INTERNATIONAL SOCIETY FOR MECHANICS AND

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Essais de laboratoire sur les géomatériaux: Effets du temps et autres observations spécifiques - Rapport général du TC 101 (session 1)

EIbraim. Ibraim E. University of Bristol, Bristol, UK

ABSTRACT: This paper presents a General Report of 29 written contributions submitted for one of the parallel sessions entitled “Time effects and other peculiar observation” of the Technical Committee 101: Laboratory Stress Strength Testing of Geomaterials. The origin of the authors shows a wide geographical distribution. The General Report reviews these contributions and presents the current research directions mainly in relation to the experimental behaviour as as the key outcome results. The topics covered by the written contributions have been grouped within the following thematic strands: time effects, expansive , consolidation/compressibility and crushable granular soils.

RÉSUMÉ : Ce document présente un rapport général des 29 contributions écrites pour l'une des sessions parallèles « Effets du temps et autres observations spécifique », soumis au Comité Technique 101: Essais de laboratoire des géomatériaux. L'origine des auteurs montre une large répartition géographique. Le rapport général examine ces contributions et présente les axes de recherche actuels principalement en ce qui concerne le comportement expérimental ainsi que les principaux résultats. Les sujets couverts par les contributions écrites ont été regroupées dans les volets thématiques suivants: les effets du temps, sols gonflants, consolidation/compressibilité et sols granulaires avec rupture des grains. KEYWORDS: soils, time effects, creep, strain rate, consolidation, expansive soil, shrinkage, swelling, breakage, .

 Expansive soils: swelling/shrinkage characterisation;  Consolidation/compressibility (loading and unloading); 1 INTRODUCTION  Crushable granular soils. This paper presents a summary in the form of a General Report The following sections develop the issues with reference to of the topics, current research directions and key outcomes of the written contributions. the written contributions submitted to the Technical Committee 101:Laboratory Stress Strength Testing of Geomaterials 2 TIME EFECTS Session. TC101 promotes and actively encourages co-operation and exchange of information concerning research and Of all aspects of settlement analysis, the issue of creep and developments in advanced laboratory geotechnical testing, secondary consolidation is one of the area in which least including apparatus, techniques and interpretation, and their use progress has been made in terms of fundamental understanding in practical geotechnical engineering, site characterisation and in the incorporation of research into practice. While the studies and ground modelling approaches. existence of creep complicates the predictions of the magnitude TC101 session contains a total of 58 written contributions. of settlement of structures founded on clay soils, further Their presentation is organised in two parallel sessions of 29 difficulties arise from the fact that the concerned elapsed time papers each on Time effects and other peculiar observations and under the constant load following the end of the in Strength properties and treated soils. This General Report a full-scale soft clay deposit is usually very long. As a refers only to the papers selected for the former session. consequence, the settlement rates are very low, significantly The origin of the authors clearly shows a wide geographical lower than those that can reasonably be measured in distribution, 12 contributions from Europe, 12 from Asia, 3 conventional laboratory testing (Leroueil 2006). In order to from North and South America, and 2 from Australia and New overcome this exertion and evaluate the creep process at very Zealand. Japan, China and France are leading in terms of low strain rates as observed in the field (order of 10-10 %/s), a number of contributions with 5, 4 and 3 papers, respectively. new laboratory one-dimensional compression test method is Although the papers in this session explore mainly the proposed by Kawabe and Tatsuoka (2013). The test procedure experimental aspects of the behaviour of fine and granular soils, consists of application of multiple unloading/reloading (UL/RL) the analysis and interpretation are enhanced due to cycles with several sustained - creep - loading (SL) stages. complementary use of various analytical and constitutive Figure 1 summarises the relationships between the creep strain modelling approaches. In general, there is a great concern for (for three hours) and the stress ratio between the stress at the conducting multi-scale investigations, including soil structure start of (UL) or (RL), σ or σ , and the stress at each (SL) analyses and correlation with macro soil response. Reference to UL RL stage, σ SL obtained during multiple UL/RL cycles and several practical applications is also considered. numbers of SL stages on two samples of reconstituted soft Despite some inherent heterogeneity, the topic covered by clays. The creep strain rates recorded during UL and RL cycles the written contributions can be grouped within the following are smaller than those during primary loading and they can thematic strands: reach a very low level. Based on relations of this type, the stress  Time effects: creep, strain rate effects in fine soils; ratio corresponding to Δε a(creep) = 0 can be deduced and based

191 Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013

on the Isotach viscous properties of clays, by starting the SL after unloading (point B, Figure 2), the zero-strain-rate relation is reached faster. Therefore, the creep behaviour at very low strain rates is reached in a relatively short period of time, much shorter than if SL would start from point A.

