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Design and Construction Guidelines. Magda Benjelloun. Download PDF. A short summary of this paper. Reinforced soil is a generic term that is applied to structures or systems constructed by placing reinforcing elements e.
Reinforced soil structures are very cost-effective which explains why the concept has emerged as one of the most exciting and innovative civil engineering technologies in recent times. This report should interest geotechnical and bridge engineers.
Government assumes no liability for its contents or use thereof. The contents of this report reflect the views of the contractor, who ;s responsible for the accuracy of the data presented herein. The contents do not necessarily reflect the official policy of the Department of Transportation. This report does not constitute a standard, specification, or regulation.
The United States Government does not endorse products or manufacturers. Trade or manufacturers' names appear herein only because they are considered essential to the object of this document. Form DOT F Retaining structures are used not only for bridge abutments and wing walls but also for slope stabilization and to minimize right-of-way required for embankments.
Not many years ago retaining walls were almost exclusively made of reinforced concrete, and were designed as gravity or cantilever walls. Such walls are essentially rigid structures and cannot accommodate significant differential settlements. With increasing height of soil to be retained and poor subsoil conditions, the cost of reinforced concrete retaining walls increases rapidly. Reinforced soil walls and slopes are cost-effective soil retaining structures which can tolerate much larger settlements than reinforced concrete walls.
Use of a facing system to prevent soil raveling between the reinforcing elements allows very steep slopes and vertical walls to'be safely constructed. In some cases, the inclusions can also withstand bending or shear stresses providing additional stability to the system. Modern applications of reinforced soil for construction of retaining walls were developed by H. Vidal in France in the mid 's. The Vidal system, called Reinforced Earth, used met?
However, there are no uniform standards for the design of reinforcement systems and, in fact, there are different design and construction criteria and procedures for every system. Moreover, each of these systems has a different performance record. This situation often complicates the selection of suitable earth retention systems. This manual was developed to assist highway engineers and others in determining the feasibility of using reinforced soil systems for walls and embankment slopes on a specific project, evaluating different alternative reinforcement systems, and performing preliminary design of simple systems.
The manual also provides a basis for evaluation and preliminary design of new earth reinforcement systems that may be proposed in the future. The design methods provided in the manual are not meant to replace rivate and ro rietar s stem-s ecific desi n methods, but the uatlng suc eSlgns. TerminologyReinforced soil is any wall or slope supporting system in which reinforcing elements inclusions are placed in a soil mass to improve its mechanical properties. Inclusion is a generic term that encompasses all man-made elements incorporated in the soil to improve its behavior.
Examples of inclusions are: steel strips, geotextile sheets, steel or polymeric grids, steel nails, steel tendons between anchorage elements.
The term reinforcement is used only for those inclusions where soil-inclusion stress transfer occurs continuously along the inclusion. Other inclusions may act simply as tendons between the wall face and an anchorage element.
Soil nailin 1 is a method of reinforcing in-situ soil by the insertion 0 long metal rods nails into an otherwise undisturbed natural soil mass. The technique is used to stabilize existing potentially unstable slopes and to support the side walls of excavations.
Facing is a component of the reinforced soil system used to prevent the soil from raveling out between the rows of reinforcement. Common facings include precast concrete panels, metal sheets and plates, gabions, welded wire mesh, shotcrete, wood lagging and panels, and wrapped sheets of geosynthetics. A generic cross section of a mechanically stabilized soil mass in its geotechnical environment is shown in figure 2.
Retained backfill is the fill material located between the mechanically stabilized soil mass and the natural soil. Basis for the ManualThis manual is based on the results of two recent research projects that were undertaken to examine the design, construction and performance aspects of a number of mechanically stabilized earth systems for use in retaining structures.
The purpose of the second project was to develop guidelines for mechanically stabilized soil systems to provide Highway engineers with guidance for selection, design and construction of the different systems of retaining wall alternatives. The study was performed by reviewing and evaluating existing design methods in terms of field experience, laboratory testing, analytical studies and a field evaluation program.
The results of the research program were then used to develop and substantiate the design procedures provided in this manual. The background information and design procedure for soil nailing was primarily developed from work performed under a separate FHWA contract Manual of Practice for Soil Nailing to be completed in Finally, information and design procedures for anchored systems were mainly developed through a literature review with a limited amount of laboratory evaluation in the "Behavior of Reinforced Soil" study.
Scope and Organization of the ManualThis manual is concerned with different systems for soil mechanical stabilization and their design.
