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12-1 CHAPTER 12 ECONOMIC ANALYSIS Contents Introduction.................................................................................................................................12-1 Background.................................................................................................................................12-3 Scope...........................................................................................................................................12-5 Research Approach .....................................................................................................................12-5 Soft Ground Treatment Alternatives...........................................................................................12-6 Characteristics and Limitations of Lightweight Fill Materials................................................12-6 Comparison of Lightweight Fill Material Properties ............................................................12-10 Summary of EPS-Block Geofoam Cost Data ...........................................................................12-13 Summary of Foundation Improvement Cost Data ................................................................12-17 Prefabricated Vertical Drains ............................................................................................12-17 Vibro-Compaction .............................................................................................................12-17 Soil Nailing........................................................................................................................12-18 Stone Columns...................................................................................................................12-18 Soil Mixing........................................................................................................................12-18 Mechanically Stabilized Earth (MSE) Walls.....................................................................12-19 Summary...................................................................................................................................12-19 References.................................................................................................................................12-20 Tables........................................................................................................................................12-22 ______________________________________________________________________________ INTRODUCTION The goal of design and construction of highway embankments over soft ground is to provide an adequate transportation facility at the lowest overall life-cycle cost (1). Life-cycle
12-2 costs include design costs, construction costs, right-of-way costs, routine maintenance costs, periodic maintenance and rehabilitation costs, operating costs, accident costs, and users' cost (1). Additionally, performance and safety (e.g., pavement smoothness, foundation stability during construction, tolerable postconstruction total and differential settlements, hazards caused by maintenance operations and potential failures), inconvenience (e.g., costs to the public resulting from closing a roadway or traffic lanes for maintenance), environmental aspects, and aesthetic aspects should also be included in a life-cycle cost analysis (1). When all of these factors are evaluated, an alternative with a higher initial material or total cost, e.g. geofoam, may prove to be the best alternative. Benefits of utilizing an EPS-block geofoam embankment or wall include: (1) ease and speed of construction, (2) placement in adverse weather conditions, (3) possible elimination of the need for surcharging and staged construction, (4) decreased maintenance costs as a result of less settlement from the low density of EPS-block geofoam, (5) alleviation of the need to acquire additional right-of-way to construct flatter embankment slopes because of the low density of EPS-block and/or the use of a vertical embankment, (6) reduction of lateral stress on bridge approach abutments, (7) excellent durability, (8) construction without utility relocation, and (9) excellent seismic behavior. In a removal and replacement situation without surcharging, the use of geofoam may result in cost savings compared to other types of lightweight fill materials and conventional fill materials because the density of geofoam is 1/10th to 1/30th of the density of foamed concrete, 1/55th to 1/145th of the in-place density of boiler slag, and 1/100th of the density of conventional granular fill material. The lower density of geofoam will have advantages over other types of lightweight fills in certain applications such as in embankment construction over existing utility corridors as occurred in the I-15 project in Utah (2). The low density of geofoam is also beneficial because seismic inertial force is proportional to the mass of the embankment. Thus, the lower
12-3 density of geofoam may alleviate the costs of soft soil removal and the possible need for an excavation support system, excavation widening, and temporary dewatering. There is a limited amount of published information related to economic assessments made explicitly for EPS-block geofoam versus other design alternatives in road embankments on soft ground. Therefore, to address the issue of economic analysis, this chapter presents the available information for EPS-block geofoam projects and compares it to cost information for other design alternatives. BACKGROUND Comparison of various design alternatives requires that an economic analysis such as a life-cycle or cost-benefit analysis be performed. A cost-benefit analysis considers the intangible consequences or impacts of an alternative in addition to the tangible costs and benefits. These intangible consequences may be required to perform an adequate cost comparison. An overview of a cost-benefit analysis is presented in (3). An approach for incorporating the intangible benefits into a life-cycle or cost-benefit analysis involves trying to quantify these benefits. For example, the benefit of reduced construction time can be quantified by estimating the value that travelers place on travel-time savings during periods of heavy congestion and incorporating the benefit into a life-cycle or cost- benefit analysis as discussed in (4). Based on traveler input from a survey performed for the State Route (S.R.) 91 corridor in Orange and Riverside Counties in Southern California, it was determined that the value that travelers place on total travel time varied from $2.64/hour for a household annual income of $15,000 to $8.05/hour for a household annual income of $95,000 (4). Reduced construction time is also important if soft ground treatment is unanticipated during the construction phase or if the section of roadway or bridge approach that is to be treated affects the critical path of the construction schedule. Remedial treatment procedures such as stabilization by preloading may require several months to more than a year to complete. Maintenance and construction costs often increase as the time available for construction decreases
12-4 (5). Therefore, some of the least costly but more-time consuming techniques have become less attractive in recent years because of shorter project times, tighter schedules, and the need to maintain traffic (5). Consequently, soft ground treatment technologies such as the use of lightweight fills have taken on an increasing role in the construction of roadway embankments. The typically higher unit cost of some types of lightweight fill materials (a "negative" cited in (5) which was prepared in the late 1980s) is usually offset by savings when all of the project costs are considered. This greater use of lightweight fills in recent years is reflected in their inclusion in the FHWA Demonstration Project 116 (6). This chapter summarizes cost data related to projects that have utilized or considered EPS-block geofoam versus other lightweight fill materials and ground improvement methods for roadway embankments on soft ground. This cost data summary along with the placement rates observed on geofoam projects in Table 11.6 are useful for performing an economic analysis of various alternatives. These placement rates can be used by contractors with little or no geofoam experience to develop reasonable bid packages instead of speculating on production rates, which usually result in an overestimate.
