AbstractExcavation induces stress changes and soil movement on existing floating piled rafts and elevated pile groups. Limited investigation of the effects of deep excavations has resulted in an ...incomplete understanding of pile foundation performance at the serviceability state. A series of three-dimensional (3D) centrifuge model tests and numerical simulations are conducted in this study to investigate the influence of raft contact on the response of an existing 2×2 piled raft in comparison to that of an elevated pile group when subjected to an adjacent multipropped deep excavation in dry sand. After rising g, an applied axial load was supported by 18% by the raft and 82% by the piles in the piled raft foundation prior to excavation. Owing to stress release and soil movement caused by the 8-m-deep excavation, the pile head load increased by 21% and 3% for the pile closer to the excavation for the piled raft and pile group foundations, respectively. Analysis of pile–soil relative settlement and raft contact pressure shows that a gap formed between the raft and ground surface in the piled raft, resulting in a load transfer from the raft to the embedded piles. A 20% larger settlement was seen in the piled raft foundation than in the pile group, to further mobilize shaft and end bearing resistances for the maintenance of vertical equilibrium. Moreover, 30% additional pile bending moment was induced due to excavation.
Tunnel driving inevitably induces changes in stress and deformation in the ground, which could cause ultimate and serviceability problems to an adjacent tunnel. The effects of induced stress on an ...existing tunnel and crossing-tunnel interaction are still not fully understood. In this study, a series of three-dimensional centrifuge tests were carried out to investigate the responses of an existing tunnel in sand to the excavation of a new tunnel perpendicularly below it. Three-dimensional tunnel advancement was simulated using a novel technique that considers the effects of both volume and weight losses. This novel technique involves using a “donut” to control volume loss and mimic soil removal in-flight. To improve fundamental understanding of the stress transfer mechanism during the new tunnel advancement, measured results were back-analyzed three-dimensionally using the finite element method. The maximum measured settlement of the existing tunnel induced by the new tunnel constructed underneath was about 0.3% of tunnel diameter, which may be large enough to cause serviceability problems. The observed large settlement of the existing tunnel was caused not only by a sharp reduction in vertical stress at the invert, but also by substantial stress transfer of overburden pressure at the crown. The section of the existing tunnel directly above the new tunnel was compressed vertically because the incremental normal stress on the existing tunnel was larger in the vertical direction than in the horizontal direction. The tensile strain and shear stress induced in the existing tunnel exceeded the cracking tensile strain and allowable shear stress limit given by the American Concrete Institute.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Advances in single-cell technologies have enabled high-resolution dissection of tissue composition. Several tools for dimensionality reduction are available to analyze the large number of parameters ...generated in single-cell studies. Recently, a nonlinear dimensionality-reduction technique, uniform manifold approximation and projection (UMAP), was developed for the analysis of any type of high-dimensional data. Here we apply it to biological data, using three well-characterized mass cytometry and single-cell RNA sequencing datasets. Comparing the performance of UMAP with five other tools, we find that UMAP provides the fastest run times, highest reproducibility and the most meaningful organization of cell clusters. The work highlights the use of UMAP for improved visualization and interpretation of single-cell data.
AbstractTunnel excavation inevitably induces stress changes in the surrounding soil leading to significant ground movements and additional stress in nearby pipelines. Most previous studies simplified ...tunnel–pipe interaction as a plane strain problem and focused on the case in which the pipeline intersects the tunnel perpendicularly. In this study, centrifuge tests were conducted to investigate the three-dimensional response of the ground and pipeline to tunneling, considering different pipeline orientations with respect to the tunneling direction. When the tunnel face was located within ±1.25D (tunnel diameter) away from the monitoring section, the ground settlement and pipe strain induced were more than 95% of the maximum recorded. When the pipeline intersected the tunnel perpendicularly, the maximum pipe strain always occurred above the tunnel centerline. However, when the pipeline intersected the tunnel at an angle of 60°, the location of maximum pipe strain shifted as the tunnel advanced. The maximum tunneling-induced pipe settlement and strain were up to 20% greater in this case than when the pipeline intersected the tunnel perpendicularly. The pipe settlement and strain may be underestimated if an oblique intersection is simply taken as a perpendicular one.
AbstractA full-scale test was carried out to investigate the interactions between an energy pile and four traditional piles connected to the same overlying reinforced beam. A series of sensors was ...installed in the energy pile, surrounding soil, traditional piles, and beam to monitor their thermal and mechanical responses. The interactions between the energy pile and the traditional piles and concrete beam were analyzed. The results show that, when the average temperature of the energy pile increased by 20°C, a notable axial stress of −4.4 MPa was induced at the top of the energy pile because of the interaction between the energy pile and the beam. Moreover, an additional axial load was observed in the four traditional piles because of their interactions with the energy pile, even though they were not subjected to thermal loading. Significant tensile axial loads of 820 and 663 kN were induced at the top of the two traditional piles adjacent to the energy pile, which were approximately five times larger than those induced at the top of the other two more distant traditional piles.
