Characteristics of wall deflections and ground surface settlements in Shanghai

2005 ◽  
Vol 42 (5) ◽  
pp. 1243-1254 ◽  
Author(s):  
Zhong W Wang ◽  
Charles WW Ng ◽  
Guo B Liu
Keyword(s):  
Similar Case ◽  
Soft Clay ◽  
Three Dimensional ◽  
Ground Surface ◽  
Maximum Displacement ◽  
Aspect Ratios ◽  
Surface Settlements ◽  
Shanghai Metro ◽  
Corner Effects ◽  
Ground Settlements

The characteristics of wall deflections and surface ground settlements at six deep multi-strutted excavations in Shanghai soft soils were studied and compared with those of similar case histories reported worldwide, particularly in Taipei and Singapore. The measured wall deflections at the six metro stations of the Pearl II Circle Line show a typical bulging profile (or deep-seated shape) at the end of the excavation. The ratio between the measured maximum wall deflection and the depth of the excavation (δhm /H) in Shanghai was <0.007, which was similar to the ratio measured in Taipei, but it was substantially smaller than the Peck bounding limit of 0.01. At each station, the measured maximum displacement was <0.45% of the final excavation depth. Because of the large aspect ratios of the underground excavations, no significant three-dimensional effects or corner effects were observed. The measured maximum settlements of the six metro excavations fell within zone I of the Peck classical normalized settlement-distance chart. These small measured settlements were consistent with the small measured wall deflections. The observed relatively small maximum wall deflections can likely be attributed to the use of prestressed struts, the constant adjustment of the stresses to about 0.7 times the total vertical stress during the excavation, and the short horizontal span of the excavation.Key words: multi-strutted excavations, soft clay, Shanghai, metro stations, horizontal deflection, settlement.

Field Performance of a Deep Multi-Strutted Excavation in Hangzhou Soft Clays

2011 ◽  
Vol 243-249 ◽  
pp. 2324-2327
Author(s):  
Hong Wei Ying ◽  
Yong Wen Yang ◽  
Xin Yu Xie
Keyword(s):  
Large Scale ◽  
Soft Soil ◽  
Soft Clay ◽  
Ground Surface ◽  
Field Performance ◽  
Soft Clays ◽  
Soil Clays ◽  
History Of ◽  
Creep Deformations ◽  
Surface Settlements

A case history of a deep multi-strutted soft clay excavation in Hangzhou is presented in this paper. What makes it particular interest is its three characteristics: large scale, deep excavation and very soft clays. The excavated area was about 99750 square meters. The depth of excavation was 12.85 m. 4 m below the ground surface located about 24 m very soft soil clays. Wall deflections and ground settlements were measured and compared with similar case histories worldwide. It was shown that the maximum horizontal deformations of the excavation was very large which this excavation reached to 220 mm. “Creep” deformations occurred apparently during the curing of the bottom slab of the basement. The distributions of the surface settlements seemed to be parabolic, and the settlement influence zone could reach to a distance of more than 2H, whereHis the final excavation depth. The ratio between the maximum ground settlement and the maximum horizontal deformation of the wall is about 0.6.

Studies for Deformation of Slurry Shield Construction under Across and Parallel Existing Tunnel

2012 ◽  
Vol 204-208 ◽  
pp. 1435-1438
Author(s):  
Yong Qi Ma ◽  
Yin Ning ◽  
Yi Dong ◽  
Feng Lin Wu
Keyword(s):  
Three Dimensional ◽  
Ground Surface ◽  
Initial Position ◽  
Practical Significance ◽  
Engineering Construction ◽  
Dimensional Finite Element ◽  
Survey Results ◽  
Three Dimensional Finite Element ◽  
Slurry Shield ◽  
Surface Settlements

The method combining the construction survey and the numerical simulation is proposed in the paper to accurately obtain the deformation of the slurry shield construction under across and parallel existing tunnel. The surface settlements of the engineering construction initial position are surveyed. The reliability of the three dimensional finite element models is verified by comparing with the survey results. The deformation variation of the existing tunnel and ground surface are obtained by the elastoplasticity nonlinear calculations, showing the feasibility and effectiveness of the proposed method and the credibility and accuracy of the calculated results. Meanwhile, the measures of control deformation are presented. The surveyed settlements after the construction process of implementing measures are smaller than those calculated, indicating the effect obviously of the measures which has practical significance.

