Alessandro Mandolini

Kinematic response analysis of piled foundations under seismic excitation

This paper presents the results of an extensive parametric study on single piles and pile groups embedded in a two-layer subsoil profile, and is aimed to evaluate kinematic bending moments developi...

Full Scale Loading Tests on Instrumented CFA Piles

Continuous flight auger piles (CFA) procedure allows the rapid installation of piles with diameters usually ranging from 0,4 to 1,0 m and a length up to 30-35 m, free from the vibration and noise of driven piles and substantially reducing the ground loosening of bored piles. CFA are becoming increasingly popular in many countries, and sometimes they are claimed to have the advantages of both driven and bored piles, without the related shortcomings. The behaviour of CFA piles, however, is actually affected by technological factors; among them the capacity of the equipment in terms of thrust and torque and the volume of concrete pumped in during auger retrieval. In the paper the results of three failure loading tests on instrumented CFA piles are presented. The analysis of the observed behaviours confirm that the CFA piles are somewhat intermediate between bored and driven piles. Introduction Continuous Flight Auger (CFA) piles are installed by means of an auger with a hollow stem having an inner diameter of 10 to 20 cm, inserted into the soil by the combined action of an axial thrust and a torque. The stem is provided with a temporary closure plate at the bottom; after the auger has reached the desired depth, the plate is pushed out by pumping concrete or mortar through the stem, and the auger is lifted removing from the ground the soil within the screw. The sides of the hole are thus supported at all times by the soil filled auger or by the pumped concrete. The procedure allows a rapid and noiseless installation of piles with diameter of 40 to 100 cm and length up to 30-35 m, and is becoming increasingly popular all over the world. The ratio between the rate of penetration and the rate of revolution of the auger is generally less than the pitch of the screw; the penetration involves thus a lateral compression but also the removal of some soil. Further removal of soil occurs during the extraction stage. If the volume of the removed soil is less than the final volume of the pile, the net resulting effect is a compression of the soil surrounding the pile; the resulting stress state within the soil is somewhat intermediate between that of a bored pile and that of a driven one.

The Role of Pile Diameter on Earthquake-Induced Bending

Pile foundations in seismic areas should be designed against two simultaneous actions arising from kinematic and inertial soil-structure interaction, which develop as a result of soil deformations in the vicinity of the pile and inertial loads imposed at the pile head. Due to the distinct nature of these phenomena, variable resistance patterns develop along the pile, which are affected in a different manner and extent by structural, seismological and geotechnical characteristics. A theoretical study is presented in this article, which aims at exploring the importance of pile diameter in resisting these actions. It is demonstrated that (a) for large diameter piles in soft soils, kinematic interaction dominates over inertial interaction; (b) a minimum and a maximum admissible diameter can be defined, beyond which a pile under a restraining cap will inevitably yield at the head i.e., even when highest material quality and/or amount of reinforcement are employed; (c) an optimal diameter can be defined that maximizes safety against bending failure. The role of diameter in seismically-induced bending is investigated for both steel and concrete piles in homogenous soils as well as soils with stiffness increasing proportionally with depth. A number of closed-form solutions are presented, by means of which a number of design issues are discussed.

Effects of residual stresses on shaft friction of bored cast in situ piles in sand

The existence of residual stresses locked-in prefabricated displacement piles is a well-known problem and has been addressed by a number of researchers in the last decades. This is not the case with cast in situ piles: as a consequence of concrete curing, pile-soil interaction starts soon after concrete casting, causing stress changes in terms of both normal and shear stresses. Such circumstance has been confirmed by few experimental evidences, reported in the paper, in saturated or dry soil conditions. In order to evaluate the influence of residual stresses on the subsequent pile response to axial loading, a broad parametric study has been carried out by means of numerical modelling. Particular focus is given to the effects induced on the shaft friction of floating bored piles embedded in wet and dry sandy soils. The results have been interpreted with the aim of highlighting errors commonly made if a stress-free pile is assumed when interpreting a specific load test results on instrumented piles and/or arranging general design methods.