0.3 FJM1008 0.2 FJM1016 (%)

a(creep) 0.1 

0.0

-0.1

-0.2 Creep axial strain, axial Creep

-0.3 0.01 0.1 1 10 100

UL/SL or RL/SL

Figure 1. Δεa(creep)- UL /σσ SL or RL /σσ SL relations, for two tests on reconstituted Fujinomori soft clay (Kawabe and Tatsuoka 2013)

Reference relation for ‘loading’ log ฀ Faster Reference relation for Figure 3 Top: drained creep strains; bottom: dynamic triaxial strain ‘first unloading’ Measured ฀ -log ฀ relation response on remoulded clay, after Yangsheng et al. (2013). Primary loading at a constant positive total strain rate ε 0 B   A First unloading at a constant negative No creep B’ total strain rate C

ir εa  0 C’ or : positive or negative creep ฀ Figure 2 Illustration of logσε and creep in Isotach theory  aa (a) The Osaka Bay clay (b) The Pisa clay (Kawabe and Tatsuoka 2013) Figure 4. Microstructure of clays observed by SEM (Watabe et al. 2013). In a similar desire to reduce the time for creep investigation of fine soils, Yangsheng et al. (2013) propose a new testing Long-term consolidation laboratory tests on two undisturbed procedure based on the application of dynamic triaxial cycles of clay soils Osaka Bay (flaky particles, typically smectite, with frequencies about 5 kHz. The similarity between the measured large number of microfossils, Figure 4a) and Pisa (platy creep strain evolution and the permanent strains-number of particles, typically illite, with a small number of microfossils, cycles relation in dynamic cyclic tests (Figure 3) is used by the Figure 4b), were conducted and the results reported by Watabe authors for the prediction of the creep strains. The analysis of et al. (2013). The interpretation of the tests was also based on the microstructure of the clay samples issued from both creep the isotach concept (Šuklje 1957) and the relations proposed by and cyclic loading by the scanning electron microscope shows Leroueil et al. (1985). While Osaka Bay clay shows high strain close resemblances. In a different approach, but somewhat rate dependency well approximated by a curve model in line related study by Noda and Xu (2013), a numerical finite with the response of a wide range of natural clay soils, the Pisa element analysis (GEOASIA) of the behaviour of remoulded clay revealed particularly smaller strain rate dependency. The clay under sustained small cyclic amplitudes followed by creep origin of this different response appears to be linked to the under undrained conditions reveals that the mechanism of presence of illite particles in Pisa clay. swelling is localised and taking place on the shear bands due to The effect of a wide range of strain rates from 0.333 to the pore water migration effects. 60,000 %/hr on the strength and stiffness of reconstituted kaolin Re-evaluation of surcharging technique to reduce the clay is investigated in triaxial testing conditions by Robinson secondary compression effects on soft organic clay soils is and Brown (2013). The strain level and drained conditions are explored by Feng (2013) by conducting one-dimensional also considered. The influence of the rate effects on the peak laboratory compression tests on samples with different effective is presented in Figure 5 where the reference data surcharge ratios, R’s, where refers to a shear strain rate of 100 %/hr and V is the normalised dimensionless velocity as previously defined by Randolph and (1) R   ss   f σσσ  f Hope (2004). While the experimental results fit well the rate effects equation (Randolph and Hope 2004), the rate effect per and σ  is the achieved at the end of s σ  log cycle (tenfold) of the shear strength increase is about 22%, surcharging and f is the permanent final effective stress. The higher than detected in various previous studies (about 10%). results show that for small effective surcharge ratios, the The applied strain rate was also found to have a significant magnitude of secondary compression still remains excessive impact on the small strain response, with the elastic shear strain while for the technique to be effective, higher values of R’s are threshold, γEL, increasing with strain rate and shear stiffness, G0, recommended. appearing to reduce with strain rate (Figure 5).

