Geofoam Applications in the Design and Construction of Highway Embankments (2004)

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3-1 CHAPTER 3 DESIGN METHODOLOGY Contents Introduction...................................................................................................................................3-2 Major Components of An EPS – Block Geofoam Embankment..................................................3-5 Design Phases ...............................................................................................................................3-6 Design Procedure ..........................................................................................................................3-7 Limitations to the Proposed Design Methodology and Design Guidelines ................................3-11 Background Investigations..........................................................................................................3-12 Introduction .............................................................................................................................3-12 Transportation Engineering.....................................................................................................3-13 Civil Engineering ....................................................................................................................3-14 Hydraulic Engineering ............................................................................................................3-14 Structural Engineering.............................................................................................................3-14 Geotechnical Engineering .......................................................................................................3-15 Design Loads ..............................................................................................................................3-17 Introduction .............................................................................................................................3-17 Gravity.....................................................................................................................................3-17 Traffic......................................................................................................................................3-19 Water .......................................................................................................................................3-19 Seismic ....................................................................................................................................3-22 Wind........................................................................................................................................3-24 References...................................................................................................................................3-26 Figures ........................................................................................................................................3-28 Tables..........................................................................................................................................3-40

3-2 ______________________________________________________________________________________ INTRODUCTION Despite the worldwide use of EPS-block geofoam, a specific design guideline for its cost- effective use as lightweight fill in roadway embankments is unavailable. Therefore, the overall objective of this research was to develop a consistent design methodology to optimize both the technical performance and cost through the development of a comprehensive design guideline including design and analysis procedures for the use of EPS-block geofoam in road embankments over soft ground. This chapter presents detailed background information on the design methodology incorporated in abbreviated form in the provisional design guideline included in Appendix B. The recommended design methodology is based on an assessment of existing technology and literature as well as findings of the research performed during this study. The chain link analogy applied to geotechnical design in Figure 3.1 is used to illustrate the general design approach for the design of embankments over problem foundations (1,2). The geotechnical design system is compared with each link representing a design stage, e.g., sampling, testing, analysis, and application of tolerable criteria, anchored to previous experience of similar structures in the project area. The key point of the analogy is that the system is only as strong as its weakest link. If any link, or if the anchorage is insufficient, failure may occur. The second point of the analogy is that if each design stage or link is performed using usual geotechnical engineering practices, designers can "build with confidence or BWC." The recommended design methodology and design guideline for the use of EPS - block geofoam in roadway embankments focuses on the analysis (design) link in the chain. As a result, if the other links are not performed satisfactorily, e.g., sampling or testing, use of the design methodology presented herein will not guarantee satisfactory performance. Figure 3.1. The geotechnical “system”. BWC = Build With Confidence (1,2).

3-3 Lightweight fill embankments are typically placed over soft saturated soils that are normally or at best slightly overly consolidated. Soft soil ground conditions as defined in the provisional design guideline is a soil subgrade that is compressible and has relatively low shear strength. Design and construction of embankments over soft ground is based on avoiding failure during construction by providing adequate stability and limiting postconstruction settlement to desirable amounts (3). The term “failure” as used in the provisional design guideline is a loss of function. Failure or loss of function may occur as either a serviceability failure (the serviceability limit state, SLS) or a collapse failure (the ultimate limit state, ULS). An embankment over soft soil may experience a serviceability failure due to excessive total or differential settlement that develops over time and which produces premature failure of the pavement system. Premature failure of the pavement system may include an uneven and often cracked pavement surface that may require frequent repaving and possibly other maintenance. An embankment over soft soil may experience a collapse failure through either a rotational (slope stability), lateral spreading, or bearing capacity failure mechanism. The collapse failure may involve at least partial, if not total, collapse. The overall design goal is to satisfy the following equations for the ULS and SLS respectively: ULS: resistance of embankment to failure > embankment loads producing failure (3.1) SLS: estimated deformation of embankment ≤ maximum acceptable deformation (3.2) The extent that resistance exceeds loads in Equation (3.1) is interpreted as representing the "safety" incorporated into the design. Thus, the "safety" or factor of safety (FS) is defined as ∑ ∑= failure producing loads embankment failure toembankment of sresistance FS (3.3)

3-4 In the traditional Allowable Stress Design (ASD) method, the actual service loads are used in the design and safety is incorporated by using a single factor of safety applied to the ULS mechanism (e.g. slope stability) being investigated. The more modern Load and Resistance Factor Design (LRFD) method, safety is incorporated through the use of separate factors applied to simultaneously increase service loads and reduce material strengths or resistances. At the time this report was finalized (2002), geotechnical design practice in the U.S.A. was still in the early stages of transitioning from ASD to LRFD although road design is on the forefront of this transition with LRFD methodologies incorporated into various American Association of State Highway and Transportation Officials (AASHTO) design standards. It appears that refinements to LRFD methodologies are still required before they will be embraced for geotechnical design (4). At the present time, design of earthworks incorporating EPS-block geofoam are only designed deterministically using service loads and the traditional Allowable Stress Design (ASD) methodology with safety factors. Regardless of whether ASD or LRFD is used, the SLS assessment reflected in Equation (3.2) is always performed using service loads. The common strategy for selecting a soft ground treatment alternative has been to use the traditional approach of satisfying Equations (3.1) and (3.2) by utilizing normal soil for the embankment. This means that the resistance and stiffness of the embankment and soft soil foundation must be increased artificially to be able to resist the loads with acceptable deformations. This is accomplished by employing one or more soft ground treatment techniques that collectively increase the strength and reduce the compressibility of the overall system (primarily the existing soft foundation soil but also the embankment soil itself to some degree). Chapter 1 presents an overview of soft ground treatment methods. Less prevalent is the alternative approach to satisfying Equations. (3.1) and (3.2) of reducing the embankment loads. This involves accepting the natural resistance (strength and compressibility) of the existing soft foundation soil as it exists and employing strategies to sufficiently reduce the loads acting on the soft soils to achieve the goals stated in Equations (3.1)

3-5 and (3.2). This is accomplished by using lightweight fill materials such as EPS-block geofoam. The most significant aspect of lightweight fill materials is that lightweight fill materials have densities less than that of soil and rock so that the resulting gravity or seismic forces from the fill material are less than those from normal earth materials (5). The use of this concept in designing embankments over soft soils may yield a more technically effective and cost efficient embankment. MAJOR COMPONENTS OF AN EPS – BLOCK GEOFOAM EMBANKMENT As indicated in Figure 3.2, an EPS – block geofoam embankment consists of three major components: • The existing foundation soil which may have undergone ground improvement prior to placement of the fill mass. • The proposed fill mass, which primarily consists of EPS-block geofoam although some amount of soil fill is often used between the foundation soil and bottom of the EPS blocks for overall economy. In addition, depending on whether the embankment has sloped (trapezoidal embankment) or vertical (vertical embankment) sides, there is either soil or structural cover over the sides of the EPS blocks. • The proposed pavement system, which is defined as including all material layers, bound and unbound, placed above the EPS blocks. The uppermost pavement layer, which serves as the finished road surface, is usually either asphaltic concrete (AC) or portland-cement concrete (PCC) to provide a smooth traveling surface for motor vehicles. AC appears to be the most predominant road surface type because AC pavements tend to tolerate postconstruction settlements better than PCC pavements as well as for economic reasons. However, in certain

