With the development of the various trenchless technologies over the past 30 years, many of the applications and product developments have occurred in the largely developed regions of Europe, North America and Japan.
While most of these areas have what is generally termed temperate climates with mostly moderate climatic variations, there are other areas that have large temperature variations throughout the changing seasons of the year. It was only once many of the technologies were developed and used in moderate climate conditions that thought was given to how the systems would react in more extreme, less hospitable climates of heat or cold.
With the forthcoming International No-Dig 2008 conference in Moscow, a significant contingent of visitors is expected from the local Russian regions that can experience some of the most extreme cold weather conditions on the planet. The applicability of trenchless technologies developed for use in more temperate climates, therefore, has to be carefully examined and any relevant precautions taken before any use can be considered in the extreme cold conditions that these regions experience.
The following is an overview of some of the comments from industry operators and manufacturers who have experience in the field covering some, but probably not all, of the problems that may be encountered when using trenchless systems in cold climates.
It might seem odd to think that equipment that is largely made of steel would have much problem in cold climates — unless you have never touched exposed steel with bare skin on a very cold day. Apart from the obvious, there are some aspects of using such equipment that need to be taken into account to ensure an efficient and, more importantly, safe operation.
Yet, surprisingly perhaps, for both installation and renovation techniques there were found to be circumstances in which working in very cold conditions could be advantageous.
For microtunneling in places like Canada, northern Russia and at higher altitudes in many mountainous regions around the world, there may be fewer problems than might be expected. One respondent noted that when working on a project in Canada in winter using both slurry and auger microtunnelers, the auger system had many advantages. As long as the drive was more than 3 m deep, the conditions in the shaft were warmer and fairly constant and the ground was not frozen at that depth, so conditions in the shafts were pretty good. For both the auger system and slurry system, the drive shaft and main control container were tented with a heating facility inside, making working more comfortable.
When using the slurry circulation system, this too was tented and background heating was installed. When circulating the slurry, as the ground in the drive was above freezing, there were no particular problems. However, there could be a problem once the system was shut down for the night. Maintaining a continuous slurry bypass can prevent freezing overnight, although this may impact costs.
In terms of the power units, anti-freeze was used in the cooling water for engines, and oils and greases designed for cold climate use were the norm. With clever sighting, the heat from the power units could be used to keep water-based consumables warm too. Spoil dumps need to be carefully sighted because wet loose material freezes rather than flows and forms a pointed heap rather than a gentle pile. So, minimum modifications are required overall to equipment but plenty of common sense is required for the sighting of ancillary equipment and onsite materials.
In the HDD sector, there are several basic precautions that can be introduced such as engine anti-freeze, pre-heaters, heaters for hydraulic systems, the correct specification lubricants, etc. Beyond this, however, there are also a range of technology-specific items that should also be considered.
If pre-heaters are not available, it may be judicious to let motors run 24 hours per day — but with the current targets for carbon emissions, this may not now be politically acceptable and can be costly. Engine sets can be placed into containers where, when using pre-heaters, they are much more efficient as there is much less exposure to the elements in general. It has also been known to utilize steam generators to heat driver cabins and other containers, as well as heating the drilling fluid systems to maintain temperatures above zero.
As a protection to the workforce, it may be advisable to tent the working area around the rig to limit personal exposure to the weather, as well as providing a cabin for the rig operator. It should be remembered that without a healthy, attentive and responsive crew, even a well-protected machine will not be able to work. Special attention must be given to the operators. Frozen drill rods, if handled, can inflict serious contact damage to bare skin and personnel using location guidance equipment are fully exposed to the cold. In severe conditions where visibility can deteriorate rapidly, life lines should be considered.
The relatively recent development of remote guidance systems for HDD may go some way to easing this problem, as it may be possible to place the receiver antenna outside without the need to have constant monitoring by an operator.
In terms of the drilling fluid itself, one respondent said that investigations had been made into whether anti-freeze could be utilized as a constituent of the drilling fluid make up. This, however, had been found prohibitively expensive in comparison to the cost of protecting the fluid systems and using heaters. A drilling fluid at above zero temperature running through drill rods also means that outside
temperatures do not really affect the drilling rod once it has been connected.
There was also agreement that despite the near surface ground being frozen, most drilling work at the cutterhead was in frost-free ground, so there is generally no need to use hard ground bits unless local geology dictates it. Installation of a guide sleeve at the start of the bore, through the frozen ground, is also good practice and some thought must be given to the way in which the drilling fluid emerging from the bore can be kept liquid for recovery to the recycling plant.
One respondent claimed that in some regions working in winter conditions was actually a bonus. This was because in summer conditions the surface frost layer tended to melt, making access with heavy equipment far more difficult than when the access was frozen.
The questions also arises how does plastic pipe behave when it gets very cold? According to a well-recognized and respected plastic pipe manufacturer, tests have shown
that PE pipe retains a degree of flexibility down to temperatures as low as -60 C. But at temperatures below 20 C, pipes become stiffer, although the pressure rating remains the same. As the temperature falls below 20 C, the minimum safe bending radius starts to reduce and the tensile forces in the pipe begin to increase. The recommendation appears to be that pull-in load limits of a level for a pipe working at 20 C should not be exceeded. It was also suggested that tenting the whole pipe length when laid out on the surface might be advantageous.
