Soil Stiffness Gauge Research Articles

Evaluation Method for Bearing Capacity of Fine‐Grained Soil Subgrade Based on Multiple Moduli

The bearing capacity of the existing fine‐grained soil subgrade is mainly achieved by measuring the modulus, and its testing methods can be divided into two categories including static method and dynamic method. The data connection between the two is still lacking in systematic research. The traditional BB (Benkelman Beam) static test has disadvantages such as slow detection speed, low accuracy, and poor reliability due to the use of deflection index, which is not fully applicable to the expressway. To this end, dynamic and static comparison tests were carried out and a rapid test method for subgrade bearing capacity based on Soil Stiffness Gauge (SSG) and Portable Falling Weight Deflectometer (PFWD) with dynamic modulus was proposed. To establish the connectivity of the static and dynamic modulus, modulus‐dependent prediction model was developed. The results show that the multiplier power model with modulus () is superior to the usual linear model (EBB = 0.9415EPFWD − 6.1507, R2 = 0.9639; EBB = 0.7878ESSG − 0.4566, R2 = 0.8894), and it can replace the traditional BB method. PFWD and SSG were found to be reliable devices with faster and more accurate monitoring of the modulus change of the fine‐grained soil subgrade. But they have the property of overestimating material modulus, the modulus ranking of the three instruments is obtained. In this way, it provides a reference for the dynamic and accurate determination and scientific evaluation of the bearing capacity of the highway subgrade.

Laboratory Performance Evaluation of Asphalt-Treated Cold Recycled Mixtures Using Existing Practical Tests

Agencies currently utilize several proxy tests, related to level of compaction (density) and moisture content, to assess the quality of a recycled pavement during construction. These proxy tests are not completely able to indicate sufficient quality or stability of recycled pavements under trafficking or surfacing, especially at early ages. The lack of sound and rapid tests for use in process control and acceptance during construction limits the use of the recycling techniques by agencies, therefore they do not fully benefit from the advantages that pavement recycling offers. This study evaluates the viability of currently available simple and practical stiffness tests (i.e., soil stiffness gauge and light weight deflectometer tests), deformation resistance tests (i.e., Marshall hammer test), and penetration resistance tests (i.e., dynamic cone penetration test) to characterize the properties of asphalt-treated cold recycled mixtures. The scope of the work included laboratory testing of 18 different cold recycled mixtures, prepared through different processes combining different binding agents and filler types, at different curing times via the selected tests. The collected data were analyzed to evaluate these tests in relation to their repeatability characteristics and versatility to capture the performance of recycled materials with respect to changes in curing time, type of stabilizing/recycling agent, and presence of active filler. The data obtained showed the ability of these tests to capture the effect of curing. Moreover, these tests were found to be sensitive to changes in the recycling agent type, recycling agent content, and presence of active filler.

Subgrade assessment using automated dynamic cone penetrometer to manage geo-infrastructures

For the efficient management of geo-infrastructures in the field, engineering properties of the subgrade should be reliably and rapidly investigated. The objective of this study is to estimate and compare the strength and stiffness parameters of subgrades using portable in-situ devices. An automated dynamic cone penetrometer (ACP), dynamic cone penetrometer (DCP), and light falling weight deflectometer (LFWD) are adopted and applied at nine points of soft ground in South Korea. The Nvalue from the ACP (NACP), which efficiently assesses the relatively deep subgrade, is correlated with the dynamic cone penetration index (DCPI) and dynamic deflection modulus (Evd). Test results show that the DCPI and Evd can be estimated in terms of NACP. In particular, the relationship between Evd and NACP is improved when the strain influence factor of the target ground is considered. For the assessment of strength and stiffness parameters, the California bearing ratio (CBR), relative density (Dr), internal friction angle (φ), and elastic moduli determined by the plate loading test (PLT), soil stiffness gauge (SSG), falling weight deflectometer (FWD) are estimated using NACP. The ACP test with the relationships between engineering parameters and NACP may be an effectively method to assess the overall characteristics of the subgrade.

