Volume 51 Issue No. 2 June 2020 – SEAGS

Pile Design in Seismic Areas: Small or Large Diameter?

itsupport installer — Thu, 18 Jun 2020 10:01:21 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

Pile Design in Seismic Areas: Small or Large Diameter?

R. Di Laora

ABSTRACT: This work investigates the role of pile diameter in resisting seismic actions, with reference to two example subsoils, namely a dry sand and a fully saturated NC clay. After a ground response analysis in free-field conditions for different values of peak rock acceleration, mobilized soil stiffness and surface acceleration are used as ingredients for assessing the kinematic and inertial moment in a concrete pile. An optimum pile diameter is identified as the one that, while guaranteeing safety, corresponds to the minimum cost. It is also proven that, with a constant value of reinforcement area and length, increasing pile diameter (i.e. increasing safety factor and cost) leads rapidly to failure. Likewise, if pile reinforcement is designed only for inertial action, increasing pile diameter is severely detrimental.

KEYWORDS: Pile design, Seismic action, Kinematic interaction, Earthquake-induced bending, Pile diameter

DOI: 10.14456/seagj.2020.57

Analysis for Laterally Loaded Offshore Piles in Marine Clay

itsupport installer — Thu, 18 Jun 2020 10:00:27 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

Analysis for Laterally Loaded Offshore Piles in Marine Clay

S. Jeong, and Y. Kim

ABSTRACT: The load distribution and deformation of offshore drilled shafts under lateral loading in Incheon grand bridge are investigated by experimental field loading tests and lateral load-transfer approach through p-y curve analysis. The main focus is on improved wedge failure model developed by considering three-dimensional combination forces and new hyperbolic p-y criterion. Through comparisons with field case studies, it is found that the rigidity of the drilled shaft is a critical factor in drilled shafts in marine clay, and the methodology proposed in this study yields more accurate and realistic results considering pile-soil interaction for laterally loaded drilled shafts in marine clay.

KEYWORDS: Drilled shaft, Lateral loading, Marine clay, p-y curve, Wedge failure model, Pile rigidity

DOI: 10.14456/seagj.2020.56

FD Analysis on Piled Raft Foundation Settlements under Vertical Loads

itsupport installer — Thu, 18 Jun 2020 09:59:35 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

FD Analysis on Piled Raft Foundation Settlements under Vertical Loads

D.W. Chang, H.W. Lien and M.H. Hung

ABSTRACT: A three-dimensional finite difference analysis has been developed to estimate the foundation settlements for vertically loaded piled raft foundations. Thin-plate theory was adopted to model the finite raft with boundary effects. Alternate spring models were used to model soil resistances under the raft while the resistances of pile were model by calculating the pile stiffness from wave equation analysis. The newly proposed analysis was examined with finite element solutions. It was found that variations of soil resistance underneath the raft and the pile-soil-pile interactions are the keys to the applicability of such analysis.

KEYWORDS: Geocell reinforcement, Composite model, Flexible pavements, Parametric study

DOI: 10.14456/seagj.2020.55

Effects of Cyclic Behaviour during Pile Penetration on Pile Performance in Model Load Tests

itsupport installer — Thu, 18 Jun 2020 09:52:21 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

Effects of Cyclic Behaviour during Pile Penetration on Pile Performance in Model Load Tests

S. Moriyasu, T. Matsumoto, M. Aizawa, S. Kobayashi, and S. Shimono

ABSTRACT: This study focuses on the effect of ‘cyclic’ behaviour of pile installation methods on the penetration resistance and bearing capacity of a model pile. A series of laboratory model tests were conducted to investigate this cyclic effect by comparing three kinds of piling methods: monotonic jack-in, pseudo-dynamic push-in and pull-out, i.e. ‘surging’, and vibratory driving in dry or saturated sand. Surging or vibratory pile driving decrease the pile penetration resistance due to negative soil dilation caused by the cyclic shearing of the soil surrounding the pile. Static load tests show that surging and vibratory pile driving provide the same or larger pile head load as the jack-in method does. Furthermore, the fluctuation of the pore water pressure strongly indicates a change in soil dilation. Both surging and vibratory pile driving prevent positive dilation more than the jack-in method due to differences in cyclic shearing and monotonic loading.