scholarly journals Investigation of Three-Dimensional Deformation Behavior due to Long and Large Excavation in Soft Clays

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Chunhui lou ◽  
Tangdai Xia ◽  
Nianwu Liu ◽  
Xiaonan Gong
Keyword(s):  
Deformation Behavior ◽  
Soft Clay ◽  
Three Dimensional ◽  
Significant Inhibition ◽  
Soft Clays ◽  
Extensive Field ◽  
Partition Walls ◽  
Reduction Coefficient ◽  
Cement Soil ◽  
Ground Settlements

By analyzing the extensive field data from a long and large excavation in soft clay, this study investigates the three-dimensional deformation behavior induced by excavation. Significant inhibition effects of corner on both wall deflections and ground settlements were observed and quantified. Thus, a modified function for estimating the distribution of deformation parallel to the excavation is proposed and evaluated. Further analyzing shows that the pipeline settlement can be well estimated by the modified function combining with settlements profile proposed by Hsieh and Ou, and the reduction coefficient is about 0.8; the calculated maximum distortion of the pipeline can provide reliable reference. In addition, it is found that the cement-soil partition walls can also considerably reduce the wall deflections and ground settlements even after the part that is above the excavation base were removed.

Effects of the construction sequence of twin tunnels at different depths on an existing pile

2014 ◽  
Vol 51 (2) ◽  
pp. 173-183 ◽  
Author(s):  
C.W.W. Ng ◽  
H. Lu
Keyword(s):  
Three Dimensional ◽  
Ground Surface ◽  
Pile Capacity ◽  
Tunnel Excavation ◽  
Construction Sequence ◽  
Pile Shaft ◽  
Different Depths ◽  
Pile Settlement ◽  
Surface Settlements ◽  
Twin Tunnels

Any tunnelling process inevitably induces changes in stress in the ground and may adversely affect nearby pile foundations. The interaction between tunnelling and an existing pile has been investigated by researchers and a certain amount of fundamental understanding has been gained. However, the effects of different tunnel excavation sequences on an adjacent pile remain to be understood. In this paper, a series of three-dimensional centrifuge model tests and numerical back-analyses were carried out to investigate the effects of construction sequence of twin tunnels on an existing pile in dry sand. Two tunnelling sequences were investigated: (i) a sequence involving tunnelling near the pile toe followed by tunnelling near the mid-depth of the pile shaft (i.e., test TS); (ii) sequence involving tunnelling near the mid-depth of the pile shaft followed by tunnelling near the pile toe (i.e., test ST). The measured cumulative pile settlement was about 33% larger for tunnelling sequence ST than for tunnelling sequence TS. Due to different tunnelling sequences, the apparent losses of pile capacity were 40% and 29% for sequences ST and TS, respectively. Although the computed reductions in normal stress acting on the pile induced by twin tunnelling were almost the same in tests TS and ST, tunnelling near the pile toe induced a larger decrease in the end-bearing and shaft resistances at the lower part of the pile in test ST than in test TS. In contrast to the measured pile head settlements, different tunnelling sequences had a limited effect on measured ground surface settlements and additional bending moments in the pile.

Effects of pile extraction and refilling with cement slurry on ground settlements

2013 ◽  
Vol 50 (3) ◽  
pp. 343-349 ◽  
Author(s):  
Y.D. Wu ◽  
J. Liu ◽  
Charles W.W. Ng
Keyword(s):  
Ground Surface ◽  
Surface Settlement ◽  
Beam Extraction ◽  
Ground Settlement ◽  
Cement Slurry ◽  
Ground Surface Settlement ◽  
Minimal Data ◽  
Maximum Surface Settlement ◽  
Surface Settlements ◽  
Ground Settlements

Secant pile walls reinforced with steel I-beams are widely used worldwide. Although ground surface settlement caused by the installation of secant pile walls has been investigated, there is minimal data available on ground surface settlement due to extraction of steel I-beams from secant pile walls. This note aims to investigate the effectiveness of cement slurry refilling on reducing ground settlements during extraction of steel I-beams. Measured ground surface settlements during the extraction of steel I-beams from secant pile walls with and without cement slurry refilling are reported, discussed, and explained. Two different influence zones due to steel I-beam extraction can be identified. Ground settlement due to steel I-beam extraction can be minimized with the refilling of cement slurry. By using such a refilling technique, measured maximum surface settlement was reduced by 70%. The average measured settlement rate was reduced by 61%.

