Showing papers on "Soil stabilization published in 2006"

Stabilizing Soft Fine-Grained Soils with Fly Ash

Abstract: The objective of this study was to evaluate the effectiveness of self-cementing fly ashes derived from combustion of sub- bituminous coal at electric power plants for stabilization of soft fine-grained soils. California bearing ratio CBR and resilient modulus Mr tests were conducted on mixtures prepared with seven soft fine-grained soils six inorganic soils and one organic soil and four fly ashes. The soils were selected to represent a relatively broad range of plasticity, with plasticity indices ranging between 15 and 38. Two of the fly ashes are high quality Class C ashes per ASTM C 618 that are normally used in Portland cement concrete. The other ashes are off-specification ashes, meaning they do not meet the Class C or Class F criteria in ASTM C 618. Tests were conducted on soils and soil-fly ash mixtures prepared at optimum water content a standardized condition, 7% wet of optimum water content representative of the typical in situ condition in Wisconsin, and 9-18% wet of optimum water content representative of a very wet in situ condition. Addition of fly ash resulted in appreciable increases in the CBR and Mr of the inorganic soils. For water contents 7% wet of optimum, CBRs of the soils alone ranged between 1 and 5. Addition of 10% fly ash resulted in CBRs ranging between 8 and 17 and 18% fly ash resulted in CBRs between 15 and 31. Similarly, Mr of the soil alone ranged between 3 and 15 MPa at 7% wet of optimum, whereas addition of 10% fly ash resulted in Mr between 12 and 60 MPa and 18% fly ash resulted in Mr between 51 and 106 MPa. In contrast, except for one fly ash, addition of fly ash generally had little effect on CBR or Mr of the organic soil.

Fundamental Characteristics of Cement-Admixed Clay in Deep Mixing

Abstract: This paper examines the compressibility and strength characteristics of high water content cement-admixed clay in deep mixing applications. During curing time, both cement content and total clay water content of the clay–water–cement mixture significantly affect the strength and compressibility of the resulting stabilized clay. To ensure optimum improvement, the selection of an appropriate total clay water content for a mixture with a certain cement content is crucial. Furthermore, the fundamental parameters such as the ratio of after-curing void ratio ( eot ) and cement content ( Aw ) have been found sufficient to characterize the strength and compressibility of cement-admixed clay. The results of unconfined compression and consolidated–undrained tests have proven that the ratio eot ∕ Aw combines together the influences of clay water content, cement content, and curing time as well as curing pressure on the strength of cement-admixed clay. In addition, useful empirical relationships on deep mixing applic...

Volume Change Behaviors of Expansive Soils Stabilized with Recycled Ashes and Fibers

Abstract: In this paper, class F fly ash, bottom ash, polypropylene fibers, and nylon fibers were evaluated as potential stabilizers in enhancing volume change properties of sulfate rich expansive soils. As a part of the research evaluation, a comprehensive laboratory experimental program was designed and conducted on two different subgrade soils from two locations in Texas. Four dosage levels of each stabilizer, two compaction moisture content levels, and 14 days curing period were investigated. Volume change behavioral tests including volumetric free swell, volumetric shrinkage strain, and vertical swell pressure tests were conducted on both isolated stabilizer treated and combined ash-fiber stabilized soils. Ash stabilizers showed improvements in reducing swelling, shrinkage, and plasticity characteristics by 20–80% whereas fibers treatments resulted in varied improvements. In combined treatments, class F fly ash mixed with nylon fibers was the most effective treatment on both Dallas and Arlington soils, where the soil property enhancements were considered average-to-moderate. Possible mechanisms that resulted in the soil property improvements are discussed along with the recommended stabilizers and their dosages for expansive soil treatments.

