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What is the mole

Mole, ground rocket, piercing tool, trenchless technology hammer, these are most frequently used names to call the machines we produce. Trenchless machines are widely used in water, sewage, gas, electrical and other installations. It is possible to make an underground installation using so called trenchless method without an interference with existing infrastructure by using the machines. It means, that there is no need to make a trench for the whole installation. It is quite enough to make two pits: a starting pit – the starting point of planned installation and a final one – an end of the planned installation or an and of its section.


On the picture below is schematically shown the most frequent trenchless bore job.



                                               MAKING A HOLE

                                          Starting from Start pit, aiming

                                          The final phase of installation.


Starting from Start pit, aiming

The final phase of installation.




The moles are usually used to make pipe installations under existing roads, pavements, others communication routes. Piercing machines allow to execute works with no need of partial dismantling of an existing road before the installation works and one’s renewal after. This gives the possibility to make savings of a project’s budget. Besides, trenchless technology installations allow to avoid local environment losses such as traffic jams, detours, an excessive noise. For drivers the most important is that the surface of road stays untouched.

We are aware that every intervention of existing road’s monolithic structure will sooner or later require regular maintenance in places where the consistency of the surface has been breached. On pictures below shown some examples of locations where an installation works were made using traditional open excavation method.



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At every location shown on pictures should be used a trenchless technology. However, due to a traffic load, a bumps start to appear on a road surface. They gradually become bigger and at some future time the road needs to be closed for repair. It was quite enough to use mole instead. The potential of the simplest but the most effective trenchless tools, namely, moles is presented below.




A source of compressed air will be required to power the mole. For this purpose mobile compressors on a wheeled chassis are most frequently used. The larger piercing tool the greater air consumption it has. Strong, powerful moles require an amount of compressed air that could be supplied by popular modern air compressors available on the market. Standard set of equipment for trenchless piercing is presented on the illustration below.





Impact moles are used to make a boreholes. They are also capable of plastic pipes pulling and steel pipes ramming. There are a lot of additional accessories allowing to make almost every installation using trenchless method. Typical installations and diameters are presented in below tables. Click on a table to zoom in.


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The drilling speed is depending on ground conditions and the size of the mole. Nonetheless, it can be said, that average drilling speed is 0,5-1,5 meters per minute. Usual length of a mole bore is 8-20 meters, although, it is possible to make an aimed bore through a distance more than 40 meters long. It depends on operator’s experience and knowledge.



Piercing works with mole have to be done at an appointed minimal depth. Generally, it should be at least 10 times more than machine’s diameter. This indispensable condition arises from the fact that the mole does not squeeze the soil ahead but it compacts the soil around a borehole. In case of heavily compacted hard soils the less depth could lead to surface distention. The maximal installation depth depends on individual design project.

Impact moles are non-steerable machines. It means that the machine can’t be controlled during the work underground. The only way to aim the machine properly is to adjust its position before the whole machine will sink underground. However, an operator should not be afraid of aim declination after the mole was properly set in starting pit. The construction of impact moles is so developed, that it is possible to use them in extremely hard ground conditions. Ran against an obstacle, the mole rather destroy it then decline the specified trajectory. A starting platform could be definitely useful for the beginners. It is a simple device, that makes aiming much more easier. Aiming and positioning itself is realized with a help of optical set which consists of spyglass and surveying rod.



Piercing works are most frequently performed on short segments, up to 10 meters. However, the good, accurate machine, can easily cope with a much longer distances, reaching up to 30 meters and more. However, it truth be told, accurate piercing work on a long distance requires reach experience.

The mole basic set itself allows to perform solo boring from the start pit to the end pit. The basic set consists of the following elements:



     Pneumatic impact mole


    Lubricator with controls


     Pneumatic air hose

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Tools and supply materials

A manual pulling tool, presented on a picture below, being secured on an air hose allows to pull a PE/PVC pipe diameters up to 55 mm into the mole’s borehole.


