Numerical analysis of a multipropped excavation in stiff clay

1998 ◽  
Vol 35 (1) ◽  
pp. 115-130 ◽  
Author(s):  
Charles WW Ng ◽  
B Simpson ◽  
M L Lings ◽  
DFT Nash
Keyword(s):  
Numerical Analysis ◽  
Small Strain ◽  
Bending Moments ◽  
Deep Excavation ◽  
Case Record ◽  
Highly Nonlinear ◽  
Nonlinear Stress ◽  
Simple Drainage ◽  
Stiff Clay ◽  
Very High

This paper presents the procedures and the results of numerical analyses of a multipropped deep excavation at Lion Yard, Cambridge, using the nonlinear Brick model. The computed results are compared with the comprehensive case record. The observed small deflections and bending moments of the wall, low prop forces, and relatively small ground movements during the main excavation have been taken into account. Shear strains which developed around the site during the main excavation were generally less than 0.3%. Significant reduction of lateral stress in the ground during wall installation and the highly nonlinear stress-strain characteristics of the Gault Clay are the chief reasons for the observed unusual behaviour. The Gault Clay exhibits first yield at a threshold shear strain of about 0.001%, beyond which the stiffness deteriorates significantly from an initial very high value. This high stiffness at very small strains may be due to cementation bonding between soil particles, as a result of the presence of calcium carbonate. Simple drainage assumptions for the stiff fissured clay on both sides of the diaphragm wall appear to be inadequate for design analyses.Key words: numerical analysis, multipropped excavation, Gault Clay, nonlinear brick model, small strain stiffness.

scholarly journals Numerical analysis on zone-divided deep excavation in soft clays using a new small strain elasto–plastic constitutive model

2021 ◽  
Author(s):  
Afnan Younis Tanoli ◽  
Bin Yan ◽  
Yong-lin Xiong ◽  
Guan-lin Ye ◽  
Usama Khalid ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
Constitutive Model ◽  
Small Strain ◽  
Deep Excavation ◽  
Soft Clays

scholarly journals Structural rehabilitation using high damping rubber bearing (HDRB)

2021 ◽  
Vol 54 (1) ◽  
pp. 49-57
Author(s):  
Ali Vatanshenas ◽  
Takahiro Mori ◽  
Nobuo Murota
Keyword(s):  
Time History ◽  
Residential Building ◽  
Small Strain ◽  
Integration Time ◽  
Absolute Maximum ◽  
Base Shear ◽  
Structural Behaviour ◽  
Highly Nonlinear ◽  
Nonlinear Stress ◽  
High Damping Rubber

High damping rubber bearings show highly nonlinear stress-strain behaviour. Deformation-history integral (DHI) model which can estimate small strain stiffness degradation and nonlinear plasticity via a relatively simple innovative formulation is implemented in this study to model HDRB as the rehabilitation method for a seismically vulnerable building. Considered structure in this study is a three-dimensional, four-story steel frame residential building with a concentrically braced system. Nonlinear direct integration time history analysis and plastic hinges approach were implemented to evaluate structural behaviour of considered structure. It was observed that structural responses enhanced significantly after rehabilitation. Absolute maximum base shear values decreased 61.8% and 92.2% in the worst and best cases, respectively. Most of structural elements remained elastic after rehabilitation and required performance level was satisfied.

3D numerical analysis of pile response due to soil movements induced by an adjacent deep excavation

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Tamir Amari ◽  
Mohamed Nabil Houhou
Keyword(s):  
Numerical Analysis ◽  
Parametric Study ◽  
Pile Group ◽  
Small Strain ◽  
Nonlinear Behaviour ◽  
Single Pile ◽  
Deep Excavation ◽  
Braced Excavation ◽  
Content Type ◽  
Pile Response

Purpose This paper aims to investigate single pile and pile group responses due to deep braced excavation-induced soil movement in soft clay overlying dense sand. The analysis focuses first on the response of vertical single pile in terms of induced bending moment, lateral deflection, induced axial force, skin resistance distribution and pile settlement. To better understand the single pile behaviour, a parametric study was carried out. To provide further insights about the response of pile group system, different pile group configurations were considered. Design/methodology/approach Using the explicit finite element code PLAXIS 3 D, a full three-dimensional numerical analysis is carried out to investigate pile responses when performing an adjacent deep braced excavation. The numerical model was validated based on the results of a centrifuge test. The relevance of the 3 D model is also judged by comparison with the 2 D plane strain model using the PLAXIS 2 D code. Findings The results obtained allowed a thorough understanding of the pile response and the soil–pile–structure interactions phenomenon. The findings reveal that the deep excavation may cause appreciable bending moments, lateral deflections and axial forces in nearby piles. The parametric study showed that the pile responses are strongly influenced by the excavation depth, relative pile location, sand density, excavation support system and pile length. It also showed that the response of a pile within a group depends on its location in relation to the other piles of the pile group, its distance from the retaining wall and the number of piles in the group. Originality/value Unlike previous studies which investigated the problem in homogeneous geological context (sand or clay), in this paper, the pile response was thoroughly studied in a multi-layered soil using 3 D numerical simulation. To take into account the small-strain nonlinear behaviour of the soil, the Hardening soil model with small-strain stiffness was used in this analysis. For a preliminary design, this numerical study can serve as a practical basis for similar projects.