3-6 applications (e.g., vehicle escape ramps in mountainous regions, logging roads) an unbound gravel or crushed-rock surface layer may be utilized. Figure 3.2. Major components of an EPS-block geofoam embankment. DESIGN PHASES To design against failure, the overall design process is divided into three phases: • Design for external (global) stability of the overall embankment. This considers how the combined fill mass and overlying pavement system interact with the existing foundation soil. It includes consideration of serviceability issues (SLS), such as global total and differential settlement, and collapse failure issues (ULS), such as bearing capacity and slope stability under various load cases, e.g., applied gravity, seismic, water and wind loading. These failure considerations together with other project-specific design inputs, such as right-of-way constraints, limiting impact on underlying and/or adjacent structures, and construction time, usually govern the overall cross-sectional geometry of the fill. Because EPS- block geofoam is typically a more expensive material than soil on a cost-per-unit- volume basis for the material alone, it is desirable to optimize the design to minimize the volume of EPS used yet still satisfy design criteria concerning settlement and stability. Therefore, it is not necessary for the EPS blocks to extend the full height vertically from the top of the foundation soil to the bottom of the pavement system. • Design for internal stability within the embankment mass. The primary consideration is the proper selection and specification of EPS properties so that the geofoam mass can support the overlying pavement system without excessive immediate and time-dependent (creep) compression that can lead to excessive settlement of the pavement surface (an SLS consideration).

3-7 • Design of an appropriate pavement system for the subgrade provided by the underlying EPS blocks. This design criterion is to prevent premature failure of the pavement system, as defined by rutting, cracking, or similar criterion, which is an SLS type of failure. Also, when designing the pavement cross-section overall consideration should be given to providing sufficient support, either by direct embedment or structural anchorage, for any road hardware (guardrails, barriers, median dividers, lighting, signage and utilities). A summary of the three-phased design procedure is shown in Table 3.1. Each of the three primary design phases shown in Table 3.1 has been divided into various failure mechanisms that need to be considered for each design phase. Each failure mechanism has also been categorized into either an ULS or SLS failure. These three design phases are conceptually similar to those used in the design process for other types of geosynthetic structures used in road construction, e.g. mechanically stabilized earth walls (MSEWs). Table 3.1. Summary of Proposed Design Procedure for EPS-block geofoam roadway embankments. DESIGN PROCEDURE The design of an EPS-block geofoam roadway embankment over soft soil requires consideration of the interaction between the three major components of the embankment, i.e., foundation soil, fill mass, and pavement system. Because of this interaction, the three-phased design procedure involves interconnected analyses between the three components. For example, some issues of pavement system design act opposite to some of the design issues involving internal and external stability of a geofoam embankment, i.e., the thickness of the pavement system will affect both external and internal stability of the embankment. Additionally, the dead load imposed by the pavement system and fill mass may decrease the factor of safety of some failure mechanisms, e.g., slope stability, while increasing it in others e.g., uplift. Therefore, some compromise is required during design.

3-8 It is possible in concept to optimize the final design of both the pavement system and the overall embankment considering both performance and cost so that a technically effective and cost efficient embankment is obtained. However, because of the inherent interaction between components, overall design optimization of a roadway embankment incorporating EPS-block geofoam requires an iterative analysis to achieve a technically acceptable design at the lowest overall cost. In order to minimize the iterative analysis, the solution algorithm shown in Figure 3.3 was developed to obtain an optimal design. The design procedure considers a pavement system with the minimum required thickness, a fill mass with the minimum thickness of EPS- block geofoam, and the use of an EPS block with the lowest possible density. Therefore, the design procedure will produce a cost efficient design. The design procedure is similar for both trapezoidal and vertical embankments except that overturning of the entire embankment at the interface between the bottom of the assemblage of EPS blocks and the underlying foundation soil as a result of horizontal forces should be considered for vertical embankments as part of seismic stability, translation due to water, and translation due to wind analysis during the external stability design phase. The purpose of the first step in the design process, background investigation, is to obtain the subsoil conditions at the project site, to obtain estimates of the loads that the embankment system will be subjected to, and to obtain the geometrical parameters of the embankment. Background investigations will be discussed in detail later in this chapter. The second step of the design procedure is to select a preliminary type of EPS-block geofoam and to design a preliminary pavement system. Although the pavement system has not been designed at this point, the pavement system should be equal to or greater than 610 mm (24 in.) in thickness to minimize the effects of differential icing and solar heating as will be discussed in Chapter 4. The design procedure depicted in Figure 3.3 is based on obtaining a pavement system that provides the least amount of stress on top of the EPS-block geofoam embankment to satisfy internal and external stability requirements. Therefore, it is recommended that the

3-9 preliminary pavement system be assumed to be 610 mm (24 in.) thick and the various component layers of the pavement system be assumed to have a total (moist) unit weight of 20 kN/m3 (130 lbf/ft3) for initial design purposes. Figure 3.3. Flow chart of design procedure for an EPS-block geofoam roadway embankment. Figure 3.3. (continued). Figure 3.3. (continued). The third step of the design procedure is to determine a preliminary embankment arrangement. Because EPS-block geofoam is typically more expensive than soil on a cost-per- unit-volume basis for the material alone, it is desirable to optimize the volume of EPS used yet still satisfy design criteria concerning settlement and stability. Therefore, to achieve the most cost-effective design, a design goal is to use the minimum amount of EPS blocks possible that will meet the external and internal stability requirements. The design failure mechanisms that will dictate the maximum stress that can be imposed on the soft foundation soil, which dictates the minimum thickness of EPS blocks needed, include settlement, bearing capacity, slope stability, and seismic stability (external). A minimum of two layers of blocks should be used for lightweight fills beneath roads because a single layer of blocks can shift under traffic loads and lead to premature failure (6). Block thicknesses typically range between 610 mm (24 in.) to 1000 mm (39 in.). Therefore, it is recommended that a minimum of two EPS blocks with a thickness of 610 mm (24 in.) each or a total initial height of 1.2 m (4 ft) be considered for the EPS block height to determine the preliminary embankment arrangement during the design process. The preliminary height of conventional soil fill is the total embankment height required based on the background investigation less the preliminary pavement system thickness of 600 mm (24 in.) and the thickness of two EPS blocks of 1.2 m (4 ft).

