چكيده لاتين :
Freezing depth is one the most important climatic indices in the field of
agriculture, civil engineering and etc. This parameter depends on different parameters such as astronomical factors, temperature of the surface air, humidity, soil characteristics such as texture, heat capacity, thermal conductivity, and specific heat. In this study, for investigating
the effect of air temperature on freezing depth, a soil freezing apparatus was made which is able to produce temperatures up to -16 °C. To measure and record the soil temperatures at depths of 10, 20, 50, and 70 cm, an automatic measurement system was designed. Sensors of
the system include electronic thermostat, which was inserted at different depths of soil. Variation of temperature measured by the sensors, were transferred to a transformer, and the results of measurements transferred to a computer in the form of binary codes. These codes
were processed by a computer program and converted to a numerical form. After calibration, several experiments were conducted using soil bins of different textures including clay, claysand, and sand at moisture contents of 0, 10, and 15 percent. The results of experiments showed: freezing depth of soil in dry state (0% moisture content) for soils having smaller pores (such as clay), is less than the soils having larger pores (such as sand). The advancing speed of freezing front has also a similar trend. By increasing the soil moisture (0% to 10%), for all soils, the depth of freezing and the advancing speed of freezing front were increased. This condition in soils having finer texture is more pronounced than the soils of coarse texture. By increasing the amount of soil moisture content, the clay soil maintains its moisture through out its depth, while in sandy and clay-sandy soils, the moisture content decreasing from top to the bottom (due to drainage). This phenomenon affects the advancing speed of freezing front in these soils.
