Light Weight Deflectometer (LWD)

Light weight deflectometer (LWD) has been widely used for quality assurance in road construction, in particular compaction of both chemically treated subgrade soil and aggregate subbase. However, it has been recognized that LWD measurements vary with many factors. Based on LWD tests in actual road construction, this presentation provides updated information on the LWD deflection measurements for both chemically treated subgrade soil and aggregate subbase

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

Chemical Modification of Uniform Soils and Soils with High/Low Plasticity Index

The addition of chemicals into the subgrade has been widely used during construction to improve the soil properties. The chemicals, often Lime Kiln Dust (LKD) and Portland cement, are added to the soil to improve its workability, compactability and engineering properties. Many DOTs have been using chemical modification for more than 20 years. In fact, 90% of the current subgrade is treated. Despite the wide experience-based in treating subgrade soils, several problems still exist. The INDOT (Indiana Department of Transportation) design manual states that subgrade clays with low plasticity (PI\u3c 10) must be treated with cement and that high plasticity clays (Density \u3c 95 pcf, or PI ≥ 25) in the subgrade must be replaced with suitable soils. Uniform granular soils do not stabilize with lime products or with low dosage of cement. Current knowledge does not provide information about stabilization of these soils. This research explores LKD, combinations of LKD and Portland cement to treat high and low plasticity clayey soils (problem soils, e.g. expansive and organic soils are not considered in the research) and treatment with Portland cement of uniform granular soils. A comprehensive laboratory testing program has been undertaken to investigate the potential for the treatment and to report the changes in mineralogy and engineering properties of the treated soils with time. Unconfined compression tests performed over time, as well as XRD tests, show that treatment is possible and that it remains over time since the strength of the treated soil improves with time and its mineralogy does not change

Development of SPT-Torque Test Correlations for Glacial Till

Torque tests, which are performed immediately after a standard penetration test (SPT), have grown in popularity since its conception in Brazil during the early 1990s. Purdue University developed the first automated torqueing hardware prototype in 2010. SPT, SPT-Torque and cone penetration test (CPT) field testing were performed in glacial till soils at four different sites in northern Indiana and one site in southern Indiana. Index tests were performed for the soil samples collected at each of these sites. Relationships between the torque ratio (the measured torque divided by the corrected SPT blow count) vs. soil type, and unit side resistance vs. normalized SPT blow count (N1,60) and normalized CPT cone resistance (qc,1) were explored for these soils. For saturated clay soils, development of a relationship between unit side resistance and undrained shear strength was also attempted. Reliable correlations based on the torque ratio were not achieved based on the data collected for all the different soils tested. However, reasonably high coefficients of determination were obtained for the normalized equations developed for clays and saturated non-plastic silt. Low coefficients of determination were obtained for saturated and unsaturated sandy soils. The low coefficients of determination values are attributed to the small population dataset for sandy soils and the difficulty of adequately determining the degree of saturation for unsaturated non-plastic soil types due to the soil structure destruction with sampling. Overall, it was found that the relationships are strong for clay and saturated non-plastic silt and it is recommended that further data be collected to continue to strengthen all relationships, especially those for sand and unsaturated non-plastic silt

