Study On Freeze-thaw Weathering Characteristics Of Jinshajiang Basalt On Lijiang-shangri-la Railway

The Lijiang-Shangri-la Railway under construction is located in the northwestern Yunnan Province.The railway line crosses the topography of mountains and canyons,with active tectonic movement and disorderly stratum and lithology.Complex geological conditions have brought many difficulties to the railway project,among which freeze-thaw weathering in the alpine mountains has seriously affected the project safety.In this paper,basalt from four construction sites on both sides of Jinshajiang Bridge are selected to study freeze-thaw weathering characteristics of jinshajiang basalt by combining engineering survey data,field reconnaissance and indoor physical property test,freeze-thaw cycle test and other methods,so as to provide reference and guidance for engineering design and construction,rock and soil parameter value and engineering maintenance.According to the sorting of literature materials and the field investigation of the work site,basalt was selected from the two sides of the Jinshajiang Bridge,and standard indoor specimens were taken back for indoor physical properties tests.Physical quantities such as the density,saturated water content,porosity and P-wave velocity of basalt specimens were obtained.Based on the correlation between P-wave velocity and the porosity of basalt specimens,different freezing(water bath)duration test schemes were designed to obtain the test duration suitable for jinshajiang basalt.The specimens were mandatory saturated before freeze-thaw cycles test.The saturated specimens were frozen in a retrigerator and conditioned at-20? for 4 h.Then they were thawed in a water bath at 20? for 1h.This freeze–thaw cycle was repeated 100 times in 4 stages.The mass,frozen P-wave velocity and saturated P-wave velocity of the basalt specimens were measured every 5 cycles.And block density test and drying P-wave velocity test were conducted every stage.After freeze-thaw cycle test,UCS and elastic modulus of basalt specimens were obtained.During the experiment,changes in the surface of the specimen were recorded.The freeze-thaw weathering characteristics of jinshajiang basalt are studied according to the changes of physical quantities such as mass,porosity,P-wave velocity and mechanical properties during freeze-thaw cycle test of basalt specimens and the changes of surface damage.And the quantitative relationship and weathering rate between uniaxial compressive strength and freezing-thawing cycle times of basalt specimens were obtained by analyzing the variation relationship among various physical quantities,and freezing-thawing weathering characteristics of jinshajiang basalt were summarized.