Test methods for specific heat capacity of frozen soil based on principles of mixing calorimetry

The specific heat capacity of soil is an important parameter in the ground freezing method. However, the specific heat capacity obtained by the exiting mixed calorimetric methods is the average specific heat capacity from a negative temperature to the equilibrium positive temperature rather than that at the negative temperature. According to the fact that the phase transition of pore water occurs gradually with temperature change in freezing process, a recursive formula to the specific heat capacity of obtain frozen soil is established based on the exiting mixing calorimetry methods. First of all, two small equal temperature increments, a negative and a positive, are set for the negative temperature of the frozen soil. Then, two samples are prepared respectively at the two temperatures and the mixing calorimetry method is performed in order to arrive at each thermal equilibrium state. From the negative temperature state to the thermal equilibrium one, the heat absorbed by the sample, Q, will be equal to the total aequum of the two stages, Q₁ for negative temperature to 0℃ and Q₂ for 0℃ to equilibrium temperature. Since there is no phase change and latent heat, the heat required by the sample from 0℃ to the equilibrium temperature can be obtained by the conventional mixing calorimetry. Therefore, the required heat for the sample from negative temperature to 0℃ can be obtained by subtracting Q₂ from Q. And Further more, the required heat can be obtained for the given temperature from the negative increment to the positive increment. Finally, the specific heat capacity of the sample at the negative temperature can be obtained according to the definition of the specific heat capacity. From the proposed method, the capacity at any temperature, other than an average over a temperature range, can be calculated. And the proposed method can take latent heat into account. Therefore, it is more reasonable and effective.