Embankment Resting on Problematic Soil A Critical Review

Journal of Geotechnical and Geoenvironmental Engineering

This case study describes the failure of an interstate connecting-ramp embankment during construction and investigates the failure mechanism, performance of the prefabricated vertical drains (PVDs) installed to accelerate consolidation of the weak embankment foundation soils, embankment shear strength parameters, and design slope stability analyses. The weak, fine-grained foundation soil experienced less drainage, and thus less consolidation and strength gain, than expected via the PVDs because of an overestimate of the design horizontal coefficient of consolidation. As a result, the inverse analyses show the failure was caused by lower than expected shear strength of the foundation soils and an overestimate of the compacted embankment shear strength. The compacted embankment fill strength was characterized using an undrained shear strength, i.e., cohesion, without a tension crack, which inflated the calculated factor of safety. Recommendations to estimate embankment shear strength parameters, depth of embankment tension crack, bearing capacity factor of safety for comparison with limit equilibrium values, and horizontal consolidation properties for PVD design for future embankment projects are presented.

2016

In many countries, essential infrastructure is built along congested coastal regions that are composed of highly compressible soft and weak soils up to significant depths. For instance, alluvial and marine clay deposits have very low bearing capacity and excessive settlement characteristics, posing obvious design and maintenance challenges for constructing tall structures and large commercial buildings, as well as for developing port and transport infrastructure. Stabilising these very soft deposits is essential before commencing construction of infrastructure. A system of prefabricated vertical drains (PVD) combined with vacuum pressure and surcharge preloading has become an attractive ground improvement alternative in terms of both cost and effectiveness. This technique accelerates consolidation by promoting rapid radial flow which decreases the excess pore pressure while increasing the effective stress. In recent decades, natural prefabricated vertical drains (NPVDs) made from bi...

Canadian Geotechnical Journal, 2001

The behaviour of geosynthetic-reinforced embankments constructed over soft cohesive soils installed with prefabricated vertical drains (PVDs) is investigated by numerically examining an embankment constructed over different foundation soils. The partial consolidation during embankment construction, the consequent shear strength gain of the foundation soil, and the effect of the use of reinforcement on the mobilization of shear strength are examined. It is shown that the combined use of reinforcement and PVDs can significantly increase embankment stability and potentially allow the rapid construction of higher embankments than could be achieved with either method of soil improvement alone. Construction rate and spacing of PVDs can significantly affect the degree of consolidation at the end of construction and the stability of the embankment. For the situation examined, the effect of well resistance of typical vertical drains is insignificant. A relatively simple method for calculating the degree of consolidation and the strength gain of the foundation soil during construction is evaluated based on finite element results and is shown to be reasonably conservative. A design procedure is proposed to combine the design of reinforcement and PVDs.

Civil Engineering Journal, 2020

The overloads of structures or embankments built on clayey soft ground are generally applied gradually, respecting a specific phasing. This phasing on construction allows the undrained shear strength of clay increasing over consolidation in order to avoid the risk of collapse during loading. In this work, the undrained shear strength of clay over the consolidation was estimated following SHANSEP method of which parameters proposed by eight researchers have been employed, as well as the slope stability analysis of embankments on soft soils during staged construction. Assessment of factor of safety for slope stability was conducted basing on the Bishop method. Additionally, the variations of undrained shear strength and factor of safety were presented. In order to validate the methods discussed in this study, slope stability analysis of five embankments constructed on clayey soft soils improved by the vertical drain technique in a high-speed railway construction project in Morocco was...

IIUM Engineering Journal

This paper presents an exhaustive review of the challenges faced in the construction of road embankments on soft ground and proposes a direction for future development. Frequently used techniques for soft ground improvement are discussed. The factors that contribute to the stability of the road embankment are reviewed by approach, results of past studies, and historical cases. The findings show that settlement, slope stability, and soil bearing capacity are all challenges to constructing the road embankment. Additionally, it is found that geometric data is a key factor in embankment design. Pre-loading with prefabricated vertical drain (PVDs) methods and lightweight fill were found to be widely used techniques in soft ground improvement. The information from this study can be used to develop design guidance systems, numerical modelling, and to give an overview and knowledge to other researchers who are or will conduct research in this field. Finally, future perspectives for research...

