Ebook: Geotechnical Synergy in Buenos Aires 2015

The Argentinian Geotechnical Engineering Society (SAIG) is pleased to present the invited lectures of the 15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (PCSMGE) and 8th South American Congress on Rock Mechanics (SCRM) that has been held in Buenos Aires (Argentina) from 15th to 18th November 2015.

These two regional conferences have been held in different countries from North, Central and South American regions from the early sixties. From the first Pan-American Conference in Mexico in 1959, the Pan-American Conferences have been held every four years in different countries of the Americas: in Brazil in 1963, in Venezuela in 1967, in Puerto Rico in 1971, in Argentina in 1975, in Peru in 1979, Canada in 1983, in Colombia in 1987, Chile 1991, in Mexico in 1995, in Brazil in 1999, in USA in 2003, in Venezuela in 2007, in Canada in 2011 and in Argentina in 2015. The SCRM is a Regional Symposium for South America of the International Society for Rock Mechanics (ISRM). Previous congresses were held in Colombia (1982, 2006), Brazil (1986, 1998), Venezuela (1990), Chile (1994), Peru (2010) and Argentina (2015).

This time, the conferences have coincided with other important events for geoprofessionals: the 6th International Symposium on Deformation Characteristics of Soils and the XXII Argentinian Congress of Soil Mechanics and Geotechnical Engineering (CAMSIG XXII).

This book include the Casagrande Lecture delivered by Luis Valenzuela, nine plenary lectures and twelve keynote lectures of both Buenos Aires conferences: 15th PCSMGE and 8th SCRM. Two additional volumes that include the peer-reviewed articles for both Conferences complement this book: “From Fundamentals to Applications in Geotechnics” (PCSMGE) and “Integrating Innovations of Rock Mechanics” (SCRM).

On behalf of Organizing Committee, the editors wish to express their gratitude to the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) and the International Society for Rock Mechanics (ISRM) and all the sponsors and institutions that generously contributed and supported to the success of the Buenos Aires 2015 Conferences. We would also like to acknowledge the commitment of the chairs, panelists, members of the international advisory committee and peer-reviewers. This collaboration effort succeeded in bringing together international experts, researchers, academics, professionals and geo-engineering companies in a unique opportunity to exchange ideas and discuss current and future practices in the areas of soil mechanics, rock mechanics, and their applications in civil, mining and environmental engineering.

Alejo O. Sfriso

Diego Manzanal

Ricardo J. Rocca

Buenos Aires, 15–18 November 2015

The significant growth of the metallic mining industry over the last few decades has made the construction of tailings deposits of large dimensions necessary, tailings being the fine mining waste resulting from the milling and concentration processes. In some cases the dams required to contain these tailings could reach a considerable height. The most common types of tailings dam in mining are the tailings sand dam, a special kind of hydraulic fill dam, for two main reasons: because such dams need to be built over a long period of time, and due to the low cost of sand available from the tailings. Both types have not only a similar construction method in common, but also negative social perception due to the history of failures associated with the original designs of these dams. These designs have evolved with time to more adequate schemes enabling a much better performance. Although these types of dam differ in many aspects, such as main objective, source of the sand for construction, and the total construction time, the evolution of their designs has some interesting similarities. At this Conference, critical aspects in the performance of both types of dams will be discussed, together with the evolution of their original designs.

In particular, this paper analyses the behavior of tailings dams in Chile, one of the most seismically active countries in the world. The worldwide tendency to design and construct taller tailings dams, as well as the effect of the resulting high confining pressures on the geotechnical behavior of the tailings sands, drain gravels, and filter materials is also discussed. The importance of the operational phase is addressed, because in tailings dams this phase can last many years and be the determinant in the final behavior of the dams. Finally, recommendations to mitigate risks along the complete life cycle of the dams are given, and new developments in tailings deposits are considered.

Hydraulic fracturing in a stiff naturally fractured rock mass such as a shale gas reservoir or a geothermal site in an igneous rock involves a complex interaction between the stress and flow effects of the induced fracture process with a geometrically complex, strongly anisotropic, and undoubtedly heterogeneous medium. Deformation mechanisms include the opening of the primary hydraulic fracture, opening of near-by joints, and small-scale shearing of near-field and more distant joints that are not fully wedged open by the high hydraulic pressures. Aspects of initial state (joint system, stresses, mechanical properties…) are complex and must be better understood. The changes to the system during hydraulic fracturing include large scale stress and pressure changes, as well as irreversible and geometrically complex changes to the joint systems. Because of the different scales involved, large-scale modeling must involve some type of upscaling, but the best approach to this in different cases and for different processes remains obscure. The article attempts to give a physical portrait of the process to help guide model development, but also to help understand what happens in real cases. Some examples of simple 2-D modeling efforts in simulated jointed media are given to show how the physical understanding can, qualitatively, be supported and extended by careful analysis, albeit of a preliminary nature.