Most often moles are used to pull casing pipes, directly behind the machine. For this purpose, the mole should be equipped with a pipe pulling sleeve fastened to the rear of the mole. The sleeve of corresponding size should be used. For pipes of larger diameter, typically 90 mm or more, an additional system is used. The system includes steel rope and a tensioner and guarantees a reliable fastening of the pulled pipe inside the pipe sleeve. Smaller pipes only require using of a sleeve provided with a specially shaped slot for attachment of the inserted pipe into it. Here is a photo with examples of accessories for pipe pulling directly behind the machine.





It may happen a situation when we need to make a solo bore or install a plastic pipe, with a diameter bigger than the diameter of your machine. Manufacturers of impact moles meet the challenge by offering so-called expanders, also known as calibrators. These are steel cylinders ended with cone, having a diameter bigger than the diameter of the mole. At first, a pilot bore should be made by the mole, and then its diameter could be extended by performing re-boring with fastened expander. Of course, the easiest way to realize such an installation is to purchase the machine with a bigger diameter, that allows a retraction of bigger diameter pipes directly behind the machine. Not always, however, the purchase of a larger machine has an economic sense. It depends on the amount and frequency of such works. If you install large pipes sporadically, it is cheaper but more difficult to install them using an already owned, smaller machine, armed with an appropriate calibrator.






The impact mole can also be used for steel pipes ramming. These pipes are used in water – sewage systems as casing for secondary installation, or directly as supply pipes. A set of cones is needed for this type of trenchless works. With a help of these cones the mole is tightened with previously prepared for ramming steel pipe. In some soil conditions, such as muddy and wet clay or other wet soil, it is impossible to perform the installation by pulling of PE / PVC pipes. Is those cases ramming of steel pipes is recommended alternative.






Smaller steel pipe are rammed with a steel cone plugged from the front of the pipe. Larger pipes, with diameter from 159 mm, are rammed open due to the resistance of the soil during pipe’s movement. Being installed underground, the pipe should be cleaned by blowing the soil out with blow-out plugs and foam pistons. It should be added that apart from impact moles, characterized, as you could see, by a high flexibility, there is a group of machines, dedicated exclusively for hammering of steel pipes. We're talking about pneumatic hammers. Their construction is much simpler and does not have to ensure accuracy. Hammer itself, does not move in the soil, its role is push ahead, ram steel pipe.


A group of moles with so called reciprocating head are available on the market. However these machines are not dedicated to ramming of steel pipes or to work with expanders. It is worth to remember if you are looking for an effective, universal solution.

Like any machinery, impact moles require periodic maintenance. It is necessary to save the reliability of the machine for years. Good machines have a lifecycle up to 10 years of operation. Some elements of the mole, are subjected to high loads and require a periodic replacement. Well-designed machines, reduce to a minimum the costs of maintenance and repairs, because that parts and elements of the machines that are subject of wear are not a monolithic structure but separate details, assembled together. The  proper approach to the machines during a service is very important. A good company provides service at the highest level, where every machine is treated individually with a diligence and a commitment.

Good machine is one that meets all the user’s expectations. We purchase impact mole for many years. It is worth choosing the appropriate machine for your own works. It is worth studying other users opinion concerning the machine. A good impact mole is the one which you could acquaint with by testing in natural conditions of a construction site, before making the final decision about purchase.

Moreover, good machines should be characterized by high level of job security, ease of use and should be environmentally friendly.



The experience and knowledge, enabling effective implementation of even the most demanding trenchless works in difficult ground conditions, gains over the years. Machines that currently commercially available are so user-friendly and easy to use that even a beginner at trenchless earthworks, should have no problems with the typical water supply connections, or other commonly performed works. There are some periodicals on the market dedicated to trenchless techniques, Internet network is rich in numerous publications and forums. So, there are places, where to get theoretical knowledge. So as practical. There is a very good initiative among producers and distributors to organize a training on a client’s construction site, where a customer receive practical knowledge in operation and maintenance of the machine. Usually, such training are accompanied with handing over a machine from producer to a customer. Using of devices that make easier a precise aiming of an impact mole could be helpful for beginners. These are a starting platform and an optical set.







