Commentary

Providing cost information for ground freezing projects involves evaluation of the different components of a specific project and vary considerably depending on project location, soil conditions, potential obstructions, depth or length of the frozen earth structure and local work rules.  Unlike other excavation support or ground improvement methods, ground freezing cannot be priced as a commodity.  In other words, there are no available methods to determine the cost to freeze a unit volume of soil.  Additionally, ground freezing costs are considered to be very confidential among the small groups of ground freezing specialty contractors and are rarely published.

Other costs:

In addition to the actual construction of the ground freezing system, other costs associated with a ground freezing project are:

• Performance bond
• Additional exploratory borings and piezometer installation.
• Frozen soil laboratory tests.
• Protection of adjacent structures.
• Operation of the ground freezing system.

Definitions

Provide definitions as needed

• Formation freezing – The time required to form the frozen earth structure before excavation or tunneling can begin requiring operation of the freeze plant(s) and the monitoring system based on the design criteria i.e., frozen wall dimension and average temperature inside the frozen wall.
• Maintenance freezing – The period while the frozen earth structure is being excavated and final structure completed.  During this time, operation of the freeze plant(s) and the monitoring system.

Potential Impacts on Production Rates and Cost

An average production rate for the installation of a ground freezing system and formation of the frozen wall can be impacted from the drilling production, thermal properties of the underlying soils and lateral groundwater flow.

The following table lists items which are associated with the potential impacts on production rates and cost for ground freezing.

These items are provided for information only. Readers should carefully examine the project characteristics and constraints and determine to what degree if any these factors may influence the actual cost associated with the ground freezing system installation and operation.

Description	Potential Cost Impact
Obstructions encountered during drilling.	Drilling labor and equipment costs will increase if unforeseen obstructions are encountered increase production rates.
Variation in thermal properties of the subsurface soils.	Variability or unanticipated soil conditions can add to the formation freeze time.
Lateral groundwater velocity.	Lateral groundwater velocity approaching or greater than 1m/day can retard or even prevent the formation of the frozen earth structure.
Difficult excavation	Obstructions or any equipment delays that increase the projected excavation schedule can add additional costs to a project.  If the excavation process is slower than anticipated, the freeze will continue to encroach into the excavation resulting in slower excavation times. The heat sources in the vicinity may hinder the freezing process or affect the frozen ground, thereby complicating the excavation work and potentially increasing costs or causing delays.

Cost Information Summary

The table below provides the range and typical costs for common pay item descriptions associated with this technology.  The Commentary, Definitions, and Potential Impacts on Production Rates and Cost sections must be utilized in conjunction with this summary to complete a project specific cost analysis.

Pay Item Description	Quantity Range	Unit	Low Unit Price	High Unit Price
Engineering and Design	1	L.S.	N/A	N/A
Mobilization	1	L.S.	N/A	N/A
Drill and Install Freeze Pipes	10-3000	Per Pipe	N/A	N/A
Furnish, install, and remove ground freezing system.	1	L.S.	N/A	N/A
Freeze equipment and supervision (formation freeze)	4-12	Week	N/A	N/A
Freeze equipment and supervision (maintenance freeze)	4-100	Week	N/A	N/A
De-mobilization	1	L.S.	N/A	N/A

Typical Estimating Procedure Used for Preliminary Project Budgeting Purposes

1. Review soil strata and properties.
2. Determine excavation or improvement zone size.
3. Perform initial structural computations to determine required size of frozen earth structure.
4. Perform initial thermal computations to determine required freezing time and refrigeration capacity.
5. Determine drilling production rates and costs, including verticality survey.
6. Evaluate the need for additional re-drills based on potential freeze pipe deviation.
7. Determine material costs.
8. Determine costs to install the refrigeration plant, coolant distribution manifold, and instrumentation system.
9. Determine electrical power costs and required union manning for formation and maintenance freezing.
10. Determine de-mobilization costs.