Iron Tunnel Research Articles

The influence of tunnel joints on the present-day condition of a grey cast iron tunnel

The present-day condition of a grey cast iron (GCI) tunnel was investigated numerically by means of a series of plane-strain geotechnical analyses that focused on establishing the influence of the modelling approach adopted to simulate the behaviour of longitudinal tunnel joints. The GCI tunnel lining was simulated in three different ways: (i) as a continuous lining; (ii) as a jointed lining adopting a simple joint model that neglects the presence of the joint bolts and (iii) as a jointed lining adopting a more sophisticated model that considers both the nonlinear response of the joint after opening and the contribution of the bolts to the ultimate capacity. The numerical results demonstrate that accounting for the tunnel joints has a considerable impact on the tunnel response. Significant differences are also observed in the results obtained with the two joint models, hence demonstrating the practical significance of employing an advanced model able to reproduce accurately the rotational behaviour of the joint. The drainage behaviour of the joints was also investigated and the numerical results indicate that drainage even through only the knee joints causes significantly more soil consolidation than that from a watertight tunnel and consequently, larger tunnel deformations and forces.

Numerical characterisation of the rotational behaviour of grey cast iron tunnel joints

The structural assessment of segmental grey cast iron (GCI) tunnel linings to nearby construction is challenging due to the presence of the joints affecting the stiffness of the tunnel lining. This paper presents an extensive investigation, using 3D finite element (FE) analyses, into the bending moment-rotation (M-θ) behaviour of two GCI tunnel joint geometries. These two geometries correspond to standard running and station tunnels of the London Underground network. The contribution of this study is two-fold. i) The novel characterisation of the M-θ response enables the development of new models for simulating the mechanical response of GCI tunnel joints with structural elements which can be used in simplified, 2D geotechnical analysis for tunnel safety assessments. ii) The analyses provide insight into the behaviour of GCI tunnel linings that would be difficult to achieve through experimental and field observations alone. More specifically, the analyses show that when the bolts are removed from the joints the possibility of tensile failure can be disregarded; that the initial bolt preload influences the rotational stiffness only after some rotation has taken place and does not alter the bending moment of opening; and that the out-of-plane displacement restraint has little influence on the joint response.

Numerical investigation of a segmental grey cast iron tunnel ring: validation with laboratory data and application to field conditions

The structural response of a segmental grey cast iron (GCI) tunnel lining ring under distortion was investigated by means of finite element (FE) analysis. Building on previous experimental investigations, a 3D numerical model, capable of reproducing accurately the behaviour observed in the laboratory, was developed with the aim of providing guidelines for the structural assessment of GCI linings in engineering practice. A comprehensive validation of the segmental ring model with the laboratory data was first completed. Subsequently, a parametric study was conducted using a set-up that replicated the widely adopted elastic continuum method, so that differences between the numerical and the analytical solution could be attributed to the presence of the longitudinal joints. In this manner, the influence of the joints on the ring response was quantitatively established and recommendations for routine engineering calculations developed. A set of bending stiffness reduction factors are proposed as a function of the tunnel ovalisation, providing upper and lower limits of the bending stiffness, as well as a global reduction factor which is an average measure of the bending stiffness reduction. These factors can be integrated into the calculation procedure of closed-form solutions in order to account for the segmental nature of GCI linings.

Harmonic clutter recognition and suppression for automotive radar sensors

In this article, we propose a novel harmonic clutter recognition and suppression method to overcome the deterioration of a target- or vehicle-detection performance due to harmonic clutters. Although several studies have been performed on the reflection and diffraction on road surfaces for automotive radar sensors, most of them did not consider the case where metallic structures such as iron tunnels with greater reflection are densely distributed. The proposed method measures the periodicity of harmonic clutters by analyzing the spectral characteristics of the received radar signal with various road conditions. The proposed method can successfully recognize harmonic clutters. In addition, experimental results show that early detection of a target vehicle in an iron tunnel under adaptive cruise control is improved using the proposed clutter suppression method.

