6. Applications

6.1 Introduction

Horvath (1992) classified the applications utilizing EPS geofoam blocks by “their function”. The four functions of EPS geofoam are lightweight fill, compressi-ble inclusion, thermal insulation and small amplitude wave damping (ground vibra-tion and acoustic). Horvath (1999b) add two more functions, drainage and structural. Another way to classify the applications is by engineering properties.

Five EPS geofoam properties appear to be very useful when utilizing EPS geofoam. These properties are: density, compressibility, thermal resistance, vibration damping and self-supporting nature of the EPS geofoam. These properties can solve many important engineering problems such as settlement problems, slope stability problems and bearing capacity problems. Conventional geotechnical solutions for such problems (e.g., deep foundations, sheet piles, retaining walls or other solutions) may be economically unfeasible. Table 2-12 shows selected engineering applications and the corresponding EPS geofoam function to be utilized. The following concepts and schematic design figures are proposed to illustrate some of these applications and examples of actual installations.

Table 2-12 Selected EPS Geofoam Applications

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6.2 Slope Stabilization

Geofoam can be utilized in slope stabilization as shown in figure 2-9. To re-duce the tendency of failure of portion of the soil the crest of the slope is excavated and replaced by the super lightweight material EPS geofoam. Alternative solutions may require the changing of the slope inclination, buttressing the toe of the embank-ment using soil nailing or any other solution that may affect the geometry of the slope or the surrounding land or may not be feasible for many reasons.

In Japan a road embankment on a steep hillside was constructed using 1834 cubic meter of EPS geofoam. The EPS was utilized in a section of the road of about 104 m long (Suzuki et. al., 1996). The total cost of stabilization efforts was reduced as a result of adopting EPS. The construction time was also reduced in this project.

In Colorado, a 61m section of US highway 160 failed and caused the east-bound lane of this heavily traveled highway to close. A 648 cubic meters of EPS geofoam was utilized as fill in the crest of the slope to increase the factor of safety. The total cost of the project was $160,000, which was much less than the $1,000,000 cost of the alternative a retaining wall solution (Yeh and Gilmore, 1989).

Figure 2-9 Slope Stabilization Utilizing EPS Geofoam

In 1994 EPS geofoam was utilized for construction of a 21m embankment for an emergency truck escape ramp in Hawaii (Mimura and Kimura, 1995). The project was originally designed as an earth fill embankment with extensive geotextile rein-forcement and wick drains to overcome stability problems and to reduce settlement. During construction, actual subsurface conditions were observed to be worse than ex-pected. About 13,500 cubic meters of geofoam was used as lightweight fill to replace the earthen embankment.

A segment of County Truck Highway “A” located within a remote region in Wisconsin required continuous maintenance of the pavement due to a creep landslide (Reuter, 2000). The slope was 4.9m height at a 14 degree angle with the horizontal. A well-defined scarp developed within the asphalt despite the frequent patching of the pavement. Instrumentation helped in defining a deep-seated slip surface, which was slowly creeping down slope. Replacing the soil in the slide mass with compacted granular fill was rejected as a solution. As this approach would have meant temporar-ily closing the highway and excavation would have to extend below the water table in order to reach the deep sliding surface. It was decided to reduce the up slope driving force of the slide by excavating the embankment fill from the head of the slide and replacing it with lightweight fill polystyrene geofoam. Both Extruded Polystyrene and type II Expanded Polystyrene were used. To reach a factor of safety of 1.5 three lay-ers of 0.81m thick geofoam each of 7.3m width was required.

In New York, expanded polystyrene geofoam blocks were utilized to treat an unstable roadway embankment slope involving clayey soil (Jutkofsky, et al., 2000). The selection of the geofoam treatment was based upon its constructability and mini-mal impact to both the environment and adjacent homeowners. Potential traffic safety problems associated with differential icing of roadways from the presence of geofoam blocks beneath pavements was minimized by using a thicker subbase layer in the geo-foam treated area. Data from an instrumentation program consisting of an inclinome-ter, extensometers and thermistors showed that the use of geofoam to reduce the driv-ing force of a slope has stabilized the slope. No slope movement has occurred since the treatment was completed in 1996. More details on this case history are shown in chapter 4.

