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Publication Number: FHWA-HRT-13-046 Date: October 2013

Publication Number: FHWA-HRT-13-046
Date: October 2013

Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support

CHAPTER 13. COST ESTIMATING

The purpose of this chapter is to present the factors that must be considered when developing a cost estimate for a DMM project for embankment or foundation support and to provide the user with a method of estimating the cost of DMM at the feasibility stage of the decision process. Cost estimating for DMM projects differs from that of conventional specialty geotechnical engineering processes because the project costs are heavily dependent on site conditions, construction methods, materials used, project performance requirements, and market conditions, all of which can vary significantly. A range of unit costs for DMM production works are provided that transportation department engineers may use to calculate reliable preliminary cost estimates for comparison with alternative technologies. These unit costs are provided for use in the preliminary stages of engineering design when limited site information is available. It is critical that engineers refine estimates based on project requirements and site-specific data. Engineers are encouraged to solicit cost estimates from qualified DMM contractors to develop more precise project budgets.

13.1 Factors that Affect DMM Costs

The factors that affect the costs of a DMM project are listed in table 21. Comments on how variations in these factors affect unit costs are also provided.

13.2 Unit Costs for DMM

Considering the factors listed in table 21, a range of unit costs may be assumed for estimating purposes. The lower and upper limits of the range reflect the general conditions outlined in table 22. These costs include production (labor and equipment) and binder material costs only. Mobilization/demobilization, QC/QA, and engineering must be estimated separately.

13.3 Mobilization/Demobilization

Mobilization/demobilization costs depend on the location of the site relative to locations of qualified contractors. Also, the size of the project dictates the number of rigs to be mobilized to a site. A reasonable suggestion for mobilization/demobilization is approximately $80,000 to $150,000 per rig for a site located up to 200 mi (320 km) from qualified contractors.

13.4 QC/QA Costs

QC/QA costs may be estimated as 3 to 5 percent of the production DMM costs. This estimate includes costs associated with the owner's tasks for assuring the quality of the work. The upper end of the range is applicable for projects with higher strength QC/QA criteria or permeability requirements less than 4.72 × 10^-5 ft/day (10^-6 cm/s) and the lower end may be applied for projects with lower strength acceptance requirements or a higher permeability criterion (greater than 4.72 × 10^-5 ft/day (10^-6 cm/s)). Pre-construction bench-scale testing may be estimated on a lump sum basis as $10,000 to $20,000.

13.5 Engineering Costs

The owner's engineering costs for conducting the site investigation, considering alternatives, designing the DMM system, developing the specifications, performing a limited bench-scale mixing program during design, and providing QA services are estimated to be about 10 percent of the DMM construction costs. The contractor's engineering costs for preparing as-built drawings, other submittals, and QC services are included in the unit costs listed in table 22.

For a design-build project, the owner's engineering costs should be added to the DMM construction costs.

Table 21. Generalized factors affecting costs of DMM projects for embankment and foundation support.

Factors Affecting DMM Costs	Comments
Type of mixing	Wet or dry.
Presence and type of environmental contamination	For the purposes of this report, the site soils for DMM work for embankment and foundation support are assumed to be uncontaminated and therefore do not require extraordinary spoils handling methods or personnel protective equipment and procedures in excess of those required for clean site requirements.
Binder materials	Using locally available conventional binders such as Portland cement, granulated blast furnace slag, and flyash result in lower costs. Transporting large quantities of binder materials to remote sites increases costs. Using higher binder/soil ratios to mix organic soils or meet higher strength QC/QA criteria increases costs.
Site access	Mixing at sites with relatively free access is less costly. Mixing at congested sites or sites with unstable platforms for equipment is more costly.
Site soils	Soils that are relatively easily mixed and free of obstructions (i.e., cobbles, boulders, or large debris) and are granular in nature cost less to mix. Stiffer/denser cohesive soils and soils containing organics/peat are more costly to mix. Predrilling increases costs.
Project size/quantity of mixing work	Unit costs ($/yd³ ($/m³)) are lower for larger projects (greater than approximately 26,000 yd³ (20,000 m³)).
Depth	Mixing to depths in excess of 25 m (80 ft) increases costs.
Application	Higher-strength requirements and higher binder injection quantities increase costs. Ground treatment applications (mass stabilization) typically have lower costs than higher strength ground improvement (load bearing columns/element) applications on the basis of cost per unit volume treated.
QC/QA	Excessively rigid QC/QA criteria or more consequences for non-conformance with specifications increase costs.

Table 22. Unit costs and associated general project conditions.

Unit Production Cost ($/m³) (includes labor, equipment, and materials)		Factors That Influence Unit Cost
Approximate low estimate (best case conditions)	$100/m³	Wet mixing is assumed. Environmental contamination is not present or is present at levels that will not affect mixing performance. Binder materials are readily and locally available. Typically cement, granulated blast furnace slag, and flyash are used. Site access is relatively free, no overhead restrictions are present, and a stable platform is available for equipment. Project is relatively large (e.g., greater than 26,000 yd³ (20,000 m³) of production mixing work). Soils may be relatively easily mixed without obstructions, cobbles, or significant peat or organic content. Typical soils would include loose to medium dense cohesionless soils, soft and wet clays and silts, and soft marine clays near the liquid limit). Depth of mixing is less than approximately 80 ft (25 m).
Approximate higher estimate (significantly more difficult site/project conditions)	$140/m³	Wet mixing is assumed. Environmental contamination is not present or is present at levels that will not affect mixing performance. Binder materials are not readily or not locally available. Materials are typically cement, granulated blast furnace slag, and flyash. Site access is congested, overhead restrictions may be present, and mats may be required to create a stable platform for equipment. Project is relatively small (e.g., less than 26,000 yd³ (20,000 m³) of production mixing work.) Soils are stiff or more difficult to mix and may contain organics or peat but are still free of cobbles and boulders. Soils may require predrilling. Depth of mixing is greater than approximately 80 ft (25 m).

13.6 measurement and payment

DMM items are typically measured and paid as indicated in table 19.

Page Owner: Office of Research, Development, and Technology, Office of Infrastructure, RDT

Topics: research, infrastructure, structures
Keywords: research, structures, Deep mixing, Design manual, Case histories, Quality control, Quality assurance, Specifications, Construction, Feasibility, Foundations, Embankments
TRT Terms: research, infrastructure, Facilities, Structures
Scheduled Update: Archive - No Update needed

This page last modified on 03/27/2014