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Soil Improvement1.1 Methods for Soil Improvement: 1.1 Methods for Soil Improvement Ground Reinforcement Ground Improvement Ground Treatment Stone Columns Soil Nails Deep Soil Nailing Micropiles (Mini-piles) Jet Grouting Ground Anchors Geosynthetics Fiber Reinforcement Lime Columns Vibro-Concrete Column Mechanically Stabilized Earth Biotechnical Deep Dynamic Compaction Drainage/Surcharge Electro-osmosis Compaction grouting Blasting Surface Compaction Soil Cement Lime Admixtures Flyash Dewatering Heating/Freezing Vitrification Compaction Shaefer, 19971.1 Methods for Soil Improvement-Jet Grouting: 1.1 Methods for Soil Improvement- Jet Grouting Courtesy of Menard-soltraitement1.1 Methods for Soil Improvement-Soil Nailing: 1.1 Methods for Soil Improvement-Soil Nailing Courtesy of Atlas Copco Rock Drilling Equipment1.2 Elephant and Compaction: 1.2 Elephant and Compaction Heavy Weight Question? The compaction result is not good. Why? He He! I’m smart.2. Compaction: 2. Compaction2.1 Compaction and Objectives: 2.1 Compaction and Objectives Compaction Many types of earth construction, such as dams, retaining walls, highways, and airport, require man-placed soil, or fill. To compact a soil, that is, to place it in a dense state. The dense state is achieved through the reduction of the air voids in the soil, with little or no reduction in the water content. This process must not be confused with consolidation, in which water is squeezed out under the action of a continuous static load. Objectives: Decrease future settlements Increase shear strength Decrease permeability (From Lambe, 1991; Head, 1992)2.2 General Compaction Methods: 2.2 General Compaction Methods Coarse-grained soils Fine-grained soils Hand-operated vibration plates Motorized vibratory rollers Rubber-tired equipment Free-falling weight; dynamic compaction (low frequency vibration, 4~10 Hz) Falling weight and hammers Kneading compactors Static loading and press Hand-operated tampers Sheepsfoot rollers Rubber-tired rollers Laboratory Field Vibration Vibrating hammer (BS) (Holtz and Kovacs, 1981; Head, 1992) Kneading dough3. Theory of Compaction(Laboratory Test): 3. Theory of Compaction (Laboratory Test)3.1 Laboratory Compaction: 3.1 Laboratory Compaction Origin The fundamentals of compaction of fine-grained soils are relatively new. R.R. Proctor in the early 1930’s was building dams for the old Bureau of Waterworks and Supply in Los Angeles, and he developed the principles of compaction in a series of articles in Engineering News-Record. In his honor, the standard laboratory compaction test which he developed is commonly called the proctor test. Purpose The purpose of a laboratory compaction test is to determine the proper amount of mixing water to use when compacting the soil in the field and the resulting degree of denseness which can be expected from compaction at this optimum water Impact compaction The proctor test is an impact compaction. A hammer is dropped several times on a soil sample in a mold. The mass of the hammer, height of drop, number of drops, number of layers of soil, and the volume of the mold are specified.3.1.1 Various Types: 3.1.1 Various Types Various types of compaction test 1 2 3 1: your test 2: Standard Proctor test 3: Modified Proctor test3.1.2 Test Equipment: 3.1.2 Test Equipment Standard Proctor test equipment Das, 19983.1.3 Comparison- Standard and Modified Proctor Compaction Test: 3.1.3 Comparison- Standard and Modified Proctor Compaction Test Summary of Standard Proctor Compaction Test Specifications (ASTM D-698, AASHTO) Das, 19983.1.3 Comparison- Standard and Modified Proctor Compaction Test (Cont.): 3.1.3 Comparison- Standard and Modified Proctor Compaction Test (Cont.) Summary of Modified Proctor Compaction Test Specifications (ASTM D-698, AASHTO) Das, 19983.1.3 Comparison-Summary: 3.1.3 Comparison-Summary Standard Proctor Test 12 in height of drop 5.5 lb hammer 25 blows/layer 3 layers Mold size: 1/30 ft3 Energy 12,375 ft·lb/ft3 Modified Proctor Test 18 in height of drop 10 lb hammer 25 blows/layer 5 layers Mold size: 1/30 ft3 