Compaction and Soil Improvement

Accelerated Strength Improvement of Silty Sand Using Nontraditional Additives

Santoni, R.L., Tingle, J. S., and Nieves, M.
U.S. Army Engineer Research and Development Centre
August 2002

A laboratory experiment was conducted to evaluate the effect of two products designed to accelerate the strength improvement during the stabilization of a silty-sand (SM) material with non-traditional stabilizers. SM soil samples were mixed with various stabilization products and accelerators and compacted. Each sample was subjected to “wet” and dry testing following the designated cure period. Nine non-traditional stabilizers were evaluated in this experiment including lignosulfonates, polymers, silicates, and tree resins. Two accelerator products were evaluated including an acrylic polymer and Type I Portland cement. Additional samples were stabilized with either an asphalt emulsion or cement to provide a comparison to traditional stabilizers under the same mixing, compaction, and curing conditions. The analysis of the data consisted of determining the average unconfined compressive strength (UCS) of three replicate samples of each mixture. The average UCS of the three replicates of each mixture was compared to the average strength results of the remaining mixtures, the traditional stabilization results, and a series of control samples that were not stabilized. The average UCS was determined at 1 and 7 days. The pH of each sample was also determined to evaluate the effect of the non-traditional stabilizer and accelerators on the stabilized soil pH. The results of the experiment indicate increased UCS of Silicate 1, Polymer 1, Polymer 2, and Polymer 3 stabilized samples when compared to both the control series and the traditional stabilization alternatives. Lignosulfonate 1, Polymer 4, Polymer 5, and Polymer 6, and Tree Resin 1 did not demonstrate significant increased strength compared to the control series for the conditions of this experiment. The USC following the 7-day cure period provided the maximum UCS of the samples evaluated in both dry and wet conditions. One accelerator, cement, in combination with a nontraditional stabilizer did show significant improvement in early strength gain when compared to the control series.

Alternative Materials for The Modification and Stabilization of Unstable Subgrade Soils

Greg Heckel
Illinois Department of Transportation
IL/PRR-125
May 1997

This study examines two lime by-products and two fly ashes for treatment of unstable (CBR<6) subgrade soils. The treatment methods include both modification and stabilization. Modification is temporarily enhancing subgrade stability to improve constructability. Stabilization is the construction of a permanent, high-strength base material which is considered a part of the pavement structure. The alternative materials include a dried lime kiln sludge (DLKS), a hydrated lime by-product (HLB), an ASTM C 618 Type C fly ast (TCFA), and a fly ash (FA) that does not meet the requirements of ASTM C 618. The performance of soils treated with these materials was compared to that of the corresponding soils treated with the control material a high calcium lime kiln dust (LKD). Test results presented in this study include the moisture-density relationships, bearing values, compressive strengths, swell potential, and plasticity index for treated soils and untreated soils. The results do not provide enough data to comprehensively evaluate the performance of FA. However, the results do indicate that the suitability of DLKS, HLB, and TCFA depends on soil type, moisture contents, and expected performance.

Dynamic Compaction

Robert G. Lukas
Geotechnical Engineering Circular #1
FHWA-SA-95-037
March 1995

This manual provides state-of-the-practice methods and techniques to assist the highway engineer in the planning, design, and construction monitoring of dynamic compaction to improve the load supporting capacity of weak foundation soils. Guidelines are presented for:

  • completing a preliminary evaluation to determine if dynamic compaction is appropriate for the site and subsurface conditions
  • detailed design for site improvement
  • preparation of a specification
  • construction monitoring

Two case histories of actual projects are presented to demonstrate the use of the guidelines.

Evaluation of Soil Modification Mixing Procedures

Robert L. Parsons, Chad P. Johnson, and Stephen A. Cross
K-TRAN: KU-00-6
January 2001

Lime is routinely used as a soil modification agent in Kansas to improve the performance of subgrade soils with the primary goal of reducing volume change. Effective mixing of lime and soil is critical to ensuring that the expected improvements occur throughout the soil mass. The results are presented herein on the effectiveness of current soil-lime mixing and construction procedures for five soils treated with powdered quicklime or lime slurry.