KEYWORDS: Pile installation method, Jack-in, Surging, Vibratory pile driving, Pore water pressure

DOI: 10.14456/seagj.2020.54

Foundation Investigation and Analysis for Tall Tower Developments

itsupport installer — Thu, 18 Jun 2020 09:51:50 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

Foundation Investigation and Analysis for Tall Tower Developments

C. M. Haberfield, J.E. Finlayson, and A. L .E. Lochaden

ABSTRACT: Many tall buildings are supported on piled rafts and / or deep bored cast in situ piles. Good engineering design requires soil-structure interaction analysis and a clear understanding of the factors controlling the performance of the footing system. These rely on a sound understanding of the ground characteristics and individual and group pile performance, including adequate collection of data and testing, which can only be achieved through detailed and targeted ground investigation and in situ testing. This paper focuses on the ground investigation methods available and how the results are used to achieve a reliable estimate of footing system performance using soil-structure interaction analysis. It highlights the importance of accurate inputs into the analyses, especially in respect to the stiffness characteristics of the ground and the load displacement performance of individual piles. This is illustrated through a number of case studies of tall tower projects that the authors have been involved in.

KEYWORDS: Geotechnical investigation, Soil-structure interaction, Tall towers, Analysis, Design, Case study

DOI: 10.14456/seagj.2020.53

The Behaviour of Pile Group and Combined Piled-Raft Foundation in Liquefiable Soil under Seismic Conditions

itsupport installer — Wed, 17 Jun 2020 16:14:27 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

The Behaviour of Pile Group and Combined Piled-Raft Foundation in Liquefiable Soil under Seismic Conditions

Aniruddha Bhaduri, Vansittee Dilli Rao and Deepankar Choudhury

ABSTRACT: This paper highlights the beneficial usage of Combined Pile-Raft Foundation (CPRF) over conventional pile group foundation subjected to seismic loading in liquefiable soil. Firstly, a single pile resting on a liquefiable soil is numerically modelled and subsequently validated with available dynamic centrifuge test result by using finite difference based computer programme, FLAC3D. Thereafter, the model is extended for simulating CPRF and pile group.Further parametric studies are performed to understand the effect of pile spacing (s), pile length (l) and different seismic motions on the behaviour of CPRF and pile group. Results are presented in terms of normalised bending moment (M/Mmax), shear forces and pore water pressure (PWP) ratio. Increase in shear resistances in the range of (35 – 60)% and (40 – 70)% are observed for the piles in CPRF over the conventional pile group foundation, having a pile spacing of 2 to 5 times of its diameter (d) and the (l/d) of 14 to 20, respectively. These outcomes portray the advantages of employing CPRF over pile group founded in liquefiable area under seismic loading.

KEYWORDS: Liquefaction, CPRF, Pile Group, Centrifuge, FLAC3D

DOI: 10.14456/seagj.2020.52

Numerical and Simplified Methods for Soil-pile Interaction Analysis

itsupport installer — Wed, 17 Jun 2020 15:59:10 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

Numerical and Simplified Methods for Soil-pile Interaction Analysis

F. Dezi, S.Carbonari, M. Morici, G. Leoni

ABSTRACT: The paper presents a review of the analytical and numerical procedures developed by the authors for the dynamic analysis of soil-pile foundation systems subjected to the propagation of seismic waves in the soil. Inclined and vertical single piles and groups constituted by piles with a generic inclination are addressed. For the former, an analytical approach based on the beam on dynamic Winkler foundation approach is adopted; the pile is modelled as a Euler-Bernoulli beam and the soil-pile interaction is captured by defining soil impedances relevant to the harmonic vibrations of rigid disks available in the literature. The coupled flexural and axial behaviour of the pile is solved analytically exploiting exponential matrices. The pile group dynamic problem is similarly formulated but the solution is achieved exploiting the finite element approach. Besides numerical models, simplified approaches based on static equivalent methods and simplified formulas are also addressed to estimate the maximum kinematic stress resultants on vertical piles subjected to lateral seismic excitations. The reliability of the presented tools in capturing the dynamic stiffness and the overall kinematic response of pile foundations is shown by comparing results with those available in the literature or achieved through refined finite element models. From an engineering point of view, the proposed approaches assure a sufficient accuracy and may substitute refined computational demanding numerical models.

