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Dynamic Cone Penetration Test (CPTu) profile offshore sediments by impact penetration. To exploit their results in full, the measured data are converted to obtain a quasi-static equivalent profile. Dynamic CPTu conversion requires calibrated correction models. Calibration is currently done by using paired (i.e., very close) quasi-static and dynamic tests. It is shown here that paired test data, which may be inconvenient to acquire offshore, are not strictly necessary to convert dynamic CPTu data. A new probabilistic methodology is proposed to call upon quasi-static results from a much wider area in the conversion procedure. Those results feed the prior distribution of a converted profile, within a Bayesian updating scheme where strain-rate coefficient and correction model error are also described by updated stochastic variables. The updating scheme is solved numerically using the Transitional Markov Chain Monte Carlo sampling algorithm. To avoid undue influence of local profile heterogeneity, the statistic treatment of the quasi-static CPTu data takes place in the frequency domain, using a discrete cosine transform. The new procedure is applied to a CPTu campaign offshore Nice (France): dynamic tests are converted with equal precision using quasi-static data acquired at distances orders of magnitude larger than what was previously employed. Key words: dynamic CPTu, strain-rate coefficient, Transitional Markov Chain Monte Carlo, cone tip resistance, Nice, 1. Introduction Free-fall penetrometers are increasingly used for offshore sediment characterization because of their rapid deployment capabilities and relative ease of operation (Randolph et al. 2018). Free-fall penetrometers with standard [...]

Sampling disturbance is a perennial problem of geotechnical site investigation. The structure of soft soils is particularly fragile and prone to disturbance during sampling. The extent by which different sampling procedures modify soil structure has been generally assessed on an empirical basis, observing the outcomes of tests performed on specimens obtained with different sampling technologies. That kind of experiment is slow, costly and laborious. In this communication we present a procedure to perform similar experiments “in silico”, by simulating the sampling procedure, examining the effect of tube sampling on the initial soil structure, obtaining sub specimens from the simulated core and testing them afterwards in simulated triaxial undrained compression and in the oedometer. The simulations are based on G-PFEM, a code developed for soil-structure interaction at large strains. The numerical experiments clarify the origin of sampling related property variability.

An attractive approach to reduce the carbon footprint for ground improvement application is to replace Portland cementbased binders by non-cementitious binders for instance by geopolymers based on metakaolin in deep soil mixing applications or by colloidal silica and acrylates in permeation based applications. Safe design requires a good understanding of the mechanical and hydraulic properties of the improved ground but little is known about how soil is improved by these products. Besides, for permeation grouting applicability criteria are frequently set in terms of the host soil water permeability. However, for novel binders the threshold value is not known and published empirical basis for available criteria is relatively scarce. This paper summarizes results from a laboratory characterization campaign of soils of variable permeability improved with different novel binders, focusing on the effect on strength, stiffness and permeability. Observations relative to the effect of curing conditions are also provided, as well as the insight gained by examining the injection process outcomes with computed tomography. Results show how these novel products have the potential to significantly improve the mechanical properties and reduce permeability in a large range of soils.

