Vinod K. Garga

STEADY STATE STRENGTH OF SANDS IN A CONSTANT VOLUME RING SHEAR APPARATUS

A modified volume ring shear test apparatus has been developed to undertake constant volume ring shear tests on sand. This constant volume test is a useful means of assessing the steady state strength of granular soils at large strain to determine the liquefaction potential of a soil mass. The apparatus and specimen preparation tools and methods are presented herein. The paper also presents the device and method used to verify the uniformity of the specimens prepared and the repeatability of the specimen preparation method. An experimental program has been conducted using both constant volume (CV) and constant load (CL) tests to investigate the effect of saturation, and of fines on the steady state line (SSL) and the steady state strength (SSS) envelope.

Modified Ring Shear Apparatus for Unsaturated Soils Testing

This paper presents the design details of an automated modified ring shear apparatus for the testing of unsaturated soils using the axis-translation technique. The components of this automated system are described, as well as the types of tests that it can be used for. The key cell components include a flushing system and a precise volume gage system. The paper presents typical test results including the continuous monitoring of water as the test proceeds. A methodology to correct the water content measurements for the effect of air infiltration and evaporation or condensation of water is included.

A Revised Contact Filter Paper Method

The filter paper method, ASTM Standard D5298-03 is generally accepted to be an inexpensive, technically simple, and reasonably accurate method that could be used to measure a wide range of soil suction. The method, however, is dependent upon the accuracy of the calibration curve that relates filter paper water content to soil suction. Additionally, applying a contact stress to the filter papers significantly influences this calibration curve. The effect of five separate contact stresses, namely, 0, 0.4, 1, 2, and 4 kPa on the calibration curve of Whatman 42 filter paper were examined. The study demonstrates that a contact stress of 1 kPa will ensure direct contact between the filter papers and the pore-water of the test specimens without significantly altering the ASTM calibration curve. The contact filter paper method was used to measure the matric suction of compacted Indian Head till specimens over a range of 20 to 300 kPa. This range was chosen to understand the performance and sensitivity of the filter paper method in the low suction range. A comparison of published calibration equations was then undertaken to show the drastically different matric suction estimates that can be obtained by the improper selection of published calibration equations.

A method for determining the surface area of quarried rocks

A coating method which used nickel powder to determine the surface area of angular rock particles was found to be reproducible and required no special equipment. The technique utilized the difference in weight between uncoated and coated rock particles. Four calibration methods were considered. Relationships between surface area and an estimate of the volume of individual rocks were obtained for graded rock having a mean diameter of 25.6 mm and for unisized rock having a mean diameter of 130 mm. The volume of each rock was estimated by measuring the three orthogonal axes of each rock. An analysis of covariance showed that whether or not a rock was spheroid in shape was statistically significant for the evaluation of surface area. Curves relating the hydraulic mean radius to porosity for a range of unisized rock sizes are presented. A procedure for estimating the hydraulic mean radius for a graded media is also discussed.

Shear strength characteristics of statically compacted unsaturated kaolin

The shear strength characteristics of statically compacted unsaturated soil specimens of commercial kaolin (Ip = 15%) were determined using conventional triaxial shear testing apparatus extending total stress analysis. The testing program consists of two different types of confined compression shear strength tests on unsaturated soil specimens. In the first series of tests, the specimens were sheared immediately after the application of the confining pressure under undrained loading conditions. In the second series of tests, the specimens were first allowed to come to equilibrium with respect to volume change and suction value under the applied confining pressure and sheared at two different rates of strain. A psychrometer was used for measuring suction values. In addition, conventional consolidated undrained tests were also conducted on specimens that were saturated using the back pressure technique before shearing. Comparisons with respect to the shear strength behavior are provided for both saturated a...

Laboratory Evaluation of Horizontal Stress in Overconsolidated Sands

This paper describes a method for the determination of in situ horizontal stresses of heavily overconsolidated sands using a stress-path triaxial apparatus. This method was proposed by Garga and Khan (1991), who applied it to overconsolidated clays. The proposed method is based on the concept that if the radial stress exceeds the in situ horizontal stress while maintaining the axial stress constant and equal to the in situ vertical effective stress, only then will the specimen experience significant axial strain. In this investigation, the above method was applied to specimens of known stress histories of overconsolidated sand. Simulation of complex stress histories was carried out by subjecting the soil specimens to one and two cycles of loading in drained conditions (rate of loading or unloading: 0.05 kPa/min). It was found that the proposed method replicated the simulated in situ horizontal stress exactly. The technique is capable of estimating K0 irrespective of the previously imposed stress history.

Integrated Air Trap and Volume Gauge for Axis Translation Systems

This Technical Note presents the design detail of a combined air trap and volume gauge burette used for flushing air bubbles from under ceramic disks in axis translation systems that are used to measure or apply matric suction to unsaturated soil specimens. Axis translation systems are commonly used in the testing of unsaturated soils to subject soil specimens to matric suction values greater than 1 atm. Diffused air may come out of solution and accumulate below the ceramic disk of the axis translation system, prompting to provide a flushing system to remove them. An apparatus consisting of two concentric glass tubes, alongside a graduated scale, two water vessels permitting the isolation of the water phase to reduce moisture exchange with the surrounding atmosphere, and connected to the flushing groove below the ceramic disk of the axis translation system through two plastic tubes was developed. The apparatus described permits an accurate measurement of the volume of water expelled from the specimen and can allow for the volume of diffused air flushed out.