Compaction Quality Monitoring of Open-Graded Aggregates by Light Weight Deflectometer and Soil Stiffness Gauge

Open-graded aggregates (OGAs) are free-draining materials often used as the base layer of permeable pavements to allow the infiltration or drainage of stormwater. Despite their widespread use, the compaction quality of OGA base layers has not been specified properly. The currently used density-based compaction quality control (QC) has limitations; obtaining the field density and maximum dry density of OGAs by typical methods is challenging, due to their unique properties. To overcome these limitations, modulus-based compaction QC can be used as an alternative. In this study, five different OGAs were chosen and compacted into a specially built soil chamber to measure their densities. The light weight deflectometer (LWD) and the soil stiffness gauge (SSG) were used to evaluate the modulus of the compacted OGAs. The vibratory hammer compaction test was conducted to obtain the maximum dry density of the aggregates. Through these tests, the relationship between the modulus of the compacted aggregates and the relative density was obtained, and efforts to find a modulus range that ensures proper compaction were made. It was found that the LWD and SSG are valid and reliable devices for monitoring the modulus change of OGAs due to compaction.

Evaluating Constructed Aggregate Layers of Working Platforms and Flexible Pavements: Adequacy of In-Place Quality Control and Quality Assurance Techniques

Quality assurance is extremely important for satisfactory end performance of a constructed pavement. Traditional quality control and quality assurance (QC/QA) procedures based on volumetric and surface property checks are becoming outdated when used for constructing pavement foundation layers and ensuring pavement longevity. Recent emphasis in QC/QA procedures has shifted from a density-based approach to stiffness- and strength-based approaches with newly adopted advanced technologies. However, the need for QC/QA is often overlooked in the construction of low-volume roads with unbound aggregate layers, which may be built with recycled or out-of-specification materials of marginal quality: both are currently common sustainable practices. This paper summarizes key findings from QC/QA tests performed on full-scale pavement test sections in a recent research study conducted by the Illinois Center for Transportation. The focus of the tests was the validation of material specifications that the Illinois Department of Transportation has recently adopted for large-size unconventional aggregates, known as aggregate subgrade, through accelerated pavement testing. Seven representative aggregate types were used to construct test sections with aggregate subgrade and virgin and recycled capping and subbase layers. Density measurements from a nuclear gauge were collected and routinely contrasted with modulus results from the lightweight deflectometer and soil stiffness gauge (GeoGauge) from the constructed layers. Further, forensic strength assessment was carried out by dynamic cone penetrometer and a variable energy PANDA penetration device. Geoendoscopic imaging, coring, and trenching were also conducted to identify the depth of the water table and the thickness of the as-constructed layer. The PANDA penetrometer results, in conjunction with geoendoscopy, proved to be effective in correlating rutting performances to QC/QA test results.

Assessing soil compaction using continuous compaction control and location-specific in situ tests

Abstract Modern compaction equipment can be outfitted with sensors that allow for real-time monitoring of the compaction process, an approach that is commonly referred to as continuous compaction control (CCC). This paper describes the results from an experimental research study that was conducted to assess the effectiveness of CCC technology for construction of a roadway embankment using a sand containing a significant percentage of silty fines. During embankment construction, simultaneous machine drive power (MDP) and compactometer value (CMV) measurements were recorded, along with the corresponding position of the roller. Location-specific in situ “spot tests” were also performed to independently assess soil compaction, including nuclear density gauge (NDG) tests, soil stiffness gauge (SSG) tests, light weight deflectometer (LWD) tests, and dynamic cone penetrometer (DCP) tests. A comparison of the CCC measurements with the location-specific in situ test results was performed using spatial data analysis tools and statistical regression. The measured data, spatial and regression analysis approaches, and associated discussion that are presented provide valuable information for researchers and practitioners that are considering the use of CCC technology.

Contribution of engineering geology for the construction of a new museum gallery over an archaeological site at Lorvão Monastery, Portugal

Abstract The rehabilitation of the Lorvao Monastery in Penacova, Portugal, included the construction of a new steel structure to house a museum gallery. The implementation of an archaeological excavation prior to construction revealed a mesh of ancient masonry walls, dating from the 16th to the 18th centuries, which needed to be preserved and made available for exhibition. To help understand the characteristics of this foundation ground, an engineering geology study was required, strongly conditioned by the presence of heritage, reduced space and difficult accessibility caused by the extensive temporary support used to ensure stability of the walls. The engineering geology study consisted of a detailed surface mapping, complemented by non-destructive in situ tests, the soil stiffness gauge (SSG) and the surface moisture-density gauge (SMDG) and by the use of the Bieniawski rock mass rating (RMR) geomechanical classification. Three geotechnical zones were defined. The non-invasive engineering geology study performed proved suitable to provide the geotechnical information necessary to redesign and construct the steel structure over a challenging archaeological site, preserving the heritage.