Behaviour of bolted cast iron joints

The structural testing and finite element (FE) analysis described in this paper were part of a major research project undertaken at Imperial College London to investigate the deformation of bolted segmental grey cast iron (GCI) tunnel linings. A key aim was to quantify how joints influence the behaviour of the lining, through a three-path approach comprising physical experiments, finite element modelling, and field instrumentation. The laboratory results have been used to assess the validity of the tunnel assessment methods used by industry.This study examined joint articulation under the serviceability limit state in the absence of hoop force focussing on factors such as applied bolt preload, the loading direction and the freedom of the circumferential flange to deflect. Two half-scale GCI lining segments were bolted together at the longitudinal flanges to form a bolted arch in a similar fashion to the tests performed by Thomas (1977). Modern instrumentation was implemented to gain detailed measurements quantifying changes in global displacements of the two segments, bolt forces and joint opening under applied loading. For the first time, the physical experiments were conducted contemporaneously with the development of a three-dimensional FE model of the joint. The experimental data and the results from the FE analysis indicate a reduction in joint stiffness as the joint articulates under applied load. It is shown that the presence of a joint has far greater influence on the behaviour of the ‘arch’ than the level of preload applied to the bolts in the joint. The FE analysis allowed the deformation behaviour of the joint under positive and negative bending to be investigated: its response under the two modes differs significantly.

Ultimate capacity of a segmental grey cast iron tunnel lining ring subjected to large deformations

Understanding the behaviour of existing tunnels subjected to in-service deformations, as a result of the construction of underground works (e.g. new tunnels) in their proximity, is of importance in order to safeguard infrastructure within the urban environment. The associated deformations that take place during tunnelling have to be carefully assessed and their impact on the existing tunnels needs to be considered. A half-scale segmental grey cast iron (GCI) tunnel lining ring was tested as part of an extensive research project investigating the impact of new tunnel excavations on existing tunnels conducted at Imperial College London. A sophisticated experimental arrangement was developed to deform the ring in a variety of modes under combined displacement and load control. This paper reports on experiments carried out to assess its structural response when subjected to large deformations. The tests reported are the first to be conducted on a realistic scale model under carefully controlled conditions, and provide valuable insight into the behaviour of a GCI segmental ring during distortions commonly observed in reality. Details of the experiments, including the adopted test set-up and the instrumentation employed, are presented. The measured bending moments around the ring, as a result of the applied deformations, are determined and compared with those predicted using the well-known equations given by Morgan (1961) and Muir Wood (1975), often used in industry, as well as those obtained assuming an elastic continuous ring.

Способ огнезащиты обделки транспортных тоннелей из чугунных тюбингов

Subways are an important part of the transport system in large cities. Damage to load-bearing structures of underground tunnels under fire for a long time disrupts the functioning of the transport pipeline. In this regard, to the structural elements lining tunnels there are imposed high requirements for fire resistance of 60-90 minutes (for escalators, subway tunnels and rail tunnels) and to 180 minutes for road tunnels. The purpose of research, the results of which are shown in the article, is the provision of fire resistance and lining of underground tunnels, made of iron tubing. The analysis of domestic and foreign experience in the field of fire resistance of cast iron structures for different purposes and different operating conditions was conducted. Initial and boundary conditions for the production and the estimated task of forming a mathematical model were formulated. Calculations of warm lining from cast iron tubing when exposed to the standard temperature of fire, depending on the thickness of construction, taking into account the heat transfer from the unheated side were conducted. Based on the results of the calculations it was determined the need for a fire-retardant action. A method of fire protection constructions, which allows you to keep the original tunnel section, was suggested. The essence of the method lies in the structural protection of structural iron tubing using fire-retardant mineral woolplates. The next stage of research was to conduct calculations of the regiment of heating the lining from cast iron tubing when exposed to the standard temperature of fire mode when using the proposed fire protection options. The calculation results have shown high efficiency of mineral wool plates use as fire protection of the iron tunnel lining. Calculations have shown that even under the worst conditions of heat irradiation into the ground it’s possible to provide the limit of fire resistance of cast iron tubing on the bearing capacity for at least 90 minutes. The results of the research show that the approach to defining the limit of fire resistance of structural metal tubing tunnels based on the achievement of critical temperature, requires experimental confirmation in tests of representative fragments of tunnels under the strain and conditions of heat irradiation into the ground close to the real. In the case of the transition to a flexible standardization in the transition to the real temperature of fire regimes on the object in question will also require further experimental work.

