Guideline and Recommended Standard for Geofoam Applications in Highway Embankments (2004) / Chapter Skim
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Recommended Design Guideline
Recommended Design Guideline
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From page 1... ...
Recommended Design Guideline
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From page 3... ...
In addition, depending on whether the embankment has sloped sides (trapezoidal embankment) or vertical sides (vertical embankment)
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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 (Step 7) , translation due to water (Step 9)
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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 Proceed to No 9 remedial procedure B Proceed to No No uplift 8 No 7 6 Proceed 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?
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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?
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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?
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Therefore, to achieve the most cost-effective design, a design goal is to use the minimum number of EPS blocks necessary to 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 external seismic stability.
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The minimum allowable block density is based on density obtained on either a block as a whole unit or an actual full-sized block. The proposed AASHTO material type designation system is based on the minimum elastic limit stress of the block as a whole in kilopascals (see Table 8)
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From page 10... ...
. If a reinforced PCC slab is considered as a separation layer between the top of the EPS blocks and the overlying pavement system, it may be possible to incorporate the PCC slab into the AASHTO 1993 flexible pavement design procedure by determining a suitable layer coefficient to represent the PCC slab.
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INHERENT RELIABILITY % EPS TYPE EPS RESILIENT MODULUS MPa (lbs/in2) Traffic (ESALs)
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INHERENT RELIABILITY % EPS TYPE EPS RESILIENT MODULUS MPa (lbs/in2) Traffic (ESALs)
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issues, such as total and differential settlement caused by the soft foundation soil, and ultimate limit state (ULS) issues, such as bearing capacity, slope stability, seismic stability, hydrostatic uplift (flotation)
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If the foundation soil is overconsolidated (i.e., σ′p /σ′v > 1, where σ′v is the existing vertical stress) , but the proposed final effective vertical stress will be less than or equal to the preconsolidation pressure (i.e., σ′vf ≤ σ′p)
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Substituting the conservative design values of σn,pavement = 21.5 kPa and σn,traffic = 11.5 kPa and γEPS = 1 kN/m3 into Equation 12 yields the following expression for the undrained shear stress required to satisfy a factor of safety of 3 for a particular embankment height: Based on Equation 13 and various values of TEPS, Figure 5 presents the minimum thickness or height of geofoam required for values of foundation soil undrained shear strength. The results show that if the foundation soil exhibits a value of su greater than or equal to 19.9 kPa (415 lbs/ft2)
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The results of stability analyses using the typical cross section were used to develop the static external slope stability design charts in Figures 7 through 9 for a two-lane (road width of 11 m [36 ft]
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10 15 20 25 30 35 40 45 50 Fa ct o r o f S af et y, FS 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 4H:1V embankment TEPS = 3.1 m = 6.1 m = 12.2 m FS = 1.5 Figure 7. Static external slope stability design chart for trapezoidal embankments with a two-lane roadway with a total road width of 11 m (36 ft )
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The results of the stability analyses were used to develop the static external slope stability design chart in Figure 11. Figure 11 presents the results for a two-lane (road width of 11 m [36 ft]
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A pseudo-static analysis was conducted on only the critical failure surfaces that passed through the foundation soil because external stability was being evaluated. As a result, the design charts for seismic stability terminated at the su value for the foundation soil that corresponded to the transition from a critical failure surface in the foundation soil to the geofoam embankment determined during external static stability analysis.
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This section focuses on the effect of seismic forces on the external slope stability of vertical EPS-block geofoam embankments. This analysis uses the same pseudo-static slope stability analysis used for external seismic stability of trapezoidal embankments presented in Section 4.5.1.1 and circular failure surfaces through the foundation soil.
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The same typical cross section through an EPS embankment used in the static slope stability analysis of embankments with vertical walls was also used for the pseudo-static stability analyses and is shown in Figure 10. 4.5.2.2 Design Charts.