Temporary and Permanent Earth Anchors: Three Monitored Installations

1974 ◽  
Vol 11 (2) ◽  
pp. 257-268 ◽  
Author(s):  
William A. Trow
Keyword(s):  
Load Transfer ◽  
Fine Sand ◽  
Deep Excavation ◽  
The Third ◽  
First Case ◽  
Stiff Clay ◽  
Design Value ◽  
Uplift Resistance ◽  
Measured Load ◽  
Very High

This paper presents the results of measurements of earth anchor performance for three separate installations in Metropolitan Toronto. The first case records the results of instrumentation on the high grout pressure Bauer anchor used to support an approximately 30 ft (9.1 m) deep excavation in dense fine sand. The second presents the load measurements made on low grout pressure earth anchors installed in very stiff clay of a 29 ft (8.8 m) excavation. The third installation involved measurements on permanent vertical anchors set in extremely dense silt till.In the first instance the average measured load was somewhat lower than the installed load and the design assumption. In the second case, in the stiff clay, the load was somewhat higher than the design value but this was attributed to the probability of load transfer because of inadequate support at lower levels. In this case, considerable variation and possible overstressing of anchor wires was noted.A very high uplift resistance was recorded for the permanent anchors in dense till. Control of groundwater during installation of these anchors was the principal lesson learned from this work.

Analysis of case histories from construction of the Central Expressway in Singapore

1996 ◽  
Vol 33 (5) ◽  
pp. 732-746 ◽  
Author(s):  
I H Wong ◽  
T Y Poh ◽  
H L Chuah
Keyword(s):  
Finite Element Method ◽  
Phase Ii ◽  
Field Measurements ◽  
Bending Moments ◽  
Deep Excavation ◽  
The Finite Element Method ◽  
Case Histories ◽  
Wall Movement ◽  
Back Calculation ◽  
Stiff Clay

The construction of the cut-and-cover tunnels and depressed roadways of the Central Expressway (CTE) Phase II, Singapore, involved deep excavations. An extensive instrumentation program was carried out to monitor the behaviour of the excavations. The performance of three instrumented excavations from the construction of the CTE Phase II have been documented and analyzed using the finite element method (EXCAV) or finite difference method (FLAC). The results of the analyses show that the computed wall movements agree well with field measurements of wall movement and the computed wall bending moments generally agree quite well with those obtained from back-calculation. Key words: deep excavation, stiff clay, numerical analysis, displacements.

The Influence of Isothermal Annealing and Structural Defects on Properties of Amorphous Fe78Si11B11 with High Magnetization Saturation

2017 ◽  
Vol 68 (3) ◽  
pp. 478-482 ◽  
Author(s):  
Katarzyna Bloch
Keyword(s):  
Numerical Analysis ◽  
Thermal Treatment ◽  
Saturation Magnetization ◽  
Isothermal Annealing ◽  
Diffusion Processes ◽  
Structural Defects ◽  
High Saturation Magnetization ◽  
Magnetization Curves ◽  
Magnetization Saturation ◽  
Very High

This paper presents the results of numerical analysis of the primary magnetization curves, which were obtained under the assumptions of the theory of approach to ferromagnetic saturation described in by H. Kronm�ller. Test samples of the Fe78Si11B11 alloy were tape-shaped materials, which were subjected to isothermal annealing, not causing their crystallization. The investigated ribbons (tapes) were characterized by a very high saturation magnetization value of approximately 2T, which the thermal treatment has increased by about 10%. It was found that reason for the change of saturation magnetization of the investigated samples was the local rearrangement of atoms due to diffusion processes leading to the release of free volumes to the surface and combining of them into larger unstable defects called pseudodislocational dipoles.

scholarly journals Mechanical Testing and Modeling of the Time–Temperature Superposition Response in Hybrid Fiber Reinforced Composites

