Modelling of long-term ground response to tunnelling under St James's Park, London

Abstract

Following a tunnel excavation in low-permeability soil, it is commonly observed that the ground surface continues to settle and ground loading on the tunnel lining changes, as the pore pressures in the ground approach a new equilibrium condition. The monitored ground response following the tunnelling under St James's Park, London, shows that the mechanism of subsurface deformation is composed of three different zones: swelling, consolidation and rigid body movement. The swelling took place in a confined zone above the tunnel crown, extending vertically to approximately 5 m above it. On the sides of the tunnel, the consolidation of the soil occurred in the zone primarily within the tunnel horizon, from the shoulder to just beneath the invert, and extending laterally to a large offset from the tunnel centreline. Above these swelling and consolidation zones the soil moved downward as a rigid body. In this study, soil–fluid coupled three-dimensional finite element analyses were performed to simulate the mechanism of long-term ground response monitored at St James's Park. An advanced critical state soil model, which can simulate the behaviour of London Clay in both drained and undrained conditions, was adopted for the analyses. The analysis results are discussed and compared with the field monitoring data. It is found that the observed mechanism of long-term subsurface ground and tunnel lining response at St James's Park can be simulated accurately only when stiffness anisotropy, the variation of permeability between different units within the London Clay and non-uniform drainage conditions for the tunnel lining are considered. This has important implications for future prediction of the long-term behaviour of tunnels in clays.

Ground settlement induced by tunnel boring in stiff clay

“…that calculations are in good agreement with field observations. It was established by parametric analysis [14] that the change in consolidation settlements is mostly influenced by drainage conditions in tunnel lining, which confirms the results obtained by Wongsaroj [4,5].…”

“…The program involving very extensive settlement measurements on the surface, soil deformation measurements along the depth, and measurements of ground water pressure variations caused by drilling, was implemented at the St. James's Park site in London in regular time intervals throughout realization of the tunnelling work. So far the most detailed study of these data is the one conducted by Wongsaroj et al [4,5]. Their analyses are based on extensive triaxial and oedometer laboratory testing of clay from goodquality undisturbed samples obtained during investigations at various localities in London, and also on various in-situ investigations of soil (geological and geophysical surveys, insitu permeability testing, etc.).…”

Test and numerical research on wall deflections induced by pre-excavation dewatering

“…To more accurately simulate a practical dewatering process, the following simulation methods were compared: (1) specify a pumping velocity on the WCS [27]; (2) set a zero pore-water pressure boundary on the WCS [28]; and (3) set the DOF boundary on the WCS [29]. These methods can all form the hydraulic gradient around the dewatering well, under the action of which the groundwater in surrounding soil will outflow via the dewatering well.…”

Vertical stress distributions around batter piles driven in cross‐anisotropic media

“…However, in this study, we adopt a very famous over-consolidated fissured clay-London clay as our demonstration. The characteristics of London clay are, respectively, discussed briefly by Hight et al [22], Gasparre et al [23,24], Nishimura et al [25], and Wongsaroj et al [26]. Consequently, the London clay anisotropic degree including the ratios E/E , G /E , and / , are interpreted to investigate their effect on the vertical stresses.…”