Geotechnical Engineering (Soil Mechanics) Compaction PDF

University of Science and Technology of Southern Philippines Civil Engineering Department Geotechnical Engineering (Soil Mechanics) COMPACTION...

University of Science and Technology of Southern Philippines Civil Engineering Department Geotechnical Engineering (Soil Mechanics) COMPACTION By: CE Faculty Reason for Compaction In the construction of highway embankments, earth dams, and many other engineering structures, loose soils must be compacted to:  Increase their unit weights  Increase the strength characteristics of soils, which increase the bearing capacity of foundations constructed over them  Decrease the amount of undesirable settlement of structures  Increase the stability of slopes of embankments  Reduce the compressibility and permeability of soil Compaction Compaction is the densification of soil by removal of air or pressing of soil particles close to each other which requires mechanical energy Compaction Compaction  Rapid process of reduction of volume by mechanical means such as rolling, tamping, and vibration  The volume of a partially saturated soil decreases because of expulsion of air from the voids Consolidation  Gradual process of reduction of volume under sustained, static loading  Causes a reduction in volume of a saturated soil due to squeezing out of water from the soil Compaction Compaction  It is an artificial process which is done to increase the density of the soil to improve its properties before it is put to any use Consolidation  It is a process which occurs in nature when the saturated soil deposits are subjected to static loads caused by the weight of the buildings and other structures University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: GENERAL PRINCIPLES By: CE Faculty Compaction: General Principles The degree of compaction of a soil is measured in terms of its dry unit weight. When water is added to the soil during compaction, it acts as a softening agent on the soil particles. The soil particles slip over each other and move into a densely packed position. The dry unit weight after compaction first increases as the moisture content increases. When the moisture content is gradually increased and the same compactive effort is used for compaction, the weight of the soil solids in a unit volume gradually increases. Beyond a certain moisture content, any increase in the moisture content tends to reduce the dry unit weight. This phenomenon occurs because the water takes up the spaces that would have been occupied by the solid particles. The moisture content at which the maximum dry unit weight is attained is generally referred to as the optimum moisture content. Compaction: General Principles Two basic compaction tests:  Standard Proctor Compaction  Modified Proctor Compaction Dry Unit Weight Moisture content Compaction: General Principles Two basic compaction tests:  Standard Proctor Compaction  Modified Proctor Compaction Mold Volume Hammer Drop Height ASTM AASHTO Compactive TEST Number Number 3 3 Mass Weight Effort (Energy) (m ) (ft ) (m) (ft) (kg) (lb) 25 blows/layer Standard 3 layers D698-70 T-90 945X106 1/30 2.5 5.5 0.30 1.0 3 Proctor (590 kJ/m or 3 12,375 ft lb/ft ) 25 blows/layer Modified 5 layers D1557-70 T-180 945X107 1/30 2.5 10.0 0.46 1.5 Proctor (2700 kJ/m3 or 56,250 ft lb/ft3) Compaction: General Principles Two basic compaction tests: Standard Proctor Compaction For retaining wall backfill, highway embankments, and low earth dams Modified Proctor Compaction For heavier load application such as airport runways, highway base courses, and high earth dams University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: STANDARD PROCTOR TEST By: CE Faculty Compaction: Standard Proctor Test For each test, the moist unit weight of compaction, γ, can be calculated as: Where: 𝑊 W = weight of the compacted soil in the mold 𝛾= Vm = volume of the mold (944cm3) 𝑉𝑚 For each test, the moisture content of the compacted soil is determined in the laboratory. With the known moisture content, the dry unit weight can be calculated as 𝛾 Where: 𝛾𝑑 = Yd = dry unit weight 𝜔 % Y = moist