Daehyeon Kim

Simplification of Resilient Modulus Testing for Subgrades

Resilient modulus has been used for characterizing the stress-strain behavior of subgrade soils subjected to traffic loadings in the design of pavements. With the recent release of the M-E Design Guide, highway agencies are further encouraged to implement the resilient modulus test to improve subgrade design. In the present study, physical property tests, unconfined compressive tests, resilient modulus (Mr) tests and Several Dynamic Cone Penetrometer (DCP) tests were conducted to assess the resilient and permanent strain behavior of 14 cohesive subgrade soils and five cohesionless soils encountered in Indiana. The applicability for simplification of the existing resilient modulus test, AASHTO T 307, was investigated by reducing the number of steps and cycles of the resilient modulus test. Results show that it may be possible to simplify the complex procedures required in the existing Mr testing to a single step with a confining stress of 2 psi and deviator stresses of 2, 4, 6, 8, 10 and 15 psi. Three models for estimating the resilient modulus are proposed based on the unconfined compressive tests. A predictive model to estimate material coefficients k1, k2, and k3 using 12 soil variables obtained from the soil property tests and the standard Proctor tests is developed. The predicted resilient moduli using all the predictive models compare satisfactorily with measured ones. A simple mathematical approach is introduced to calculate the resilient modulus. Although the permanent strain occurs during the resilient modulus test, the permanent behavior of subgrade soils is currently not taken into consideration. In order to capture both the permanent and the resilient behavior of subgrade soils, a constitutive model based on the Finite Element Method (FEM) is proposed. A comparison of the measured permanent strains with those obtained from the Finite Element (FE) analysis shows a reasonable agreement. An extensive review of the M-E design is done. Based on the test results and review of the M-E Design, implementation initiatives are proposed.

Evaluation of Resilient Modulus of Subgrade and Base Materials in Indiana and Its Implementation in MEPDG

In order to implement MEPDG hierarchical inputs for unbound and subgrade soil, a database containing subgrade M R, index properties, standard proctor, and laboratory M R for 140 undisturbed roadbed soil samples from six different districts in Indiana was created. The M R data were categorized in accordance with the AASHTO soil classifications and divided into several groups. Based on each group, this study develops statistical analysis and evaluation datasets to validate these models. Stress-based regression models were evaluated using a statistical tool (analysis of variance (ANOVA)) and Z-test, and pertinent material constants (k 1, k 2 and k 3) were determined for different soil types. The reasonably good correlations of material constants along with M R with routine soil properties were established. Furthermore, FWD tests were conducted on several Indiana highways in different seasons, and laboratory resilient modulus tests were performed on the subgrade soils that were collected from the falling weight deflectometer (FWD) test sites. A comparison was made of the resilient moduli obtained from the laboratory resilient modulus tests with those from the FWD tests. Correlations between the laboratory resilient modulus and the FWD modulus were developed and are discussed in this paper.

Effects of Particle Size on the Shear Behavior of Coarse Grained Soils Reinforced with Geogrid

In order to design civil structures that are supported by soils, the shear strength parameters of soils are required. Due to the large particle size of coarse-grained soils, large direct shear tests should be performed. In this study, large direct shear tests on three types of coarse grained soils (4.5 mm, 7.9 mm, and 15.9 mm) were performed to evaluate the effects of particle size on the shear behavior of coarse grained soils with/without geogrid reinforcements. Based on the direct shear test results, it was found that, in the case of no-reinforcement, the larger the maximum particle size became, the larger the friction angle was. Compared with the no-reinforcement case, the cases reinforced with either soft geogrid or stiff geogrid have smaller friction angles. The cohesion of the soil reinforced with stiff geogrid was larger than that of the soil reinforced with soft geogrid. The difference in the shear strength occurs because the case with a stiff geogrid has more soil to geogrid contact area, leading to the reduction in interlocking between soil particles.