Contrôle de la stabilité des remblais par la mesure des déplacements horizontaux

1974 ◽  
Vol 11 (1) ◽  
pp. 182-201 ◽  
Author(s):  
René Marche ◽  
Robert Chapuis
Keyword(s):  
Factor Of Safety ◽  
Soft Clay ◽  
Ground Surface ◽  
Soft Layer ◽  
The Stability ◽  
Horizontal Displacements

The horizontal displacements measured at the toe of eight embankments are analyzed as a function of the factor of safety. The embankments are built on layers of soft clay. Only the undrained stage is studied.When the factor of safety of the embankments is higher than about 1.4, the horizontal displacements on the ground surface, at the toe of the embankment seem to follow an elastic law which is highly dependent on the ratio of the thickness of the soft layer to the width of the embankment. When the factor of safety is lower than about 1.4, the horizontal displacements do not follow an elastic law, they increase considerably. Consequently, it is suggested that the horizontal displacements be precisely measured at the toe of embankments during construction. These measurements are simple and sensitive to the approach of failure, they can be efficiently used to control the stability of embankments. This study also gives some information concerning the variation of horizontal displacements versus depth.

Stabilized hp-DGFEM for Incompressible Flow

2003 ◽  
Vol 13 (10) ◽  
pp. 1413-1436 ◽  
Author(s):  
D. Schötzau ◽  
C. Schwab ◽  
A. Toselli
Keyword(s):  
Boundary Layer ◽  
Discontinuous Galerkin ◽  
Incompressible Flow ◽  
Discontinuous Galerkin Methods ◽  
Stokes Problem ◽  
Three Dimensional ◽  
Stability Result ◽  
Approximation Order ◽  
Galerkin Methods ◽  
Aspect Ratios

We consider stabilized mixed hp-discontinuous Galerkin methods for the discretization of the Stokes problem in three-dimensional polyhedral domains. The methods are stabilized with a term penalizing the pressure jumps. For this approach it is shown that ℚk-ℚk and ℚk-ℚk-1 elements satisfy a generalized inf–sup condition on geometric edge and boundary layer meshes that are refined anisotropically and non quasi-uniformly towards faces, edges, and corners. The discrete inf–sup constant is proven to be independent of the aspect ratios of the anisotropic elements and to decrease as k-1/2 with the approximation order. We also show that the generalized inf–sup condition leads to a global stability result in a suitable energy norm.

Unravelling the large-scale circulation modes in turbulent Rayleigh–Bénard convection

2021 ◽  
Author(s):  
Susanne Horn ◽  
Peter J. Schmid ◽  
Jonathan M. Aurnou
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Mean Flow ◽  
Large Scale Circulation ◽  
Convective Systems ◽  
Aspect Ratios ◽  
Mode Decomposition ◽  
Coherent Flow Structure

Abstract The large-scale circulation (LSC) is the most fundamental turbulent coherent flow structure in Rayleigh-B\'enard convection. Further, LSCs provide the foundation upon which superstructures, the largest observable features in convective systems, are formed. In confined cylindrical geometries with diameter-to-height aspect ratios of Γ ≅ 1, LSC dynamics are known to be governed by a quasi-two-dimensional, coupled horizontal sloshing and torsional (ST) oscillatory mode. In contrast, in Γ ≥ √2 cylinders, a three-dimensional jump rope vortex (JRV) motion dominates the LSC dynamics. Here, we use dynamic mode decomposition (DMD) on direct numerical simulation data of liquid metal to show that both types of modes co-exist in Γ = 1 and Γ = 2 cylinders but with opposite dynamical importance. Furthermore, with this analysis, we demonstrate that ST oscillations originate from a tilted elliptical mean flow superposed with a symmetric higher order mode, which is connected to the four rolls in the plane perpendicular to the LSC in Γ = 1 tanks.

