Acrylate is a popular polymer grouting material that has been widely used to control groundwater seepage. However, the vulnerability of acrylate slurry to dynamic water washout restricts its application in groundwater environments characterized by high flow velocity and water pressures. In this paper, lithium bentonite (Li-B) was used to modify the traditional magnesium acrylate (AC) grouting material. The influence of Li-B to AC ratios on the modified materials’ washout resistance was explored, and the modification mechanism was analyzed using X-ray diffraction (XRD), infrared spectroscopy (IR), and scanning electron microscopy (SEM). Finally, the anti-washout ability of the modified slurry was verified through engineering applications. Results revealed that LiB-AC grout had adjustable setting times (10.5 to 395.6 s), minimal bleeding (0.1%), higher viscosity (65 mPa·s) and expansibility (350%), stronger anti-water dispersibility (24 times that of pure AC slurry), higher mechanical strength (compressive strength is 0.386 MPa, tensile strength is 0.088 MPa), and better impermeability (2.23 × 10⁻⁸ m/s). The lithium bentonite was beneficial to the setting time, bleeding, viscosity, slurry retention rate, impermeability, and mechanical strength of the acrylate grout. However, it diminished the expansibility of the acrylate grout. At the optimal acrylate content (20%), the mechanical strength and impermeability of the LiB-AC grout were the highest. The better performance of LiB-AC grout was attributed to the formation of a more stable and dense interlaced spatial network structure after the modification by Li-B. The LiB-AC grout was used in the dynamic water grouting project of a metro shield tunnel segment and achieved better anti-washout performance than cement-water glass and pure AC slurry.

The asymmetric three-cabin structure is one of the favourite choices in urban utility tunnel engineering, as it can provide a higher space utilization and clearer classification for pipelines. However, few work has been done on utility tunnel in such special cross-section during undercutting construction until now. Besides, as the loose soil layers such as sand and silt are often encountered during the utility tunnelling, its influence on surface settlement become one of the main concerns. This study focuses on the influence of the construction scheme on the surface settlement details for an asymmetric three-cabin utility tunnel. A 3D finite element method (FEM) model was established including both the stratum and a utility tunnel based on the Beijing Daxing International Airport (BDIA) Expressway Urban Utility Tunnel project. With this model, the behaviour of the surface settlement with the undercutting construction of the utility tunnel was investigated, and the causes and values of surface settlement in five construction stages were analyzed. By changing the construction spacing and sequence of mid and side cabins, the surface settlement and structural deformation were compared. The numerical results demonstrated a strong correlation between the cross-section shape and surface settlement characteristics. And the symmetry line of the surface settlement trough was offset by 1 m to the side with the larger cross-section. The second (excavation of upper bench in mid-cabin) and fourth (excavation of upper bench in side-cabin) stages caused the largest surface settlement, which were 41.9% and 18.07% of the total settlement, respectively. In addition, after optimizing the field tunnelling scheme, the surface settlement was reduced by 31.9% using the side-tunnel first construction sequence. The proposed numerical model is able to predict the settlement characteristics in each construction stage, which is important and provides a basis for further studies on the surface settlement mechanism and optimal design of the asymmetric three-cabin utility tunnelling scheme.

Sheet piles are extensively used as foundation structures in urban environments. However, the vibrations associated with sheet pile construction can potentially adversely affect existing buildings, as well as cause discomfort to nearby residents. This study aims to analyze ground vibration response during the driving and extraction of sheet piles. To this end, field tests of U-shaped sheet piles were conducted in Beijing silty clay, during which ground vibrations in the near-field were monitored. Subsequently, a numerical model was developed using the coupled Eulerian–Lagrangian method to simulate the pile–soil interaction characteristics and to investigate ground vibration intensity in the far-field. The research results indicate that the ground vibration response modes during the driving and extraction of sheet piles are distinctly different. Due to the entry effect, the critical depth during pile driving typically occurs in shallow soil layers, while during pile extraction, the critical depth generally corresponds to the pile’s embedded depth to overcome the soil locking effect. Ground vibrations rapidly decrease in the near-field (6 m), the attenuation rate significantly slows down. Vibrations can be widely perceived by residents at radial distances of less than 12 m. Through a systematic assessment, it was concluded that sheet pile construction is unlikely to directly damage surrounding buildings but may inconvenience nearby residents. Additionally, a parametric analysis of the vibration source revealed that appropriately adjusting the driving frequency and amplitude can effectively reduce vibration levels.