Daniel Levacher

PROCEDURES USED FOR DYNAMICALLY LATERALLY LOADED PILE TESTS IN A CENTRIFUGE

Most of the experimental work carried on pile behavior on centrifuge has been limited to monotonic or cyclic loading, or both. As dynamic loads generated by shocks and earthquakes are difficult to model in centrifuge, not much work has been reported in the literature on the impact mechanism to produce shock in-flight, though seismic loads can be well simulated by in-flight shakers. A complete experimental procedure, i.e., hammering system, measurements, and test procedures, has been developed to test on centrifuge lateral impact on piles. In the first part of the paper following the test procedure, the experimental set-up is detailed from the soil preparation and piles equipment to the horizontal hammering or impact system. Innovative parts of the system such as the impact system and its monitoring are described. The second part describes the feasibility and the practice of the impact device and the adopted procedure to test on centrifuge different types of piles _jacked, cast-in, and 1 g driven_ in sand. The first series of tests are focused on the evaluation of possible errors and influences due to pile position, boundary effects, and repeatability of tests. Scale effects have been studied by carrying out a series of modeling of models tests at 40 and 60 g. In conclusion, all these preliminary centrifuge tests have demonstrated that the complete experimental set-up including the impact system and its use procedure is achieved and able to perform horizontal impacted piles tests on centrifuge.

Effects of the use of fly ash as a binder on the mechanical behaviour of treated dredged sediments

The objective of this work was to evaluate the suitability of dredged sediments treated with pozzolanic binders as a pavement base material, and to assess the usefulness of fly ash as a soil mixture/binder with the aim of improving the engineering properties of the stabilized dredged sediments in order to make them capable of taking more load from the foundation structures. Comparing the results with other binders currently used in road construction, the addition of fly ash shows significant positive advantages. The present study covers the characterization of the dredged sediments and fly ash, compaction behaviour, pH measurement, effect on unconfined compressive strength, and the effect of cyclic wet–dry and freeze–thaw tests.

Utilization of fly ash for stabilization of marine dredged sediments

ABSTRACT Disposal of large sediment from dredging activities is increasingly intractable problem in France. The reuse of dredged sediment as a new material for the construction of foundation and base layers for roads is one of the solution. The main objective of this paper is to describe the behavioral aspect of dredged sediment stabilized with fly ash as a binder for a use in road pavement work. The addition of fly ash as a partial cement replacement is realized due to its engineering, economic and ecological benefits. The first stage contains a determination of the physical and mechanical characteristics of the fly ash and the dredged sediments. In the next stage, the dredged sediment from harbor of Cherbourg has been considered using 2 different types of fly ash and different percentage of fly ash ranging from 5 to 30% by weight of sediment. Finally, the mechanical characteristics of the mix with fly ash addition are compared with the mix with conventional used binders (cement).The experimental results show that the addition of fly ash gives a positive influence on the strength gained of the sample.

Caractérisation de sédiments marins pour une mise en dépôt à terre et en remblai

ABSTRACT To reuse dredged sludge for earth structures such as unconfined or non embankments, a methodology is proposed to characterize marine sediments. This concerns physical, hydraulic and consolidation properties which constitutes a basis for the design of any embankment with sediments. A series of 8 marine sediments coming from the French Channel coast (2) and Mediterranean sea (6) is studied using different sedimentation, oedometric and creep testing. All the results are analyzed and presented in this paper. The main data are relative to the grain size distribution and Atterberg limits and relationships between permeability and void ratio or concentration. Finally some consolidation data are summarized in comparison with compressible soils.

L'envasement dans les ports: Etudes de cas en Loire-Atlantique

ABSTRACT The distributions of mud deposits and turbidities are studied in the estuary of the river Loire and in the coastal area of Loire-Atlantique (France). A description of the sedimentary dynamics is given in regard to tidal streams and water agitation due to waves. The silting up of the harbour sites is investigated in relation with the environmental conditions and local hydrodynamics associated with the harbour infrastructures. Some configurations are suggested for the implantation of fishing ports and marinas, taking into account economical and environmental conditions. A possible solution for the long term harbour planning in the estuary of the river Loire is suggested; it would induce an important decrease of the maintenance dredgings.

