Predicting tunnelling-induced ground movements and interpreting field measurements using numerical analysis: Crossrail case study at Hyde Park

Ground response to the construction of the Crossrail tunnels in London Clay beneath Hyde Park has been modelled numerically using advanced finite-element analyses. The soil model used for modelling the London Clay was a kinematic hardening soil model (named M2-SKH). This model, when used for the St James's Park greenfield site, provided excellent predictions of tunnelling-induced ground movements. Comparison of the results from the analysis of the Hyde Park greenfield site with associated field monitoring data also suggests excellent predictions, even though in this case the tunnels were: of larger diameter; deeper in the London Clay; and constructed with earth-pressure-balance machines. The influence of lining permeability was found to influence significantly short- and longer-term predictions. Interpretation of the predicted surface and subsurface vertical and horizontal displacements due to the construction of the Crossrail tunnels exemplifies how numerical analysis can assist in explaining and identifying potential ambiguities in field measurements

Investigating the effect of tunnelling on existing tunnels

A major research project investigating the effect of tunnelling on existing tunnels has been completed at Imperial College London. This subject is always of great concern during the planning and execution of underground tunnelling works in the urban environment. Many cities already have extensive existing tunnel networks and so it is necessary to construct new tunnels at a level beneath them. The associated deformations that take place during tunnelling have to be carefully assessed and their impact on the existing tunnels estimated. Of particular concern is the serviceability of tunnels used for underground trains where the kinematic envelope must not be impinged upon. The new Crossrail transport line under construction in London passes beneath numerous tunnels including a number of those forming part of the London Underground networ

Measured short-term ground surface response to EPBM tunnelling in London Clay

Earth-pressure-balance machines (EPBMs) were used for the construction of Crossrail tunnels in London, providing opportunities for field investigation of consequent ground response. Analysed results from an instrumented research site in Hyde Park with extensive surface and subsurface monitoring arrays are presented and discussed. The Crossrail tunnels at the site are 34·5 m below ground, deeper than those in most case histories of tunnelling in stiff clay in the UK. This paper characterises the tunnelling-induced ground response, both ‘greenfield’ and in the proximity of the existing Central Line tunnels, dealing with measurements at the ground surface. A companion paper covers the subsurface ground response. Vertical and horizontal ground surface displacements were obtained from manual precise levelling and micrometer stick measurements. Several key findings will benefit future tunnelling projects involving EPBMs. Volume loss values measured at the instrumented site were low, being less than 0·8% and 1·4% for the first and second tunnel drives respectively, higher values being associated with ground softening from the first tunnel construction. Smaller volume losses were recorded in the vicinity of the existing Central Line tunnels, compared with the greenfield location, suggesting that their presence inhibited the development of ground movements. Asymmetric settlement troughs developed due to either the nearby pre-existing tunnels or the construction of the first tunnel. Marginally smaller values of trough width parameter, Ky, were determined for these deeper tunnels compared with previous greenfield ground case histories. Resultant vectors of ground surface displacement were directed to well-defined point-sinks above the tunnel axis level

Measured short-term subsurface ground displacements from EPBM tunnelling in London Clay

Subsurface ground displacements from the construction of the twin-bore Crossrail tunnels in London Clay by earth pressure balance machines (EPBMs) are presented and discussed, complementing a companion paper by the authors that focused on the surface response. Both papers report vertical and horizontal displacements, in this case measured using comprehensive arrays of instruments installed within boreholes in Hyde Park, London. The Crossrail tunnels are deeper than those cited in most UK case histories concerning tunnelling in stiff clay. Clear insights were gained into subsurface displacement mechanisms: an ‘inward’ displacement field was observed around the Crossrail tunnel construction, in contrast to the ‘outward’ displacement field that developed around the shallower Channel Tunnel Rail Link tunnels constructed east of London using similar EPBMs in London Clay. This has important implications when estimating subsurface displacements using currently available empirical methods. Appraisal of the EPBM operational variables suggests that the relative magnitude of face and tail grout pressures to overburden stress is the key factor contributing to the opposing senses of the observed displacement fields. Earlier tunnelling-induced strain softening of the London Clay is evident from greater subsurface incremental volume losses and settlement trough width parameters relating to subsequent tunnel construction

Pore water pressure and total horizontal stress response to EPBM tunnelling in London Clay

The ground response, in terms of surface and subsurface displacements, to twin-bore Crossrail tunnel construction beneath a research monitoring site in Hyde Park, London, using earth-pressure-balance machines (EPBMs) in London Clay, has recently been reported in two companion papers by the authors. This third paper presents and discusses corresponding changes in pore water pressure and total horizontal stress measured using multi-level piezometers and pushed-in spade cells. The three papers together provide a comprehensive and completely unique field monitoring case history of the short-term ground response to EPBM tunnelling in London Clay, making them invaluable for validating future numerical analyses. The fully grouted vibrating-wire piezometers were able to measure the rapid pore water pressure changes around the tunnels as they were constructed. Five distinct immediate pore water pressure responses are identified, induced by different stages of the tunnel drives as the EPBMs approached and passed the instruments. The responses are correlated with tunnel-boring machine operation variables and a postulated arching mechanism, identified for the first time through field measurements. The sense and magnitude of changes in horizontal total stress were reasonable and are correlated with overall pore water pressure changes. Both responses are linked where possible with measured subsurface displacements and generally correlate well, at least qualitatively. Limitations to the measurements and influencing factors are also discussed

Effect of Arm Position and Foot Placement on the Five Times Sit To Stand Test Completion Times of Female Adults Older than 50 Years of Age

[Purpose] The five times-sit-to stand test (FTSTS) is a clinical test which is commonly used to assessed the functional muscle strength of the lower limbs of older adults. The aim of this study was to examine the effect of different arm positions and foot placements on the FTSTS completion times of older female adults. [Subjects and Methods] Twenty-nine healthy female subjects, aged 63.1±5.3 years participated in this cross-sectional study. The times required to complete the FTSTS with 3 different arm positions (hands on thighs, arms crossed over chest, and an augmented arm position with the arms extended forward) and 2 foot placements (neutral and posterior) were recorded. The interaction effect and main effect of arm positions and foot placements were examined using a 3 (arm position) × 2 (foot placement) two-way repeated measures analysis of variance (ANOVA). [Results] There was no interaction effect among the 3 arm positions in the 2 foot placements. A significant main effect was identified for foot placement, but not arm position. Posterior foot placement led to a shorter FTSTS time compared to that of normal foot placement. [Conclusion] With the same arm position, FTSTS completion times with posterior foot placement tended to be shorter. Therefore, the standard foot placement should be used for FTSTS administration

Effect of arm position and foot placement on five times Sit-to-Stand Test completion times for female adults older than 50 years of age

Conference Theme: Aging with Confidenc