Study On Physical And Mechanical Properties Of Rocks And Slope Stability Under Rfeeze-thaw Cycle

The new cut slope rock mass of open pit mining in the alpine regioneffected by freeze-thaw cycle, will lead to the change of its physical andmechanical properties. This change must be considered when we analysisslope stability. This paper based on the Tibet Yulong Copper Co. Ltd.Phase II project of open pit slope stability studies, selected threerepresentative rock (quartz sandstone, limestone and granite porphyry) ofthe open pit slope parts, then studied on the physical and mechanicalproperties of rocks change,freeze-thaw temperature range and frozencycle times is the control conditions.At last, analyzes the impact of thischange on slope stability. This paper main work and research results areas follows:（1）Test study on physical properties of rock under freeze-thawcyclesThis experiment by simulating natural conditions of alpine area，three kind of rock is putted under freeze-thaw cycles30times.Every10times of freeze-thaw cycle, measuring geometric dimensions, weight andwave velocity of the specimen. Then take part of the saturated specimento do uniaxial compressive strength and Brazilian tensile strength test.（2）The variation law of rock physical and mechanical propertiesunder freeze-thaw cyclesStudies show that within30times of freeze-thaw cycle, saturatedspecimen quality, wave velocity, volume, weight with the cycle offreeze-thaw changes are very small, and the strength is reduced greatly.For different rock conditions, the variation of physical and mechanicalparameters of amplitude and trend are also different. Quartz sandstone,limestone specimen is relatively hard and compact, its quality, weightwith the cycle of freezing and thawing continued to rise slightly, thevolume is reduced; the granite porphyry sample fissure, quality, weightwith freeze-thaw cycles decreases slightly, and volume increase. Threekinds of rock sample wave velocity with the cycles of freeze-thawincreasing. Rock tensile strength decreases faster than the compressivestrength, more sensitive to freeze-thaw.Test analysis finded that sample fracture more development, more significant effect of frozen-thawed.（3）Freeze thaw cycle impact on slope stability analysisWe chose open border southeastern section of slope as an exampleand select the slope safety factor is1.20and use the conventional methodof the limit equilibrium and strength reduction method to calculate thestability of slope profile. To meet the requirements of the calculation, theslope profile final slope angle of40°. Taking geotechnical freeze-thawmaximum depth of2m, the calculated slope subjected to10,20,30freeze-thaw cycle, the safety factor is not changed, freeze-thaw cycledoes not cause slope instability, as a whole is stable.Using finite element method to analyze slope stress field,displacement field and plastic failure area distribution under the action ofthe freeze-thaw. Calculation shows that the slope surface tensile stressrapid growth with the freeze-thaw cycles, displacement continues toexpand,no significant changes in plastic zone. Therefore, the slope underthe influence of freeze-thaw, the slope failure mode is the surface localinstability, slumping.