Ebook: From Fundamentals to Applications in Geotechnics
The work of geotechnical engineers contributes to the creation of safe, economic and pleasant spaces to live, work and relax all over the world. Advances are constantly being made, and the expertise of the profession becomes ever more important with the increased pressure on space and resources.
This book presents the proceedings of the 15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (XV PCSMGE), held in Buenos Aires, Argentina, in November 2015. This conference, held every four years, is an important opportunity for international experts, researchers, academics, professionals and geo-engineering companies to meet and exchange ideas and research findings in the areas of soil mechanics, rock mechanics, and their applications in civil, mining and environmental engineering. The articles are divided into nine sections: transportation geotechnics; in-situ testing; geo-engineering for energy and sustainability; numerical modeling in geotechnics; foundations and ground improvement; unsaturated soil behavior; embankments, dams and tailings; excavations and tunnels; and geo-risks, and cover a wide spectrum of issues from fundamentals to applications in geotechnics.
This book will undoubtedly represent an essential reference for academics, researchers and practitioners in the field of soil mechanics and geotechnical engineering.
In this proceedings, approximately 65% of the contributions are in English, and 35% of the contributions are in Spanish or Portuguese.
The Argentinean Geotechnical Engineering Society (SAIG) is pleased to present the proceedings of the 15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (XV PCSMGE), held in Buenos Aires (Argentina) from 15th to 18th November 2015.
From the first Pan-American Conference in Mexico in 1959, Pan-American Conferences have been held every four years in different countries in the Americas: Brazil in 1963, Venezuela in 1967, Puerto Rico in 1971, Argentina in 1975, Peru in 1979, Canada in 1983, Colombia in 1987, Chile 1991, Mexico in 1995, Brazil in 1999, the USA in 2003, Venezuela in 2007, and Canada in 2011.
This time, PCSMGE XV – Buenos Aires 2015 has coincided with another three important events for geo-professionals: the 8th South American Conference on Rock Mechanics, the 6th International Symposium of Deformation Characteristics of Soils and the XXII Argentinean Congress of Soil Mechanics and Geotechnical Engineering (CAMSIG XXII).
This meeting has brought 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.
The Proceedings are divided into nine technical sessions covering the modern trends and classical topics of Soil Mechanics and Geotechnical Engineering. They collect the articles accepted for publication after anonymous peer-review. Four hundred and forty five articles were submitted, and after the peer-review process, 405 were accepted for publication. The articles cover significant advances in the areas of Transportation Geotechnics, In-situ testing, Geo-engineering for Energy and Sustainability, Numerical Modeling in Geotechnics, Foundations & Ground improvement, Unsaturated Soil Behavior, Embankments, Dams and Tailings, Excavations and Tunnels, and GeoRisks. The proceedings are complemented by the book “Geotechnical Synergy in Buenos Aires 2015” which includes the Casagrande Lecture, the Mercer Lecture, 3 plenary lectures, 9 keynote lectures and 6 panelists' contributions, authored by eminent researchers and professionals in the field and covering a wide spectrum of issues from fundamentals to applications in geotechnics. This collection of papers will surely represent an essential reference for academics, researchers and practitioners.
The Conference was organized under the auspices of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) and the International Society of Rock Mechanics (ISRM). On behalf of the Organizing Committee, the editors would like to express their gratitude for the contribution of the members of the National and International Advisory Committee and all the sponsors and institutions who generously contributed to and supported the success of the Buenos Aires Conferences 2015.
Finally, we would like to extend our thanks to all the authors who submitted papers to the conference and to the reviewers who invested significant effort and dedicated some of their valuable time to enhancing the quality of these contributions. We would also like to acknowledge the work and the support of the Session Chairs.
We hope that these Proceedings will strengthen the unity between academics, researchers and geo-practitioners from the Americas that was evident at the Conference, and we trust that it will be considered an essential reference volume in the field of our profession.