3-10 After the design loads, subsurface conditions, embankment geometry, preliminary type of EPS, preliminary pavement design, and preliminary fill mass arrangement have been obtained, the design continues with external (global) stability evaluation (Steps 4 through 10), internal stability evaluation (Steps 11 through 14), and final pavement system design (Step 15). Because pavement system design aspects must be considered to obtain a preliminary pavement system design, it is presented first (see Chapter 4). External (global) stability evaluation and internal stability evaluations are presented in Chapters 5 and 6, respectively. As with any design in geotechnical engineering practice, the design procedure of embankments over soft foundations must incorporate tolerable criteria such as minimum factor of safety and maximum allowable settlement. Minimum factor of safety values typically utilized in geotechnical design are based on precedence and can be found in local codes, design manuals, and geotechnical literature. The recommended factors of safety for each failure mechanism calculation that can be considered in preliminary design is summarized in Figure 3.3. However, tolerable settlements for highway embankments are not well established in practice nor is information concerning tolerable settlements available in the geotechnical literature. Postconstruction settlements as much as 0.3 to 0.6 m (1 to 2 ft) during the economic life of a roadway are generally considered tolerable provided that the settlements are uniform, occur slowly over a period of time, and do not occur next to a pile-supported structure (7). If postconstruction settlement occurs over a long period of time, any pavement distress caused by settlement can be repaired when the pavement is resurfaced. Although rigid pavements have undergone 0.3 to 0.6 m (1 to 2 ft) of uniform settlement without distress or objectionable riding roughness, flexible pavements are usually selected where doubt exists about the uniformity of postconstruction settlements and some states utilize a flexible pavement when predicted settlements exceed 150 mm (6 in.) (7). Tolerable settlements of bridge approach embankments depend on the type of structure, location, foundation conditions, operational criteria, etc (1). The

3-11 following references are recommended for information on abutment movements: (8-11). Settlement considerations are further discussed in Chapter 5. Design charts were developed as part of this research to aid in obtaining a technically optimal design. Therefore, these design aids can be used with the proposed design algorithm to assist in developing a cost efficient design. As indicated previously, the design algorithm will assist the designer in developing a cost efficient design. LIMITATIONS TO THE PROPOSED DESIGN METHODOLOGY AND DESIGN GUIDELINES The design methodology in Chapters 4, 5, and 6 and the design guideline in Appendix B are intended to provide guidance to civil engineers experienced in geotechnical engineering and pavement engineering when designing lightweight fills that incorporate EPS-block geofoam. The proposed design guideline is limited to embankments that have a transverse (cross-sectional) geometry such that the two sides are more or less of equal height as shown conceptually in Figure 3.4 and are underlain by soft soil defined as relatively compressible and weak. Applications where the fill sides are markedly different and closer to those shown in Figure 3.5 (sometimes referred to as side-hill fills) are excluded from this study because they are the subject of a separate study (12). It should be noted from Figure 3.4 (b) that unlike other types of lightweight fill embankments, a vertical embankment can be utilized with EPS- block geofoam. The use of a vertical-face fill embankment, sometimes referred to as a geofoam wall (see Figure 3.4 (b)), will minimize the amount of right-of-way needed and will also minimize the impact of the embankment loads on nearby structures. The design charts developed as part of this research are based on embankment models with various geometric parameters. Embankment side slopes of 0 (horizontal):1 (vertical), 2 (horizontal):1 (vertical), 3 (horizontal):1 (vertical), and 4 (horizontal):1 (vertical) were predominantly evaluated. Widths at the top of the embankment of 11 m (36 ft), 23 m (76 ft), and 34 m (112 ft) were evaluated. These widths are based on a 2-lane roadway with 1.8 m (6 ft)

3-12 shoulders, 4-lane roadway with two 3 m (10 ft) exterior shoulders and two 1.2 m (4 ft) interior shoulders, and a 6-lane roadway with four 3 m (10 ft) shoulders. Each lane was assumed to be 3.66 m (12 ft) wide. Embankment heights ranging between 1.5 m (4.9 ft) to 16 m (52 ft) were evaluated. For simplicity, the fill mass was assumed to consist entirely of EPS blocks. Figure 3.4. Typical EPS-block geofoam applications involving embankments (13). Figure 3.5. Typical EPS-block geofoam applications involving side-hill fills (13). The design guideline included in Appendix B is expected to be suitable for the preliminary design for most typical projects (projects with either critical or noncritical conditions) and for final design for projects with predominantly noncritical conditions. Examples of critical and noncritical design conditions are provided in Table 3.2. Engineering judgment is required to determine if critical or noncritical design procedures exist for a specific project situation. The concept of critical and noncritical design and construction conditions was adapted by (1) from (14) which applies this concept to filtration and drainage applications using geotextiles. More detailed design is required for embankments with critical conditions than with noncritical conditions. Table 3.2. Examples of critical and noncritical embankment design and construction conditions (1). BACKGROUND INVESTIGATIONS Introduction Prior to beginning design of a proposed embankment on soft soil, certain background investigations need to be conducted and the relevant results communicated to the embankment designer. Background studies required for typical projects can be categorized into studies related to transportation, hydraulic, structural, and geotechnical engineering. An overview of issues that should be evaluated during the background investigation phase are presented subsequently. Special projects may require modification of these studies and/or additional studies. In addition,

3-13 various design jurisdictions may find it useful to reallocate responsibilities from those given here to better match jurisdictional practice or historical precedent. Transportation Engineering Transportation engineering issues that the designer needs to assess include issues related to general planning, traffic, and site specific. General transportation items include whether the project involves the rehabilitation or widening of an existing road or an entirely new or relocated road, general vertical and horizontal road geometry, unusual or non-standard vehicle loading, design life of the embankment if not permanent, restrictions on the posted speed limit, and restrictions on the number of traffic lanes. Known restraints and considerations for the general area where construction will occur should also be assessed. Examples of project restrictions and constraints include: • Any restrictions on maximum duration of construction time, season of construction, days of construction (e.g., no weekends or holidays), times of day for construction and access roads prohibited for construction traffic. • Any restrictions on physical limits on the right-of-way to be occupied by the permanent structure as well as land available for temporary construction purposes (areas for temporary storage, etc.). • Identification of known surface and subsurface structures (buildings, utility lines, etc.), especially those that might be particularly sensitive to settlement (e.g., natural gas transmission lines) and thus impact design. • Identification of overhead obstructions that could impact design or construction, both "hard" (e.g., electrical transmission wires) and "soft" (e.g., glide paths to airports). Traffic issues that will impact design of the embankment include: vertical, horizontal and cross-sectional geometry of the road surface; posted speed limit; maximum vehicle loading;

