Ch. 5 - Compaction Page 1. Learning Objectives. Thursday, February 03, 2011

Transcription

1 Ch. 5 - Compaction Page 1 Learning Objectives

2 Ch. 5 - Compaction Page 2 Symbols

3 Ch. 5 - Compaction Page 3 Compaction - Introduction

4 Ch. 5 - Compaction Page 4 Compaction - Introduction (cont.)

5 Ch. 5 - Compaction Page 5 Types of Compaction Static (rolling) Dynamic (impact) Kneading (remolding) Vibratory (shaking) Static Compaction laboratory Field Smooth drum roller

6 Ch. 5 - Compaction Page 6 Types of Compaction (cont.) Dynamic Compaction Laboratory Field Dynamic compaction at a site in Bangladesh. The 100-ton crane is dropping a 16-metric-ton weight 30 m (courtesy of S. Varaksin, Techniques Louis Ménard, Longjumeau, France). rod (i.e., hammer inside soil mold lifts ups and free falls to compact soil.)

7 Ch. 5 - Compaction Page 7 Types of Compaction (cont.) Kneading Compaction Laboratory Field Sheepsfoot Roller Kneading compaction of clay by potter Modern compactor with tamping drum Laboratory Kneading Compactor

8 Ch. 5 - Compaction Page 8 Types of Compaction (cont.) Vibratory Compaction Laboratory Vibrating Table in lab Field Vibratory plate compactor Vibratory drum roller (static + vibratory compaction

9 Ch. 5 - Compaction Page 9 Comparison of Compaction Methods Note that the type of compaction used varies with type of material (clay vs sand vs gravel).

10 Ch. 5 - Compaction Page 10 Design Process

11 Ch. 5 - Compaction Page 11 Desired Engineering Properties Soil compaction is a vital part of the construction process. It is used for support of structural entities such as building foundations, roadways, walkways, and earth retaining structures to name a few. For a given soil type certain properties may deem it more or less desirable to perform adequately for a particular circumstance. In general, the preselected soil should have adequate strength, be relatively incompressible so that future settlement is not significant, be stable against volume change as water content or other factors vary, be durable and safe against deterioration, and possess proper permeability Pasted from < Note that part of this house is being placed on fill. It is important that the fill be compacted properly to prevent damage to the structure and other adjoining items. cracking from improper compaction Damage to masonry wall from settlement

12 Ch. 5 - Compaction Page 12 Desired Engineering Properties (cont.) Compaction is required for almost all constructed works in one form or another. It is routinely done to improve the performance of the soil so that it can used as part of a geosystem without causing adverse effects to the constructed works. Engineering Objectives of Compaction Reduce Differential Settlement Structures Driveways and Walkways Roadways Pipelines Other Utilities Embankments Dams Improve Shear Strength and Bearing Capacity Embankment and Earthen Dams Stability Slope Stability Shallow Foundations and Footings Retaining walls Roadways Prevent Undesirable Volume Change Reduce Shrinkage Reduce Swell Decrease permeability Clay core of earthen dams Covers and liners of landfills and waste containment facilities

13 Ch. 5 - Compaction Page 13 Laboratory Testing Laboratory testing is required to determine the compactive nature of the soil and its ability to achieve the desired engineering properties. Standard Proctor Test (ASTM D698) Note that compactive effort is in terms of potential energy per volume of soil (see below).

14 Ch. 5 - Compaction Page 14 Laboratory Testing (cont.) Equipment for Standard and Modified Proctor Test Molds Standard Proctor Hammer Modified Proctor Hammer

15 Ch. 5 - Compaction Page 15 Laboratory Testing (cont.) Modified Proctor Test (ASTM D1557)

16 Ch. 5 - Compaction Page 16 Laboratory Compaction Curves Optimum moisture content is where the dry density reaches a peak (See next page for answer to this question)

17 Ch. 5 - Compaction Page 17 Laboratory Compaction Curves (cont.) Because water is less dense than the soil and by adding too much water one can actually cause the density of soil to decrease during the compaction process.

18 Ch. 5 - Compaction Page 18 Laboratory Compaction Curves and the Line of Optimums Circles represent a single compaction test at varying moisture content The zero air voids curve shown below represents a theoretical soil where all of the air void has been removed (i.e., saturation equals 100 percent). Note that the line of optimum moisture content is about saturation equals 80 percent and that the slope of the line parallels that of the zero air voids curve. Is it possible to remove all of the voids if a sample is compacted completely dry? If it were possible, what would be the value of d if all of the air voids were removed by compaction? Is it possible to remove all of the voids, if a sample is compacted with some water in its fabric? Is it possible to remove all of the air voids, if a sample is compacted with some water in its fabric.

