The stress state is the fundamental for evaluating the soil strength and stability, playing a crucial role. However, during the stress testing, local damage and other uncertain factors may lead to partial sensor data missing, causing the existing three-dimensional stress calculation method to fail. To accurately restore the soil stress state during data missing, a three-dimensional stress calculation method was developed based on three-dimensional stress testing principles, incorporating axisymmetric and one-dimensional compression characteristics. The three-dimensional stress, principal stress , the first invariant of stress I-1, the second in variant of stress J(2) and stress Lode angle of a sandy soil foundation under one-dimensional compression conditions with different data missing were calculated and compared to results with complete data. The results show that the method is highly accurate; as the load increases, the relative error decreases and converges. The principal stresses, the first invariant of stress I-1, the second invariant of stress J(2) and the stress Lode angle align with one-dimensional compression response, suggesting that this calculation method supports advanced data mining. This study offers a novel approach and a practical method for fully utilizing the test data.

In order to accurately measure the internal stress-strain curve of plain concrete specimens and confined concrete specimens under compression, a new measurement method is proposed, which adopts conventional strain gauges to measure the internal strain data of the specimens, and the micro soil pressure box with ultra-large range is developed to measure the internal stress of the specimens. The uniaxial compression tests of 3 plain concrete specimens and 9 confined concrete specimens are completed, and the macroscopic failure process of the specimens and the stress-strain curves at different internal points are obtained. Combined with the experimental results, the accuracy of the calculation results of several classical confined concrete constitutive models is compared, and a modified constitutive model is proposed. Solid finite element analysis is used to analyze the stress-strain curves at different points inside the specimens, and the prediction accuracy of different constitutive models is compared. On this basis, nonlinear finite element analysis is used to verify the quasi-static test of RC columns, and the accuracy of different constitutive models in the nonlinear analysis at the component level is compared and analyzed. The results show that the measurement method proposed in this study can accurately measure the stress-strain data internal the concrete. The calculation results of the modified constitutive model proposed in this study are in the best agreement with the test results, and have a wide range of applications, which can be applied to the measurement of internal stress-strain curves of other different types of specimens.

Due to its distinct characteristics of instantaneity and abruptness, the stress variation characteristics of unsaturated soil under impact loads significantly differ from those under static and conventional dynamic loads. To investigate the spatial stress state under impact loads, in-situ testing was conducted on an unsaturated soil roadbed using three-dimensional stress testing technology. The three-dimensional soil pressure cells were set at depths of 0.3 m and 0.6 m below the ground surface. Continuous vertical impact loads were applied at the ground projection of the buried points. Stress testing data was collected in real time, and stress transformation methods were applied to obtain the corresponding three-dimensional stress, principal stresses, and the evolution of principal directions. Based on this, a comparison was made with existing one-dimensional stress testing methods and results, further illustrating the rationality and scientific validity of three-dimensional stress testing. The testing data revealed that under impact loads, the stress component in the impact direction (i.e., the z-axis direction) shows a notable instantaneous increase with a positive increment, whereas the increment of positive stress in the y-direction is negative. The principal stress direction angles alpha, beta, and gamma undergo considerable deviations during the impact. Specifically, alpha varies within a 90 degrees range, while beta and gamma rapidly decrease from their initial values to their supplements. Moreover, all three directional angles experience multiple reciprocating changes within a single impact duration. This research has theoretical significance in deepening the understanding of stress response and evolution processes in unsaturated soils under impact loads, providing valuable references for constitutive models, engineering design, and construction research related to seismic or other impact loadings.