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dependency based on the normal consolidation line (NCL) on e–lnσ plane strain rate dependent shift and using the subloading surface concept by Hashiguchi (1980). The new model is extended for over-consolidated clay cases, by introducing a new state parameter - the difference between the current and the void ratio on the NCL. The introduction in the model of another state variable, linked to an imaginary increase of density due to bonding effect, successfully captures the response of structured clays as well.

3 EXPANSIVE SOILS Expansive soils are soils that undergo significant volume change associated with variations in . These Normalised Velocity, V volume changes can either be in the form of swell or in the form shrinkage and they are derived from clay minerals that undergo hydration due to rainfall and dehydration due to evaporation. However, water access to individual clay particles depends on, and The shrink-swell potential of expansive soils is determined by the soil state (void ratio, the initial water content), internal structure (micropores within soil peds and macropores between the soil peds), vertical stresses, as well as the type and amount of clay minerals like smectite, montmorillonite, nontronite, , illite, and chlorite in the soil (Jones and Jefferson 2012). Maison et al. (2013) present a new experimental device incorporated into an Environmental Scanning Electron Microscope (ESEM). This new apparatus allows the simultaneous measurements of both surface area of clay minerals and water content evolution. The latter is deduced from the sample weighting, while the former is based on the image analysis technique. A complete wetting-dry cycle can be Figure 5. Top: Rate effect against normalised velocity at peak strength performed in less than 24 hours, faster than the classic tests on experimental data and model by Randolph and Hope (2004) using a representative soil element samples. Figure 6 shows the shear strain rate of 100%/hr as the reference rate; bottom: variation of evolution of the surface strain, s, with the moisture content for G0 against shear strain rate (Robinson and Brown 2013). several homogenous and heterogeneous natural clays. s represents the relative change of the surface area S of the clay Characterisation in one-dimensional loading and undrained i minerals at time t in respect with the initial area S : triaxial compression of a bentonite mixed with different i o amounts of silicon sand performed by Yin and Tong (2013) showed creep, swelling and strain rates effects dependent on the  SS oi ε  (2) amount of sand. Zhakulin et al. (2013) present results of long- s S term observations (over 50 years) of settlements of some o industrial structures in Kazakhstan founded in clayey soils. Laboratory investigation of the volumetric creep behaviour of the clayey soils is also studied in laboratory on undisturbed samples. Interestingly, it is also shown that the settlements calculated by two different design methods are much higher than the settlements experienced by the real structures. The settlement behaviour of clay soils, including the effects of time and timescale effects between a thin laboratory specimen and a thick in situ soil layer is not a new research topic, yet still very open as the interpretation of different results remains controversial and does not appear to converge towards a clear and unique framework. The work of Degago et al. (2013) goes at the heart of these controversies by analyzing the validity of creep hypothesis A in open conflict with creep hypothesis B (as previously defined by Ladd et al. 1977). Based on a critical review of relevant experimental Figure 6. Variation of the surface strain with moisture content measured investigations from the literature, the main misconceptions with the new experimental device developed by Maison et al. (2013). around the hypothesis A are discussed and detailed argumentation is advanced. It is also emphasized that the creep Internal structure evolution of undisturbed and remoulded hypothesis B agrees well with the measured behaviour of expansive soils during triaxial loading conditions and with the cohesive soils, the experimental results can be consistently application of several wet-dry cycles is studied by Chen (2013) explained using a model based on the isotache concept. on a CT scanning device. Both loading conditions accelerate the The performance of one-dimensional (1D) formulations of development of the initial structural cracks and fissures (Figure two elasto-viscoplastic models for normally consolidated clays, 7). The process of shrinkage causes structural cracks, which on one based on non-stationary flow surface type (Sekiguchi 1977) re-wetting, do not close-up and facilitates the access of the and the other one over-stress type (Perzna 1963) is assessed water. Nakai et al. (2013) against a new model that describes the time-