12-5 SCOPE An important aspect of the research was to quantify the economic advantages of using EPS-block geofoam as a design alternative compared to other lightweight fill materials and traditional alternatives such as soil fill with ground improvement techniques (prefabricated vertical drains, geosynthetic reinforcement) or a structurally supported roadway. A brief summary of soft ground treatment alternatives available for the construction of embankments and bridge approaches and the results of a questionnaire distributed during this study relating to cost issues are presented. Cost-benefit data are tabulated for geofoam and alternative designs, where available, for each case history. Additionally, cost aspects of reinforced concrete caps over the geofoam are presented. RESEARCH APPROACH Because of limited published cost data for geofoam embankments, various strategies were employed to obtain cost comparison data: ⢠Cost information was solicited via a geofoam usage questionnaire (see Appendix A). ⢠Several Midwestern DOTs (Illinois, Indiana and Michigan) were contacted in an effort to obtain cost data. These states were chosen both for their proximity to the University of Illinois and their use of EPS-block geofoam technology for road construction. ⢠Personal contacts were made with individuals suggested in the usage questionnaire replies that indicated a knowledge of cost data. ⢠DOTs, companies, and individuals referenced in relevant geofoam technical literature were contacted.
12-6 ⢠Cost data presented in the draft manual for the FHWA Demonstration Project No. 116 (6) and the National Cooperative Highway Research Program (N.C.H.R.P.) Synthesis No. 147 (5) were utilized. SOFT GROUND TREATMENT ALTERNATIVES A summary of various alternatives for treatment of problem foundations for highway embankments that have been used in the United States can be found in (5). These alternatives are also summarized in Table 12.1. Various categories have been used to classify lightweight fills. Categories used in (6) include lightweight fill materials with compressive strength (geofoam, foamed concrete) and granular lightweight fills (wood fiber, blast furnace slag, fly ash, boiler slag, expanded clay or shale, shredded tires). Lightweight fill categories used in (7) include artificial fills (foam plastics and foamed concrete) and waste materials (shredded tires and wood chips). Lightweight fills are separated in (8) as traditional light material (wastes from the timber industry such as sawdust and bark, wastes from the production of building blocks of cellular concrete, and expanded clay aggregate) and superlight fill (EPS-expanded polystyrene block). Table 12.1. Problem Foundation Treatment Alternatives (5). Characteristics and Limitations of Lightweight Fill Materials There is a significant range in material costs, engineering properties, and construction costs for various lightweight fills. The use of lightweight fill materials for embankments as an alternative to ground improvement increased during the 1990s. Although there are many reasons for this, two that appear to be among the more significant are: ⢠overall time for construction is typically much shorter when lightweight fills are used and ⢠the fact that lightweight fills produce relatively small undrained (initial) and consolidation settlements. Large undrained (initial) and consolidation settlements during construction may negatively affect adjacent existing roads, bridges,
12-7 buildings, utilities, etc. However, the use of lightweight fill materials will have no affect on the magnitude and time-dependent behavior of creep ("secondary consolidation") settlements but these settlements are significantly smaller than undrained (initial) and consolidation settlements. Creep is a function of the geometry and properties of the underlying soft soil subgrade only, and is thus independent of the external stresses applied to the subgrade. Of course, soil fill will also induce creep settlements. Cost comparisons between different types of lightweight fills should be made on the price per cubic meter ($/yd3) because of the wide variation of densities between the various lightweight fill materials (6). Equation (12.1) below is recommended in (6) for converting costs in dollars per ton to dollars per cubic meter: dollars per ton x density in kg/m3 x ( 1 ton/910 kg) = dollars per m3. (12.1) Geofoam blocks may also be priced in dollars per board foot (1 ft by 1 ft by 1 in) so conversion to dollars per cubic meter can be achieved using Equation (12.2) below: dollars per board feet x (1 foot/ 0.305 m) x ( 1 inch/ 2.54 cm)(100 cm/1 m) = dollars per m3. (12.2) Table 12.2 provides a general summary of lightweight fill material costs. As indicated in Table 12.2, lightweight fill material costs vary considerably. Factors that influence costs of utilizing the various types of lightweight fills include quantity required for the project, transportation costs, availability of materials, contractorâs experience with the product, placement or compaction costs, and specialty items that may be required (6,9). Additionally the cost of using some waste fills will be dependent on the availability of state rebate programs. Although some waste materials such as sawdust, bark, shells, cinders, slag, flyash, and bottom ash may be almost free at the source, transportation costs alone have made the use of some waste lightweight fill material uneconomical (5). The quantity required of a specified
12-8 lightweight fill type may not be available from just one vendor or source. In a project that used approximately 6,400 Mg (7,050 ton) of shredded tires as lightweight fill, four different vendors were required because no single vendor could provide the full quantity needed (10). The vendors were located about 240 to 440 km (150 to 275 mi) from the site, which resulted in a range of transportation costs. A summary of the responses to the geofoam usage questionnaire are included in Appendix A. Questions B1, B2, and B3 of the questionnaire yielded information on costs associated with geofoam projects. Bid prices provided in the questionnaire replies varied widely and ranged from $39.00 to $98.00 per m3 ($30.00 to $75.00 per yd3) (see Table A.2 in Appendix A). These bid prices include material, transportation, placement, and contractor profit. The questionnaire responses show that the placement costs range from 35 to 45 percent of the unit bid price for geofoam. For example, if the unit bid price for geofoam, which includes material and labor, is $70.00 per m3 ($53.52 per yd3), the placement costs will range from $24.50 to $31.50 per m3 ($18.75 to $24.10 per yd3). However, another respondent indicates that placement costs range from about $13.00 to $20.00 per m3 ($10.00 to $15.00 per yd3) not including contractor profit. In summary, the placement cost of EPS-block geofoam in roadway embankments can be assumed to range from $13.00 to $31.50 per m3 ($10.00 to $24.10 per yd3). This large range is probably caused by a large range in site conditions and contractor experience with geofoam. Items that were identified by the replies to have a significant impact on the overall cost of an EPS-block geofoam embankment or bridge approach are a reinforced-concrete capping slab, a facing system in the case of vertical geofoam fills, the cost of providing temporary dewatering during construction to prevent buoyancy of the geofoam from runoff that may accumulate in the excavation, the potential for a permanent drainage system, and the cost of lack of familiarity by local contractors with constructing a geofoam embankment which can result in over pricing of the geofoam alternative in the bid phase. Table 12.2. Costs for Various Lightweight Fill Materials(6).