The behaviour of organic matter in the process of soft soil stabilization using cement

Abstract: In some projects where cement is used to stabilize soft soil foundations, it is found that the organic matter influences the stabilization effect. As a consequence, extra admixtures are added to accelerate the reactions of cement and improve the stabilization effect. In this study, different kinds of extra admixtures were used with cement to stabilize a soft soil with a high organic content. Direct shear and unconfined compression tests were undertaken and the mechanical indices in different conditions obtained. The total amount and components of the organic matter in every sample were also determined. The results show that the addition of extra admixtures improves the properties of cement-stabilized soils and that different extra admixtures play a different role.

Utilization of cement kiln dust (CKD) in cement mortar and concrete—an overview

Abstract: Solid waste management is one of the major environmental concerns around the world. Cement kiln dust (KKD), also known as by-pass dust, is a by-product of cement manufacturing. The environmental concerns related to Portland cement production, emission and disposal of CKD is becoming progressively significant. CKD is fine-grained, particulate material chiefly composed of oxidized, anhydrous, micron-sized particles collected from electrostatic precipitators during the high temperature production of clinker. Cement kiln dust so generated is partly reused in cement plant and landfilled. The beneficial uses of CKD are in highway uses, soil stabilization, use in cement mortar/concrete, CLSM, etc. Studies have shown that CKD could be used in making paste/mortar/concrete. This paper presents an overview of some of the research published on the use of CKD in cement paste/mortar/concrete. Effect of CKD on the cement paste/mortar/concrete properties like compressive strength, tensile strength properties (splitting tensile strength, flexural strength and toughness), durability (Freeze–thaw), hydration, setting time, sorptivity, electrical conductivity are presented. Use of CKD in making controlled low-strength materials (CLSM), asphalt concrete, as soil stabilizer, and leachate analysis are also discussed in this paper.

Soil Stabilization in Semiarid and Arid Land Agriculture

Abstract: Soil and water conservation is essential for sustaining food production and for preserving the environment. This review considers the potential of four types of soil amendments, namely gypsum, organic polymers, organic matter waste materials, and fly ash, as soil stabilizers. Addition of gypsum to soil can limit clay swelling and dispersion, and thus improve soil structural stability, by both soil solution electrolyte effects and cation-exchange effects. Synthetic organic polymer addition to soil surface aggregates leads to their stabilization, improved bonding between adjacent aggregates, and clay flocculation. Organic matter, also used for promoting aggregate stabilization, enhances soil microbial activity that transforms the newly added organic matter into polysaccharides and long chain aliphatic compounds capable of binding and stabilizing aggregates. Fly ash additives can improve soil physical characteristics including texture, structure, water holding capacity, hydraulic properties, and aeration. However, fly ash has a number of inherent qualities that under certain circumstances may limit its usefulness for soil stabilization, and which may even result in increased erosion and soil loss.

Influence of Compactive Efforts on Lime-Slag Treated Tropical Black Clay

Abstract: The results of a laboratory study on the influence of standard Proctor and West African Standard (WAS) compactive efforts on the compaction and strength characteristics of tropical black clay with a maximum of 8% lime and 10% slag (by dry weight of soil) is presented. Lime stabilized soil was admixed with slag in order to establish its soil improving potentials. Unconfined compressive strength and California bearing ratio tests on the soil-lime-slag mixtures yielded peak values at 8% lime and 7.5% slag concentrations in all the cases considered. The soil-lime-slag mixtures can be used as subbase and base courses of lightly trafficked roads when compacted at the energies of the standard Proctor and WAS, respectively.

Experimental analysis of the effect of some compaction methods on mechanical properties and durability of cement stabilized soil

Abstract: Cement stabilized soil is usually compacted by different mechanical methods to increase its strength and durability. This paper summarizes the results of an experimental study on the effect of different compaction methods on the performance of stabilized soil. The compaction methods investigated were either static compaction by applying a static pressure using an universal compression testing machine, dynamic compaction by a drop weight method, or static compaction coupled with vibration. All methods were applied on unstabilized soil or cement stabilized soil. The effect of each method of stabilization on compressive strength, shrinkage and water resistance are reported. Dynamic compaction with about 8% of cement content seems to give the best performance for the soil investigated.