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The influence of swelling on the mechanical properties of Clay Geosynthetic Barrier that contains bentonite (predominantly montmorillonite) is studied by Domitrović and Zelić (2013). Initial swelling behaviour is explored through long-term swelling tests using an oedometer. The intensity of swelling decreases as normal stress level increases, however, the time for completion of the primary swelling is independent on the stress level, approximately 31 days. The shear behaviour of the bentonite is studied in direct shear box on samples under three normal stresses and with different hydration time (7, 14 and 21 days). Table 1 shows the value of the peak and residual shear strength parameters; the angle of increases while ฀ the decreases with the hydration time. ฀ ฀ ฀ Table 1. Shear strength parameters (Domitrović and Zelić 2013). Hydration Peak parameters Residual parameters time c (kPa) (°) c (kPa) (°) Figure 7. Internal structure evolution by CT scanning (section located at 1/3 of height) during: left - triaxial compression and right - several wet- 7 days 11.99 11.23 11.05 7.80 dry cycles (Chen 2013). 14 days 8.04 12.47 4.79 9.38 21 days 6.32 12.27 3.63 9.31 A comprehensive characterisation of the engineering properties of the expansive glacio-lacustrine Regina clay Residual strength of three clay soils (clay fraction between (Canada) is conducted by Azam et al. (2013). The clay contains 70% and 80%) from North-Eastern Greece with high and very minerals like smectite, hydrous mica and chlorite, whereas the high swelling potential is evaluated by performing ring shear clay size fraction (material finer than 0.002mm) is around 65%. tests on remoulded samples at their optimum moisture content The soil water characteristic curve (SWCC) determined to by Markou (2013). While the residual failure envelope appears investigate the water retention capacity of the soil showed the curved, for normal stresses up to 200 kPa it can be considerd as bimodal shape with two air entry values: an initial low value linear. In all cases, the residual friction angle does not exceed corresponding to macroporous (through fissures) 14o. followed by a high value related to microporous flow (Figure 8, The analysis of expansive properties of natural Neogen clays top). The shrinkage curve was found to be S-shaped and (smectite, illite minerals) that forms the main included a low structural shrinkage followed by a sharp decline stratum of Northern Poland is performed by Kumor (2013). during normal shrinkage and then by a low decrease during Expansive clays of Northern Poland can be classified as very residual shrinkage (Figure 8, bottom). expansive with a contractibility range (LL –SL) of 82.1% > 50%, where LL is the liquid limit and SL is the contractility 50 Fissure AEV limit. Swelling pressures that cause lifting of structures and shrinkage that cause differential settlements are the main causes Matrix AEV 40 of structural failures in Poland (Figure 9). The examination of the volumetric changes in clays during laboratory shrinkage and swelling phases allowed the refinement of the in-situ 30 Fissure shrink/swell predictions. AEV

20 Matrix AEV 43 cm

Gravimetric Water Content (%) 10 In situ soil Compacted soil 0 100 101 102 103 104 105 106 Soil Suction (kPa)

1.4 % % % 0 0 0% 5 6 70 8 % = = = = S S 100 S S = S

1.0

Figure 9. An example of a construction failure resulting from the application of natural swell-shrink cycles in Poland (Kumor 2013). Void Ratio 0.6 4 CONSOLIDATION/COMPRESSIBILITY In situ soil Compacted soil It is known that three-dimensional effects may significantly 0.2 accelerate the rate of settlement of foundations on clay, 0 10 20 30 40 50 primarily because of the ability of excess to Gravimetric Water Content (%) Figure 8. Top: SWCC with gravimetric water content; bottom: dissipate horizontally as well as vertically. These effects are shrinkage curves (Azam et al. 2013). further accelerated by the use of radial drainage. However, most

194 Technical Committee 101 - Session I / Comité technique 101 - Session I

of the analytical solutions for consolidation under radial t/h 0 drainage are based on the assumption that only vertical 0 20 40 60 80 100 compression occurs. A new physical consolidation model test under plane strain condition, which enables the observation of -0.005 Experiment data the deformation of a specimen through digital image analysis, Numerical result:variable parameters and the measurement of the total vertical stress as well as the pore water pressures, is developed by Kim et al. (2013). A Settlement (m) -0.01 Numerical result:constant parameters schematic view of the apparatus is shown in Figure 10.