Size Limitations for Piles in Seismic Regions

A novel theoretical study exploring the importance of pile diameter in resisting seismic actions of both the kinematic and the inertial type is reported. With reference to a pile under a restraining cap, it is shown analytically that for any given set of design parameters, a range of admissible pile diameters exists, bounded by a minimum and a maximum value above and below which the pile will yield at the top even with highest material quality and amount of reinforcement. The critical diameters depend mainly on seismicity, soil stiffness and safety factor against gravity loading, and to a lesser extent on structural strength. This scale effect is not present at interfaces separating soil layers of different stiffness, yet it may govern design at the pile head. The work at hand deals with both steel and concrete piles embedded in soils of uniform or increasing stiffness with depth. Closed-form solutions are derived for a number of cases, while others are treated numerically. Application examples and design issues are discussed.

3M Analytical Method: Evaluation of Shaft Friction of Bored Piles in Sands

AbstractThis study presents 3M, an analytical method to estimate the skin friction of bored piles in sands. It is based on the fundamental mechanic behavior of sands and keeps track of the major mechanisms occurring in the soil close to the pile during loading. These include the development of a shear band, its potential expansion as induced by soil dilatancy, and the ensuing increment of horizontal stresses owing to the restraining effect of surrounding soils. The resulting analytical equations are easy to apply and insert in a worksheet. The procedure to evaluate the shear band expansion is calibrated against results of direct shear tests at constant normal load, whereas the increment of horizontal stresses is evaluated by the closed-form solution for the expansion of a cylindrical cavity into a dilatant elastic–perfectly plastic medium. The effectiveness of the 3M method in predicting shaft friction has been checked against numerical results, centrifuge, and full scale pile load tests. Nevertheless, pr...

Effects of the filtering action exerted by piles on the seismic response of RC frame buildings

Abstract The inertial interaction analysis of a structure founded on piles is usually performed assuming the free-field motion as seismic action at the foundation level, thus neglecting the filtering action often exerted by piles. By contrast, the existence of frequency filtering is confirmed through works referring to theoretical and experimental studies, even if this effect is generally neglected in design practice. In this paper the seismic performance of frame buildings, excited by filtered and free-field input motions is evaluated. The results of these analyses, expressed in terms of top displacement and base shear, allow for assessing the importance of the beneficial effect coming from the piles on the inertial response of the superstructure.

Corrigendum to "Kinematic response of single piles for different boundary conditions

Corrigendum to ‘‘Kinematic response of single piles for different boundary conditions: Analytical solutions and normalization schemes’’ [Soil Dynam. Earthquake Eng. 44 (2013) 183–195] George Anoyatis , Raffaele Di Laora , Alessandro Mandolini , George Mylonakis a,n a Department of Civil Engineering, University of Patras, 26500 Rio, Patras, Greece b Department of Civil Engineering, Second University of Naples, Aversa (CE), Italy

Corrigendum to “Kinematic response of single piles for different boundary conditions: Analytical solutions and normalization schemes”

Corrigendum to ‘‘Kinematic response of single piles for different boundary conditions: Analytical solutions and normalization schemes’’ [Soil Dynam. Earthquake Eng. 44 (2013) 183–195] George Anoyatis , Raffaele Di Laora , Alessandro Mandolini , George Mylonakis a,n a Department of Civil Engineering, University of Patras, 26500 Rio, Patras, Greece b Department of Civil Engineering, Second University of Naples, Aversa (CE), Italy

Corrigendum to “Kinematic response of single piles for different boundary conditions: Analytical solutions and normalization schemes”: [Soil Dynam. Earthquake Eng. 44 (2013) 183–195]

Corrigendum to ‘‘Kinematic response of single piles for different boundary conditions: Analytical solutions and normalization schemes’’ [Soil Dynam. Earthquake Eng. 44 (2013) 183–195] George Anoyatis , Raffaele Di Laora , Alessandro Mandolini , George Mylonakis a,n a Department of Civil Engineering, University of Patras, 26500 Rio, Patras, Greece b Department of Civil Engineering, Second University of Naples, Aversa (CE), Italy