A collection of symposium papers covers such topics as; braced excavations and shafts; construction aspects of bored tunnels; ground treatment for bored tunnels; modelling and prediction for bored tunnels; settlement effects of bored tunnels; and an overview of the Jubilee line extension project.

Geotechnical aspects of underground construction in soft ground : proceedings of the International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground/London/UK/15-17 April 1996

Developments and research directions in pipe jacking and microtunneling

A method to estimate the jacking force for pipe jacking in sandy soils

An analytical model to predict the limit support pressure on a deep shield tunnel face

A new model to predict ground surface settlement induced by jacked pipes with flanges

Earth pressure on shield excavation face for pipe jacking considering arching effect

Analysis of jacking forces during pipe jacking in granular materials using particle methods

Demands for underground space (e.g., metro stations, deep basements, and underpass) in congested urban areas have been increasingly growing in recent years. The top-down excavation technique becomes an attractive alternative compared to the conventional cut-and-cover construction method, as the ground traffic can be disrupted for a much shorter period. In this investigation, an underpass project linking two large-scale basements under heavy ground traffic constructed by the top-down approach is introduced. The specialty of the project is that the geometry in plane is irregular, which makes the excavation challenging since all empirical design criteria cannot be applied directly. The lateral supports are not applied all around the perimeter of the excavation (only two short sides are constrained by lateral supports). Finite element simulations are conducted to optimize the construction procedure. A comprehensive field monitoring program is implemented to the project, which is excavated using the optimal solution obtained from numerical analyses. Field measurements demonstrate that the top-down technique is effective in minimizing differential settlement and lateral displacement of columns and piles.

Top-down excavation of an underpass linking two large-scale basements in sandy soil

An oversized pit-in-pit (PIP) excavation, which comprised an octagonal pit outside and two cross-shaped pits inside, was excavated in soil-rock mixed strata, Shenzhen, China. There were two shield tunnels connected to the north and south of the PIP excavation after the main structures completed. Extensive instruments were adopted throughout the construction process to guarantee the safety of the project. Based on the massive field data, the performance of the ground settlement, retaining structures and adjacent building deflection were investigated. Field data indicate that the influence zone of ground settlement in depth was above the stiff clay layer. The maximum lateral displacement (δhm) of the retaining structures occurred at 0.4 He (He is the excavation depth), and δhm decreased when the excavation depth was over 0.5 He. The maximum ground settlement δvm occurred at 0.2 He which gradually decreased with d (d is the distance from the monitoring point to the excavation edge). This large discrepancy of the ground settlement induced 3.13‰ tilting of the adjacent buildings. The ground settlement influence zone was 1.7 He away from the pit edge (d ≤ 1.7 He). A half-3D numerical model was established to investigate the influence of different excavation sequences. The results show that the maximum principal stress (σm) of the cover plate increased to peak value due to the excavation of subsoil, which indicated that the sidewall construction and subsoil excavation should be carried out simultaneously to reduce the stress concentration of the cover plate. TD excavation can effectively minimize the ground and building settlement, while the excavation may induce uneven displacement of the interior supporting columns. Push in failure of the sidewalls may occur during the construction which was the combined result of unloading and increase in the excavation depth.

Xinbo Ji

Papers

A method to estimate the jacking force for pipe jacking in sandy soils

Earth pressure on shield excavation face for pipe jacking considering arching effect

Analysis of jacking forces during pipe jacking in granular materials using particle methods

Top-down excavation of an underpass linking two large-scale basements in sandy soil

Investigation into the Performance of a Covered Top-Down Pit-in-Pit Deep Excavation in Shenzhen Soil-Rock Mixed Strata