The Investigation of Hysteresis on Calibration Curve of Gypsum Block Affected by Soil Texture and Compaction

In the current study، the effects of hysteresis on calibration curve of gypsum block affected by soil texture and compaction were investigated. For this، calibration curve of gypsum block in 3 soil texture including Sandy Loam، Loam and Silty Clay in three bulk density (natural in the farm and plus 10% and minus 10%) for two phases of wetting and drying were provided. The results showed that block calibration curves were different in two phases of wetting and drying in the different soil compaction and texture. By reducing soil compaction، hysteresis and its effect on shape of calibration curve of block were increased because of fine pores reduction and more non-uniformity of soil pores distribution. The effect of soil compaction on block calibration curve was different during drying and wetting phases such as for specific soil moisture، with increasing soil compaction، the block electric resistance increased and reduced during drying and wetting phases، respectively. During drying and wetting phases، increasing of soil compaction caused 16% increase and 3% decrease in field capacity، respectively. Accordingly، it is recommended that soil compaction of installation place of gypsum block and around be equal.