Analysis and prediction of surface settlements during the digging of underground mining works (Algeria)

Purpose. To analyze, study and predict surface settlements during the digging of a tunnel in an urban area located in the Algerian capital and to take the necessary measures. Methodology. Based on the physical and mechanical parameters and the geological characteristics of the actual traversed layer, and taking into account the geometric parameters of the tunnel, the mechanical model is established, and the numerical simulation is designed to determine the settlement deformation and displacement of the overlying zone under mining disturbance. Findings. Due to the impact of the excavation works, the land will undergo large deformations such as collapse. So, it is necessary to take corrective measures to limit its effect on the surrounding environment and protect urban areas. Originality. The application of a complex of methods allowed providing a predictive assessment of the safety of mining workings in urban conditions. The study was conducted in two main stages; a geotechnical characterization in situ and in the laboratory to determine the necessary properties of the soil and rock mass used in our model, and in a second step, the development of feedback analysis using numerical modelling based on the data collected. Practical value. From this study, the results obtained seem to show vertical displacements that exceed international standards in urban areas (1/1000, which can induce significant ground movements and therefore an influence on the surrounding environment. As a solution, there is a possibility of reducing the deformations by improving the mechanical properties of the soil carrying the project using the Jet-Grouting technique – the technique has shown its effectiveness in reducing settlements with a reduction rate of 78 %.