3-14 estimated annual traffic mix and volume; and ancillary road hardware requirements (shoulder guardrails or barriers, median barriers, overhead lighting, signage). Civil Engineering Site specific items that will impact design include existing topography; minimum desired pavement life based on policy of the owning agency; criterion for defining pavement failure (e.g., rutting of a certain depth) for pavement-life calculations; owner preferences, if any, for pavement type; pavement drainage requirements; and below-ground utility requirements for pavement drainage, electrical conduits for overhead lighting and signage, and any others that may cross the proposed right-of-way. The use of an EPS-block geofoam embankment may alleviate the need to relocate underground utilities that may cross the proposed embankment alignment. The Interstate 15 project in Utah presented in Chapter 11 is an example of the use of EPS-block geofoam to alleviate the need for removing underground utilities that crossed the embankment. The use of an EPS-block geofoam with vertical sides will minimize the impact to nearby structures including underground utilities. Hydraulic Engineering Evaluation of hydraulic engineering issues is important if the project site is located adjacent or nearby surface-water bodies, particularly rivers and tidal water bodies, that may be subject to significant increases in elevation of their water surface at some time during the design life of the structure due to extreme events such as floods or storms. The hydraulic specialist should estimate the design water elevation for extreme events based on a probability of occurrence that is consistent with the design life of the embankment. Structural Engineering If the project involves use of the EPS-block geofoam as backfill behind the abutment of a bridge, the structural engineering specialist designing the bridge should be contacted about overall details such as the type of bridge superstructure, nature of the approach slab (if any), any special geotechnical requirements regarding settlement of the bridge or approach slab, and the

3-15 velocity of extreme wind events for which the bridge is being designed. Even if the proposed embankment does not involve a bridge, the structural specialist should still be consulted for input concerning design wind velocity for the project area. Geotechnical Engineering Geotechnical engineering issues that the designer needs to assess include issues related to site characterization, design criteria and considerations, and assessment of alternatives. The geotechnical site characterization program should focus on the following four areas: defining the nature and geometry of the relevant soil and rock strata; defining variations with depth of stress history, compressibility, and shear strength of the soft-soil strata in the proposed area of construction; determining the piezometric profile through all relevant soil strata, including potential seasonal and other variations in the ground water table; and assessing relevant seismic design issues based on owning-agency policy and/or the methodologies given in (15). The geoenvironmental site characterization program should focus on identifying any potential sources of ground and ground water contamination within the area of proposed construction. If any excavation into or placement of EPS blocks below ground water (including an allowance for future rises in ground water) is anticipated, particular attention must be placed on the nature and concentration of contaminants in the ground water that may affect disposal during construction dewatering or durability of the EPS. Geotechnical design criteria and considerations that should be evaluated include relevant aspects related to the proposed fill, adjacent structures, and the existing soil conditions. Relevant geotechnical design criteria for the proposed embankment must be established with regard to maximum allowable total settlement of the completed structure and minimum Allowable Stress Design (ASD) safety factor for slope stability of the completed structure. An assessment should be made of any adjacent structures, utilities and transportation facilities (roads, railroads), both existing or proposed, that may be affected by the loads imposed on the ground by the proposed embankment. An assessment should be made of any foundation soil issues over which the use of

3-16 EPS-block geofoam in the embankment would have little or no benefit. This includes but is not limited to issues such as creep of existing soft soils, seismic liquefaction of any coarse-grain strata above or below the soft soils, and long-term decomposition and concomitant vertical compression of any underlying non-soil waste materials. The need for pre-construction ground improvement to correct any potential problems should be identified (15,16). A summary of ground improvement methods was presented in Chapter 1. Because the use of EPS-block geofoam is a category of ground improvement, i.e., lightweight fill, the geotechnical engineer should perform an assessment of alternatives. As discussed in Chapter 1, typical alternatives include: • an embankment consisting of traditional soil fill plus the use of ground improvement (16). The possibility that an all-soil embankment would require a different cross-sectional geometry (e.g., flatter side slopes) and thus a larger volume of material as well as right-of-way acquisition should be considered. Note that the direct and indirect costs of time for ground improvement strategies such as preloading and staged construction as well as the cost of necessary geotechnical instrumentation to monitor and quantify ground improvement should be included in this assessment. A discussion of the necessary instrumentation can be found in (17,18); • other lightweight fill materials (16). The unique issues associated with alternative fill materials (e.g., compressibility, environmental impact, weather restrictions on construction) should also be considered; and a structure (bridge or viaduct) supported on deep foundations. Design alternatives to the use of EPS-block geofoam should be identified, a preliminary design for each alternative performed, and a cost estimate for each alternative prepared to provide baseline information against which the geofoam alternative will be assessed.

3-17 DESIGN LOADS Introduction Loads that need to be considered when designing an EPS-block geofoam embankment on soft ground include gravity, traffic, water, seismic, and wind loads. For ultimate limit state calculations, the worst expected loadings are typically used while for serviceability limit state calculations, the typical or average expected loadings are used. It should be noted that the load chosen to represent the worst expected loading in ultimate limit state calculations may differ depending on the failure mechanism being analyzed. For example, for design against hydrostatic uplift (flotation), translation due to water (hydrostatic sliding), and seismic stability the worst expected dead load from the EPS-block geofoam is the dry unit weight. However, for design against bearing capacity failure, slope stability, and load bearing of the EPS, the worst expected dead load from the EPS-block geofoam is the greatest dead load expected, which may be a higher unit weight that considers the potential increase in unit weight of the EPS due to water absorption especially if the EPS blocks are permanently submerged. Gravity Components of the embankment system, which are depicted in Figure 3.6, that contribute to gravity loading and need to be considered in external and internal stability analysis include • The weight of the overlying pavement system (Item A in Figure 3.6), which includes any reinforced PCC slab that might be used at the pavement system and geofoam interface. The issue of utilizing a PCC slab at the bottom of the pavement system is discussed in Chapters 4 and 6. • The weight of soil cover placed on the sides of a sloped-side embankment (Item B in Figure 3.6) or the weight of the wall elements of a vertical-side embankment (geofoam wall, Figure 3.4(b)). • The net effective weight of any earth material placed between the existing ground surface and the bottom of the EPS blocks (Item C in Figure 3.6).

3-18 Figure 3.6. Components contributing to gravity loads. Gravity loads can be calculated based on a preliminary assumed cross-section of the embankment, including the pavement system, and any cover material over the sides of the embankment. Although the pavement system has not been designed at this point, it will typically be equal to or greater than 610 mm (24 in.) in thickness to minimize the effects of differential icing and solar heating. The design procedure depicted in Figure 3.3 is based on obtaining a pavement system that provides the least amount of stress on top of the EPS-block geofoam embankment to satisfy internal and external stability requirements. Therefore, it is recommended that the preliminary pavement system be assumed to be 610 mm (24 in.) thick and the various component layers of the pavement system be assumed to have a total (moist) unit weight of 20 kN/m3 (130 lbf/ft3) for initial design purposes. EPS-block geofoam used for lightweight fill applications has a density of the order of 20 kg/m3 (1.25 lbf/ft3), which is approximately 1 percent of the density of earth materials. Consequently, the effect of gravity on the assemblage of EPS blocks is negligible and can be omitted in internal stability calculations although this quantity is easily included in calculations if desired. The dry unit weight of the EPS can be taken to be 200 N/m3 (1.25 lbf/ft3). Any portion of the EPS blocks that is permanently submerged under normal ground water conditions is assumed to have a total unit weight of 1,000 N/m3 (6.37 lbf/ft3) not the dry value of 200 N/m3 (1.25 lbf/ft3) for general gravity stress calculations, to conservatively allow for long-term water absorption. Supplemental water considerations such as the potential for flotation from unanticipated rises in water level and horizontal sliding due to any unbalanced water head across the embankment are discussed as part of water loads. If any permanent excavation of any existing material is performed such that the embankment subgrade level on which the EPS blocks are to be placed is below the existing ground surface, the reduction in load should be considered.

