Soil liquefaction is one of the most destructive problems produced during earthquakes and its analysis presents difficulties associated with taking samples and performing tests under the surface. Against this, in situ analysis method based on penetration tests (CPT, SPT) have been developed. Each penetration equipment has its own characteristics and different application possibilities, so it is necessary to expand the analysis methods to other equipment. This paper presents a state of the art on the application of the PANDA® variable energy light dynamic penetrometer in the analysis of resistance to liquefaction. An exhaustive bibliographic review of the PANDA® penetrometer developed methods has been carried out. It is concluded that the methods presented are applicable for the preliminary analysis of liquefaction resistance.

The Francis Cour® Monocell probe is an innovative pressuremeter probe that takes advantage of recent developments in membrane technology. Its enhanced capabilities open access to the in-situ measurement of the shear modulus G at small strains (between 10 and 10), a domain generally reserved for flexible dilatometers. The validation of its measurement capabilities is underway. This paper focuses on validation tests with the Francis Cour Monocell probe carried out on a reference field site. Special testing procedures including unload-reload loops were performed aiming to assess soil non-linear elastic response. The testing site subsoil, mainly composed by overconsolidated clay, has been previously characterized by various in-situ and laboratory tests. Testing procedures and interpretation methods are described and discussed. Shear moduli obtained are compared to geophysical and laboratory data collected on the site. This work is part of the French National Project ARSCOP.

Soil liquefaction is one of the most destructive phenomena caused by earthquakes. Nowadays, it has been mainly studied regarding the risk assessment trough in-situ penetration tests (SPT, CPT) that allow identification of potentially liquefiable layers. However, most of these techniques are limited by site accessibility, cost and amount of information collected during the survey. Development of portable, cost effective and efficient equipment as well as the methods to assess cyclic resistance ratio (CRR) are necessary. This paper presents the first results aimed at establishing a pseudo-empirical laboratory methodology for liquefaction risk assessment of sandy soils through a lightweight instrumented dynamic penetrometer. A series of dynamic test on sand samples were performed in calibration chamber. Filling material of each sample is sand of Fontainebleau, different density and overburden pressure has been reproduced. On each sample, a dynamic penetration test was conducted and for each hammer blow, strain, forces, acceleration and displacement were recorded as well as dynamic penetration resistance ( ), computed by wave equation analysis, are obtained. At the end, graphs or charts for correlating qd, density index and overburden pressure are presented in order to assess CRR of soil.

The study of the influence of fines particles on the phenomenon of liquefaction of sands has been a controversial subject where no clear conclusions can be drawn as to in what manner the presence of these particles affect the liquefaction resistance of sand. This paper presents a study of the influence of non-plastic fines on the resistance to liquefaction of sand-fines mixtures. The study is carried out using a triaxial apparatus on reconstituted sand-silica mixtures for low fractions of fines. After presenting the soils used in this study, this paper presents the results of undrained monotonic liquefaction tests performed of sand specimens containing different fines fractions. Experimental results show that the increase in fines content up to 5% increases the resistance of sand to liquefaction. This result is due to the contribution of the fine particles to the overall chain forces and therefore they increase the resistance against liquefaction.

: Abstract An offshore wind farm will be developed in France at the Fecamp site covering in excess of 67 km². In this location, medium to high density chalk containing flint nodules is found. In this paper, some of the hydro-mechanical properties of this specific marine chalk are presented, aiming to characterize the first meters of the chalk more precisely for the design of gravity base foundations. A series of undrained static and cyclic triaxial tests carried out on 100 mm and 300 mm diameter specimens of weathered chalk are presented. Specimens have been recovered from 100 mm, 300 and 500 mm diameter vibrocore sections. Results show, upon undrained static tests, that the material presents essentially dilative behaviour and usually generates negative excess pore water pressures during shear. Upon undrained cyclic tests, the material shows a progressive development of fairly significant positive excess pore water pressures and relatively high values of axial strains. Results also indicate that the excess pore water pressure dissipation, after a sequence of cycles, induces a densification of the material which results, upon post-cyclic undrained static shear, in a more dilative response resulting in higher values of undrained shear strength.