USE OF RECYCLED AND WASTE MATERIALS IN INDIANA

The improved generation, handling, and safe disposal of waste and recycled materials have become a major concern in the United States. Generators of waste are under growing pressure either to find new facilities to dispose of it, as old facilities reach their capacity, or to recycle the waste. In addition to a scarcity of disposal facilities and the associated escalating costs, stringent regulations and public perceptions have caused local governments to seek ways to use waste materials in a productive way. The Indiana Department of Transportation has been proactive and has initiated and funded several research projects in cooperation with generators to determine safe and beneficial uses in road construction. Efforts are still under way to find economically feasible and environmentally sound geotechnical applications of waste and recycled materials. This study consolidates results of research on geotechnical applications of coal combustion by-products, foundry sand, tire shreds, and crushed glass. Project case histories and revised construction specifications based on postconstruction evaluations are also presented. These geotechnical applications suggest that significant cost savings can be attained, in addition to the positive environmental impact, with the use of these materials.

Effects of Ground Conditions on Microbial Cementation in Soils

The purpose of this study is to understand the effect of ground conditions on microbial cementation in cohesionless soils. Since the method of microbial cementation is still at the experimental stage, for its practical use in the field, a number of laboratory experiments are required for the quantification of microbial cementation under various ground conditions, such as relative densities, relative compactions and particle size distributions. In this study, in order to evaluate the effectiveness of microbial cementation in treated sands and silts, an experiment was performed for different relative densities of silica sands, for different relative compactions of silts and for different particle size distributions of weathered soils sampled from the field. Scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy and mapping analyses were implemented for the quantification of the levels of microbial cementations for sand, silt and weathered soil specimens. Based on the test results, a considerable microbial cementation was estimated depending on the soil conditions; therefore, an implementation of this new type of bio-grouting on a weak foundation may be possible to increase the strength and stiffness of weak ground.

Family of Compaction Curves for Chemically Modified Soils

Lime and Lime Kiln Dust (LKD) are widely used for modifying/stabilizing pavement subgrades. The addition of lime or LKD involves chemical processes that are dependent on many parameters. For natural subgrades, quality control is based on moisture and unit weight requirements using manual interpolations of one-point test data on a family of curves. For modified soils, moisture and unit weight measurements are insufficient for quality control and other tests must be considered. Various possible quality control methods for LKD-modified subgrades were evaluated. This research produced an Excel-based program to automate the generation of a family of curves and one-point data interpolation. Families of curves for LKD-modified soils did not vary systematically, limiting their usefulness in quality control. Dynamic cone penetrometer (DCP) and Time domain reflectometry (TDR) tests were considered as alternative means to achieve field quality control. The DCP test although promising, requires supplementary tests for completely characterizing a modified subgrade. LKD modification of soil involves chemical reactions which can be indirectly studied by measuring the electrical properties. The dielectric constant and electrical conductivity of a LKD-modified soil were measured using the Purdue TDR apparatus. Preliminary test results show that with the knowledge of two calibration constants, the dielectric constant of a soil measured following the Two-Step TDR test (ASTM D 6780) can be used for water content and unit weight determinations. The electrical conductivity of a LKD-modified soil decreases with time in a manner that is similar to the one-dimensional consolidation of a soil. The variation in electrical conductivity with time of a LKD-modified project soil was correlated to its strength and was also used to estimate the amount of LKD present in the soil. Future research should focus on extending these observations to other soils and to formulating a protocol for using the TDR test along with the DCP test for quality control of LKD-modified soils.

