Excavations near an existing tunnel are often encountered in underground construction. The influence of the excavation on the adjacent tunnels is not yet fully understood. This study presented a centrifugal model test about excavation next to existing tunnels in soft soil foundation. The bending moment of diaphragm wall, surface settlement, tunnel deformation, and earth pressure around the tunnel were mainly studied. The influence of tunnel location is further studied by numerical simulation. During the stabilization stage of foundation pit, the diaphragm walls present convex deformation towards foundation pit, and the surface settlement outside the diaphragm wall appears to be the concave groove type. During the overexcavation stage, the diaphragm walls are almost damaged, and the shear bands are nearly tangent to the tunnels. The displacement of the tunnels and the surface settlement rapidly increase. The deformation of the diaphragm wall and the surface settlement are limited by the existing tunnel. The numerical results indicate that the change of tunnel location has little effect on the retaining wall but an obvious effect on the tunnel itself.

Prefabricated vertical drains (PVDs) are a widely used in situ remediation technology for contaminated fine-grained soil. The current analytical solution that considers the infinite extraction boundary is not suitable for describing the short distance between the injection PVD (IPVD) and the extraction PVDs (EPVDs). The Dirichlet injection boundary proposed by the existing solution cannot meet the requirements for mass conservation. An analytical solution is developed based on the proposed simplified axisymmetric model. Vertical dispersion is considered in the model, and the initial concentration is exponentially distributed along the depth of the drain. The good agreement between the results obtained using the analytical solution and those obtained using the finite-element method validates the proposed solution and indicates that the simplified model can provide a simple and efficient solution to the prediction of the soil flushing process using a PVD-enhanced system. The model with the Dirichlet injection boundary can lead to significantly lower estimated flushing times for cleaning up a contaminant zone. The results show that the flux-type extraction boundary was better than the infinite extraction boundary. The dispersion can significantly affect soil flushing because the contaminant migrates from the highly contaminated zone to the low-contaminant-concentration zone.

The overall requirements of substation engineering are very high, and the differential settlement control of substation engineering is relatively strict. On the soft foundation of the tidal flats at the Zhenhai 500 kV substation in China, a field test was carried out to study the working characteristics of the pile–net composite foundation during the soil filling and consolidation stage. Variation laws of the settlement, earth pressure, pile–soil stress ratio, geogrid tension and axial force of pile were obtained and analysed. When the height of the filled soil increased to 2 m, a plane of the equal settlement was formed. Because of the soil arch effect, the earth pressure on the pile top was always higher than that between the adjacent piles. The pile–soil stress ratio rapidly increased from 1.2 at the stage of soil filling to 6.0 at the initial stage of consolidation. The ability of the geogrid to transfer the load was limited, and the soil arch effect was the main reason that the load was transferred to the pile top. Due to the lateral negative friction resistance of the pile in the shallow soil, the axial force of the pile first increased and then decreased along the depth.