The Influence of Needle Eccentric Motion On Hole-to-Hole Injection Characteristics of a Two-Layered 8-Hole Diesel Injector

2021 ◽  
Author(s):  
Tianyu Jin ◽  
Yu Sun ◽  
Chuqiao Wang ◽  
Adams Moro ◽  
Xiwen Wu ◽  
...  
Keyword(s):  
Fuel Injection ◽  
Lateral Displacement ◽  
Three Dimensional ◽  
Injection Rate ◽  
Hole Injection ◽  
Three Dimensional Model ◽  
Maximum Displacement ◽  
Fuel Flow ◽  
Diesel Injection ◽  
Eccentric Motion

Abstract The stringent emission regulations diesel engines are required to meet has resulted in the usage of multi-hole and ultra-multi-hole injectors, nowadays. In this research study, a double layered 8-hole diesel injection nozzle was investigated both numerically and experimentally. A three-dimensional model of the nozzle which was validated with experimental results was used to analyze the injection characteristics of each hole. The validation was conducted by comparing experiment and simulation injection rate results, acquired simultaneously from all the holes of the injector and the model. The fuel flow rates of the lower layered holes are higher than those of the upper layered holes. Two different needle eccentricity models were established. The first model only included the lateral displacement of the needle during needle lift. The needle reached maximum displacement at full needle lift. The second model considered the needle inelastic deformation into consideration. The needle radially displaces and glides along with the needle seat surface during needle lift. When the eccentricity reached maximum in the radial direction, the needle began to lift upwards vertically. The differences in injection characteristics under the different eccentricity models were apparent. The results indicated that the cycle injection quantity, fuel injection rate and cavitation of each hole were affected during the initial lifting stages of the needle lift. As the eccentricity of the needle increases, the injection rate uniformity from the nozzle hole deteriorates. The result showed that the upper layered holes were affected by the needle eccentricity during needle lift.

RESPONSE OF SOFT CLAY STRATA AND CLAY-PILE-RAFT SYSTEMS TO SEISMIC SHAKING

2007 ◽  
Vol 01 (03) ◽  
pp. 233-255 ◽  
Author(s):  
SUBHADEEP BANERJEE ◽  
SIANG HUAT GOH ◽  
FOOK HOU LEE
Keyword(s):  
Soft Clay ◽  
Ground Surface ◽  
Model Tests ◽  
Pile Foundations ◽  
Kaolin Clay ◽  
Natural Period ◽  
Soil System ◽  
Centrifuge Model ◽  
Inertial Loading ◽  
Centrifuge Model Tests

The behavior of pile foundations under earthquake loading is an important factor affecting the performance of structures. Observations from past earthquakes have shown that piles in firm soils generally perform well, while the performance of piles in soft or liquefied ground can raise some questions. Centrifuge model tests were carried out at the National University of Singapore to investigate the response of pile-soil system under three different earthquake excitations. Some initial tests were done on kaolin clay beds to understand the pure clay behavior under repetitive earthquake shaking. Pile foundations comprising of solid steel, hollow steel and hollow steel pile filled with cement in-fill were then embedded in the kaolin clay beds to study the response of clay-pile system. Superstructural inertial loading on the foundation was modeled by fastening steel weight on top of the model raft. The model test results show that strain softening and stiffness degradation feature strongly in the behaviour of the clay. In uniform clay beds without piles, this is manifested as an increase in resonance periods of the surface response with level of shaking and with successive earthquakes. For the pile systems tested, the effect of the surrounding soft clay was primarily to impose an inertial loading onto the piles, thereby increasing the natural period of the piles over and above that of the pile foundation alone. There is also some evidence that the relative motion between piles and soil leads to aggravated softening of the soil around the pile, thereby lengthening its resonance period of the soil further. The centrifuge model tests were back-analyzed using the finite element code ABAQUS. The analysis shows that the simple non-linear hypoelastic soil model gave reasonably good agreement with the experimental observations. The engineering implication arising from this study so far is that, for the case of relatively short piles in soft clays, the ground surface motions may not be representative of the raft motion. Other than the very small earthquakes, the raft motion has a shorter resonance period than the surrounding soil.

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