Prediction of Ground Surface Settlements Caused by Deep Excavations in Sands (original) (raw)
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An elastoplastic constitutive model for assessing ground settlements induced by deep excavations
Studia Geotechnica et Mechanica
Ground movements induced by deep excavations may cause damages on neighboring existing buildings. Finite element simulations generally give acceptable estimates of the horizontal displacements of the retaining wall, but results are less satisfactory for the vertical displacements of the ground surface behind the structure. A possible explanation is that most constitutive models describe volumetric strains in a simplified way. This paper proposes an elastoplastic constitutive model aimed at improving the prediction of vertical displacements behind retaining walls. The model comprises a single plastic mechanism with isotropic strain hardening, but has a specific flow rule that allows to generate contractive plastic strains. Identification of the parameters based on triaxial tests is explained and illustrated by an example of calibration. A numerical analysis of a well-documented sheet pile wall in sand in Hochstetten (Germany) is presented. The results given by the model are compared ...
2020
The current study is aimed at investigating the basic soil behavior involved in a TBM-EPB excavation and the capability of the Modify Cam Clay (MCC) model is verified for the analysis of the soil settlement in cohesive soils. Tunnel excavation in urban areas can engender considerable ground movements, which is known as one of the complicated issues that may have negative effects on the extant structures. In this paper, the construction of the second line of the Mashhad metro is considered as a case study. Each section of the ground was modeled by two constitutive models, namely MCC and Mohr-Coulomb (MC). Afterwards, the results of numerical analyses and monitoring data were compared with each other. In addition, real parameters of soil, such as volume loss and the inflection point, were obtained via empirical approaches verified by tunnel monitoring. Numerical modeling was performed by FLAC3D software. Based on the transverse and longitudinal sections settlement, the MCC model showe...
Japanese Geotechnical Society Special Publication
This paper presents long-term predictions of the ground behavior, including secondary consolidation via the particle filter, using model test results. There have been some difficulties in evaluating lateral displacements, because an unsuitable value for Poisson's ratio and the constitutive model are generally employed for consolidation simulations. In this paper, the Poisson's ratio is identified in addition to the compression index, the permeability, the initial volumetric strain, and the secondary compression index in the modified Cam-clay model considering anisotropy, to achieve more accurate predictions of lateral displacements. The prediction is performed using the identified parameters, and numerical examples of accurate predictions of the ground behavior are shown.
Ground deformation mechanism due to deep excavation in sand: 3D numerical modelling
In densely built areas, development of underground transportation system often involves excavations for basement construction and cut-and-cover tunnels which are sometimes inevitable to be constructed adjacent to existing structure. Inadequate support systems have always been major concern as excessive ground movement induced during excavation could damage to neighbouring structure. A detailed parametric analysis of the ground deformation mechanism due to excavation with different depths in sand with different densities (D r =30%, 50%, 70% and 90%) is presented. 3D finite element analyses were carried out using a hypoplastic model, which considers strain-dependent and path-dependent soil stiffness. The computed results have revealed that the maximum settlement decreased substantially when the excavation is carried out in the sand with higher relative density. This is because of reason that sand with higher relative density possesses higher stiffness. Moreover, the depth of the maximum settlement of the wall decreases as the sand become denser. The ground movement flow is towards excavation in retained side of the excavation. On the other hand the soil heave was induced below the formation level at excavation side. The maximum strain level of 2.4% was induced around the diaphragm wall.
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...
Numerical Analyses of Soil Deformations Around Deep Excavations
2013
In this study, the deep excavation of Cincin Station located along the Bağcılar-Otogar metro line which is currently under construction in Istanbul is modeled numerically. The excavation (depth 32.5 m) of the station is carried out with a surrounding slurry trench diaphragm wall and top-down construction method. The six slabs of the station building and the foundation mat are used as support elements. Lateral soil displacements are measured with inclinometers placed in the wall and nearby soil layers. The results of numerical analysis using soil profile and geotechnical parameters obtained from conventional field and laboratory tests and measured lateral displacements are compared. Then using the same soil model, soil displacements expected to occur if some other alternative excavation support systems were used is investigated. As alternative support systems use of steel pipes as internal bracing and a piled wall with pre-stressed tie-backs are considered. The calculated soil displacements for different support systems are compared with each other and the measured values. The effects of certain design parameters such as the rigidity of internal bracing elements, the pile diameters and the pre-stressing level of tie-backs are investigated through numerical analysis.
Measurement: Journal of the International Measurement Confederation, 2014
This paper determines the residual soil stiffness parameters at a deep excavation for a basement car park in the Kenny Hill Formation. Parametric studies revealed that the horizontal wall deflection at each stage of excavation could be reasonably predicted with a simple correlation between stiffness parameters with field standard penetration tests (SPTs) N value for Hardening Soil model. The correlation between tri-axial stiffness and oedometer stiffness with standard penetration test (SPT) N value is found to be 1.5 N (MPa) with unloading-reloading stiffness three times of tri-axial stiffness. The Hardening Soil model and the correlation obtained may be applied to similar soil conditions as the Kenny Hill Formation. © 2013 Elsevier Ltd. All rights reserved. http://ac.els-cdn.com/S0263224113004685/1-s2.0-S0263224113004685-main.pdf?\_tid=2a814a02-66e4-11e3-a9a7-00000aacb35f&acdnat=1387261770\_5b9bb01a3e94946e1000152bf39fcb9e http://www.sciencedirect.com/science/article/pii/S0263224113004685
Predicting and Controlling Ground Movements Around Deep Excavations
Proceedings of the DFI and EFFC 11th International Conference in the DFI Series: Geotechnical Challenges in Urban Regeneration, London, United Kingdom, 26th to 28th May 2010, 2010
Deep excavations frequently cause problems, and sometimes trigger catastrophic collapses, especially in soft clay. In principle, these problems are well understood, but designers may fall between the two stools of naive empiricism and over-elaborate finite element analysis (FEA). A new approach, Mobilizable Strength Design (MSD), has been developed to bridge this gap. MSD specifies deformation mechanisms tailored to each stage of construction. Each stage is analysed for energy balance, with incremental subsidence creating a drop of potential energy which must equal the work done deforming the soil and the support system. Incremental deformations are summed, while soil non-linearity is allowed for. The non-linear response of a representative shear stress-strain test is required, but estimates can be based on routine soil characterisation. It is demonstrated that MSD back-analyses not only fit FEA results for soft clay within ± 30%, but also fit the soil-structure deformation data of 110 field studies within a factor of 1.4. Finally, a new set of dimensionless groups is defined to characterise deep excavations in clay without the need for any analysis at all. These are used to chart the maximum wall displacements taken from the field database, and an elementary formula is proposed which predicts these 110 maximum displacements within a factor of 2.9. Guidelines are deduced for designers. In particular, it is shown that wall stiffness within the typical range of sheet-piles, secant piles and diaphragm walls has little or no effect on wall deformations.
Synopsis: Two main different approaches have been previously proposed to predict time dependent behaviour of soft soils. (I) end of primary consolidation is unique although creep starts simultaneously with primary consolidation (Hypothesis A); (II) As creep and primary consolidation commence at the same time and creep is a time dependant phenomenon, then end of primary consolidation cannot be unique (Hypothesis B). In Hypothesis A, soil settlement is divided into two parts: primary consolidation and secondary compression which follows by primary consolidation. In Hypothesis B, soil settlement is estimated based on elasto-viscoplastic constitutive model simulating soil creep and consolidation settlement simultaneously. In this study, details of first approach based on creep ratio () concept is discussed with a worked example to be used by practicing geotechnical engineers.