Care should also be taken when joining pipe lengths together by butt or electrofusion. Most techniques and equipment are designed assuming they will work within a specific temperature range. Details for individual pieces of equipment and systems should be checked and for any circumstances that may fall outside these design ranges, advice should be sought from the relevant manufacturer or supplier of both the equipment and the pipe. Further recommendations are that as temperature drops and pipes become stiffer, their impact properties also change; so handling should be done with care to avoid creating temporary small support contact areas or impacts with edges or sharp points.
Individual pipe manufacturers will be able to advise how any particular pipe behavior will change with temperature, how they should be jointed and what consideration should be made when jointing into existing or different pipe materials and they should be consulted early. They will also be able to advise on any specific testing that could be done to monitor pipe characteristics and therefore potential performance changes in any given situation.
Changes in characteristics will also apply to plastic pipe being used in fold-and-form lining situations so that temperature conditions should be considered by pipe replacement and renovation contractors and planners when these techniques are being considered — which brings us to the other side of the trenchless technology fence, on-line replacement.
In terms of on-line replacement, the basic equipment precautions used for installation systems outlined above should be applied. The simple test to know if pipe bursting will work is: If the pipeline is located below the frost layer, it should work. If it is not and the pipe is within the frost, it probably won’t. This is because a pipe encased in frozen ground is more or less the same as a pipe encased in concrete. If the replacement is below the frost level, the normal pipe bursting considerations apply although advice is needed if the replacement depth is close to the frozen layer which could affect the displacement characteristics of the soil and the behavior of displaced pipe shards during bursting.
Cold climates are known to have an effect on CIPP lining systems, particularly in regard to resin mixing and pumping, although this can often be accommodated with the use of heated facilities. Handling of impregnated tubes and the like can be difficult, as they stiffen in the cold and some liner coatings become brittle at low temperatures. There is a benefit in that the cold delays curing and can make transportation of the impregnated liners less worrying. A careful study of the complete installation route from plant to site to benefit from all these different temperature effects will pay dividends.
Water provision, inversion and circulation can also be a problem. Pipe cleaning will have to be considered as a separate project in its own right since it involves substantial volumes of water. For curing the liners in cold ambient conditions, the exposure of boilers and boiler hoses to low temperatures increases the losses due to wild heating and can put a strain on boiler capacity, making it difficult to achieve target temperatures. A very thorough heat loss estimation and balance is essential and the insertion of thermocouples in the lining for quality assurance purposes will increase the customer’s confidence that the correct curing temperature has been achieved. For example, some resins can freeze solid in extremely cold temperatures below -20 C and resins tend to need heating to around 15 C to ensure proper impregnation of liners. This can mean that if a resin tanker is being used and is left unprotected the resin has to be preheated prior to delivery.
But there are some cold condition advantages. During the installation, operators have more time to work with the impregnated tube than they would normally. In terms of site operation, with most, if not all, precipitation being snow, the risk of unexpected flows in storm water pipelines is virtually zero and this may eliminate the need to establish a flow bypass system on any individual pipe length during renovation. Further, depending on local groundwater conditions and the depth of the frost zone from surface, infiltration may be eliminated, as there is no free running water or a very reduced groundwater level. This may affect the choice of liner material or installation technique at any given site.
In terms of project costs, there can be additions that need to be considered such as increased fuel consumption (possibly as much as 25 percent) to run trucks full time to ensure they remain operational, which significantly increases equipment general wear and tear and maintenance costs. Where equipment uses water, such as vacuum trucks, jetters and boilers, they may have to be drained and a facility to keep them inside, particularly overnight, needs to be available.
When working outside with water, it needs to be constantly circulated to prevent freezing, which in turn requires that power/drive units have to run longer and faster to run pumps full time. With water passing through hoses, there may be a tendency for the water to start to freeze, which can cause pump damage so shortening the working life of a unit. In some cases, equipment has to be modified to ensure that low points can be fully drained to prevent freezing damage. Furthermore, braking systems, tires and cold weather systems like tire chains may be needed simply to gain access to sites. To ensure motors run correctly, diesel conditioner has to be used as well as non-gelling winter fuel. In some instances, the starting of electronic equipment in cold conditions can cause damage to the electronics.
Finally and probably most important of all is site safety. With a site that can become very icy, and operators who are dressed to withstand the weather conditions and so therefore possibly less able to handle and operate equipment through gloves, and in lower light conditions (particularly at higher latitudes), the potential for simple mishaps increases. Good training, supervision and a constant awareness by individuals for themselves and those around them has to be instilled into the workforce from the outset to ensure successful and safe project completion.
ISTT would like to thank the following for their invaluable input into this article: American Augers, Ditch Witch, Herrenknecht, Insituform Technologies, Jason Consultants, Tracto-Technik and Vermeer Corp.
Ian Clarke is a freelance writer and owner of No-Dig Media Services, based in the United Kingdom.