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6.3 Reducing Lateral Pressure on Retaining Structures

EPS Geofoam can be placed between the retaining structure and the soil. Two main geofoam configurations are used as shown in figure 2-10. Differences between the two configurations are shown in chapter 6.

Figure 2-10 Lateral Stress Reduction Utilizing EPS Geofoam

To reduce the static earth pressure acting behind a 14 m height abutment dur-ing and after construction of the backfill and the dynamic earth pressure due to earth-quakes and traffic loads after the construction; 0.5m strip of EPS geofoam was util-ized as a cushion between the abutment and the backfill (Matsuda et. al., 1996). Finite element analysis, showed 85% reduction in the overall bending moment during roll-ing compaction when utilizing 12kg/m3 EPS geofoam. The 20kg/m3 geofoam showed 70% reduction compared with the case of no geofoam. The geofoam blocks configu-ration is utilized in portions of the basement wall in the Syracuse Mall (Sun, 1997). Results are shown in chapter 6.

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6.4 Embankment Fill to Reduce Settlement

Figure 2-11 shows a situation of constructing a new embankment on soft ground. In such a case large settlement can be experienced under the load of the con-ventional embankment fill. Also, soil may take years to achieve its full settlement. Any existing utility line will be damaged if it is not designed for large deflections. By excavating part of the soil and placing geofoam to reach the required embankment’s height and placing the pavement structure on the top of the geofoam a fast lightweight solution is achieved. Zero net stress increase is reached if the amount of excavated soil is equal to the weight of the pavement structure.

In the city of Issaquah, Washington (Cole, 2000) predicted settlement from conventional bridge approach fill of 0.3~ 0.54m. Approximately 1.25-cm settlement was reported after 180 days of utilizing 1822 cubic meters of EPS geofoam as fill ma-terial.

In Salt Lake City, Utah, EPS geofoam was utilized as an embankment fill. The primary use of geofoam is to minimize settlement impacts to buried utility lines. These utilities were required to be in service during construction. In areas where con-ventional borrow is used for backfill, expected construction settlement of the clayey foundation soils is about 0.5 to 1.0 meter (UDOT, 1998). This large amount of set-tlement exceeds almost all strain tolerance for buried utilities. EPS geofoam reduced the settlement. More details on this case history are shown in chapter 5.

EPS was utilized as backfill of a bridge abutment to reduce the settlement of the approach (Ishihara, et al., 1996a). It was essential to complete the fill work in a short time, because further settlement may have occurred had conventional fill been used. A 1040 cubic meter volume of EPS geofoam was used with a height of 9m. Work was completed in the required time with minimum settlement.

A 139m section of a road in Solbotmoan, Norway experienced significant set-tlement. The road was flooded twice each year (Rygg and Sorlie, 1981). Each addi-tion of new materials to compensate for settlement would cause a further settlement. The rate of settlement had been large and increasing. The subgrade condition was 5m of peat. Below the peat there is 13m of soft silty clay. In 1975 the road embankment was excavated and bark was added up to the ground water level. Foam of height 1.2m to 2.0m was utilized on the top of the bark. For the following five years (until the time of publishing the paper) the road has been subjected to traffic. The total settle-ment varies between 0 and 80mm with a reduced rate of settlement.

Figure 2-11 Settlement Reduction on Utility Pipes Utilizing EPS Geofoam

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6.5 Widening Embankments

Another embankment application is shown in figure 2-12. For a limited right of way, widening of embankments can be easily achieved utilizing EPS geofoam. As shown in the figure the self-standing property will reduce the additional space without the need of a retaining wall. However a fascia wall will be required to protect the geo-foam face.

Figure 2-12 Widening Embankments Utilizing EPS Geofoam

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6.6 Stress Reduction on Buried Pipes

The compressible inclusion of EPS geofoam may be utilized to reduce loading above rigid conduits (Vaslestad, 1990). Virtually all conduits can be designed to benefit from the effect of soil arching (GeoTech, 1999c). Figure 2-13 shows conduits of different cross sections and how thin layers of EPS geofoam are placed some 0.5m above the rigid conduit. The main point is to mobilize arch action for the soil above the foam.

