scholarly journals The Responses of an End-Bearing Pile to Adjacent Multipropped Excavation: 3D Numerical Modelling

2019 ◽  
Vol 5 (3) ◽  
pp. 552 ◽  
Author(s):  
Dildar Ali Mangnejo ◽  
Naeem Mangi
Keyword(s):  
Soft Clay ◽  
High Stress ◽  
Three Dimensional ◽  
Bending Moment ◽  
Small Strain ◽  
Ground Movement ◽  
Stress Regime ◽  
Moment Capacity ◽  
Negative Skin Friction ◽  
End Bearing Pile

It is well recognised that superstructure load is transferred to surrounding soil through piled foundation. Consequently, the high stress regime (stress bulb) is generated surrounding of the pile. On the other hand, the excavation in the ground inevitably results in the ground movement due to induced-stress release. These excavations are sometimes inevitable to be constructed adjacent to existing piled foundations. This condition leads to a big challenge for engineers to assess and protect the integrity of piled foundation. This research presents three-dimensional coupled consolidation analyses (using clay hypoplastic constitutive model which takes account of small-strain stiffness) to investigate the responses of an end-bearing pile due to adjacent excavation at different depths in soft clay. The effects of excavation depths (i.e., formation level) relative to pile were investigated by simulating the excavation near the pile shaft (i.e., case S) and next to (case T). It was revealed that the maximum induced bending moment in the pile after completion of excavation in all the cases is much less than the pile bending moment capacity (i.e. 800 kNm). Comparing the induced deflection of the end-bearing pile in the case T, the pile deflection in case S is higher. Moreover the piles in cases of S and T were subjected to significant dragload due to negative skin friction.

Effect of Underlying Sand Layer on Undrained Capacity of Spudcan Foundations in Soft Clay Under Combined Loading

2018 ◽  
Author(s):  
Yifa Wang ◽  
Mark J. Cassidy ◽  
Britta Bienen
Keyword(s):  
Soft Clay ◽  
Three Dimensional ◽  
Small Strain ◽  
Combined Loading ◽  
Sand Layer ◽  
Element Analysis ◽  
Moment Capacity ◽  
Soil Failure ◽  
Failure Envelopes ◽  
Vertical Bearing

During the operational phase, the spudcan foundations of a mobile jack-up rig are subjected to combined vertical, horizontal and moment loading. Although previous research has indicated a substantial increase in vertical bearing capacity when a spudcan penetrates through a soft clay layer towards a sand layer, the response of spudcan foundations subjected to combined loadings in such stratification has yet to be understood. This study investigates the effect of the underlying stronger sand layer on the undrained VHM capacity of a spudcan foundation using three-dimensional small-strain finite element analysis. Results show the significant increase in vertical and moment capacity, whereas the horizontal capacity is minimally affected. The soil failure mechanisms are identified and changes in the size and shape of failure envelopes, accounting for the sand layer underneath, are quantified. An analytical expression is proposed to predict the combined capacity of a spudcan foundation in clay overlying sand.

scholarly journals Parametric Study of Pile Response to Side-by-Side Twin Tunneling in Stiff Clay

2020 ◽  
Vol 10 (2) ◽  
pp. 5361-5366
Author(s):  
N. Mangi ◽  
D. K. Bangwar ◽  
H. Karira ◽  
S. Kalhoro ◽  
G. R. Siddiqui
Keyword(s):  
Parametric Study ◽  
Three Dimensional ◽  
Bending Moment ◽  
Small Strain ◽  
Percentage Difference ◽  
Stiff Clay ◽  
The One ◽  
Numerical Parametric Study ◽  
Pile Response ◽  
Twin Tunnels

A three dimensional coupled-consolidation numerical parametric study was carried out in order to gain new insight of single pile response to side-by-side twin tunneling in saturated stiff clay. An advanced hypo plasticity (clay) constitutive model with small-strain stiffness was adopted. The effects of relative to the pile tunnel depths were investigated by simulating the twin tunnels near the pile at various depths of tunnels, namely near the pile shaft, adjacent to the pile toe, and below the pile toe. It was found that the second tunneling in each case resulted in a larger settlement than the one due to the first tunneling with a maximum percentage difference of 175% in the case of twin tunneling near the mid-depth of the shaft. This occurred due to the degradation of clay stiffness around the pile during the first tunneling. Conversely, the first tunneling-induced bending moment was reduced substantially during the second tunneling. The most critical location of twin tunnels relative to the pile was found to be below the pile toe.

