École nationale des ponts et chaussées ParisTech, France and
President of ISSMGE
Prof. Roger Frank
Topic: "Some Aspects of Research and Practice for Pile Design in France"
This paper summarises some aspects of the methods used in France for designing pile foundations under axial and transverse loadings. These methods mostly use the results of Ménard pressuremeter (MPM) tests and concern the determination of the bearing capacity, as well as the prediction of axial and transverse displacements. The prediction of the bearing capacity from CPT results is also given. After mentioning the general context of foundation design in France, the details of these methods are described and some of their experimental background is explained. These methods are now included in the French standard for pile design (published by AFNOR in 2012), fully compatible with Eurocode 7 on ‘Geotechnical design’.
Topic: "Skin Friction of Prebored and Precast Piles in Weathered Rocks"
Yonsei University, Korea & Vice Chairman of TC 212, ISSMGE
Prof. Sang Seom Jeong
Prebored and precast piles are being frequently used for various structures to reduce nuisance caused by vibration and noise, substituting driven piles. In prebored and precast pile design, skin friction is the most critical factors affecting the bearing capacity and the settlement behavior. Main focus of this paper is to establish an analysis model considering the interface behavior between the pile-cement milk-surrounding soil interface during the installation and in-use of prebored and precast pile. The case of single pile was analyzed through a three-dimensional finite element approach and pile loading tests. In the analysis, t-z curve allowing a slip along the interfaces were proposed, designating a certain length of slip for each interfaces. A series of numerical analysis on the interface of pile-cement milk-soil was conducted based on a proposed t-z curve. It is shown that the use of cement milk around the pile increases the skin friction to some extent and reduces the pile settlement.
Topic: “Unsatisfactory Behavior of Structures Resting on Pile Foundations: Recent Experiences.”
Vice President of ISSMGE for Asia
Prof. Ikuo Towhata
This paper picks up three recent cases in which pile foundation did not perform so satisfactorily as expected. Particularly the tilting of a condominium building in Yokohama, Japan, triggered a national dispute about the reliability of construction technology, although the extent of tilting was very minor. The Japanese Geotechnical Society established a special committee to express an unbiased opinion about the significance of this incidence that the public should pay more attention to the importance of geotechnical site investigation. Without reliable data, elaborate or advanced design cannot guarantee good performance of designed structures. The second case is still mysterious. A bridge foundation pile sank down several meters during the 2016 Kumamoto earthquake although the surrounding area did not have damage. This incidence may suggest the lack of quality control of cast-in-place piles. The third case addresses a minor tilting of a piled-raft foundation. Although piles were designed with good bearing capacity, the induced tilting significantly affected the serviceability of the building and reduced its value. The first and the third cases imply that the public is now more concerned about the serviceability performance of structures than about bearing capacity and safety as in the previous times. This situation is very strict to the construction business and can be accommodated by making more efforts on good data acquisition on soil conditions and controlling the quality of construction practice.
Topic: “Piling in Seismic Conditions: Some Case Studies”
Principal of ARUP Sydney, Australia
Piling is frequently used when faced with soft or liquefiable ground. However, under seismic conditions, the use of piles, whether individual or a group needs to face additional scrutiny due to change in loading and change in behaviour of the entire system, which are not adequately considered through use of pseudo static or necessarily even modal analysis. It is also important to achieve economy in the design without compromising the safety and integrity. Some structures are life line structures such as dams and water/waste water treatment facilities. The governing failure criteria on these would be somewhat different from those for buildings and these facilities are required to resist earthquake events with return periods in excess of 2500 to 20,000 years. These considerations are examined in this paper through consideration of a number of case studies. These case studies focus on what the pile and system is really doing as compared to the design considerations.