unit weight 1+ w = moist unit weight 100 Compaction: Standard Proctor Test For a given moisture content w and degree of saturation S, the dry unit weight of compaction can be calculated as: Where: 𝐺𝑠 𝛾𝑤 Yd = dry unit weight 𝛾𝑑 = Y = moist unit weight 𝐺𝑠 𝜔 1+ w = moist unit weight 𝑆 Gs = Specific Gravity S = degree of saturation For a given moisture content, the theoretical maximum dry unit weight is obtained when no air is in the void spaces—that is, when the degree of saturation equals 100%.Hence, the maximum dry unit weight at a given moisture content with zero air voids can be obtained by substituting S = 1: 𝐺𝑠 𝛾𝑤 𝛾𝑤 Where: 𝛾𝑧𝑎𝑣 = = Yzav = zero-air-void unit weight 1 + 𝜔𝐺𝑠 𝜔 + 1 𝐺𝑠 University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: MODIFIED PROCTOR TEST By: CE Faculty Compaction: Modified Proctor Test Omar et. Al (2003) Where: ρd(max) = maximum dry density (kg/m3 ) wopt = optimum moisture content(%) Gs = specific gravity of soil solids LL = liquid limit, in percent R#4 = percent retained on No. 4 sieve  modified Proctor compaction tests on 311 soil samples.  Of these samples, 45 were gravelly soil (GP, GP-GM, GW, GW-GM, and GM), 264 were sandy soil (SP, SP-SM, SW-SM, SW, SC-SM, SC, and SM), and two were clay with low plasticity (CL). Compaction: Modified Proctor Test Patra et. Al (2010) Where: Dr = maximum relative density of compaction achieved with compaction energy E (kN-m/m3 ) D50 = median grain size (mm)  For granular soils with less than 12% fines (i.e., finer than No. 200 sieve), relative density may be a better indicator for end product compaction specification in the field.  Based on laboratory compaction tests on 55 clean sands (less than 5% finer than No. 200 sieve) Compaction: Modified Proctor Test Gurtug and Sridharan(2004) For modified Proctor test, E = 2700 kN/m3. Hence, Where: PL = plastic limit (%) E = compaction energy (kN-m/m3 )  proposed correlations for optimum moisture content and maximum dry unit weight with the plastic limit (PL) of cohesive soils Compaction: Modified Proctor Test Osman et. Al (2008) Where: wopt = optimum water content (%) PI = plasticity index (%) γd(max) = maximum dry unit weight (kN/m3 ) E = compaction energy (kN-m/m3 )  analyzed a number of laboratory compaction test results on fine-grained (cohesive) soil, including those provided by Gurtug and Sridharan (2004) Compaction: Modified Proctor Test Matteo et. Al (2009) Where: LL = liquid limit (%) PI = plasticity index (%) Gs = specific gravity of soil solids  analyzed the results of 71 fine-grained soils and provided the following correlations for optimum water content (wopt) and maximum dry unit weight [γd(max)] for modified Proctor tests (E =2700 kN-m/m3) University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: FACTORS AFFECTING THE COMPACTION By: CE Faculty Compaction: Factors Affecting the Compaction A. Soil Type For sands, the dry unit weight has a general tendency first to decrease as moisture content increases and then to increase to a maximum value with further increase of moisture. The initial decrease of dry unit weight with increase of moisture content can be attributed to the capillary tension effect. At lower moisture contents, the capillary tension in the pore water inhibits the tendency of the soil particles to move around and be compacted densely. Typical compaction curves for four soils (ASTM D-698) Compaction: Factors Affecting the Compaction B. Compaction Effort The compaction energy per unit volume used for the standard Proctor test is: Compaction: Factors Affecting the Compaction B. Compaction Effort If the compaction effort per unit volume of soil is changed, the moisture–unit weight curve also changes. Four compaction curves for a sandy clay - The standard Proctor mold and hammer were used to obtain these compaction curves. The number of layers of soil used for compaction was three for all cases. However, the number of hammer blows per each layer varied from 20 to 50, which varied the energy per unit volume Observation: 1. As the compaction effort is increased, the maximum dry unit weight of compaction is also increased. 