Physical modelling of consolidation behaviour of a composite foundation consisting of a cement-mixed soil column and untreated soft marine clay

Abstract: A physical model test of a composite foundation in a steel cylindrical mould was conducted to investigate the consolidation behaviour of the composite foundation treated by the deep cement mixing (DCM) method. Pore water pressures at different locations in the untreated soft clay and the earth pressure and load acting on the untreated soft clay and the DCM column in the composite foundation model were measured throughout testing. Settlement, radial drainage behaviour and loading distribution and transfer were studied. The failure mode of the composite foundation was examined and failure of the composite foundation was largely attributed to the local failure of the DSM soil column.

Lessons Learned for Ground Movements and Soil Stabilization from the Boston Central Artery

Abstract: This paper summarizes lessons learned about soil stabilization with the deep mixing method (DMM) as it was developed and applied over 10 years during construction of the Boston Central Artery and Tunnel (CA/T). It also summarizes lessons about the control of excavation-induced ground movements and their characteristics. Deep deposits of marine clay were stabilized with DMM for large open cuts at Bird Island Flats and Fort Point Channel, both of which are described with respect to site conditions, soil properties, DMM installation and characteristics, and measured field performance. Topics addressed in this paper include water pressure distribution behind DMM walls, statistical characterization of soil cement properties, quality control/quality assurance procedures, comparison of measured and numerically simulated deformation in clay stabilized with various configurations of soil cement elements, shear modulus degradation characteristics of in situ soil cement, and ground movement patterns. Recommendations are made for soil cement properties, installation procedures, analytical modeling, design, and inspection.

Stabilization of desert sands using municipal solid waste incinerator ash

Abstract: This paper presents experimental results on the use of incinerator ash in stabilizing desert sands for possible use in geotechnical engineering applications. The incinerator ash was added in percentages of 2, 4, 8, 10 and 12%, by dry weight of sand. Laboratory tests such as compaction, unconfined compression, shear box and hydraulic conductivity were performed to measure the engineering characteristics of the stabilized material. The results showed substantial improvements in unconfined compressive strength and shear strength parameters (c and φ). Thus, incinerator ash can be used to improve the shear strength characteristics of desert sands. The permeability of the sand–incinerator ash mixture was relatively low.

Stress Path Testing of Realistically Cured Lime and Lime/Cement Stabilized Clay

Abstract: This paper aims to show that the addition of lime and lime/cement can significantly improve both the stiffness and the resistance to permanent deformation of clay soils even under adverse, though realistic, curing conditions. The AASHTO Guide for Design of Pavement Structures incorporates a method of calculating subgrade resilient modulus ( MR ) , using repeated load triaxial testing, with respect to seasonal variations of the soil’s moisture content and temperature, while the equivalent British specifications adopt a “soaked California bearing ratio” approach. In practice 8°C is a realistic worst case curing temperature in situ and a (necessarily) wetter underlying clay will allow water to be drawn into the chemically treated layer during curing as a result of suctions, while the material will experience a small degree of confinement after compaction. These conditions have been replicated in a series of repeated load triaxial tests on lime and lime/cement stabilized, predominantly kaolinitic clay and the...

