Ebook: Deformation Characteristics of Geomaterials

On behalf of the organizing committee of the 5^th International Symposium on Deformation Characteristics of Geomaterials that was held in Seoul, in September 2011 (IS-Seoul 2011), every participant is welcomed and thanked for their effort and collaboration. IS-Seoul 2011 was prepared under the auspices of the Korean Geotechnical Society (KGS) and the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) – Committee TC101, and based on the success of previous symposia: IS-Hokkaido 1994, IS-Torino 1999, IS-Lyon 2003, and the latest, IS-Atlanta 2008.

The main themes of the 5^th symposium include:

1. Experimental investigations from very small strains to beyond failure

2. Behavior, characterization and modeling of various geomaterials

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

This symposium explores and shares ideas about the complex load-deformation response in geomaterials, including laboratory methods for small and large strains; anisotropy and localization; time-dependent responses in soils; characteristics of treated, unsaturated, and natural geomaterials; applications in field methods; evaluation of field performance in geotechnical structures; and physical and numerical modeling in geomechanics.

During the symposium, 7 novel invited lectures including the first Bishop lecture by Professor Fumio Tatsuoka were provided to review the state of the art, improve knowledge, and shape the future of geotechnical engineering. Total of 182 technical papers were submitted and discussed in this symposium. 17 papers were published in a special issue of a peer-reviewed Soils and Foundations and 165 papers were published in this proceeding to exchange advanced knowledge and ideas in geotechnical engineering and promote the partnership among participants from all over the world.

We would like to express our thanks to all the members of the local organizing committee and international advisory board of IS-Seoul for their sincere effort and intense collaboration. We must give special thanks to Professors Yun-Tae Kim, Junhwan Lee, Yong-Joo Lee, Duhee Park, Seong-Wan Park, and Sung-Sik Park for completing the proceedings and organizing the symposium program. Special thanks are extended to Professor Satoru Shibuya and other core-members of the journal of Soils and Foundations. Mr. Heon-Joon Park and Dr. Ilhan Chang, whose devotion made this workshop successful, are appreciated. Finally, the great support from ISSMGE TC101 headed by Professor Herve Di Benedetto is indelible. Most of all, we want to thank all the authors and participants who contributed to this international symposium, IS-Seoul 2011.

Choong-Ki Chung

Young-Hoon Jung

Hyun-Ki Kim

Jong-Sub Lee

Dong-Soo Kim

Seoul, 1 ~ 3 September 2011

Significant roles of laboratory stress-strain tests of geomaterial for developments in geotechnical engineering research and practice are shown by summarising several recent advances in our understanding and modelling of the following properties of geomaterial: 1) quasi-elastic stress-strain behaviour; 2) rate-dependent stress-strain behaviour due to elasto-viscoplastic properties; and 3) strength and pre-failure stiffness of compacted soil related to field fill compaction control and design values of strength and stiffness. Several related findings obtained from laboratory stress-strain tests are presented and related issues of Geotechnical Engineering practice are discussed.

This lecture outlines a research approach, procedure and strategy aimed at the development of clay modeling in the context of natural clays of varying geological history. The aim is at providing evidence of the clay features causing given behavioral facets, at the micro to the meso-scale, in order to connect classes of behavior and corresponding models, to classes of clays. The approach to micro-macro is not that of deducing macro-behavior from modeling the micro-processes, not so feasible for clays, but to join systematically the knowledge of the micro to meso features and processes and the observations of macro-response. The procedure entails the development of analyses spanning from those generally carried out in clay science, at the micro-scale, to characterizations of the meso-scale, to analysis through element testing of the macro-behavior. Furthermore, the procedure includes studies of the geological history of the material. Examples of application of the research strategy to different case studies are presented, that document how it is possible to both identify the internal factors generating given clay behavioral facets and model clay behavior within a simple general framework. This framework represents an example of formalization of the variability of clay response with the micro to meso-features of the clay.