2. As the compaction effort is increased, the optimum moisture content is decreased to some extent. University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: EFFECTS OF COMPACTION ON PROPERTIES OF SOIL By: CE Faculty Compaction: Effects of compaction on properties of soil A. Soil Structure Flocculated structure (A, B and E).  Dispersed structure (E and D) According to Lambe (1958) Compaction: Effects of compaction on properties of soil B. Strength Samples compacted in the dry side of optimum tend to be more rigid and stronger than samples compacted wet-of-optimum Compaction: Effects of compaction on properties of soil C. Compressibility One-dimensional consolidation 1. At low stress - soil samples compacted at the wet side of optimum tend to be more compressible 2. At high stress – soil samples compacted at the dry side of optimum tend to be more compressible due to collapse of soil structure Compaction: Effects of compaction on properties of soil C. Compressibility One-dimensional consolidation 1. At low stress - soil samples compacted at the wet side of optimum tend to be more compressible 2. At high stress – soil samples compacted at the dry side of optimum tend to be more compressible due to collapse of soil structure Compaction: Effects of compaction on properties of soil D. Permeability Increasing water content results in a decrease in permeability in the dry side and a slight increase in the wet side Compaction: Effects of compaction on properties of soil E. Water Absorption Dry side of optimum compaction - There is more potential for water absorption and high swelling potential University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: FIELD COMPACTION By: CE Faculty Compaction: Field Compaction In the field, the soil is compacted by applying energy in three ways: Vibration Rolling and Kneading - By using vibrators - By using rollers equipment equipment - Rollers consist of smooth - Vibrators comprise of out- wheel, pneumatic, and of-balance type or sheepsfoot pulsating hydraulic type mounted on plates or Ramming rollers - By using rammers equipment - Rammers include dropping weights by internal combustion or pneumatic types Compaction: Field Compaction In the field, the soil is compacted by applying energy in three ways: Ramming - A hand-operated tamper consists of a block of iron (or stone), about 3-5kg in mass, attached to a wooden rod. The tamper is lifted for about 0.30m and dropped on the soil to be compacted. A mechanical rammer is operated by compressed air or gasoline power. It is much heavier, about 30-150kg. Tampers can be used for all types of soils Compaction: Field Compaction In the field, the soil is compacted by applying energy in three ways: Rollers - The compaction using a roller depends upon the following factors: (i) Contact pressure The compaction increases with an increase in the contact pressure. For a smooth-wheel roller, the contact pressure depends upon the load per unit width and the diameter of the roller. (ii) Number of passes The compaction of a soil increases with an increase in the number of passes made. For economy consideration, the number of passes is restricted to a reasonable limit between 5 to 15. (iii) Layer thickness The compaction of a soil increases with a decrease in the thickness of the layer. However, for economy consideration, the thickness is rarely ept less than 15cm. (iv) Speed of roller The compaction depends upon the speed of the roller. The speed should be so adjusted that the maximum effect is achieved. Compaction: Field Compaction In the field, the soil is compacted by applying energy in three ways: Rollers Smooth-wheel rollers (or smooth-drum rollers) -Smooth-wheel rollers are suitable for proof rolling subgrades and for finishing operation of fills with sandy and clayey soils. These rollers provide 100% coverage under the wheels, with ground contact pressures as high as 310 to 380 kN/m2. They are not suitable for producing high unit weights of compaction when used on thicker layers. Compaction: Field Compaction In the field, the soil is compacted by applying energy in three ways: Rollers Pneumatic rubber-tired rollers