Figure 2-13 Stress Reduction on Pipes Utilizing EPS Geofoam

Vaslestad, et al., (1993) reported the results of three tests for concrete culverts with EPS geofoam placed above them. In the first test the instrumented culvert was a 1.95m diameter pipe beneath a 14m high rock fill embankment. In the second test a 1.71m diameter pipe was used beneath a 15m high rock fill. In the third test a 2 m width box culvert was used beneath 11m of silty clay. Reduction of the vertical stresses between 30% and 50% of the overburden stresses was reported in the three tests. Strains in the EPS geofoam were 27 to 42 percent. Use of the compressible in-clusion above rigid culverts in Norway has resulted in cost reductions of the order of 30% and has made possible the use of concrete pipes beneath high fills.

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6.7 Decreasing Foundations Depth in Cold Regions

Foundations in cold climate areas are usually placed below the anticipated frost penetration depths. Basements or crawl spaces are constructed to meet the re-quired foundation depth. That means extra floor level to construct and more time and more money to spend. Figure 2-14 shows an alternative solution where EPS geofoam strips are placed in such a way to insulate the soil beneath in contact with the founda-tion. This insulation system has to surround the building. The wing part of the insula-tion is utilized to reduce the excavation depth for placing the geofoam (Negussey, 1997).

In 1990, a 180 square meter addition to an aircraft control tower was con-structed at Galena, Alaska (Danyluk, 1997). Because of limited resources, a shallow insulated foundation was specified instead of traditional foundation. In other words, a 0.5m deep foundation was constructed instead of one at 3.6m depth. Insulation as in figure 2-14 was utilized. The wing side was 14.8 m length at a depth of 0.65m. The insulation utilizes heat from the building and surrounding soil, redirects it to the area around the foundation and thus reduces the frost penetration. Instrumentation was utilized to measure the temperature at various points. Results show the effectiveness of the insulation system, which was geofoam but not EPS.

Figure 2-14 Building Insulation & Shallower Foundations Utilizing EPS Geofoam

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6.8 Pavement and Railway Insulation

The cycle of winter freezing and spring thawing of soil can affect transporta-tion facilities such as roads and railroads. This is because the ground surface heaves as a result of freezing and settles upon thawing. Thus the lifetime of the pavement section is reduced. The subgrade is weakened and this could be of safety concern for road, railways or airfields. The cross section in figure 2-15 shows the placement of EPS geofoam layers below a pavement section.

Figure 2-15 Pavement Insulation Utilizing EPS Geofoam

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6.9 Bridge Support

Another application (Frydenlund and Aab?e, 1996) of EPS has been as a sup-port foundation for bridge abutments in Norway, as shown in figure 2-16. Higher strength EPS geofoam is required with some resultant increase in cost per unit vol-ume. This solution has been used for both single span bridges with up to 5m high EPS geofoam fill and also for multi span bridges. In all cases the EPS material has per-formed satisfactorily with no adverse effects on the bridge.

An example of such application is L?kkeberg Bridge in Norway. It is a single lane steel bridge with one 36.8m span crossing road E6 close to the Swedish border. The bridge was built in 1989 directly on top of EPS fills (height equals to 4.5m and 5m on both sides) as an alternative to placing the bridge on pile foundations. After 10 years of operation field records show that the average deformation is slightly over 1% of the total fill height (Aab?e, 2000).

Figure 2-16 EPS Geofoam Bridge Abutments

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6.10 Compressible Inclusion Against Expansive Soil

Another application for utilizing EPS geofoam is to use it as a compressible inclusion adjacent to a structural element when it is in contact with expansive soil (Horvath 1996). Expansive soils or swelling soils are those soils that have the ten-dency to increase in volume when water is available and to decrease in volume if wa-ter is removed (Ranjan and Rao, 1993). Figure 2-17 shows part of a structure on pile foundations. The compressible inclusion EPS geofoam is utilized below the structural slab. Upon soil heave EPS geofoam compresses according to its own stress strain re-lation as shown in figure 2-3. The stresses on the structural slab will be limited to a specified value depending on the density of the EPS geofoam. The geofoam will also act as a form for the slab.