19 Ch. 5 - Compaction Page 19 Laboratory Compaction Curves Calculations As an alternative, the chart on the following page can be used to verify a solution.

20 Ch. 5 - Compaction Page 20 Laboratory Compaction Curve Calculations (cont.) Solution of the soil solids water-voids relationships of soil masses (Bureau of Public Roads, now the Federal Highway Administration).

21 Ch. 5 - Compaction Page 21 Laboratory Compaction Curves Calculations Soils with different soil type and gradations will have different compactions curves, thus the compactability of soil must be determined on a case-by-case basis.

22 Ch. 5 - Compaction Page 22 Specify Design Values - Concept of Relative Compaction Note that maximum dry density obtained in the laboratory from the compaction test does not necessarily represent the maximum density that will be obtained in the field using construction compaction equipment. The field values are compared with the laboratory curves using the relative compaction. To calculate the relative compaction, this requires a field measurement of the compaction achieved by the compaction equipment using field compaction control measurements, as discussed later.

23 Ch. 5 - Compaction Page 23 Specify Design Value - Equipment Selection Considerations Comparison of field and laboratory compaction. (1) Laboratory static compaction, 2000 psi; (2) modified Proctor; (3) standard Proctor; (4) laboratory static compaction, 200 psi; (5) field compaction, rubber-tired load, 6 coverages; (6) field compaction, sheepsfoot roller, 6 passes. Note: Static compaction from top and bottom of soil sample. (After Turnbull, 1950, and as cited by Lambe and Whitman, 1969.) (See also USAE WES 1949.)

24 Ch. 5 - Compaction Page 24 Specify Design Value - Importance of Vibration Compaction results on 30 cm (12 in.) layers of silty sand, with and without vibration, using a 7700 kg (17000 lb) towed vibratory roller (after Parsons et al., 1962, as cited by Selig and Yoo, 1977). Vibratory Steel Drum Roller Compactor

25 Ch. 5 - Compaction Page 25 Specify Design Value - Importance of Weight and Vibration Frequency for Various Soil Types Variation with frequency of compaction by smooth-drum vibratory rollers (after several sources as cited by Selig and Yoo, 1977).

26 Ch. 5 - Compaction Page 26 Specify Design Values - Importance of Speed and No. of Passes Effect of roller travel speed on amount of compaction with 7700 kg ( lb) towed vibratory roller (after parsons et al., 1962, as cited by Selig and Yoo, 1977).

27 Ch. 5 - Compaction Page 27 Specify Design Values - Effect of Roller Passes on Depth Density-depth relationship for a 5670 kg ( lb) roller operating at 27.5Hz for a 240 cm (94.5 in.) lift height.

28 Ch. 5 - Compaction Page 28 Specify Design Values - Determining Lift Thickness Approximate method for determining lift thickness required to achieve a minimum compacted relative density of 75% with five roller passes, using data for a large lift thickness (after D Appolonia et al., 1969).

29 Ch. 5 - Compaction Page 29 Specify Design Value - Effects of Compaction on Permeability for Clayey Soils Used for Landfill Liners and Covers

30 Ch. 5 - Compaction Page 30 Specify Design Value - Effects of Compaction on Permeability for Clayey Soils Used for Landfill Liners and Covers

31 Ch. 5 - Compaction Page 31 Specify Design Values - Controlling Shrinkage and Swell (Clayey Soils)

32 Ch. 5 - Compaction Page 32 Specify Design Values - Controlling Shrinkage and Swell (Clayey Soils)

33 Ch. 5 - Compaction Page 33 Specify Design Values - Controlling Shrinkage and Swell (Clayey Soils)

34 Ch. 5 - Compaction Page 34 Write Specification - Specification Checklist Items usually found in most specifications Type(s) of items to be compacted base subbase embankment select fill structural fill liners and covers Material specification for acceptable material(s) acceptable soil type (USCS or AASHTO classification) acceptable gradation range limits on plasticity (granular soils) limits on fines content (granular soils) limits on over-sized particles (granular soils) Acceptable minimum value of relative compaction based on modified Proctor test or standard proctor test Acceptable moisture content range Maximum lift thickness Minimum number of passes Maximum allowable permeability value (clay covers and liners only) Quality control requirements Type of field verification (nuclear density gage, sand cone, etc.) Frequency of field testing every 1000 to 3000 m 3 when material changes minimum one test per lift depth test within the lift Frequency of allowable failures Corrective action for non conformance Replace Rescarify and recompact Note that some items, such as type of equipment are not specified because this is usually determined by the contract. However, sometimes a list of acceptable types of equipment is furnished.