This overview paper discusses the use of laboratory testing in conjunction with in situ determination of reference parameters as a step forward to have consistent analyses of the behaviour of geotechnical constructions. In the first part of the paper, the key role of those reference properties, such as the elastic stiffness values obtained in field conditions at repose stress state, is highlighted. By comparing these values with those determined in laboratory reconditioned samples, their “undisturbed” conditions are evaluated and the reliability of advanced laboratory techniques can thereby be assured. The use of seismic wave velocity (V_s) measurements in the field and the laboratory is discussed, and examples are given. Particular emphasis is placed on using the ratio of V_s,field/V_s,lab for the correction of constitutive stress-strain laws – i.e. the stiffness “decay” (G–γ) curves determined in laboratory tests. This is becoming a more feasible approach because of the increasing prevalence of laboratory V_s measurement using “bender elements” in laboratory tests at different stages of testing and under diverse stress paths, coupled with the increasing use of seismic cone penetration tests (SCPT) for determination of V_s,field. A second subject that is discussed in some detail is the advantage of looking at soil liquefaction as an elasto-plastic mechanical behaviour that is well modelled by critical states concepts, while recognising that it takes places in a wide range of materials and conditions. These issues are outlined in this section, as the critical state framework has now been extended to other materials apart from sands. This approach integrates the knowledge of influence of the micro-mechanics of particles and their contacts on the observed behaviour, and takes account of the effects of continued particle breakage and change in uniformity. The objectives of performance-based design are presented in the light of laboratory and field tests that may be able to identify the triggering risk of both cyclic and static liquefaction and how those tests can be performed and their results interpreted to predict these phenomena, under a global mechanical modelling approach. The third part of the paper describes some special geotechnical testing procedures (equipment and methods of interpretation of test results) that are commonly used in advanced laboratories working for the offshore industry. Being scarcely known and used in current laboratories, even with advanced equipment, these techniques have a great potential in answering to the challenging problems involved in this area of activity, but is it also demonstrated that they can give very useful information in other geotechnical problems. The final section describes a new dosage methodology, based on rational criteria, for cement-soil mixtures, where porosity/cement ratio plays a fundamental role in the assessment of the target mechanical properties of artificially cemented soils, which are used increasingly in many geotechnical engineering solutions.

Investigations of parameters that affect the dynamic properties of geotechnical materials are regularly performed in the laboratory. For municipal solid waste (MSW), dynamic laboratory studies are only beginning to be performed. Parametric studies of both materials are rarely, if ever, performed in the field. In the past decade, field methods have been developed with which parametric investigations can be conducted. The field methods involve applying staged, static and dynamic loads at the ground surface using footings or load plates as a surface platen. Horizontal dynamic loading to the platen creates a seismic source that generates downward propagating, horizontally polarized shear waves. Embedded arrays of small sensors in the loaded material beneath the surface platen are used to monitor linear and nonlinear shear wave propagation. The field test methods, associated equipment, and testing procedures are described. Field studies of the effects of stress state, strain amplitude and pore pressure generation on shear moduli are presented. Three types of material are investigated: (1) an unsaturated sand, (2) a municipal solid waste, and (3) a saturated, liquefiable silty sand. Shear strains in the range of about 0.0002 to 0.2% were generated in these tests.

The mitigation of geo-hazards caused by heavy rainfall is a common issue in Asian community of geotechnical engineers. Such geo-hazards are often highlighted by the catastrophic failure of natural slopes and manmade fills comprising initially unsaturated soil. Despite that we can learn a lot from such case history, it is regrettable that the cause of failure is rarely pursued or disclosed. Moreover, the mechanical behavior of unsaturated soil subjected to cycles of saturation/desaturation should be better understood so that much better idea for preventive works may be hinted. In this keynote paper, the small-strain stiffness and strength characteristics of unsaturated soils are, first, described by showing the results of laboratory tests recently performed in Geotechnical Engineering Laboratory at Kobe University. Second, engineering practices for evaluating the mechanical behavior of largely-deformed (or failed) natural slopes and reinforced earth walls are described by portraying a series of well-documented case studies in Japan. Finally, lessons learnt from each of these case studies are exposed.

The analysis of comparative digital photographs by Particle Image Velocimetry (PIV) offers a powerful technique for the demonstration of deformation mechanisms in soil models. Where small-scale models can be tested in a geotechnical centrifuge at a sufficiently uniform acceleration to broadly recreate full-scale stresses, it will follow that soil stiffness and strength will equally be appropriate to the full scale. If sufficient attention has been paid to the creation of appropriate boundary conditions, and to the actuation of a representative construction and loading sequence, the observed mechanism can be used to deduce the characteristic features of similar processes in the field. This requires a further step of simplification and mathematical characterization. Any recommendation for the use of such a mechanism in design should depend on a consistency check of the conservation of energy in the model, leading to sufficiently accurate predictions at model scale. Such a demonstration is consistent with the Mobilizable Strength Design (MSD) method which has been shown to serve as an efficient means of predicting and controlling ground deformations. Examples will be given of the behavior of tunnels, deep excavations and slopes.