An Innovative Laboratory Box for Testing Nail Pull-Out Resistance in Soil

Abstract: This paper introduces a new soil nail pull-out box with full instrumentation for investigating the soil nail pull-out shear resistance under different controlled conditions. The new box has overcome some limitations of previous pull-out boxes developed by other researchers, the first author, and his co-workers. The box has the following new features: (a) comprehensive transducers are installed, (b) an extension chamber is provided to house an extension part of the soil nail to keep the nail length inside the box constant throughout the testing, (c) a waterproof front cap is placed to cover and seal the soil nail head so that back water pressure can be applied to accelerate the saturation of the soil, and (d) a pressure grouting apparatus is constructed to make it possible to investigate the influence of the cement grouting pressure. The pull-out box can be used to study influences of (a) hole drilling process and stress release, (b) degree of saturation of the soil, (c) cement pressure grouting, (d) overburden pressure, etc. Two copies of such a new soil nail pull-out box have been constructed to accelerate the testing program. A series of soil nail pull-out tests has been conducted using the two boxes. This paper presents details of the new pull-out box, from design, boundary effect analysis, and instrumentation to setup. Typical results from soil nail pull-out tests are presented and discussed.

Stabilization of Marginal Soils Using Recycled Materials

Abstract: Loose sand, soft clays, and organic deposits are often unsuitable for use in construction due to their less-than-desirable engineering properties Traditional methods of stabilizing these soils through in-situ ground improvement or replacement techniques are costly Recycled materials such as scrap tires, plastics, ash, slag, and construction debris provide a viable alternative both for their relatively lower cost and desirable engineering properties Furthermore, use of recycled materials prevents their disposal into landfills, which are approaching capacity in Florida and across the nation This report provides a comprehensive assessment of various recycled materials that can be used to stabilize marginal soils in Florida Particular attention is given to material availability and environmental properties in addition to engineering properties A methodology is proposed to guide Florida Department of Transportation (FDOT) personnel in evaluating, testing, and approving any new material for use as a highway construction material

Strength of compacted earth: linking soil properties to stabilizers

Abstract: The influence of stabilizers and soil properties on the strength of stabilized, compacted earth is investigated. This is achieved by establishing relationships between natural soil properties (two measures each of gradation and plasticity and one of shrinkage), stabilizer treatments (0–6% of lime and/or cement and/or asphalt), and stabilized unconfined compressive strength (UCS). A total of 219 strength tests were performed on 104 different soils. The soils can be categorized into two groups according to whether single soil properties or combinations of them are “favourable” or “unfavourable” in their predisposition to stabilization. The mean UCS for favourable soils ranges from 2.98–3.25 MPa (90% ≥ 2 MPa) and for unfavourable soils from 2.32–2.48 MPa (60% ≥ 2 MPa), having controlled for stabilizer treatment variation. Soil linear shrinkage is the best single discriminator of stabilization suitability based on the categorization results. In linear modelling (analysis of covariance), the UCS of favourable ...

Lime stabilization of expansive clay

Abstract: The effect of lime treatment on the engineering properties of soil was investigated by comparing the physical properties, strength, compressibility, and swelling potential of natural and lime treated expansive soils. Test results indicated that addition of lime increased the valency of absorbed cations associated with cation exchange phenomenon and decreased plasticity. Significant reduction in the swell potential and compressibility of the lime treated soils was obtained. Scanning electron microscope (SEM) was used to bring out the qualitative changes occurring in the microstructure of the lime treated soils. Lime treatment produced a soil with a more open fabric and less water absorption potential. Lime treatment has tremendous potential as an economical method for soil stabilization.

Evaluation of the effectiveness of olive cake residue as an expansive soil stabilizer

Abstract: The quantity of the by-product olive cake residue generated in most parts of the Mediterranean countries continues to increase and expected to double in amount within 10–15 years. This increase intensifies the problems associated with the disposal of this by-product. Olive cake residue has a potential for use as a soil stabilizer and large volumes can be beneficially used. This study is directed toward determining if olive cake residue can be utilized to increase the strength and stability of expansive soils which constitute a costly natural hazard to lightweight structures on shallow foundations. A series of laboratory tests using engineering properties, such as Atterberg limits, moisture-density relationship (compaction), swell, unconfined compressive strength were undertaken to evaluate the effectiveness and performance of the olive cake residue as a soil stabilizer. Test results indicate that an addition of only 3% burned olive waste into the soil causes a reduction in plasticity, volume change and an increase in the unconfined compressive strength. However, it was observed that the presence of burned olive waste in the soil greater than 3% caused an increase in the compressibility and a decrease in the unconfined compressive strength. Test results indicate that the use of olive waste in soil stabilization gives greater benefits to the environment than simply disposing of the by-product, olive cake residue.