The construction of embankments and other earth hydraulic structures using coarse soils requires assessing their potential for internal erosion by suffusion, defined as detachment and transport of fine particles through the matrix constrictions under internal flow. For potentially erodible coarse soils containing a certain amount of clays, a possible remedial solution is the lime treatment which is studied in this work in an experimental program consisting in: erosion test, crumb test, unconfined compression test and microstructure characterization tests (SEM, mercury intrusion porosity). The experiments were carried out on a reconstituted soil owing similar characteristics to natural coarse soils. The treatment reported in this study is carried out using a minimum lime content of only 1%, which can be achieved in situ in a cost-effective manner. Comparisons of results on treated and untreated soils showed that the lime treatment is effective after only 24h of treatment. The suffusion is stopped, the agglomeration of the particles generated by the treatment seems to be maintained after samples immersion and the unconfined compressive strength (UCS) is improved. The microstructure observations of the fine part of the soil (particles smaller than 1mm) showed the appearance of agglomerates generating an increase of the pore volume.

The 'Interlayer' soil in the French conventional railways track-beds, a coarse grain soil with low permeability, was studied at different hydric conditions: w = 4% (OPM) and w = 10% (Saturated) using a large-scale triaxial ((sic) = 300 mm) cell. For each test, 5 different cyclic loading levels has been considered (from Delta q = 10 kPa to Delta q = 30 kPa per cycle). The loading levels simulate the real loading at the interlayer depth in a real railway track-bed. The results clearly show the influence of the non-saturation on the evolution of elastic modulus and damping ratio. When the loading level is increased, the elastic modulus decreases and the damping ratio increases. The accumulation of plastic strains after 90000 cycles was also analyzed for both hydric conditions, showing that the initial moisture content and the elastic modulus greatly affect the accumulative strains.

The influence of initial sand structure on the liquefaction properties of a reference French sand is studied based on the use of two modes of reconstitution of specimens, namely dry pluviation and wet tamping. Undrained compression tests carried out in the triaxial apparatus for the same initial void ratio of specimens show well-differentiated behaviors as a function of the mode of reconstitution used. Wet tamping favors the initiation of a static liquefaction type of phenomenon (unstable behavior), whereas dry pluviation favors a dilating type of response characterized by a strain-hardening type of behavior (stable behavior). Electron microscope observations have allowed to identify two different sand structures corresponding to the two types of reconstitution methods: an aggregates and macropores type of structure is observed for specimens prepared using wet tamping method whereas a more regular single-grained arrangement is observed for specimens prepared using dry pluviation. The differences in behavior observed are then interpreted in terms of volumetric behavior of the sand (contractancy and dilatancy), which depends on the initial sand structure.

Various mechanisms can affect the permeability of dense unconsolidated sands: volumetric dilation can lead to permeability increase whereas strain localization in shear bands may increase or decrease the permeability depending on the state of compaction and on the level of grains breakage inside the band. In order to investigate these various mechanisms, an experimental study has been performed to explore the effect of different factors such as grain size and grain shape, confining pressure, the level of shear, and the formation of one or several shear bands on the permeability of dense sands under triaxial loading. The experimental results show a reduction of permeability during the consolidation phase and during the phase of volumetric contraction of shear loading which can be related to the decrease of porosity. The experimental results also show that, depending on the confining pressure, the permeability remains stable or decrease during the phase of volumetric dilation despite the increase of the total porosity. This permeability reduction is attributed to the presence of fine particles which result from grains attrition observed during pre-localization and grains breakage inside the shear band observed during the post-localization phase.

