Geological disasters caused by city ground subsidence are typical examples of soil failure, which significantly impact urban planning and development. The sediment transport in the soils leads to the increasing porosity of soils, and changes the elastic modulus and Poisson’s ratio, thus the carrying capacity of the soil is reduced and ground subsidence appears. Therefore, the sediment transfer and loss driven by the underground water becomes a key reason for ground subsidence. Studies in this area thus present significant meanings. In this paper, mutual effects between the sediment particles and groundwater seepage are analyzed. We partially fix sediments in soils. Using the numerical simulation, hydraulic pressure is applied to scour so as to study the regular patterns of sediment transport in the soil mass: as time extended, the porosity in soils is gradually enlarged, tending to be stable; as more particles are fixed, porosity is reduced. It is also found that fixed particles, with a part of free sediment particles, form some new fixed sediment structures that hinder the transfer of the free sediment. In addition, parameters like scour time, hydraulic pressure, and the porosity evolution equation relating to the amount of fixed sediment particles are acquired. Findings of this research are expected to provide references for predicting, forecasting, and treating ground subsidence, which is led by sediment transport from the perspective of the soil mass porosity evolution.