Under the freezing-thawing cycles

three types of rocks (clastic-rock

mudstone

and sandstone) chosen from the protecting-slope and berm of the Qinghai-Tibet Railway were studied. Their failure processes and weight were observed. The results show that the severe longitudinal and circumferential cracks appeared on the outside of the clastic-rock specimen; and that the debris shedding caused the weight changes less than 1% during the period of 30 freezing-thawing cycles. In the crack growth process of mudstone specimen

a horizontal

circumferential crack initialized almost parallel to the bottom of the cylinder; the growth of the crack tip then tilted gradually toward the bottom to a degree such that the direction of the crack was almost perpendicular to the axel of the cylinder. Such tilt did not appear in the sandstone specimen

in which only a short-slim circumferential crack grew outside. However

both rocks had no reduction in weight because no debris was shed. Their ultrasonic velocity testing was made by the digital acoustic-waves-monitor (RSM-SY5). According to the changes of the ultrasonic velocity at different freezing-thawing cycles

elastic modulus

rigidity modulus

bulk modulus

and Poisson's ratio of the three types of rocks were calculated and analyzed. The results show that the ultrasonic velocity

three moluli and Poisson's ratios all decrease with the increase of the freezing-thawing cycles

especially the Poisson's ratios begin to be negative values after the tenth freezing-thawing cycle

disclosing the severe failures inside of the rocks. At last

by the uniaxial compression tests of the three types of rocks subjected to different cycles of freezing and thawing

of which the compressive strengths gradually decrease with the increase of the freezing and thawing cycles.