Consolidation tests of reconstituted kaolin samples (150 mm -0.015 height, 140 mm width, and 40 mm thickness) were performed using the new consolidation apparatus under radial drainage, along with test under vertical drainage. Radial deformations as -0.02 well as vertical deformations during consolidation were monitored and compared for the two different drainage -0.025 conditions. Significant horizontal displacements are occurring during the early stages of the consolidation process, whereas during the intermediate stage, only minor horizontal Figure 12. Comparison of the settlement between the numerical displacements are identified. The horizontal displacements are results (two models) and recorded data (Hu et al. 2013). higher near the boundaries and this induces uneven void ratio distribution at the end of consolidation. Meanwhile, for the Compression properties of Swedish fine-grained sulphide vertical drainage, only minor variations of the horizontal clay soils are explored by Westerberg and Andersson (2013) displacements inferior of 0.006 mm were observed. through the monitoring and analysis of the long-term response of two instrumented real scale test embankments. Actually, the predicted settlements of a construction founded on sulphide Compressor Pneumatic Actuator soils deviates significantly from those measured in situ, and Silicon LVDT normally the predicted settlements are too small. In sulphide soils, the structure is often relatively porous and the voids between the mineral grains and clay particles are filled with pore water, organic material and iron sulphide. Field investigations of the properties of the sulphide soil were performed by cone penetration tests, field vane tests and Earth pressure Swedish piston sampling and an extensive program of gauge 1 3 5 Drainage Earth pressure laboratory investigation, in oedometer, both by incremental hole gauge Digital loading and constant rate of strain, creep tests, permeability as Camera well as undrained direct simple shear tests, were conducted for Back pressure 2 4 6 Pore pressure reservoir the determination of compression and strength properties. Very measuring points good agreement between data given by different field instrumentations is reported. Figure 10. Schematic view of the consolidation test apparatus (Kim et The heave rebound strain prediction of overconsolidated al. 2013) soils represents an important engineering design issue since the development of major infrastructures that involve deep A laboratory apparatus for axi-symmetric electro-osmotic excavations and . Based on the use of simple oedometer consolidation of cylindrical samples of 37.6cm diameter and tests combined with an analysis of stress paths approached by 20cm height is developed by Hu et al. (2013) with capabilities Ylight model (Leroueil, Magnan & Tavenas, 1985), Petit et al. of measuring the electrical voltage, soil mass displacement, (2013) present a quantification method of those heave rebound water discharge, and electrical current parameters (Figure 11). strains. The results of the calculations of the heave rebound over While tests on kaolin clay showed non-linear variation of soil a 120m deep clay deposit for three excavation depths of 10, 20 parameters and complex coupling effects between water flow, and 40m are shown in the Figure 13. The estimations show that soil deformation and electrical properties, a theoretical model the elastic rebound are relatively small, between 0.01 and that integrates Biot’s consolidation equation with the electro- 0.02m. osmotic flow and the equation for an electric field is proposed. Figure 12 shows the comparison of the surface settlement at one location between the numerical results and the experiment data. The simulations of the model with variable electrical conductivity agree better with the experimental data than those of the model with constant electrical conductivity.

Data acquisition instrument power source

Top cap ammeter Vacuum pump displacement sensor Voltage sensor Cathode Soil Sample Anode z drain hole Vertical drain moisture trap Outlet of water r Figure 13. The profile of the heave rebound for three different excavation depths (Petit et al. 2013). Figure 11. Electro-osmotic apparatus (Hu et al. 2013)