Rapid Soil Stabilization of Soft Clay Soils for Contingency Airfields

Abstract: : Since World War II, the military has sought methods for rapid stabilization of weak soils for support of its missions worldwide. Over the past 60 years, cement and lime have consistently been found to be among the most effective stabilizers for road and airfield applications, although recent developments show promise using nontraditional stabilizers. The purpose of this research is to determine the most effective stabilizers and dosage rates of stabilizers to increase the strength of soft clay soils (initial CBR = 2) within 72 hours for contingency airfields to support C-17 and C-130 aircraft traffic. Pavement design charts for various aircraft loading conditions were generated using the Pavement- Transportation Computer Assisted Structural Engineering Program, which was developed by the Engineering Research and Development Center to determine ranges of required strength and thickness for an underlying subbase layer and a top base layer, such as stabilized soil, crushed-aggregate, or aluminum matting. From laboratory studies, the required design strengths for many loading conditions were achieved by treating clay with 2%-4% pelletized quicklime for the underlying subbase layer, and treating clay with 2%- 4% pelletized quicklime, 1% RSC15 fibers, and 11% Type III cement for the top base layer. While the base layer requires a minimum thickness of six inches, the required subbase layer thickness is often quite large and may be difficult to construct. However, newly developed construction equipment currently used for subgrade stabilization on civilian projects should be able to stabilize the soil down to these large required depths and make construction possible.

Reclaimed Hydrated Fly Ash as a Geomaterial

Abstract: To effectively use recycled geomaterials in earthwork and pavement base/subgrade construction, engineering properties, design values, proper construction practices, and long-term behavior must be known. Recent experience in Iowa reveals that reclaimed hydrated fly ash (HFA) can be designed and constructed to meet performance objectives as demonstrated by three field test projects where HFA materials were used in construction of structural pavement base layers. In addition to construction operations and field performance monitoring, this paper summarizes HFA engineering properties determined from laboratory tests including: compaction characteristics, shear strength parameter values, hydraulic conductivity, freeze–thaw durability, and microstructural features. Results are also presented for HFA materials activated with high calcium stabilizers including hydrated lime, cement kiln dust, Class C fly ash, and atmospheric fluidized bed combustion residue. Successful use of these materials follows 10 years of research and field performance monitoring in Iowa.

The Effects of Using Compost as a Preventive Measure to Mitigate Shoulder Cracking: Laboratory Studies

Abstract: Composting is a successful method of recycling organic waste material such as yard trimmings, municipal biosolids, and animal manure into stabilized materials that could be used for bioremediation, erosion control, landscaping, and roadside vegetation. The process of composting organic wastes is expanding rapidly in the United States since landfill spaces for disposal of organic wastes are becoming scarce and expensive. If not recycled, certain composts such as Dairy Manure would potentially contaminate streams and rivers through migration. Hence, it is essential to seek new application areas for composts. Compost materials, given their moisture affinity (hydrophilic), fibrous and low permeability characteristics, could provide stabilization of natural expansive subgrades by mitigating shrinkage cracking and covering subsoil surfaces. In order to verify this stabilization, a research study is being conducted. This study has two phases, laboratory and field to evaluate the effectiveness of compost treatments to soils. This research report summarizes the first phase results, which include geotechnical characteristics of Dairy Manure and Biosolids composts and compost manufactured topsoils (CMTs). A local expansive soil from Stephenville, Texas, was used as the control soil. Laboratory test results indicate that linear shrinkage strains are reduced and strength and swell strains are increased with compost amendments. Environmental assessments of using these materials are also addressed. Construction of test plots for the second phase investigations are described. Current field monitoring of the test plots will provide better assessments of CMTs to mitigate shoulder cracking in field conditions.