12-9 Placement and compaction costs can be higher for some types of lightweight fills than for conventional soil fill. For example, flyash and boiler slag are moisture sensitive and therefore, moisture control is critical for proper compaction of flyash and boiler slag. Proper compaction of shredded tires may require a greater number of compactor passes than for conventional soil fill (6). Of course, geofoam does not require moisture and compaction control, which allows placement in adverse conditions. Additionally, adverse weather conditions typically do not affect placement rates of geofoam. Therefore, the higher material cost of EPS-block geofoam may be offset by lower installation costs. The difference between loose and compacted density of some lightweight fill materials should be considered in the transportation and placement costs. The wire strands exposed from tire shreds may puncture tires on construction equipment and prevent haul trucks from being routed over the fill (10). Thus the placement procedure for tire shreds may require additional measures to minimize the puncture hazard to construction equipment. These measures can result in extra placement costs. In addition, the thickness of shredded tires should be limited to 3 m (10 feet) to prevent spontaneous combustion fires. The placement rate of foamed concrete may be slower than for EPS-block geofoam. Foamed concrete placement lifts are limited to depths of 0.6 m (2 ft) to minimize the presence of voids next to structures or formwork and to minimize the development of excessive heat of hydration which can negatively affect the foamed concrete air void content (9). Additionally, a 12-hr waiting period is required prior to the placement of subsequent foamed concrete lifts (9). The placement rates for geofoam embankments projects vary from 175m3 (229 yd3) to 428 m3 (560 yd3) per day as shown in Table 11.6. The use of some types of lightweight fills may require the use of specialty items such as geotextiles, geomembranes, drainage blankets, and soil cover (6). The costs associated with the use of specialty items will depend on the specific lightweight fill embankment or bridge approach
12-10 design and these costs are not included in Table 12.2. For example, a geomembrane has been used to protect EPS-block geofoam from hydrocarbon spills. An example of a project in which an item that could not be easily quantified but had an impact on the selection of a construction alternative is demonstrated by the new Charter Oak Bridge project in Hartford, CT. The bridge opened to traffic in August 1991 (12). Although an earthen embankment with a toe berm placed in the river was the most economical solution of the stabilization alternatives considered, it was rejected because of the delays associated with the time required to obtain environmental permits (12). The lightweight fill alternative consisting of expanded-shale aggregate, which cost an additional $2 million in construction compared with the conventional earth fill/berm/surcharge design, was used to construct the east approach. A total of 62,730 m3 (82,050 yd3) of lightweight fill was utilized. As indicated in Chapter 11, the cost of the EPS-block geofoam on one bridge approach for the N.F. Shoshone River Bridge Rehabilitation project was higher than the mechanically stabilized earth wall alternative, but the Wyoming DOT utilized geofoam because of its greater speed of construction and placement in adverse conditions. EPS-block geofoam was placed in utility corridors as part of the I-15 reconstruction project in Utah because of the potential cost and time savings associated with not having to re- locate utilities or repair utilities that were left in place and damaged by foundation settlement and the accompanying service interruption (13). In summary, geofoam provides a number of intangible benefits such as not requiring an environmental permit, greater speed of construction, placement in adverse conditions, long-term durability, consistent material properties, and no utility replacement that should be considered in the design and selection process. Comparison of Lightweight Fill Material Properties Most lightweight fills have favorable Mohr-Coulomb shear strength properties (i.e., cohesion and angle of internal friction) which may increase the internal stability of an embankment and increase the overall global stability of the embankment (6). Additionally, EPS- block geofoam and foamed concrete have low Poissonâs ratio and low density resulting in
12-11 reduced lateral stresses applied to walls compared to conventional soils. Manufactured materials such as EPS-block geofoam and foamed concrete also have more uniform and consistent material properties than waste materials. EPS-block geofoam, foamed concrete, expanded shale and clay, flyash, boiler slag, and air cooled slag have a compressibility and elasticity similar to natural soil and consequently these materials will behave under static and dynamic loads similar to conventional earth materials (14). However, shredded tires and wood fiber fills have a higher compressibility than conventional compacted soils (6). Thus, this higher compressibility must be considered in the pavement design. Settlements on the order of 10 to 15 percent have been observed in various shredded tire embankment projects (15). In the U.S. Route 42 project near Roseburg, Oregon, the shredded tire embankment (10) compressed 15 percent of its initial height between January and September 1991. This compression included compression due to the soil cap, aggregate base, and pavement surcharges as well as 3 months of traffic (15). The results of the settlement plate data indicate that a correlation existed between the thickness of shredded tire fill and compression measured. Although the use of shredded tires and wood fiber as lightweight fill may not result in intolerable settlement due to consolidation of the underlying soft foundation soil, a staged construction procedure, consisting of placing the pavement at a later date, may be required to allow for some settlement of the tire shreds or wood fibers to occur. Shredded tires and wood fiber fills have a larger resiliency than geofoam and conventional compacted soils. Thus, this higher resiliency must be considered in the design and an appropriate soil cover must be placed over these materials to reduce the resiliency. A soil cover of at least 1m (3.3 ft) thick is typically placed over these materials (6). A 15.2 m (50 ft) section of embankment constructed as part of a landslide repair project on U.S. Route 42 near Roseburg, Oregon experienced cracking and rutting because the soil cap was only 0.5 to 0.6 m (1.5 to 2 ft) thick instead of the required 1.0 m (3.3 ft) (10). Thus, a thick soil cap is typically required over tire fills in order to increase the confining pressure and should be included in the