It could be initially difficult to choose the right machine for client’s needs considering the amount of manufacturers and products currently available on the marker.  Beginning our acquaintance with trenchless technologies, it is difficult to define challenges of the nearest future. It is better to send qualifying questions concerning client’s expectations directly to the manufacturer or distributor. Through a series of questions, it will help to choose a set according to individual preferences, taking into account economic aspects of purchase also.

But there is a universal set of desirable features that should have any trenchless machine, that is common to all devices of this type. The most important features are:


Accuracy. This is undoubtedly the most important feature of trenchless machines. Missing target during trenchless work may lead to significant costs in consequence to the necessity of repairing the damaged infrastructure. Most of machines, considered as accurate, that are currently presented on the market, have stepped shape of the head part. This solution minimizes the potential consequences of mole’s collision with extremely difficult obstacles. The proper length and machine’s balance is very important for mole’s accuracy. Constructing an impact mole, manufacturers consider accuracy as the most important parameter.


Design and durability. Features that ensures long-term using of an impact mole. It is worth to purchase a machine with simple design, that is resistant to extreme working conditions. Materials with increased resistance to stress, metal fatigue, corrosion, the effect of friction in the ground should be used for the production of moles. Many of well-known manufacturers apply simple and easy replaceable sliding and sealing elements that assume itself effects of work and friction in difficult conditions including contaminations by loose sand, water and mud. Such a design solution requires periodic replacement of these elements, but it eliminates the necessity of expensive regeneration or replacement of basic mole’s parts, damaged by friction. It is worth to pay attention if external parts of the mole create a monolithic block, or it is possible to dismantle individual parts, allowing changing of only one. This significantly reduces the cost of servicing the machine. 


Ease of use. It is worth to have an impact mole that could easily and quickly change its working direction in any circumstances. A technical solution called pneumatic steering satisfies that condition best of all. It is based on remote change of machine’s working direction from forward to reverse and vice versa by changing the position of control valve handle on a lubrication control station. Other operations are not required for this purpose. Unfortunately, there are situations when the machine encounters a difficult obstacle and does not have a possibility to continue the work in a given place. An urgent necessity to withdraw the mole may appear for many other reasons. It is worth to have such an ace in the hole as the possibility of quick mole’s withdrawal, without having to close the air inlet supply.


Eco-friendliness. Modern piercing machines can be freely used in all kinds of terrain, even in areas covered by the specific regulations of environmental protection. Such places include parks, direct water intake areas, other public places. Original design solutions, materials and technologies being used for the production, allow the use of harmless lubricants based on glycol to lubricate a machine.


Functionality. The scope of works, that could be realized by a given machine, depends on its size. Generally, it is possible to install plastic pipes with diameters up to 200 mm with the help of typical piercing machines. Moles allow for the ramming of steel pipes up to a diameter of 406 mm. Fixed head moles are widely used. It is possible to effectively realize steel pipe ramming and to work with expanders. According to the opinion of a part of users and some manufacturers, moles with fixed head cope better in typical soils, compared to machines with active head. Besides, fixed head moles, have less moving parts to wear out, so it decreases maintenance costs.


Practical use of moles is presented on the following examples.


1. Building to building installation



Let’s imagine that a building to building installation of the Internet cable should be made and, for some reason, it is impossible to perform it in the form of an aerial line. Such line could be polluted by birds while roof transceiver/receiver equipment could be devastated by cats. Using a mole, just go down to the basement level of the building, carve a hole in the wall and start a mole in it aiming neighboring building’s basement wall. As soon as the mole reaches the target it "knocks" to the wall of a neighboring building, marking a place for executing of a hole through which a casing pipe for the cable line could be installed.

In this case, we have an alternative in the form of an  open trench, but why should we use it, if we have moles, accurate moles.


