Ebook: Deformation Characteristics of Geomaterials

We are pleased to present herein the Proceedings of the 6th International Symposium on Deformation Characteristics of Geomaterials, held in the city of Buenos Aires (Argentina) from 15 to 18 November 2015. IS-Buenos Aires 2015 was carried out in parallel with the 8th South-American Conference of Rock Mechanics (VIII SCRM), the 15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (XV PCSMGE), and the 22th Argentinean Congress of Soil Mechanics and Geotechnical Engineering (CAMSIG XXII).

IS-Buenos Aires 2015 was organized under the support of the Argentinean Geotechnical Society (SAIG) and the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) – Technical Committee TC 101, after the successful previous Symposia first set in Hokkaido 1994, and thereafter in Torino 1999, Lyon 2003, Atlanta 2008, and most recently Seoul 2011.

This proceeding includes 7 lectures delivered by invited keynote speakers and the Third Bishop Lecture delivered by Professor Herve Di Benedetto from the University of Lyon, France, who presented a reference work on the advanced testing and modeling of bituminous bounded and unbounded granular materials. A total of 128 articles were presented and discussed during the symposium. The 118 articles selected for publication in this proceeding were peer-reviewed by an international review board and 7 additional articles were published in a special number of the Journal of Soils and Foundation.

The Symposium brought together practitioners, researchers and educators from all around the world who are engaged in the understanding of the deformation properties of geomaterials before failure, and the small strain parameters as fundamental characteristics of geomaterials. The main topics covered by the symposium include:

1. Experimental investigations from very small strains to beyond failure including multiphysical approach.

2. HTCM coupling behavior, characterization and modeling of various geomaterials and Interfaces.

3. Practical prediction and interpretation of ground response: field observation and case histories

Buenos Aires is a charming metropolis where history and modernity come together. It has a wide cultural and tourist life. IS-Buenos Aires-2015 was held at the Hilton Hotel, in one of the most fashionable and exclusive areas of the city, Puerto Madero.

We would like to express our gratitude to the International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE) – Technical Committee TC 101 –, the Sociedad Argentina de Ingeniería Geotécnica (SAIG), and all the sponsors and organizations who generously contributed and supported to the success of IS-Buenos Aires 2015. We also acknowledge the great effort, compromise and enthusiasm in cooperation of all members of the local organizing committee, the international advisory board and the local reviewer board. We finally thank the editorial board of the Journal of Soils and Foundations for providing and preparing a special number for this event.

Victor A. Rinaldi

Marcelo E. Zeballos

Juan Jose Clariá

Buenos Aires, 15–18 November 2015

This lecture presents an overview of some of the results obtained by the author's team on the mechanical behaviour of unbound granular materials (UGM) and bituminous mixtures (BM). Experimental advanced devices and obtained results, rheological modelling and calculation of practical cases are proposed. Linear and non-linear domains of behaviour are considered including viscous and therrmal effects. A unified framework allowing describing complex behaviour of geomaterials is proposed.

The conventional fill compaction procedure usually controls the dry density ρ_d and the water content w referring to the maximum dry density (ρ_d)_max and the optimum water content w_opt determined by laboratory compaction tests performed at a certain compaction energy level (CEL). However, (ρ_d)_max increases and w_opt decreases with CEL, while, since Proctor (1933), CEL practically available in the field has been increasing and the required ρ_d value has generally been becoming higher for more satisfactory performance of soil structures. Besides, the values of (ρ_d)_max and w_opt change with soil type. In a single earthwork project, the actual CEL and soil type may vary and it is very difficult to accurately estimate the field CEL and identify the actual soil type at a given moment at a given place. Therefore, the actual values of (ρ_d)_max and w_opt are usually unknown. On the other hand, the optimum degree of saturation (S_r)_opt defined as S_r when (ρ_d)_max is obtained for a given CEL and the ρ_d/(ρ_d)_max vs. S_r−(S_r)_opt relation are rather independent of CEL and soil type. The unsoaked and soaked strength and stiffness and the saturated hydraulic conductivity are a function of ρ_d and compacted S_r not including CEL as a variable. It is proposed to control S_r of compacted soil to be close to (S_r)_opt and ρ_d to be large enough to achieve the physical properties required in design, together with pre-compaction control of water content.