평판재하시험, 흙강성측정기 및 동적콘관입시험기를 이용한 노상토의 탄성계수 비교

본 연구는 노상토의 다짐특성 평가를 위해 특성이 다른 세 가지 강성측정 시험법으로 측정한 탄성계수의 상관관계 및 연관성에 대해 논의하였다. 미소변형률(<TEX>${\approx}0.001%$</TEX>) 범위의 흙강성측정기(SSG), 중변형률(<TEX>${\approx}0.01{\sim}0.1%$</TEX>) 범위의 정적 평판재하시험(PLT), 관입저항을 이용하는 동적콘관입시험기(DCP)가 탄성계수 측정에 이용되었다. 변형률 범위가 다른 시험방법에 의해 측정한 탄성계수를 실무에 적용하기 위해서는, 각각의 측정치에 대한 상관관계 및 연관성에 대해 사전에 파악되어야 한다. 국내 외 여러 조건의 노상토에 대해서 세 가지 방법을 이용하여 측정한 탄성계수(<TEX>$E_{SSG}$</TEX>, <TEX>$E_{PLT}$</TEX>, <TEX>$E_{DCP}$</TEX>)를 비교 분석한 결과에 따르면, 흙의 종류 및 응력 조건에 따라 각 방법에 의해 측정된 탄성계수가 상이한 결과를 나타내었다. 전체 수집된 데이터 중 시멘트 처리토를 제외한 일반적인 노상토를 대상으로 한 상관성 분석결과, 정적 탄성계수(<TEX>$E_{PLT}$</TEX>)는 동적 탄성계수(<TEX>$E_{SSG}$</TEX>) 대비 60~80%의 크기를 나타나는 것으로 평가되었다. 시멘트 처리토와 같은 특이 토질은 정적 탄성계수(<TEX>$E_{PLT}$</TEX>) 측정 시 구속압의 영향을 크게 받기 때문에, 다른 일반 토질과 상관관계 비교시 응력보정을 수행하여야 한다. 또한, 동적콘관입시험 결과를 이용하여 탄성계수(<TEX>$E_{DCP}$</TEX>) 예측 시, 200MPa 이내의 범위에서 탄성계수 데이터가 좀더 신뢰도 높은 상관관계를 나타내었다. This paper describes the correlation and relationship between elastic moduli measured by three stiffness measurement methods with different mechanical characteristics to evaluate the compaction characteristics of subgrade soils. The Soil Stiffness Gauge (SSG) with very small strain (<TEX>${\approx}0.001%$</TEX>) ranges, static Plate Loading Test (PLT) with mid-level strain (<TEX>${\approx}0.01{\sim}0.1%$</TEX>) ranges, and Dynamic Cone Penetrometer (DCP) using penetration resistance were implemented to measure the elastic modulus. To use the elastic modulus measured by different measurement methods with a wide range of strain in practice, it is required to identify the correlation and relationship of measured values in advance. The comparison results of the measured elastic moduli (<TEX>$E_{SSG}$</TEX>, <TEX>$E_{PLT}$</TEX>, <TEX>$E_{DCP}$</TEX>) using the three measurement methods for domestic and overseas subgrade soils under various conditions indicate that the evaluated elastic modulus relies on the types of soils and the level of stress condition. The correlation analysis of the measured elastic moduli except the data of cement treated soils indicates that the static elastic modulus (<TEX>$E_{PLT}$</TEX>) is evaluated as about 60 to 80% of the dynamic elastic modulus (<TEX>$E_{SSG}$</TEX>). Unusual soils such as cement treated soils are required to be corrected by the stress correction during the correlation analysis with typical soils, because these types of soils are sensitive to the stress condition when measuring the static elastic modulus (<TEX>$E_{PLT}$</TEX>) of soils. In addition, when considering the use of DCP data for the evaluation of the elastic modulus (<TEX>$E_{DCP}$</TEX>), the measured data of the elastic modulus less than 200 MPa show more reliable correlation.

