Re-Analysis of Deep Excavation Collapse Using a Generalized Effective Stress Soil Model (original) (raw)
Related papers
2015
Many constitutive models are available nowadays to predict soil-structure interaction 30 problems. It is sometimes not very easier for engineers to select a suitable soil model to carry 31 out their design analyses in terms of complexity versus accuracy. This paper describes the 32 application of three constitutive models to back-analyse a well-instrumented centrifuge model 33 test, in which the effect of basement excavation on an existing tunnel was simulated. These 34 three models include a linear elastic-perfectly plastic model with the Mohr-Coulomb failure 35 criterion (called MC model), a nonlinear elastic Duncan-Chang model (DC) and a 36 hypoplastic model (HP), the last of which can capture the state-, strain-and path-dependent 37 soil stiffness even at small strains and path-and state-dependent soil strength. By comparing 38 with measured data from the centrifuge model test, it is found that the HP model yielded the 39 best predictions of tunnel heave among the three models. Not only the gradient but also the 40 magnitude of tunnel heave is predicted well by this HP model. This can be explained by the 41 fact that the HP model can capture the state-, strain-and path-dependent soil stiffness even at 42 small strains and path-and state-dependent soil strength but not the MC and DC models. 43
Elastoplastic Soil Models for Numerical Analysis of Underground Constructions
2008
The constitutive model frequently used in numerical calculations of tunnel execution is linear-elastic perfectly plastic with a Mohr-Coulomb failure criterion (MC). Generally, this does not leave to realistic soil movement around the excavated tunnel. In this paper, constitutive models representing the behaviour of an overconsolidated clay with different levels of complexity are implemented in FLAC. The study is based on the results of triaxial tests representing London Clay (Gasparre, 2005). The mechanical parameters calibrated from these tests for the different constitutive models adopted in this study are then applied to the excavation of a shallow tunnel. The influence of the chosen model and the cover depth over a tunnel are highlighted on soil displacements. It is concluded that it is unsatisfactory to simulate soils by the MC model when modeling underground structures and it is therefore necessary to adopt advanced models incorporating non linear behavior under small-strain.
Research, 2021
The applications of constitutive model for underground structures may be not assessed completely. Several researchers proposed various constitutive models to present details of different aspects of the soil performance. Therefore, the current study attempts to present 2D convenient finite element model for adopting a comparison study between different model parameters in soft soils to understand the effects of deep excavation on lateral movement and on the ground surface with tunnel presence. The tunnel was simulated at buried depths (C = 3, 6, and 9 m), with two different shapes (circular and horseshoe) and with diameter (D = 6 m). The analysis was by Hardening Soil (HS) and Soft Soil (SS) models in case of tunnel presence once before deep excavation beside and other once under the effect of close deep excavation. In the case of only tunnel presence, and the mass of soil unloading due to excavated tunnel, explicit heave revealed in the soil surface above tunnel body. In the case of close deep excavation where (He = 12 m), significant draw down for the soil surface above the zone of buried tunnels. The suitable tunnel depth without substantially disrupting the surface above may be with increasing the tunnel depth more than 4D.
Impact of constitutive models on the numerical analysis of underground constructions
Acta Geotechnica, 2008
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.
Computers and Geotechnics, 2009
This paper presents the results of finite element analyses carried out using different constitutive models for overconsolidated clay: the Modified Cam clay model and the Three-Surface Kinematic Hardening (3-SKH) model. These analyses are evaluated against data from an extensive series of physical model tests examining the influence of an embedded wall placed near a tunnel on ground movements and tunnel stability. It is shown that for heavily overconsolidated soils reasonable predictions of both deformations and failure can be obtained from kinematic hardening models such as the 3-SKH model, which allow plastic deformation inside a Modified Cam clay state boundary surface.
This paper is focused on soil subsidence of small extend and amplitude caused by tunnel boring or the collapse of underground cavities, whether natural or man-made. The impact of the movements of the ground on existing structures is generally dramatic. It is therefore necessary to accurately predict these movements (settlements and horizontal extension or compression displacements). Even though it is obvious that the overall stiffness and weight of the structure influences the size and shape of the soil movement, the main features of this soil-structure interaction phenomenon are not well established. Caudron et al. (2006) developed an original small-scale physical model to take the soil-structure interaction into account. It is based on the use of the frictional Schneebeli material (assembly of small diameter rods) and a modified version including cohesion in order to reproduce a cohesive layer above a cavity. The displacements of the soil are obtained from digital images processin...
Dynamic response of a tall building next to deep excavation considering soil–structure interaction
Asian Journal of Civil Engineering, 2018
Soil-structure interaction refers to the process in which a structure can change the response of underlying soil and a soil can change the response of structure. In the present study, the hardening soil model with small strain stiffness (HS-small) was used along with the software PLAXIS to analyze a 17-story building located next to a deep excavation with three approaches: using a fixed-based structure model, using a soil-structure interaction model, and using a soil-structure-excavation interaction model. Static analyses showed an upward deformation in the soil adjacent to excavation caused by strong post-tensioning force of the anchors, which may result in outward rotation of the adjacent structure. The results of seismic analysis suggested that the base shears in the two interaction models are lower than the base shear given by the fixed-based model. Although, the peak horizontal accelerations and the horizontal displacements in floors decrease significantly in interaction models but internal forces in some cases are higher than counterparts in the fixed-based model. The presence of deep excavation adjacent to a structure increases the permanent settlements after the earthquake and thus undermines the distribution of internal forces of the structure, which may lead to significant structural damage.
Analysis of Excavation-Induced Deformation with Different Soil Models
The monitored case of deep excavation works located in the centre of Warsaw is described and back analysed as a boundary value problem with the finite element method. The excavation was carried out in over-consolidated clayey layers under the support of braced diaphragm walls. Accurate simulation of such soil-structure interaction problems requires advanced soil constitutive models – especially for the pre-failure range of small strains. On the other hand, such models should not be very complex and their material parameters should be relatively simple to obtain from laboratory and in situ surveys. By means of a case study, this paper examines several simple elasto-plastic constitutive models for the simulation of the behaviour of soil layers. The influence of such characteristics of the soil behaviour, as anisotropy and non-linearity of stiffness, is studied in the paper. The discussion concerns the problems related to the application of the models for a practical example. The compa...
Geotechnical and Geological Engineering, 2019
Tunnels are structures which have vital roles in the development of societies. In the numerical models of underground cavities, such as tunnels, loading due to zone elimination is induced instantaneously in the soil mass, and it might cause a disturbance in the stress state especially around the excavation area. However, this is not compatible with the principles of elastoplastic constitutive models used in soil behavior simulations. Besides, the predicted load on the tunnel liner will be larger than the actual value in this kind of modeling. In other words, it causes the so-called overestimated design. Using an appropriate constitutive model could lead the numerical analyses to accurate results. In this research, loading increment in the simulation of soil behavior is evaluated according to experimental data. Next, a correct way for numerical simulation related to underground excavation is described according to gradually eliminating (incremental) stress around tunnels based on the numerical modeling in the finite-difference code called FLAC. Hence, the effect of releasing the stress on the results is illustrated by the stress paths and deformations around a tunnel. Finally, the installation time of the tunnel liner and its impact on the numerical results are considered based on some experimental and field data. It is concluded that the use of software default in modeling the tunnel issues might lead to extreme oscillations in the stress paths, and it could affect the numerical results. Therefore, it is reasonable to utilize a proper way to release the stress around the excavation area gradually.