Energy 56,250 ft·lb/ft3 Higher compacting energy3.1.4 Comparison-Why?: 3.1.4 Comparison-Why? In the early days of compaction, because construction equipment was small and gave relatively low compaction densities, a laboratory method that used a small amount of compacting energy was required. As construction equipment and procedures were developed which gave higher densities, it became necessary to increase the amount of compacting energy in the laboratory test. The modified test was developed during World War II by the U.S. Army Corps of Engineering to better represent the compaction required for airfield to support heavy aircraft. The point is that increasing the compactive effort tends to increase the maximum dry density, as expected, but also decrease the optimum water content. (Holtz and Kovacs, 1981; Lambe, 1991)3.2 Variables of Compaction: 3.2 Variables of Compaction Proctor established that compaction is a function of four variables: Dry density (d) or dry unit weight d. Water content w Compactive effort (energy E) Soil type (gradation, presence of clay minerals, etc.) For standard Proctor test3.3 Procedures and Results: 3.3 Procedures and Results Procedures Several samples of the same soil, but at different water contents, are compacted according to the compaction test specifications. The total or wet density and the actual water content of each compacted sample are measured. Plot the dry densities d versus water contents w for each compacted sample. The curve is called as a compaction curve. Derive d from the known and w The first four blows The successive blows3.3 Procedures and Results (Cont.): 3.3 Procedures and Results (Cont.) Results Zero air void Water content w (%) Dry density d (Mg/m3) Dry density d (lb/ft3) Line of optimums Modified Proctor Standard Proctor Peak point Line of optimum Zero air void Holtz and Kovacs, 1981 d max wopt3.3 Procedures and Results (Cont.): 3.3 Procedures and Results (Cont.) The peak point of the compaction curve The peak point of the compaction curve is the point with the maximum dry density d max. Corresponding to the maximum dry density d max is a water content known as the optimum water content wopt (also known as the optimum moisture content, OMC). Note that the maximum dry density is only a maximum for a specific compactive effort and method of compaction. This does not necessarily reflect the maximum dry density that can be obtained in the field. Zero air voids curve The curve represents the fully saturated condition (S = 100 %). (It cannot be reached by compaction) Line of optimums A line drawn through the peak points of several compaction curves at different compactive efforts for the same soil will be almost parallel to a 100 % S curve, it is called the line of optimums3.3 Procedures and Results (Cont.): 3.3 Procedures and Results (Cont.) The Equation for the curves with different degree of saturation is : You can derive the equation by yourself Hint: Holtz and Kovacs, 19813.3 Procedures and Results-Explanation: 3.3 Procedures and Results-Explanation Below wopt (dry side of optimum): As the water content increases, the particles develop larger and larger water films around them, which tend to “lubricate” the particles and make them easier to be moved about and reoriented into a denser configuration. At wopt: The density is at the maximum, and it does not increase any further. Above wopt (wet side of optimum): Water starts to replace soil particles in the mold, and since w << s the dry density starts to decrease. Holtz and Kovacs, 1981 Lubrication or loss of suction??3.3 Procedures and Results-Notes: 3.3 Procedures and Results-Notes Each data point on the curve represents a single compaction test, and usually four or five individual compaction tests are required to completely determine the compaction curve. At least two specimens wet and two specimens dry of optimum, and water contents varying by about 2%. Optimum water content is typically slightly less than the plastic limit (ASTM suggestion). Typical values of maximum dry density are around 1.6 to 2.0 Mg/m3 with the maximum range from about 1.3 to 2.4 Mg/m3. Typical