the volume of which i m 3. The weight of the pecimen i 250 N and the water content i 21.1%. Calculate the dry unit 7 Teneur en eau 8 humide

5 Soil Mechanic Phyical Propertie of Soil and Compaction page 5 weight. If the pecific gravity of the particle i 2.68, find the void ratio and the degree of aturation. 5. The ma of an oven-dried ample of clay i gm and it (total) volume i 5.83 cm 3. If the pecific gravity of the oil particle i 2.67 determine the hrinkage limit of the oil. The hrinkage limit i the water content the oil would have had if fully aturated at it minimum volume. 6. The dry unit weight cannot be meaured directly. It i deduced from the meaured bulk unit weight γ bulk and water content. Prove that γ dry (1+w) 2.3 Compaction One important application of the phyical propertie i the compaction of oil. Compaction i the application of mechanical energy to a oil to rearrange the particle and reduce the void ratio Purpoe of Compaction Compaction : reduce ubequent ettlement under working load. increae the hear 9 trength of the oil, reduce the void ratio making it more difficult for water to flow through oil. Thi i important if the oil i being ued to retain water uch a would be required for an earth dam. can prevent the build up of large water preure that caue oil to liquefy during earthquake Compaction 10 Tet For a given quantity of oil, if the total volume i reduced (the expected reult of compaction), the dry unit weight ( γ dry ) increae. T Proctor, an American engineer, wa the firt to tudy, in 1933, the compaction proce and noticed the influence of the water content and energy of compaction on the dry unit weight. He developed a tandard compaction tet till in ue today. Thi tet involve compacting oil into a mould 11 at variou water content Standard Compaction Tet A ample of oil i compacted, at different water content, into a mould in 3-5 equal layer, each layer receiving 25 blow 12 of a hammer of tandard weight. The apparatu i hown in Fig The important dimenion are : olume of mould Hammer ma Drop of hammer cm kg mm 9 ciaillement 10 Compactage 11 Un moule 12 coup

6 Soil Mechanic Phyical Propertie of Soil and Compaction page 6 Figure 2.3 Standard Proctor Apparatu for laboratory compaction tet Becaue of the benefit from compaction, contractor have built larger and heavier machine to increae the amount of compaction of the oil. It wa found that the Standard Compaction tet could not reproduce the denitie meaured in the field and thi led to the development of the Modified Compaction tet not decribed here. Preentation of Reult From the different compaction tet realied on the ame oil, with different water content, a graph like Fig. 2.4 can be drawn. From thi graph we can determine the optimum water content, w opt, alo called Proctor optimum, for the maximum dry unit weight, (γ dry ) max. There i a limiting dry unit weight for any water content and thi occur when the void are full of water. Increaing the water content for a aturated oil reult in a reduction in dry unit weight. For a aturated oil : γ dry γ bulk + w + w 1 + w (1 + w) ( + ) (1 + w) T w Now w G γ γ γ w w w w w Hence G γ w γ dry G w + 1 The relation between the water content and dry unit weight for aturated oil i hown on the graph in Fig Thi line i known a the zero air void line.

7 Soil Mechanic Phyical Propertie of Soil and Compaction page 7 Fig. 2.4 A typical compaction tet reult Fig. 2.5 Typical compaction curve howing noair-void line Effect of water content during compaction A water i added to a oil (at low water content) it become eaier for the particle to move pat one another during the application of the compacting force. A the oil compact the void are reduced and thi caue the dry unit weight to increae. Initially then, a the water content increae o doe the dry unit weight. However, the increae cannot occur indefinitely becaue the oil tate approache the zero air void line which give the maximum dry unit weight for a given water content. Thu a the tate approache the no air void line further water content increae mut reult in a reduction in dry unit weight. A the tate approache the no air void line a maximum dry unit weight i reached and the water content at thi maximum i called the optimum water content. Effect of increaing compactive effort Increaed compactive effort enable greater dry unit weight to be achieved which becaue of the hape of the no air void line mut occur at lower optimum water content. The effect of increaing compactive energy can be een in Fig It hould be noted that for water content greater than the optimum, the ue of heavier compaction machinery will have only a mall effect on increaing dry unit weight. For thi reaon it i important to have good control over water content during compaction of oil layer in the field. Fig. 2.6 Effect of increaing compactive effort on compaction curve It can be een from thi figure that the compaction curve i not a unique oil characteritic. It depend on the compaction energy. For thi reaon it i important when giving value of (γ dry ) max and w opt to alo pecify the compaction tet procedure (for example, tandard or modified).