Coupled Numerical Analysis of Tunnel Excavation in Saturated Soft Clay under High Groundwater

2011 ◽  
Vol 368-373 ◽  
pp. 2533-2536
Author(s):  
Hua Yuan ◽  
Hai Tao Wan ◽  
Zhi Liang Zhao
Keyword(s):  
Soft Clay ◽  
Three Dimensional ◽  
Bending Moment ◽  
High Water ◽  
Shield Tunnel ◽  
Deep Soil ◽  
Tunnel Excavation ◽  
Axial Forces ◽  
Reduction Effect ◽  
Saturated Soft Clay

A coupled numerical simulation of a river-crossing shield tunnel excavation in saturated soft clay with high groundwater has been performed using a three-dimensional finite difference model, which takes into account variation of soil permeability with stress, anisotropy of permeability, reduction effect of joints on segment bending stiffness and the hardening process of synchronized grouting material. Groundwater seepage conditions around the tunnel, bending moment, axial forces and strength safety factor of tunnel segment as well as deep soil displacement during tunnel diving are investigated numerically. The analyses provide valuable information concerning the mechanical behavior of tunnel segment and hydrological field in soil around tunnel during advancing. The result also is benefited to control groundwater for river-crossing tunnel in soft clay under high water table.

scholarly journals Single Pile Settlement and Load Transfer Mechanism due to Excavation in Silty Clay

2018 ◽  
Vol 8 (1) ◽  
pp. 2485-2492 ◽  
Author(s):  
M. A. Soomro ◽  
K. F. Memon ◽  
M. A. Soomro ◽  
A. Memon ◽  
M. A. Keerio
Keyword(s):  
Load Transfer ◽  
Bending Moment ◽  
Small Strain ◽  
Transfer Mechanism ◽  
Ground Movement ◽  
Major Influence ◽  
Silty Clay ◽  
Single Pile ◽  
Load Transfer Mechanism ◽  
Pile Settlement

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 piled foundations. In order to gain new insights into single pile responses (i.e. settlement and load transfer mechanism) to an adjacent excavation in saturated silty clay, a three-dimensional coupled- consolidation numerical analysis is conducted in this study. An advanced hypoplasticity (clay) constitutive model with small-strain stiffness was adopted. A linear increase in pile settlement was observed due to excavation-induced stress release. This is because part of the pile is placed within the boundaries of a major influence zone due to excavation-induced ground movement. Based on a settlement criterion, apparent loss of pile‘s capacity is 14%. A maximum bending moment of about 350 kNm is induced in the pile with the maximum deflection of 28 mm. In addition, mobilisation of shear strength at the pile-soil interface was found to be a key factor governing pile-soil-excavation interaction. During excavation, a downward load-transfer mechanism in the piles can be identified.

Drag load on end-bearing piles in collapsible soil due to inundation

2016 ◽  
Vol 53 (12) ◽  
pp. 2030-2038 ◽  
Author(s):  
Ibrahim Mashhour ◽  
Adel Hanna
Keyword(s):  
Experimental Investigation ◽  
Skin Friction ◽  
Soft Clay ◽  
Soil Layer ◽  
Design Procedure ◽  
Collapsible Soil ◽  
Negative Skin Friction ◽  
Collapsible Soils ◽  
Surrounding Soil ◽  
End Bearing Pile

