Design and Performance of Embankments on Very Soft Soils

Embankment construction projects on very soft soil often give rise to serious problems. This volume on geotechnics and soft soil engineering therefore treats all phases of the design and construction process exhaustively, from the first investigation step to the monitoring of constructed work. The book presents the development concepts necessary for the project stages and discusses in great detail construction methods, displacement estimations, stability analyses, monitoring, and various other aspects involved. Extensive attention is furthermore paid to the application of geosynthetics as a tool to improve the stability of soft soils and embankments. Including various tables and practical data for many geographical areas in the world, this reference volume is essential reading for engineers and researchers in geotechnical engineering, construction, and related disciplines.

1 Construction methods of embankments on soft soils 1.1 Replacement of soft soils and displacement fills 1.1.1 Replacement of soft soils 1.1.2 Displacement fills 1.2 Conventional embankment with temporary surcharge 1.3 Embankments built in stages, embankments with lateral berms and reinforced embankments 1.4 Embankment on vertical drains 1.5 Lightweight fills 1.6 Embankments on pile-like elements 1.7 Construction methodologies for harbor works 1.8 Final remarks 2 Site investigation 2.1 Preliminary investigations 2.1.1 Borings 2.1.2 Characterization 2.2 Complementary investigations 2.2.1 In situ tests 2.2.2 Laboratory tests 2.3 Vane tests 2.3.1 Equipment and procedures 2.3.2 Undrained strength 2.3.3 Clay sensitivity2.3.4 Stress history 2.3.5 Clay anisotropy 2.3.6 Test correction 2.4 Piezocone test 2.4.1 Equipment and procedures 2.4.2 Correction of cone resistance 2.4.3 Preliminary soil classification 2.4.4 Undrained strength (Su) 2.4.5 Stress history 2.4.6 Coefficient of consolidation 2.5 T-bar test 2.6 Soil sampling for laboratory tests 2.7 Oedometer consolidation tests 2.7.1 Other consolidation tests 2.7.2 Sample quality 2.8 Triaxial tests 2.9 Final remarks 3 Geotechnical properties of very soft soils: Rio de Janeiro soft clays 3.1 Overall behavior of very soft soils: Cam clay models 3.1.1 Stress and strain variables 3.1.2 Model parameters 3.1.3 Yield conditions 3.2 Index properties of some Rio de Janeiro clays 3.3 Compressibility and stress history 3.3.1 Compressibility 3.3.2 Overconsolidation ratio (OCR) 3.4 Hydraulic conductivity and coefficient of consolidation 3.5 Soil strength 3.5.1 Undrained strength – laboratory and in situ data 3.5.2 Effective strength parameters 3.6 Deformation data 3.7 Viscous behavior 3.7.1 Strain rate during shearing 3.7.2 Strain rate during constant loading oedometer tests 3.8 Field studies 3.8.1 Embankment I 3.8.2 Embankment II 4 Prediction of settlements and horizontal displacements 4.1 Types of settlements 4.1.1 Immediate settlement 4.1.2 Primary consolidation settlements 4.1.3 Secondary compression settlement 4.2 Staged embankment settlements 4.3 Prediction of horizontal displacements 4.4 Final remarks 5 Acceleration of settlements: use of vertical drains and surcharge 5.1 Embankments on vertical drains 5.2 Vertical drains 5.2.1 Theoretical solutions 5.2.2 Consolidation with purely radial drainage 5.2.3 Diameter of influence and equivalent diameter of PVDs 5.2.4 Consolidation with combined radial and vertical drainage 5.2.5 Influence of smear in PVD performance 5.2.6 Influence of mandrel size on soil disturbance 5.2.7 Parameters for consideration of disturbance (smear) 5.2.8 The effect of well resistance 5.2.9 Specification of PVD 5.2.10 Sequence for radial drainage calculations 5.3 Design of the horizontal drainage blanket 5.4 Use of temporary surcharge 5.4.1 Use of surcharge with and without vertical drains 5.4.2 Vacuum preloading 5.4.3 Use of surcharge to minimize secondary compression settlements 5.5 Final remarks 6 Stability of unreinforced and reinforced embankments 6.1 Design parameters 6.1.1 Undrained strength of clay 6.1.2 Embankment strength 6.1.3 Geosynthetic reinforcement parameters 6.2 Failure modes of embankments on soft soils 6.3 Foundation failure: Critical height of embankment 6.4 Global stability analysis of unreinforced embankments 6.4.1 Circular failure surfaces 6.4.2 Non-circular failure surfaces 6.5 Reinforced embankments 6.5.1 Effects of reinforcement 6.5.2 Foundation failure 6.5.3 Failure due to lateral sliding of embankment 6.5.4 Global failure 6.5.5 Definition of tensile force in reinforcement 6.6 Stability analysis of stage constructed embankments 6.6.1 Conceptual aspects 6.6.2 Undrained strength of the clay for staged construction 6.6.3 Illustration of stability analysis of staged construction 6.6.4 Considerations on the stability analysis for staged constructed embankments 6.7 Sequence for stability analysis of embankments on soft soils 6.7.1 Unreinforced embankments 6.7.2 Reinforced embankments 6.7.3 Reinforced embankment built in stages 6.8 Final remarks 7 Embankments on pile-like elements 7.1 Piled embankments with geosynthetic platform 7.1.1 The working platform settlement and overall embankment behavior 7.1.2 Arching effect on soils 7.1.3 Defining the geometry of piled embankments 7.1.4 Calculation of vertical stresses acting on the geosynthetic 7.1.5 Calculation of tensile force acting on the reinforcement 7.1.6 Case histories of piled embankments 7.2 Embankments on traditional granular columns 7.2.1 Traditional granular columns using the vibro-replacement method 7.2.2 Design and analysis principles 7.2.3 Settlement reduction factor (soil improvement factor) 7.2.4 Settlement computations 7.2.5 Stability analysis 7.2.6 General behavior of embankments on granular columns 7.3 Encased granular columns 7.3.1 General description 7.3.2 Execution methods 7.3.3 Calculation methods 7.3.4 Case histories for applications of embankments over encased granular columns 7.4 Final remarks 8 Monitoring embankments on soft soils 8.1 Monitoring vertical displacements 8.1.1 Settlement plates 8.1.2 Depth extensometers 8.1.3 Settlement Profiler 8.2 Measurement of horizontal displacements 8.3 Measurements of pore pressures 8.4 Monitoring of the tensile forces in geosynthetic reinforcements 8.5 Interpretation of monitoring results 8.5.1 Asaoka’s method (1978) 8.5.2 Pore pressure analysis 8.5.3 Discussion on obtaining cv and ch from monitoring data 8.5.4 Stability of embankment by horizontal displacements analysis 8.5.5 In situ compression curves 8.6 New trends in geotechnical instrumentation 8.7 Final remarks References Annex Subject index