12-12 cost estimate. This resiliency also may limit the type of pavement used over shredded tires and wood fiber fills to a flexible pavement type. Falling weight deflectometer (FWD) tests were performed as part of the U.S. Route 42 project near Roseburg, Oregon after the aggregate base was placed, after the first lift of asphalt pavement was placed, and after the final asphalt pavement lift was placed (10). The results of the deflectometer tests performed after the first lift of asphalt pavement was placed resulted in the addition of 5.1 cm (2 in.) of asphalt pavement as part of the second lift. Thus, the total thickness of pavement is 25.4 cm (10 in.). Based on the results of the deflectometer tests, it was concluded that the shredded tire fill represented a softer subgrade than the in-situ subgrade. Favorable construction aspects of EPS-block geofoam embankments include possible placement in adverse weather conditions and the ease and speed of construction. Placement of EPS fill is not greatly affected by rainy weather (16) nor by cool temperatures as was demonstrated by the Route 23A case history in Greene County, New York (17). The use of conventional earth fill as well as some types of lightweight fills such as fly ash and boiler slag require favorable weather conditions to achieve proper compaction because these materials are moisture sensitive. Limitations to the use of some lightweight materials include difficulty in placing and handling such as fly ash when it is too dry or wet (6). Shredded tires may also be difficult to place because of their resiliency under compaction equipment. Sawdust and bark are difficult to compact (15). Other limitations of some lightweight fill materials include the need to incorporate protective measures to maintain good durability, to minimize leachate into the surrounding environment, and to maintain suitable geothermal properties. Lightweight fill materials need to be protected to maintain good durability (6). The surface of EPS-block geofoam must be covered for protection against long-term ultraviolet radiation. If desired measures can also be taken to protect the EPS blocks from potential liquid petroleum hydrocarbon (gasoline, diesel fuel/heating oil) spills and damage from insect
12-13 infestation. Sufficient cover must be maintained over fly ash embankments to minimize erosion of the side slopes. A potential problem associated with sawdust and bark are that they are biodegradable and need to be encapsulated by a soil cover to minimize deterioration of the outer part of the wood fiber embankment with time (15). Some lightweight fill materials must incorporate measures to minimize leachate that some lightweight fill materials may produce (6). Sawdust and bark require treatment to prevent groundwater pollution (15). Slags, cinders, and fly ash leachates may adversely affect groundwater quality or the structures in the vicinity of the waste material fill (15). Leachate of metals and hydrocarbons is a possible concern with using tire shreds. However, field study reports have shown that shredded automobile tires are not a hazardous material because the parameters of concern do not generally exceed the EP toxicity and Toxicity Characteristic Leaching Procedure (TCLP) criteria (15). Most lightweight fill materials have geothermal properties that are different from soil (6). Problems with accelerated deterioration of flexible pavements or differential icing may occur if adequate design methods are not used. Potential combustible nature of tires is a concern with the use of shredded tires in roadway embankments and caution is required during construction to avoid any fire in tires that are stockpiled or already placed in the embankment (15). In general, the thickness of shredded tires should be limited to 3 m (10 ft) to prevent fires. A suitable thickness of protective earth cover is typically required on the top and side slopes of tire embankments. As with any plastic material, geofoam is flammable (14). Fire concerns with EPS- block geofoam can be alleviated by the addition of flame-retardant during the production of the geofoam blocks and adequate seasoning times as described in Chapter 9. SUMMARY OF EPS-BLOCK GEOFOAM COST DATA Table 12.3 summarizes cost data from the geofoam case histories in Chapter 11 and the usage questionnaire replies.
12-14 It can be seen from Table 12.3 that the unit cost for EPS-block geofoam varies widely and ranges from $39.00 to $104.00 per m3 ($30.00 to $80.00 per yd3) including transportation and placement costs. In (6) it is indicated that the cost ranges from $35.00 to $65.00 per m3 ($26.00 to $50.00 per yd3) FOB (freight on board) at the plant. The EPS Molders Association provided the cost data shown in Table 12.4 in a letter dated 10 April 2001. The material cost is a function of geofoam density but ordering more than one density should not affect the price significantly beyond the cost of the higher density material. The results of the usage questionnaire indicate that placement costs range from 35 to 45 percent of the unit bid price for geofoam. Based on the I-15 project in Utah, the cost of a fascia wall system is about $10.00 per m3 ($7.00 per yd3) (2). A summary of costs associated with utilizing a reinforced concrete cap slab as a separation material between the pavement system and the EPS blocks is included in Table 12.5. As indicated in this table, the cost of a reinforced cap is relatively high and can range from 20 to 30 percent of the total project cost. Table 12.3. Summary of EPS-Block Geofoam Embankment Costs. Table 12.4. Geofoam material costs from EPS Molders Association based on 2000 business conditions. Table 12.5. Summary of Reinforced PCC Separation Slab Costs. Table 12.6 presents a list of all of the costs that could be incurred on a geofoam embankment project. This list is comprehensive and thus not all items will be required on a project. However, the large number of costs provides some insight to why the cost of EPS-block geofoam embankments ranges from $39.00 to $104.00 per m3 ($30.00 to $79.52 per yd3) including transportation and placement. Many of the costs in Table 12.6 are also incurred on embankment projects that do not utilize geofoam. It can be seen that Table 12.6 subdivides the costs into manufacturing costs, design detail costs, and construction costs.