optimum water contents are between 10% and 20%, with an outside maximum range of about 5% to 40%. Holtz and Kovacs, 19813.4 Effects of Soil Types on Compaction: 3.4 Effects of Soil Types on Compaction The soil type-that is, grain-size distribution, shape of the soil grains, specific gravity of soil solids, and amount and type of clay minerals present. Holtz and Kovacs, 1981; Das, 19983.5 Field and Laboratory Compaction: 3.5 Field and Laboratory Compaction It is difficult to choose a laboratory test that reproduces a given field compaction procedure. The laboratory curves generally yield a somewhat lower optimum water content than the actual field optimum. The majority of field compaction is controlled by the dynamic laboratory tests. Curve 1, 2,3,4: laboratory compaction Curve 5, 6: Field compaction (From Lambe and Whitman, 1979)4. Properties and Structure of Compacted Fine-grained Soils: 4. Properties and Structure of Compacted Fine-grained Soils4.1 Structure of Compacted Clays: 4.1 Structure of Compacted Clays For a given compactive effort and dry density, the soil tends to be more flocculated (random) for compaction on the dry side as compared on the wet side. For a given molding water content, increasing the compactive effort tends to disperse (parallel, oriented) the soil, especially on the dry side. Lambe and Whitman, 19794.2 Engineering Properties-Permeability : 4.2 Engineering Properties-Permeability Increasing the water content results in a decrease in permeability on the dry side of the optimum moisture content and a slight increase in permeability on the wet side of optimum. Increasing the compactive effort reduces the permeability since it both increases the dry density, thereby reducing the voids available for flow, and increases the orientation of particles. From Lambe and Whitman, 1979; Holtz and Kovacs, 19814.3 Engineering Properties-Compressibility : 4.3 Engineering Properties-Compressibility At low stresses the sample compacted on the wet side is more compressible than the one compacted on the dry side. From Lambe and Whitman, 1979; Holtz and Kovacs, 19814.3 Engineering Properties-Compressibility: 4.3 Engineering Properties-Compressibility At the high applied stresses the sample compacted on the dry side is more compressible than the sample compacted on the wet side. From Lambe and Whitman, 1979; Holtz and Kovacs, 19814.4 Engineering Properties-Swelling : 4.4 Engineering Properties-Swelling Swelling of compacted clays is greater for those compacted dry of optimum. They have a relatively greater deficiency of water and therefore have a greater tendency to adsorb water and thus swell more. w d (wopt, d max) Higher swelling potential From Holtz and Kovacs, 1981 Higher shrinkage potential4.5 Engineering Properties-Strength: 4.5 Engineering Properties-Strength Samples (Kaolinite) compacted dry of optimum tend to be more rigid and stronger than samples compacted wet of optimum From Lambe and Whitman, 19794.5 Engineering Properties-Strength (Cont.): 4.5 Engineering Properties-Strength (Cont.) The CBR (California bearing ratio) CBR= the ratio between resistance required to penetrate a 3-in2 piston into the compacted specimen and resistance required to penetrate the same depth into a standard sample of crushed stone. Holtz and Kovacs, 1981 A greater compactive effort produces a greater CBR for the dry of optimum. However, the CBR is actually less for the wet of optimum for the higher compaction energies (overcompaction).4.6 Engineering Properties-Summary: 4.6 Engineering Properties-Summary Dry side Wet side Permeability Compressibility Swelling Strength Structure More random More oriented (parallel) More permeable More compressible in high pressure range More compressible in low pressure range Swell more, higher water deficiency Higher Please see Table 5-1 *Shrink more4.6 Engineering Properties-Summary (Cont.): 4.6 Engineering Properties-Summary (Cont.) Please find this table in the handout Holtz and Kovacs, 19814.6 Engineering Properties-Notes: 4.6 Engineering Properties-Notes Engineers must consider not only the behavior of the soil as compacted but