Collapsible soils may experience sudden and excessive settlement when inundated. The use of pile foundations that penetrate the collapsible soil layer to reach a firm stratum is widely used in practice. However, when the ground is inundated, large and sudden settlement of the surrounding soil may take place, causing negative skin friction on the pile’s shaft, which may lead to catastrophic failure. In the literature, research dealing with negative skin friction for piles in collapsible soil is lagging due to the complexity of modeling collapsible soil analytically. Alternatively, results of sophisticated experimental investigation may produce valuable information to predict the negative skin friction and accordingly the drag load on these piles. This paper presents the results of an experimental investigation on a single end-bearing pile in collapsible soil. The investigation is tailored to measure the soil collapse before and during inundation and the associated drag load on the pile. The theory proposed by Hanna and Sharif in 2006 for predicting negative skin friction on piles due to consolidation of the surrounding soft clay was extended to predict the negative skin friction for these piles in collapsible soils. A proposed design procedure is presented.

scholarly journals Effects of Construction Sequences and Volume Loss on Perpendicularly Crossing Tunnels

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Yanwei Zang ◽  
Penglu Gan ◽  
Jia-jia Yan ◽  
Shiming Liu ◽  
Zihai Yan
Keyword(s):  
Urban Areas ◽  
Rapid Development ◽  
Three Dimensional ◽  
Ground Surface ◽  
Stress Transfer ◽  
Bending Moment ◽  
Small Strain ◽  
Research Attention ◽  
The Past ◽  
Three Dimensional Finite Element

The number of constructed tunnels has been gradually increasing for the past decades due to rapid development in urban areas. However, the soil-structure interaction problems arising from perpendicularly crossing tunnels attract relatively little research attention in the past. In this study, six three-dimensional finite element analyses were conducted to simulate tunnel excavation nearby a perpendicularly crossing existing tunnel, in an attempt to investigate the effects of construction sequences on cross-cutting tunnels. The hypoplastic constitutive model for sand is adopted in the numerical analysis to consider the soil small-strain stiffness. Computed results are presented and discussed in terms of ground surface settlement, displacement and deformation of the existing tunnel, and bending moment induced on the existing tunnel. The stress-transfer mechanism in soil nearby the existing tunnel due to tunnelling is also studied.

scholarly journals A Parametric Study of Effect On Single Pile Integrity Due to An Adjacent Excavation Induced Stress Release in Soft Clay

2018 ◽  
Vol 8 (4) ◽  
pp. 3189-3193 ◽  
Author(s):  
D. A. Mangnejo ◽  
M. A. Soomro ◽  
N. Mangi ◽  
I. A. Halepoto ◽  
I. A. Dahri
Keyword(s):  
Soft Clay ◽  
Bending Moment ◽  
Small Strain ◽  
Single Pile ◽  
Stress Release ◽  
Pile Shaft ◽  
Induced Stress ◽  
Parametric Studies ◽  
Pile Settlement ◽  
Pile Integrity

To gain new insights into single pile responses to adjacent excavations in soft ground, numerical parametric studies are carried out. An advanced hypoplastic (clay) constitutive model which takes account of small-strain stiffness is adopted. The effects of excavation depths (i.e. formation level) relative to pile were investigated by simulating the excavation near the pile shaft (i.e., He/Lp=0.67), next to (He/Lp=1.00) and below the pile toe (He/Lp=1.33). Among the three cases, the excavation in case of He/Lp=1.33 resulted in the largest pile settlement (i.e. 7.6%dp). On the other hand, the largest pile bending moment was induced in case of He/Lp=0.67.

scholarly journals 3D Centrifuge Modeling of the Effect of Twin Tunneling to an Existing Pile Group

2017 ◽  
Vol 7 (5) ◽  
pp. 2030-2040
Author(s):  
M. A. Soomro ◽  
M. A. Keerio ◽  
M. A. Soomro ◽  
D. K. Bangwar
Keyword(s):  
Axial Force ◽  
Urban Areas ◽  
Load Transfer ◽  
Three Dimensional ◽  
Bending Moment ◽  
Pile Group ◽  
Centrifuge Modeling ◽  
Pile Groups ◽  
Moment Capacity ◽  
Centrifuge Tests