Particle breakage explains the specific features of rockfill behaviour. Relevant features concern the dilatant behaviour under increasing confining stress, the long term deformations (creep) and the response under changes in relative humidity (RH). RH effects on deformation are well known in practice and result in marked collapse behaviour of rockfill structures as a consequence of full or partial saturation. The lecture will first present an ordered set of experimental results. The following aspects will be introduced: Suction effects on compressibility and yielding of compacted gravel specimens of different nature and grain size distribution, delayed creep deformations under isotropic conditions, deviatoric behaviour, dilatancy and the evolution of grain size distribution. These results sets the ground for the presentation and discussion of a Distinct Element model developed in an attempt to create a “numerical” laboratory capable of predicting real behaviour. The model includes particle shapes which reproduce, in a reasonable manner, the irregular shape of real rock fragments. Particle breakage is introduced as a fundamental deformation mechanism. Unlike other approximations reported in the literature, particle breakage was approached from the perspective offered by fracture mechanics. Particle breakage is the consequence of the propagation of pre-existing cracks. Crack propagation velocity of each individual particle is approximated by means of analytical solutions. Delayed deformations are a natural consequence of the model and the effect of RH can also be introduced in a simple manner. The process of parameter determination will be discussed with specific reference to large diameter oedometer and triaxial tests.

Critical state soil mechanics has provided an invaluable framework, essential for a proper understanding of the mechanics of many soils, both reconstituted and natural, at both small and larger strains. A limitation in its applicability results from robust forms of fabric in natural and reconstituted soils that mean that the critical states that can be defined in conventional tests do not correspond to a unique fabric. “Transitional” behaviour, in which the initial soil density plays a major role, seems also to result from robust fabrics. A number of examples of transitional behaviour are explored, emphasising that this type of behaviour does not threaten the applicability of critical state soil mechanics, but only the definition of intrinsic behaviour, such as we might require to examine the effects of structure. A range of behaviour appears from the examples, from very little convergence of specific volumes during compression or shear to a slow but gradual convergence. Even slow convergence, however, may still preclude the definition of normal compression and critical state lines that are independent of initial density within a useful stress range.

This paper considers the deformation behaviour of four geologically aged, medium-plasticity, heavily overconsolidated stiff clays that affect a broad swathe of infrastructure projects in the SE of the United Kingdom. Static triaxial and hollow cylinder stress path experiments on high quality samples are examined along with dynamic multi-axial bender element and resonant-column measurements. Patterns of undrained shear strength anisotropy are revealed that are governed by the clays' meso and micro-structures. The clays are brittle in shear and their stiffness characteristics are shown to be markedly anisotropic, highly non-linear and pressure dependent. The results obtained have many implications for practical geotechnical engineering.

The shear wave velocity (V_s), which is directly related to the small strain shear modulus, G_max, can be measured by both field and laboratory tests and has a great potential in applications to various geotechnical problems. Soil exhibit nonlinear stress-strain behavior from very small strains and the reliable strain dependent modulus is usually determined by combining G_max obtained from field seismic test and G/G_max curve from the laboratory test. Therefore, the Vs is a key soil parameter for the deformation analysis of geotechnical structures. In this paper, the advantages of using Vs in geotechnical applications are discussed. The main features of various intrusive and non-intrusive Vs measuring techniques in the field, resonant column, torsional shear and bender element tests in the laboratory, and bender tomography in centrifuge model are summarized. Test results obtained by various field tests, laboratory element tests, and centrifuge models are compared and critically discussed considering parameters affecting soil stiffness as well as reliability of the test results. The V_s has been traditionally applied to earthquake related problems but its use has expanded to cover even the static deformation analysis problems. In this study, three cases of using V_s to geotechnical problems are introduced: (1) Evaluation of K_o value using V_s in centrifuge model, (2) settlement prediction of shallow foundation using V_s profile, and (3) evaluation of ground improvement and densification using V_s. The background theory, procedure, laboratory and field tests, physical modeling, and case studies for each application are discussed.