Engineering Properties of Marls

The term “marl” is used to designate soft, carbonate-rich, fine-grained soils, which pose concerns related to both settlement and stability. Despite the prevalence of marls in Indiana and the concerns associated with their behavior, very limited work has been done to study the engineering properties of these soils. This was the motivation for this research project, which involved two primary activities: a) the creation of a map and database of existing information on marl deposits in Indiana; and b) an in-depth characterization of the properties of a marl deposit in Daviess County, which was considered representative of similar deposits encountered in Indiana. The marl database was generated using ArcGIS 10.0.from information available at the INDOT, and involved mining data from over five thousand boreholes. The second part of the project involved field tests (seismic cone penetration tests, standard penetration tests, field vane shear tests), and laboratory experiments (index tests, incremental and constant rate of strain consolidation tests, and K0-consolidated undrained triaxial tests) conducted on high quality Shelby tubes samples. Additionally, the mineralogy and the microstructure of the soil were studied in detail. The laboratory tests reveal that the deposit was not homogeneous as was initially anticipated, but was, instead, formed by two types of soils that repeat in horizontal thin layers. These two soils, referred to as ‘soil M’ and ‘soil C’, are both characterized by very high calcium carbonate contents but show distinct index and engineering properties, that may be ascribed to differences in mineralogy and composition. This stratification is not detected by the field tests. The consolidation tests show that the deposit has an OCR less than 2 and compressibility parameters markedly dependent on stress level, as typical of sensitive soils. K0-consolidated undrained compression triaxial tests show that both soils exhibit normalized behavior, and that the relationship between strength and stress history is well described by the SHANSEP equation (although the SHANSEP parameters differ for the two soils). Comparison of the field data and laboratory results provides the means to validate published correlations for interpretation of the geotechnical properties of marls from field results. For the site examined, correlations to estimate shear wave velocity, stress history, and undrained strength from CPT results are identified. Implementation recommendations are provided for soil identification, sampling and specimen preparation, interpretation of filed data, and preliminary design

QA/QC of Subgrade and Embankment Construction: Technology Replacement and Updated Procedures

The Dynamic Cone Penetrometer (DCP) is a device that is used for the estimation of in situ compaction quality of constructed subgrades and embankments. It is a relatively inexpensive, light-weight and easy to use device that measures the dynamic penetration resistance of the compacted soil, from which an estimate of soil strength and stiffness characteristics can be made. Owing to its ease of use, many DOTs in the U.S. have employed the DCP in their compaction quality control procedures, and over the past few decades, extensive research has been carried out on the development of correlations between the results of the DCP test and the results of strength and stiffness tests performed on compacted soils (e.g., California bearing ratio, and resilient modulus) The objectives of this research are to refine DCP-based quality assurance and quality control correlations for compaction quality control developed by previous research studies carried out at Purdue for the Indiana Department of Transportation, especially focusing on i) grouping of the soils based on their mechanical response to the DCP loading, and ii) limiting the in situ moisture range of the soils used for development of correlations within -2% of the optimum moisture content of the tested soil. The factors outlined above are studied, and in particular, soil grouping is examined critically. The AASHTO (‘A-based’) classification employed previously for classification of soils is replaced by a new classification criteria specifically developed for the DCP test. Soils are grouped into one of the two categories of coarse-grained or fine-grained soils on the basis of the size of the dominant particle in the soil. The criteria developed for the classification of soil into one of these two categories is based on index properties of the soil, such as the standard Proctor maximum dry density, optimum moisture content, plasticity index (PI) and fines content (percentage passing0.075 mm sieve size). For the purpose of refinement of the QA/QC correlations, extensive field and laboratory tests (more than 750 DCP tests) were carried out on soils found in Indiana to add to the existing database of DCP test results. The database was then statistically analyzed for extraction of the representative DCP test value (number of DCP blows required for a specific depth of penetration into the compacted soil) for different types of soil. Results show that the DCP test results for fine-grained soils have a good correlation with the PI, which is indicative of the clay content of the soil, while the DCP test results for coarse-grained soils have good correlations with the optimum moisture content of the soil, which is indicative of the targeted in situ density of the soil. Furthermore, a statistical analysis of the distribution of DCP blow counts in the field revealed that the mean of a minimum of 7 closely spaced tests is required to get a representative blow count of the compacted soil at a given location. More targeted testing is needed to assess the frequency of DCP testing required for larger areas

Light Weight Deflectometer (LWD)

Recent advances in the performance and monitoring of earthwork compaction can lead to faster, more consistent and more cost-effective roadway construction. Learn about INDOT’s progress towards broader implementation of the light-weight deflectometer, dynamic cone penetrometer and intelligent compaction technologies

Dynamic Cone Penetrometer (DCP)

Recent advances in the performance and monitoring of earthwork compaction can lead to faster, more consistent and more cost-effective roadway construction. Learn about INDOT’s progress towards broader implementation of the light-weight deflectometer, dynamic cone penetrometer and intelligent compaction technologies