Effects of Tunneling-Induced Ground Movements on Stability of Piled Raft Foundation: Three-Dimensional Finite-Element Approach
01 Aug 2020-International Journal of Geomechanics (American Society of Civil Engineers)-Vol. 20, Iss: 8, pp 04020104
TL;DR: In this article, the authors discuss the need to construct tunnels within the vicinity of high-rise buildings supported on piled raft foundations, as a consequence, ground movements must be taken into account.
Abstract: Across the globe, rapid urbanization demands the construction of tunnels within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements ...
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TL;DR: In this paper, simplified analytical solutions for longitudinal tunnel settlements induced by axially loading single pile and pile group were proposed based on the extended shear shear (ESH) model.
Abstract: This paper proposes simplified analytical solutions for longitudinal tunnel settlements induced by axially loading single pile and pile group. The solutions are based on the extended shear ...
4 citations
TL;DR: In this article , the authors investigated the responses of two-by-two piled rafts to twin side-byside tunnels either near the mid-depth of the pile shaft or adjacent to or below the pile toe in stiff clay.
Abstract: Due to urbanization, development of society, and growth of population, there are new demands for tunneling technique to facilitate the public transport as well as high-rise buildings to accommodate an increasing population. Piled foundations are commonly preferred for the construction of high-rise buildings. It is, therefore, unavoidable that tunnels must be constructed near extant buildings resting on piled foundations. Inevitable movement of the ground due to stress changes induced by a tunnel can induce additional settlement and reduce the load-carrying capacity of nearby pile foundation systems. This numerical parametric study investigates the responses of two-by-two piled raft to twin side-by-side tunnels either near the mid-depth of the pile shaft or adjacent to or below the pile toe in stiff clay. In addition, it investigates the effects of different group configurations of the piled raft and elevated pile group. The ground in all the finite-element analyses was modeled using the hypoplasticity (clay) model because of its ability to capture degradation of soil stiffness at a small-strain level. Twin tunneling below the pile and near the middepth of the pile shaft caused the largest and smallest settlement of the piled raft, respectively. Unlike induced piled raft settlement, the most significant transverse tilting of the raft is induced after the advancement of the first tunnel. After the twin tunneling near the pile shaft was completed, the raft was separated from the ground, and a portion of the working load carried by the raft was transferred to the piles. The computed results have revealed that the induced settlement of the elevated pile group was significantly larger than that of the piled raft. A significant effect number of piles in the group was found on the piled raft responses to tunneling.
3 citations
TL;DR: In this article, a simplified two-stage approach is employed to derive the vertical and lateral responses of the existing pile during adjacent pile installation, and extensive parameter studies are conducted to systematically discuss the variation of the behavior of the single pile and pile group.
1 citations
TL;DR: In this paper, a detailed 3D numerical model of the double-line tunnels of the Qingdao Metro Line 4 passing under the Cuobuling station was taken as the engineering background, and the deformation of the station structure due to tunnel excavation was analyzed.
Abstract: In the construction of the tunnel passing through the existing structure at an ultra-close distance, the existing structure will produce obvious deformation. It is very important to understand the deformation characteristics of the existing upper structure at different positions, especially to ensure the safety of the upper structure and improve the effectiveness of tunnel construction. In this study, the double-line tunnels of Qingdao Metro Line 4 passing under the Cuobuling station were taken as the engineering background, and a detailed 3D numerical model was established. This study comprehensively considered the on-site construction process, including grouting hardening, stress release of the excavated rock mass, grouting pressure and so on. The influence of tunnel excavation on the ground settlement was compared with or without a station structure, and the result was fitted with an empirical formula. Finally, the deformation of the station structure due to the excavation of the double-line tunnels was analyzed. The results of the analysis were as follows: (1) In the presence of the station structure, the excavation of the tunnels had a significant impact on the surface settlement. (2) The settlement of the sidewall caused by the excavation of the left-line tunnel was greater than that of the right-line tunnel, and the settlement at the junction of the sidewall and the bottom plate was smaller than that at other positions of the sidewall. (3) Compared with the roof and middle slabs, the floor of the station was more susceptible to the influence of tunnel excavation. Overall, the research could provide guidance and reference for similar double-line tunnels through existing stations.