The geomechanical behaviour of shales is quickly becoming one of the most important issues in modern geomechanics, largely driven by the geological storage of nuclear waste, the extraction of shale gas and the sequestration of CO₂. In this context, fundamental issues come along with the complex multiphysical conditions and a deep understanding of the hydro-mechanical behaviour of shales becomes of primary significance. In this paper selected results on the high pressure oedometric compression behaviour and on the water retention behaviour of shales are presented and discussed.

Laboratory tests are well recognized as highly appropriate for defining the engineering properties of geomaterials, in terms of constitutive law parameters for modeling geotechnical engineering problems. The strong development of advanced techniques, both in equipment and in data interpretation, has increased the confidence in laboratory testing, while on the other hand the limitations due to the quality of soil sampling with depth and the spatial representativeness of the samples are less consensual. Still, the development of new methods for assuring high quality samples is increasing, together with sampling quality assessment by non-destructive methods using vibration wave velocities. Interpretation methods of in situ tests for ground characterization has also evolved significantly, increasing the reliability of these methods. Their versatility to cover large areas on site and the fact that these tests are, in principle, performed at the actual state (physical and stress) conditions, as well as the improvements in the correlations between field tests and hydraulic and geomechanical parameters, allows joining the quality of data and theoretical approaches, namely through critical state soil mechanics. Current techniques are usually associated either with very low stress-strain levels, such as in geophysical surveys, or with very high stress-strain levels, near failure, as in dynamic penetration tests. This practice means that the complete range of stress-strain response is rarely covered in the investigation. Exceptions can be made when using the pressuremeter test, especially the self-boring technique, although time-consuming and expensive. New research trends are making use of a single technology for characterization at different scales (e.g. element, layer and global characteristics), which is the case of the use of high-resolution fiber optic distributed sensing technology for in situ moduli profiling and in laboratory element testing.

Unsaturated soils are most common in geotechnical practice. In order to study mechanical behavior of unsaturated soil a series of constant water content tests were performed in this study. Soil specimens were tested under isotropic loading-unloading, monotonic and cyclic loading sequences to study the effects of stress history on change in void ratio and suction, and on shear characteristics of unsaturated soil. It was concluded that the mechanical behavior of silty soil named as DL clay is not affected significantly by loading sequences incorporated.

An experimental technique for the K₀, the coefficient of earth pressure at rest, is presented. The technique consists of drained vertical compression of a triaxial specimen using the strain path control, in which a positive control of the strain increments rather than the conventional stress increments is exercised. The method does not require the use of any lateral strain sensors as used in previous studies and is free from any side friction affects, typical of oedometer testing. A detailed series of tests on three (3) sands are presented to illustrate the capabilities of the proposed technique. Possible influence of stress/strain history the soil inevitably experiences during sampling or reconstitution together with the initial state of stress prior to initiating zero lateral strain loading on the measured K0 are critically reviewed and evaluated. It is shown that the requirement of absolute zero lateral strain may not be essential for obtaining credible estimates of K0 as long as the ratio of radial to axial strain during vertical compression does not exceed about 3 to 5 %.