Predicting behavior of soil in the field in response to construction activities and natural events is the reason why so much effort in the past 50 years has been put into developing constitutive models. It is the field responses of soils that are of interest to geotechnical practitioners, and this aspect of the problem has not received nearly enough attention. There are many logical reasons for this, e.g., the need for establishing behavior under well-defined boundary conditions, the difficulty of obtaining high quality samples, the effects of sample disturbance, the effort required to obtain field performance data of sufficient quality and quantity such that it can be correlated with a causative construction activity, to name a few. The author and his colleagues have collected detailed field performance data from a number of supported excavations in the Chicago area and have correlated the responses with construction activities. As part of the effort, block samples have been cut as the excavations have proceeded. Detailed laboratory evaluations of the stress-strain strength responses have been conducted on specimens from these blocks and from thin-wall tube samples. Inverse analyses have been conducted on results of finite element simulations of the excavations using the field observations as a basis of comparison so that best fit parameters for several constitutive models were determined based on the field data. This paper summarizes the techniques used and describes the lessons learned from this effort. Comments are made regarding applicability of laboratory data, the relation between the capabilities of the constitutive model and selection of observations for inverse analyses and numerical modeling.

Soil compaction is one of the most frequent and important activities in infrastructure construction, a multi-billion dollars industry. Huge amounts of testing and time are devoted to soil compaction quality control in any engineering project of significant size. In this article, we aim to show the potential of using small-strain shear wave velocity, V_s, as an indicator of soil compaction. A compilation of experimental data found in the literature suggests such correlation. Direct knowledge of the shear wave velocity allows a more fundamental interpretation of the deformation characteristics of geomaterials through soil shear modulus. This may set the bases for the development of new in-situ compaction estimation technologies that could have a very significant impact on industry and the practice of civil engineering today.

A small strain triaxial apparatus was developed which is capable of measuring accurately the small strain behaviour of soil. The system utilized three submersible miniature linear variable differential transducers (LVDTs), mounted on the periphery of the soil specimen. Furthermore, a bender element system was incorporated to provide an additional means of measuring the small shear modulus of the soil. The system was used to measure the small strain behaviour of undisturbed Auckland residual soil, which occupies much of the Auckland region and areas to the north. Auckland residual soil is characterized by the presence of macro-voids, as confirmed by the images from X-ray CT scanning. Based on the test results, G_max values obtained from LVDT measurement matched closely the results from bender element measurements, confirming the capability of the integrated small strain testing apparatus.

The results of a comprehensive experimental program focused on the study of progressive degradation processes on a low permeability argillaceous rock induced by hydraulic cycles is presented in the paper. Relative humidity cycles were applied with vapour transfer technique, and bender elements were used to evaluate the evolution of shear stiffness during the application of hydraulic paths. The characterisation of the material included the determination of the water retention properties (water retention curve), as well as the pore size distribution using mercury intrusion porosimetry, complemented with SEM micrographs and elemental analysis using X-ray spectroscopy to characterise micro-structural features and detect clayey and non-clayey constituents. Results showed cumulative and irreversible swelling of the samples with the application of relative humidity cycles. Regarding shear stiffness, an important reduction (around 80%) was observed at the end of the hydraulic paths applied. Evidence of rock degradation at macro-scale was linked to structural modifications at micro-level.

This paper presents the measurement of the shear wave velocity at the Soil Mechanics Laboratory of the Department of Civil and Environmental Engineering Technology, College of Industrial Technology, King Mongkut's University of Technology North Bangkok. The research purposes a new technique to measure the shear wave velocity by using the piezoelectric film. This piezoelectric film is a very thin, light and high sensitive sensor and is used as a receiving sensor. The details of this new technique and its interpretations on Bangkok clay material are explained. The research found that this new technique is a reasonable technique, giving the shear wave velocity result in good agreement with the shear wave velocity data of the field test.

A Resonant-Column apparatus was modified by replacing the internal generator by an arbitrary function generator. A PC oscilloscope was used to acquire both the input current in coils and the vibration response of the system. Software developed in LabVIEW® controls the equipment, acquires data and then processes the information, computing the shear modulus and damping ratio of soil. This calculation is performed utilizing a curve fitting method involving a complex-value function carried out by a Matlab® script included in the software. Four types of tests can be performed in the program: the conventional test, sine sweep test, random noise test and non-resonance test. Results reveal the advantages of the new automated system; all tests in small-strain regime can be applied consecutively on the same specimen, being possible to obtain additional information of the dynamic properties.

