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Due to the effect of structure, Bangkok clay is stable in a metastable state. Its void ratio, e, is the summation of the void ratio sustained by the intrinsic fabric, eR, and the additional void ratio due to the structure, es. The intrinsic state line (eR versus log σ′v, where σ′v is the effective vertical stress) is developed in terms of the void ratio at the liquid limit, eL. At the post-yield state, es is inversely proportional to σ′v. The residual additional void ratio, esr, which cannot be eliminated by the increase in effective vertical stress, is constant at about 0.20 for soft Bangkok clay and 0.12 for medium stiff Bangkok clay. From these findings and the ideal condition of zero compression at the pre-yield state, the field yield stress and field compression curve can be assessed. The undrained shear strength is directly related to the field yield stress, since both reflect the structure. The soil structure does not significantly influence the permeability. The permeability of the clay in structured and destructured states is identical under the same void ratio and can be determined from the generalized state parameter, e/eL. These observations result in a simple and practical method for assessment of the engineering properties of natural Bangkok clay.Key words: Bangkok clay, destructured state, compression, intrinsic state line, permeability, structured state, vane shear strength.

A multi-axial strength criterion is developed to describe the distortional strain energy density of rock salt at failure as a function of the mean strain energy. The temperature effect on salt strength is implicitly considered by incorporating empirical relations between the elastic parameters and temperatures of the tested specimens. The proposed criterion agrees well with the test results obtained under temperatures ranging from 273-467 K. The proposed criterion is useful and practical for a conservative determination of the stability of compressed-air or gas storage caverns where the surrounding salt is subject to fluctuations of temperature during product injection and withdrawal periods.

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This report was prepared as a n account of work sponsored by a n agency of the United States Government. Neither t h e United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for t h e accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that itsuse would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by t h e United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISC LAlM ER Portions of this document'may be illegible in electronic image products. Images are produced from the best available original document.

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Uniaxial and triaxial compressive strength tests have been performed using a polyaxial load frame to assess the influence of loading rate on the strength and deformability of three Thai sandstones. The applied axial stresses are controlled at constant rates of 0.001, 0.01, 0.1, 1.0 and 10 MPa/s. The confining pressures are maintained constant at 0, 3, 7 and 12 MPa. The sandstone strengths and elastic moduli tend to increase exponentially with the loading rates. The effects seem to be independent of the confining pressures. An empirical loading rate dependent formulation of both deformability and shear strength is developed for the elastic and isotropic rocks. It is based on the assumption of constant distortional strain energy of the rock at failure under a given mean normal stress. The proposed multiaxial criterion well describes the sandstone strengths within the range of the loading rates used here. It seems reasonable that the derived loading rate dependent equations for deformability and shear strength are transferable to similar brittle isotropic intact rocks.

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