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The use of optical fiber for measuring strain and or temperature is increasing in civil engineering. Optical fiber is known to be relatively cheap, compared to the more traditional sensors commonly used, and can, depending on the chosen technology, give a complete distribution along the instrumented element, which can be very interesting in case of an element with variable dimensions along the length of said element. Therefore, for static pile loading tests, the use of optical fiber should present many advantages, compared to more conventional methods of strain measurements. The aim of this paper is to shed new light on the advantages and disadvantages of using optical fiber for the measurement of deformations along a foundation element. After a review of the state of the art of the most commonly used methods, the contribution of the optical fiber for the instrumentation of the foundation elements is evaluated, by comparing the results obtained by the use of the fiber with those obtained with more traditional methods, in some examples of full-scale load tests. Finally, some recommendations are given to maximize the awareness of the potential use of optical fiber in foundation monitoring.

JNGG 2020, Journées Nationales de Géotechnique et de Géologie de l'Ingénieur, LYON, FRANCE, 02-/11/2020 - 03/11/2020; Le développement de la géothermie utilisant des structures thermoactives pose des questions au sujet des interactions qui peuvent exister entre différentes installations, dues aux phénomènes d'advection induits par les déplacements de nappe. Une étude des perturbations thermiques induites entre structures est menée sur le cas test d'un groupe de neuf pieux thermoactifs via une approche physique et numérique.

The thesis aims to study the mechanical behaviour of sand under simple shear condition and to apply the results to the numerical simulation of pile foundation. First, a recently developed critical state sand model (SIMSAND) is introduced with a straight forward procedure of parameters determination, implemented into a finite element code and then subjected to a series of validations. Then, the model is enhanced by considering the inherent anisotropy during the principal stress rotation under the simple shear condition and validated by using results of both triaxial tests and simple shear tests on Fontainebleau sand. Simple shear tests are analysed by simulating in three-dimensions the real conditions imposed by the simple shear apparatus. The inhomogeneity of the samples with the effect of sample size is also investigated. Furthermore, undrained and drained cyclic simple shear tests on Fontainebleau sand are conducted to investigate the cyclic responses, such as the effective normal stress degradation and the volumetric strain accumulation, respectively, considering some impact factors such as the initial void ratio, the normal stress, the cyclic shear stress ratio and the average shear stress ratio. Based on these results, two analytical models are proposed to predict the long-term degradation of the effective normal stress and the accumulation of the volumetric strain with the number of cycles. Moreover, the cyclic simple shear tests are simulated by the enhanced SIMSAND model by incorporating the stress reversal technique. Finally, a series of model pile tests under monotonic and cyclic loadings are simulated based on which the cone resistance of the piles is evaluated as well as the response of the soil surrounding the pile.; La thèse vise à étudier le comportement mécanique des sables sous la condition de cisaillement simple et à son application au calcul des pieux. Tout d'abord, un modèle de sable récemment développé (SIMSAND) prenant en compte l'état critique est introduit avec une procédure directe de détermination des paramètres. Le modèle est implanté dans un code de calcul aux éléments finis qui a fait l’objet de différentes validations. Ensuite, le modèle est amélioré en considérant l'anisotropie inhérente lors de la rotation des contraintes principales sous la condition de cisaillement simple et a été validé en utilisant les résultats des essais tri axiaux et de cisaillement simple sur le sable de Fontainebleau. Les essais de cisaillement simple sont analysés en imposant les conditions de sollicitations réelles tridimensionnelles appliquées par l’appareillage utilisé. L'inhomogénéité de l'échantillon avec l'effet de la taille de l'échantillon est également étudiée. Puis, des essais de cisaillement simple cycliques drainés et non-drainés sur le sable de Fontainebleau sont effectués pour étudier les caractéristiques sous charges cycliques, telles que la dégradation de la contrainte normale effective et l'accumulation de la déformation volumique, compte tenus de certains facteurs comme l’indice des vide initial, la contrainte normale appliquée, le rapport de contrainte de cisaillement cyclique et le rapport de contrainte de cisaillement moyenne. Sur la base de ces résultats, deux modèles analytiques sont proposés pour prédire la dégradation à long terme de la contrainte normale effective et l'accumulation des déformations volumiques en fonction du nombre de cycles. En outre, les essais cycliques de cisaillement simple sont simulés par le modèle SIMSAND amélioré en utilisant une technique d'inversion de contrainte. Enfin, on simule une série de pieux modèles sous charges monotone et cyclique pour laquelle la résistance en pointe du pieu est évaluée ainsi que la réponse du sol entourant le pieu.

Bellow-hose settlement gauges were used to measure vertical soil heave during the installation of concrete piles in sensitive marine clay. The equipment is described and the sources of error are discussed.

