Search

The construction of new bridge piles adjacent to existing subway tunnels poses a significant threat to the safety of the tunnels. To accurately assess the impact of the construction of the steel casing of bridge piles on nearby subway tunnels, a simplified analytical method incorporating a mechanical model is developed in this study. Specifically, modified calculation formulas for the additional force are proposed, taking into consideration the characteristics of casing segmental construction and the soil-squeezing effect. The two-stage analysis method is employed to determine the additional stress and longitudinal vertical deformation of the tunnel. Subsequently, a series of calculations are performed to gain further insights into the effects of varying lengths and diameters of bridge piles, as well as the relative distance between the pile and tunnel on the tunnel–pile interactions. As the construction depth increases, the existing tunnel experiences a slight initial rise followed by progressively larger settlement that eventually levels off. The maximum settlement exhibits a linear increase with the increasing length and diameter of the bridge piles, while it exponentially increases with decreasing relative distance between the pile and tunnel. Moreover, impact zones of varying degrees of the bridge pile construction on the nearby tunnel are proposed. Based on the Response Surface Methodology, the relative distance is found to exert the greatest influence on the deformation of the existing tunnel, and an optimal relationship among the parameters is provided. The theoretical results are well validated with field-measured data from a representative engineering project and numerical simulation results. The proposed solution can be proved to offer reasonable theoretical support for risk assessment of tunnels under the influence of adjacent piles construction. [ABSTRACT FROM AUTHOR]

During the time that Professor John Burland was an expert witness for the Parliamentary hearings for the Jubilee Line Extension Project (JLEP), he realised that although tunnels had been constructed in London for more than a century, there were very few well documented case studies describing the response of buildings to tunnelling-induced settlement. Professor Burland had extensive knowledge of the effects of ground movement on buildings, having studied and published his seminal work with Professor Peter Wroth in the 1970s which he with others developed into a staged process for assessing potential structural damage from excavation-induced ground movements. Construction of the JLEP provided an ideal opportunity to compile a set of exemplary case studies (involving different structural forms, foundation types, tunnelling methods and geological conditions) and he harnessed this to its full extent. At the start, a number of ‘gaps in knowledge’ were identified and these were addressed over the following years of monitoring and data analysis. The research culminated in a two-volume book that is still widely referenced almost twenty years later. In this paper a background to Professor Burland’s tunnelling- and deep-excavation-related research is given and the gaps in knowledge are summarised along with how they were answered through the JLEP research findings. They are reinforced with other more recent tunnelling projects in London that he has been involved with, in particular the Crossrail project, thus furthering the understanding of ground and structural response to tunnelling, benefitting both industry and academia. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study develops an analytical approach to quantitatively model the efficiency of the pretensioning of grouted rockbolts in terms of reduction of tunnel convergence. In this study, the distribution of force along the pretensioned fully grouted bolt is calculated by the assumption of a rigid connection between the bolt and the rock mass. A compressive force is then applied to the bolt head on the tunnel surface to consider the shear relative displacement between the bolt and the rock mass. The magnitude of this compressive force is found by modeling the bolt boundaries' stiffness. The theoretical proposed approach is simplified to be used for practical purposes. The results show that if the stiff end plate is tightened to the bolt head (complete planner contact), the grouting effect of the pretensioned fully grouted bolts on tunnel stability can be neglected. [ABSTRACT FROM AUTHOR]

The interaction between parallel closely spaced tunnels is inevitable especially when tunneling in soft soil. In this research, a displacement monitoring was performed on two parallel closely spaced highway tunnels in soft marine clay excavated by slurry shields in Shanghai, China. Soil movement between the tunnels and liner displacement of the first constructed tunnel induced by the construction of the second tunnel were analyzed and discussed. It was found that the soil between the tunnels moved in directions both perpendicular and parallel to the tunnels due to the effects of thrust, extrusion, and grouting by the second shield tunneling. The maximum horizontal displacements of the soil between the tunnels occurred at 0.2D (D = outer diameter of the tunnels) above the tunnel springline, which forced the upper semicircle of the existing tunnel liner deformed downward while lower semicircle deformed outward, and the semicircle close to the second tunnel deformed more than the opposite semicircle. The discrepancy between displacements of the existing tunnel liner and the soil in the middle of the tunnels increased with increases of displacements due to increasing stiffness of the liner. [ABSTRACT FROM PUBLISHER]

This paper develops an analytical method to obtain distribution of the axial force in the pretensioned fully grouted rockbolts around a circular tunnel. For his purpose, the axial force along the bolt is calculated by the assumption of rigid connection between the bolt and rock mass. To include the effect of relative shear displacement, the condition of end boundaries of bolt is focused on i.e. the reduction of the force on the bolt head is calculated through modeling of the flexibilities of its component (washer, plate ...) and tunnel surface. Then, this force is simulated by applying a fictitious compressive force on the bolt head. The distribution of this fictitious force along the bolt is obtained to subtract from that of rigid connection. According to a case study, the theoretical prediction of axial force in the passive cases is comparable to the in-situ measured data. The magnitude of pre-tensioning force, delay in installing of bolts, stiffness of bolt head, and rockbolt density are considered as parameters to perform the sensitive analysis. [ABSTRACT FROM AUTHOR]