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1178
Author(s):  
Aggelos Koutsomichalis ◽  
Thomas Kalampoukas ◽  
Dionysios E. Mouzakis
Keyword(s):  
Hybrid Composites ◽  
High Stress ◽  
Woven Fabrics ◽  
Mathematical Function ◽  
Ballistic Performance ◽  
Three Point Bending ◽  
Highly Nonlinear ◽  
Nonlinear Stress ◽  
Temperature Superposition ◽  
Time Temperature Superposition

The purpose of this study was to manufacture hybrid composites from fabrics with superior ballistic performance, and to analyze their viscoelastic and mechanical response. Therefore, composites in hybrid lay-up modes were manufactured from Vectran, Kevlar and aluminum fiber-woven fabrics through a vacuum assisted resin transfer molding. The specimens were consequently analyzed using static three-point bending, as well as by dynamic mechanical analysis (DMA). Apart from DMA, time–temperature superposition (TTS) analysis was performed by all available models. It was possible to study the intrinsic viscoelastic behavior of hybrid ballistic laminates, with TTS analysis gained from creep testing. A polynomic mathematical function was proposed to provide a high accuracy for TTS curves, when shifting out of the linearity regimes is required. The usual Williams–Landel–Ferry and Arrhenius models proved not useful in order to describe and model the shift factors of the acquired curves. In terms of static results, the highly nonlinear stress–strain curve of both composites was obvious, whereas the differential mechanism of failure in relation to stress absorption, at each stage of deformation, was studied. SEM fractography revealed that hybrid specimens with Kevlar plies are prone to tensile side failure, whereas the hybrid specimens with Vectran plies exhibited high performance on the tensile side of the specimens in three-point bending, leading to compressive failure owing to the high stress retained at higher strains after the maximum bending strength was reached.

A New Nonlinear Stress-Strain Model for Soils at Various Strain Levels

2013 ◽  
Vol 631-632 ◽  
pp. 782-788
Author(s):  
Cheng Chen ◽  
Zheng Ming Zhou
Keyword(s):  
Compression Test ◽  
Triaxial Compression ◽  
Small Strain ◽  
Empirical Formulas ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Proposed Model ◽  
Nonlinear Stress ◽  
London Clay ◽  
Strain Model

Soils have nonlinear stiffness and develops irrecoverable strains even at very small strain levels. Accurate modeling of stress-strain behaviour at various strain levels is very important for predicting the deformation of soils. Some existing stress-strain models are reviewed and evaluated firstly. And then a new simple non-linear stress-strain model is proposed. Four undetermined parameters involved in the proposed model can be obtained through maximum Young’s module, deformation module, and limit deviator stress and linearity index of soils that can be measured from experiment directly or calculated by empirical formulas indirectly. The effectiveness of the proposed stress-strain model is examined by predicting stress-strain curves measured in plane-strain compression test on Toyota sand and undrained triaxial compression test on London clay. The fitting results of the proposed model are in good agreement with experimental data, which verify the effectiveness of the model.

Experimental study on the progressive collapse mechanism in the braced and tied-back retaining systems of deep excavations

2020 ◽  
Author(s):  
Gang Zheng ◽  
Yawei Lei ◽  
Xuesong Cheng ◽  
Xiyuan Li ◽  
Ruozhan Wang
Keyword(s):  
Large Scale ◽  
Large Deformations ◽  
Load Transfer ◽  
Progressive Failure ◽  
Progressive Collapse ◽  
Collapse Mechanism ◽  
Bending Moments ◽  
Failure Path ◽  
Transfer Mechanisms ◽  
Very High

Collapses of braced or tied-back excavations have frequently occurred. However, the influence of the failure of some retaining structure members on the overall safety performance of a retaining system has not been studied. Model tests of failures of retaining piles, struts or anchors were conducted in this study, and the load transfer mechanisms underlying these conditions were analysed. When failures or large deformations occurred in certain piles, the increasing ratios of the bending moments in adjacent piles were much larger in the braced retaining system than in the cantilever system and more easily triggered progressive failure. When the strut elevation was lower or the excavation depth was greater, the degree of influence and range of pile failures became larger. When certain struts/anchors failed, their loads transferred to a few adjacent struts/anchors, possibly leading to further strut/anchor failure. The influence mechanisms of strut or anchor failure on piles were different from those of pile failure. As the number of failed struts or anchors increases, the bending moments of the piles in the failure zone first decrease and then increase to very high values. Therefore, the progressive failure path extends from struts/anchors to piles and will lead to large-scale collapse.

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