There is growing interest in using microbially induced calcite precipitation (MICP) for ground improvement. As part of a study to assess the performance of ex-situ mixed bio-cemented sand columns, a series of triaxial tests has been conducted to quantify the effects of the bio-cementation. Bender elements mounted in the end platens of a triaxial cell have been used to monitor the shear wave velocity throughout the cementation process and then during application of stress in the triaxial shearing tests. The results of tests on the bio-cemented sand are compared with tests on gypsum cemented and uncemented specimens. To assess the bio-cemented specimens a series of standard drained triaxial tests with bender elements were performed on Sydney sand which was mixed with urea contents in the range of 5 to 20% by weight, urea to calcium chloride in a 1:1 molar ratio, and a bacterial broth containing Bacillus Megaterium. Bacillus Megaterium is a ureolytic bacterium which hydrolyses urea to precipitate calcium carbonate (calcite). After curing the samples were subjected to various levels of mean effective pressure. The results show a good correlation between the amounts of urea and calcite precipitated and between the calcite precipitated and the degree of cementation achieved. For a given amount of cementation higher moduli and strengths were measured for the bio-cemented specimens than when using gypsum. Creating the bio-cementation by mixing produces homogeneous specimens with similar strengths and stiffnesses to the commonly used flushing technique.

Small-strain stiffness is one of the prominent characteristics of geo-materials on analysis of deformation behavior. Elastic wave measurement technique is becoming stronger non-destructive tool than other technique. In this paper, authors have focused on the application of the flat surfaced transducer ‘Disk transducer’, enabling to measure both compression and shear wave on triaxial specimen. Disk transducer was built the University of Tokyo using piezo- ceramic element and encapsulated in the top cap and pedestal of small scaled triaxial apparatus then performed the tests. This paper presents the results of three sorts of granular materials, fine, medium and coarse sand, were investigated statically and dynamically at isotropic and anisotropic stress states in the laboratory. The elastic parameters obtained on the granular materials; Young's modulus (E) and shear modulus (G), obtained by statically and by means of disk transducer method were examined and compared. It was observed, the statically and dynamically obtained results are mutually comparable and in agreement with previous studies. It is also confirmed the elastic parameters are to be a unique function of stress states with experimental evidence.

A series of undrained cyclic loading tests of three types of saturated and unsaturated soils were conducted on a triaxial apparatus. To overcome the difficulties of this type of test, cell pressure control system to maintain constant p, membrane filter technique to measure pore water pressure and double cell system to measure volumetric strain (ε_v) were introduced to the apparatus. Test results shown that the cell pressure control system reduced more than 60% variation of p which would be induced by applying vertical cyclic loading. The membrane filter technique could measure negative pore water pressure in a prompt manner and as a result suction of the unsaturated specimens was well monitored under the 0.1 Hz cyclic loading. The time delay problem of electric transducer employed in the ε_v measurement system, which may bring significant system error, was recognized and the measurement error of ε_v was discussed. Regarding the resistance against liquefaction of the unsaturated soils, the test results shown increase in resistance with reduction in degree of saturation and the p-constant condition was necessary to correctly evaluate the resistance for the unsaturated soils.

Multiple liquefactions phenomenon gained much attention in the Geotechnical Engineering field after the 2011 Off the Pacific Coast of Tohoku Earthquake in Japan and Christchurch Earthquakes in New Zealand. It was found that not just liquefaction can appear twice, but also can appear multiple times at the same sites. In addition, the damage caused by the multiple liquefactions were often more severe than the damage caused by the single liquefaction. This issue raises great concern on the reoccurrence of liquefaction in the future great earthquakes.

So far, several pioneer works have been able to investigate soil behaviors during re-liquefaction. However, most of those studies were limited mostly up to 2 stages of liquefaction due to the limitation of the apparatus itself. In this paper, a newly developed apparatus, so-called stacked-ring shear apparatus, is introduced. This apparatus aims to investigate the soil behaviors not just during 2 stages of liquefaction, but also during multiple liquefactions, by applying cyclic shear loading under constant volume condition.

The stacked-ring shear apparatus has a unique feature as compared to the common type of ring shear apparatus. However, both of these types of apparatuses still have common drawback, which is excessive friction between the soil particles and the metal rings. In the current study, several attempts have been employed to reduce the amount of excessive friction within the specimen. First attempt was done by reducing the number of rings composing the stacked-ring from 31 rings to 11, 8, and 5 rings. The second attempt was done by layering the surface of the ring using frictionless coating material. It is shown that reducing number of rings (reducing specimen's height) is more effective than the use of frictionless coating. However, there exists a certain limit, at which the number of rings can be reduced. Below this limit, fair comparison cannot be made since fewer stacked rings tend to generate un-equal amounts of friction on each stage of multiple liquefactions.

