Bhaskar C. S. Chittoori

Quantitative estimation of clay mineralogy in fine-grained soils

Stabilization design guidelines based on soil plasticity properties have certain limitations. Soils of similar plasticity properties can contain different dominant clay minerals, and hence, their engineering behavior can be different when stabilized with the same chemical additive and dosage. It is essential to modify stabilizer design guidelines by including clay mineralogy of the soil and its interactions with chemical additives used. Chemical properties of a soil including cation exchange capacity (CEC), specific surface area (SSA) and total potassium (TP) are dependent on clay mineral constituents, and an attempt is made in this study to develop a rational and practical methodology to determine both clay mineralogy distribution and dominant clay mineral in a soil by using three measured chemical soil properties and their analyses. This approach has been evaluated by determining and evaluating clay minerals present in artificial and natural clayey soils of known and unknown clay mineralogy. A total of twenty natural and six artificial soils were considered and used in the chemical analyses. Test results and subsequent analyses including the development of artificial neural network (ANN) based models are evaluated and described in this paper.

Experimental Studies on Stabilized Clays at Various Leaching Cycles

AbstractThe effectiveness of chemical stabilization and its permanency were investigated by subjecting chemically treated soils to leaching tests by internal water flushing, which simulates moisture ingress/digress into subsoils from rainfall events. Control and chemically stabilized soils from eight different locations were subjected to these leaching tests over 14 cycles in the laboratory. Each leaching cycle represents one pore volume of water flushed through the soil specimen. Leaching samples were collected after 3, 5, 7, and 14 cycles and were chemically analyzed to address pore fluid chemical composition changes and possible leaching of the chemical additives. Unconfined compressive strength tests were conducted on soil specimens after 3, 7, and 14 leaching cycles to study soil strength variations. The effects of soil type, stabilizer type and dosages, and the curing method on the leaching of stabilizers are analyzed. Test results and analyses indicate that leaching of stabilizer did occur, but the...

Sustainable Reutilization of Excavated Trench Material

The Integrated Pipeline (IPL) project which involves a 147 mile pipe line is a joint effort between the Tarrant Regional Water District (TRWD) and Dallas Water Utilities (DWU) that will bring additional water supplies to the Dallas/Fort Worth metroplex. As a part of the pipeline layout and construction, large amounts of soil will be excavated during the pipeline installation process. Similarly, large amounts of soil need to be imported for bedding and backfilling of the trench. Both importing new fill material and exporting excavated trench material for landfilling will have serious implications on both the economic and environmental aspects of the construction project. As a result, a research study was initiated to identify insitu soil material that can be reused as either bedding, zone or backfill materials for the pipeline installation. For this purpose soil samples were collected along the pipeline alignment and comprehensive geotechnical characterization studies including estimation of expansive clay minerals are attempted. Based on these studies, the sampling materials are identified for potential reuse as backfill, bedding and zone materials. Cost and environmental benefits as well as emissions reductions of using insitu native material versus imported fill material are also discussed.

Strength and Stiffness Characterization of Controlled Low-Strength Material Using Native High-Plasticity Clay

AbstractA research attempt was made to design a controlled low-strength material (CLSM) mix that can be used as bedding and haunch material for a pipeline by using the native soil as fine aggregate. Several CLSM mix designs were attempted using native high-plasticity clay as fine aggregate material. Comprehensive material characterization studies including flowability to strength tests were performed. These results were analyzed to address the applicability of each mix to serve as pipe bedding/backfilling zones in a pipeline construction. Both flowability and density test results are first evaluated, and as a result, several mixes are formulated. These mixes were further subjected to engineering characterization-related studies, and this paper presents these test results. Setting time, strength, and stiffness results as well as excavatability evaluations of these mixtures are covered as a part of these studies. These results indicate that the CLSMs can be produced using native high-plasticity soils with s...

Stabilization of High-Sulfate Soils by Extended Mellowing

The use of lime to stabilize expansive soils has been the preferred technique for many years. However, heaving and premature pavement failures in lime-treated expansive subgrades containing sulfates led to the search for alternative stabilization techniques. Of the several techniques developed, precompaction mellowing has the potential to be effective in stabilizing sulfate-bearing soils. Yet this method needs experimental evaluation. In the current study, an attempt was made to assess the stabilization effectiveness of precompaction mellowing on high-sulfate soils. For this task, six natural expansive soils from Texas, with sulfate contents varying from 200 to 44,000 ppm, were collected. Soils with low-sulfate contents were spiked with additional sulfates to make them high-sulfate soils. Basic classification and chemical tests were performed to establish the clay mineralogy of the soils. Three mellowing periods (0, 3, and 7 days) were studied. The test soils were treated with lime and allowed to mellow for the specified periods. Following the mellowing, the samples were subjected to three-dimensional tests for volumetric swell, shrinkage, and unconfined compressive strength (UCS). To study the consumptions of alumina and silica during sulfate–soil–lime reactions, reactive alumina and silica measurements were also attempted. The authors observed that shrinkage was of no concern in treated soils because the shrinkage invariably reduced with lime treatment. In four of the six soils, precompaction mellowing reduced sulfate-induced swell to a level below the natural expansive swelling. The UCS strengths of treated soils decreased slightly with mellowing. Reasons for the anomaly in UCS strengths and ineffectiveness of precompaction mellowing in two soils were explained.