12-15 Table 12.6. Potential Costs Associated with an EPS-Block Geofoam Project. Cost data does not exist in published literature that allows a cost breakdown to account for all of the items listed in Table 12.6. Additionally, cost information that the various DOTs provided during this study are based on unit prices that include both material and installation. Thus, a cost breakdown of separate items such as manufacturing, transportation, placement, flame and insect retardant, and connection plates could not be performed during this study. However, based on the literature search, some general conclusions can be made regarding several geofoam cost issues. ⢠Design optimization requires an iterative analysis that considers the interaction between the three major components of the embankment or bridge approach (foundation soil, fill mass, and pavement system) to achieve a technically acceptable design at the lowest overall cost. An example of this interaction is the pavement system thickness which affects both the internal and external embankment stability by affecting the applied surcharge at the top of the embankment. ⢠The selection of an appropriate cross-sectional geometry as well as selection of the volume and density of EPS block should be carefully considered during the design process. For example, the use of a fill geometry with vertical sides as opposed to the more-traditional sloped-side geometry will provide the following advantages and disadvantages:  The volume of fill material, especially of the EPS blocks, is minimized, which reduces both material cost and construction time.  The footprint of the embankment and concomitant right-of-way acquisition is minimized, which can have cost, environmental potential, and other benefits.  The cost of covering the vertical faces of the EPS blocks with some type of structural material (which can impart a significant concentrated vertical force on the soft subgrade) as well as the need for a PCC slab on top of the EPS blocks (for anchorage of road hardware) may offset some of the savings of using vertical sides. Shotcrete is often the
12-16 least expensive facing alternative when architectural concerns are minimal or non- existent. When a more-attractive finish is desired, full-height precast PCC panels are used most often and can impart a significant cost.  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 design to minimize the volume of EPS used yet still satisfy settlement and stability criteria. The selection of an appropriate EPS block density must also be optimized because the cost of EPS block increases with increasing density. For example, an EPS block with an overall average density of 32 kg/m3 (2.0 lbf/ft3) would use twice as much raw material as an EPS block with an overall average density of 16 kg/m3 (1.0 lbf/ft3) . In the U.S., raw material cost accounts for one half or more of the manufacturing cost of an EPS block so the impact of EPS density on project costs can be significant as shown in Table 12.4. ⢠End users should be aware of the fact that purchasing EPS-block geofoam through a distributor, as opposed to purchasing directly from a local block molder, generally results in a greater unit cost for the product because of distributor markup for overhead and profit. In many cases, there is no value added by a distributor. ⢠Specification of an insect deterrent will, in most parts of the U.S., restrict the number of molders that can supply a project. Because of this lack of competition and the inherent cost of the additive, the unit cost of the EPS blocks can be significantly higher. ⢠The routine use of mechanical connectors should be avoided because, while not technically detrimental, the connectors add a significant cost to a project. ⢠Typically, site preparation cannot be achieved by mechanical equipment alone so some manual labor will be required to achieve a reasonably planar ("smooth") subgrade surface prior to the placement of the first block layer.
12-17 ⢠Where possible, it is desirable to try to use EPS blocks in their full as-molded size, assuming that the blocks meet certain dimensional quality criteria for straightness, etc. Although it is possible to factory cut a seasoned block into a smaller size, such cutting can add significantly to the unit cost of the final EPS-block geofoam product. Summary of Foundation Improvement Cost Data A lack of cost comparison data between EPS-block geofoam and various ground improvement techniques exists in the published literature. However, foundation improvement techniques are generally more expensive and more uncertain than the use of geofoam or another lightweight fill. Cost data on foundation improvement techniques are included here to provide a convenient means of performing a general cost comparison between the use of geofoam and various ground improvement techniques. The cost information for ground improvement techniques was obtained from (6). Prefabricated Vertical Drains Prefabricated vertical drains (PVDs), also referred to as wick drains, are used to accelerate consolidation of soft saturated compressible soils under load (preloading and/or surcharging). The main benefit of using PVDs with a surcharge compared to only using a surcharge include decreasing the time required for completion of settlement and final construction, which increases the rate of strength gain and associated increase in stability of the underlying soft soils (6). Limitations of using PVDs include the time required for consolidation to occur even with PVDs and the magnitude of secondary compression settlements are not reduced by the use of PVDs. Table 12.7 provides typical price ranges for PVDs. A mobilization and demobilization charge of $8,000 to $10,000 is typically added to these prices. Table 12.7. Typical Prefabricated Vertical Drain Unit Prices (6). Vibro-Compaction The typical price per linear meter of vibro-compaction is approximately $15/m ($13.72/yd) when no backfill is placed around the probe and $25/m ($7.62/ft) when granular
12-18 backfill is added (6). The cost of the backfill will vary depending on the location of the project. A mobilization and demobilization cost of $15,000 per piece of installation equipment should also be added to the project cost. Soil Nailing Based on review of historical bid data compiled under FHWA-SA-96-069, the average bid price determined in (6) is approximately $380/m2 ($318/yd2) of wall. This is the average price for a soil nailed wall with a cast-in-place wall facing without a complicated architectural treatment. Architectural finishes on the facing augment the cost by $30/m2 ($25/yd2) of wall. Precast panel or timber faced walls average $600/ m2 ($502/yd2). Stone Columns The minimum cost of vibro-replacement stone column installation with readily available backfill material is $45 per linear metre ($13.72 per linear feet) and a dry vibro-displacement stone column starts at $60 per linear metre ($18.29 per linear feet) (6). Vibro-concrete columns raise the minimum cost of the column to $75 per metre ($22.87 per linear feet). Mobilization and demobilization costs approximately $15,000 per piece of installation equipment. The material cost of the stone backfill is a major component of the project and can account for over 40 percent of the estimated cost of stone column installation. Soil Mixing Based on deep soil mixing cost data from over a dozen projects completed in the last decade in the United States, soil mixing costs range from $100 to $150 per cubic metre ($76.50 to $115 per cubic yard) of volume treated (6). Mobilization and demobilization costs are about $100,000. The cost of the first lime-cement column project in the U.S. for the I-15 project in Salt Lake City is $30 per linear metre ($9.00 per linear feet). On average this is about $60 per cubic metre ($45.00 per cubic yard) or about one-half the cost of deep soil mixing construction.