A series of tests was performed on each soil as part of the evaluation process. Test procedures included field density determination, dynamic cone penetrometer, unconfined compression, lime content, pH, Atterberg limits, swell testing, and determination of the maximum unit weights and optimum moisture contents for the native soil and lime treated soil. The effect of significantly reducing the mellowing period for ease of construction was evaluated and determined to negatively affect subgrade compaction and strength due to high water contents remaining from the mixing process.

Additionally, the results of the testing showed that two passes with a rotary mixer were sufficient to effectively pulverize and mix the soil and lime to achieve modification. However, the results also suggested that there was the potential for additional strength gains with additional mixing. The consistency of lime distribution on a larger scale was also evaluated and determined to be adequate at the locations observed, although there was some evidence that the mixing of soil with lime in a slurry form appeared to yield a more consistent final product than mixing with powdered quicklime.

Several recommendations were proposed for consideration by KDOT for soil modification procedures. These included moving from a specified percentage of lime for all projects to a lime percentage based on soil testing.

Recommendations also included the introduction of a mellowing period after preliminary mixing to allow the lime more time to react with the soil to break down clay lumps and to give the soil time to dry to a water content closer to optimum. Also proposed for consideration was the adoption of National Lime Association specifications for final mixing, which include the use of AASHTO T-180 as the compaction standard and requiring rotary mixing during the final stage of mixing. Further evaluation of the performance of soils mixed with lime slurry compared with soils mixed with quicklime was recommended to determine if lime slurry yields a significantly better product.

Other recommendations proposed for consideration included an evaluation of the benefits of making soil stabilization a goal of soil treatment and taking advantage of the benefits of including the stabilized layer as a component in the pavement design. Construction costs beyond those already incurred for modification should be relatively small and the additional structural benefits could yield significant savings.

Stabilization of Clay Soils with Nontraditional Additives

Jeb S. Tingle and Rosa L. Santoni
U.S. Army Engineer Research and Development Center
Paper ID Number LVR8-1136
17 June 2002

A laboratory experiment was conducted to evaluate the stabilization of low- and high-plasticity clay soils with non-traditional chemical or liquid stabilizers. Clay soil specimens were mixed with various stabilization products and compacted using a gyratory compaction machine to approximate American Society for Testing Materials (ASTM) D 1557 moisture-density compaction. Each specimen was subjected to “wet” and dry testing following a 28-day cure period. Twelve non-traditional stabilizers were evaluated in this experiment including an acid, enzymes, a lignosulfonate, a petroleum emulsion, polymers, and a tree resin. Additional specimens were stabilized with Type I portland cement and hydrated lime to provide a comparison to traditional stabilizers under the same mixing, compaction, and curing conditions. The analysis of the test data consisted of determining the average strength, in terms of unconfined compression strength, of three replicate specimens of each mixture. The average strength of the three replicates of each additive was compared to the average strength results of the remaining nontraditional additives, the traditional stabilization results, and a series of control specimens that were not stabilized. The results of the experiment indicate increased strength of some nontraditionally stabilized specimens when compared to both the control series and the traditional stabilization alternatives. Other nontraditional stabilizers did not demonstrate significant increased strength compared to the control series for the conditions of this experiment. Many of the stabilized specimens were highly moisture susceptible indicating the potential for poor performance when exposed to adverse environmental conditions, while a few specimens demonstrated excellent performance when exposed to moisture. Specific product categories are recommended for stabilizing low- and high-plasticity clay soils.

Use of Best Fit Line of Optimums (BFLO) for Recompacted Soil Liner Construction

State of Ohio Environmental Protection Agency
Guidance Document #0665
1 June 2005

This educational guideline outlines a procedure for using site-specific maximum dry density and optimum moisture content points (MDD/OM) from standard and modified proctor tests to develop a best fit line of optimums (BFLO). The BFLO is one option that can be used to determine if there is a significant change in soil material properties. It can also be used as the pass/fail criteria for compacted density and compacted moisture content during construction of recompacted soil liners as well as separatory liner/leachate collection systems and cap system soil barrier layers.

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