Geofoam Applications in the Design and Construction of Highway Embankments (2004) / Chapter Skim
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From page 128... ...
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
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From page 129... ...
3-2 ______________________________________________________________________________________ INTRODUCTION Despite the worldwide use of EPS-block geofoam, a specific design guideline for its costeffective 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.
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From page 130... ...
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.
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From page 131... ...
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.
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3-5 and (3.2)
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3-6 applications (e.g., vehicle escape ramps in mountainous regions, logging roads) an unbound gravel or crushed-rock surface layer may be utilized.
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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.
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From page 135... ...
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.
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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)
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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)
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3-11 following references are recommended for information on abutment movements: (8-11)
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3-12 shoulders, 4-lane roadway with two 3 m (10 ft) exterior shoulders and two 1.2 m (4 ft)
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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.
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3-14 estimated annual traffic mix and volume; and ancillary road hardware requirements (shoulder guardrails or barriers, median barriers, overhead lighting, signage)
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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.
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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.
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From page 144... ...
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.
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3-18 Figure 3.6. Components contributing to gravity loads.
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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.
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3-20 200 N/m3 (1.25 lbf/ft3) suggested for general gravity stress calculations, to conservatively allow for long-term water absorption.
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3-21 (soil, pavement, etc.) on top of the EPS blocks to counteract the effects of buoyancy or for every 100 millimeters (4 in.)
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3-22 Chapters 5 and 6 provide procedures for estimating the overburden required on top of the EPSblocks to counteract the effects of translation due to water (hydrostatic sliding)
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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.
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3-24 magnitude scales (moment, local (Richter)
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3-25 foundation soil) , the resisting force (which equals the dead weight times the tangent of δ)
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3-26 REFERENCES 1. Holtz, R
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3-27 20. Frydenlund, T
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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
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FIGURE 3.2 PROJ 24-11.doc 3-29
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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?
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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.
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From page 159... ...
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.
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FIGURE 3.4 PROJ 24-11.doc (a) Sloped-side fill.
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FIGURE 3.5 PROJ 24-11.doc (a) Sloped-side fill.
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FIGURE 3.6 PROJ 24-11.doc Item A (Pavement System) EPS Blocks Item B (Soil Cover)
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FIGURE 3.7 PROJ 24-11.doc 3-36
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FIGURE 3.8A PROJ 24-11.doc Foundation Soil Embankment (Pavement, Geofoam, Soil) Modeled Explicitly 3-37
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FIGURE 3.8B PROJ 24-11.doc Foundation Soil Only Vertical Normal Stress Imposed on Subgrade By Embankment Considered.
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FIGURE 3.9 PROJ 24-11.doc θU θD W P R P Wind Direction U D DUR Horizontal Resisting Forces 3-39
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TABLE 3.1 PROJ 24-11.doc DESIGN PHASE Limit State* Failure Mechanism Determines Accounts for External (global)
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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)
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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
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