Evaluation of swell behavior of expansive clays from internal specific surface and pore size distribution

AbstractThe interdependency of microsoil fabric-related properties and swell/shrink behavior of expansive soils needs to be identified to achieve a more thorough and accurate prediction of heave of expansive soils. In a recent research study, two microsize-related properties of a soil—pore size distribution and specific surface area—were identified and examined in an effort to address their synergistic effects on swelling behavior of soils. To study this aspect in detail, eight natural expansive clayey soils from known expansive soil regions were sampled and studied by using two test methods: conventional one-dimensional vertical swell tests and novel three-dimensional volumetric swell strain tests. Microinternal structural details, including pore void distribution, were obtained from mercury intrusion porosimetry (MIP) studies on compacted soil specimens. Specific surface area (SSA) details of the same soils were determined using the chemical ethylene glycol monoethyl ether (EGME) method. Attempts were m...

Durability Studies on Native Soil-Based Controlled Low Strength Materials

The Integrated Pipeline Project (IPL) is a collaborative effort between the Tarrant Regional Water District (TRWD) and Dallas Water Utilities (DWU), which bring additional water supplies to the Dallas / Fort Worth area. As part of a sustainability initiative, several studies were conducted to assess the reuse potential of excavated materials along the IPL project. One of these studies involved using the excavated material as an ingredient in Controlled Low Strength Material, often known as CLSM or flowable fill. This flowable fill can be used as bedding and haunch material in pipeline construction. These CLSMs meet the specifications in the short-term; however their long-term performance should be verified in order to be successfully used in the field, especially when these materials are subjected to seasonal changes such as wetting and drying. Hence, durability studies were conducted on CLSMs from two different geologic formations, namely Eagle Ford and Queen City formations. The variations in retained strength and volumetric strain changes, along with the amount of stabilizer leached out of the CLSM samples at different durability cycles, are presented in this paper. It was observed that Eagle Ford soil CLSM lost more than 50% of its initial strength while Queen City sand CLSM lost approximately 50% of its initial strength when subjected to durability studies. The loss in strength was attributed to both volume change and stabilizer loss in case of Eagle Ford soil while stabilizer loss alone caused the loss of strength in the case of Queen City sand.

In Situ Matric Suction and Moisture Content Measurements in Expansive Clay During Seasonal Fluctuations

In the design of flexible pavements using the mechanistic-empirical pavement design guide (MEPDG), water flow analyses are used to predict changes in the mechanical behavior of unsaturated subgrade soils. However, the water flow analyses in the MEPDG are not well validated using field measurements of moisture content and matric suction with time. A research study was initiated to measure the variation in matric suction and moisture content in an expansive soil during seasonal fluctuations. Specifically, a thermal conductivity-based suction sensor was fully evaluated and calibrated in the laboratory and was later installed with moisture sensors at different sites in Texas. This paper presents a summary of field measurements of matric suctions and moisture contents from a site in Houston. Comparisons of field measurements of matric suctions are compared with those interpreted from the soil water characteristic curve using field moisture content measurements, and a decent match was obtained up to matric suctions close to 800 kPa.

Target Reliability Approach to Study the Effect of Fiber Reinforcement on UCS Behavior of Lime Treated Semi-Arid Soil

AbstractThis paper evaluates the effectiveness of stabilizing expansive soil with two different types of fibers, fiber mesh (FM) and fiber cast (FC), in conjunction with chemical stabilization. The...

Effect of Fiber Reinforcement on the Hydraulic Conductivity Behavior of Lime-Treated Expansive Soil—Reliability-Based Optimization Perspective

The use of synthetic fibres as reinforcement to stabilise expansive soils is gaining momentum. As a contribution towards this growing field of research two different types of synthetic fibres, Fiber Mesh® and Fiber Cast®, were evaluated as a stabilisation alternative for expansive soils in the presence of lime. California bearing ratio (CBR) is chosen as a performance indicator as it is a good pointer towards pavement effectiveness. Variables such as length and amount of the fibres as well as curing period were studied. Both deterministic and probabilistic (or reliability) analyses is presented in this paper. While the deterministic analysis helps in understanding the measured experimental data, the probabilistic approach accounts for the stochastic nature of the experimental data and provides a better rationale for the design methods. The deterministic approach showed that the improvement in CBR increased with higher fibre contents and longer lengths and the effect was prominent when lime was used as a s...