Pneumatic rubber-tired rollers are better in many respects than the smooth-wheel rollers. The former are heavily loaded with several rows of tires. These tires are closely spaced—four to six in a row. The contact pressure under the tires can range from 600 to 700 kN/m2, and they produce about 70 to 80% coverage. Pneumatic rollers can be used for sandy and clayey soil compaction. Compaction is achieved by a combination of pressure and kneading action. Compaction: Field Compaction In the field, the soil is compacted by applying energy in three ways: Rollers Sheepsfoot rollers Sheepsfoot rollers are drums with a large number of projections. The area of each projection may range from 25 to 85 cm2. These rollers are most effective in compacting clayey soils. The contact pressure under the projections can range from 1400 to 7000 kN/m2. During compaction in the field, the initial passes compact the lower portion of a lift. Compaction at the top and middle of a lift is done at a later stage. Compaction: Field Compaction In the field, the soil is compacted by applying energy in three ways: Vibration Vibratory rollers Vibratory rollers are extremely efficient in compacting granular soils. Vibrators can be attached to smooth-wheel, pneumatic rubber-tired, or sheepsfoot rollers to provide vibratory effects to the soil. Vibratory compactors can compact the granular soils to a very high maximum dry density. Compaction: Field Compaction Special Compaction Technique (1) Vibroflotation Vibroflotation is a technique for in situ densification of thick layers of loose granular soildeposits. It was developed in Germany in the 1930s. The first vibroflotation device was used in the United States about 10 years later. The process involves the use of a Vibroflot unit (also called the vibrating unit). Compaction: Field Compaction Special Compaction Technique (1) Vibroflotation Vibroflotation is a technique for in situ densification of thick layers of loose granular soildeposits. It was developed in Germany in the 1930s. The first vibroflotation device was used in the United States about 10 years later. The process involves the use of a Vibroflot unit (also called the vibrating unit). Compaction: Field Compaction Special Compaction Technique (1) Vibroflotation The grain-size distribution of the backfill material is an important factor that controls the rate of densification. Brown (1977) has defined a quantity called the suitability number for rating backfill as: where D50, D20, and D10 are the diameters (in mm) through which, respectively, 50, 20, and 10% of the material passes Compaction: Field Compaction Special Compaction Technique (2) Dynamic Compaction Dynamic compaction is a technique that has gained popularity in the United States for the densification of granular soil deposits. This process consists primarily of dropping a heavy weight repeatedly on the ground at regular intervals. The weight of the hammer used varies over a range of 80 to 360 kN, and the height of the hammer drop varies between 7.5 and 30.5 m. The stress waves generated by the hammer drops aid in the densification. The degree of compaction achieved at a given site depends on the following three factors: 1. Weight of hammer 2. Height of hammer drop 3. Spacing of locations at which the hammer is dropped Leonards, Cutter, and Holtz (1980) suggested that the significant depth of influence for compaction can be approximated by using the equation Compaction: Field Compaction Special Compaction Technique (3) Blasting Blasting is a technique that has been used successfully in many projects (Mitchell, 1970) for the densification of granular soils. The general soil grain sizes suitable for compaction by blasting are the same as those for compaction by vibroflotation. The process involves the detonation of explosive charges, such as 60% dynamite at a certain depth below the ground surface in saturated soil. The lateral spacing of the charges varies from about 3 to 9 m. Three to five successful detonations are usually necessary to achieve the desired compaction. Compaction (up to a relative density of about 80%) up to a depth of about 18 m over a large area can easily be achieved by using this process. Usually, the explosive charges are placed at a depth of about two-thirds of the thickness of the soil layer desired to be compacted. The sphere of influence of compaction by a 60% dynamite charge can be given as follows (Mitchell, 1970): University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: SUITABILITY OF VARIOUS METHODS OF COMPACTION By: CE Faculty Compaction: Suitability of Various Methods of Compaction 1. Cohesionless soils only – smooth-wheel rollers are suitable or compacting layers of small thickness in base courses. 