the behavior of the soil in the completed structure, especially at the time when the stability or deformation of the structure is most critical. For example, consider an element of compacted soil in a dam core. As the height of the dam increases, the total stresses on the soil element increase. When the dam is performing its intended function of retaining water, the percent saturation of the compacted soil element is increased by the permeating water. Thus the engineer designing the earth dam must consider not only the strength and compressibility of the soil element as compacted, but also its properties after is has been subjected to increased total stresses and saturated by permeating water. Lambe and Whitman, 19795. Field Compaction Equipment and Procedures: 5. Field Compaction Equipment and Procedures5.1 Equipment: 5.1 Equipment Smooth-wheel roller (drum) 100% coverage under the wheel Contact pressure up to 380 kPa Can be used on all soil types except for rocky soils. Compactive effort: static weight The most common use of large smooth wheel rollers is for proof-rolling subgrades and compacting asphalt pavement. Holtz and Kovacs, 19815.1 Equipment (Cont.): 5.1 Equipment (Cont.) Pneumatic (or rubber-tired) roller 80% coverage under the wheel Contact pressure up to 700 kPa Can be used for both granular and fine-grained soils. Compactive effort: static weight and kneading. Can be used for highway fills or earth dam construction. Holtz and Kovacs, 19815.1 Equipment (Cont.): 5.1 Equipment (Cont.) Sheepsfoot rollers Has many round or rectangular shaped protrusions or “feet” attached to a steel drum 8% ~ 12 % coverage Contact pressure is from 1400 to 7000 kPa It is best suited for clayed soils. Compactive effort: static weight and kneading. Holtz and Kovacs, 19815.1 Equipment (Cont.): 5.1 Equipment (Cont.) Tamping foot roller About 40% coverage Contact pressure is from 1400 to 8400 kPa It is best for compacting fine-grained soils (silt and clay). Compactive effort: static weight and kneading. Holtz and Kovacs, 19815.1 Equipment (Cont.): 5.1 Equipment (Cont.) Mesh (or grid pattern) roller 50% coverage Contact pressure is from 1400 to 6200 kPa It is ideally suited for compacting rocky soils, gravels, and sands. With high towing speed, the material is vibrated, crushed, and impacted. Compactive effort: static weight and vibration. Holtz and Kovacs, 19815.1 Equipment (Cont.): 5.1 Equipment (Cont.) Vibrating drum on smooth-wheel roller Vertical vibrator attached to smooth wheel rollers. The best explanation of why roller vibration causes densification of granular soils is that particle rearrangement occurs due to cyclic deformation of the soil produced by the oscillations of the roller. Compactive effort: static weight and vibration. Suitable for granular soils Holtz and Kovacs, 19815.1 Equipment-Summary: 5.1 Equipment-Summary Holtz and Kovacs, 19815.2 Variables-Vibratory Compaction: 5.2 Variables-Vibratory Compaction There are many variables which control the vibratory compaction or densification of soils. Characteristics of the compactor: (1) Mass, size (2) Operating frequency and frequency range Characteristics of the soil: (1) Initial density (2) Grain size and shape (3) Water content Construction procedures: (1) Number of passes of the roller (2) Lift thickness (3) Frequency of operation vibrator (4) Towing speed Holtz and Kovacs, 19815.2.1 Frequency : 5.2.1 Frequency Holtz and Kovacs, 1981 The frequency at which a maximum density is achieved is called the optimum frequency.5.2.2 Roller Travel Speed: 5.2.2 Roller Travel Speed For a given number of passes, a higher density is obtained if the vibrator is towed more slowly. Holtz and Kovacs, 19815.2.3 Roller Passes: 5.2.3 Roller Passes Holtz and Kovacs, 1981 When compacting past five or so coverages, there is not a great increase in density 240 cm think layer of northern Indiana dune sand 5670 kg roller operating at a frequency of 27.5 Hz.5.2.4 Determine the Lift Height: 5.2.4 Determine the Lift Height Holtz and Kovacs, 19815.3 Dynamic Compaction: 5.3 Dynamic Compaction Dynamic compaction was first used in Germany in the