Characteristics of volcanic ash and natural lime based stabilized clayey soils

Abstract: Clayey soils are stabilized with various percentages of volcanic ash (VA), finely ground natural lime (NL), Portland cement, and their combinations. The influence of stabilizers and their combinations is evaluated through standard Proctor compaction, unconfined compressive strength, splitting tensile strength, modulus of elasticity, and California bearing ratio (CBR) tests. The durability of stabilized soil mixtures is judged based on drying shrinkage and the influence of water immersion on strength. Correlations between compressive strength, modulus of elasticity, and CBR are also established. Stabilized soil mixtures can be used in various constructions, including road pavements and low-cost housing.Key words: soil stabilization, volcanic ash, natural lime, mechanical properties, durability.

CBR and DCP Correlation for Class C Fly Ash-Stabilized Soil

Abstract: The dynamic cone penetrometer (DCP) test is being increasingly used for assessing the California bearing ratio (CBR) values of sub-grade soil in the field. The purpose of this laboratory investigation was to establish a correlation between CBR and DCP for soils stabilized with Class C fly ash. In this laboratory study, natural soil (Type CL-lean clay) mixed with Class C fly ash was used to establish the correlation at different percentages of Class C fly ash and moisture. It was found that a good correlation exists between CBR and DCP for Class C fly ash-stabilized soils and that the correlations are similar to those developed by other researchers. The correlations developed here may be used for rapid field determination of CBR values of clay soils stabilized with Class C fly ash.

Physical and Mechanical Properties of Injected Sand with Latex—Superplasticized Grouts

Abstract: This paper reports on a comprehensive laboratory study that was conducted in order to investigate the rheological properties of acrylic resin (latex)—superplasticized grouts and their influence, when injected, on the physical (water permeability, porosity) and mechanical characteristics (compressive strength, elastic modulus, durability) of a granular soil. Findings showed that the addition of acrylic resin to cementitious grouts, combined with superplasticizer, modifies their rheological properties resulting in the enhancement of their penetrability and the grout propagation into the soil mass. A small dosage of acrylic resin increases compressive strength and modulus of elasticity and decrease porosity, permeability and slaking of all the parts of grouted soil. A higher dosage of acrylic resin improves the properties of the grouted soil only to a limited extent. Overall results indicate that the use of acrylic resin as an additive for cement grouting purposes contributes significantly to the improvement of grouted soil properties when added in control dosages and in respect to the water/cement ratio.

Soil stabilization system

Abstract: A construction article including a compacted mixture that includes soil and a crop plant biomass microorganism-expressed enzyme composition. A method of stabilizing soil including: (i) mixing together soil, water and a crop plant biomass microorganism-expressed enzyme composition to form a mixture; (ii) causing the mixture to be shaped into a selected structure; and (iii) causing the structure to be compacted.

Performance Evaluation and Numerical Modeling of Embankment over Soft Clayey Soil Improved with Chemico-Pile:

Abstract: The stabilization of soft clay is one of the most important construction techniques in geotechnical engineering. The injection method using chemical grouting in the ground has been widely used to improve soft ground. Chemical admixture stabilization (with lime and cement as the chemical admixture) has been extensively used in both shallow and deep stabilization to improve the inherent properties of soil, such as strength and deformation behavior. These methods involve mixing soil with chemicals. The other technique—the so-called chemico-lime pile or chemico-pile method—involves forming columns of chemically treated lime in the soil without mixing. This method is widely used in Japan and Singapore and is a fast, effective, and well-recognized way of improving soil with soft clay deposits. The chemico-pile method has been used in a full-scale test embankment project at the Nong Ngo Hao site near Bangkok, Thailand. The site is part of the second Bangkok International Airport project, located in the Samutprak...