12-19 However, this project was implemented under a design-build contract and therefore detailed cost information is not readily available. Mechanically Stabilized Earth (MSE) Walls The typical total cost for MSE walls range from $160 to $300 per m2 ($134 to $251 per yd2) of face. The cost of the system is a function of wall height and the cost of the select fill. Bid prices for the I-94 project constructed in the City of St. Paul, MN indicates that the bid cost was $270 per square metre ($226 per square yard) installed for an MSE wall with dry cast segmental blocks facing units and a bid price of $409 per square metre ($342 per square yard) for cast-in- place concrete walls. In general, the use of MSE walls results in savings on the order of 25 to 50 percent and possibly more in comparison with a conventional reinforced concrete retaining structure, especially when the latter is supported on a deep foundation system. The low bid price for an MSE wall with precast concrete facing units for the US 23 (I-18 Extension) Unicoi County Tennessee was $313/m2 ($262/yd2). This price included the placement and compaction of the select fill within the reinforced soil zone. The average erection rate was 60 square meters per day (646 square feet per day). For segmental pre-cast concrete faced MSE wall structures, the cost of the wall in terms of its principal components can be estimated as 20 to 30 percent of the total cost for erection of panels and contractors profit, 20 to 30 percent of total cost for reinforcing materials, 25 to 30 percent of total cost for facing system, and 35 to 40 percent of total cost for backfill materials including placement where the fill is a select granular fill from an off-site borrow source. The cost of excavation which may be somewhat greater than for other wall systems also needs to be considered. An approximate cost comparison between MSE walls and EPS-block geofoam is provided in the Utah I-15 reconstruction case history in Chapter 11. SUMMARY The case histories presented in Chapter 11 and summarized in this chapter reveal that EPS-block geofoam is cost competitive with other options for embankment and wall applications
12-20 even though the blocks have a higher material cost than soil fill material. The case histories show a cost of geofoam and MSE walls of $39 to $104 per m3 ($30.00 to $80.00 per yd3) and $100 to $300 per m3 ($76.00 to $230.00 per yd3) of wall face, respectively. The case histories show a cost of a trapezoidal geofoam embankment and a removal and replacement soil embankment of $13 to $220 per m3 ($10 to $169 per yd3) and $9 to $13 per m3 ($7 to $10 per yd3), respectively. The typical range of a trapezoidal geofoam embankment is $13 to $31.50 per m3 ($10 to $24 per yd3). In summary, vertical geofoam embankments are extremely cost-effective because they are more cost-effective than MSE walls, which are usually 25 to 50 percent more cost-effective than conventional reinforced concrete retaining structures. By comparison, trapezoidal embankments made of geofoam versus soil appear to be less favorable on a cost basis because the intangible benefits of using geofoam are not adequately reflected. These intangible benefits include shorter construction time because of faster placement rates, reduced utility relocation, or reduced maintenance costs. However, the low end of the cost of geofoam is in agreement with a soil embankment ($13 per m3 ($10 per yd3)), which suggests that if a knowledgeable contractor is available, geofoam is a cost-effective alternative to soil fill. The wide range of EPS-block walls and embankments that have been constructed indicate that a number of factors contribute to the cost of geofoam structures including material, site preparation, and contractor familiarity with geofoam. Thus, site specific cost estimates should be developed before comparing EPS-block solutions to more traditional solutions. REFERENCES 1. Ceran, T., and Newman, R. B., âMaintenance Considerations in Highway Design.â NCHRP Report 349, Transportation Research Board, Washington, D.C. (1992) 81 pp. 2. Bartlett, S., Negussey, D., Kimble, M., and Sheeley, M., âUse of Geofoam as Super- Lightweight Fill for I-15 Reconstruction (Paper Pre-Print).â Transportation Research Record 1736, Transportation Research Board, Washington, D.C. (2000) . 3. Campbell, B., and Humphrey, T. F., âMethods of Cost-Effectiveness Analysis for Highway Projects.â NCHRP Synthesis 142, Transportation Research Board, Washington, D.C. (1988) 22 pp. 4. Small, K. A., Noland, R., Chu, X., and Lewis, D., âValuation of Travel-Time Savings and Predictability in Congested Conditions for Highway User-Cost Estimation.â NCHRP Report 431, Transportation Research Board, Washington, D.C. (1999) 74 pp.