Soil Stiffness Gauge (SSG) and Dynamic Cone Penetrometer (DCP) tests for estimating engineering properties of weathered sandy soils in Korea

Laboratory tests are conducted using nondestructive and penetration methods for in-situ estimation of the engineering properties of weathered sandy soils in Korea. Soil Stiffness Gauge (SSG), Dynamic Cone Penetrometer (DCP), Plate Load Test (PLT), and California Bearing Ratio (CBR) are performed with three uncemented soil groups: poorly graded sand (SP), silty sand (SM), and well-graded sand with silt (SW-SM) that were compacted in a large container. The SSG and DCP results show acceptable repeatability. Dynamic Penetration Index (DPI) and the modulus of elasticity obtained from the SSG test (ESSG) are significantly affected by the water content of SM and SW-SM soils, whereas the SP sample showed no clear effect of water content in either the DPI or ESSG test. Compared with previous reports in the literature, the relationship obtained between CBR and DPI shows a similar trend although at a given DPI it produces significantly larger CBR values. For elastic moduli ESSG is linearly proportional to EPLT and is 1.7 times larger than EPLT. For all three soils considered, the void ratio (e) is linearly proportional to the DPI divided by the median particle size (DPI/D50) while the angle of internal friction is inversely proportional to DPI/D50. The dry density of compacted soil appears to increase nonlinearly with increase in ESSG·D50/e. It is, therefore, concluded that ESSG, DPI, and D50 can provide complementary information for the estimation of void ratio and dry density.

비파괴시험 및 관입시험을 이용한 기초지반의 다짐특성 평가를 위한 실내 모형토조 시험

The paper describes the use of the nondestructive and penetration tests such as the Soil Stiffness Gauge (SSG), the Dynamic Cone Penetrometer (DCP), and the Time Domain Reflectometry (TDR) for evaluating the compaction characteristics of foundation soils. A comprehensive laboratory experimental program was conducted for the SP, SW-SM, SM, CL soil specimens. The SSG, DCP, TDR, plate load test (PLT), California Bearing Ratio (CBR) test, and the sand cone test were performed for compacted soil specimens with various water contents. The interpreted results show that the nondestructive and penetration tests can quickly and quantitatively evaluate the compaction characteristics of soils with similar performance. The TDR can measure the water content of soils with high accuracy when testing soils with a water content of less than 15%. The results show that the SSG modulus is approximately two times higher than the PLT modulus. The SSG and DCP measurements have a log-log correlation between the soil stiffness and the shear strength of soils.

In-place evaluation of a limestone base course modulus, using a van-integrated falling weight deflectometer (FWD) and the GeoGauge (SSG)

A comparative evaluation of the in-place stiffness modulus using a van-integrated falling weight deflectometer (FWD) and the GeoGauge (soil stiffness gauge – SSG) was done on a limestone all-in-aggregate (AIA), used in the base course of a highway pavement. The tests were done in two campaigns, one for each unbound granular layer of 0.15 m thickness, along 510 m, using five alignments. Considering the whole granular materials used, the dry unit weight (γd) is related with the stiffness modulus obtained with the SSG. The stiffness moduli obtained for the SSG and for the FWD in the same test point are not correlated. Considering as reference the equivalent modulus obtained with the FWD, the moduli computed for the 85th percentile with both the FWD and the SSG show a difference lower than 20%. These results emphasise the possible use of the SSG as a reliable procedure for stiffness modulus evaluation of unbound limestone bases.

A Comparison of Density-Based and Modulus-Based In Situ Test Measurements for Compaction Control

Abstract This paper presents and compares the results from a series of in situ density-based and modulus-based compaction control tests that were conducted during construction of a coarse-grained soil embankment. To simulate current construction practices as closely as possible, these in situ tests were performed on an embankment that was constructed and compacted by a vibratory smooth drum roller in a series of lifts. During construction of the test embankment, the compaction process was monitored using the nuclear density gauge device and a number of alternative modulus-based devices, including the lightweight deflectometer, the dynamic cone penetrometer, and the soil stiffness gauge. Comparison of the in situ test results illustrates that point-to-point variability in measured values is quite common for each of these test devices, to varying degrees for the different devices that were examined. Consistent increases in measured soil properties from pass-to-pass of the compactor are considered critical for proper control of the compaction process, with some devices faring better than others in this area of performance. The measured modulus values correlated poorly to the nuclear density gauge dry unit weights, and also correlated poorly with other measured moduli when the results from different devices were compared. This lack of agreement was likely caused by a variety of factors including: variations in the magnitude of strain and rate of strain application between the different modulus-based devices, variations in the tested volume between the different devices, and variations in the local moisture content and matrix suction conditions. Finally, the effect of soil moisture content was shown to be critically important when interpreting the results from modulus-based tests, and the utility of multiple regression analyses was explored for including this effect.