In densely built urban areas, it is inevitable that tunnels will be constructed near existing pile groups. The bearing capacity of a pile group depends on shear stress along the soil-pile interface and normal stress underneath the pile toe while the two would be adversely affected by the unloading process of tunneling. Although extensive studies have been conducted to investigate the effects of tunnel construction on existing single piles, the influence of twin tunnel advancement on an existing pile group is merely reported in the literature. In this study, a series of three-dimensional centrifuge tests were carried out to investigate the response of an existing pile group under working load subjected to twin tunneling at various locations in dry Toyoura sand. In each twin tunneling test, the first tunnel is constructed near the mid-depth of the pile shaft, while the second tunnel is subsequently constructed either next to, below or right underneath the pile toe (Tests G_ST, G_SB and G_SU, respectively). Among the three tests, the 2nd tunnel excavated near the pile toe (Test G_ST) results in the smallest settlement but the largest transverse tilting (0.2%) of pile group. Significant bending moment was induced at the pile head (1.4 times of its bending moment capacity) due to the 2nd tunnel T. On the contrary, tunneling right underneath the toe of pile (i.e., Test G_SU) results in the smallest tilting but largest settlement of the pile group (4.6% of pile diameter) and incremental mobilisation of shaft resistance (13%). Due to stress release by the twin tunneling, the axial force taken by the front piles close to tunnels was reduced and partially transferred to the rear piles. This load transfer can increase the axial force in rear piles by 24%.

scholarly journals The Effects of Multipropped Deep Excavation-Induced Ground Movements on Adjacent High-Rise Building Founded on Piled Raft in Sand

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Mukhtiar Ali Soomro ◽  
Naeem Mangi ◽  
Wen-Chieh Cheng ◽  
Dildar Ali Mangnejo
Keyword(s):  
Three Dimensional ◽  
Bending Moment ◽  
Small Strain ◽  
High Rise ◽  
Piled Raft ◽  
Interstorey Drift ◽  
Numerical Parametric Study ◽  
Soil Behaviour ◽  
Pile Length ◽  
Storey Building

In this paper, a three-dimensional numerical parametric study was conducted to predict the deformation mechanism of a 20-storey building sitting on a (4 × 4) piled raft to an adjacent 25 m deep basement excavation. The influences of different excavation depths were investigated. An advanced hypoplastic sand model (which is capable of taking small-strain stiffness into account) was adopted to capture soil behaviour. The computed results revealed that excavation adjacent to a building resting on the piled raft caused significant settlement, differential settlement, lateral deflection, and interstorey drift in the building. With settlement due to working load (i.e., 4.8dp%), the total settlements of the building (7.8dp%) exceed the maximum allowable foundation settlement (i.e., 50 mm). In addition, substantial bending moment, shear forces, and changes in axial load distribution along pile length were induced. The findings from this study revealed that the building and pile responses are significantly influenced by the excavation depth.

DYNAMIC ANALYSIS OF OFFSHORE PILES EMBEDDED IN ELASTOPLASTIC SOFT CLAY

2016 ◽  
Vol 3 (2) ◽  
Author(s):  
Anis Mohamad Ali ◽  
Mohamad J. K. Essa ◽  
Abdulameer Qasim Hassan
Keyword(s):  
Soft Clay ◽  
Three Dimensional ◽  
Bending Moment ◽  
Pile Head ◽  
Finite Element Program ◽  
Head Displacement ◽  
Element Program ◽  
Pile Length ◽  
Elastoplastic Soil ◽  
Offshore Piles

This work deals with the dynamic behavior of offshore piles embedded in soft clay, and an attempt is made to estimate the critical embedded pile length. ABAQUS finite element program is used to simulate the problem. The soil was modeled as an elastic state and elastoplastic state and represented by cam-clay model. Three dimensional elements were used to represent the interaction between pile and soil, laboratory tests are used to obtain the real properties of soil and to describe interface. The results obtained are used to develop the elastic equation used by Matlock and Reese to calculate the critical embedded pile length for pile embedded in elastoplastic soil. Also, show that the critical embedded pile length is increased by about (20 % to 40 %) due to changing soil model from elastic to elastoplastic. The pile embedded in an elastoplastic soil is dependent on soil strength, interface properties and pile rigidity. The pile head displacement is increased about 90 % while the bending moment is deceased by 10 % at pile head.

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