Summary
In recent years many attempts have been made to utilize snow in the snowy areas of Japan. Among basic technologies for snow utilization, compaction and shaping of snow are important in order to use storage space effectively and to delay snow melt.
A snow compactor with a “screw-feed” system was developed: collected natural snow is compressed by a screw into a solid cylindrical snow column. Extrusion speed of the compressed column is about 60 cm min−1 and the productivity of this snow compressor is over 0.5 th−1.
The wet density of the compacted columns is over 790 kg m−3. Pressure at the screw blades is 15-30kgfcm−2 during continuous production of snow columns.
The cross-section of a compacted-snow column is circular or rectangular. The center part of the column, where coarse ice grains are observed, is mechanically weak and thought to be less compacted. The outer shell of the column is more transparent with many small air bubbles.
Wet density of the resultant snow column was measured as 790-940 kg m−3, which is two to four times greater than the original snow density. Water content was about 8% for the natural snow and around 10% for the resultant compacted column.
Results of mechanical test are shown in Figure 1 with dry snow as a reference (Reference MellorMellor, 1975). Fracture strength increases with decreasing water content. Observed strength of all is less than one half of the dry snow strength. Measured tensile strength is shown in Figure 2. For the snow columns immediately after extrusion, tensile strength decreases with increasing water content. For the stored samples, frozen snow columns show similar strength to the homogeneous dry specimens, and columns stored at 0°C show rather smaller values than frozen ones.
Fig. 1. Compressive fracture strength (samples tested immediately after extrusion).
Fig. 2. Tensile fracture strength.
Compacted-snow columns are weak immediately after compression before snow grains have time to bond. Storing the snow columns at 0°C may increase their strength. Mechanical tests indicate that stored columns can be used as building materials (e.g. in snow festivals) or for storage of snow.
Acknowledgements
We are grateful to Dr Tadayuki Ohnuma and Professor Katutoshi Tushima, Dr Tsutomu Nakamura and Dr Toshiich Kobayashi for much advice during the test. Thanks are also due to Professor Shunichi Kobayashi and Dr Kaoru Izumi for the use of their cold room and compressive-test machine.
