Subsurface settlement profiles above tunnels in clays

The constitutive model frequently used in numerical calculations of tunnel excavation is linear-elastic perfectly plastic with a Mohr-Coulomb (MC) failure criterion. Generally, this leads to shallower and wider surface settlement troughs than those observed experimentally. It is therefore necessary to use adapted constitutive models for the design of underground works. In this paper, three constitutive models are implemented in a two-dimensional simulation of an underground excavation in plane strain: a linear-elastic perfectly plastic model (the MC model), an elastoplastic model with isotropic hardening [the hardening soil (HS) model, Schanz et al., Beyond 2000 in computational geotechnics, Balkema, Rotterdam, pp. 281-290, 1999 and an extension of this model which implies an evolution of the stiffness modulus in the small-strain range according to the strain level (the HS model with smallstrain stiffness ''HS-Small'', Benz, Small-strain stiffness of soils and its numerical consequences. Ph.D. thesis, Universitat Stuttgart, 189 pp., 2007). The study is based on the results of drained triaxial compression tests representing an overconsolidated clay (Gasparre, Advanced laboratory characterisation of London clay. Ph.D. thesis, Imperial College London, 598 pp., 2005); and is then applied to a shallow tunnel. The impact of the constitutive model is highlighted as well as the limits of the simplest constitutive model.

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“…Addenbrooke et al [1] and Mair et al [22]) contrary to the MC model which leads to a trough that fails to coincide with a Gaussian curve.…”

Section: Reference Calculation (H = 2d and K D = 35%)mentioning

confidence: 98%

“…The settlement curves obtained in this way were then compared with different empirical equations in the literature (e.g. Attewell [5]; Clough and Schmidt [13]; O'Reilly and New [25]; Sagaseta [29]; Rankin [27]; Chapeau [12] and Mair et al [22]) summarized by Dias [14] (Fig. 10).…”

Section: Sensitivity Studymentioning

confidence: 99%

Impact of constitutive models on the numerical analysis of underground constructions

2008

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“…It is worth noting that Jones (2010) showed that the Mair et al (1993) expression can overestimate the value of K for deep tunnels. Based on field data measurements, Jones proposed a logarithmic formula for the prediction of K which depends on the height above the tunnel z t À z rather than the relative depth z/z t .…”

Section: Empirical Methodsmentioning

confidence: 99%

“…Ground movements due to greenfield tunnelling in undrained clay are generally well understood (Mair et al, 1993;Mair & Taylor, 1997;Grant & Taylor, 2000). However, the available data for ground movements above tunnels in coarse-grained soils from case studies (Dyer et al, 1996;Sagaseta et al, 1999;Fargnoli et al, 2013) and centrifuge tests Marshall et al, 2012) are rather limited.…”

Section: Introductionmentioning

confidence: 99%

Greenfield tunnelling in sands: the effects of soil density and relative depth

2019

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Tunnel construction is vital for the development of urban infrastructure systems throughout the world. An understanding of tunnelling-induced displacements is needed to evaluate the impact of tunnel construction on existing structures. Recent research has provided insight into the complex mechanisms that control tunnelling-induced ground movements in sands; however, the combined influence of relative tunnel depth and soil density has not been described. This paper presents data from a series of 15 plane-strain centrifuge tests in dry sand. The cover-to-diameter ratio, C/D, of the tunnels ranges between 1·3 and 6·3, thereby including relatively shallow and deep tunnels. The sand relative density varies between 30 and 90%, corresponding to loose and dense soils. The effects of C/D, soil density and volume loss on vertical and horizontal soil movements, shear strains and ground reaction curves are discussed. Analysis of surface and subsurface settlement trough characteristics shows that the mechanisms are non-linear and the effects of soil relative density and volume loss on deformation patterns are highly dependent on C/D. The role of soil arching in the definition of the displacement mechanisms and a discussion of the implications of the results to the assessment of damage to existing structures are also provided.

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“…The characteristics of an excavation damaged zone (EDZ) vary with the geological conditions, ground stress, excavation method and opening geometry [2], and have been extensively investigated with different methods [3]. Traditionally, the empirical methods [4,5,6] based on limited field data had frequently been used in calculating surface settlement. As advancement of the technologies for tunnel excavation, numerical modeling method has played an important role in simulating the stress path in the stress redistribution field created by the tunneling impacts [7,8], the swelling phenomenon around tunnels [9], acoustic emission in large-scale underground excavations [10], EDZ development in brittle rocks [11], time-dependent nature of EDZ [12], etc.…”

Section: Introductionmentioning

confidence: 99%