3-19 Traffic The effect of vehicle loads on the road surface is generally negligible compared to the dead load of the pavement system and thus can be ignored in global settlement and stability calculations. However, vehicle loads can be included if desired by dividing the total assumed weight of a vehicle by its footprint area to arrive at an equivalent uniform vertical stress that can be included in calculations. The magnitude of the vehicle weight and footprint area of the design vehicle can be based on either design policy of the owning agency or information in textbooks such as (19). Alternatively, 0.67 m (2 ft) of a 18.9 kN/m3 (120 lbf/ft3) surcharge material can be used to model traffic stresses at the top of the embankment. Traffic loading should be considered when assessing the internal stability of an embankment containing EPS-block geofoam and for design of the pavement system. A more detailed discussion on estimating traffic loads is included in Chapter 6. Water Sites that have soft soil conditions where EPS-block geofoam is usually used will often have ground water at or close to the ground surface. In addition, such sites are often close to surface water bodies such as rivers that are subject to periodic significant changes in water level due to storms and floods (extreme events). Therefore, both normal as well as extreme-event water levels must be considered in design. The 100-year flood water level is typically utilized to represent the extreme-event water level. However, a suitable extreme-event water level should be based on local codes and/or recommendations by a civil engineer. Three design issues related to water that need to be addressed include increase in total unit weight of the EPS due to long-term water absorption, potential for flotation from unanticipated rises in the normal water level, and horizontal sliding due to an unbalanced water head across the embankment. Any portion of the EPS blocks that is permanently submerged under normal ground water conditions is assumed to have a total unit weight of 1,000 N/m3 (6.37 lbf/ft3), not the dry value of

3-20 200 N/m3 (1.25 lbf/ft3) suggested for general gravity stress calculations, to conservatively allow for long-term water absorption. EPS is a closed-cell foam that contains approximately 98 percent air per unit volume. EPS is different than soil in that its void spaces are essentially sealed against any significant water intrusion. Thus, a block of EPS will tend to float if subjected to immersion in water. Consequently, ground and surface water intrusion is a particularly important consideration in problems involving embankments containing EPS-block geofoam and the effect of buoyancy of the EPS must be considered in the net vertical stress calculations. Increases in ground water levels due to extreme events such as floods and a hurricane storm surge should be considered. There have been a few projects (6) where embankments containing EPS-block geofoam have suffered an ULS failure due to flotation from unanticipated rises in ground water. As reported in (20) and (6), the first EPS embankment built in Norway in 1972 failed due to hydrostatic uplift (flotation) in 1987. Although the embankment was designed against the potential for uplift, the design water level used was 0.85 m (2.8 ft) lower than the flood level that occurred in 1987. Thus, the biggest uncertainty in design against uplift is the selection of an appropriate flood elevation to utilize in the design. It is also important that proper temporary dewatering be maintained during construction to prevent hydrostatic uplift due to groundwater rise or surface water intrusion that may collect along the embankment during heavy rainfall. A project in Orland Park, Illinois partially failed during construction due to hydrostatic uplift during a heavy rainfall (21). Consequently, each project where EPS-block geofoam is being considered for embankment construction requires a careful assessment of not only the normal seasonal range of ground water levels but also the potential for extreme events due to severe storms that could lead to a temporary rise in ground water. As an approximate rule of thumb, each meter (3.28 ft) of submergence of a block of EPS below water requires approximately 500 mm (20 in.) of normal-weight surcharge fill material

3-21 (soil, pavement, etc.) on top of the EPS blocks to counteract the effects of buoyancy or for every 100 millimeters (4 in.) of submergence of an EPS block there must be 50 millimeters (2 in.) of soil or pavement on top of the EPS blocks to counteract buoyancy effects. Chapters 5 and 6 provide procedures for estimating the overburden required on top of the EPS-block to counteract the effects of hydrostatic uplift. Therefore, the use of EPS-block geofoam alone may not be feasible in areas where there can be significant rises in ground water elevations during the design life of the structure because the overburden required to prevent flotation of the EPS blocks during an extreme flood event may cause excessive settlement and/or instability. In such cases, other design alternatives, including the use of other types of lightweight fill materials that do not have the buoyancy potential of EPS blocks, such as a lightweight fill material with an open texture to better accommodate inundation, should be considered at least for the lower portion of the embankment that may be inundated (22). One possible type of lightweight fill that can be considered is ultra light cellular structures (ULCS) now called geocomb because of their honeycomb appearance in cross section (22,23). Geocomb blocks have an open-cell structure that can flood and drain, and thus will not float. Alternatively, the assemblage of EPS blocks can be tied down using passive (initially unstressed) vertical ground anchors. The use of vertical ground anchors has been successfully used in Japan (24). The vertical ground anchors can penetrate the EPS blocks and be founded in the underlying foundation soil. The heads of the anchors could be secured by a reinforced-concrete slab cast over the surface of the EPS blocks. The potential for the embankment to act as a de facto levee for surface water intrusion during extreme-event water levels also needs to be considered especially in cases where the road embankment is adjacent to an open body of water such as a stream, river or lake. An unbalanced head of water acting on the embankment would produce an unbalanced lateral force that may result in translation (horizontal sliding) of the embankment in addition to uplift (Figure 3.7).

3-22 Chapters 5 and 6 provide procedures for estimating the overburden required on top of the EPS- blocks to counteract the effects of translation due to water (hydrostatic sliding). Figure 3.7. Unbalanced water force acting on the side of an EPS-block geofoam embankment. Seismic Seismic loading is a short-term event that must be considered in geotechnical problems including road embankments. Seismic loading can affect both external and internal stability of an embankment containing EPS-block geofoam. Most of the considerations for static and seismic external stability analyses are the same for embankments constructed of EPS-block geofoam or earth materials. These considerations include various SLS and ULS mechanisms such as seismic settlement and liquefaction that are primarily independent of the nature of the embankment material because they depend on the seismic risk at a particular site and the nature and thickness of the natural soil overlying the bedrock. A discussion of these topics can be found in (15). Mitigation of seismic induced subgrade problems by ground improvement techniques prior to embankment construction is beyond the scope of this study. However, a discussion on ground improvement to reduce potential seismic-induced subgrade problems can be found in (1,15,25,26). The state of practice for evaluating the external seismic stability of geofoam embankments involves using pseudo-static slope-stability analyses (15) involving the critical failure surface obtained from the static stability analyses, e.g., Figure 3.8(a). Several road embankments (27,28) incorporating EPS-block geofoam have survived relatively severe earthquakes in Japan without any observable damage, which also suggests that this is a conservative analysis and is the basis for the design charts presented in Chapters 5 and 6. Terzaghi (29) developed the pseudo-static stability analysis to simulate earthquake loads on slopes and the analysis involves modeling the earthquake shaking with a horizontal force that acts permanently, not temporarily, and in one direction on the slope. Thus, the primary difference between a pseudo-static and static external