Mixing Efficiency for Stabilized Subgrades for Low-Volume Roads

Lime is widely used to stabilize fine-grained subgrades beneath pavements. The procedure used to apply lime and the effectiveness of the mixing stage can have a significant impact on the quality of the stabilized sub-grade. For this study, lime was applied to two test sections in slurry and quicklime forms and samples were taken at various stages of mixing. Strength values were determined for field- and laboratory-mixed samples. Strength and stiffness of the subgrades were tracked for up to 33 days by using the dynamic cone penetrometer and soil stiffness gauge. Results showed that additional mixing reduced average lump size, particularly when conducted after a mellowing stage, and significantly improved the subgrade for up to at least four passes. Strengths also increased substantially with time for the stabilized soil, and long-term strengths were highest for soils mixed wet of optimum moisture.

Application of Soil Stiffness Gauge in Assessing Small-Strain Stiffness of Sand with Different Fabrics and Densities

Abstract The soil stiffness gauge (SSG) exhibits particular promise for determining the in situ soil stiffness at small strains. Because the SSG is new, its application in laboratory stiffness measurements is limited. The use of the SSG in assessing small-strain stiffness of sand with different fabrics, densities, and specimen sizes is presented herein. Two types of test containers were utilized and the results indicate that the SSG stiffness obtained from both containers show a similar trend but are offset by a constant value, which might be due to the effect of specimen dimensions and boundary configurations. A comparison with other small-strain stiffness tests indicates that the Young's moduli obtained from the seismic tests are consistently higher than those from the SSG tests. The plots of shear modulus versus shear strain amplitude suggest that the SSG modulus appears to be corresponding to a strain amplitude level higher than the strain amplitude of the seismic test, even though the SSG induces a strain amplitude comparable to that of seismic tests. Nonetheless, the SSG is found to be a potential and useful device for assessing the stiffness of sand with different fabrics and densities.

Evaluating stiffness and strength of pavement materials

Current mechanical empirical-based pavement design requires use of the mechanical properties of pavement materials. For quantitative evaluations of the mechanical properties (i.e. stiffness and strength), field tests are emphasised. In this paper, a recently developed instrument called the soil stiffness gauge (SSG) and the dynamic cone penetrometer (DCP) have been used to assess respectively the in-situ stiffness and strength of natural earthen materials, industrial byproducts, and chemically stabilised soils from ten highway construction sites around the state of Wisconsin, USA. The SSG and DCP survey data were analysed to develop a relationship between the SSG stiffness and DCP penetration index (DPI) values for individual material types and for all materials combined. A simple linear semi-logarithmic model is obtained between the SSG stiffness and DPI values, with the coefficient of determination, R2, ranging from 0·47 to 0·75 for individual material types and an R2 value of 0·72 for all materials combined. The SSG stiffness and DPI values can be also correlated with the modulus (E) and California bearing ratio (CBR) of the materials respectively. A good relationship is obtained between E from the SSG and CBR from the DCP, and is compared with the well-known equations developed by Powell et al. and AASHTO as well as other available correlations from different in-situ tests: the falling weight deflectometer, German light drop weight, and plate load tests. Finally, the proposed power model is validated with a data set from two other test sites. Either or both devices show good potential for future use in pavement and subgrade materials evaluation. The in-situ stiffness and strength properties of various materials can be rapidly and directly monitored in companion with the conventional compaction control tests during pavement construction. The modulus of pavement and subgrade materials is uniquely related to CBRs regardless of soil type and site, and their relationship is also applicable to both as-compacted and post-construction states.