KEYWORDS: Soil-pile interaction, Pile foundations, Kinematic interaction, Numerical models

DOI: 10.14456/seagj.2020.51

Effective Stress Friction Angle of Normally Consolidated and Overconsolidated Intact Clays from Piezocone Tests

itsupport installer — Wed, 17 Jun 2020 15:52:00 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

Effective Stress Friction Angle of Normally Consolidated and Overconsolidated Intact Clays from Piezocone Tests

Z. Ouyang and P.W. Mayne

ABSTRACT: The effective stress friction angle (Φ′) is an important fundamental property for all soil types. A modified effective stress limit plasticity solution is presented in this paper for the evaluation of Φ′ of normally-consolidated to overconsolidated clays from piezocone penetration tests (CPTu). The solution takes account of stress history effect by introducing the equivalent stress concept from critical state soil mechanics (CSSM). Values of Φ′ obtained from laboratory triaxial compression tests on high quality samples are taken as the benchmark reference. The method is applicable to clays that are intact, insensitive, and inorganic. Example results of piezocones performed in normally consolidated kaolin in the laboratory and field tests on overconsolidated clay from Alaska are presented to elaborate application of the solution. A compiled database from 132 piezocone soundings in intact clays at field sites, 1-g chamber tests, and centrifuge series is compared with triaxial tests to show the full range of 18° < Φ′< 45° of natural and artificial clays.

KEYWORDS: Clay, Friction angle, Piezocone, Effective stress friction angle, Overconsolidation ratio

DOI: 10.14456/seagj.2020.50

BEM and FEM Approaches to the Analysis of Negative Skin Friction on Piles

itsupport installer — Wed, 17 Jun 2020 15:46:15 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

BEM and FEM Approaches to the Analysis of Negative Skin Friction on Piles

G. Russo, L. Di Girolamo and G. Marone

ABSTRACT: Negative skin friction (NSF) may be a relevant problem in the design of piles in soft soils, when significant areas around the piles are loaded at the ground surface. The downdrag on piles is traditionally evaluated by reversing a part of the shaft resistance in an applied load and considering it in the evaluation of a safety factor against a bearing capacity failure. Such an approach is totally inadequate, because NSF is actually a problem of soil-pile interaction. Two methods of analysis of a pile subjected to both an external load and NSF are presented: Boundary Element Method (BEM) and Finite Element Method (FEM). The former method is based on a BEM approach and concentrates non-linearity effects at the pile-soil interface while the latter is a FEM approach using the package PLAXIS 2D. The accuracy of the methods is checked back analysing a well-documented case history of bored piles in soft soils.

KEYWORDS: Negative Skin Friction (NSF), Dragload, Downdrag, Boundary Element Method (BEM), Finite Element Method (FEM)

DOI: 10.14456/seagj.2020.49

Model Vibration Tests on Piled Raft and Pile Group Foundations in Dry Sand

itsupport installer — Wed, 17 Jun 2020 14:54:07 +0000

Geotechnical Engineering Journal of the SEAGS & AGSSEA ISSN 0046-5828

Vol. 51 No. 2 June 2020

Model Vibration Tests on Piled Raft and Pile Group Foundations in Dry Sand

Anh-Tuan Vu, Tatsunori Matsumoto and Kohei Kenda

ABSTRACT: In this research, the authors carried out vibration load tests on piled raft and pile group models to investigate dynamic behaviours of the foundations. Foundation models consisting of 6 piles, with or without batter piles, were used in the experiments. They were pile rafts (6PR and 6BPR) if the raft was in contact with ground surface, while they were pile groups (6PG and 6BPG) if the raft was not in contact with ground surface. To create dynamic load acting on the foundation, a vibro-hammer, placed on the raft, was used. The vibro-hammer can provide vibration load (active shaking) mainly in the vertical direction (called vertical loading) or in the vertical and horizontal directions simultaneously (called combination loading) by rotating two discs of eccentric mass synchronously in opposite directions or the same direction, respectively. Active shaking tests were conducted on 4 types of pile foundation models (6PR, 6BPR, 6PG and 6BPG) in a consistent dry sand ground. The experimental results indicate that the piled rafts are more effective foundation type to decrease settlement and inclination under dynamic loading than the pile groups.

KEYWORDS: Piled raft, Pile group, Dry sand, Model test, Dynamic load

DOI: 10.14456/seagj.2020.48