Alejo O. Sfriso
Buenos Aires, 15–18 November 2015
There was in recent years a great offer of patented additives (enzymes) to the road market as solution to soil stabilization. However, they are many times rejected because there are no theoretical foundation to prove such uses, and also because researches themselves don't see research opportunities. Anyway, these products has been marketed, and frequently municipalities and states waste resources by choosing for a solution that is not yet well studied. This study aims to present a methodology to solve the problems that affects the use of additives in laboratory, because his use in conventional tests do not shown efficient for these purposes. For this, it was used a portable traffic simulator, easy handling and common in pavement laboratories. It is a standardized equipment, used to assess the effect of compression and the strain characteristics of asphaltic coating layers. It was developed a set with several accessories to mold samples in the shape of tablets (380 x 50 x 10 mm), may be easily adapted to the equipment selected as simulator. The soils used for the production of the tested tablets were lateritic soils from Rio de Janeiro–RJ, and the enzymatic products were imported. A rigorous care was followed in the production of each tablet to ensure equality and, after, compare results each other. These tablets were molded and tested in order to obtain a series of experimental results, comparing the soil treated with enzymes with the soil without any kind of treatment. The study concludes, in principle, that the equipment used and the developed accessories are appropriate for this purpose and that the use of enzymes showed effective for some applications, but lacks more studies, including with the use of other types of soil to prove such effectiveness.
In this work the behaviour of fouled ballast with sand has been analysed by large triaxial tests (23 cm of diameter). Previously, the breakage resistance of ballast particles was determined and the different ways of quantifying the fouling degree were described.
The paper presents the results obtained by the application of recycling rigid pavements through Rubblizing technique by resonant vibration, with no precedent in Argentina. This methodology, was used in National Route N° A008 (Rosario City Bypass) in Santa Fe Province during the period 2010–2013. It consists on fracturing the slab into angular interlocking pieces by using a resonant pavement breaker machine which transmits a dynamic load of low amplitude and high frequency, generating a granular layer of high Modulus. Main advantages of rubblizing technique, among others, are the resulting layer of homogeneous structural response and the daily high performance execution with no damage in the sub base layer. In this urban roadway, two representative experimental sections were adopted for further studies. Those studies were divided in two geotechnical campaigns: the first aimed to characterize the bearing capacity of the subgrade and sub base soil cement by DCP tests, laces and pits. The second one used Falling Weight Deflectometer (FWD) equipment on each structural reinforcement performed on the fractured layer to obtain the structural coefficient of the granular layer. It should be noted that for the structural design of the flexible pavement layers it was adopted a structural coefficient of 0.098 1/cm ai taking as antecedent the results obtained in the experience carried out on the Del Sol Roadway, New Access to the Port of San Antonio, Chile. The values obtained in the present work were satisfactory and confirm those adopted for the project. Both the site evaluation and the in situ behaviour of structural layers were also satisfactory. Although in some sections the annual average daily traffic exceeds 40,000 vehicles, there were no structural problems verified.
La estructura económica del Paraguay se sustenta básicamente en el sector agropecuario. El país está realizando esfuerzos importantes para fomentar procesos de industrialización de sus productos agropecuarios y aumentar su diversificación. Estas actividades son altamente dependientes de los niveles de cobertura, accesibilidad y de la calidad de infraestructura vial. El transporte terrestre moviliza el 90% de las cargas de exportación y el 89% de las cargas de importación, debiendo estas cargas recorrer grandes distancias (1.325 km en promedio) para llegar a los principales puertos de exportación del país. La red vial básica del Paraguay cuenta con un total general de 61.816,81 kilómetros de longitud entre rutas asfálticas, de hormigón, empedradas, enripiadas y de tierra no pavimentadas en tiempo seco (MOPC, 2010). La mejora de ésta red vial primaria nacional es de suma importancia para la comunicación interna e integración territorial para el movimiento de carga y personas entre las zonas productivas, los centros urbanos y los corredores de exportación. El Estado invierte anualmente importantes recursos económicos para la obtención de información geotécnica en cada nuevo proyecto de infraestructura. Como no existe sistematización, estos antecedentes se pierden, y eventualmente el Estado vuelve a contratar servicios para la obtención de datos similares, con el consiguiente gasto innecesario para el país. La elaboración de mapas geotécnicos, proporcionan una base de información fundamental para el conocimiento, planificación y proyecto de construcción o gestión de infraestructura vial. Los Sistemas de Información Geográfica (SIG) constituyen una potente herramienta para el procesamiento, mantenimiento y mejoramiento de las bases de datos en formato digital. La creación del Mapa Geotécnico y Mapas de Riesgo para el Paraguay a partir de estudios pre-existentes, colabora en la optimización de utilización de recursos destinados a la ejecución de infraestructuras, a la vez de brindar información preliminar valiosa acerca de las zonas desfavorables o de riesgos para nuevas estructuras.