3-23 stability analyses is that a horizontal force is permanently applied to the center of gravity of the critical slide mass and in the direction of the exposed slope. If a stability method is used that involves dividing the slide mass into vertical slices, the horizontal force is applied to the center of gravity of each vertical slice that simulates the inertial forces generated by horizontal shaking. This horizontal force (F) equals the slide mass or the mass of the vertical slide (m) multiplied by the seismic acceleration (a), i.e., F=m*a. The seismic acceleration is usually derived by multiplying a seismic coefficient, k, by gravity. In addition to gravity loads of the overlying pavement and soil cover on the sides of the embankment (if a sloped-sided embankment design is used) and transient traffic loads, seismic forces must be considered in the internal stability analyses. Extensive research in Japan during the late 1980s to early 1990s period demonstrated two key aspects with respect to internal seismic response of geofoam embankments: • The internal seismic response is more complex than the overall external response. This is caused by the EPS-block geofoam acting as a flexible, not rigid, structure and slippage possibly occurring between the blocks. This slippage may result in the mobilization of a post-peak interface strength, which did not have to be considered in the external stability analyses because the shear resistance of the geofoam was assumed to be negligible. • The inherent inter-block friction between EPS blocks is insufficient to prevent lateral shifting between blocks during a "significant" seismic event. Therefore, the friction must be supplemented by using some mechanical connectors between blocks. From a solid-mechanics perspective, these connectors provide a component of an apparent pseudo cohesion at the interface that is additive to the inherent frictional component provided by the EPS-EPS interface. These connectors are typically some type of barbed metal plate. Unfortunately, no criteria are currently available to quantify "significant" in terms of any of the

3-24 magnitude scales (moment, local (Richter), etc.) traditionally used for rating earthquakes on an energy basis. Therefore, the present state of knowledge suggests that a conservative approach is warranted so any embankment designed for seismic loading should incorporate mechanical connectors on all horizontal surfaces between blocks and the geofoam interface shear resistance be measured using laboratory tests that do not utilize mechanical connectors. The main difference between internal and external seismic stability analysis is that sliding is assumed to occur only within the geofoam embankment in internal seismic stability analysis. Therefore, the interface shear strength data presented in Chapter 2 is used in the internal stability analyses to represent the shear resistance mobilized along geofoam interfaces. (a) Failure considering the shear strength of embankment materials. (b) Failure ignoring the shear strength of embankment materials. Figure 3-8. Typical slope modes of failure involving EPS-block geofoam. Wind EPS-block geofoam used as lightweight fill usually has a density of 20 kg/m3 (1.25 lbf/ft3), which is approximately 1 percent of the density of earth materials. Because of this extraordinarily low density, the potential for translation (horizontal sliding) of the entire embankment at the interface between the bottom of the assemblage of EPS blocks and the underlying soil foundation due to wind is a potential failure mechanism. This ULS failure mechanism, which is an external stability issue, is unique to embankments containing EPS-block geofoam. The short-term tendency of the entire embankment, such as during construction or immediately after construction, to slide under wind loading is resisted primarily by the undrained shear strength, Su, of the foundation soil if it is a soft clay. However, the long-term tendency of the entire embankment to slide under wind loading is resisted primarily by the EPS-foundation interface friction angle at the base of the embankment. Although the friction angle, δ, for this interface is relatively high (it approaches the Mohr-Coulomb angle of internal friction, φ, of the

3-25 foundation soil), the resisting force (which equals the dead weight times the tangent of δ) is small because the dead weight of the overall embankment is small. Additionally, geosynthetics such as geotextiles are sometimes used as a separation layer between the fill mass and the natural foundation soil. Consequently, the potential for the entire embankment to slide in a direction perpendicular to the proposed road alignment due to wind is a possible failure mechanism, however there is no documented sliding failure of a geofoam embankment due to wind. At the present time there is no case history data available that provides data on the behavior of an EPS- block geofoam embankment subjected to extreme wind events such as hurricanes, typhoons, and tornados, which might produce a sliding failure. To date only the French national design guide for EPS-block geofoam road embankments explicitly recognizes the potential for translation of the entire embankment due to wind loading (30). The wind driving forces come from applied stresses on both the windward and leeward sides of the embankment as shown in Figure 3.9. Note that the downwind (leeward side) stress is due to suction. The magnitudes of these horizontal stresses can be derived from fluid mechanics theory and are given in (30) as: 2 U Up 0.75V sinθ= (3.4) 2 D Dp 0.75V sinθ= (3.5) with V = the wind speed in meters per second, pU and pD have units of kilopascals and the other variables are defined in Figure 3.9. Figure 3.9. Definition of parameters for wind-loading analysis (13). As will be shown in Chapter 5, results from analyses performed during this study on typical EPS-block geofoam embankment geometries indicate that the wind pressures obtained from Equations (3.4) and (3.5) may be too conservative. It is recommended that a more realistic procedure for evaluating the potential for basal translation (sliding) due to wind loading especially under Atlantic hurricane conditions be developed.