Early-Age Strength Assessment of Cement-Treated Base Material

To avoid early-age damage to cement-treated base (CTB) materials, the cement must be allowed to cure before the pavement can be opened to traffic. The purpose of this research was to evaluate the utilities of the soil stiffness gauge (SSG), the heavy Clegg impact soil tester (CIST), the dynamic cone penetrometer, and the falling weight deflectometer for assessing early-age strength gain of cement-stabilized materials. Experiments were performed at four sites on a pavement reconstruction project along I-84 in Morgan, Utah, where cement stabilization was used in conjunction with full-depth recycling. Each site was stationed to facilitate repeated measurements at the same locations with different devices and at different curing times. Because of the considerable attention from the pavement construction industry for routine quality control and quality assurance programs, the SSG and CIST were the primary focus of the research. Statistical techniques were used to evaluate the repeatability of these devices and their sensitivity to curing time. The results indicated that although the SSG was more repeatable at one site, the CIST data were markedly more sensitive to curing time than the SSG data at all cement-treated sites during the first 72 h after construction. For this reason, the data suggest that the CIST offers greater overall utility than the SSG for monitoring early-age strength gain of CTB. Further research is needed to investigate appropriate thresholds and protocols for these testing methods that ensure adequate reliability of the collected data.

Early-Age Strength Assessment of Cement-Treated Base Material

To avoid early-age damage to cement-treated base (CTB) materials, the cement must be allowed to cure before the pavement can be opened to traffic. The purpose of this research was to evaluate the utilities of the soil stiffness gauge (SSG), the heavy Clegg impact soil tester (CIST), the dynamic cone penetrometer, and the falling weight deflectometer for assessing early-age strength gain of cement-stabilized materials. Experiments were performed at four sites on a pavement reconstruction project along I-84 in Morgan, Utah, where cement stabilization was used in conjunction with full-depth recycling. Each site was stationed to facilitate repeated measurements at the same locations with different devices and at different curing times. Because of the considerable attention from the pavement construction industry for routine quality control and quality assurance programs, the SSG and CIST were the primary focus of the research. Statistical techniques were used to evaluate the repeatability of these devices and...

Use of Soil Stiffness Gauge in Thermoplastic Pipe Installation

The soil stiffness gauge is a new tool for measuring the stiffness of a soil layer quickly in the field. It is anticipated that this type of portable device will be utilized in a variety of geotechnical projects in the future, since stiffness is a better indicator of the quality of soil fill than dry density. This paper examines the usefulness of the soil stiffness gauge in thermoplastic pipe installation work. Comprehensive data obtained during the initial stage of the thermoplastic pipe deep burial project in Ohio are reviewed to discuss the ability of the soil stiffness gauge to realistically measure the stiffness of the backfill soil placed around thermoplastic pipe and the ability of the soil modulus derived from the soil stiffness gauge readings to predict the horizontal deflections of the thermoplastic pipe under moderate to deep soil cover.

Relationship Between Soil Stiffness Gauge Modulus and Other Test Moduli for Granular Soils

Recently, there has been a concerted effort to develop methods for direct measurement of soil stiffness, modulus, or both. A new field test device called the soil stiffness gauge (SSG), which is currently marketed as GeoGauge, shows potential to assess near-surface stiffness. A comparison is presented of moduli obtained from the SSG with moduli obtained from other tests on granular soils. The maximum singleamplitude dynamic force produced during the SSG measurement is determined to be 17.3 N. On this basis, an estimate of the shear strain amplitude produced from the SSG is made by finite element analysis. A plot of shear modulus versus shear strain amplitude on a medium sand obtained from different laboratory tests, including the SSG, is presented. The comparison of the SSG modulus with the moduli from other laboratory tests indicates that the SSG outputs a dynamic modulus corresponding to a strain amplitude approximately 20 times higher than the expected range and with a magnitude lower than it should be on the basis of the induced strain. Nevertheless, the SSG modulus is still higher than that from the resilient modulus test typically used for pavement design.

Engineering Behavior of Stabilized Soils

Stabilization of soils is an effective method for improving soil properties and pavement system performance. For many soils, more than one stabilization agent may be effective, and financial considerations or availability may be the determining factor on which to use. A series of tests was conducted to evaluate the relative performance of lime, cement, Class C fly ash, and an enzymatic stabilizer. These products were combined with a total of seven different soils with Unified Soil Classification System classifications of CH, CL, ML, and SM. Durability testing procedures included freeze–thaw, wet–dry, and leach testing. Atterberg limits and strength tests also were conducted before and after selected durability tests. Changes in pH were monitored during leaching. Relative values of soil stiffness were tracked over a 28-day curing period using the soil stiffness gauge. Lime- and cement-stabilized soils showed the most improvement in soil performance for multiple soils, with fly ash–treated soils showing substantial improvement. The results showed that for many soils, more than one stabilization option may be effective for the construction of durable subgrades. The enzymatic stabilizer did not perform as well as the other stabilization alternatives.