A list of systems discussed in this manual is given in section 1. The intent of this manual is to provide guidance for design evaluation and to ensure that engineers using mechanically stabilized soil systems follow a safe, rational, and economical procedure from site investigations through construction.
The first chapter includes a brief history of the development of reinforced soil systems and presents a classification of the various types of systems. Brief reference is also made to alternate systems of retaining walls other than the reinforced soil systems. The advantages and disadvantages of reinforced soil systems are discussed, and potential applications are reviewed.
Chapter 1 also includes a brief discussion of design philosophy and practical design considerations. Background information and material requirements necessary for design are reviewed in chapter 2. Soil and site evaluation requirements, including subsurface exploration to evaluate stability, settlement and behavior of the selected system are given. Properties of various reinforcement, retained fill requirements and soil-reinforcement interaction evaluation are also discussed.
The next four chapters are concerned with design methods. Chapter 3 is devoted to reinforced soil walls, chapter 4 to reinforced soil slopes, chapter 5 to nailed soil structures, and chapter 6 to multianchored structures. Each of these four chapters includes design examples. Chapters 7 through 9 are devoted to practical aspects.
Chapter 7 deals with the construction aspects of the different systems. Chapter 8 deals with monitoring programs to assist highway engineers in evaluation of the systems used in their regions.
The final chapter, chapter 9, presents suggested general specifications and recommended bidding procedures. A bibliography of the references cited in the manual is provided at the end of this volume. Historical DevelopmentInclusions have been utilized since prehistoric times for the improvement of soil.
The use of straw to improve the quality of adobe bricks dates back to earliest human time. Many primitive people used sticks and branches for reinforcement of mud dwellings. During the 17th and 18th centuries, French settlers along the Bay of Fundy in Canada used sticks for reinforcement of mud dikes. Some other early examples of man-made soil reinforcement include dikes of earth and tree branches which have been used in China for at least 1, years and along the Mississippi River in the 's.
Other examples include wood pegs for erosion and landslide control in England, and bamboo or wire 6 mesh, used universally for revetment erosion control. Soil reinforcing can be achieved by plant roots. The modern methods of soil reinforcement were pioneered by the French architect and engineer Henri Vidal as a result of his research in the early 's which led to the invention and development of Reinforced Earth, a system in which steel strip reinforcement is used.
The first wall to use this technology in the united States was built in on California State Highway 39 northeast of Los Angeles. More than 4, walls have been built in the United States since Since the introduction of Reinforced Earth, several other proprietary and nonproprietary systems have been developed and used. Table 1 provides a summary of many of the current systems by proprietary name, reinforcement type and facing system.
Some of these systems are reviewed in the following paragraphs. A detailed description of each system is included in volume II, section 1. The Hilfiker Retaining Wall, which uses welded wire mesh type reinforcement and facing system, was developed in the mid's, and the first experimental wall was built in The first commercial use was for a wall built for the Southern California Edison Power Company in for repair of some roads along a power line in the San Gabriel Mountains of Southern California.
Hilfiker also developed the Reinforced Soil Embankment RSE system, which uses continuous welded wire reinforcement and a precast concrete facing system. The first experimental Reinforced Soil nailing is an in-situ reinforcement technique which consists of inserting long rods or "nails" into otherwise undisturbed natural soil to stabilize the soil mass. The method has emerged essentially as an extension of rock bolting techniques.
Nailing differs from tie back support systems in that the soil nails are passive elements that are not pretensioned as are the tendons in the case of tiebacks. The method can be used to support the sides of excavations or to improve the stability of relatively unstable natural slopes, and when combined with reinforced shotcrete or precast panel facings, the system can provide permanent support of vertical cuts. In North America, the system was first used in Vancouver, B. Reinforced walls:Use simple and rapid construction which does not require large equipment.
Do not require experienced craftsmen with special skills for construction. Require little site preparation. Need little space in front of the structure for construction operations. Reduce right-of-way acquisition by constructing or excavating steeper slopes.
Earth Reinforcement and Soil Structures provides a coverage of the basic aspects of reinforced soil. The book is comprised of 12 chapters that cover the theoretical elements up to the practical applications. The first two chapters provide the introduction and historical review of the subject of reinforced soil. The third chapter presents a catalogue of some of the application areas for the use of earth reinforcement, while the fourth chapter covers the theoretical concepts. The next six chapters deal with the practical aspects of earth reinforcements, such as design, construction, costs, and durability. The remaining two chapters provide some worked examples and discuss the developments in earth reinforcement, respectively.
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