Figure 2-17 Soil Expansion Stress Reduction Utilizing EPS Geofoam

On the Channel Tunnel project in England EPS geofoam was utilized as a compressible inclusion (Horvath, 1995a). The purpose of utilizing EPS geofoam was to reduce heave pressure below the floor system of the channel tunnel.

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6.11 Reducing Differential Settlement

In Syracuse, New York, 28,000 cubic meters of EPS geofoam are placed next to outside perimeter of the basement of the Carousel Mall (Stewart, et al, 1994). The purpose of utilizing the rectangular cross section collar of EPS geofoam is to reduce the settlement of the edge of the structure. Since it was necessary to raise grades up to 2.7m around the edge of the 65,000 square meter load compensated mat foundation structure over a deep soft soil, there would be a significant and abrupt changes in stress at the subgrade level at the mat edge had traditional fill is used.

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6.12 Concrete Forms

EPS was utilized as buried form for a large concrete abutment (Yoshihara and Kawasaki, 1996). The traditional and alternative method to build such abutment is to use a sand form and the concrete was than placed. Finally the sand has to be with-drawn using a sand pump and the hole provided in the footing was filled with con-crete to complete the structure. Saving construction time as a result of reduced mate-rial and labor required for form was one of the advantages of using geofoam instead of sand or wood forms.

Another application for EPS as a concrete form is reported by Miyamoto, et., al., 1996. Continuous footings made of EPS geofoam forms are studied. A shortened construction period, heat retention improvement and work saving was achieved.

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6.13 Reducing Lateral Soil Flow on Existing Deep Foundations

Another application is reported by Wano, et al., (1996). A bridge abutment was constructed on soft ground utilizing EPS. The purpose is to reduce the lateral soil flow and the horizontal movement of the bridge substructure. Field observation over a considerable period of time showed that the horizontal movement of the bridge sub-structure had essentially stopped and was stable.

In Japan, 11,000 cubic meter of EPS geofoam are utilized as a lightweight fill nearby a pile foundation (Ishihara et al., 1996b). The soil layer to a depth of 30m was very soft. The 0.6m diameter piles with a 55m length are likely to be severely dam-aged resulting from lateral flow caused by the weak subsoil upon utilizing conven-tional fill.

A 2000 cubic meter of EPS geofoam was utilized in a similar application on a soft ground. EPS backfilling of the abutment on the Moriyama tollgate side of Grand Lake Biwa Bridge is utilized to reduce lateral displacement on pile foundations (Ni-shimura, 1996).

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6.14 Stress Reduction on Buried Structures

In Tokyo, Japan, a pedestrian 150m long and 5m width access link was con-structed to span an elevation difference of 8m (Nishizawa, 1996). The access link ex-ists over an existing structure, which restricted the load both during and after con-struction. Disturbance to local residents had to be taken into account by reducing both the construction time and the noise during construction. 1430 cubic meter of EPS geofoam was utilized in this project.

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6.15 Shallow Foundations

EPS geofoam was utilized in the foundations of an emergency staircase of an overpass (Ojima, et al., 1996). The ground at the site contains a layer of soft clay. Deep foundation was restricted by the existence of a four-meter diameter sewer pipe below the footing of the staircase. Load compensated foundation was the solution by utilizing 3m height of foam directly below the footing. No extra settlement occurred of the utility line occurred.

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6.16 Load Bearing Walls

EPS geofoam is utilized in manufacturing load-bearing walls. EPS is used as the core of panels with oriented strand boards being the face of the panel (R-control, 1999c).

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6.17 Frost Shielding for Buried Conduits

In climates that experience freezing temperatures, water and sewer pipes are normally buried below the depth of maximum frost. A shallower trench is desirable in many situations. Frost shielding methodology is the technique of placing insulation in some configuration around a pipe to protect the pipe from freezing (Coutermarsh and Carbee, 1998, Coutermarsh, 1997). Savings in time and money afforded by de-creased burial depth balance the increased cost of insulation and the time to install it.

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