Se describe un proyecto de investigación de desempeño de pavimentos con capa de base de suelos modificados con ceniza de bagazo de caña de azúcar (CBCA) y cal mediante la construcción y monitoreo de un tramo experimental de calle a escala real en Bella Unión. El material granular utilizado fue una grava limosa, de origen fluvial asociado a sedimentos cuaternarios del río Uruguay, extraído de una cantera próxima a la localidad. El diseño de mezcla óptima del suelo con CBCA y cal se realizó aplicando el Método de Thompson. Los parámetros óptimos de compactación del material fueron determinados con ensayos Proctor modificado. La caracterización de la ceniza indica baja reactividad alcalina, sin embargo la ocurrencia de reacciones cementantes fue verificada en los ensayos de resistencia a la compresión inconfinada. El tramo experimental se monitoreó con medidas de deflexión con Viga Benkelman. A pesar de la baja reactividad de la CBCA, se observó una notable disminución de las deflexiones a tres semanas de construido el tramo experimental respecto a las medidas inmediatamente después de su construcción. Con un año de vida, el pavimento del tramo experimental muestra una buena condición estructural y de servicio, indicando que este tipo de material puede ser una alternativa para capa de base de pavimentos de bajo volumen de tránsito con beneficios económicos y ambientales.
In order to study the behavior of railway ballast under vibration and the distribution of pressure under the ballast layer, experimental and numerical studies have been performed. A physical model of ballast was used to study repeated impact loadings in the laboratory. The instrumented equipment enables the measurement of vertical force at the impact and under the ballast layer.
The Interstate Highway 35 East (IH-35E) running through Dallas and Denton Counties in Texas, United States will undergo significant construction improvements for approximately 48 kms (30 miles). The 1.5 billion US dollars Design-Build project is expected to relieve traffic congestion in one of the most heavily traveled corridors in the North Texas region. In this project, over 120 Mechanically Stabilized Earth (MSE) Retaining Walls are planned to be constructed over the sandy lean and fat clay soils overlying the Eagle Ford Shale and Woodbine Sandstone. To characterize the engineering properties of the foundation soils, 13 consolidated-undrained triaxial compression tests and 13 stress-history controlled direct simple shear tests on reconstituted samples were conducted. The results were analyzed along with the database containing 17 laboratory shear test results from previous projects in the area. Historically, the soils derived from the Eagle Ford shale are known to be problematic resulting in stability issues when exposed to changes in moisture content. These soils usually have an overconsolidation ratio (OCR) between 1 and 6. Statistical analyses were performed to provide recommendations for Mohr-Coulomb effective (long term) strength parameters to be used in external stability analyses of the MSE walls. The analyses were performed on the basis of type of laboratory tests (difference in failure mechanism), index classification (liquid limit and percent sand content), and overconsolidation ratio to account for the desiccated soil layers. Based on the results from these analyses, there exist significant differences in soils engineering parameters in the lean (CL) and fat (CH) clays and the sandy lean (SC) clays and in relation to the sample degree of overconsolidation. The studied behavior and engineering used to propose five Mohr-Coulomb effective strength envelopes to be used in the external stability analyses of the MSE walls.
The company Geotecnia Ambiental together with the Geotechnical Group of the Pontificia Universidad Católica de Valparaíso, with financing from INNOVA-CORFO of Chile, approached the challenge of adapting innovative, efficient, environmentally sustainable and precise technologies as alternatives in the process control of soil compaction of Chilean road infrastructure and backfill projects, through an investigation from 2012 and 2014. During the investigation more than twenty state of the art control technologies that exist on a world level were reviewed. Based on the background information dynamic lightweight penetrometer PANDA and the dynamic load plate LFG Pro were selected, of French and German engineering respectively, for use in Chile. Advantages and disadvantages for each system, as well as fields of application, output parameters and proposed methodology were all considered for use in future compaction control projects.
Esta investigación consistió en determinar la relación óptima para uso vial de la dosificación de silicato de sodio líquido con los sedimentos loéssicos erodables de la provinciade Córdoba (Argentina). El silicato de sodio puede ser utilizado en la estabilización de suelos cuando se tiene presencia de sales de calcio diluidas en agua, pues esto origina silicatos gelatinosos de calcio insolubles, que al hidratarse producen un magnífico agente cementante. La utilización del silicato de sodio empleado para mejorar los materiales de construcción data de hace más de un siglo. Una de las últimas publicaciones al respecto fue de S. Moretto (2006) de la Universidad Católica de Córdoba, quien investigó al silicato de sodio líquido en la estabilización de loess colapsibles mediante un proceso de inyección in-situ del terreno. En esta oportunidad la aplicación responde a estabilizar subrasantesde caminos rurales erodables yacarcavados; representando éstos el 92% de la red vial total de la provincia de Córdoba según la Dirección Provincial de Vialidad (D.P.V.). La dosificación loess-silicato, garantizará una disminución de la erodabilidad superficial como del índice de plasticidad y, un aumento de la resistencia al corte no drenado.
