To study the stability of surrounding rocks for shield tunneling under overpass structures and the safety of existing bridge structures, a practical example of the method was cited through a shield tunneling project under the overpass structure between K1+110 and K1+700 on Line 2 of Shenyang Subway, China. The sub-area reinforcement was proposed according to surrounding rock deformation characteristics during shield tunnel excavation. The bridge foundation (i.e., the clear spacing to the shield tunnel is less than 2 m) was reinforced by steel support, the bridge foundation (the clear spacing is about 2~7m) used "jet grouting pile" reinforcement, whereas the bridge foundation (the clear spacing is greater than 7 m) did not adopt any reinforcement measures for the moment. For this study, the mean value and material heterogeneity models were established to evaluate the reinforcement effect from several aspects, such as surrounding rock deformation, plastic zone development, and safety factor. The simulation results were consistent with those of field monitoring. After reinforcement, the maximum deformation values of the surrounding rock were reduced by 4.9%, 12.2%, and 48.46%, and the maximum values of surface subsidence were decreased by 5.6%, 72.2%, and 88.64%. By contrast, the overall safety factor was increased by 4.1%, 55.46%, and 55.46%. This study posited that this reinforcement method can be adopted to solve tunnel construction problems in engineering-geological conditions effectively. References for evaluating similar projects are provided.

Combined with the project example of column buried depth nondestructive testing, the influence factors of signal-to-noise ratio of column buried depth nondestructive testing are analyzed. At the same time, the control measures to improve the accuracy are put forward according to the influencing factors.

To solve the key issues of stress transfer law and settlement mechanism in a pile-net composite foundation, the geosynthetic-reinforced and short pile-supported embankment over gravel clay with low to moderate compressibility at the DK86+998.0-DK87+191.2 section of the Ganzhou-Longyan High-speed Railway was selected as a case study. Field tests that combine theoretical analysis with analytic calculation were conducted to investigate the change laws of stress acting on the pile and the subsoil, pore water pressure, and foundation deformation, as well to predict pile-net composite foundation settlement. Results show that the stress distribution exhibits a saw-toothed shape across the foundation, and the reaction force of the foundation varies against the filling embankment load. After constructing the embankment, the average pile-soil stress ratio is 4.0 and the pile-soil load ratio reaches 50%. Foundation deformation mainly appears during the construction phase with an accumulative ground settlement of 55 mm and an accumulative lateral displacement of 25 mm. Unlike that of in-situ measurement, the accumulative settlement of the foundation is predicted to be 62 mm in a 2000-day duration, whereas the accumulative settlement increases only by 7 mm following the 800-day predictive period. Result also indicates that soil consolidation mainly occurs during the construction period and the effect of the engineering control of using short piles for the foundation is evidently effective. This approach is low-cost and convenient to construct. Prior selection of short piles for foundation enforcement is suggested for cases under similar geological conditions.