J. Ma’s scientific contributions

Based on the artificially frozen soil test, finite element numerical simulation and large-scale physical model test, the construction technology of long-distance horizontal ground freezing method and undermining method adopted for the construction of shallow-buried subway tunnel with large-section was studied. The physical and mechanical indexes of the frozen soil were obtained after the artificially frozen soil test on the in-situ undisturbed soil sample. The finite element numerical analysis results indicate that the strength and the stability of the frozen wall are improved along with the increase of the frozen wall thickness. The results of the large-scale physical model test show that both the frost heaving and the thawing settlement increase obviously with the thickness of the frozen wall. It is predicted that when the thickness of the frozen wall is 4.5 m, the surface frost heaving and the thawing settlement both have exceeded the allowable values in the practical engineering. The design and optimization of the freezing construction scheme were conducted according to the above research results. During the construction process, the connection mode was improved for the long-distance horizontal freezing pipe, and the new technology of drilling with simultaneous casing was adopted to ensure the completion quality of the freezing holes. The surface frost heaving and thawing settlement were effectively controlled by several technical measures, such as applying pressure relief vents, increasing brine flow, tracing and grouting the thawing settlement, which ensured the successful completion of the engineering.