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10 15 20 25 30 35 40 45 50 Se ism ic F ac to r o f S af et y, FS ' 0.0 1.0 2.0 3.0 4.0 5.0 4H:1V embankment TEPS = 3.1 m = 6.1 m = 12.2 m FS' = 1.2 Figure 13. Seismic external slope stability design chart for trapezoidal embankments with a six-lane roadway with a total road width of 34 m (112 ft)
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Seismic external slope stability design chart for trapezoidal embankments with a six-lane roadway with a total road width of 34 m (112 ft)
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10 20 30 40 50 Se ism ic F ac to r o f S af et y, FS ' 0.0 1.0 2.0 3.0 4.0 5.0 FS' = 1.2 FS' = 1.2 FS' = 1.2 kh = 0.05 kh = 0.1 TEPS = 12.2 m TEPS = 6.1 m TEPS = 3.1 m TEPS = 12.2 m TEPS = 6.1 m TEPS = 3.1 m TEPS = 12.2 m TEPS = 6.1 m TEPS = 3.1 m kh = 0.2 Figure 17. Seismic external stability design chart for a four-lane roadway vertical embankment and a total width of 23 m (76 ft)
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From page 25... ...
of the entire embankment at the interface between the bottom of the assemblage of EPS blocks and the foundation soil must be considered in external stability evaluations. For the case of the vertical height of accumulated water to the bottom of the embankment at the start of construction, h, equal to the vertical height of tailwater to bottom of the embankment at the start of construction, h′ (see Figure 20)
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The accumulated water level indicated in the design charts is the sum of the vertical accumulated water level to the bottom of the embankment at the start of construction and the estimated total settlement, h + Stotal. The design engineer then compares this value of OREQ with the weight of the pavement system and cover soil.
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2 A g a i n s t H y d r o s t a t i c U p l i f t ( k N / m o f r o a d w a y ) 0 2000 4000 6000 8000 10000 12000 14000 H=16 m H=12 m H=8 m H=4 m H=2 m H=1.5 m = h + Stotal H Two-Lane Road Width = 11 m Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R e q u i r e d O v e r b u r d e n F o r F a c t o r o f S a f e t y o f 1 .
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2 A g a i n s t H y d r o s t a t i c U p l i f t ( k N / m o f r o a d w a y ) 0 500 1000 1500 2000 2500 3000 3500 4000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m = h + Stotal H Four-Lane Road Width = 23 m Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R e q u i r e d O v e r b u r d e n F o r F a c t o r o f S a f e t y o f 1 .
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Figures 22 through 25 present the design charts for all of the embankment geometries considered during this study for equal upstream and tailwater levels and uplift at the EPS block/foundation soil interface. The values of OREQ shown in Figures 22 through 25 are the required weight of material over the EPS blocks in kilonewtons per linear meter of embankment length.
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2 A g a i n s t H y d r o s t a t i c U p l i f t ( k N / m o f r o a d w a y ) 0 1000 2000 3000 4000 5000 6000 7000 8000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m = h + Stotal H Two-Lane Road Width = 11 m Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R e q u i r e d O v e r b u r d e n F o r F a c t o r o f S a f e t y o f 1 .
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2 A g a i n s t H y d r o s t a t i c U p l i f t ( k N / m o f r o a d w a y ) 0 500 1000 1500 2000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m = h + Stotal H Four-Lane Road Width = 23 m Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R e q u i r e d O v e r b u r d e n F o r F a c t o r o f S a f e t y o f 1 .
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Therefore, the weight of the EPS, equivalent to the height of the pavement system times the unit weight of the EPS, must be subtracted in the result of OREQ, as shown by Equation 21. The accumulated water level used in the design charts is the sum of the vertical accumulated water level to the bottom of the embankment at the start of construction and the estimated total settlement, i.e., h + Stotal.
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Four-Lane Road Width = 23 m = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN ) 0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m h + Stotal H = δ δ = 30o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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∑ ∑ 1 2 1 3 29 ( ) R ECO M M ENDED DESIG N G UIDELINE Six-Lane Road Width = 34 m δ = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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From page 35... ...
0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m h + Stotal H = = 20o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq ui re d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro st at ic S lid in g (kN ) 0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m h + Stotal H= δ δ δ Two-Lane Road Width = 11 m = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq ui re d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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From page 36... ...
However, the findings of NCHRP Project 24-11 revealed that the wind pressures obtained from the current wind analysis equations may be too conservative because there is no documented sliding failure of an embankment containing EPS-block geofoam due to wind loading. Therefore, based on the results of NCHRP Project 24-11 and the absence of documented sliding failure due to wind loading, it is recommended that the R ECO M M ENDED DESIG N G UIDELINE Six-Lane Road Width = 34 m = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq ui re d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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From page 37... ...
Four-Lane Road Width = 23 m = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN ) 0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m h + Stotal H= = 30o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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From page 38... ...
-high EPS trapezoidal embankment with sideslopes of 2H:1V that was used in the pseudo-static internal stability analyses is shown in R ECO M M ENDED DESIG N G UIDELINE Six-Lane Road Width = 34 m = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq ui re d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN ) 0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m h + Stotal H= = 30o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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From page 39... ...
