Ice Thickness – Measurement & Reporting
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Ice Thickness – Measurement & Reporting

Measuring Ice Thickness Construction of ice bridges and ice roads has unique safety hazards because of the danger and risk of ice failure. To mitigate this risk for those working on the road as well as for the travelling public, strict attention must be paid to ice thickness measurements especially for load bearing capacity analysis of the ice.
The following section provides guidelines on how to measure the ice thickness and for selecting the ice thickness to be used to determine the capacity of the ice to carry loads. Experience in ice profiling has shown that the ice thickness within a natural ice sheets can vary by as much as 70% of its average thickness over just a few 100 meters. Therefore, it is very important to gather and record sufficient information about the thickness of an ice road to determine its load capacity or delineate thin ice areas. The number (density) of ice thickness 19 measurements is a key factor in determining the confidence level in the overall ice thickness to be used to calculate allowable loads.

A historic method for determining ice thickness is to manually drill holes at prescribed intervals in the ice sheet and use the measured minimum ice thickness to determine bearing capacity. This method provides a low density of coverage and is normally acceptable when the ice thickness comfortably exceeds that required to support the specified load.

Newer technology supports Ground Penetrating Radar (GPR) ice profiling, which provides significantly more ice thickness measurements compared to manual drill holes. This method provides a very high density of coverage and consequently provides a much higher level of confidence that thin ice zones over a given area have been detected. The level of confidence in the ice thickness is an important consideration in calculating the allowable bearing capacity of the ice. Currently GPR is the primary method for ice thickness measurements.

 

Measuring ice thickness with ICEMAP GPR unit

ICE HAZARDS

The main hazards of operating on ice covers are:

  • Operating on an ice cover that has been damaged or where the
    integrity of the ice cover has been compromised (this damage could be
    localized or widespread)
  • Overloading an ice cover beyond its capacity to support a load
  • Undetected areas of thin ice layers

These hazards can be controlled through a variety of engineering and
administrative controls that will provide operators overall confidence in:

  • the integrity of the ice cover
  • the knowledge of the load that is to be placed on the ice cover
  • the minimum ice thickness present

With confidence in these three elements, operations on ice can be carried
out very safely.

Ice Integrity Hazards and Controls

Any ice cover can develop cracks by thermal contraction, ice movement or
frequent loading on the ice cover. Minor cracks do not necessarily indicate a
loss in the load-bearing capacity of the ice. However, during spring thaw or in
areas subject to excessive damage, the load bearing capacity of the ice may
be negatively impacted. The main features affecting ice integrity are:

  • Dry cracks
  • wet cracks
  • snowbanks
  • thermal contraction cracks
  • thermal expansion cracks
  • warming ice
  • high winds
  • water level changes

Recording And Reporting Ice Thickness Measurements
The ice thickness survey and inspection data must be recorded in the log book or recorded electronically to enable review by supervisors if
required. The records will be filed as part of the permanent record and will be made available to senior department
officials. These records will be held on
file for a minimum of 5 years. It is very
important that the log book is filled
out accurately and in a professional
manner. In addition to the distances and
thicknesses, the following information
must also be recorded:

    • date of test
    • time of start and finish
    • names of testing crew
    • air temperature during testing
    • the presence of wide, wet cracks and other significant cracking
    • details of load reductions and/or traffic detours
    • location, i.e., Peel, Mackenzie at Arctic Red, Tsiighetchic Branch at
      Mackenzie, Liard River, Aklavik, Tuktoyaktuk, etc.
    • general ice and road conditions
    • printed name and signature

For GPR profiling results, — all electronic files shall be saved for a minimum
of 4 years.

Monitoring and Reporting

A key component of any operation on ice cover is the frequency and nature
of inspections that are required for Quality Control. Section 5 of this guide
outlines the minimum frequency and nature of inspections required.
This section identifies in detail the requirements for reporting of ice thickness
measurements, visual inspections, road opening dates, weight increases, and
other advisories.
The following reports are to be completed regularly and retained
at Regional offices:

  • ice condition / thickness log book
  • ice thickness reports from manual ice measurements
  • GPR Ice Profile raw data and electronic files including any ancillary
    information used for analysis/decision support (e.g. core information,
    start/end position).
  • ice cover inspection reports
  • road opening and crossing opening and closing announcements
  • allowable load increase announcements