12-21 5. Holtz, R. D., âTreatment of Problem Foundations for Highway Embankments.â NCHRP Synthesis 147, Transportation Research Board, Washington, D.C. (1989) 72 pp. 6. Elias, V., Welsh, J., Warren, J., and Lukas, R., âGround Improvement Technical Summaries.â Publication No. FHWA-SA-98-086, 2 Vols, U.S. Department of Tranportation, Federal Highway Administration, Washington, D.C. (1999) . 7. Monahan, E. J., Construction of Fills, 2nd ed., John Wiley & Sons, Inc., New York, N.Y. (1994) 265 pp. 8. Flaate, K., âThe (Geo) Technique of Superlight Materials.â The Art and Science of Geotechnical Engineering At the Dawn of the Twenty-First Century: A Volume Honoring Ralph B. Peck, E. J. Cording, W. J. Hall, J. D. Haltiwanger, J. A.J. Hendron, and G. Mesri, eds., Prentice Hall, Englewood Cliffs, N.J. (1989) pp. 193-205. 9. Harbuck, D. I., âLightweight Foamed Concrete Fill.â Transportation Research Record 1422, Transportation Research Board, Washington, D.C. (1993) pp. 21-28. 10. Upton, R. J., and Machan, G., âUse of Shredded Tires for Lightweight Fill.â Transportation Research Record 1422, Transportation Research Board, Washington, D.C. (1993) pp. 36-45. 11. âProcessed Blast Furnace slag, The All-Purpose Construction Aggregate.â Bulletin No. 188-1, National Slag Association (1988) . 12. Dugan, J. P., âLightweight Fill Solutions to Settlement and Stability Problems on Charter Oak Bridge Project, Hartford, Connecticut.â Transportation Research Record 1422, Transportation Research Board, Washington, D.C. (1993) pp. 18-20. 13. Bartlett, S. F., âResearch Initiatives for Monitoring Long Term Performance of I-15 Embankments, Salt Lake City, Utah.â Proceedings of the 34th Symposium on Engineering Geology and Geotechnical Engineering, Utah State University, Logan, Utah, (1999) pp. 54-67. 14. Horvath, J. S., Geofoam Geosynthetic, , Horvath Engineering, P.C., Scarsdale, NY (1995) 229 pp. 15. Ahmed, I., and Lovell, C. W., âRubber Soils as Lightweight Fill.â Transportation Research Record 1422, Transportation Research Board, Washington, D.C. (1993) pp. 61- 70. 16. Mimura, C. S., and Kimura, S. A., âA Lightweight Solution.â Geosynthetics '95 Conference (1995: Nashville, Tenn.) Conference Proceedings, Nashville, Tenn., Vol. I (1995) pp. 39-51. 17. Jutkofsky, W. S., âGeofoam Stabilization of an Embankment Slope, A Case Study of Route 23A in the Town of Jewett, Greene County.â Geotechnical Engineering Bureau, New York State Department of Transportation, Albany (1998) 42 pp.
TABLE 12.1 PROJ 24-11.doc Method Variations of Method Berms; flatter slopes Reduced-stress method Lightweight Fill: bark, sawdust, peat, fuel ash, slag, cinders, scrap cellular concrete, low-density cellular concrete, expanded clay or shale (lightweight aggregate), expanded polystyrene, shells. Pile-supported roadway Removal of problem materials and replacement by suitable fill Complete excavation, partial excavation, displacement of soft materials by embankment weight assisted by controlled excavation, displacement by blasting. Stabilization of soft-foundation materials by consolidation By surcharge only, by surcharge combined with vertical drains, by surcharge combined with pressure relief wells or vertical drains along toe of fill. Consolidation with paving delayed (stage construction) Before paving, permit consolidation to occur under normal embankment loading without surcharge, accept postconstruction settlements. Chemical alteration and stabilization Lime and cement columns, grouting and injections, electro-osmosis, thermal, freezing, organic. Physical alteration and stabilization; densification Dynamic compaction, blasting, vibrocompaction and vibroreplacement, sand compaction piles, stone columns, water. Reinforcement Geotextiles and geogrids, fascines, Wager short- sheet piles, anchors, root piles. 12-22
TABLE 12.2 PROJ 24-11.doc Lightweight Fill Type Range in Density/Unit Weight, kg/m3 (lbf/ft3)(4) Range in Specific Gravity Approximate Cost, $/m3 ($/yd3) Source of Costs EPS (expanded polystyrene)- block geofoam 12 to 32 (0.75 to 2.0) 0.01 to 0.03 35.00 - 65.00 (26.76 - 49.70)(2) Supplier Foamed portland-cement concrete geofoam 335 to 770 (21 to 48) 0.3 to 0.8 65.00 - 95.00 (49.70 - 72.63)(3) Supplier, (9) Wood Fiber 550 to 960 (34 to 60) 0.6 to 1.0 12.00 - 20.00 (9.17 - 15.29)(1) (11) Shredded tires 600 to 900 (38 to 56) 0.6 to 0.9 20.00 - 30.00 (15.29 - 22.94)(1) (10) Expanded shales and clays 600 to 1,040 (38 to 65) 0.6 to 1.0 40.00 - 55.00 (30.58 - 42.05)(2) Supplier, (9) Boiler slag 1,000 to 1,750 (62 to 109) 1.0 to 1.8 3.00 - 4.00 (2.29 - 3.06)(2) Supplier Air cooled blast furnace slag 1,100 to 1,500 (69 to 94) 1.1 to 1.5 7.50 - 9.00 (5.73 - 6.88)(2) Supplier Expanded blast furnace slag Not provided Not provided 15.00 - 20.00 (11.47 - 15.29)(2) Supplier Fly ash 1,120 to 1,440 (70 to 90) 1.1 to 1.4 15.00 - 21.00 (11.47 - 16.06)(2) Supplier Notes: These prices correspond to projects completed in 1993 - 1994. Current costs may differ due to inflation. (1) Price includes transportation cost. (2) FOB (freight on board) at the manufacturing site. Transportation costs should be added to this price. (3) Mixed at job site using pumps to inject foaming agents into concrete grout mix. (4) Lightweight fill materials typically are characterized in the U.S.A. using the quantity of unit weight with I-P units. Therefore, the dual unit system of density in SI units of kg/m3 and unit weight in I-P units of lbf/ft3 is used in this table. 12-23
