Experimental Study On Snow Hardness And Its Testing Technology

Antarctica is the most logistically challenging location on Earth.Since the 21 st century,more and more countries have transported scientific research personnel and equipment to Antarctica by air.More efficient logistics provides the opportunity to increase the research effort.The development of air transport systems and supporting infrastructure,especially ice and snow runways,is therefore assuming greater importance.Based on the national demand for ice and snow runway construction and the lack of experience in the construction of polar snow projects and relevant snow mechanical tests,two innovative snow hardness testing equipments,Dynamic Cone Penetrometer(DCP)and Motor-driven Snow Penetrometer(MSP),have been developed.A total of 178 groups of penetration tests were conducted in Harbin,northeastern China,in January 2018 and January 2019.The data were analyzed qualitatively and quantitatively.Additional supporting testing included assessment of layered compaction method and observation of snow microstructure.The test results demonstrated that the modified cone penetrometer is capable of assessing the strength of layered compacted seasonal snow.For snow with densities ranging from low to high(400-600 kg·m-3),the penetration resistance was quantified so that it was used as an index to qualify the mechanical behavior of snow.A series of comparative tests revealed that the assessment of the strength of layered compacted seasonal snow via the cone penetrometer was affected by many factors,including confining pressure,penetration energy and snow material properties,particularly the compaction degree of the snow undergoing penetration.A linear relationship between penetration pressure and density of snow was established,which indicated the penetrometer' ability to provide information on the internal structure of snow.The effect of age hardening on penetration pressure was studied and the microstructure of snow particles at different stages of aging were observed through a microscope.These tests showed that the cone penetrometer provided a rapid estimate of the snow strength.On the basis of Dynamic Cone Penetrometer,in order to adapt to the development level of contemporary science and technology and keep pace with foreign advanced penetration equipments,innovative Motor-driven Snow Penetrometer(MSP)has been developed.The feasibility of measuring snow hardness by MSP was analyzed in detail.The experimental results showed that the motor could drive the penetration rod to penetrate into snow with different compaction degree.The penetration rod can maintain constant speed when penetrating into snow although there were errors between the real speeds and the set speeds of the penetration rod,and there was no change in speed when it penetrated adjacent snow layer.The influence of penetration velocity on hardness measurement was studied,and the power law distribution relationship between the depth-average hardness and penetration velocity of compacted snow at 400 kg·m-3 was established.The correlation between snow hardness and density was established,and the validity of the test data was confirmed by comparing with the results of SMPT.The effect of long-time metamorphism on the hardness of snow with different densities was studied.The strength growth rate and range of snow with different densities at the same metamorphic time were analyzed and the relationship between the hardness and density of snow after metamorphism was re-established.Testing technology and quantitative analysis method of snow hardness are deeply explored in this paper,which lays a foundation for the further development of the technology and application described in this paper.Penetrometer is a kind of instrument with wide application prospects,it's possible to install many additional sensors on it,so that a lot of information can be obtained in one test,including mechanics,microstructure,vision,avalanche and so on.After further modification,the technology and equipment described in this paper have the potential to be applied to the polar environment,so as to provide technical support for the construction of Antarctic ice and snow airport in China.