195 Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013

The problem of estimation of the at rest coefficient Ko for under various stress path tests is conducted by Casini et al. overconsolidated soils is treated by Bohac et al. (2013). At a site (2013). The material was reconstituted, with a maximum containing highly overconsolidated clays,Ko was measured by particle size of 2 mm, into curves with the same mean using Marchetti (1980) flat dilatometer.The Ko values are diameter, d50, and different coefficients of uniformity, U (= 3.5, higher than those estimated from oedometer yield point and 7, 14, 28) or the same U and different d50 (= 0.5, 1mm). empirical correlations by Main and Kulhawy (1982). Numerical Changes in of the grading at the end of the tests (one modelling of the flat dilatometer penetration into the soil based dimensional, isotropic and triaxial compression) were described on a hypoplastic model (Mašín, 2005) combined with the using two parameters defined as the mean diameter and intergranular strain concept proposed by Niemunis and Herle coefficient of uniformity of the final distribution over the values (1997) were also performed. However the K0 values are slightly of the initial distributions, d50/d50i and U/Ui, respectively. Poorly underpredicted. graded samples show more pronounced decrease in mean diameter and increase of uniformity with higher applied stresses (Figure 14). 5 CRUSHABLE GRANULAR SOILS Experimental evidence of size effects in rockfill shear strength and the link with the crushing strength of rock The significance of particle crushing to the mechanical aggregates is presented by Frossard et al. (2013).Compression behaviour of granular materials has been well identified and in test results on individual chalk (CP) and quartz rock (STV) the particular field of geomechanics, it is recognized as having a particles have been statistically analysed and it was shown that major effect in a wide range of practical problems involving the probability of survival for each grain size fraction follows shallow foundations, of piles, stability of earth Weibull distribution given by: structures, seepage properties, , and pore- pressures distribution in earth dam water retaining structures, n m   d  d  σ   pavement and railway substructures. However, the laboratory   (3) s dP exp      investigation and interpretation of crushable materials show   d  σ   some inherent difficulties and there is a need for consideration   o   o   of appropriate approaches that may differs from non-crushable, where o is the value of the strength of do size particles such cohesionless . In this respect, Wils et al. (2013) identify that 37% of the total number of tested particles survive. The and analyse several issues like: determination of the minimum exponent m is called the Weibull modulus, which increases with and maximum density, sieving and the need for advanced grain decreasing variability in strength of the material. For each morphology characterisation by means of microscopy, the material, drained triaxial tests on dry samples (maximum abrasion of particles and the apparent cohesion due to particle diameter sizes of 40mm (CP1 and STV1) and 160mm interlocking of the angular particles creating sand clusters with (CP2 and SV2)) under different confining presures were the appearance of larger particles, as well as the existence of performed. Considering that individual particle breakages affect larger shells sheltering smaller grains. the shear strength of the entire granular medium, a method to predict the effects of scale on shear strength envelopes of rockfills is proposed. Figure 15 shows the comparison between measurements and predictions for shear strength envelopes for both CP2 and STV2 materials, based on the best fit of CP1 and STV1 data with the failure envelope given by De Mello (1977) b (τ=A.σn ).

0.8 CP1

0.6 CP2

0.4 STV1: dmax=40mm

0.2 STV2: dmax=160mm

0.0 De Mello's fitting Shear stress (MPa) 0.0 0.2 0.4 0.6 0.8 Prediction for CP2 & STV2 Normal stress (MPa)

Figure 16. Scale effect on shear strength (Frossard et al. 2013).

Investigations performed by Shahnazari et al. (2013) on the mechanical behaviour in triaxial apparatus of two calcareous natural soils obtained from the Persian Gulf, Hormuz Island sand (HI) and Bushehr Port sand (BP) (Figure 16), and comparison with the triaxial response of a silica sand, Firoozkuh (F) showed behavioural contrast between the sand materials, and through global measurements, clear evidence of particle

Figure 14. Evolution of ratios: (a) d50/d50i and (b) U/Ui with mean breakage of the former soils. effective stress applied in 1D-compression (Casini et al. 2013). Results from a series of basic characterisation tests conducted on reconstituted samples of carbonate sand to An experimental investigation into the mechanical response understand its behaviour are reported by Safinus et al. (2013). of an artificial granular material, consisting of crushed Compared to silica sand, carbonate sand has considerably expanded clay pellets, LECA (Light Expanded Clay Aggregate) higher angularity, lower grain hardness and higher intra-particle