The liquefaction susceptibility of saturated sand-silt mixture samples is evaluated by cyclic undrained triaxial tests that were carried out on reconstituted specimens of three Algerian sands at a density index, ID, of 0.5 and an initial confining pressure, σ′c, of 100 kPa. The sand material matrix is kept as a constant parameter for the entire range of fines content due to the difficulty of determining experimentally the extreme void ratios of soil mixtures for fines content, FC, exceeding 15%. The test results were used to conclude on the effect of the fines content and other parameters on the liquefaction resistance of the sand-silt mixtures. Indeed, the fines content affects considerably the liquefaction resistance and the generated excess pore pressure. Moreover, the effect of fines is in good agreement with the published literature, where the cyclic resistance ratio decreases first to a threshold value of fines content and then increases. This study can be used in soil classification and liquefaction potential assessment of seismic zones with small fines content.

Pile foundations are usually subjected to cyclic loading which can be either environmental or in dustrial. Loading and unloading sequences of the pile cause very significant variation in the behavior of the pile -soil system and generate degradation of the bearing capacity and an accumulation of irreversible displacement. The paper presents a study ofthe behavior of piles subjected to axial cyclic loading for large numbers of cycles using a physical modeling approach in a calibration chamber. To focus on the degradation of the friction in soil -pile interface, the experiments are carried out in two -way displacementcontrolled tests. Firstly, The experimental set -up was presented, then the typical results of the evolution of skin friction under cyclic loading. The results indicate that the application of a large number of cycles to the pile, the skin fric tion decrease initially then increase continually up to the end of the cyclic sequence. It can be concluded that the phase of friction reinforcement is due to a partially constrained dilatancy phenomenon of the sand within the interface zone .

This paper presents the driving factors for the interlayer creation and mud pumping phenomena in railway sub-structure. Physical model tests on a ballast layer overlying a sub-soil layer were carried out under different conditions in terms of water content, loading and sub-soil dry unit mass. The physical model was equipped with various sensors and devices allowing pore water pressure, axial displacement to be monitored. Visual observations were also made using a digital camera. It was observed that the ballast behavior depends on the sub-soil state. Both the interlayer creation and mud pumping are related to the migration of fine particles, and the water content of the sub-soil is the most important factor for this migration. Under the unsaturated conditions, the ballast/sub-soil interface did not change. On the contrary, under the near saturated conditions, significant migration of fine particles occurred. In case of low dry unit mass, the dissipation of high pore water pressure in the sub-soil gave rise to mud pumping. In case of higher dry unit mass, the excess pore water pressure was lower due to the smaller volume change of sub-soil. As a result, the effect of water pressure dissipation was limited and the upward migration of fine particles was only due to the penetration of ballast into the sub-soil, thereby, forming the interlayer.

The fundamental understanding of the behaviour of dry sand as it is being vibrated is necessary to properly address a number of engineering issues, such as the vibrocompaction process. The present paper first summarizes experimental works focusing on the effects of vibrations on the volume change of dry cohesionless soils. Original experiments characterizing the behaviour of dry sand subjected to vertical vibration are then presented. The volume change and the motion pattern displayed by vertically vibrated sand particles are discussed. When cohesionless soil, placed in a cylindrical container, is vertically vibrated under the gravitational field (g), experiments performed on dry Fontainebleau sand allow the distinction between three types of dynamic behaviours depending on the acceleration amplitude (a): the densification behaviour (a/g < 1), the instability surface behaviour (a/g ≈ 1), and the vibrofluid behaviour (a/g > 1). In the densification range, the sand simply settles. When the acceleration amplitude is increased beyond 1g, granular convection is observed and there is an instability in the sand mass leading to the emergence of an inclined free surface. If the acceleration amplitude is further increased, the free surface progressively flattens. There is an impressive dilatation of the whole sample and grain saltation is observed. The sand becomes fully vibrofluidized. The efficiency of the vibrocompaction process is finally discussed especially with regard to these dynamic behaviours.