Compacted soils are important for geotechnical engineering investigation due to their complex behavior and broad applicability in geotechnical structures. However, compaction in clay soils is a topic that still has not been completely understood due to the difficulty of measuring the principal state variables involved during compaction and after it. The evolution of these state variables has strong importance for understanding the behavior of compacted soils and for characterizing their mechanical and hydraulic properties. Therefore, a new one-dimensional consolidation equipment for modelling the behavior of compacted soils has been designed. This device can reproduce one-dimensional compaction while principal mechanical properties are observed. Also, this apparatus allows obtaining undisturbed samples after the compaction process. The principal features of the equipment are presented in this article as the results of different tests using speswhite kaolin. A new laboratory testing methodology for compacted clay soils research is proposed, supporting known insights and providing new ones.
Este trabalho apresenta resultados de pesquisas desenvolvidas na Universidade Federal de Sergipe em parceria com a PUC-Rio utilizando solo de característica areno-argilosa da região de Sergipe estabilizado com cimento Portland CP V-ARI numa proporção de 0, 3, 5, 7 e 9%, com o objetivo de avaliar se o aditivo causará melhorias na matriz do solo natural. O solo natural foi submetido aos ensaios de caracterização (análise granulométrica, limites de Atterberg e massa específica dos grãos), compactação (Proctor Intermediário) e resistência à compressão simples. Ao solo natural foram adicionados os teores de cimento e as misturas foram submetidas aos ensaios de compactação, resistência e limites de Atterberg. Os resultados permitiram concluir que a adição de cimento tende a diminuir a umidade ótima, aumenta a resistência, altera a ação modificadora para aglutinadora das partículas do solo e reduz fortemente a plasticidade.
Unpaved roads constitutes a significant portion of road networks in developing countries. These roads are constructed by a succession of layers of unbound granular materials having different characteristics. From the geotechnical point of view, unpaved roads involve numerous complexities in their behavior such as: repetitive loads producing accumulation of plastic strains, stress rotation, abrasion and crushing; and all that occurs in unsaturated soils having strong interaction with the environmental conditions. The principles of current applied to unpaved roads are based on the results of the California Bearing Ratio tests (CBR). However this test is more related with the strength characteristics of the material (friction angle and apparent cohesion) than its stiffness (young modulus and Poisson ratio). This paper presents the influence of the intrinsic variability of soil parameters in the California Bearing Ratio tests by means of numerical simulations. These simulations were performed to penetrate a soil sample with a plunger of standard area using a random finite element method, in terms of soil parameters. The results of the CBR test are discussed.
Unbound granular materials used in pavement structures are subjected to a complex stress path that includes rotational stresses. Hollow cylinder apparatuses (HCAs) are suitable laboratory devices for reproducing stress paths found in the field. However, as the size of the HCA depends on the size of the granular particles, their use for testing unbound granular materials for pavements has received limited attention in the literature. This paper presents some results about the behavior of granular materials for pavements tested in a hollow cylinder apparatus. This large HCA has hydraulic actuators for vertical movement and torsion while shear and vertical stresses are servo-controlled to reproduce stress paths produced by a heavy vehicle moving on a pavement structure. Confining stress is applied using rings with controllable stiffness. The results show the effect of stress rotation on the behavior of unbound granular materials used in pavement structures.
With the advent of high speed trains, large cyclic stresses are exerted on ballasted rail tracks which in turn cause excessive settlements and lateral deformations of granular materials leading to frequent maintenance of track. The use of planar reinforcement is well established in rail environment to address such aspects. Recent studies have shown that geocell can provide much better lateral confinement to infill soil compared to planar reinforcement. However, a limited number of researches have been performed to examine the performance of reinforced sub-ballast under cyclic loading in railway environment. In this study, the large-scale prismoidal triaxial apparatus have been employed to investigate the performance of reinforced and unreinforced sub-ballast during cyclic loading. A series of drained tests were carried out to examine the behaviour of unreinforced and geocell reinforced sub-ballast subjected to cyclic loading exerted by train passes. The laboratory experiments were carried out in plane strain condition at very low confining pressure to simulate railway environment. Effects of varying apparent confining pressure (σ′3), frequency (f) and number of load cycles (N) were also studied.