The L.N. Gumileyov Eurasian National University, Kazakhstan & Chair of TC 305 - ISSMGE: Geotechnical Infrastructure for Megacities and New Capitals
Prof. Askar Zhussupbekov
Topic: "The Analysis of Field Tests of Soils by Joint Piles on the Construction Site of the Caspian Sea Area in Kazakhstan
At present time the large-scale constructions are built highly in Kazakhstan in particular a building with pile foundations on problematic soils. The application of pile foundations in those cases required a load testing for determining the bearing capacity of soils and foundations. In this paper are presented the results of pile field test in construction site in Caspian Sea Port Bautino (Mangystau Region, Kazakhstan) and Caspian Sea Port Prorva (Atyrau Region, Kazakhstan). In this construction sites were carried out the static load test with ASTM and Kazakhstan standards (GOST) and dynamic load test with GOST. Also using of the Pile Dynamic Analyzer testing method needs for quickly determination of bearing capacity for single joint piles and bored piles. These investigations are important for understanding of interaction mechanism of joint piles and bored piles with problematical soil ground of coastal area Caspian Sea, Kazakhstan.
Universitas Katolik Parahyangan, Indonesia
Prof. Paulus P. Rahardjo
Topic: “Problems of Pile Design and Construction in Indonesia and Lessons Learned from Measurement of Pile Behavior in Problematic Soils”
Hong Kong University of Science and Technology, Hong Kong
Prof. Charles Wang Wai Ng
Topic: “Energy Piles: Challenges and Opportunities”
Energy piles are a type of green foundations that can reduce the amount of energy consumed for space heating and cooling by up to 75%. It is inevitable that the operation of energy piles imposes heating and cooling cycles not only the pile but also the surrounding soil. Thus, complex thermo-mechanical pile-soil interaction takes place during the operation of energy piles. This may induce detrimental effects on the capacity as well as the serviceability of energy piles. Two series of centrifuge model tests are reported in this paper to shed light on the effects of temperature change on the ultimate capacity and long-term serviceability of energy piles. In the first series of tests, three floating energy piles embedded in saturated sand were monotonically heated or cooled, then loaded to failure to determine their respective ultimate capacity in-flight. In the second series of tests, cyclic heating and cooling of replacement (bored) and displacement (driven) floating energy piles installed in both saturated sand and clay were conducted to investigate the vertical pile displacement under constant working load (i.e., the serviceability limit state). As expected, heated pile was found to have higher pile capacity than non-heated pile. The increase in pile capacity was due to expansion of pile from heating, which increased the shaft resistance of pile. In addition, there was net settlement during heating. This compacted the soil below the pile toe, increasing the toe resistance. On the other hand, a cooled pile also had an apparent increase in pile capacity as compared with that of a non-cooled pile. This was attributed to pile settlement during cooling, leading to an increase in toe resistance due to compaction of soil below the pile toe. The increase and decrease of shaft resistance with respect to temperature was found to be linear. In contrast to existing framework, it is found that the neutral plane of a floating energy pile is not located at the mid-depth of the pile. Not only it is a function of applied load but it is also governed by temperature change. Under constant working load and operating heating and cooling cycles, replacement floating energy piles exhibit ratcheting settlement but at a reducing rate, irrespective of soil type. In contrast, displacement floating energy piles exhibit heave behaviour. This suggests that care must be taken when designing replacement floating energy piles.
Topic: “Advantages of Piled Rafts Over Pile Groups from Model Load Tests in Dry and Saturated Sand Grounds”
Kanazawa University, Japan
Prof. Tatsunori Matsumoto
Piled raft foundation subjected to vertical load has been recognised as an economical and effective foundation system to reduce average and/or differential settlements with less number of piles compared to the corresponding pile group where the soil resistance acting on the raft is ignored in design. Pile foundations are subjected to combination of horizontal load and over-turning moment as well as vertical load, due to winds and waves acting on the super-structure, and due to inertial force of the super-structure during earthquakes. Pile foundations are subjected also to kinematic effects (ground displacements during earthquakes) during earthquakes. The authors have been investigating the responses and the resistance mechanisms of pile foundation models including piled rafts and pile groups in dry or saturated sands through experimental approach and numerical approach. The first part of this keynote paper focuses on the static horizontal cyclic loading of piled raft and pile group models in dry sand. Effects of inclusion of batter piles on responses of the foundation models are included. Model piles were instrumented with strain gauges to obtain axial forces, shear forces and bending moments. The soil resistances acting on the raft, vertical and horizontal resistances, were also estimated. Moreover, numerical simulations of the experiments were conducted, to get more insight into the resistance mechanisms of the foundation models. In the second part, shaking table tests of the foundation models in saturated sand are presented. In these shaking tests, pore water pressures in the model ground were measured, in addition to the responses of the raft and the piles. It is shown that the piled raft model is much more stable compared to the pile group model during shaking.
