Abstract: In order to clarify the concept confusion and to avoid repeated calculation of the force in the groundwater condition, the characteristics of three kinds of groundwater forces in soil, namely pore water pressure and buoyancy and seepage force, are discussed. It is emphasized that the pore water pressure in seepage environment is related to water depth and hydraulic slope according to the energy conservation theory. Then the equivalent relationships for two volume forces (buoyancy and penetration) to the boundary force (pore water pressure) are discussed. The calculation method of groundwater force acting on the separate soil skeleton and the unity of soil skeleton and pore water in a seepage environment is explored. The former should use seepage force and effective gravity of soil particle to calculate equilibrium. The latter should use pore water pressure and saturated gravity of soil to calculate equilibrium. Then the improper use of the groundwater force in present codes for landslide stability analysis related to landslide control engineering is discussed in this paper. In addition, the calculation deviation caused by the improper use of the groundwater force is illustrated in an engineering example. The results show that two problems exist in the relevant specification: pore water pressure is calculated without considering hydraulic slope angle and the concept of pore water pressure and buoyancy are confused. Both cases will cause partial conservative design and engineering management based on the latter case will arise large economic waste.

Key words: soil stability, pore water pressure, seepage force, buoyancy, design code