8 Soil Mechanic Phyical Propertie of Soil and Compaction page Effect of oil type The table below contain typical value for the different oil type obtained from the Standard Compaction Tet. Typical alue (γ dry ) max (kn/m 3 ) w opt (%) ell graded and S 22 7 Sandy clay SC Poorly graded and SP Low platicity clay CL Non platic ilt ML High platicity clay CH Note that thee are typical value. Becaue of the variability of oil it i not appropriate to ue typical value in deign, tet are alway required Field pecification To control the oil propertie of earth contruction (e.g. dam, road) it i uual to pecify that the oil mut be compacted to ome pre-determined dry unit weight. Thi pecification i uually that a certain percentage of the maximum dry unit weight, a found from a laboratory tet (Standard or Modified) mut be achieved. For example we could pecify that field dry unit weight mut be greater than 98% of the maximum dry unit weight a determined from the Standard Compaction Tet. It i then up to the Contractor to elect machinery, the thickne of each lift (layer of oil added) and to control water content in order to achieve the pecified amount of compaction. Accept Reject Fig. 2.7 Poible field pecification for compaction There i a wide range of compaction equipment. For pavement ome kind of wheeled roller or vibrating plate i uually ued. Thee only affect a mall depth of oil (20 to 30cm maximum), and

9 Soil Mechanic Phyical Propertie of Soil and Compaction page 9 to achieve larger depth vibrating pile and drop weight can be ued. The applicability of the equipment depend on the oil type a indicated in the table below Equipment Mot uitable oil Typical application Leat uitable oil ell graded andgravel, cruhed rock, ubgrade 15 Running urface 14, Uniform and aphalt Smooth wheeled roller 13, tatic or vibrating Coare grained oil with ome fine Pavement ubgrade Coare uniform oil and rock Rubber tyred roller 16 eathered 17 rock, well graded coare oil Subgrade, ubbae 18 Clay, ilty clay, uniform material Grid roller Fine grained oil with > 20% fine Dam, embankment, ubgrade Coare oil, oil with cobble, tone Sheepfoot roller 19, tatic Sheepfoot roller, vibratory a above, but alo and-gravel mixe ubgrade layer 13 Rouleaux lie 14 Surface de roulement 15 Couche de fondation, la couche la plu bae dan la compoition d'une route 16 Rouleaux à pneu 17 érodé 18 Couche de bae, ituée entre la urface de roulement et la couche de fondation 19 Rouleaux à pied de mouton

10 Soil Mechanic Phyical Propertie of Soil and Compaction page 10 Coare oil, 4 to 8% fine Small patche 21 clay and ilt ibrating plate 20 All type Difficult acce area Tamper, rammer 22 Mot aturated and moit oil Dry, and and gravel Impact roller Exercie 7. In a compaction tet a bulk unit weight of 16 kn/m 3 wa meaured at a water content of 8%. hat would the water content have been if the oil had been fully aturated. Aume G On the application of the tandard compaction tet to a oil, the reult tabulated below were obtained. Obtain an etimate of the optimum water content, maximum dry unit weight and draw the line of zero air void relating dry unit weight and water content. Aume the pecific gravity i ater content (%) Bulk unit weight (kn/m 3 ) Plaque vibrante 21 Petite réparation 22 Pilonneue