Thin Ice

[CANPRO]

My parents have always drilled it in my head that ice has to be at least 6" thick before I could go skate...which was hard sometimes as a young child because I could see the older (and less supervised) kids out playing hockey on the thin ice.

I'm sure 6" is the safe number, and I'm not about to go jump around on 3" of ice...but this got me thinking..how would you go about figuring out on paper how thick the ice had to be?

I did some looking around on the internet and found a range of values for the tensile strength of ice...in the range of 1 - 3 MPa.

Any suggestions on how to do this...besides throwing the whole problem into some FEM software?

 

[shobroco]

Why did no one mention the ice bridges in the Canadian (and presumably Alaskan) north? The Mackenzie River is crossed by tractor trailers for several months every winter, governed by the engineers who regulate when, how often, and how fast the trucks can cross it. I don't know much about what they do, but when I was in university 35 years ago a couple of friends drove truck from Edmonton to Yellowknife one winter & told me about their first trips across it. Obviously the guys setting the rules aren't flying by the seat of their brothers' pants, or by their potatoes.

 

[concretemasonry]

The bridges over the ice ridges were on the larger lakes where the freezing and expansion create lateral pressure that cause upheavals or ridges that stop the traffic.

The prime example is Lake Mille Lacs is MN that is generally circular (20 miles across)and is very heavily used in the winter. On week-ends and the population can be over 10,000 for the week-end (Fri PM to Mon AM) with many people spending the full time. Many of the houses are towed out in the early winter by dozers or tractors and require 12' wide roads over where the ice happens to be. Before the ice goes out, many are slid off the lake and placed on foundation to serve as summer homes on the shores. - The homes/ice houses generally have generators, satellite dishes, TVs, refrigerators, freezers, furnaces and several rooms. I have heard there are a few 2 story ones.

There is little engineering or science in the timing, so the owners "feel" their way out by drilling holes out and fish to the desired placement and use portable shelters as they explore and go. The ultimate decision on the loads on the ice resides with the resort owners moving the loads out because of the value of the equipment used. The resort owners generally maintain and move the bridges over the ridges as they change. They are governed by the conditions as they see them and analyze then by the mile or yard.

The speeds for the heavy house loads are low (unlike the ice road haulers), but the cars and SUVs usually go at 55 maximum. The ice roads on TV usually are not traversed at high speeds and the speed is decreased when they get near shore to decrease the lateral thrust of the waves in the ice. Everything is moving and floating.

It is a unique situation and not controlled by engineers or programs, but it has worked for decades since it is flexible according to the day-by-day conditions.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[woodman88]

Attached is some information, the fourth page has minimum depths from the Alaska Dept. of Fish and Game. Done sure what the date of the information is. I got it by sreaching with "ice bridges army design" and clicking open the "ICE THICKNESS AND ICE BRIDGES" hit.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.