35 Ch. 5 - Compaction Page 35 Write Specification - Typical Required Max. Dry Density Typical Requirements for Relative Compaction - Highway Construction Recompaction of subgrade after scarifying A1 Soils - 96% Modified Proctor A2 - A7 Soils - 96% Standard Proctor Recompaction of embankment after scarifying A1 Soils - 90% Modified Proctor A2 - A7 Soils - 90% Standard Proctor Embankment Construction A1 Soils - 96% Modified Proctor A2 - A4 Soils - 96% Standard Proctor Untreated Base Course (UTBC) 97% Modified Proctor + 2% of Optimum moisture content Hydrated lime treated roadbed 96% Modified Proctor Typical Requirements for Relative Compaction - Commercial Construction Under footings and bearing elements Structural Fill - 95% Modified Proctor Under concrete slabs (sidewalks, driveways, parking lots, etc.) 90% Modified Proctor Under roadways 95% Modified Proctor Compaction of Roadbase 95% Modified Proctor

36 Ch. 5 - Compaction Page 36 Write Specification - Example Specification Wednesday, February 13, 2013

37 Ch. 5 - Compaction Page 37 Write Specification - Example Specification (cont.) Wednesday, February 13, 2013

38 Ch. 5 - Compaction Page 38 Write Specification - Example Specification (cont.) Wednesday, February 13, 2013

39 Ch. 5 - Compaction Page 39 Write Specification - Example Specification (cont.) Wednesday, February 13, 2013

40 Ch. 5 - Compaction Page 40 Write Specification - Example Specification (cont.) Wednesday, February 13, 2013

41 Ch. 5 - Compaction Page 41 Write Specification - Example Specification (cont.) Wednesday, February 13, 2013

42 Ch. 5 - Compaction Page 42 Write Specification - Example Specification (cont.) Wednesday, February 13, 2013

43 Ch. 5 - Compaction Page 43 Compaction Control - Field Verification - Nuclear Density Gage Friday, February 15, 2013 Nuclear Density Gage A nuclear density gauge is a tool used in civil construction and the petroleum industry, as well as for mining and archaeology purposes. It consists of a radiation source that emits a directed beam of particles and a sensor that counts the received particles that are either reflected by the test material or pass through it. By calculating the percentage of particles that return to the sensor, the gauge can be calibrated to measure the density and inner structure of the test material Pasted from < e> Different variants are used for different purposes. For density analysis of very shallow objects such as roads or walls, a gamma source emitter such as 137 Cesium is used to produce gamma radiation. Those particles are effective in analyzing the top 10 inches (25 centimeters) with high accuracy. 226 Radium is used for depths of 328 yards (300 meters). Such instruments can help find underground caves or identify locations with lower density that would make tunnel construction hazardous. Another variant is to use a strong neutron source like 241 Americium to produce Neutron radiation and then measure the energy of returning neutron scattering. As hydrogen characteristically slows down neutrons, the sensor can calculate the density of hydrogen - and find pockets of underground water, humidity up to a depth of several meters, moisture content, or asphalt content. Neutron sources can also be used to assess the performance of a Separator (oil production) in the same way. Gas, oil, water and sand all have different concentrations of hydrogen atoms which reflect different amounts of slow neutrons. Using a head which contains an 241 AmBe neutron source and a slow neutron detector, by scanning it up and down a separator it is possible to determine the interface levels within the separator Pasted from <

44 Ch. 5 - Compaction Page 44 Compaction Control - Field Verification - Nuclear Density Gage Friday, February 15, 2013 Direct transmission: The retractable rod is lowered into the mat through a pre-drilled hole. The source emits radiation, which then interact with electrons in the material and lose energy and/or are redirected (scattered). Radiation that loses sufficient energy or is scattered away from the detector is not counted. The denser the material, the higher the probability of interaction and the lower the detector count. Therefore, the detector count is inversely proportional to material density. A calibration factor is used to relate the count to the actual density. Nuclear density and water content determination: (a) direct transmission; (b) backscatter; and (c) air gap (after Troxier Electronic Laboratories, Inc., Research Triangle Park, North Carolina) Backscatter: The retractable rod is lowered so that it is even with the detector but still within the instrument. The source emits radiation, which then interact with electrons in the material and lose energy and/or are redirected (scattered). Radiation that is scattered towards the detector is counted. The denser the material, the higher the probability that radiation will be redirected towards the detector. Therefore, the detector count is proportional to the density. A calibration factor is used to correlate the count to the actual density Pasted from < auge>

45 Ch. 5 - Compaction Page 45 Compaction Control - Field Verification - Sand Cone Test Sand Cone Test

46 Ch. 5 - Compaction Page 46 Blank Friday, January 04, :43 AM