2. Cohesive soils only – sheep-foot rollers are suitable for compaction of cohesive soils. 3. Both cohesive and cohesionless soils – The following methods are universal which can be used for both soils: (i) Tampers are effective for compacting soils in a confined space of all types (ii) Pneumatic-tyred rollers are extremely useful for compacting all types of soils (iii) Pounding method has a great promise for compacting all types of soils University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: SPECIFICATIONS FOR FIELD COMPACTION By: CE Faculty Compaction: Specifications for Field Compaction For control of field compaction, construction specifications require that the dry unit weight of field compacted soils be equal to or greater than a given percentage of the maximum dry unit weight, which typically 90% - 100% Where R = Relative Compaction Compaction: Specifications for Field Compaction For the compaction of granular soils, specifications sometimes are written in terms of the required relative density Dr or the required relative compaction. Where Dr = Relative Density Where R = Relative Compaction Lee and Singh (1971) devised a correlation between R and Dr for granular soils based on the observation of 47 soil samples: University of Science and Technology of Southern Philippines Civil Engineering Department GEOTECHNICAL ENGINEERING (SOIL MECHANICS) COMPACTION: DETERMINATION OF FIELD UNIT WEIGHT OF COMPACTION By: CE Faculty Compaction: Determination of Field Unit Weight of Compaction The standard procedures for determining the field unit weight of compaction include: 1. Sand cone method 2. Rubber balloon method 3. Nuclear method Sand cone method The sand cone device consists of a glass or plastic jar with a metal cone attached at its top. The jar is filled with uniform dry Ottawa sand. The combined weight of the jar, the cone, and the sand filling the jar is determined (W1). In the field, a small hole is excavated in the area where the soil has been compacted. If the weight of the moist soil excavated from the hole (W2) is determined and the moisture content of the excavated soil is known, the dry weight of the soil can be obtained as: Compaction: Determination of Field Unit Weight of Compaction The standard procedures for determining the field unit weight of compaction include: 1. Sand cone method 2. Rubber balloon method 3. Nuclear method Sand cone method After excavation of the hole, the cone with the sand-filled jar attached to it is inverted and placed over the hole. Sand is allowed to flow out of the jar to fill the hole and the cone. After that, the combined weight of the jar, the cone, and the remaining sand in the jar is determined (W4), so: where W5 = weight of sand to fill the hole and cone The volume of the excavated hole can then be determined as: Compaction: Determination of Field Unit Weight of Compaction The standard procedures for determining the field unit weight of compaction include: 1. Sand cone method 2. Rubber balloon method 3. Nuclear method Sand cone method The values of Wc and γd(sand) are determined from the calibration done in the laboratory. The dry unit weight of compaction made in the field then can be determined as follows: Compaction: Determination of Field Unit Weight of Compaction The standard procedures for determining the field unit weight of compaction include: 1. Sand cone method 2. Rubber balloon method 3. Nuclear method Rubber Balloon Method (ASTM Designation D-2167) The procedure for the rubber balloon method is similar to that for the