mid-1930’s. The depth of influence D, in meters, of soil undergoing compaction is conservatively given by D ½ (Wh)1/2 W = mass of falling weight in metric tons. h = drop height in meters From Holtz and Kovacs, 19815.4 Vibroflotation: 5.4 Vibroflotation From Das, 1998 Vibroflotation is a technique for in situ densification of thick layers of loose granular soil deposits. It was developed in Germany in the 1930s.5.4 Vibroflotation-Procedures: 5.4 Vibroflotation-Procedures Stage1: The jet at the bottom of the Vibroflot is turned on and lowered into the ground Stage2: The water jet creates a quick condition in the soil. It allows the vibrating unit to sink into the ground Stage 3: Granular material is poured from the top of the hole. The water from the lower jet is transferred to he jet at the top of the vibrating unit. This water carries the granular material down the hole Stage 4: The vibrating unit is gradually raised in about 0.3-m lifts and held vibrating for about 30 seconds at each lift. This process compacts the soil to the desired unit weight. From Das, 19986. Field Compaction Control and Specifications: 6. Field Compaction Control and Specifications6.1 Control Parameters: 6.1 Control Parameters Dry density and water content correlate well with the engineering properties, and thus they are convenient construction control parameters. Since the objective of compaction is to stabilize soils and improve their engineering behavior, it is important to keep in mind the desired engineering properties of the fill, not just its dry density and water content. This point is often lost in the earthwork construction control. From Holtz and Kovacs, 19816.2 Design-Construct Procedures: 6.2 Design-Construct Procedures Laboratory tests are conducted on samples of the proposed borrow materials to define the properties required for design. After the earth structure is designed, the compaction specifications are written. Field compaction control tests are specified, and the results of these become the standard for controlling the project. From Holtz and Kovacs, 19816.3 Specifications: 6.3 Specifications End-product specifications This specification is used for most highways and building foundation, as long as the contractor is able to obtain the specified relative compaction , how he obtains it doesn’t matter, nor does the equipment he uses. Care the results only ! (2) Method specifications The type and weight of roller, the number of passes of that roller, as well as the lift thickness are specified. A maximum allowable size of material may also be specified. It is typically used for large compaction project. From Holtz and Kovacs, 19816.4 Relative Compaction (R.C.): 6.4 Relative Compaction (R.C.) Relative compaction or percent compaction Correlation between relative compaction (R.C.) and the relative density Dr It is a statistical result based on 47 soil samples. As Dr = 0, R.C. is 80 Typical required R.C. = 90% ~ 95%6.5 Determine the Water Content (in Field): 6.5 Determine the Water Content (in Field) Control (1) Relative compaction (2) Water content (dry side or wet side) Holtz and Kovacs, 1981 Note: the engineering properties may be different between the compacted sample at the dry side and at the wet side. 100% saturation Water content w % wopt Dry density, d d max Line of optimums 90% R.C. a c Increase compaction energy b6.6 Determine the Relative Compaction in the Field: 6.6 Determine the Relative Compaction in the Field Where and When First, the test site is selected. It should be representative or typical of the compacted lift and borrow material. Typical specifications call for a new field test for every 1000 to 3000 m2 or so, or when the borrow material changes significantly. It is also advisable to make the field test at least one or maybe two compacted lifts below the already compacted ground surface, especially when sheepsfoot rollers are used or in granular soils. Method Field control tests, measuring the dry density and water content in the field can either be destructive or nondestructive. Holtz and Kovacs, 19816.6.1 Destructive Methods: 6.6.1 Destructive Methods