Numerical Simulations of Construction of Shield Tunnel with Small Clearance to Adjacent Tunnel without and with Isolation Pile Reinforcement

Techniques including pre-grouting, long pipe roof, and parameter optimization were employed to ensure the safety of loess metro tunnelling under an existing glass building. Their effects were proved through monitoring the settlement of building and surface during tunnelling. Besides, division of settlement monitoring according to processes, a new method, was conducted to control settlement in time. The highest surface settlement after construction was 16 mm only, meeting the requirement. The result indicates that it is practicable to control the tunnelling settlement strictly in extremely difficult geological areas. The settlement regularities were also studied through numerical simulation; their deformation is larger compared with in situ results while their change trends coincide during most processes. Soil excavations cause settlement primarily, accounting for more than 60%. It is suggested that dual slurry pre-grouting and process-based measurement should be employed before each excavation in water-rich loess areas.

Section: Introductionmentioning

confidence: 99%

Tunnelling‐Induced Settlement and Treatment Techniques for a Loess Metro in Xi’an

Lai

et al. 2020

“…Based on a stable triangulation program, the finite element mesh is generated by PLAXIS automatically [37]. 15node triangular elements are used to form unstructured meshes.…”

Section: Model Establishmentmentioning

confidence: 99%

Sensitivity of Multistage Fill Slope Based on Finite Element Model

Yuan

et al. 2021

Based on the strength reduction method, the laws of slope displacement and the changing positions of the sliding surface during the filling process are studied. The model of multistage fill slope is established by the finite element software PLAXIS. The difference is compared between the slope with no reinforcement and with reinforcement under the same working condition. Sensitivity analysis is carried out from two aspects which are internal factors and external factors. The finite element analysis shows that the settlement of the multistage fill slope with no reinforcement is mainly concentrated on the right side of the slope and gradually decreases with the increase of the filling height. The position of the sliding outlet is located at the joint of the first and the second grade of the slope. The effect of the reinforcement on the sliding surface is ideal. It is obvious that the reinforcement can supply the slope with a better position of the sliding surface, which is beneficial to the stability of the slope. The sensitivity analysis shows that unit weight, ratio of slope, and height of each grade are negatively correlated with the safety factor. At the same time, the platform width, cohesion, and internal friction angle are positively correlated with the safety factor. The internal friction angle has the greatest influence on the stability of the slope. Besides, the platform width and the height of each grade should be controlled at about 4 m. The sensitivity analysis provides a reference for the design of the multistage filling slope.

“…erefore, other means should be combined to control the retaining wall deformation. Grouting and isolation piles are two common means to protect adjacent structures in close construction [26][27][28][29][30][31]. However, in past engineering practices, the selection of grouting and isolation piles was often blind.…”

Section: Comparison Of the Protection Effect Between Foundationmentioning

confidence: 99%

The Influence of Complex Subway Station Construction on High Retaining Walls and Appropriate Countermeasures

Wang

et al. 2020

Anzhen Bridge Station of Beijing metro line 12, which adopts a separated-island platform constructed by the undermining method, passes along the retaining wall of the North Third Ring Road. A numerical simulation method is adopted to study the deformation laws of the retaining wall under the influence of station construction. The simulation data show that the affected retaining wall will have large settlement and tilt, and countermeasures must be taken. Four countermeasures are formulated, and their control effects are analyzed. The calculation results show that the combination of anchor cables and waist beams can effectively control the tilt of the retaining wall, but the control effect on the absolute settlement is not obvious. The control effect of isolation piles is better than that of foundation grouting. The joint control method of anchor cables combined with waist beams, isolation piles, and deep hole grouting makes the deformation meet the target, and according to this measure, a concept of joint control aiming at the influence of the “source,” “propagation,” and “object” is proposed, which can provide a reference for similar projects with a great difficulty in deformation control.