World records for drill-and-blast tunnelling from Norwegian contractors, bear witness to numerous weeks of more than 100m, and an exceptional 5.8 km in 54 weeks, also from one face. Earlier hard-rock world records using high-powered TBM in Norway, but most frequently and more recently, the records with Robbins TBM through non-abrasive limestones in the USA, provide numbers in meters per day, per week, and per month, which are of course, even more remarkable. Unfortunately there are contrary and undesirable TBM records, which are occasionally recurring events so not records, which see TBM stopped for months or even years in fault zones, or permanently buried in mountains. The many orders of magnitude range of performance suggest the need for better investigations, better choice of TBM, and better facilities for improving the ground ahead of TBM, when probe-drilling indicates that this is essential. Control of water, and improved stand-up behaviour in significant weakness zones and faults may demand drainage, which can be unending, and pre-injection. Fortunately there are increasing signs that this is recognized by TBM manufacturers: more guide-holes for drilling pre-injection umbrellas are seen through front-shields nowadays. A little acknowledged fact is that when all hours are included, TBM will generally decelerate as tunnel length and time increases. This is usually seen after improved performance during the learning curve. Deceleration is also a general trend during world-record setting performances. This means that utilization U is equal to the ratio of actual advance rate and penetration rate, AR/PR, only for specified time intervals, because U is time-dependent. This is rarely quantified by designers, and is therefore a source of risk, by default. Another important item for correct prognosis is the recognition that reduced penetration rate PR can sometimes occur when thrust is increased by the TBM operator, due to exceptionally resistant rock mass formations. Each of the above, and PR sensitivity to a wide range of cutter forces, UCS and abrasiveness, are provided in the empirical QTBM method. This method explains variable progress in jointed rock, which is sometimes fast, and also quantifies the likely delays in untreated, or pre-injected, fault zones.

In highway construction, earthworks refer to the tasks of excavation, transportation, spreading and compaction of geomaterial (e.g. soil, rockfill and soil-rockfill mixture). Whereas relying heavily on machinery and repetitive processes, these tasks are highly susceptible to optimization. In this context Artificial Intelligent techniques, such as Data Mining and modern optimization can be applied for earthworks. A survey of these applications shows that they focus on the optimization of specific objectives and/or construction phases being possible to identify the capabilities and limitations of the analyzed techniques. Thus, according to the pinpointed drawbacks of these techniques, this paper describes a novel intelligent earthwork optimization system, capable of integrating DM, modern optimization and GIS technologies in order to optimize the earthwork processes throughout all phases of design and construction work. This integration system allows significant savings in time, cost and gas emissions contributing for a more sustainable construction.

The best possible program for geotechnical soils exploration involves a blend of rotary drilling, undisturbed sampling, laboratory testing, in-situ field tests, and geophysics, all taken within the context of engineering geology. Yet, this is only viable when sufficient allocations of time and funds are available, namely large or critical projects. Therefore, for routine site investigations, the use of hybrid geotechnical-geophysical methods should be adopted, including the seismic piezocone test (SCPTù) and seismic dilatometer (SDMTà), since they collect as many as five independent readings with depth, thereby optimizing the information gathered in an efficient, expeditious, and economical manner.

The paper presents an overview of the concepts and philosophies of sustainability and connects it to the practice of geotechnical engineering. The definitions, philosophies, and principles behind sustainability and its development are presented along with a historical perspective. How sustainability is incorporated in engineering practice is discussed next. Finally, the scope of sustainability in geotechnical engineering is outlined and sustainable practices in geotechnical engineering are described with real field examples demonstrating utilization of recycled materials.

Soils and rocks typically exhibit strongly nonlinear, inelastic load-deformation behavior. Their complex mechanical responses persist across the scales, from nanometer up to kilometer scale, and are generally linked to other multiphysical processes such as fluid flow, heat conduction, and chemical/biological transport. Capturing these complex multiphysical responses requires sound theoretical framework and robust computational algorithms.

In this work, I will present a computational framework that captures the microfracture processes triggering shear band bifurcation in porous crystalline rocks. The framework consists of computational homogenization on a representative elementary volume (REV) that upscales the pore-scale microfracture processes to the continuum scale. The assumed enhanced strain (AES) finite element approach is used to capture the discontinuous displacement field generated by the microfractures. Homogenization at the continuum scale results in incrementally nonlinear material response, which gives rise to an overall constitutive tangent tensor that varies not only with the stress state but also with loading direction.