Holtz and Kovacs, 1981 Methods (a) Sand cone (b) Balloon (c) Oil (or water) method Calculations Know Ms and Vt Get d field and w (water content) Compare d field with d max-lab and calculate relative compaction R.C. (a) (b) (c)6.6.1 Destructive Methods (Cont.): 6.6.1 Destructive Methods (Cont.) Sometimes, the laboratory maximum density may not be known exactly. It is not uncommon, especially in highway construction, for a series of laboratory compaction tests to be conducted on “representative” samples of the borrow materials for the highway. If the soils at the site are highly varied, there will be no laboratory results to be compared with. It is time consuming and expensive to conduct a new compaction curve. The alternative is to implement a field check point, or 1 point Proctor test. Holtz and Kovacs, 19816.6.1 Destructive Methods (Cont.): 6.6.1 Destructive Methods (Cont.) Check Point Method Water content w % wopt Dry density, d d max 100% saturation Line of optimums A B M C X Y(no) 1 point Proctor test Known compaction curves A, B, C Field check point X (it should be on the dry side of optimum) Holtz and Kovacs, 19816.6.1 Destructive Methods (Cont.): 6.6.1 Destructive Methods (Cont.) The measuring error is mainly from the determination of the volume of the excavated material. For example, For the sand cone method, the vibration from nearby working equipment will increase the density of the sand in the hole, which will gives a larger hole volume and a lower field density. If the compacted fill is gravel or contains large gravel particles. Any kind of unevenness in the walls of the hole causes a significant error in the balloon method. If the soil is coarse sand or gravel, none of the liquid methods works well, unless the hole is very large and a polyethylene sheet is used to contain the water or oil. Holtz and Kovacs, 19816.6.2 Nondestructive Methods: 6.6.2 Nondestructive Methods Holtz and Kovacs, 1981 Nuclear density meter (a) Direct transmission (b) Backscatter (c) Air gap (a) (b) (c) Principles Density The Gamma radiation is scattered by the soil particles and the amount of scatter is proportional to the total density of the material. The Gamma radiation is typically provided by the radium or a radioactive isotope of cesium. Water content The water content can be determined based on the neutron scatter by hydrogen atoms. Typical neutron sources are americium-beryllium isotopes.6.6.2 Nondestructive Methods (Cont.): 6.6.2 Nondestructive Methods (Cont.) Calibration Calibration against compacted materials of known density is necessary, and for instruments operating on the surface the presence of an uncontrolled air gap can significantly affect the measurements.7. Estimating Performance of Compacted Soils: 7. Estimating Performance of Compacted Soils7.1 Definition of Pavement Systems: 7.1 Definition of Pavement Systems Holtz and Kovacs, 19817.2 Characteristics Pertinent to Roads and Airfield : 7.2 Characteristics Pertinent to Roads and Airfield Please refer to the handout Holtz and Kovacs, 19817.2 Characteristics Pertinent to Roads and Airfield (Cont.) : 7.2 Characteristics Pertinent to Roads and Airfield (Cont.) Holtz and Kovacs, 1981 Please refer to the handout7.3 Engineering Properties of Compacted Soils: 7.3 Engineering Properties of Compacted Soils Holtz and Kovacs, 1981 Please refer to the handout8. Suggested Homework: 8. Suggested Homework Read Chapter 5 (Holtz’s book) Example 5.1 ~ Example 5.4 Problem 5.9, 5.12, 5.149. References: 9. References Main References: Holtz, R.D. and Kovacs, W.D. (1981). An Introduction to Geotechnical Engineering, Prentice Hall. (Chapter 5) Others: Das, B.M. (1998). Principles of Geotechnical Engineering, 4th edition, PWS Publishing Company. Lambe, T.W. and Whitman, R.V. (1979). Soil Mechanics, SI Version, John Wiley & Sons. Schaefer, V. R. (1997). Ground Improvement, Ground Reinforcement, Ground Treatment, Proceedings of Soil Improvement and Geosynthetics of The Geo-Institute of the American Society of Civil Engineers in conjunction with Geo-Logan’97. Edited by V.R. Schaefer. You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.