2. Time for rails




In this case, there is no way out. Nobody will allow to close a railway, even temporarily, to make an open trench installation. So, the mole or another trenchless technology machine is the only choice. But any other machine is much more expensive so the installation cost is correspondingly higher. Moles are the cheapest equipment for that type of work. And the most effective one


3. Intersections



Construction or renovation of street lighting system, without the proper methods of implementation, may cause many troubles. The use of traditional methods, certainly will significantly increase blood pressure among customers that use the closed section of the road every day. Traffic jams, problems with access to work and back home, wasted time, fuel, money, bad mood accompanying pre-arranged visits’ delays, sadness on the faces of our children, been picked-up from of kindergartens and schools with tardiness. These are losses that difficult to calculate and hard to fix. Using of accurate mole may prevent situations mentioned above and no one will close a road for us the during the installation work.


4. Usual road



Here is typical, the most common installation. Even there, where road closing probably will not cause much inconvenience, the costs and time of installation convinces us to use trenchless technology machines such as impact moles. 


5. Steel pipes



It rarely occurs that there is a need of steel casing pipe installing according to the project documentation. Being multifunctional equipment the mole can easily cope with this type of work. Depending on the place available for the starting pit, pipe can be in one piece or divided into sections, welded together during the assembly of each subsequent section.


6. No way out situations



Here is an entrance to the center of a big city. An expansion of the existing road infrastructure causes an expansion of the existing retention system, a new network connection to the existing water storage. Trenchless techniques limited traffic problems to one of the three lanes only. And even this reduced the traffic flow. We could only imagine what would have happened here if the entire road is closed?


7. What do we have here?



We do not know why this part of the installation was made using open method here. A mole have been used on other sections of the installation, running under paved surface. Why have not been used at this section? Probably, there was no space for final pit. However, so-called pneumatic reverse moles can be withdrawn and picked up from the starting pit.


8. Property entrance



The new installation was built along the existing roadway and under the driveway to a property. An impact mole allows to make an installation without any embarrassments for the property owners in getting to it.


9. Vertically is also possible



In African countries, our moles are used for the so-called micro-piling (reinforcement of bearing capacity of building basements by vertical steel piles ramming it a predetermined depth where piles are coupled with a basement).


10. You can do more with accurate impact mole



Properly balanced, accurate moles enable to install multiple casing pipes next to each other without any problems. We can see an installation of two parallel casing pipes on the following photo. Just remember that the mole operates on the principle of soil compaction while moving under the ground.  Depending on soil conditions, you should leave some space between pipes that are installed.


11. To/from the median grass strip



We should not have any problems in the case of dual carriageway roads with grass strip separating them. In addition to start pit and end pit you should make a middle pit on the grass strip, make a first bore to it as a first stage and start the second stage of the installation beginning in it.


12. What about winter?



Good impact moles usually work well in sub-zero outside temperatures. To prevent mole’s freezing in extremely low temperatures, a compressed air heater is used. Please contact our Sales Managers about the heater. It will be available in our commercial proposal soon.


13. Mud bath



Modern engineering solutions allow mole’s work, even in such hard conditions. Interchangeable sliding and sealing wear elements, ensure protection of mole’s moving parts from negative effects of water, sand, mud. Moles without interchangeable sliding and sealing elements when working in these conditions could have damages of the moving part’s surfaces due to metal to metal contact. It will significantly shorten the life of such moles. The impact energy of machines will also gradually decrease due to the formation of a clearance gap between mating parts. The larger clearance gaps will be the higher demand for compressed air will have the machine without teflon elements. It can be seen on a rising speed of a compressor’s engine. Of course, it will affect the cost of installation. In impact moles that use teflon technology, it is enough to equip a mole in a new set of interchangeable sliding and sealing wears, and we will have a machine acting as good as new. That is why life cycle of moles that use teflon technology in its construction reaches 8 years or more, even with heavy use.




TERMA Sp. z o.o.
Czaple 100
80-298 Gdańsk

 +48 607 451 268
ilustracja +48 607 451 268





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