In recent times, new demands in geotechnical engineering, mainly in transportation geotechnics, require the use of advanced characterization techniques in order to accurately assess soil stiffness parameters. From this perspective, seismic wave-based techniques have received significant attention, since these allow performing the same basic measurement in the laboratory and field. With an enormous potential, bender elements are currently one of the most popular techniques used to measure reference soil properties in the very small strain range, namely the shear modulus. Bench and triaxial tests conducted on a wide range of geomaterials already demonstrated the applicability of this technique. However, the combined use of bender elements with other testing techniques, as the resonant column, is quite important in order to compare and validate some of the procedures used. In this context, bench bender elements tests were carried out on stiff sandy silt/silty sand specimens and the interpretation of seismic wave velocities was performed using time domain methods under a variety of excitations. Resonant column tests were also conducted on the same material to validate the obtained results with the bench bender elements setup. A critical discussion is made on the advantages and limitations of bender elements usage in contrast with the resonant-column for the assessment of the shear modulus, as well as some insights regarding damping. Additional tests were carried out in two distinct BE setups, one of which installed in the resonant column device, as well as ultrasonic measurements, with the purpose of validating the BE procedure and results interpretation. From this research, it was possible to compare and analyze the results obtained with the three different bender element setups and derive recommendations towards achieving reliable measurements.
The State of Qatar is having a construction boom since the early 2000's and the pace of construction has even increased in the early 2010's after Federation International of Football Association (FIFA) awarded Qatar to host the 2022 World Cup. The preparation for 2022 World Cup and the Qatari governments' plan to upgrade the infrastructure in the country included major transportation projects in the State of Qatar and particularly in the city of Doha and its vicinities. The Ministry of Municipality and Urban Planning (MMUP) of Qatar is heavily involved in planning the transportation roadway projects and introducing the concept designs for the implementation agencies in Qatar. MMUP has divided the Doha city and other areas in the State of Qatar into different projects (packages) to cover some of the concerned areas of roadway network system with most of these packages are in the greater Doha area. Packages 1 through 27 were awarded to different consultants to study and introduce concept designs for the roadway network in the City of Doha and other areas in Qatar as part of MMUP's master plan for transportation and infrastructure. In some projects, the geotechnical aspect of had a significant impact on the outcome of some these studies. This impact was related to the efficient design, construction and optimum solution for transportation problems. The studies included geotechnical investigations for roadways and infrastructures, soil and rock testing , subgrade evaluation, groundwater measurements and studies, and geophysical surveying to deduct any karst formations or cavities. All the geotechnical data used in these studies are being included in a national geotechnical database for the State of Qatar. The database will include any geotechnical data available in the entire country particularly in Doha, including Qatar Rail (QR) data for rail lines and metro stations. gINT software is being used to build the database and import it into to a Geographic Information System (GIS) friendly model.
Compacted materials are fundamentally unsaturated soils whose behaviour can be expansive or collapsible depending upon changes in water content or stresses. Their behaviour is strongly dependent on matric suction, water content, and stress history. This paper presents a methodology for investigating the stress/strain, and suction/water content paths during one dimensional compaction of unsaturated soils. It focuses on anisotropic behaviour. The testing program was carried out in an automated oedometer apparatus that allows measurement of axial strain, radial and axial stresses, suction, and water content during tests. The laboratory component used in this study involves kaolin compacted with different water contents. After compaction, the soil was subjected to wetting while the volumetric changes and stress paths were being examined.
El artículo presenta uno de los primeros casos de estudio de control de calidad de pavimentos mediante la utilización de deflectómetro de impacto, georradar y calibración con extracción de testigos realizado por la Facultad de Ingeniería UdelaR. Los ensayos se realizaron en el acceso al puerto de M´Bopicuá, de 6,2 km de longitud. Se muestra como fueron analizados de forma estadística los datos obtenidos a los efectos de evaluar los principales parámetros estructurales del pavimento en cuestión.
A obtenção da curva de fluência de um geossintético requer ensaios com tempos muito prolongados, os chamados ensaios convencionais. Para reduzir este tempo pode ser utilizado o ensaio SIM (Stepped Isothermal Method) conhecido como ensaio acelerado. Este trabalho apresenta resultados de ensaios convencionais e acelerados, para avaliar a fluência de um geotêxtil não tecido de poliéster de fibra curta. Em comparação com dados da literatura, os resultados demonstraram que houve menor variabilidade do alcance temporal das curvas de fluência acelerada.