1 citations
TL;DR: In this paper , the authors present the application of the finite element method integrated with Terzaghi's principle for settlement estimation of a building after the construction of a tunnel, including the effect of terzaghi principle, and demonstrate the need for a minimum of three methodological states to estimate said settlement.
Abstract: This study presents the application of the finite element method integrated with Terzaghi’s principle. The definition of a model in oedometric or confinement conditions for settlement estimation of a building after the construction of a tunnel, including the effect of Terzaghi’s principle, is an unresolved problem. The objectives of this work include the demonstration of the need for a minimum of three methodological states to estimate said settlement. For this, a specific methodology is applied to a case study, with eight load steps and four types of coarse-grained soils. In the studied case, two layers of 50 m and 5 m with different degrees of saturation are overlaying an assumed impermeable rock layer. The excavation of a tunnel of 15 m in diameter at a depth of 30 m with drainage lining inside the tunnel is assumed. The minimum distance from the tunnel’s outline to the mat foundation is 15.8 m. It is determined that the settlement, according to Terzaghi’s principle, is around 11% of the total settlement for the most compacted soil types, reaching 35% for the loose soil type, from the tunnel’s outline. In the mat foundation, it implies an increase in the differential settlement of up to 12%. It shows a nonlinear relationship between some of the variables in the analysis. To detect the collapse due to uplifting the tunnel invert, it was determined that it was not appropriate to model in oedometric conditions. The novelty of the investigation relies on identifying and determining the need for a minimum of three states for methodological purposes for a proper quantification of the total settlement: (i) before the construction of the tunnel, (ii) immediately after the excavation of the tunnel, but without groundwater inflow into the tunnel, and (iii) after the tunnelling, with stabilised groundwater inflow into the tunnel.
1 citations
References
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TL;DR: In this article, the authors used available field measurements and centrifuge model test data to determine how the widths of the settlement profiles and the magnitudes of settlement vary with depth above tunnels constructed in clays.
Abstract: Designers assessing the possible effect of tunnelling on structures relatively close to the tunnel crown need to know how subsurface settlement profiles develop, and how these relate to surface settlement profiles. The effect on piled foundations or existing tunnels depends on the width of the subsurface settlement profile and on the magnitude of the settlement. This note uses available field measurements and centrifuge model test data to determine how the widths of the settlement profiles and the magnitudes of settlement vary with depth above tunnels constructed in clays. The results reveal a fairly consistent pattern of behaviour: the width of the subsurface settlement troughs at depth is significantly greater than would be predicted by assuming a constant trough width parameter K of 0.5. Smaller more realistic subsurface settlements and strains will be predicted if account is taken of the proportionally wider trough widths at depth.
464 citations
272 citations
TL;DR: In this paper, a simple numerically based procedure for the estimation of the so-called gap parameter is described, which represents the vertical displacement above the crown of the tunnel and is a m...
Abstract: A simple, numerically based procedure for the estimation of the so-called gap parameter is described. The gap parameter represents the vertical displacement above the crown of the tunnel and is a m...
259 citations
TL;DR: In this article, the impact of urban tunnel construction on adjacent pile foundations is analyzed using an elastoplastic three-dimensional finite element modeling, and it is shown that tunneling induces significant internal forces in adjacent piles.
Abstract: This paper concerns analysis of the impact of construction of urban tunnels on adjacent pile foundations. It is carried out using an elastoplastic three-dimensional finite element modelling. Numerical simulations are performed in two stages, which concern, respectively, the application of the pile axial loading and the construction of the tunnel in presence of the pile foundations. Analysis is carried out for both single piles and groups of piles. Results of numerical simulations show that tunneling induces significant internal forces in adjacent piles. The distribution of internal forces depends mainly on the position of the pile tip regarding the tunnel horizontal axis and the distance of the pile axis from the centre of the tunnel. Analysis of the interaction between tunneling and a group of piles reveals a positive group effect with a high reduction of the internal forces in rear piles.
169 citations
TL;DR: In this article, the effects of tunnelling on nearby single piles in dense dry sand were investigated, and the surface settlement profiles recorded during tunnel-induced volume loss were discussed, as well as the settlement of piles installed at various distances from the tunnel.
150 citations