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A high-precision, complex, three-dimensional (3D) geological model can directly express the attributes of stratum thickness, geological structure, lithology and spatial form, which can provide a reliable basis for the development and utilization of underground space and planning decisions. However, it is difficult to perform accurate modelling due to the lack of basic data. As such, this paper proposes coupling a machine learning algorithm (K-nearest neighbour (KNN)) with the kriging algorithm to construct the topological relationship between the Delaunay triangle and the Thiessen polygon in order to perform the simulation and prediction of virtual drilling. Based on KNN, support vector machine (SVM) and neural network algorithms as well as the virtual borehole encryption data, data standardization processing and analysis are carried out. Through model verification, algorithm optimization is realized, and the optimal modelling method is explored. The results show that the fine KNN algorithm improved by Bayesian optimization can effectively improve the modelling accuracy through 0.1-m encryption, standardization processing and 5-fold cross-validation. Stratum modelling combined with the fine KNN and kriging algorithms can obtain a more accurate modelling without adding virtual boreholes. The improved levels of upper and lower hybrid modelling with an appropriate number of profile boreholes can also effectively optimize model accuracy. Both modelling accuracy and efficiency can be significantly improved by using Delaunay triangles and Thiessen polygons with virtual boreholes. Stratum modelling can effectively express the geological pinch-out in areas with adequate degrees of stratification, and hybrid modelling performs well in irregular geological bodies such as karsts and lenses. [ABSTRACT FROM AUTHOR]

Based on the research status of phase-change material (PCM) energy piles, this paper proposes a new type of PCM energy pile-spiral tube-encapsulated PCM energy pile. In order to study the related properties of the energy pile, this study designed and processed the relevant test equipment and built an indoor scale model experimental system. The thermodynamic performance of the spiral tube-encapsulated phase-change energy pile under summer conditions was studied by the test system. Through the indoor scale model test, it is found that compared with the traditional energy pile, the spiral tube-encapsulated PCM energy pile improves the heat exchange capacity of the unit pile body in the early and middle stages of operation, and reduces the surface temperature of the pile body and the heating rate of the surface temperature of the pile body. The upward displacement of the energy pile top is reduced. The heat exchange capacity of the unit pile depth is increased by 6.52 W/m, the maximum pile surface temperature difference is 0.62 °C, and the maximum pile top displacement difference is 0.005 mm. In addition, the total heat transfer of the spiral tube-encapsulated PCM energy pile during the whole operation period is 3.38% higher than that of the traditional energy pile. However, during the whole operation period, the surface stress value of the spiral tube encapsulated PCM energy pile is higher than that of the traditional energy pile. The maximum difference between the two is 9.84 kPa and the maximum difference is 10.8%. The difference between the two is finally stabilized at 1.4 kPa with an increase in time, and the final difference is only 8.8%. [ABSTRACT FROM AUTHOR]