Two models are proposed for describing the stress–strain behavior of sand–bentonite (buffer) mixtures at elevated temperatures: (1) isothermal pseudoelasticity and (2) isothermal elastic-plasticity. Data to support the models come from consolidated undrained triaxial compression tests performed on dense saturated buffer specimens at effective confining stresses up to 9.0 MPa and temperatures of 26°, 65°, and 100 °C. Measurements indicate that volumes decrease with increasing temperature if the tests are carried out under drained conditions. These trends can be modelled by a family of hardening lines in semilog compression space. Power law relationships are presented for undrained shear-strength envelopes that increase in size with an increase in temperature. The slopes of unload-reload lines, κ, in semilog compression space vary with temperature and can be related to systematic variation in the friction angle [Formula: see text]. The shear modulus G50 at 50% peak strength also depends on temperature. Several plotting techniques are used to show the existence of different state boundary surfaces for each test temperature. Key words : sand–bentonite, buffer, compression, shear strength, temperature, modelling.
Interpretation of the cone penetration test in sands is generally based on empirical calibrations from tests in large-diameter calibration chambers. Although interpretation of these calibration data for clean sands in terms of the state parameter is expected to be broadly applicable to other sands, material-specific correlations are desirable for many projects. This paper describes a series of calibration chamber tests carried out on a sand dredged from the Beaufort Sea for construction of artificial islands. This Erksak sand is a uniformly graded, subrounded medium-grained sand with a fines content of 3–6%. The testing chamber described is 1.4 m in diameter, and allows independent control of vertical, horizontal, and back pressures on the sand sample. Samples of the sand were prepared by moist compaction to preserve the fines content, and then back pressure saturated.The chamber test data are presented and confirm that the Erksak sand fits the general trends observed for other sands very well. A method is also described that allows the interpretation to be consistent, even in the event that nonuniform void ratios occur in the samples. Measurements of horizontal stress behind the cone tip, which is a new development in cone penetrometer testing, are also presented. Key words: cone penetrometer, sands, in situ tests, state, calibration chamber, horizontal stress measurement.
Side drains are used in triaxial tests to increase the rate of consolidation and equalize pore water pressures within the specimen. However, the efficiency of the side drains has been shown to be a function of time and effective confining pressure.
This paper presents the results of (1) a mail survey on side drain practice, which indicates that many laboratories use side drains not recommended by standard references, and (2) an experimental program to assess the effects of time and moderate-to-high effective confining pressure on the flow properties of four side drain materials.
The four side drain materials used in the testing program were: (1) a single layer of Whatman No. 1 filter paper; (2) a single layer of Whatman No. 54 filter paper; (3) a double layer of Whatman No. 54 filter paper; and (4) a single layer of geotextile. The lengthwise flow of these materials was examined as a function of effective confining pressure up to 6000 kPa and also of time at a fixed effective confining pressure of 750 kPa.
Tests were also conducted on specimens of natural clay to compare consolidation rates using different drain materials.
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