In order to design and construct the underground structures rationally, accurate elastic shear modulus of soils is an important parameter. The real ground formed by sands and/or clay has usually anisotropic mechanical behaviour. Although many researchers have discussed the anisotropy of strength, anisotropy concerning deformation modulus under small strain level have not been deeply understood. Anisotropy can be classified as an inherent anisotropy and an induced anisotropy, and the former anisotropy is treated in this study. Specimens are made using Toyoura sand with changing the angle of sedimentation. Local small strain (LSS) tests, by which precise deformation modulus can be measured, and bender element (BE) tests were simultaneously conducted in the same specimens to examine the influences of inherent anisotropy on deformation modulus and strength under triaxial state of stresses. The results show that drained shear strength decreases with the angle of sedimentation direction, which is defined as the angle of the depositional plane from the vertical. On the contrary, elastic shear modulus increases with the sedimentation angle.

Lumpy soils are inhomogeneous materials which can be encountered in open pit mining. The initial structure of the clayfills is similar to that of the granular material, which is stable due to the absence of a reconstituted soil. However, it might be transformed into a lumpy-composite structure due to the influence of climate. The lumps are randomly distributed in the reconstituted soil, which can be bounded by two basic configurations. For this purpose, two series of triaxial shear tests were performed on artificially prepared samples with parallel and series configurations of the different constituents. The test results show that the shear strength of the series samples is only slightly higher than that of the weaker constituent and the strength of the parallel samples lies between those of the constituents. For the parallel samples, there is a significant difference in the stress concentration ratio at different consolidation stress; while, the strain concentration ratio of the series samples is not significantly affected by the consolidation stress.

An artificial/reconstituted clay was prepared by mixing kaolin (K) and silt (S) in the proportion of 50% kaolin and 50% silt by weight employing a slurry deposition technique. The K-S clay has been used extensively to simulate natural clays for geotechnical centrifuge testing, often involving dynamic loading. It is necessary to accurately measure the soil shear wave velocity (V_s) or the low-strain shear modulus (G_max) for the analysis of geotechnical problems involving dynamic loading. In this study, V_s and G_max of K-S clay were measured using a novel device, utilizing piezoelectric transducer ring actuators, incorporated in an oedometer. The new device eliminates some of the shortcomings of the bender element test. For example, the piezoelectric transducer ring actuators do not penetrate the soil and hence do not cause any sample disturbance.

The value of V_s of the K-S clay was measured at different effective vertical pressure increments ranging between 25 and 500 kPa. The obtained values of V_s and G_max were independently compared with the values predicted using empirical correlations available in the literature for clay soil. An excellent agreement was found between the measured and the predicted values. The results of the present study are presented as V_s−σ′_m and G_max−σ′_m models. The proposed models will be helpful in designing a K-S clay testbed with a targeted stiffness for dynamic centrifuge applications.

This paper study the influence of water content on the mechanical behavior and failure process of an unsaturated argillaceous rock. For this, uniaxial compression tests with acoustic emission recording were conducted on specimens at different levels of relative humidity. Results indicate that uniaxial compressive strength and the elastic modulus increases with a reduction in the water content. Additionally, rock moisture seems to influence the volumetric deformation. Analyzing the volumetric stress-strain curves in conjunction with acoustic emission technique was possible to identify the crack initiation and damage stress thresholds at different values of relative humidity.

