Development and verification of subgrade service performance test system considering the principal stress rotation

Abstract

To accurately simulate the three-dimensional stress state and service performance of subgrade under long-term traffic loads, a subgrade service performance test system was developed. The test system consists of the loading system, a fully digital servo control system, and a data acquisition system. Based on the time-history characteristics of total stress components (three normal stresses and three shear stresses) of subgrade soil elements under traffic loads, the loading system was designed with four dynamic actuators and three static actuators. The loading system can simulate the rotation of principal stress axis in any subgrade soil elements through coordinated dynamic and static loading. The calculation method of load system was established to achieve the three-dimensional stress state of subgrade soil element under traffic loads. Furthermore, the model tests were conducted on the developed test system to verify the three-dimensional stress state of subgrade under the typical traffic loads, such as highways, railways and airports. Results shows that the actual output load deviation of each dynamic and static servo actuator is under 1%. The time-history curves of dynamic stress components and the attenuation of vertical dynamic stress are in good fit with the theoretical calculations. Besides, the vertical dynamic stress in the subgrade decreases progressively with depth, and the stress path of the soil element is approximately “heart-shaped”. The above validated results indicate that the test system accurately simulates the three-dimensional stress state of subgrade under different traffic loads. Therefore, the subgrade service performance test system developed in this study offers a new concept, method, and technology for investigating the evolution of subgrade service performance under long-term traffic loads.