For soft soils, sampling methods, specimen preparation and subsequent test results are all affected by the degree of soil structure and level of destructuration occurring during these phases. Consolidation has been shown to be a primary means for restoring a soft soil's structure, or an approximation of that structure. The amount of this restoration can be quantified by comparing the measured shear wave velocity values before and after various test phases. Shear waves can be generated and received by bender elements that are composed of piezoceramic plates. When bender elements are inserted into a triaxial testing system, they provide non-destructive testing during an ongoing triaxial test. In this research, bender elements are implemented in an automated triaxial apparatus using methods developed by Landon (2004). Two different soil types, one sampled using conventional tube sampling and one using Sherbrooke-type block sampling, were tested to assess how reconsolidation affects the structure of the soil, by comparing bender element data. A MatLab® based program was used to actuate the excitation of benders, and to measure and analyze the resulting shear wave transmission. By comparing shear wave velocity results at various stages of the test, the change in the soil structure as a result of those test stages can be inferred. The results show that, based on bender element shear wave velocity measurements, the back pressure and consolidation phases help to restore the shear wave velocity values and the shearing phase only marginally degrades the structure, even at relatively high, end-of-shear strains.

A series of triaxial compression tests was performed on undisturbed gravelly soils that were retrieved from two tunnel excavation sites in Toyama prefecture, Japan. At each site, cylindrical samples having a dimension of 30 cm in diameter and about 100 cm in height were retrieved from the excavated base by employing a special coring method using thick water-soluble polymer. A specimen having a height of 50 to 60 cm was trimmed from these samples, and it was set to a large-scale triaxial testing apparatus. In the course of isotropic consolidation and drained triaxial compression, small strain deformation properties were measured by both static and dynamic methods and compared to each other. As a result, small strain Young's moduli and shear moduli which were obtained by static and dynamic measurements, respectively, increased with the increase in the effective stress levels in a manner that was similar to each other.

Identification of compressibility of soft rock has been and is still a challenging task since the early days of geotechnical engineering. Numerous techniques and procedures exist to characterize the compressibility of soil-like material and of rock-like material. However if the site stratigraphy shows alternating layers of distinct almost completely weathered and more or less soil like material and layers of rock like material these techniques can no longer be applied to assess the overall rock mass compressibility. The paper proposes a field oriented method using a combination of known characterization methods (for rock and soil materials) to describe the soft rock profile with respect to identify its overall compressibility in terms of Young's moduli. The Moduli are calculated from an averaging scheme assuming that the soft rock layers can be described by mixtures of rock-like material and soil like material. An example application is presented including a first discussion of applicability and limitations of the method.

A series of drained triaxial monotonic and cyclic tests was carried out to study the influence of particle breakage on the behaviour of a crushable limestone. Special attention was paid to the analysis of grain breakage during the loading and unloading process and the movement of the critical state line caused by grain breakage in the e-log (p') diagram. Monotonic test results show typical features of the behaviour of crushable granular materials compared to non crushable materials. For cyclic tests, it was found that certain particles were crushed during the cyclic loading and quantities of grain breakage increased slowly with the augmentation of loops.

This paper outlines the loading, control and instrumentation systems of two Hollow Cylinder Apparatus' used at Imperial College in recent research into the potentially strong anisotropy of brittle stiff clays and mudrocks. The HCAs can apply a wide range of stress paths and modes of shearing allowing the direction of the major principal stress axis, α (or that of the principal stress increment, α_dσ) and the α₂ parameter, b = (α₂-α₃)/(α₁-α₃) to be controlled independently. The paper describes how representative intact HCA specimens were formed from rotary cores and block samples and reports on the steps taken to minimize stress-strain non-uniformity and specimen set-up disturbance set up. While the characterization of anisotropic shear strength is reported elsewhere, it is shown how non-linear and anisotropic mudrock stiffness was characterized and improved simple shear tests conducted.

This paper presents the elasto-viscoplastic stress-strain behavior of pure kaolin soil and its cementmixture under drained one-dimensional compression. A study was made of the effects of the degrees of wetting combined with ageing effects on the stress-strain-time behavior. Effects of the degree of saturation and its variations for a wide range (0.8% to 100%) on the stress-strain-time behaviour during creep and subsequent continuous monotonic loading in one-dimensional compression tests were evaluated. Also the effects of ageing that develop at different stress levels on the behavior of unsaturated specimens were evaluated. A new mathematic model developed in the framework of a non-linear three-component model is proposed on the basis of test results.