196 Technical Committee 101 - Session I / Comité technique 101 - Session I

, which result in high friction angles and tend to deform in one-dimensional compression way, with compressibility. The corresponding dilatancy is affected practically no change in the diameter of the sample, also a strongly by the confining stress (Figure 17): even for low consequence of the large amount of particle crushing. An relative densities, dilation occurs at low confining stresses, example of observed incremental strain ratio evolution for one reflecting the greater particle interlocking compared to silica of the materials during triaxial testing is shown in Figure 19. sand, while with the increase of confining stress, the dilatancy is suppressed quickly, and finally diminishes completely at a q relatively low stress level, due to particle degradation. The Vertical bearing pressure, u (kPa) 0 100 200 300 400 influence of the observed characteristics of carbonate and silica 0 sands on practical applications was examined through model Punch- Soft clay tests in drum centrifuge of spudcan foundations penetrating through 0.25

through four-layer soils, with a carbonate or silica sand layer D / Carbonate interbedded in soft clay. All measures of spudcan punch- d sand Silica sand through severity were significantly lower for interbedded 0.5 I = 38%; ID = 38%; D φ ° φ = 34° carbonate sand despite its higher friction angle (φcrit = 40) crit = 40 crit compared to silica sand (φcrit = 34), Figure 18. 0.75

1 Layer interface Soft clay 1.25

1.5

Normalised penetration depth, 1.75 Stiff clay 2 Figure 18. Effect of interbedded sand mineralogy on load penetration response: severity of punch-through (Safinus et al. (2013).

2

JPN 2 γd=5.77kN/m JPN pumice 2

a 1600kPa γd=5.70kN/m ε 400kPa Figure 16. Microscopic images of Hormuz Island sand (top) and d / v 1 Bushehr Port sand (bottom) from Shahnazari et al. (2013). ε d

JPN pumice 2 One dimensional γd=5.70kN/m compression 100kPa 0 Strain ratio

-1 0 2 4 6 8

Axial strain εa (%)

Figure 19. Incremental strain ratio against axial strain for drained triaxial tests on pumice sand from Japan (Kikkawa et al. 2013).

6 CONCLUSION This paper presents a General Report of 29 written contributions from authors representing 22 countries submitted Figure 17. Volumetric change of carbonate sand in drained simple shear for one of the parallel sessions, Time effects and other peculiar test with lateral stress ratio K = 0.4 (Safinus et al. (2013). observation, of the Technical Committee 101: Laboratory Stress Strength Testing of Geomaterials. The General Report reviews Observations of the experimental behaviour of two pumice these contributions and presents the current research directions sands from Japan and New Zealand are made by Kikkawa et al. mainly in relation to the experimental behaviour as well as the (2013). While the composition of Pumice sands is dominated by key outcome results. The topics covered by the written silica and aluminium oxide, they are normally characterised by contributions have been grouped within the following thematic the presence of particles that are easily crushed against a hard strands: surface under fingernail pressure. Considerable particle  Time effects: creep, strain rate effects in fine soils; breakage is occurring in triaxial compression loading, while  Consolidation/compressibility (loading and unloading); mobilization of the drained shear strength is increasing steadily  Expansive soils: swelling/shrinkage characterisation; with the shear strain. However, owing to a different stress path,  Crushable granular soils. less crushing is occurring in undrained testing. A particularly Various analytical and constitutive modelling approaches interesting feature of the drained shear behaviour of these two successfully assisted the interpretation of the presented materials is that with a sufficiently large confining pressure they experimental data and in general, the research methodology

197 Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013

adopted considered multi-scale investigations, including soil Mayne, P.W. and Kulhawy, F.H. (1982) K0-OCR relationships in soil. J. structure analyses and correlation with macro soil response. Geotech. Eng. Div. ASCE, GT6, 851-872. Reference to practical applications was also considered. Maison, T., Laouafa, F., and Delalain, P. 2013. Mise au point d’un dispositif expérimental pour l’analyse du retrait-gonflement des sols argileux. Proceedings of the 18th International Conference on REFERENCES Soil Mechanics and Geotechnical Engineering, Paris Marchetti, S. (1980) In situ tests by flat dilatometer. J. Geot. Eng. Div. Azam, S, Ito,M and Chowdhury, R. 2013. Engineering properties of an ASCE, Vol. 106, NoGT3, 299-321. expansive soil. Proceedings of the 18th International Conference on Markou, IN 2013. Residual shear strength behavior of swelling soils. 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