Experimental investigations of bolted segmental grey cast iron lining behaviour

The need for the research reported in this paper was driven by the Crossrail project in London for which new tunnels were constructed close to numerous existing operational tunnels of the London Underground (LU) network.This research is based on experimental work conducted on half-scale grey cast iron (GCI) tunnel lining segments with chemical composition similar to the Victorian age GCI segments in the LU network. This paper discusses the deformation behaviour of the bolted segmental lining under the influence of factors such as overburden pressure, bolt preload and presence of grommets at small distortions. The measured behaviour of the segmental lining is compared against the calculated response of a continuous lining based on the assumption of elasticity.The industry practice for tunnel lining assessment is to calculate the induced bending moment in the tunnel lining using an elastic continuum model, while adopting a reduced lining stiffness to take into account the presence of the joints. Case studies have recorded that both loosening and tightening of lining bolts have been used as mitigation measures to reduce the impact of new tunnel excavations on existing GCI tunnels.The experimental work on the half-scale GCI lining has shown that a bolted segmental lining behaves as a continuous ring under small distortions imposed when subjected to hoop forces relevant to the depth of burial of LU tunnels. In the presence of hoop force, joint opening was minimal and the magnitude of preload in the bolts had little impact on the behaviour of the lining. It is therefore concluded that disturbance of the bolts in existing tunnels is not recommended as a mitigation measure as in addition to being ineffective it is both time consuming and introduces the risk of damaging the tunnel lining flanges.

Enhanced Iron-Tunnel Recognition for Automotive Radars

In this paper, we propose a novel iron-tunnel recognition method to overcome the deterioration of the target or vehicle detection performance due to iron-tunnel clutters. Although a few studies on the reflection and diffraction on road surfaces have been conducted for automotive radar sensors, most of these studies did not consider the situation in which structures with larger reflection, such as an iron tunnel, are densely distributed. The proposed method measures the degree of spectral spreading through the analysis of the spectrum characteristics of the received radar signal under different road conditions. The proposed method can successfully detect iron tunnels. In addition, experimental results show that early detection and missing problem of a forward target vehicle in an iron tunnel under adaptive cruise control (ACC) is improved.

The monitoring of an existing cast iron tunnel with distributed fibre optic sensing (DFOS)

Instrumentation is vital to tunnelling projects for validation of design assumptions, monitoring of trigger levels during construction and also serving as a feedback loop to understand the deformation mechanisms of the particular problem which could be used to improve future designs. It can also be used for long term monitoring of the tunnel for maintenance purposes. Distributed fibre optic sensing (DFOS) systems based on brillouin optical time domain reflectometry are able to provide continuous and distributed strain measurements to be taken along the entire length of, for example, an existing cast iron tunnel where the fibre optic cable length is fully attached. This enables engineers to understand the stresses and strains that develop within the lining caused by external influences; which in this case, the construction of a new tunnel directly underneath it, rather than relying on discrete point measurements of displacement from conventional methods of monitoring. Nonetheless, proper installation of DFOS is of paramount importance to obtain high quality data. This paper aims to provide some practical guidance on the planning and installation of DFOS and presents a brief case study on the monitoring of London’s Royal Mail tunnel during the construction of the large Crossrail platform tunnel, located directly below it at Liverpool Street Station. It demonstrates the potential benefits of using such systems in complex tunnelling scenarios.

The adverse influence of geology and groundwater on the behaviour of London Underground railway tunnels near Old Street Station

A number of cast iron tunnel lining segments have cracked in two sections of the London Underground between Old Street and Moorgate Stations that are located in the Palaeocene Woolwich and Reading Beds facies. There are also several slow seepages of highly corrosive acidic groundwater. Investigation of the ground has shown that water derived from the consolidation of the overlying London Clay is collecting in a lens of sand which is crossed by the tunnels. Such water, together with air from the tunnels, is oxidising pyrite in the sand lens to yield a sulphate-rich acidic water which is damaging the tunnel, both by corrosion of the cast iron lining and by producing expansive pressures from the precipitation of gypsum crystals, causing the tunnel to be squeezed horizontally and move up at the crown.

Measuring the structural performance of cast iron tunnel linings in the laboratory : Thomas, H S H Ground Engng, V10, N5, July 1977, P29–36

The structural behavior of bolted cast iron segments has been investigated under simple, known loading conditions. This knowledge was required to help ascertain the structural behavior of segments in actual tunnels where complex loading conditions exist. One of two kinds of segment studied was an experimental segment of unusual proportions. Some structural properties of tunnel segments for which evidence had previously been inconclusive were clearly displayed by these experimental segments. Among the conclusions drawn are that the modulus of flexural rigidity of the segments is changed by variation in the applied bending movement, and also with variation in uniform pressure on the back of the segment. The joints between segments do not always behave as simple butt joints.

V. Proposal for constructing, and putting in its place, an iron tunnel under the river Thames

(1810). V. Proposal for constructing, and putting in its place, an iron tunnel under the river Thames. The Philosophical Magazine: Vol. 36, No. 147, pp. 34-39.