Mechanical Behavior and Modified Constitutive Model of Sandy Pebble Soil Considering the Influence of Moisture Content

Sandy pebble soil particles, influenced by their generation environment, exhibit high strength, large permeability, and significant size variation, causing construction disturbances that alter their deformation and strength characteristics. This study examines the effect of moisture content on the initial modulus and peak strength of sandy pebble soil through large-scale triaxial tests. For the first time, the Duncan–Chang model is modified, incorporating moisture content as a disturbance factor, resulting in a revised D-C model for sandy pebble soil. This model is built using finite element software via secondary development to study the impact of moisture content on the soil’s mechanical properties. The results show the following: (1) when the moisture content is constant, the peak stress and initial modulus of sandy pebble soil increase with the increase of the perimeter pressure, and when the perimeter pressure is constant, the peak stress and initial modulus decrease with the increase of the moisture content. Also, the effect of moisture content on the peak stress is much larger than that of the perimeter pressure. (2) Perturbation theory is used to establish a perturbation function for sandy pebble soil, leading to a modified D-C model. A comparison of the indoor test results, the modified D-C model, and the original D-C model reveals that the stress values from the modified D-C model align closely with those of the indoor tests. (3) Applied to numerical simulation software via the midpoint incremental method, the modified D-C model’s experimental, calculated, and simulated values show strong agreement. The simulation also explores how moisture content affects mechanical properties, establishing relationship equations between internal friction angle, cohesion, and moisture content.