The design of tunnels and groundwater collection and filtration systems requires evaluation of water pressure on the structures and/or leakage (inflow rate) into the structures. However, a great deal of uncertainty remains concerning the control of pore-water pressure and inflow rate in underwater tunnels, because there are various factors that influence the hydraulic interaction between the structure and the groundwater. In this paper the relationship between pore-water pressure () and inflow rate () is investigated using a theoretical method for laminar and turbulent flow. The relationship is validated by performing simple experimental studies. [ABSTRACT FROM AUTHOR]

Prediction of the long-term settlement of clay soils over tunnels requires a knowledge of the permeability of the soil and of the tunnel lining; however, determination of the lining permeability in the field is difficult. An important contributor to this problem is the lack of knowledge concerning the permeability of the grout between the lining and the soil. This paper presents the results of tests to characterise the properties of grout samples from London Underground tunnels, investigating permeability, porosity, microstructure and composition. The tests revealed that the newer grout was impermeable relative to the surrounding clay. However, the older samples showed much greater permeabilities and an altered grout composition, suggesting that degradation had taken place. Exposure to groundwater appeared to have caused carbonation and sulfate reaction. The combination of chemical reaction and leaching of cementitious and degradation products appears to have made these grouts more permeable, so that the grout could act as a drainage path rather than a barrier. This challenges the typical assumption that the grout acts as an impermeable barrier. [ABSTRACT FROM AUTHOR]

Tropical residual clays with a highly porous structure react to the stress changes induced by tunneling in such a way that surface settlements can be larger than crown-level settlements along a tunnel axis. This behavior, which is not readily simulated by most numerical analyses, was also observed in the Paraiso tunnel, built for the São Paulo Metro, Brazil. This is a shallow tunnel driven through porous clayey soils by the sequential method. Detailed results of field monitoring are presented and discussed. 3D finite-element analyses that allowed a detailed simulation of the construction sequence have been carried out, considering two distinct constitutive models for the soil: a simple elastic-perfectly-plastic Mohr-Coulomb model, and the elastoplastic model developed by Lade. The results of these analyses are compared with the observed behavior as well as with the results from a plane strain finite-element analysis. It is shown that only the 3D finite-element analysis coupled with the more sophisticated soil constitutive model provides a full reproduction of field performance, with particular relevance for the deformations in the soil mass over the tunnel. [ABSTRACT FROM AUTHOR]

Groundwater control encompasses the range of techniques used to allow construction projects such as tunnels or basement excavations to be carried out in dry and stable conditions. Two principal approaches can be used: groundwater control by pumping, which lowers groundwater levels in the vicinity of an excavation; or groundwater control by exclusion, which relies on low-permeability cut-off walls around the excavation. Existing groundwater control technologies have been developed pragmatically, often on an empirical basis, in response to groundwater problems encountered on construction projects in the past. In the future, it is unlikely that there will be significant changes in groundwater control technology. The real challenge for the future of groundwater control methods will be the need to better predict, monitor and mitigate the impacts on the groundwater environment. The greater focus on environmental impacts from groundwater control is partly the result of increasing regulation of groundwater control works, and partly because of the increasing importance of environmental management in the planning of construction projects. [ABSTRACT FROM AUTHOR]

Copyright of Géotechnique is the property of Thomas Telford Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Géotechnique is the property of Thomas Telford Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper reports the findings of a field study of the ground conditions around an old tunnel in London Clay at a greenfield site in Kennington, South London. Ground conditions were identified from a borehole investigation incorporating a programme of in situ pore water pressure monitoring, geotechnical testing and sampling. Additionally, laboratory classification of the samples and a suite of high-quality triaxial tests were carried out. The results of this investigation are presented and discussed in conjunction with published London Clay data. The presence of a tunnel beneath the site allowed the investigation of its influence on the local soil and groundwater conditions. [ABSTRACT FROM AUTHOR]

summary the mechanical behaviour of a shotcrete lining is analysed in this paper using the convergence-confinement approach. a calculation procedure is presented which is able to provide the reaction curve of a lining with increasing stiffness, by taking into account the variability due to time of the shotcrete stiffness and strength, as well as the face advancement rate. the proposed procedure is also able to provide the change of the safety factor of the lining in time. this results to be a very useful tool for understanding the behaviour of this widely used support and for assigning its thickness to guarantee stability (also in transient conditions), with a known safety factor, during tunnel excavation. [ABSTRACT FROM AUTHOR]