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Abstract Some experiments are conducted including measuring basic physical indices and uniaxial compressive strength(UCS)，mineral composition，grain area ratio(GAR)，packing density(PD)，and grain contact(GC) of cretaceous red sandstone from Western Hunan by physico-mechanics tests through polarized microscope analysis，and powder X-ray diffraction analysis. The average grain diameter and cumulative relative curve of red sandstone are obtained by the grain size analysis. In order to analyze the wetting soften mechanism of sandstone，the uniaxial compressive tests of different red sandstone samples are conducted under the dry state，the nature state and the saturation state. Additionally，how the basic physical indices and microstructure parameters impact the UCS and strength reduction(SR) due to wetting is investigated. Experimental results indicate that the UCS shows a negative exponential relationship with porosity and saturated water adsorption，but a positive exponential relationship with dry density，and a positive linear relationship with GAR，PD，and GC. However，the average grain diameter has no obvious influence on the UCS of red sandstone. When the clay content is higher than 25%，the UCS and SR decrease with the increase of the clay content. Among multifactorial regression analysis，the GAR and saturated water absorption are found to be the key parameters. As a result，the regression equations of UCS and SR due to wetting，in terms of GAR and saturated water absorption，are proposed.
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Received: 11 May 2009
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