Behavior of twin inclined shafts excavated for +30 levels surface stability in Ha Lam coal mine

The process of excavating roadway, shafts, and exploiting coal seams located near the ground may cause subsidence of the ground surface, cracking, damage to structures on the surface. Therefore, it is necessary to rely on the specific conditions of the site to calculate and forecast the level of impact on the works on the surface, ground subsidence when excavated roadway, shafts, exploiting coal seams located near the ground. Based on the topographical conditions, geological hydrogeological conditions and current status of works on the surface, the technical design of the excavation of the twin inclined shafts from +30÷-300 levels in the Ha Lam coal mine is proposed. This paper uses the numerical method by FLAC3D software to build the model with a height of 450 m and a width of 700 m to study the effect of the twin inclined shafts construction on the deformation of rock mass on the ground surface. This research has shown that after the construction of the twin inclined shafts from +30÷-300 levels, the area of ​​each inclined shaft is 15.8 m2, rock mass on the ground surface is deformed, the maximum value of vertical deformation is about 5 cm, horizontally deformation is about 3 cm, the effect range of deformation the surface is within a radius of 25 m. So on the +30 level of Ha Lam coal mines when constructing works serving the coal mining within a radius of 25 m in the twin inclined shafts entrance area, it is necessary to consider the impact excavation of the twin inclined shafts. But when constructing works outside a radius of 25 m in the twin inclined shafts entrance area will not be affected. Recommendations for the Ha Lam coal mine process need to install more deformation monitoring stations to monitor the deformation process of the surface of +30 level when excavation of the twin inclined shafts.