Seismic behaviour of soft clay and its influence on the response of friction pile foundations

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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Influence of the phase difference between kinematic and inertial loads on seismic behaviour of pile foundations in layered soils

Canadian Geotechnical Journal ◽

10.1139/cgj-2019-0547 ◽

2020 ◽

Author(s):

Thejesh Kumar Garala ◽

Gopal Madabhushi

Keyword(s):

Natural Frequency ◽

Free Field ◽

Phase Relationship ◽

Phase Variation ◽

Bending Moment ◽

Pile Group ◽

Pile Foundations ◽

Single Pile ◽

Seismic Behaviour ◽

Soil Layers

A series of dynamic centrifuge experiments was conducted on model pile foundations embedded in a two-layered soil profile consisted of soft-clay layer underlain by dense sand. These experiments were specifically designed to investigate the individual effect of kinematic and inertial loads on a single pile and a 3×1 row pile group during model earthquakes. It was observed that the ratio of free-field soil natural frequency to the natural frequency of structure might not govern the phase relationship between the kinematic and inertial loads for pile foundations as reported in some previous research. The phase relationship obtained in this study agrees well with the conventional phase variation between the force and displacement of a viscously damped simple oscillator subjected to a harmonic force. Further, as expected, the pile accelerations and bending moments can be smaller when the kinematic and inertial loads act against each other compared to the case when they act together on the pile foundations. This study also revealed that the peak kinematic pile bending moment will be at the interface of soil layers for both single pile and pile group. However, in the presence of both kinematic and inertial loads, the peak pile bending moment can occur either at the shallower depths or at the interface of soil layers depending on the pile cap rotational constraint.

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A Review on Effect of Pile Stiffness on Seismic Response of Structure

International Journal for Research in Applied Science and Engineering Technology ◽

10.22214/ijraset.2021.39357 ◽

2021 ◽

Vol 9 (12) ◽

pp. 772-774

Author(s):

Mohit Bharat Dange

Keyword(s):

Seismic Response ◽

Pile Foundation ◽

Seismic Loading ◽

Pile Foundations ◽

Seismic Behaviour ◽

Foundation Design ◽

Earthquake Loads ◽

Pile Cap ◽

Seismic Forces ◽

Shaky Ground

Abstract: Pile foundations are widely employed for a variety of structures on shaky ground. The importance of seismic design in ensuring the effective operation of a structure under severe seismic loading conditions cannot be overstated. For the analysis of seismic forces on a structure, IS 1893 will be employed. This research entails the choosing of a specific form of building structure. A comparison of buildings with and without pile foundations will be shown. Because of the differences in their properties, the seismic behaviour of the various structures differs. The influence of pile stiffness on the structure's seismic response will be investigated. The rigidity of the piling foundation could have an impact on the structure.With the rise in seismic activity, there may be a need for more efficient pile foundation design to withstand earthquake loads. The major goal of this study is to compare pile stiffness with changes in diameter and zone. Keywords: Pile Foundation, STAAD-Pro, Structure, Stiffness, zone, Pile Cap, Load Estimation, Pile cap, Pattern of Pile.

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