Alan F. Rauch

Measured Effects of Liquid Soil Stabilizers on Engineering Properties of Clay

Stabilization of pavement subgrade soils and base materials has traditionally relied on treatment with lime, cement, and sometimes fly ash. Marketed as alternatives to these conventional bulk soil stabilizers, a variety of concentrated liquid chemical products are sold by several companies. Most transportation agencies, however, are hesitant to specify these nontraditional liquid stabilizers without reliable data to support vendor claims of product effectiveness. Standard laboratory soil tests were conducted to measure changes in the engineering properties of five clay soils when treated with three liquid chemical products. The tests involved three reference clays (kaolinite, illite, montmorillonite), two high-plasticity natural clays, and three representative liquid stabilizers (ionic, polymer, enzyme types). Tests were conducted on untreated control soil samples and on samples treated with each product at the suppliers’ recommended application rates. All of the test specimens were prepared in accordance with a specified 10-step protocol that allowed objective comparisons of the test results. Each treated and untreated soil was characterized in terms of the Atterberg limits, compacted unit weight, one-dimensional free swell potential, and undrained triaxial shear strength. Given some variation in the test samples, the test results did not show consistent, significant changes in the properties of these soils as a result of treatment with these three products. Higher application rates might yield more favorable results. Clearly, independent laboratory evaluations with project-specific soils are warranted before the use of these proprietary liquid stabilizers in the field.

Mechanisms of Soil Stabilization with Liquid Ionic Stabilizer

Numerous commercial suppliers are marketing liquid chemical products for stabilizing pavement subgrade and base soils. These nontraditional chemical stabilizers may offer viable alternatives for stabilizing sulfate-rich soils where conventional lime or cement treatment can lead to excessive soil expansion. Typically sold as concentrated liquids that are diluted in water before application, these products may be less expensive to use than lime or cement. However, many transportation agencies are hesitant to specify nontraditional liquid stabilizers without better information on the stabilizing mechanisms and documented field experiences. To identify the mechanisms associated with one class of these products, a representative ionic soil stabilizer and a sodium montmorillonite clay were selected for a detailed physical-chemical study. Laboratory testing included chromatography, spectroscopy, X-ray diffraction, electron microscopy, and standard titration analyses. These tests have shown that the principal active constituents of the selected ionic stabilizer are d-limonene (a by-product of citrus processing) and sulfuric acid, which react to form a concentrated, low-pH solution of sulfonated limonene. The observed changes in clay chemistry following treatment indicated that this product would stabilize a soil by altering the clay lattice. The result is the formation of a more highly weathered, less-expansive clay structure. On the basis of this understanding of the underlying mechanisms, ionic stabilizers applied at sufficiently high application mass ratios may improve the properties of certain soils on some highway construction projects.

SHEAR AND INTERFACE STRENGTH OF CLAY AT VERY LOW EFFECTIVE STRESS

Thin-specimen direct shear (TSDS) tests were conducted to measure the shearing strength of kaolinite, and interface strengths between kaolinite and acrylic plastic and anodized aluminum, at normal effective stresses from 1 to 2400 Pa (0.02 to 50 lb/ft2). At the lowest effective normal stresses, curved strength envelopes fitted through the data exhibited no cohesion and high secant friction angles. Accurate information on the behavior of soil in this low-pressure range is needed to properly interpret the behavior of prototype foundations in laboratory-scale model tests.

LABORATORY CORRELATION OF LIQUEFACTION RESISTANCE WITH SHEAR WAVE VELOCITY

Laboratory data, which relate the liquefaction resistance of two sandy soils to shear wave velocity, are presented and compared to liquefaction criteria derived from seismic field measurements. Recent studies using field case history data have lead to new criteria for assessing liquefaction potential in saturated, granular deposits based on in-site, stress-corrected shear wave velocity. However, the relatively small number of case histories and the limited rage of site conditions represented in the data catalog hinder this approach. Additional data are needed to more reliably define liquefaction resistance as a function of shear wave velocity. Because shear wave velocity can be measured in-situ in the laboratory, laboratory testing can be used to augment the available field data. In the work described herein, cyclic triaxial and resonant column tests were conducted on specimens of clean uniform sand and a silty sand. Cyclic undrained strength and small-strain shear wave velocity were determined for identical specimens formed by water sedimentation. The data from these tests were found to be consistent with published field performance criteria, even with the uncertainties of relating laboratory data to field response. This study demonstrates the link between field and laboratory measurements that are possible with shear wave velocities. This link creates the opportunity to extend this approach to study other materials, such as silty sands and gravelly soils, and to study the influence of other parameters, such as high confining pressure, where little to no field performance data are available.

