Compaction and Ground Improvement GLE/CEE 330 Lecture Notes Soil Mechanics William J. Likos, Ph.D. Department of Civil and Environmental Engineering University of Wisconsin-Madison

Ground Improvement Methods “Reinforcement” “Improvement” “Treatment” Stone Columns Soil Nails Deep Soil Nailing Micropiles (Mini-piles) Jet Grouting Ground Anchors Geosynthetics Fiber Reinforcement Lime Columns Mechanically Stabilized Earth (MSE) Biological (e.g. roots) Compaction Preload/Surcharge Electro-osmosis Compaction grouting Blasting Deep dynamic compaction Cement Lime Admixtures Dewatering Heating/Freezing Vitrification Biotreatment Could also add “Replacement” (often not cost effective) (after Shaefer, 1997)

Some Reinforcement Methods Jet Grouting Soil Nailing Fiber Reinforced Soil (Atlas Copco) (Menard)

Some Improvement Methods Deep Dynamic Compaction Compaction Grouting Surcharge with Drainage (UC Davis)

Some Treatment Methods Microbial Treatment Lime Treatment Ground Freezing (Max Bogl) (J. Dejong)

Compaction Objectives of Compaction: Densify soil by reducing volume of voids (Vv = Va + Vw) We primarily reduce the volume of air (Va) Compaction ≠ Consolidation !!!!! Consolidation is compression from loss of water squeezed out over time resulting from applied load. Objectives of Compaction: Decrease settlements Increase shear strength Decrease permeability

Adding water to reach “optimum water content Loose Vv Vt Adding water to reach “optimum water content High n High e Vs Adjust w and Compact Vv Vt Vs Low n Low e Dense

(Holtz and Kovacs, 1981; Head, 1992) Compaction Methods Coarse-grained soils Fine-grained soils Vibration Kneading Falling weight and hammers Kneading compactors Static loading and press Vibrating hammer (BS) Laboratory Hand-operated vibration plates Motorized vibratory rollers Free-falling weight; dynamic compaction (low frequency vibration) Hand-operated tampers Sheepsfoot rollers Rubber-tired rollers Field (Holtz and Kovacs, 1981; Head, 1992)

Smooth-Wheeled Roller Sandy (non-cohesive) soils 100% coverage Contact pressure = 300-400 kN/m2 Static or vibratory “Proof” rolling (smooth surface) (Das, 2000)

Pneumatic Rubber-Tired Roller Sandy or clayey soils 70 – 80 % coverage Contact pressure = 600-700 kN/m2 Combination of pressure and kneading Articulated wheels find “soft spots” (Das, 2000)

Sheepsfoot Roller Small projections for kneading action Clayey or silty soils Contact pressure = 1400-7000 kN/m2 (Das, 2000)

Portable Compactors Retaining wall backfills Foundation backfills Compaction close to existing structures Usually vibratory (Das, 2000)

Intelligent Compaction Feedback on vibratory compaction

Applicability for Soil Types (Coduto, 1999)

Proctor Compaction Curve Line of optimums Zero air void curve (ZAV) d max Dry density d (Mg/m3) Dry density d (lb/ft3) Modified Proctor Standard Proctor wopt Water content w (%) Holtz and Kovacs, 1981

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 optimums

Zero Air Voids (ZAV) Curve Recall: Holtz and Kovacs, 1981

Laboratory Compaction Procedures Standard Proctor test equipment Das, 1998

Report (gd)max and wopt 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 unit weight gd versus water contents w for each compacted sample. The curve is called as a compaction curve. Report (gd)max and wopt

Laboratory Compaction Procedures Summary of Standard Proctor Compaction Test Specifications (ASTM D-698, AASHTO) Das, 1998

Laboratory Compaction Procedures Summary of Modified Proctor Compaction Test Specifications (ASTM D-698, AASHTO) Das, 1998

For 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 Volume of mold Number of blows per layer Number of layers Weight of hammer Height of drop of hammer  E = For standard Proctor test

Effects of Soil Type Holtz and Kovacs, 1981; Das, 1998

Suitability of Soil Types for Construction Strength Compressibility Permeability Interaction with Water Uses Problems Gravel High Low V. High No effect Pavement bases Filters Prone to caving Small clay content affects properties Sand Workable over wide range Wide range of uses Fills (hydraulic) Backfill Poor at ground surface Prone to erosion Low plasticity silts/clays Lose strength when wetted Fills Prone to frost heave Collapse potential High plasticity silts/clays V. Low Landfill covers/liners Poor workability (sticky) Swell/shrink potential Organics - Landscaping Typically removed

Compaction and Soil Fabric Clay particles are plate-like (e.g., kaolinite) Flocculated Fabric – orientation and arrangement of particles (clay); has influence on soil behavior Soil fabric tends to be more flocculated (random) for compaction dry of optimum. Soil fabric tends to be more dispersed (oriented) for compaction wet of optimum. Dispersed Lambe and Whitman, 1979

Engineering Behavior - 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, 1981

Engineering Behavior - Strength s1 – s3 Samples compacted dry of optimum tend to be more rigid and stronger than samples compacted wet of optimum s3 From Lambe and Whitman, 1979

Engineering Properties - Summary Dry side Wet side Structure Flocculated Dispersed Permeability More permeable Less permeable Compressibility More compressible in high pressure range More compressible in low pressure range Swelling Higher *Shrinks more Strength Higher Lower Holtz and Kovacs, 1981; Das, 1998 29

Field Quality Control 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, 1981

Quality Control – Relative Compaction 100% saturation Control (1) Relative compaction (2) Water content (dry side or wet side) Line of optimums gd max 90% R.C. Dry density, gd    Increase compaction energy wopt a b c From Holtz and Kovacs, 1981 Water content w %

QA/QC Methods (a) Sand cone (b) Balloon (a) (c) Oil (or water) method Calculations Measure Wt, Vt Get gd field and w Compare d field with d max-lab and calculate relative compaction R.C. (b) (c)

QA/QC Methods (a) Direct transmission (a) (b) Backscatter (c) Air gap Holtz and Kovacs, 1981 QA/QC Methods Nuclear density meter (a) Direct transmission (b) Backscatter (c) Air gap (a) Principles Density Gamma radiation is scattered by the soil particles and the amount of scatter is proportional to the total density of the material. Gamma radiation is typically provided by radium or a radioactive isotope of cesium. Water content Water content can be determined based on neutron scattering by hydrogen atoms. Typical neutron sources are americium-beryllium isotopes. (b) (c)

“Borrow Pit” Problem volume Compacted Embankment Borrow pit Truck Transport (10 m3/truck) 30 m X 1.5 m X 1000 m Sandy Soil w = 15% e = 0.69 yd = 18 kN/m3