This paper introduces a new permanent deformation model proposed from a research study recently conducted at the University of Illinois aimed at characterizing the deformation behavior of unbound aggregate materials used in pavement base/subbase applications. Sixteen different aggregate materials, commonly used for base/subbase applications in the state of North Carolina were tested in the laboratory for shear strength and permanent deformation behavior. An analysis framework was established to consider the strong correlation that commonly exists between permanent deformation and shear strength characteristics. Accordingly, the trends of permanent strain accumulations from repeated load triaxial tests were captured in a new rutting model developed by taking into account the shear stresses applied at certain fractions, i.e., 25%, 50% and 75%, of the shear strength properties of these materials under similar loading conditions. Finally, justification has been provided to highlight how this model would present an improvement over the unbound aggregate rutting damage model currently used in AASHTO's mechanistic-empirical pavement design approach. Physical significance of individual model parameters has also been analyzed in this paper, and inferences regarding expected values of these parameters have been drawn. It is concluded that the proposed model has the ability to predict deformation characteristics of aggregate materials by incorporating number of load cycles, shear strength and stress state components.
Ballast, typically comprising large sized aggregate particles with uniform gradation, is an essential layer in the railroad track substructure. Functions of ballast include facilitating load distribution and drainage, maintaining track geometry and track stability, and providing track resilience and noise absorption. Throughout its service life, ballast goes through changes in gradation and particle shape properties due to aggregate breakdown/degradation. In United States freight lines, mineral aggregate breakdown/degradation has been reported as the main mechanism causing ballast fouling, which covers up to 76% of all the fouling cases. To investigate the effects of ballast aggregate breakdown and degradation on the mechanical behavior, a series of Los Angeles (LA) abrasion tests were performed to generate fouled materials caused by particle degradation under a controlled laboratory environment. In what follows, large-scale triaxial tests were performed on both clean and heavily fouled ballast specimens using a triaxial test device recently developed at the University of Illinois specifically for testing ballast size aggregate materials. The triaxial testing efforts also focused on (a) the effects of gradation considering those finer materials or fines, i.e. particles less than 9.5 mm (3/8 in.), generated through ballast degradation and (b) the effects of aggregate shape properties, such as angularity and flatness and elongation, for particles larger than 9.5 mm (3/8 in.). Accordingly, triaxial tests were also performed only on those aggregate particles still kept after the LA abrasion tests larger than 9.5 mm (3/8 in.) in size, which would constitute the skeleton of the fouled ballast layer in the field. The experimental study results indicated that ballast degradation did not necessarily result in significant strength loss from the monotonic compression tests on dry specimens. On the contrary, in most cases, the dry degraded ballast with or without fines yielded higher strength properties than those observed in the new ballast specimens. Smaller particles provided a “stabilizing” effect that caused a strengthening of the aggregate matrix and accordingly, fines served as a “stabilizer” to fill the voids and increase density in the ballast aggregate matrix.
The Empirical-Mechanistic Design Method used for the structural design of pavements is based on the determination of stresses at critical points of the structure to establish if the deterioration will remain between some acceptable limits which do not affect the serviceability level offered to the user for the design period. Under traffic loads, soil responds with two different deformations: the resilient or recoverable one and the permanent or plastic one. This work presents a study on the resilient and plastic behavior of unbound granular soils based on laboratory test results carried out using both the repeated load triaxial apparatus and the monotonic triaxial shear strength apparatus. Test results of different types of sand and granular material used as pavement subgrades or subbases are shown; different constitutive models to predict the accumulation of permanent deformation are compared; and finally the evolution of the resilient modulus during the test is analyzed.
The main runway of A Coruña airport in Spain is being lengthened by 400 m. The natural ground surface is sloping down gently, and this lead to a maximum height of the new embankment extension of about 35 m. The embankment has been made with a good quality granite rockfill, with slopes 1.4(H):1(V). The foundation ground is formed by schist of weathering degree II-III, with a soil cover 5 to 12 m thick. The allowable post-construction log-term settlement was fixed as 0.20 m. Preliminary design calculations showed that this limit would be exceeded in about 30% of the area. Hence, stone columns were used, in addition to excavation and replacement of the inadequate shallow soft soils. Recorded settlements showed a rapid development during the construction period, which extended to about 2 years. The analysis pays special attention to the effect of the stone columns on the overall ground stiffness. Stability analyses are also presented. The interaction with nearby structures and facilities was also relevant, given the uncommon height of the embankment.