Potential Soil Contamination in Areas Where Ferronickel Slag Is Used for Reclamation Work

This study aims to analyze contamination with the use of soil reclaimed with ferronickel slag (FNS). In order to investigate any contamination due to FNS disposal, soils were collected from three sites. The contamination analysis was done on these samples through a series of laboratory tests. Furthermore, laboratory tests simulating field conditions were performed in a soil chamber. In the lab test, three leaching agents, namely fresh water, acidic water and seawater, were used. The soil samples used were sand and silt with a relative density of 40% and a compaction ratio of 90%, respectively. The pH of the effluent discharged from the experimental soil chamber was also analyzed. After leaching, soil samples were subjected to analysis. The results showed that pH was higher in the silt than in the sand. The results of the laboratory tests exhibited that leaching of hazardous elements from FNS is limited, so that it can be used as a substitute for natural aggregate in the cement industry or construction applications.

Use of In Situ Tests in Compaction Control of a Bottom Ash Embankment

Since 1994, the Indiana Department of Transportation has constructed numerous recycled materials projects that use bottom ash, fly ash, foundry sand, crushed glass, and tire shreds in transportation facilities. All these projects were constructed in accordance with procedural specifications based on conventional compaction control tests such as the nuclear gauge. However, the nuclear gauge does not give accurate density and moisture content results because of the presence of numerous elements in recycled materials. In addition, sand cone tests are cumbersome and time-consuming. There is a need to develop criteria for in situ test methods such as the dynamic cone penetration test and lightweight deflectometer (LWD) testing. Once an initial criterion is established, criteria for compaction control of similar recycled materials can be developed. In a study, a test pad using coal ash was constructed with a combination of roller passes. On the basis of the results of dynamic cone penetration and LWD tests conducted in the test pad, in conjunction with a combination of roller passes, the criteria for compaction control of bottom ash was provided for the construction of the remaining 11-m-high embankment. The subsequent construction monitoring and postconstruction evaluation of the bottom ash embankment revealed that the criteria are very effective.

Effect of Strength Enhancement of Soil Treated with Environment-Friendly Calcium Carbonate Powder

This study aims to investigate the effects of the strength improvement of soft ground (sand) by producing calcium carbonate powder through microbial reactions. To analyze the cementation effect of calcium carbonate produced through microbial reaction for different weight ratios, four different types of specimens (untreated, calcium carbonate, cement, and calcium carbonate + cement) with different weight ratios (2%, 4%, 6%, and 8%) were produced and cured for a period of 3 days, 7 days, 14 days, 21 days, and 28 days to test them. The uniaxial compression strength of specimens was measured, and the components in the specimen depending on the curing period were analyzed by means of XRD analysis. The result revealed that higher weight ratios and longer curing period contributed to increased strength of calcium carbonate, cement, and calcium carbonate + cement specimens. The calcium carbonate and the calcium carbonate + cement specimens in the same condition showed the tendency of decreased strength approximately 3 times and two times in comparison with the 8% cement specimens cured for 28 days, but the tendency of increased strength was approximately 4 times and 6 times in comparison with the untreated specimen.

Long-Term Performance of Chemically Modified Subgrade Soils in Indiana

Chemical modification of soils with lime in Indiana is widely used to improve the workability and compactability of weak subgrade soils. Although the modification process is primarily aimed at construction expediency, additional effects such as long-term improvement of stiffness or strength by pozzolanic and carbonation cementation processes of the treated soils have been expected but have not been quantified. Because of a lack of confidence in the long-term performance of the chemically modified soils, their enhanced stiffness has not been taken into account in pavement design, leading to a conservative design of the asphalt or concrete pavement layers. Six roads that have been in service for 5 to 11 years were selected to conduct field tests. The selection was performed considering (a) location of road project in Indiana, (b) class of road, (c) year when chemical treatment was done, (d) type of chemical modifier used, (e) type of pavement, (f) availability of geotechnical information for postconstruction evaluation, and (g) traffic and safety control for field testing. The results from the field tests show that the long-term stiffness or strength of subgrades that were chemically treated 5 to 11 years ago is 4 to 11 times higher than that of natural sub-grades. This finding suggests that the enhanced stiffness of the chemically modified subgrade could be accounted for in pavement design, which would lead to a reduction of the thickness of asphalt or concrete pavement layers.