International Perspectives on Soil Reinforcement Applications

(Part of International Perspectives on Soil Reinforcement Applications - GSP 141)Geosynthtic reinforcement has been used in road pavement, both in the unbound granular layers and in the overlay, in Europe for more than 40 years. Despite a number of good experiences from the field, technically sound design methods and methods for verification of the effect in the field are still missing. Recommendations for use in road pavements in national guidelines to a large extent are also missing.

Geosynthetics usage in pavement systems grew steadily from the early 1970's through the early 1990's and appears to have reached a plateau. Paving fabric interlayers hold the largest share of the market; however, there has been a slow growth in the use of geosynthetic reinforcement in the subgrade and base layers. Geosynthetics which serve a reinforcement function are gaining some acceptance in the overlay market. The critical issue slowing wider acceptance and use of geosynthetic reinforcement in pavement systems remains the lack of an accepted design model in each application area; however, we suggest that designers adopt a usage philosophy such that geosynthetics are viewed as another pavement material used to effect things like cracking and rutting (just like one would view cement treated bases) and not be viewed as special materials to correct only problem areas. In this paper, we provide a look at current practices, recent advances and current research areas, and suggest future directions for the use of geosynthetics as reinforcement materials in pavement systems.

Brazil has large regions of its territory covered with soft soil deposits. Some of these deposits can be over 40m deep with very low shear strength. These types of situations pose important challenges for designers and contractors in civil engineering works. In this context geosynthetics can be effectively employed as reinforcement and its use has increased markedly in the last decades in the country. The same applies to the use of prefabricated vertical drains for the acceleration of soft soil consolidation. This paper presents the Brazilian perspectives on the use of geosynthetics in such applications. A case-history is also presented and discussed.

This paper presents promising technologies in the use of marginal soils generated from construction work using functional materials. Some of the techniques covered include liquefied soil stabilizing, sandwich and geo-tube methods. Also covered are several applications of geo-tubes method to treat bottom sediments in rivers, lakes, wetlands, port and harbors and to trapping toxic substances. As well, the concept on new lightweight banking method combined with geosynthetics and low improvement ratio cement column method is introduced concerning new technologies for soft foundations.

Geosynthetics have been successfully used as reinforcements for embankments and shallow foundation on soft soils. Their applications include the use of geosynthetics for increasing stability of embankments, increasing bearing capacity of footing on soft foundations, creating construction platforms, and bridging over sinkholes. In recent years, geosynthetics mats have also been used in combination with pile or column systems to support embankments over soft foundations. This paper identifies current practices in the above applications including the most prevalent approaches in the US and other countries and presents recent advances reported in literature. Gaps in our current knowledge are identified and possible future directions for research and development are proposed.

Reinforcement applications in landfills in the Australasian region are very limited due to the fact that pressure on land use is minimal. The waste disposal industry in the region has relied for many years on the infilling of worked mineral voids and hard rock quarries as the primary means of waste disposal resulting in less use of land. This paper presents some case studies that can be considered as innovative in the limited Australasian experience in landfill reinforcement

(Part of International Perspectives on Soil Reinforcement Applications - GSP 141)Stability of Geosynthetic Lining Systems is, from a geotechnical standpoint, a complex matter. Two geotechnical questions are identified: sliding of the geosynthetic lining system on the slope and pull-out strength of the geosynthetic anchorage at the top of the slope. Research programmes carried out in France on these topics, are presented and related to the two following topics: (1) Large scale experimentations on actual slopes is especially emphasized. The observations derived from the tests and their detailed interpretation are very fruitful, as they highlight specific local interaction behaviour between soil and geosynthetics. These aspects are not taken into account in design methods, in particular the effects of wrinkles and real relative displacements of the geosynthetics along the slope. (2) The behavior of the anchorage of geosynthetics sheets at the top of a slope is a decisive factor when it comes to designing geosynthetic lining systems on slopes. In order to optimize the geometry of the structures in question (to reduce the area taken up by the anchorage at the top of the slope), anchorage solutions using trenches of varying forms are sometimes used. Large scale experimentations and a theoretical approach of this problem were carried out and are presented in this paper.

Geosynthetic reinforcement in landfill applications in the US has involved conventional reinforced soil structures and veneer stabilization with reinforcements placed along the landfill slope and anchored at the crest. In addition, innovative approaches have been recently implemented in the US to reinforce landfill covers and base liners. This includes horizontally placed geosynthetic reinforcements, which are anchored into solid waste, and fiber reinforcement to enhance the shear strength of the soil liner material and the interface shear strength between the soil liner and texture geomembranes. This paper presents a framework for the design of steep reinforced liners. Recent case histories illustrating the use of the different geosynthetic reinforcement applications are also presented to document the different approaches in specific projects.

This paper presents a summary of recent research results relative to soil reinforcement in Brazil. Initially the historical aspects of geosynthetic application in Brazil are presented and related to the current construction practice. Following, design parameters such as tensile strength, pullout and creep behavior are discussed in the light of the last researches. Finally developments in design methods which consider modern approaches of the interaction soil-inclusion and construction sequence and examples of history cases are presented.

The objective of this paper is to present a state of the art report on geosynthetic-reinforced soil walls in Japan. From 1996 to 2005, Japanese Geotechnical Society (JGS) has been in charge of the Technical Committee No.9 on earth reinforcement set up by International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE). This paper summarizes the current activities of geosynthetic-reinforced soil walls in Japan including design procedures and case histories. It is noted that most of the contents in this paper was prepared by the members of the Japanese Supporting Committee.

This paper provides a brief review of developments and current perspectives of reinforced soil structures and slopes in Europe. A number of innovations and studies in reinforced soil technology have been introduced in recent years. Improved reinforcing materials have been introduced which include new forms of conventional geogrid reinforcements, composite materials providing combined drainage and reinforcement, and electrically conductive reinforcements. Research has resulted in a better understanding of the residual creep strength of geosynthetic materials and the influence of a seismic event on the long-term strength of geosynthetic reinforcement. Analytical methods continue to be developed and the use of reinforced soil in construction is being promoted by the introduction of new International and National Codes of Practice. This report provides details of these developments.

The economics and successful performance of geosynthetic reinforced soil walls and slopes resulted in a significant increased use of these systems. Currently there are three different design methodologies: lateral earth pressure analysis, limit equilibrium analysis, and continuum mechanics.based analysis. This paper discusses the advantages of each approach as well as its limitations. Lateral earth pressure approach is easy to apply but limited to walls, based on calibration, and it usually yields very conservative results. Limit equilibrium approach is an extension of slope stability analysis, applicable to slopes and walls, typically yields conservative results but requires computer program to apply. Continuum mechanics.based approach such as finite element or finite difference is rigorous but requires good characterization of all elements composing the problem and accurate modeling of the problem or else it may lead to unconservative results. A detailed example problem illustrates the relative performance of each approach. Also briefly discussed is an ongoing research effort to refine existing designs while keeping it simple.