Geological conditions and supporting structures are critical factors influencing the deformation characteristics of deep excavations. This study investigates the deformation characteristics and corresponding control measures for typical deep excavations, focusing on a metro station excavation within a mixed soil-rock stratum in Guangzhou. Using field measurement data collected during the excavation phase, we perform a statistical analysis to examine the relationship between maximum deformation and various influencing factors, including excavation depth, spatial effects, and the insertion ratio of the support structure. Additionally, we explore the distribution of excavation deformations, the relationship between lateral and vertical displacements, and deformation modes, offering engineering recommendations for optimization. Our analysis shows that, due to significant variations in the thickness of soft soil layers in Guangzhou, the maximum lateral displacement of the support structures predominantly ranges from 15 to 30 mm, while vertical ground deformations range from 0.86 parts per thousand to 2.35 parts per thousand of the excavation depth. Increasing the insertion ratio of the support structures improves their stiffness and reduces surface settlement caused by excavation. However, when the base of the support structure is embedded in the load-bearing rock layer and the insertion ratio exceeds 0.25, further increases in the insertion ratio lead to diminishing returns in controlling surface settlement. Both vertical ground deformations and lateral displacements of the support structures are positively correlated with excavation depth, while negatively correlated with the length-to-width ratio, width-to-depth ratio, and insertion ratio of the excavation. Based on these findings, we propose construction measures to enhance the stability of deep excavations and protect adjacent structures.

This paper addresses stability challenges at excavation faces in shield tunneling through water-rich soil-rock formations, particularly focusing on partial failure caused by significant strength differences between soil and rock layers. A three-dimensional discrete rotational failure mechanism model is developed under the limit analysis upper-bound theorem, considering the influence of pore water pressure. This model leads to a novel method for calculating ultimate support pressure in complex strata, with its reliability confirmed through comparison with existing solutions. Key findings reveal a roughly linear positive correlation between soil layer proportion, water level, soil saturation weight, and ultimate support pressure. Conversely, cohesion, tunnel depth and friction angle demonstrate an inverse correlation. Notably, the relationship between soil layer proportion and ultimate support pressure exhibits significant nonlinearity. Cohesion and water level exert the most significant effects on ultimate support pressure, while the impact of soil layer proportion is notably complex. Additionally, a normalized design method is established using tunnel diameter and soil saturation weight, supported by design charts for varying normalized cohesion, normalized water level, and friction angles. A detailed example of a classic case is provided to illustrate the use of these design charts, aiding practical engineering applications.

Underground engineering construction will inevitably change the stress state of surrounding strata, which will force a negative impact on the surrounding environment, even leading to the large deformation and damage of some adjacent structures. With a focus on the deformation of a typical soil-rock composite stratum site in the construction of Changchun Metro, relying on the shield construction of a parallel twin tunnel project between Northeast Normal University Station and Gong-Nong Square Station, which belongs to the Changchun Metro Line 1, the site deformation characteristics during the shield driving process of parallel twin tunnels were studied. Based on the data obtained from field monitoring and numerical simulation, ground settlement in shield driving was analyzed, the settlement trough was studied with the Peck formula, and the action of shield driving on the adjacent tunnel was discussed. Moreover, the influence range of shield driving was suggested, and the interaction between the twin tunnels with different axis spacings in shield driving was discussed. Some regular results obtained can provide support through data for similar projects in Changchun, China.