Vibration measurements in the main powerhouse at Inuvik, NWT, were taken to determine the amplitudes of vibration present in a structure supported on pile foundations in permafrost and subjected to large dynamic periodic forces. Accelerometers were placed on the support system for the main diesel generator and on the floor and pile foundation of the one-storey industrial building. One-third octave band RMS acceleration amplitudes produced by the generator, a 5.2 MW system, are presented. In comparison to ambient acceleration amplitudes (generator off), amplitudes produced by the generator were approximately 430 times larger on the structural system supporting the generator and five to ten times larger throughout the remainder of the powerhouse.

The adfreeze strength developed during freezing of cylindrical piles to fine Ottawa sand mixed with 14% by weight of water was measured under constant rates of pile displacement on an Instron testing machine and under constant load [in a creep equipment]. Four types of pile were studied: natural B.C. fir, concrete, steel coated with a red oxide primer, and creosoted B.C. fir. Constant rate tests showed that adfreeze strength increased with increasing load rate. Preliminary data from the constant load creep tests indicate that the load dependence of the steady-state creep rate for piles in frozen sand agrees with the displacement rate dependence of the adfreeze strengths determined by extrapolation of the results of the constant rate tests. In general, maximum adfreeze strength developed with natural B.C. fir, and the minimum with creosoted B.C. fir.

Results of several long-term creep tests of piles in frozen soils are analyzed; the primary or attenuating creep is predominant in most cases. For effective design of pile foundations in permafrost areas, this aspect should be taken into consideration., ASCE Spring Convention: Foundations in Permafrost and Seasonal Frost, April 29, 1985, Denver, Colorado, USA

Preliminary results of laboratory studies on the behaviour of model piles of wood, concrete, and steel, having different surface finishes, embedded in artificially frozen sand and subject to constant loads, are reported in this paper. The displacement rate [Formula: see text], was found to vary with the applied stress [Formula: see text]f, according to a steady state creep equation of the type [Formula: see text], as found for other viscoelastic materials such as metals at high temperature. The value of the exponent n varied between 6.7 and 9.1 for various types of piles.The results agreed favourably with field data obtained from pile pull-out tests carried out at Gillam and Thompson, Manitoba. The value of n from Gillam and Thompson tests, 8.05 and 7.5, respectively, were within the range of the present experimental values. Comparison with pile pull-out tests carried out in ice, and theoretical predictions for ice showed that the value of the exponent n was much larger for frozen soil than for ice. The bearing capacity at a particular displacement rate was also found to be almost an order of magnitude larger in frozen soil than in ice.

The Quebec autoroute on the North Shore of the St. Lawrence River between Montreal and Quebec City traverses deep deposits of compressible marine clay. One of the overpass structures at Berthierville is supported on twelve 39-in. (1 m) diameter reinforced concrete piles, which pass through 270 ft (82 m) of soil and finally rest on shale bedrock. The paper presents measurements of settlement and pore water pressures in the soil at various depths under the fill, and of axial deformations in two of the piles. It provides a set of relatively rare field observations on which to base an approximate evaluation of the rate and magnitude of negative skin friction development under the described field conditions.

La moitié environ de la superficie totale du pays est occupée par le pergélisol, un terrain qui reste toujours gelé en profondeur, et comme le Canada se développe vers le nord, cette particularité du sol doit être prise en considération. Le présent Digeste décrit brièvement le pergélisol et ses traits caractéristiques, et traite des questions touchant le genre de fondations convenables dans les régions où il existe.

The paper gives results of field studies on uplift forces on small-diameter columns of steel, concrete, and wood caused by adfreezing in frost-susceptible Leda clay. Adfreeze strength values would appear to be highest for steel and concrete, followed closely by wood. The heaving pattern and the heaving force transmitted are shown to be different for long foundation walls than for isolated columns. This compares favorably with the deformation pattern induced in an ice cover around offshore structures, during a change in water level. Attention is also given to the relative movement of the heaving soil with respect to the structure and the influence of the heave pattern on the transmission of forces.

About one half of the total land area of Canada is underlain by perennially frozen ground, more commonly known as permafrost, and as development moves northward consideration must be given to this feature of the terrain. This Digest briefly describes permafrost and its characteristics and discusses problems related to foundation design in permafrost areas.

While permafrost provides excellent bearing for structures, it may lose its strength to such an extent that it will not even support light structures when thawed. Differential settlement is normal and usually results in serious damage or building collapse. Pile foundations were used extensively at Inuvik, NWT, an area of continuous permafrost to depths of over 300 ft. The use of piles at Inuvik was a suitable foundation type for the majority of buildings and facilities., Permafrost International Conference, 1966