Basement excavation may induce unsymmetrical and highly skewed loadings and (or) stress changes in an existing tunnel, not only in the transverse, but also in the longitudinal direction of the ...tunnel. Although basement–tunnel interaction has attracted intense academic interest recently, it is often simply treated as a plane strain problem. In this study, however, based on a dimensional analysis of the governing parameters, two three-dimensional centrifuge tests were designed and carried out in dry sand to investigate the effects of a basement excavation on an existing tunnel located in two horizontal offsets in relation to the basement. In addition, a preliminary three-dimensional numerical analysis was conducted to back-analyse the centrifuge test and to investigate the effects of the tunnel cover-to-diameter and unloading ratios on the existing tunnel. For the specific conditions simulated and soil type tested, a maximum heave of about 0.07% of the final depth of the basement excavation (H
e
) was induced in the tunnel that ran parallel to and beneath the basement. On the contrary, a maximum settlement of 0.014% H
e
was induced in the tunnel located at the side of the basement. For the former tunnel, the influence zone by the basement excavation on vertical tunnel displacement along the longitudinal direction was 1.2L (basement length). By inspecting the measured strains in the longitudinal direction of the existing tunnel, it was found that the inflection point, where the shear force is at a maximum, was located at 0.8L away from the basement centre. Due to stress relief from the basement excavation, the tunnel located directly beneath the basement was vertically elongated, but the one that lay at the side of the basement was distorted. A preliminary numerical parametric study found that tunnel heave decreased as the cover-to-diameter ratio increased, but at a reduced rate.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
AbstractDeep excavations inevitably induce stress relief and soil movement, which may affect the safety and serviceability of nearby existing pile foundations. Although the effects of excavation on ...adjacent piles have been studied, excavation-induced pile settlement and change of shaft resistance deserve more investigation. In this paper, centrifuge simulation of the effects of multipropped excavation in-flight on vertically loaded floating piles in sand is reported. Piles were restrained in terms of rotation and lateral deflection at or above ground-surface level in three different tests. In addition, three-dimensional numerical analyses using an advanced soil model were carried out to back analyze the centrifuge tests. A pile-raft settled a similar amount due to excavation as a free-head pile and an elevated pile group. During excavation, a downward load-transfer mechanism in the piles can be identified. Shaft resistance in the upper part of the pile decreases due to the downward soil movement and the reduction of normal stress acting on the pile. In order to maintain vertical equilibrium, the pile has to settle to mobilize higher shaft resistance in the lower part of the pile and toe resistance. Lateral restraints imposed on the pile head have a significant influence on induced pile bending moment. Induced bending moment due to excavation can exceed the pile bending capacity.
AbstractMultiple barriers with basal clearance are usually adopted in engineering practice to mitigate large volumes of debris flows. This approach allows for sufficient discharge and minimizes the ...need for cleaning and maintenance over the service life of the barriers. Despite the effectiveness, the design of basal clearance is still based on empirical methods, which can lead to uncertainty in safety. In this study, a new dimensionless overflow number Nof is proposed for designing dual rigid barriers with basal clearance and validated with physical and numerical results. The physical tests were conducted using a 28 m long flume model. A finite element model calibrated using the physical test results is utilized for numerical parametric study to investigate the effects of basal clearance on debris flow impact force against dual barriers. Physical and numerical results reveal that Nof can serve to determine whether the impact force on the second barrier is governed by basal discharge or overflow from the first barrier. A threshold value of Nof=1 can be used to design dual barriers with basal clearance to achieve the lowest impact force on the second barrier. The proposed Nof also enables engineers to predict the impact force on the second barrier by only considering the impact force from basal discharge.
Three-dimensional coupled consolidation analysis is conducted to gain insight into the response of a 2×2 floating pile group adjacent to deep excavation in soft clay. By using a validated finite ...element model, the influence of the excavation depth, pile length, pile group location from excavation, the supporting system stiffness, soil state and permeability, and working load are systematically studied. The analysis revealed that the maximum settlement occurs when the pile group is founded at the excavation level and at a distance of 0.75-times the excavation depth, although the induced bending moment is minimum. In contrast to pile group settlement, tilting is maximum when it gets closer to the wall and minimum at a distance of 0.75-times the excavation depth. It is also observed that the influence of system stiffness is more pronounced for the flexible wall and when the pile group is located at the excavation level. Applied working load influences pile group settlement but has relatively minor effects on pile group tilting. Excess negative pore water pressures are generated in the soil elements due to excavation. Pile group experiences progressive long term settlement with the dissipation of excess negative pore water pressure.
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