A parameter estimation method subject to finite cylindrical heat source model for in-situ testing of soil thermal conductivity

The infinite-line heat source model is commonly used at in-situ thermal conductivity tests for soils are simplified and neglect the effects of convection. To improve the traditional model, a theoretical finite cylindrical heat source model is proposed in this study considering convective heat transfer. Meanwhile, a new parameter estimation method is developed to refine the thermal conductivity calculations. Real-time temperature from corresponding simulations of in-situ testing with and without groundwater seepage was used as acquired data. Subsequently, thermal conductivity was calculated, and its accuracy evaluated by the steady-state method. The procedure foresees the comparison of temperature, instant values with those obtained observed results with the initial input parameters. It results that the proposed method, compared with traditional methods, minimizes the error to 4.97% from 10.61% with extremely short test duration. Under groundwater seepage conditions, the proposed method achieved an error rate of 5.17%. Thermal conductivity increases with the increase of groundwater seepage velocity. In addition, a short heating duration and increased dimensions of the testing instrument significantly improves the calculation accuracy. Furthermore, the accuracy of the proposed method is validated through case studies involving laboratory model tests and field tests. It resulted that the proposed method overcomes the limitations of the traditional methods, and it is more suited to in-situ thermal tests in geothermal engineering design.