Solidification d'une vase de dragage : Etude de l'amélioration des propriétés physico-mécaniques par addition de ciment

ABSTRACT Important quantities of sludge are dredged and moved to deposit sites or sea. Limited sites and stringent regulations on land and sea disposal of dredged materials are prompting researchers and developments of improved methods to modify their natural structure. In this paper, the investigations are conducted to assess the physical and mechanical improvement of dredged sludge properties by cement-based solidification. The study is performed to evaluate the effect of several parameters such as: cement content, nature of cement and curing conditions. As for the results, they concern the compressive strength, water content after solidification, porosity and the ultrasonic velocity. Statistics analysis is made in order to draw the main factors. Further, the ultrasonic velocity. Statistics analysis is made in order to draw the main factors. Further, the findings show that air cured specimens result in drop of the compressive strength (up to 8%) after immersion in water.

Durability properties of marine sediments stabilised by pozzolan and alkali-activated binders

The Mont-Saint-Michel Project has been carried out to restore the maritime characteristics that existed before 1995. Attempts have been made to use marine sediments e.g. in the construction of pavements and driveways. Hence, methods to stabilise marine sediments have recently been developed. A new approach to sediment stabilisation is here proposed by using pozzolan and alkali-activated binders. Freeze–thaw and wet–dry tests are conducted to determine the durability of the sediments and to examine their suitability for use as construction material. The binders are prepared by alkali activation using pozzolan, and different amounts of the binders are mixed with marine sediment. The surfaces of one group of sediments are treated by a substance containing liquid glass. We compare the durability properties and deformation behaviours of two different types of specimen, by conducting tests and taking into consideration climatic conditions. The sediments stabilised by surface treatment showed high durability properties. Dans le cadre du projet de restauration du caractère maritime du Mont-Saint-Michel s’est posée la question du devenir de la quantité des sédiments résultant de l’aménagement prévu. Les stabiliser et les réutiliser en tant que matériau routier et de voirie constitue une filière intéressante. Une nouvelle approche utilisant des liants poussolaniques et l’alcali activation, est proposée. Des essais de durabilité ont été menés sur des éprouvettes préparées pour différents taux de liants pouzzolaniques mélangés au sédiment. Un groupe d’éprouvettes a fait l’objet d’un traitement de surface à base d’un produit industriel de durcissement. L’analyse comportementale porte sur la comparaison des propriétés mécaniques et de durabilité notamment pour les sédiments stabilisés et traités en surface.

Cone penetration technology for coastal environmental monitoring

ABSTRACT Cone penetration technology has increasingly been used for environmental characterization and monitoring purposes. Cone penetration testing has made a great progress in last 15 years and the interpretations of obtained results are based on established principles. Incorporation of geophysical techniques into CPT offers a new way to characterize subsurface conditions in coastal areas. In the present paper, the authors review some of the technologies to delineate the soil conditions. Two case histories are presented, one comparing the performance of conventional monitoring well with that of cone penetrometer enabled well and the second is the CPT based laser induced fluorescence to detail the concentration of polyaromatic hydrocarbon (PAH) in harbour sediments.

Effet des cycles sur le comportement d'un pieu isolé dans un sable dense sous chargement latéral

ABSTRACT Many tests have been conducted these last few years in the centrifuge of the LCPC centre in Nantes in order to study the behaviour of laterally loaded piles. This paper concerns a feasibility study performed in the year 2000 on a single pile submitted to lateral cyclic loads. The experimental set up, measurements and data acquisition techniques are briefly given. Analyses are focused on the obtained results concerning the influence of cycles—mainly their amplitude—on the pile stiffness, on the top displacements, on the maximal bending moment and on the P-y reaction curves.

NON-LINEAR BEHAVIOR OF LATERAL-LOADED PILE TAKING INTO ACCOUNT THE SHEAR STRESS AT THE SAND

Due to recent research advances in understanding mechanisms that govern the behavior of deep foundations, vertical piles can now be used to correctly support lateral loads. This paper concerns the development of a computer program for studying non-linear behavior of lateral-loaded piles taking into account the shear stress at the sand. Some examples issued from the numerical code are compared with experimental results from centrifuge modeling loaded piles tests and with other numerical results from a well-known code used in France. The influence of shear stress at the soil on the behavior of laterally loaded piles was also studied.