I will motivate the talk with experimental data obtained from nanoindentation tests on Woodford shale conducted at Stanford University. Results of these indentation tests reveal strong anisotropy in the constitutive mechanical response, which is postulated to arise mainly from preferential orientation of clay particles comprising the shale sample. Indeed, this preferential orientation has been seen from FIB/SEM and TXM images of the same rock samples, which also quantify the heterogeneity of the rock at the nanometer scale. The work motivates the development of a mechanistic model for microfracturing of heterogeneous rock samples at nanometer and larger scales.

A general overview of the different solutions to the problem of foundation of buildings on highly compressible soft soils such as those found in Mexico City valley is presented. Special attention is given to deep foundations systems that were developed to control settlement or protruding in consolidating soils. Recent techniques for modeling the behavior of deep foundations are also reviewed.

Gas and water in soils interact through the physical laws of Boyle, Henry, Darcy and Fick and through the capillarity law; this interaction has a large number of practical implications and applications in geotechnical engineering. Those examined in this paper are: cavitation; implications of occluded gas; implications of gas exsolution on hydraulic conductivity, pore pressures and sampling; gas hydrate dissociation; saturation of soil samples; infiltrations in soils; capillary barriers; and transient pore pressures in earth dams.

This paper has been adapted from an original presentation by the author to a national workshop in the U.S. (Dobry, 2014). After a discussion on the two successive stages of liquefaction triggering in the free field, associated with small cyclic strains, and post-triggering due to earthquake shaking, it is concluded that most liquefaction consequences of engineering significance involve high strains and hence are post-triggering phenomena. The liquefaction consequences are classified in four main categories: (i) flow slides and large deformations of embankments and slopes; (ii) free field deformations including lateral spreading; (iii) structural effects driven by the free field deformations; and (iv) structural damage that includes effects of gravitational and inertial structural forces. Each one of the four categories are discussed separately with focus on the current State-of-Practice of their evaluation and technical challenges.

This paper presents the contributions from the three invited panelists of the Panel 1-C on ‘Geo-Engineering for Energy’; organized by the ISSMGE TC308 on ‘Energy Geotechnics’ in the framework of the XV Pan-American Conference on Soil Mechanics and Geotechnical Engineering, hold in Buenos Aires between 15^th to 18^th November 2015. This contribution also presents a brief description of the TC308 activities, as well as the questions suggested to the invited panelists.

The most significant development in upstream oil and gas in the last decade has been the surge in development of unconventional resources, especially shale oil and gas. Hydraulic fracturing (the most important stimulation technique in these reservoirs) has evolved rapidly, mostly through operational trial and error. The primary challenge to economically optimal development of unconventional resources is the current inability to reliably predict production from individual wells, and hence to make stimulation design decisions for the specific well or area. One of the largest impediments to such predictions is the limited knowledge of the pre-existing fracture network and its impact on the success of stimulation treatments. Microseismic data, and the rigorous inclusion of the DFN into hydraulic fracture design and simulation tools is critical to removing this impediment.

The article is devoted to present the key aspect of the mathematical, constitutive and numerical modelling of the failure of geomaterials in the transition from solid to fluid. The aim is to provide the reader with an overview of the role of modelling the most relevant phenomena in soils behaviour in fast landslides.

The porosity/binder ratio, η/C_iv, is possibly the main development in the field of soil stabilization over the last many decades. η/C_iv is shown to be the controlling factor of artificially cemented materials mechanical behavior. Experimental results were presented to highlight this ratio applicability for determination of artificially cemented soils unconfined compressive strength, splitting tensile strength, triaxial compression behavior, shear and volumetric stiffness, stress-dilatancy behavior and strength envelopes. Moreover, fiber reinforcement use and its benefits were presented as a solution for geotechnical problems and as a future challenge to be incorporated into engineering practice.

Mechanized tunnelling in soft ground has evolved significantly over the last 20 years. However, the interaction between the tunnel boring machine (TBM) and the ground is often understood through idealized concepts, focused mostly on the machine actions in detriment of the reactions from the ground. These concepts cannot be used to explain several mechanisms that have been observed during the construction of mechanized tunnels. Therefore, this paper presents the path from field observations to the theoretical developments to model the TBM-ground interaction more realistically. Some ideas on how these developments can be applied into practice are presented. Finally, a discussion is proposed about how an effective collaboration between academia and industry can alleviate the current concentration of knowledge in the state of practice.

The number of underground constructions has increased massively due to environmental, social and economic reasons. Furthermore, design and construction solutions are even more challenging when attempting to obtain optimal underground solutions. This article is focused on the development of underground constructions in Chile, highlighting the necessary improvements in the design and construction areas, where key topics are seismic design related to urban tunnels, mechanized excavation method promise, and collaborative work between the industry and academics.