A discrete element method (DEM) implementation is developed to study the micromechanics of liquefaction in granular materials. In a liquefaction event, the pore water acts as a cushion between the grains, reducing the contact and friction forces and the overall soil strength. The proposed model reproduces this phenomenon by introducing the effect of pore water as a constraint over the DEM particles' mechanics. The DEM particles will suffer resistance to any displacement changing the pore volume, which takes into account the very small compressibility of water. It is found that this constraint is enough to simulate soil liquefaction under quasistatic deformation. Finally, it is shown that the initial density of the granular skeleton, defined by the number of contacts between grains, plays a critical role in determining if the soil will liquefy or not. This critical value opens the possibility of treating liquefaction in soils as a bifurcation problem.