Behavior of Suction Caissons Measured in Laboratory Pullout Tests

Laboratory experiments are being conducted to study the behavior of suction casissons used for deep offshore moorings. Tests with a 100-mm diameter by 910-mm long caisson prototype, which is installed using dead weight or suction, are performed in a 1.1-m thick deposit of normally consolidated kaolinite. Instrumentation is used to record displacements, axial forces, and pore water pressures (at five locations along the interior and exterior surfaces of the caisson) during extraction of the caisson. Axial pullout tests have been conducted on caissons inserted using dead weight only or dead weight plus suction pressure, on caissons pulled with a vented or sealed top cap, and with rapid (undrained) versus slow (drained) pullout. Measured pullout capacities are interpreted in terms of the weight of extracted soil, side resistance on the caisson walls, and the reverse end bearing capacity at the tip.Copyright

Wavelet-Based Three-Dimensional Descriptors of Aggregate Particles

Morphological characteristics of stone aggregates, including particle shape, angularity, and surface texture, have a significant impact on the performance of hot-mix asphalt materials. To accurately identify and quantify these critical aggregate characteristics, well-defined particle descriptors are essential. Moreover, because a large number of irregular particles must be assessed to adequately characterize an aggregate material, descriptors that can be quantified with automated machines are preferred. In processing true three-dimensional (3-D) data from a laser scanner, wavelet-based 3-D particle descriptors are proposed as a way to characterize individual stone particles. Aided by the multiresolution analysis feature of the wavelet transform, these descriptors provide a generalized, comprehensive, and objective way of describing aggregates. This approach was implemented in conjunction with an automated laser-profiling device built for rapidly characterizing the size and shape properties of aggregate samples. Tests with this equipment have produced data that show strong correlations between the wavelet-based particle descriptors and visual perceptions of the aggregate morphological properties. These results demonstrate that the wavelet-based approach is a promising method for quantifying these important aggregate properties.

A PRACTICAL METHOD FOR PREDICTING EXPANSIVE SOIL BEHAVIOR

A practical and direct method is explored for predicting volumetric strains due to moisture changes in highly plastic, expansive soils. Seasonal, differential movements from swelling and shrinking of expansive soils are a common cause of distress in highway pavements and light foundation in Texas and elsewhere. The problem of expansive soils has been studied by a number of researchers, but most published methods for predicting ground surface movements suffer from a reliance on limited empirical data, a need to run expensive and time consuming tests, and/or a lack of verification for highly plastic natural soils. The proposed approach relies on test data acquired with conventional, commonly available test equipment, and predicts volume changes due to variation in water content at different total stress levels. Data on the shrink and swell behavior of a soil are obtained in a conventional consolidation test apparatus and are used to define a response surface relating one-dimensional strains to water content and total stress. The proposed method is demonstrated for Taylor Clay, a highly expansive soil commonly found in central Texas.

Development of a Laser-Based System for Testing Construction Aggregate

A Laser-based Aggregate Scanning System (LASS) was developed at the University of Texas at Austin for rapid characterization of various properties of construction aggregates. For the determination of shape and size parameters, the “virtual proportional caliper” and “virtual sieve” concepts are introduced, where 3D particle data are rotated about different axes to find elongation and flatness ratios, and the smallest mesh opening size through which a particle can pass. This paper also proposes a group texture based quality control method using wavelet analysis. This method is expected to provide fast group characterization of aggregates during production, enabling real time quality monitoring.

Compaction Control of Crushed Concrete and Recycled Asphalt Pavement using Nuclear Gauge

Crushed concrete (CC) and recycled asphalt pavement (RAP) are sometimes used as substitute fill material in retaining wall and pavement applications. The accuracy of the nuclear gauge device for density and moisture content measurements on these two recycled materials may be unreliable, due to their chemical compositions being different than typical earth fill. An experimental study was initiated to compare moist density and water content measured from the nuclear gauge with those from traditional rubber balloon and test pit methods. Test results show that the nuclear gauge consistently measured larger moist densities than the rubber balloon method for all materials tested. However, the discrepancies were most likely due to the inadequate size of the hole used in the rubber balloon test relative to the maximum particle size of the materials. This result was confirmed with test pit measurements, which showed closer correspondence with the nuclear gauge results. Water content measurements indicate that the nuclear gauge reports larger values of moisture content than oven drying for CC and RAP. This difference can be attributed to the misinterpretation by the nuclear gauge of inherit hydrogen atoms in CC and RAP as water molecules.

Performance evaluation of automated machines for measuring gradation of aggregates

Several automated devices are commercially available for measuring the gradation of stone aggregates. These computerized machines, which provide a rapid alternative to manual sieving, capture and process two-dimensional digital images of aggregate particles to determine grain size distribution. Five of these automated gradation devices were evaluated for accuracy using fifteen aggregate test samples. To quantify how well the machine results compare with data from standard sieve analyses, the CANWE (Cumulative And Normalized Weighted Error) statistic was developed and used. While the machine data did not match the sieve data exactly, the evaluated devices were found to provide good measures of particle gradation for most samples. These tests also indicate that some machines will give more repeatable results in multiple tests of a given material, while others yield better results when testing different materials. The methodology used in this study is suitable for objectively evaluating the accuracy of other rapid gradation machines for various applications.