0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m h + Stotal H= = 20o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN ) 0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=4 m H=1.5 m, H=2 m H=8 m h + Stotal H= δ δ δ Four-Lane Road Width = 23 m = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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From page 40... ...
R ECO M M ENDED DESIG N G UIDELINE Six-Lane Road Width = 34 m = 40o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN ) 0 1000 2000 3000 4000 5000 6000 7000 H=16 m H=12 m H=8 m H=4 m H=1.5 m, H=2 m h + Stotal H= = 30o Accumulated Water Level Embankment Height 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R eq u ire d O ve rb ur de n Fo r F ac to r o f S af et y o f 1 .2 A ga in st H yd ro sta tic S lid in g (kN )
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From page 41... ...
This analysis uses the same pseudo-static slope stability analysis used for internal seismic stability of trapezoidal embankments in Section 5.4.1 and noncircular failure surfaces through the EPS or the EPS interface at the top or bottom of the embankment. A typical cross section through a vertical EPS embankment used in the internal static stability analyses is shown in Figure 38.
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From page 42... ...
The internal seismic stability design chart for vertical embankments in Figure 39 presents the seismic factor of safety for each seismic coefficient as a function of interface friction angle. This chart provides estimates of seismic internal factors of safety for vertical embankments with any of the geometries considered during this study -- i.e., embankment heights of 3.1 m (10 ft)
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From page 43... ...
The basic procedure for designing against load-bearing failure is to calculate the maximum vertical stresses at various levels within the EPS mass (typically the pavement system/EPS interface is most critical) and select the EPS that exhibits an 42 elastic limit stress that is greater than the calculated or required elastic limit stress at the depth being considered.
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From page 44... ...
In summary, the vertical stress charts in Figures 41 through 43 can be used to estimate the applied vertical stress on top of the EPS due to a tire load, σLL; on top of an asphalt concrete, PCC system; and on top of a composite pavement system, respectively. For example, the vertical stress applied to the top of the EPS blocks under a 178-mm (7-in.)
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From page 45... ...
Vertical stress on top of the EPS blocks, σLL, due to traffic loads on top of a 610-mm (24-in.) asphalt concrete pavement system.
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From page 46... ...
The minimum required elastic limit stress of the EPS block under the pavement system can be calculated by multiplying the total vertical stress from Step 5 by a factor of safety, as shown in Equation 38: Where σe = minimum elastic limit stress of EPS and FS = factor of safety = 1.2. The main component of σtotal is the traffic stress and not the gravity stress from the pavement.
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From page 47... ...
distribution of vertical stresses through EPS blocks, as shown in Figure 44, should be used to estimate the applied vertical stress at various depths in the geofoam. In order to use the 1(horizontal)
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From page 48... ...
Equations 45, 46, and 47 can be used to determine the increase in vertical stress caused by the gravity load of the pavement system: Where b = one-half the width of the roadway. Where qpavement = vertical stress applied by the pavement system, kN/m3; ∆σZ,DL = increase in vertical stress at depth z due to pavement system dead load, m; γpavement = unit weight of the pavement system, kN/m3; and Tpavement = thickness of the pavement system, m.
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From page 49... ...
5.5.2.11 Step 11: Calculate Total Stresses at Various Depths Within the EPS Blocks. The total vertical stress induced by traffic and gravity loads at a particular depth within the EPS, σtotal, is as follows: 5.5.2.12 Step 12: Determine the Minimum Required Elastic Limit Stress at Various Depths.
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From page 50... ...
6.2 Gravity Loads The assumed components of the gravity loads acting on a vertical wall or abutment are as follows (see Figure 49) : • The uniform horizontal pressure acting over the entire depth of the geofoam caused by the vertical stress applied by the pavement system to the top of the EPS, which can be estimated from Figures 41 through 43; • The horizontal pressure generated by the vertical stress imposed by the pavement system, which can be assumed to be equal to 1⁄10 times the vertical stress; and • The lateral earth pressure, PA, generated by the soil behind the EPS/soil interface, which is conservatively assumed to be transmitted without dissipation through the geofoam to the back of the abutment.
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From page 51... ...
The one exception to the dual SI and I-P unit usage involves the quantities of density and unit weight. Density is the mass per unit volume and has units of kg/m3 (slugs/ft3)
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From page 52... ...
10. NCHRP Synthesis of Highway Practice 29: Treatment of Soft Foundations for Highway Embankments.
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