1st Edition

Underwater Embankments on Soft Soil A Case History

    Ground improvement is an established technique in foundation engineering. In recent decades, modern methods of ground improvement have utilised explosives, impact energy, thermal treatment of the soil, vacuum consolidation, vibratory compaction technologies, stabilization and solidification of soft soils, as well as combined systems of ingenious grouting systems and deep mixing technique. Internationally, deep mixing techniques are often the chosen method for dealing with increasingly-demanding foundation problems. Initial experiences, using inventive new developments of soft soil deep mixing technologies and various advanced high pressure mixing methods, have proved successful both onshore and offshore.  This publication illustrates a challenging example, sited in the Port of Antwerp, Belgium, of the design and construction of a large underwater embankment on very soft soil. This text will be a valuable reference case history for the geotechnical engineer, both from the academic's as well as from the practitioner’s point of view.

    1 Introduction

    2 Construction on soft soil

    • 2.1 Clay foundation behavior
    • 2.2 Staged construction
    • 2.2.1 Methodology for analysis
    • 2.2.2 Consolidation analysis

    3 Discussion on undrained shear strength of soft soils

    • 3.1 Preamble
    • 3.2 Shear behavior of normally consolidated clay
    • 3.3 Normalized behavior
    • 3.4 Shear behavior of overconsolidated clay
    • 3.5 Laboratory testing techniques
    • 3.5.1 Overview
    • 3.5.2 SHANSEP
    • 3.5.3 Discussion
    • 3.6 Undrained strength anisotropy
    • 3.7 Final recommendations

    4 Discussion on slope stability evaluation

    • 4.1 Preamble
    • 4.2 Causes of slope instability
    • 4.3 Stability conditions for analysis
    • 4.4 Stability analysis procedures
    • 4.4.1 Limit Equilibrium methods
    • 4.4.2 Strength reduction methods
    • 4.4.3 Limit equilibrium vs. Strength reduction methods
    • 4.5 Failure mechanisms for highly sensitive clays
    • 4.5.1 Flake type sliding of quick clay
    • 4.5.2 Analysis taking pore water pressures into account
    • 4.5.3 Mechanism of sliding in quick clay masses
    • 4.5.4 Conclusions
    • 4.6 Risk of liquefaction
    • 4.7 Slope stability analysis of the Doeldok embankment

    5 Evaluation of consolidation

    • 5.1 One-dimensional consolidation theory
    • 5.2 Infinitesimal strain theory
    • 5.2.1 Numerical solution
    • 5.2.2 Applications of SSCON-FD
    • 5.3 Finite strain theory
    • 5.4 Infinitesimal strain vs. Finite strain theory
    • 5.5 Consolidation at the Doeldok site
    • 5.6 Conclusions

    6 Geotechnical characterization of the site

    • 6.1 Overview
    • 6.2 Soil profile and characterization
    • 6.3 Selection of parameters for design
    • 6.3.1 Dredged material
    • 6.3.2 Boom clay
    • 6.3.3 Sand
    • 6.3.4 Summary of soil properties

    7 Design of underwater embankment of soft soil

    • 7.1 Overview
    • 7.2 Geometry of the embankment
    • 7.3 Stability analysis
    • 7.3.1 Undrained analysis
    • 7.3.2 Drained stability analysis
    • 7.4 Settlements
    • 7.5 Conclusions

    8 Ground improvement by Deep Mixing

    • 8.1 Introduction
    • 8.2 Deep Mixing applications
    • 8.3 Mechanism of stabilization
    • 8.3.1 Stabilization with lime
    • 8.3.2 Stabilization with cement-like binders
    • 8.4 Methods of installation
    • 8.5 Belgian experience on on-land Deep Mixing
    • 8.5.1 Properties of untreated soils on land
    • 8.5.2 Binders employed on land
    • 8.5.3 Lime-cement stabilization in the laboratory
    • 8.5.4 Lime-cement stabilization in-situ
    • 8.5.5 Remarks on the experience of dry deep mixing on land
    • 8.6 Deep mixing assessment on the underwater site
    • 8.6.1 Properties of the artificially cemented soil in the laboratory
    • 8.6.2 Properties of the cemented soil in the field
    • 8.6.3 Laboratory versus in-situ behavior

    9 Construction and monitoring of embankment

    • 9.1 Introduction
    • 9.2 Construction
    • 9.3 Quality control of the embankment sand
    • 9.4 Instrumentation and monitoring
    • 9.4.1 Excess pore water pressure
    • 9.4.2 Settlements
    • 9.5 Conclusions

    References

    Biography

    William F. Van Impe, R. Daniel Verastegui Flores