Early attempts to increase the soil strength by mixing it with other materials date back 3000 years ago in construction of ziggurats when the soil was mixed with plant roots. Coupled usage of cement and fiber in soil, however, refers to more recent years. Reinforcement with cement and fiber is one of the soil improvement methods for increase in bearing capacity and reduction of settlements. Cemented soils are usually found naturally, however, artificially cemented samples are widely used in the laboratory to investigate deformation and shear strength characteristics due to the limitations in undisturbed sampling. In present study, series of conventional triaxial tests were carried out to investigate the effects of cement type on the mechanical behavior of fiber reinforced sand. Accordingly, Portland cement type (II), hydrated lime and gypsum plaster were used as the cementing agents. The cement content was 3% (dry wt.) of the base soil. Fibers 0.012 m in length and 23 μm thicknesses were added at 0.0%, 0.5% and 1.0% (dry wt.) of the sand-cement mixture. Samples were prepared at 70% relative density and triaxial tests were performed under confining pressures of 100, 200 and 300 kPa. Samples cemented with Portland cement were cured for 7 days in humid room, however, samples with hydrated lime cured for 7 days in a constant temperature about 40°C and samples with gypsum cured for 24 hr in a constant temperature about 50°C. Samples with Portland cement and hydrated lime were tested in saturated condition but gypsum cemented ones were tested in dry condition. The results of experiments showed that fiber inclusion increases peak and residual strengths, axial strain at failure and energy absorption for all cement types. For the mentioned curing condition, samples cemented with Portland cement indicated the most shear strength and samples with hydrated lime showed the least value. Also, fiber addition was more effective on the peak shear strength of samples cemented with hydrated lime and had the least influences on the strength of gypsum cemented samples.

The interrelationship between undrained shear strength (s_u) and downhole shear wave velocity (V_sVH) of normally consolidated (NC) and lightly overconsolidated (LOC: OCR < 2) to overconsolidated (OC) to highly overconsolidated (HOC: OCR > 10) clays is investigated in the presented study. The main objective of this research program is to develop a worldwide database of high quality in-situ geophysical and laboratory strength data from thirty seven well-documented geotechnical sites from locations in Australia, Brazil, Canada, China, Italy, Japan, South Korea, North Sea, Norway, Singapore, Sweden, Thailand, United Kingdom, USA, and Vietnam. The study includes undrained shear strength measurements on undisturbed samples of normally to lightly overconsolidated intact to overconsolidated and fissured clays using anisotropically-consolidated triaxial compression tests (CAUC). Shear wave velocities were measured in the field by downhole tests (DHT), in many cases via seismic piezocones (SCPTu). Analyses of the compiled database found approximate trends between undrained shear strength and shear wave velocity. Tentative correlations are explored by including other various parameters such as Atterberg limits, void ratio, overconsolidation ratio (OCR), and effective vertical stresses. The correlative trends may aid geotechnical engineers in helping to assess s_u profiles in clay deposits in preliminary investigations and as an independent method in collaboration with sampling, lab testing, and other field data.

A new type of Disk transducer with the size of 80 mm diameter has been developed by assembling p-type piezo ceramic elements and s-type piezo ceramic elements, in order to carry out the elastic wave study of small to large grain size geomaterials. It has been proved that by using multiple numbers of piezo ceramic elements, development of required size of wave measurement device (i.e. disk transducer) is possible. To clarify the workability of such disk transducer, elastic properties of Toyoura sand (D50 = 0.20mm) were evaluated by three sorts of method (i.e. static method, disk transducer method and Trigger accelerometer method) by using the large triaxial apparatus with the rectangular prismatic specimen of 50cm*23cm*23cm. All tested sample were in completely dry condition. Applying 11 number of very small strain (i.e. strain less than 0.001%) cyclic loading young's modulus and Poisson's ratios were derived and shear modulus were calculated. Both the axial and radial strain was locally measured by local deformation transducers. Newly developed large size disk transducer has been used to evaluate the elastic properties by wave measurement method. Trigger Accelerometer method was also used to compare the elastic wave properties obtained by elastic wave propagation method. To prove the reliability, consistency and further application on the geotechnical engineering study elastic properties measured by newly developed disk transducer method were compared with previous research and the stiffness found to be fallen in similar range within allowable scatters.