Márcio Almeida earned his Civil Engineering degree at the Federal University of Rio de Janeiro, in 1974 and obtained his MSc at COPPE/UFRJ in 1977 when he joined COPPE as Assistant Lecturer. Marcio got his PhD from the University of Cambridge, UK in 1984. Then he returned to UFRJ and in 1994 became Professor of GeotechnicalEngineering. His postdocs were in Italy (ISMES) and at NGI, Norway in the early 1990s and he was also visiting researcher at the universities of Oxford, Western Australia and ETH, Zurich. He is currently one of the leading researchers of the National Institute of Science and Technology – Rehabilitation of Slopes and Plains (INCT-REAGEO). He has been the Director of COPPE’s MBA “Post-Graduate Program in Environment’’ since 1998. He has published numerous articles in journals and conferences in Brazil and abroad and has supervised over 60 doctoral and master dissertations. He received the Terzaghi and Jose Machado awards from the Brazilian Association of Soil Mechanics and Geotechnical Engineering (ABMS). His experience ranges from soft clay engineering, environmental and marine geotechnics tosite investigation, physical and numerical modeling as well as extensive experience in geotechnical consulting. Esther Marques holds a degree in Civil Engineering – emphasis in Soil Mechanics, from UFRJ. She obtained her MA and PhD in Civil Engineering from COPPE/UFRJ, with researches conducted at Université Laval, Canada. She worked at Tecnosolo and Serla and was a researcher at COPPE/UFRJ from 2001 to 2007. She is currently an associated professor at the Institute of Military Engineering, where she teaches undergraduate and graduate Transportation Engineering and Defence Engineering. She has experience in Civil Engineering with emphasis in Soil Mechanics, working mainly with the following: laboratory testing, field-testing, instrumentation, soft soils behavior, embankments on soft soils and environmental geotechnics.