International Journal of Advanced Trends in Computer Science and Engineering, 2019

This article provides an assessment study of the embankment stability on soft soil improved with prefabricated vertical drains (PVDs). An empirical approach based on Barron theory is used to predict settlement grounds with PVDs and compared to measured. This comparative study is essential to validate the soil parameters in analyzing the stability of the embankment with a limit equilibrium method (LEM). The effectiveness of PVDs and geotextiles installations has also been investigated in stabilizing the soft soil beneath the embankment. This study reveals that the ground improvement by PVDs has an effect on reducing the vertical displacements of subsoil. The geotextiles installed under the embankment provides higher stability to the surface soil, and the maximum settlement can be reduced in the long term period.

1993

Prepared in cooperation with the U.S. Department of Transportation, Federal Highway Administration.

In this lecture the interpretations of fully instrumented tests embankments and their role in the development of appropriate ground improvement techniques for highways, motorways and airfields on soft clay deposits is illustrated through well documented case studies in Bangkok, Thailand; Muar Flat Site in Kuala Lumpur and in Southeast Queensland. For the Bangkok Plain and with sand backfills the performance of embankments with different schemes of vertical drains was evaluated over a period of 25 years. Aspects such as recharging effects due to the drains, inadequate measures in maintaining vacuum during vacuum applications and possible hydraulic connections with large diameter drains are discussed. For the Muar test embankments, the role of fill strength in residual soil embankment and the field deformation analysis in separating consolidation settlement from immediate settlement and creep settlements is presented. Novel interpretations of settlement from pore pressure dissipations, secondary settlement from field measurements and decay of lateral deformation rate with time were also made.

In this paper, the geotechnical aspects of soft clay improvement using prefabricated vertical drains (PVDs) with special reference to embankments will be demonstrated. The Cavity Expansion Theory is employed to predict the smear zone caused by the installation of mandrel driven vertical drains. Analytical and Numerical analyses adopting the equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacements. The advantages and limitations of vacuum application through vertical drains avoiding the need for high surcharge embankments are discussed using the proposed solutions. A few selected case histories are discussed and analyzed, including the site of the 2nd Bangkok International Airport, the coastal stretch of Muar Clay Plains in Malaysia and the Sunshine embankment, Australia. The predictions are compared with the available field data, verifying that the equivalent plane strain model can be used confidently with acceptable accuracy. Cyclic loading of PVDs is also examined in the laboratory in a manner appropriate for railway environments. It is shown that short PVDs can dissipate excess pore pressure as fast as they are built up under repeated loading conditions. Some selected on-ground experience of the first Author through the Ministry of Science and National Science Foundation during post-tsunami reconstruction efforts is described with specific reference to appropriate ground improvement requirements.

Engineered science, 2022

The effectiveness of lime columns to improve the stability of embankments constructed on soft consolidating soil is investigated. Along with this, the effectiveness of prefabricated vertical drains (PVDs) with lime columns is also compared. Further, the combination of lime columns and PVDs is also studied to improve the embankment stability on consolidating soil. A numerical study is carried out using the two-dimensional plane strain finite element method. To study the effectiveness of lime columns on the embankment stability, the foundation soil settlement, excess pore water pressure, and factor of safety for embankment are obtained at various time intervals during the consolidation of foundation soil. This study shows that the settlement and excess pore water pressure decrease, and the factor of safety increases due to the provision of lime columns. Also, the settlement is lesser, and the factor of safety is larger for soil with lime columns compared to soil with PVDs, whereas, excess pore water pressure dissipates faster in soil with PVDs compared to soil with lime columns. This study concludes that, compared to PVDs, lime columns are more effective to improve the embankment factor of safety and foundation soil settlement, whereas PVDs are more effective in accelerating excess pore water pressure dissipation. The lime columns and PVDs combination is observed to be effective to improve all parameters.