3-26 REFERENCES 1. Holtz, R. D., “Treatment of Problem Foundations for Highway Embankments.” NCHRP Synthesis 147, Transportation Research Board, Washington, D.C. (1989) 72 pp. 2. Harr, M. E., Reliability-Based Design in Civil Engineering, McGraw-Hill, New York (1987) 291 pp. 3. Hunt, R. E., Geotechnical Engineering Analysis and Evaluation, McGraw-Hill, Inc., New York (1986) 729 pp. 4. Goble, G., “Geotechnical Related Development and Implementation of Load and Resistance Factor (LRFD) Methods." NCHRP Synthesis of Highway Practice 276, Transportation Research Board, Washington, D.C. (1999) 69 pp. 5. Horvath, J. S., “Geofoam and Geocomb: Lessons from the Second Millennium A.D. as Insight for the Future.” Research Report No. CE/GE-99-2, Manhattan College, Bronx, NY (1999) 24 pp. 6. Horvath, J. S., “Lessons Learned from Failures Involving Geofoam in Roads and Embankments.” Research Report No. CE/GE-99-1, Manhattan College, Bronx, NY (1999) 18 pp. 7. “Treatment of Soft Foundations for Highway Embankments.” NCHRP Synthesis 29, Transportation Research Board, Washington, D.C. (1975) 25 pp. 8. “Bridge Approach Design and Construction Practices.” NCHRP Synthesis of Highway Practice 2, Transportation Research Board, Washington, D.C. (1969) 30 pp. 9. Wahls, H. E., “Shallow Foundations for Highway Structures.” NCHRP Synthesis of Highway Practice 107, Transportation Research Board, Washington, D.C. (1983) 38 pp. 10. Moulton, L. K., GangaRao, H. V. S., and Halvorsen, G. T., “Tolerable Movement Criteria for Highway Bridges.” FHWA/RS-85/107, Federal Highway Administration, Washington D.C. (1985) . 11. Moulton, L. K., “Tolerable Movement Criteria for Highway Bridges.” FHWA-TS-85-228, Federal Highway Administration, Washington, D.C. (1986) 93 pp. 12. “Slope Stabilization with Geofoam (in prep.).” Syracuse University and The Society of Plastics Industries . 13. Horvath, J. S., Geofoam Geosynthetic, , Horvath Engineering, P.C., Scarsdale, NY (1995) 229 pp. 14. Carroll, R. G., Jr., “Geotextile Filter Criteria.” Transportation Reserach Record 916: Engineering Fabrics in Transportation Construction, Transportation Research Board, National Reserach Council, Washington, D.C. (1983) pp. 46-53. 15. Kavazanjian, E., Jr., Matasovic, N., Hadj-Hamou, T., and Sabatini, P. J., “Geotechnical Engineering Circular No. 3; Design Guidance: Geotechnical Earthquake Engineering for Highways; Volume I - Design Principles.” FHWA-SA-97-076, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C. (1997) 186 pp. 16. Elias, V., Welsh, J., Warren, J., and Lukas, R., “Ground Improvement Technical Summaries.” Publication No. FHWA-SA-98-086, 2 Vols, U.S. Department of Tranportation, Federal Highway Administration, Washington, D.C. (1999) . 17. Dunnicliff, J., “Geotechnical Instrumentation for Monitoring Field Performance.” NCHRP Synthesis of Highway Practice 89, Transportation Research Board, Washington, D.C. (1982) 46 pp. 18. Dunnicliff, J., Geotechnical Instrumentation for Monitoring Field Performance, , Wiley- Interscience, New York (1988) 577 pp. 19. Huang, Y. H., “Pavement Analysis and Design.” , Prentice-Hall, Inc., Englewood Cliffs, NJ (1993) 805 pp.

3-27 20. Frydenlund, T. E., and Aaboe, R., “Expanded Polystyrene - A Light Solution.” International Symposium on EPS Construction Method (EPS Tokyo '96), Tokyo, Japan (1996) pp. 31-46. 21. Taccola, L. J., Telephone conversation with Arellano, D. 16 November 1999. 22. “Matériaux Légers pour Remblais/Lightweight Filling Materials.” Document No. 12.02.B, PIARC-World Road Association, La Defense, France (1997) 287 pp. 23. Perrier, H., “Ultra Light Cellular Structure - French Approach.” Geotextiles and Geomembranes, Vol. 15, No. 1-3 (1997) pp. 59-76. 24. Ninomiya, K., and Ikeda, M., “Design & construction of EPS method which surfacing and uses anchor for prevention.” International Symposium on EPS Construction Method (EPS Tokyo '96), Tokyo (1996) pp. 162-167. 25. Elias, V., Welsh, J., Warren, J., and Lukas, R., “Ground Improvement Technical Summaries.” FHWA-SA-98-086, U.S. Department of Transportation, Federal Highway Adminstration, Washington, D.C. (1999) . 26. Elias, V., Welsh, J., Warren, J., and Lukas, R., “Ground Improvement Technical Summaries.” FHWA-SA-98-086, Vol. 2, 2 Vols, U.S. Department of Transportation, Federal Highway Adminstration, Washington, D.C. (1999) . 27. Hotta, H., Nishi, T., and Kuroda, S., “Report of Results of Assessments of Damage to EPS Embankments Caused by Earthquakes.” Proceedings of the International Symposium on EPS Construction Method (EPS Tokyo '96), Tokyo, Japan (1996) pp. 307- 318. 28. Miki, G., and Tsukamoto, H., “Behaviour of EPS Embankment in a Scale of Actual Banking by Using EPS Construction Method.” Technical Reports of Construction Method Using Expanded Polystyrol, Expanded Polystyrol Construction Method Development Method, Tokyo, Japan (undated) . 29. Terzaghi, K., “Mechanisms of Landslides.” Application of Geology to Engineering Practice, Berkey Vol., Geological Society of America (1950) pp. 83-123. 30. “Utilisation de Polystyrene Expanse en Remblai Routier; Guide Technique.” Laboratoire Central Ponts et Chaussées/SETRA, France (1990) 18 pp.

FIGURE 3.1 PROJ 24-11.doc BWC Sampling Testing Analysis Criteria Tolerable Application of Previous Experience in Area Es pe cia lly of Pr ojec t 3-28

FIGURE 3.2 PROJ 24-11.doc 3-29

FIGURE 3.3 PROJ 24-11.doc acceptable? fill mass arrangement Determine a preliminary system design Yes Yes Yes Yes Yes Yes FS>1.2? FS>1.2? FS>1.2? FS>1.5? FS>3? Translation water (external)and overturning due to (flotation) Hydrostatic and overturning (external) Seismic stability Settlement Slope stability capacity Bearing preliminary pavement of EPS and assume a Select preliminary type Background investigation remedial procedure A remedial procedure C Procede to No 9 remedial procedure B Procede to No No uplift 8 No 7 6 Procede to No 5 No 4 3 2 1 stability (internal) No significant change stress compared to the preliminary a significant change in overburden Does required Final embankment design developed in step pavement system design 17 pavement system result in 15 16 Pavement system design Yes 14 Load bearing FS>1.2? FS>1.2? Yes remedial procedure G Yes Procede to Procede to remedial procedure F No 12 13 Seismic wind (internal) FS>1.2? due to Translation Yes 11 Translation due to water (internal) FS>1.2? Yes Yes 10 FS>1.2? Translation wind (external) and overturning due to Procede to remedial procedure E No No Procede to remedial procedure D No Procede to remedial procedure C No Main Procedure 2 ? 3-30

