Underexcavation is an engineering term that refers to the phenomenon where the perimeter of the cross-section of a shaft, tunnel, or other underground project is smaller than the design size after blasting. This term is mainly applied in fields such as coal mining, water conservancy and hydropower engineering, and highway tunnels.

　　In the construction of underground projects such as tunnels and tunnels, excavation is usually required according to the designed cross-sectional dimensions. However, due to various reasons, the actual excavated section may have some areas that do not meet the design requirements, which is called under excavation.

　　The reasons for under excavation may include: low drilling accuracy, resulting in the outer insertion angle, opening position, or drilling depth of the surrounding boreholes not meeting the requirements; Improper blasting techniques, such as unreasonable types and structures of explosives, unreasonable arrangement of surrounding holes, or unreasonable blasting design; Construction operations are not standardized, such as inaccurate contour lines, poor control of drilling positioning or drilling angle deviation, insufficient drilling or unauthorized reduction of drilling depth.

　　Underexcavation may bring some problems, such as affecting the quality and safety of the project, requiring additional treatment to meet design requirements, which will increase construction costs and time. In order to reduce the phenomenon of under excavation, a series of measures need to be taken during the construction process, such as improving drilling accuracy, optimizing blasting design, strengthening construction management and measurement work, etc.

　　For example, strengthening the training of drillers to enable them to master drilling techniques proficiently; Reasonably determine the depth of the borehole based on geological conditions and construction requirements; Carefully carry out drilling and blasting design, select appropriate explosive varieties and loading methods; Using high-precision instruments for measurement, accurately drawing excavation contour lines, etc. At the same time, it is necessary to strengthen inspections during the construction process, promptly identify and address any issues of under excavation.

　　In tunnel engineering, it is very important to control over excavation (actual excavation section exceeding the design size) and under excavation, which helps to ensure project quality, reduce costs, improve construction efficiency, and ensure the stability of surrounding rock.