The Anisotropic and isotropic strength behavior of an illitic clay

The cause and the nature of anisotropy in a cohesive soil was investigated by direct shear and triaxial compression tests. Laboratory techniques and procedures used to prepare isotropic clay samples are given where consolidation was accomplished under hydrostatic pressure. Direct shear tests were performed on these specimens trimmed at different inclinations to the physical horizontal from the block samples. The ratio of undrained shear strengths in any direction to shear strength in the vertical direction was found to be equal to one, proving isotropy existed. Similar tests were performed on specimens trimmed from the same clay consolidated one-dimensionally. Results from these tests showed the shear strength ratio to be maximum for specimens trimmed at 90° to the horizontal plane. In this case, the aniso- tropic characteristics were directly attributed to the sample stress history. These samples indicated preferred particle orientation. Undrained triaxial compression tests were performed on both hydrostatic and one-dimensionally consolidated samples. Triaxial test results confirmed the results of the direct shear tests and more accurately defined the stress/strength parameters. The angle between the failure plane and the test specimens axis was essentially constant and the ratio between pore water pressure at failure and the mean consolidation stress remained a constant.For each maximum consolidation stress, pore pressure was isotropic, but in all cases was higher for hydrostatically prepared samples. The hydrostatic method of preparing isotropic test specimens was effective and produced reliable results

Nicotine Enhances the Hypnotic and Hypothermic Effects of Alcohol in the Mouse

BACKGROUND: Ethanol (EtOH) and nicotine abuse are 2 leading causes of preventable mortality in the world, but little is known about the pharmacological mechanisms mediating co-abuse. Few studies have examined the interaction of the acute effects of EtOH and nicotine. Here, we examine the effects of nicotine administration on the duration of EtOH-induced loss of righting reflex (LORR) and characterize the nature of their pharmacological interactions in C57BL/6J mice. METHODS: We assessed the effects of EtOH and nicotine and the nature of their interaction in the LORR test using isobolographic analysis after acute injection in C57BL/6J male mice. Next, we examined the importance of receptor efficacy using nicotinic partial agonists varenicline and sazetidine. We evaluated the involvement of major nicotinic acetylcholine receptor (nAChR) subtypes using nicotinic antagonist mecamylamine and nicotinic α4- and α7-knockout mice. The selectivity of nicotine\u27s actions on EtOH-induced LORR was examined by testing nicotine\u27s effects on the hypnotic properties of ketamine and pentobarbital. We also assessed the development of tolerance after repeated nicotine exposure. Last, we assessed whether the effects of nicotine on EtOH-induced LORR extend to hypothermia and EtOH intake in the drinking in the dark (DID) paradigm. RESULTS: We found that acute nicotine injection enhances EtOH\u27s hypnotic effects in a synergistic manner and that receptor efficacy plays an important role in this interaction. Furthermore, tolerance developed to the enhancement of EtOH\u27s hypnotic effects by nicotine after repeated exposure of the drug. α4* and α7 nAChRs seem to play an important role in nicotine-EtOH interaction in the LORR test. In addition, the magnitude of EtOH-induced LORR enhancement by nicotine was more pronounced in C57BL/6J than DBA/2J mice. Furthermore, acute nicotine enhanced ketamine and pentobarbital hypnotic effects in the mouse. Finally, nicotine enhanced EtOH-induced hypothermia but decreased EtOH intake in the DID test. CONCLUSIONS: Our results demonstrate that nicotine synergistically enhances EtOH-induced LORR in the mouse