Abstract: Strength and stability of soil mass, far more complex than those of metals, are two major and heatedly discussed issues in soil mechanics. Various strength models have been published in literature. However, most models are associated with assumptions or rely on experimental analysis with limitations, with fundamental theories insufficiently explored. In this study, a hat model which is similar to the Cambridge strength model is proposed based on the studies of soil mass with random uniform mesh particle chain structure. Various strength curves on the π plane have been derived subjected to different assumptions. The most conservative case can be represented by a hat model with a strength curve being regular hexagon on the π plane and parabolic in the longitudinal direction. When the particle chain is damaged and the length of the chain is becoming shorter, vertices of the strength curve move towards infinity, and form a curve with an opening. That is, the Cambridge hat model is transformed into the conical Mohr-Coulomb model. The long particle chain model essentially unifies the Cambridge strength model and the Mohr-Coulomb model.