April 2006 ISSUE
READERS' FORUM
Tunneling Article Leaves Out
Important Elements of Austrian Method
Re: Vietnam Tunnels Far, World Watch, The PEGG, March 2006.
The story states that “the design incorporated a new Austrian tunneling
method using ‘shotcrete’ . . .” It would appear that the writer
of the article has poor knowledge of the subject and has done very little research
into it.
This “new Austrian tunneling method,” or NATM, is an almost trademark name for a design philosophy, as well as an approach to tunnel construction under certain defined conditions.
This method has been around for over 40 years, and shotcrete — which has been around much longer — doesn’t have to be described in simple layperson’s terms to most engineers. As much as shotcrete is an important element of the approach, the essence of the philosophy is that the surrounding rock in a tunnel excavation becomes part of the main support around the tunnel.
Extensive and continuous stress measurements and monitoring of the surrounding rock are also key features. The shotcrete provides additional support but mainly helps to keep the newly excavated surface intact and safe.
Such a poorly researched news item doesn’t reflect well on an engineers’ magazine.
One way for The PEGG to deal with this matter is to research and write a comprehensive article about the NATM, its special features and its use and application in Canada. As far as I know, specifically in Alberta, the only use of the NATM was for the LRT tunnels below the university in Edmonton.
Readers interested in finding our more should visit http://en. wikipedia.org/wiki /New_ Austrian_Tunneling_method and http://en.wikipedia. org/ wiki/NATM.
Heinz K. Unger, P.Eng.
Cochrane
----------------------------------------------------------------
International Panel Report Represents Consensus
Re: Climate Change Correction, Allan M.R. MacRae, P.Eng., and Not a Matter of Quibbles, D.L. Barss, P.Geol., Readers’ Forum, The PEGG, February 2006.
It needs to be reiterated that International Panel on Climate Change documents are the most rigorously tested scientific documents ever produced and represent a remarkable degree of consensus within the scientific community. To quote Andrew J. Weaver, in an article published in the Geoscience Canada in September 2003, “This debate is not about if human caused climate change is happening — but rather how quickly, to what magnitude, and with what regional implications.”
The work of Dr. Richard Lindzen, quoted by both Mr. Barss and Mr. MacRae, disputes the magnitude and sign of feedback due to water vapour. In his 1990 paper he interprets feedback due to water vapour to be much less than predicted by models and possibly slightly negative.
He has since revised this interpretation. The conclusion of a chapter in Climate Change 2001, coauthored by Dr. Lindzen, concludes: “The balance of evidence favours a positive clear-sky water vapour feedback of a magnitude comparable to that found in simulations.”
Mr. MacRae’s contention that the pattern of current warming does not conform to enhanced greenhouse warming is not correct. Once again to quote Andrew Weaver: “The observed warming and large scale-geographical distribution are consistent with what coupled models have suggested should have occurred.” Minimum warming around Antarctica and in the Northern Atlantic which Mr. MacRae alludes to is due to deep oceanic mixing in these areas.
Global warming due to enhanced greenhouse effect is not a uniform, steady
process. Rather, warming interacts with existent weather patterns, amplifying
some and diminishing others.
Mr. MacRae’s assertion that
satellite data indicates that there is no long-term warming trend is no longer
valid. Satellite and balloon measurements of the lower troposphere indicate a
decadal warming of approximately 0.04 C and 0.03 C.
Mr. Barss’s suggestion that the cooling from 1940 to 1975 is aberrant, given increasing CO2 levels, assumes a linear response of warming due to rising greenhouse gas concentrations. Rather, warming or cooling is the summation of all climate-forcing agents coupled with internal readjustments. A striking level of agreement between observed warming and simulation of the global temperature can be achieved using all climate forcers, both natural and anthropogenic.
Confidence that the observed warming is real, the so-called “hockey stick” graph that Mr. Barss derides, is indicated by comparing various portions of the climate record. Warming of the southern hemisphere mirrors warming of the northern hemisphere. Ocean surface temperatures mimic atmospheric temperatures. Indirect measures of atmospheric temperature from borehole temperatures, sub-surface ocean temperature, decrease in snow cover and shrinking of glaciers provide independent checks on observed warming.
Mr. MacRae is correct: greenhouse gases make up a mere 0.03 per cent of the
atmosphere. Without greenhouse gases the temperature at the earth’s surface would be
approximately -6 C, not the current average 15 C. Water vapour is the most abundant
greenhouse gas, yet its insulating properties are not equivalent to other greenhouse
gases. Although CO2 comprises three per cent of greenhouse gases, it contributes
10 to 25 per cent of the natural greenhouse effect (IPCC 1990).
The mention of local climate change, which Mr. Barss alludes to as meaningless
in terms of global climate change, is in no way irrelevant. Rather, it is part
of an emerging picture of climate change affecting Canada.
Full accounts of the effects of climate change in Canada both now and in the future are contained in Climate Change Impacts and Adaptations by Natural Resources Canada, Threats to Water Availability, by Environment Canada, and Vulnerability and Adaptations to Climate Change, by the Meteorological Service of Canada in conjunction with Global Change Strategies International Inc.
J. Edward Mathison, P.Geol.
Calgary