Macro/Microtesting and Damage and Degradation of Sandstones under Dry-Wet Cycles

Abstract

In terms of the degradation of mechanical parameters of rock mass in the hydrofluctuation belt of a reservoir bank slope arising from rainfall and the reservoir level fluctuation, the moderately weathered sandstone in a side slope of the Three Gorges Reservoir Region is selected as a research object to carry out “drying-saturation-drying” tests for disks with two thicknesses (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi>h</mml:mi><mml:mo>=</mml:mo><mml:mn fontstyle="italic">25</mml:mn></mml:math> mm,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi>h</mml:mi><mml:mo>=</mml:mo><mml:mn fontstyle="italic">50</mml:mn></mml:math> mm) in different cycles; a spiral CT machine, an ultrasonic velocity meter, and a light Schmidt hammer are utilzed to conduct nondestructive testing on dry-wet cycles; through the Brazilian splitting test, the uniaxial tensile strength of “dry” and “saturated” sandstones under different dry-wet cycles is obtained. The research shows that, with the increase of the dry-wet circles (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:math>), the longitudinal wave velocity and the rebound strength of sandstones are linearly decreased with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:math>; the uniaxial tensile strength of sandstones and the mean CT number of cross sections are logarithmically decreased with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:math>; the fitting equation of macro/micromechanical parameters and dry-wet cycles (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M6"><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:math>) of sandstones is raised, which is provided as a reference basis for the weathering process of sandstones under dry-wet cycles.