sand cone method; a test hole is made and the moist weight of soil removed from the hole and its moisture content are determined. However, the volume of the hole is determined by introducing into it a rubber balloon filled with water from a calibrated vessel, from which the volume can be read directly. The dry unit weight of the compacted soil can be determined by using: Compaction: Determination of Field Unit Weight of Compaction The standard procedures for determining the field unit weight of compaction include: 1. Sand cone method 2. Rubber balloon method 3. Nuclear method Nuclear Method Nuclear density meters are often used for determining the compacted dry unit weight of soil. The density meters operate either in drilled holes or from the ground surface. It uses a radioactive isotope source. The isotope gives off Gamma rays that radiate back to the meter’s detector. Dense soil absorbs more radiation than loose soil. The instrument measures the weight of wet soil per unit volume and the weight of water present in a unit volume of soil. The dry unit weight of compacted soil can be determined by subtracting the weight of water from the moist unit weight of soil. University of Science and Technology of Southern Philippines Civil Engineering Department SAMPLE PROBLEMS By: CE Faculty SAMPLE PROBLEMS Situation 1 The laboratory test results of a standard Proctor test are given in the following table. a. Determine the maximum dry unit weight of compaction and the optimum moisture content. b. Calculate and plot γd versus the moisture content for degree of saturation, S = 80, 90, and 100% (i.e., γzav). Given: Gs = 2.7. c. Determine the void ratio at the optimum moisture content at GS = 2.68 d. Determine the degree of saturation at the optimum moisture content Solution 1: Part a: Determine the maximum dry unit weight of compaction and the optimum moisture content. The plot of γd versus Moist unit weight (a) w is shown. From the plot, we see that the 𝑊 16.81 maximum dry unit Dry Unit Weight 𝛾 = = = 17.81 weight γd(max) = 17.15 𝑉𝑚 944 kN/m3 and the optimum moisture Dry unit weight (b) content is 14.4%. 𝛾 17.81 Moisture Content 𝛾𝑑 = 𝜔 = = 16.19 1 + 10 100 1 + 100 Solution 1: Part b: Calculate and plot γd versus the moisture content for degree of saturation, S = 80, 90, and 100% (i.e., γzav). Given: Gs = 2.7. Dry unit weight (b) 𝐺𝑠 𝛾𝑑 2.7 9.81 𝛾𝑑 = 𝐺𝑠 𝜔 = 2.7 8 = 20.84 1+ 1+ 𝑆 80 Solution 1: Part c: Determine the void ratio at the optimum moisture content at GS = 2.68 3 𝛾𝑑𝑟𝑦 = 17.15 𝑘𝑁/𝑚 𝐺𝑠 𝛾𝑤 𝛾𝑑𝑟𝑦 = 1 + 𝑒 2.68 9.81 17.15 = 1 + 𝑒 Part d: Determine the degree of saturation at the optimum moisture content Degree of saturation at the optimum moisture content 𝜔𝐺𝑠 14.4 2.68 𝑆= = = 72.4% 𝑒 0.533 SAMPLE PROBLEMS Situation 2 Following are the details for the backfill material in a vibroflotation project. D10 = 0.36mm D20 = 0.52mm D50 = 1.42mm D75 = 1.65mm D25 = 0.60mm a. Determine the suitability number (SN) b. Determine the rating of this backfill materials Solution 2: Part a: Suitability Number. 3 1 1 𝑆𝑁 = 1.7 + + (𝐷50 )2 (𝐷20 )2 (𝐷10 )2 3 1 1 𝑆𝑁 = 1.7 2 + 2 + (1.42) (0.52) (0.36)2 𝑆𝑁 = 6.10 Part b: Rating of this backfill. SAMPLE PROBLEMS Situation 3 The maximum and minimum dry unit weights of a sand were determined in the laboratory to be 18.31 kN/m3 and 15.25 kN/m3, respectively. a. What is the relative compaction in the field if the relative density is 64%? b. What is the dry unit weight in the field? c. What is the Moist unit weight in the field if its moisture content is 28%? Solution 3: Part a: Relative compaction in the field: 𝛾𝑑(min) 15.25 𝑅𝑜 = = = 0.8329 𝛾𝑑(max) 18.31 𝑅𝑜 0.8329 𝑅 = = = 0.933 = 93.3% 1 − 𝐷𝑟 1 − 𝑅𝑜 1 − 0.64 1 − 0.8329 Part b: Dry unit weight in the field 𝛾𝑑(𝑓𝑖𝑒𝑙𝑑) 𝑅= 𝛾𝑑(𝑚𝑎𝑥−𝑙𝑎𝑏) 𝛾𝑑(𝑓𝑖𝑒𝑙𝑑) 0.933 = 18.31 𝛾𝑑(𝑓𝑖𝑒𝑙𝑑) = 17.08 𝑘𝑁/𝑚3 Solution 3: Part C: Moist unit weight in the field 𝛾𝑚𝑜𝑖𝑠𝑡 𝛾𝑑 = 1 + 𝜔 𝛾𝑚𝑜𝑖𝑠𝑡 = 𝛾𝑑 1 + 𝜔 = 17.08 1 + 0.28 = 21.86 𝑘𝑁/𝑚3 University of Science and Technology of Southern Philippines Civil Engineering Department ANY QUESTIONS? By: CE Faculty University of Science and Technology of Southern Philippines Civil Engineering Department THANK YOU! By: CE Faculty