Electroosmosis has been extensively employed as an effective method for the dewatering treatment of soils and thus the reinforcement of weak soils. At the microscopic level, this treatment process is inherently complex due to in situ chemical and electrochemical reactions, migration of ions and particles, and the dependence of zeta potential of various particles on the local pH value in the soil. This complexity has hindered further understanding of mechanisms underlying the electroosmosis technology. Here, we design an external electric field in which alternating pulse wave potentials were partially used to adjust the pH value of the soil and manipulate the dynamics of in situ formed nanoparticles and their interconnectivity. The experimental results reveal that the in situ formation of Ca-rich particles, instead of water drainage, may serve as the main mechanism underlying the observed soil reinforcement when using calcium chloride as the treatment electrolyte. The interconnectivity of such particles may be the key for the shear strength improvement without significant settlement of the soil.