TABLE 12.3 PROJ 24-11.doc Date Location of Project Project Type Quantity of EPS- Block m3 (yd3) Unit Cost of EPS-Block $/m3 ($/yd3) (1) Approximate Placement Rate m3/day (yd3/day) Contract Value $ 1993 Wyoming Bridge Approach 377 (493) 39.00 - 72.00 (30.00-55.00) (2) - 79,732 1993- 1994 Hawaii Embankment 13,470 (17,618) - 175-250 (229-327) - 1995 Indiana Embankment 4,708 (6,157) 86.58 (66.20) 428 (560) 607,207 1995 New York Slope 3,116 (4,075) 85.01 (65.00) 382 (500) - 1995 Washington Bridge Approach 1,835 (2,400) 72.00 (55.00) - - 1995 ± Washington Embankment 411 (537) 105.94 (81.00) - - 1997- 1999 ± Wyoming Bridge Approach 146 (191) 104.00 (79.52) - 30,326 1999 ± Connecticut Embankment 321 (420) 98.00 (75.00) - - 1999 ± Maine Embankment - 57.21 (43.74) FOB Site 1999 ± Michigan Embankment 1,052 (1,376) 52.50/ 43.00 (40.14/32.88) (3) - 1,960,245/ 2,202,667 1999 ± Michigan Embankment 4,919 (6,434) 58.50/ 50.00 (44.73/38.23) (3) - 5,696,732/ 5,970,269 1999 ± Utah Vertical Embankment - 65.00 (50.00) (w/o facing wall) 75.00 (57.00) (with facing wall) 470 (615) - 1999 Illinois Embankment 15,291 (20,000) - 313 (410) - 1999 Wisconsin Slope - 61.50 (47.00) - - Notes: - Data not available. (1) Unit cost of EPS blocks includes transportation and placement unless indicated otherwise. (2)From usage questionnaire reply. (3)The lowest two bid values are reported. 12-24
TABLE 12.4 PROJ 24-11.doc Density, kg/m³ (lbf/ft³) 16 (1.0) 20 (1.25) 24 (1.50) 32 (2.00) Typical price range for flame retardant foam (Based on 2000 business conditions) $35.31-$49.70 per m3 ($27-$38 per yd3) $51.01-$54.93 per m3 ($39-$42 per yd3) $60.17-$74.55 per m3 ($46-$57 per yd3) $77.17-$88.94 per m3 ($59-$68 per yd3) Impact of volume Generally a reduction of 10-25%, volume not quantified Cutting or trimming blocks to size Up to 10% depending upon extent required Third party certification, if required 0-10% depending upon level of certification 12-25
TABLE 12.5 PROJ 24-11.doc Date Location of Project Thickness cm (in.) Area m2 (yd2) Unit Cost $/ m2 ($/yd2) Total Cost of Concrete Cap Total Cost of Concrete Cap as a Percentage of Total Contract Value 1997- 1999 ± Wyoming 25.5 (10) 88 (105) 96.00 (80.27) $8,448.00 28% 1999 ± Utah 15.24 (6) - 55.00 (46.00) - - 1995 Indiana 10.2 - 12.7 (4-5) 3,066 (3,667) 40.66 (34.00) $124,678.00 21% 12-26
TABLE 12.6 PROJ 24-11.doc MANUFACTURING COSTS: 1. Raw material price 1.1 Flame retardant chemicals 1.2 Use of low-VOC expandable polystyrene 1.3 Shipping from raw material supplier to molder 1.4 Subjective marketing factors 2. Density 2.1 Cost of blocks with increasing density. 2.2 Use of only one density versus using different product densities on the same project. 3. Manufacturerâs cost 3.1 Direct purchase from molder 3.2 Purchase from a distributor 4. Shop drawings 5. Complexity of factory cut of blocks 6. Insecticide 7. Transportation from molder to job site 8. Overall project volume 9. Project schedule DESIGN DETAIL COSTS: 1. Use of connector plates 2. Geometeric complexities of block layout 3. Wall facing system for vertical-faced embankment or soil cover for slope-sided embankment 4. Pavement system 4.1 Separation/stiffening material 5. Permanent drainage system 6. Other specialty items such as geotextiles and geomembranes CONSTRUCTION COSTS: 1. On-site handling and storage 2. Subgrade preparation 2.1 Smooth, free of large objects, reasonably dry, leveling layer (if required) 3. Use of connector plates 4. Field cutting and block placement 5. Number of different density blocks 6. Season of year construction takes place 7. Misc. project constraints 7.1 Hours allowed 7.2 Days allowed 7.3 Relationship of geofoam work to other components 8. Temporary dewatering 9. Wall facing system for vertical-faced embankment or soil cover for sloped-sided embankment 10. Pavement system 10.1 Separation/stiffening material 11. Permanent drainage system 12. Other specialty items such as geotextiles and geomembranes 12-27
TABLE 12.7 PROJ 24-11.doc Site Category Size Range m (ft) Unit Price Range Small 3,000 to 10,000 (9,843 to 32,808) $2.25 to $4.00 per m ($0.69 to $1.22 per ft) Medium 10,000 to 50,000 (32,808 to 164,042) $1.60 to $2.50 per m ($0.49 to $0.76 per ft) Large 50,000 and greater (164,042 and greater) $1.20 to $2.00 per m ($0.37 to $0.61 per ft) 12-28