This paper intends to show advantages of piled rafts in static horizontal loading and in shaking over pile groups, and discuss these mechanisms.
Bengt H. Fellenius, Dr. Tech., P. Eng.
Bengt Fellenius Geotechnical Inc., Canada
Topic: “Design of Single Piles, Small Pile Groups, and Wide Piled Foundations”
The response of single piles and small pile groups to load differs considerably from that of wide piled foundations. Single piles interact with settlements of the soil layers surrounding the piles and develop a force and settlement equilibrium (neutral plane) which location to a large extent depends on the pile toe response to the soil forces and movements. Similar to single piles, perimeter piles of a wide pile group in subsiding soils will be affected by increasing load due to negative skin friction. They will, therefore, appear softer than the interior piles, which are more or less unaffected by shaft resistance (or negative skin friction). Indeed, the load applied to a wide pile group will more or less unimpededly be transferred down the pile (i.e., contact stress is a chimera) and only be reduced by shaft resistance immediately above the pile toe. The process links the pile-toe penetration and the upward compression of the soil surrounding the piles.
All piles are of course affected by the settlement of the soil below the pile toe level due to occurrences, such as regional settlement and stress changes due to adjacent foundations, fills, excavations, etc. Wide pile groups will, in contrast to single piles, also be affected by the compression of the soils below the group due to the sustained load on the pile group.
For pile groups in non-subsiding soil, the response of perimeter piles is stiffer than that of the interior piles. Thus, in order to minimize differential settlement of the piles across the pile raft, the perimeter piles may have to be installed shorter than the interior piles. In contrast, for pile groups in subsiding soil, the perimeter piles may have to be installed longer than the interior piles.
Prof. Ing Alessandro Mandolini
Università degli Studi della Campania "Luigi Vanvitelli", Italy & Chair of TC 212, ISSMGE
Topic: “Lessons Learned from Careful Monitoring of Piled Foundation : Italian Experience”
The prediction of pile response to loading is a very uncertain exercise. During the years, several initiatives (class “A” prediction events) were taken in order to check our real capability to predict pile behavior. The outcomes surely were not encouraging. Further efforts by the scientific and technical community are needed to cover the gap.
One possibility, in the author’s opinion, is represented by the adoption of Local Pile Design Methods (LPDM) calibrated on local practice and experience.
Based on huge and good quality experimental data as collected during the years in a specific area in Napoli (Italy), a proposal about how to set-up LPDM is described in the paper.
The application of the proposed LPDM with regard to a full-scale case history clearly shows that it can be of particular interest for practical purposes, especially in the preliminary stage of the design when the fundamental design choices have to be made (for instance, pile type and geometry).
Helical piles are typically manufactured of straight steel shafts (pipe or square section) fitted with one or more helices and are installed using mechanical torque. Their installation technique may cause disturbance to the soil, especially clay, which may reduce their axial capacity. They can sustain static and dynamic loading and are increasingly used in applications that induce complex loading conditions on them. The behavior and design of single vertical helical piles subjected to static loading is well investigated. However, a few studies investigated the dynamic or seismic behavior of single helical piles and their group behavior. This paper presents recent advances in evaluating the axial and lateral capacity and performance of helical piles and their response to dynamic and seismic loads.