As society moves towards decarbonisation, it is important to assess the hydromechanical behaviour of binders that could offer a low-carbon alternative to Portland cement in ground improvement technologies. This work considers two such alternatives: one still largely unexplored (metakaolin-based geopolymers) and a better known one (colloidal silica). Results from unconfined compressive strength, permeability tests, undrained monotonic and cyclic triaxial tests on granular soils (sand and silty sand) treated with those two binders are presented and discussed, emphasizing similarities and differences with the response of similar soils treated with other conventional and unconventional binders. Effects of silt content, curing conditions and soil/binder ratios are examined. Both colloidal silica and metakaolin-based geopolymer significantly improve the mechanical properties of the treated soils, although the geopolymer results in a stronger and stiffer material. Both treatments reduce much the permeability of the treated soil, but the reduction achieved with colloidal silica is larger. Key words: sand-silt mixture, triaxial tests, permeability, metakaolin-based geopolymer, colloidal silica. Dans un contexte de decarbonisation de la societe, il est important d'evaluer le comportement hydromecanique des liants qui pourraient offrir une alternative a faible teneur en carbone au ciment Portland dans les technologies d'amelioration des sols. Ce travail considere deux de ces alternatives : une encore largement inexploree (geopolymeres a base de metakaolin) et une plus connue (silice colloidale). On presente et discute les resultats d'essais de resistance a la compression non confinee, d'essais de permeabilite, d'essais triaxiaux monotones et cycliques non draines sur des sols granulaires (sable et sable silteux) traites avec ces deux liants, en soulignant les similitudes et les differences avec la reponse de sols similaires traites avec d'autres liants conventionnels et non conventionnels. On examine les effets de la teneur en limon, des conditions de durcissement et des rapports sol/liant. La silice colloidale et le geopolymere a base de metakaolin ameliorent tous deux de maniere significative les proprietes mecaniques des sols traites, bien que le geopolymere donne un materiau plus fort et plus rigide. Tous deux diminuent considerablement la permeabilite du sol traite, mais la reduction obtenue avec le silice colloidale est plus importante. [Traduit par la Redaction] Mots-cles : melange de sable et de limon, essais triaxiaux, permeabilite, geopolymere a base de metakaolin, silice colloidale., Introduction Ground improvement techniques enhance the mechanical and hydraulic properties of soils for engineering applications. Several ground improvement methods involve the addition of binders to soils. These methods are usually [...]

A case history is reported in which tire-derived aggregate (TDA) was successfully applied to reduce the weight of fill upon a cut-and-cover railway tunnel. Subsequent three-dimensional numerical analyses are used to explore the effect of different assumptions about the constitutive model of the TDA material. Alternative dispositions of TDA around the tunnel section are also examined. Reductions of up to 60% in lining bending moment may be achieved. For the case analyzed, the elastic description of the TDA has little influence on tunnel lining loads, although it is important for fill settlement estimates. Key words: end-of-use tires, tire-derived aggregate (TDA), monitoring, numerical modelling, tunnels. Une histoire de cas est rapportee dans laquelle l'agregat derive de pneus (<< TDA >>) a ete applique avec succes pour reduire le poids de remplissage sur un tunnel ferroviaire decoupe et couvert. Des analyses numeriques tridimensionnelles ulterieures sont utilisees pour explorer l'effet de differentes hypotheses sur le modele constitutif du materiau TDA. D'autres dispositions de TDA autour de la section du tunnel sont egalement examinees. Des reductions allant jusqu'a 60 % du moment de flexion de la doublure peuvent etre obtenues. Pour le cas analyse, la description elastique de la TDA a peu d'influence sur les charges de revetement des tunnels, bien qu'elle soit importante pour les estimations de tassement de remplissage. [Traduit par la Redaction] Mots-cles: pneus de fin d'utilisation, agregat derive de pneus (<< TDA >>), surveillance, modelisation numerique, tunnels., Introduction Large quantities of used tires are generated worldwide. For instance, recent figures indicate productions of 12.6 kg/resident/year for the USA (USTMA 2017), 6.4 kg/resident/year for EU28 countries (ETRMA 2016) [...]

The Standard Penetration Test (SPT) is the most widely used method for dynamic testing of soils. The test is simple and robust but difficult to control and not fully standardized. As a result, experimental results typically show large variations and poor repeatability. To mitigate that correction factors such as energy normalization and rod length have been introduced in SPT practice. This study provides an examination of the two correction factors using models based on the discrete element method (DEM).

The incremental behaviour of crushable sands is investigated by means of a Discrete Element Method (DEM) based analogue. The DEM sample is subjected to a comprehensive set of small stress perturbations in the triaxial plane in order to identify the basic mechanisms contributing to the corresponding strain response. Three contributions to incremental strains are distinguished: elastic, plastic-structural and plastic-crushing. The behaviour observed appears to be consistent with the classic tenets of elasto-plasticity. It is also shown that high resolution probing is required to identify significant features such as elastic anisotropy and irreversible effects on the tangent bulk and shear moduli. As a consequence, computational efficiency is therefore a must for numerical studies of incremental response.