FIGURE 3.3 PROJ 24-11.doc Note: These remedial procedures are not applicable to overturning of a vertical embankment about the toe of the embankment at the embankment and foundation soil interface. If the factor of safety against overturning of a vertical embankment is less than 1.2, consideration can be given to adjusting the width or height of the vertical embankment. Proceed to step 1 the thickness of EPS? or Start of Remedial Procedure A soil subgrade be decreased to increase proposed between the EPS blocks and of any soil fill that may be Can the thickness Can the foundation soil be partially excavated to vertical stress that will yield a depth that will decrease the effective adequate stability? tolerable settlements or A-1 No Yes Satisfy current step requirements and proceed to the next step in main Select a supplemental technique to be used in ground improvement conjunction with EPS lightweight fill. A-2 procedure. Start of Remedial Procedure B soil fill be removed and substituted on top of the EPS anchoring suitable? system or a ground with pavement system materials soil, can a portion of the proposed the EPS blocks and the foundation fill is being proposed between If conventional soil Proceed to step NoA-2 Is a drainage B-2 No blocks? B-1 to the next step in main Yes Satisfy current steprequirements and proceed to the next step in main requirements and proceed Satisfy current step Yes procedure. procedure. pavement system materials on top of the EPS blocks? material that will provide a larger interface friction angle? If conventional soil fill is being proposed between the of the proposed soil fill be removed and substituted with EPS blocks and the foundation soil, can a portion soil be replaced with an alternative separation Proceed to step A-2 Is a drainage system suitable (for the translation due to water failure or mechanism)? No between the fill mass and foundation material being proposed or Can any separation Start of Remedial Procedure C requirements and proceed to the next step in main Satisfy current step Yes procedure. Start of Remedial Procedure D materials on top of the EPS blocks? fill be removed and substituted with pavement system soil, can a portion of the proposed soil the EPS blocks and the foundation fill is being proposed between Is the use of inter-block connectors suitable? Is a drainage system suitable (for the translation due to water failure Proceed to step A-2 mechanism)? or or No If conventional soil requirements and proceed to the next step in main Satisfy current step Yes procedure. 3-31

FIGURE 3.3 PROJ 24-11.doc Note: These remedial procedures are not applicable to overturning of a vertical embankment about the toe of the embankment at the embankment and foundation soil interface. If the factor of safety against overturning of a vertical embankment is less than 1.2, consideration can be given to adjusting the width or height of the vertical embankment. being considered? with a lower unit weight using pavement system materials pavement system and/or decreasing the inter-block connectors unit weight be used? system materials with a lower decreased and/or can pavement Can the pavement system thickness be Is the use of Proceed to step 8 Yes to step 14 . requirements and proceed Satisfy current stepNo Is suitable? or Start of Remedial Procedure E resulting overburden stress greater, modifying the one currently being proposed. Can also inquire if EPS blocks with a larger elastic limit stress can be greater Proceed to step 4 was modified, is the less Proceed to step 15Proceed to step change No significant previous overburden less, or near the same as the 8 locally produced. If the pavement system adding a separation layer or pavement system by Modify the Start of Remedial Procedure F stress? EPS blocks and foundation soil be decreased so that the EPS block thickness in an increase or decrease requirements and proceed to step 17 Proceed to step 4 No system overburden? the increase in pavement can be increased to offset Satisfy current step of any soil fill between the Can the thickness increase Yes decreaseDid the requiredpavement system result in overburden Proceed to step 8 Start of Remedial Procedure G stress? 3-32

FIGURE 3.4 PROJ 24-11.doc (a) Sloped-side fill. (b) Vertical-face fill. EPS block (typical) EPS block (typical) 3-33

FIGURE 3.5 PROJ 24-11.doc (a) Sloped-side fill. (b) Vertical-face fill. EPS block (typical) EPS block (typical) 3-34

FIGURE 3.6 PROJ 24-11.doc Item A (Pavement System) EPS Blocks Item B (Soil Cover) Item C (Soil Embankment Fill and/or Seperation Layer) 3-35

FIGURE 3.7 PROJ 24-11.doc 3-36

FIGURE 3.8A PROJ 24-11.doc Foundation Soil Embankment (Pavement, Geofoam, Soil) Modeled Explicitly 3-37

FIGURE 3.8B PROJ 24-11.doc Foundation Soil Only Vertical Normal Stress Imposed on Subgrade By Embankment Considered. 3-38

FIGURE 3.9 PROJ 24-11.doc θU θD W P R P Wind Direction U D DUR Horizontal Resisting Forces 3-39

TABLE 3.1 PROJ 24-11.doc DESIGN PHASE Limit State* Failure Mechanism Determines Accounts for External (global) Stability SLS Settlement* Need for additional ground improvement (See Table 1.1) Excessive and/or differential settlement from vertical and lateral deformations of the underlying foundation soil. ULS Bearing capacity* Need for additional ground improvement (See Table 1.1) Downward vertical movement of the entire embankment into the foundation soil due to bearing capacity failure of the entire embankment ULS Slope stability* Need for additional ground improvement (See Table 1.1) Downward vertical movement of the entire embankment into the foundation soil due to deep-seated rotational type slope instability Need for additional horizontal shear resistance between the embankment and foundation soil Horizontal sliding of entire embankment due to seismic loading. ULS Seismic stability* Need for adjusting the width or height of an embankment with vertical walls. Overturning of a vertical embankment about the toe of the embankment at the embankment and foundation soil interface ULS Hydrostatic Uplift (flotation) Need for ground anchors Upward vertical movement of the entire embankment due to a rise in ground water table Need for additional horizontal shear resistance between the embankment and foundation soil Horizontal sliding of entire embankment due to an unbalanced water head across the embankment. ULS Translation due to water (hydrostatic sliding) Need for adjusting the width or height of an embankment with vertical walls. Overturning of a vertical embankment about the toe of the embankment at the embankment and foundation soil interface Need for additional horizontal shear resistance between the embankment and foundation soil Horizontal sliding of entire embankment due to an extreme wind event. ULS Translation due to wind Need for adjusting the width or height of an embankment with vertical walls. Overturning of a vertical embankment about the toe of the embankment at the embankment and foundation soil interface Internal Stability ULS Seismic stability* Need for additional horizontal shear resistance between blocks and Adequate horizontal shear resistance between blocks and adequate shear resistance between the pavement system 3-40

TABLE 3.1 PROJ 24-11.doc between the pavement system and the upper layer of blocks and the EPS mass to include the separation material, if any used. ULS Translation due to water (hydrostatic sliding) Need for additional horizontal shear resistance between blocks Adequate horizontal shear resistance between blocks due to an unbalanced water head across the embankment. ULS Translation due to wind Need for additional horizontal shear resistance between blocks Adequate horizontal shear resistance between blocks SLS Load bearing* EPS properties Excessive vertical deformation Pavement System SLS Flexible or rigid pavement design procedure Most economical arrangement and thickness of pavement system materials, density of upper EPS block, and need for a separation layer between the pavement system and EPS mass Subgrade support provided by the EPS blocks and loads from traffic and environment to protect the pavement and EPS mass from distress and to minimize the potential for differential icing and solar heating effects Notes: SLS = serviceability limit state ULS = ultimate limit state *An increase in overburden defined as the dead load stress imposed by the pavement system and/or fill mass may decrease the factor of safety of the failure mechanism. 3-41

TABLE 3.2 PROJ 24-11.doc Critical Noncritical Large, unexpected, catastrophic movements Slow, creep movements Structures involved No structures involved Stability No evidence of impending instability failure Large total and differential Small total and differential Occur over relatively short distances Occur over large distances Settlements Rapid direction of traffic Slow transverse to direction of traffic Repairs Repair cost much greater than original construction cost Repair cost less than original construction cost 3-42