Roughness of Flexible Pavements with Cement-Treated Base Layers

Abstract: Although cement treatment is a proven method for improving the strength and durability of soils and aggregates used in pavement construction, cement hydration can cause shrinkage strains in cement-treated base (CTB) layers that can lead to reflection cracking in asphalt surfaces. Cracking may then cause accelerated pavement deterioration and increased roughness. The overall purpose of this research was to investigate the use and classification of CTB layers and evaluate the relative impact of cement content on roughness development in asphalt pavements. Data collected through the Long-Term Pavement Performance program were used as the basis for this study, which included 52 sites in 13 different states with cement contents ranging from 3.0 to 9.5 percent. Factors including construction date, functional classification, air freezing index, asphalt concrete (AC) and CTB layer thicknesses, cement content, base type, soil classification, International Roughness Index (IRI), and traffic loads were considered. A roughness equation developed in this research can be utilized to estimate the roughness of an AC pavement comprised of a CTB layer through time. Based on calculations using average values of AC and CTB thicknesses, the equation predicts increases in IRI of between 32.7 and 37.1 percent over a 30-year period, depending on cement content. As cement content increases from 3.0 to 9.0 percent, IRI increases 14.2 percent, on average, over a given time period. Because increasing cement contents are correlated to increasing pavement roughness over time, the use of reduced cement contents and thicker CTB layers may be appropriate in pavement design.

Overview of Mechanism of Plant Roots Improving Soil Reinforcement and Slope Stabilization

Abstract: Plant root system plays important roles in soil stabilization and control of soil and water loss.Based on some recent information about it,an overview was taken on root anti-scouribility,root materials mechanics and soil reinforcement mechanism in form of a root-soil composite,as well as its application and prospect,etc.Finally,further research in the respect is urgently needed in order to best serve our country vegetation restoration during the ecological environmental management and construction.

Characteristics and engineering properties of the soft soil layer in highway soil subgrades.

Abstract: The objective of this research was to examine the conditions and characteristics of soil subgrades that had been stabilized using mechanical compaction. Goals of the study are to identify and examine the engineering properties and behavior of the “soft layer’ of material observed at the top of untreated, highway pavement soil subgrades. Alternative methods of preventing, or mitigating, the development of the soft layer are discussed. Evidence is presented that shows that a soft layer of soil frequently develops at the top of untreated, highway soil subgrades. Data are presented that show strengths obtained from mechanical compaction are largely destroyed when untreated compacted soils are exposed to moisture. California Bearing Ratio (CBR) values of compacted clayey soils initially are high but become small when exposed to saturation. In situ CBR values measured at the tops of untreated subgrades, where mechanical compaction was the only means used to stabilize the soil subgrade, were smaller than unsoaked and soaked laboratory Kentucky CBR values. At the 85th percentile test value, the laboratory KYCBR value of compacted, unsoaked clayey specimens was 11.5 while the CBR value of soaked specimens was 3.0. For comparison, the in situ CBR value of untreated subgrades at the 85th percentile test value, as shown in this study, was only 2. Using a bearing capacity model, based on limit equilibrium of layered media, bearing capacity analyses of flexible pavement sections were performed. The analyses show that when the in situ CBR is equal to or below 3, the pavement was unstable, i. e., the factor of safety against failure was 1.0 or below. However, when the in situ CBR value was 6, or greater, the pavement was generally stable and the factor of safety was 1.5, or greater. Chemical admixture stabilization of soil subgrades is the most effective means of maintaining large CBR values during construction and throughout the life of the pavement. In situ CBR values at the 85th percentile of tests performed on the tops of soil subgrades treated chemically with lime kiln dust, hydrated lime, and portland cement and that had been in place for 8 to 15 years were 24, 27, and 59, respectively. At the 85th percentile test value, in situ CBR values of chemically treated subgrades were about 12 to 30 times larger than the in situ CBR value of 2 of untreated subgrades.