Accuracy of moles

Moles are unsteerable devices. This means that it is not possible to change the direction of the machine's work LEFT / RIGHT and UP / DOWN during the pressing. It is only possible to change the direction BACK / FRONT, through the valve in the oiler. However, the correction of the machine's course is only possible at the beginning of the pressing, before the entire machine disappears into the ground. The accuracy of the pressing will depend on how we set it at the beginning.

One of the most important elements of a mole, which has a direct impact on the accuracy of the push, is the head, or more precisely its shape. The best moles are those with a head stepped:

This head shape minimizes the possibility of the machine changing its path when encountering hard obstacles. The obstacle is broken down by the successive, increasing head diameters until the machine makes its way through hard ground along its entire diameter.

A mole equipped with a different type of head - conical head, shows slightly higher speed in performing the push. However, it loses significantly in accuracy. And it is the accuracy that is the key feature of moles. An inaccurately performed push, especially in the vertical axis, may cause unplanned high costs resulting from damage to the surface under which the push is performed. A mole with a conical head, when encountering an obstacle, most often slips on it, changing the originally set direction. A change in the angle of the mole's track by just 1^o, causes a deviation of up to 20 cm from the planned machine exit point, over a distance of 10 meters of pressing. The conical head is only good in places where we are dealing with uniform soil, with the same degree of compaction regardless of depth, without inclusions of hard structures. Such ground conditions are difficult to obtain, so it is worth always using machines equipped with a head for safety stepped. All our machines have such heads. On special request, we can make conical heads, according to individual expectations, but we definitely do not recommend this solution.

The following illustrations show how the shape of the head affects the accuracy of the push. The first image shows how the mole copes when it encounters a hard obstacle. The impact energy of the machine is so high that it is able to crush such an obstacle. For example, the MAX K130S has a single impact energy of over 400 J. This value corresponds to the situation when we dropped a 20 kg weight from a height of 2 meters.

The next illustration shows how a mole with a stepped head copes with a hard obstacle at its extreme. Segment by segment, diameter by diameter, such a head will push the obstacle out until it is completely removed from the assumed pressing corridor.

And in the last illustration we show what happens in such a case, when our mole is equipped with a conical head or when the segmented head is so worn/worn that it can be compared to a conical head. Due to its conical shape, the machine will give in to the obstacle, change its original direction and will continue to follow the intended trajectory.

In the best case scenario, when the mole escapes downwards or in some horizontal direction, we will be forced to find it somewhere near the planned target location. Worse, when the mole escapes upwards, as a result of encountering a hard obstacle. As we reach a depth above the safe depth of squeezing (depending on the mole diameter and the degree of soil compaction), the surface under which we are working will rise and a hump will be created on the road or sidewalk. The costs of removing such damage to the surface may significantly exceed our income from the implemented installation.

The situation is similar when making a mole push, the head of which shows significant wear. We show such a head below.

In this case, it is really worth investing in a new head.

Other important parameters include the correct relationship between the diameter of the machine, its length and mass, and the resulting position of the center of gravity. These parameters are optimized during the design phase and then verified during prototype tests of the machine. In our moles, during the design phase, we adopted the principle that the mole's center of gravity (CG) should be located around half of the mole's length, but at the same time closer to the mole's head than the mole's center of pressure (CP). The location of the mole's center of gravity (CG) around half of its length has a positive effect on maintaining the set trajectory during the pressing, and reduces the impact of the machine's weight on the potential possibility of deviating from the set course. Such mutual positioning of these centers (CG in relation to CP) is intended to maintain a constant set trajectory during driving, and to automatically return the mole to the set, correct trajectory, especially in the case of variable and difficult ground conditions, where we deal with different density, humidity and different types of soil. Additionally, the distance between the indicated centers is important.

This principle unfortunately cannot be applied to so-called short versions of moles. In these devices, unfortunately due to the need to provide them with appropriate energy and operating frequency, the mole's center of gravity (CG) is located at a greater distance from the mole's head than the mole's center of pressure (CP). Unfortunately, this results in the mole having a tendency after deviating from the set trajectory to sink further in the direction of this deviation instead of returning to the initially set path. Therefore, wherever the terrain conditions allow it, we suggest using standard LONG moles. Of course, it is not the case that short moles are absolutely incompetent when it comes to accuracy. Their accuracy will be satisfactory at short distances, from 10 to 20 meters, depending on the ground conditions. Let's remember what was mentioned earlier: changing the mole's trajectory angle by just 1° causes a deviation of as much as 20 cm from the planned exit point of the machine, over a distance of 10 meters of pressing. The greater the pressing distance, the more in the event of a mole deviation (due to ground conditions), this deviation will increase in proportion to the pressing distance.

The operator himself also has a great influence on the accuracy of the push, through the correct positioning of the mole at the beginning of the push, and any further corrections before it is completely sunk into the ground. Details can be found in the document placed in the tab ABOUT THE COMPANY / DOWNLOADABLE MATERIALS - Instructions for the optical set.

We must remember that when aiming, the optical set should be in a perfectly vertical position on the mole. For this purpose, we use the libella (level) (1) placed in the front part of the optical set housing (5)

After setting up the Optical Set on the mole, you should first make sure that the Level (1) indicated the vertical. Only after fulfilling this condition should the mole be set so that the crosshair (2) was at the correct height of the Optical Set Pole (3).

The accuracy of moles also allows for the construction of sewage systems, the so-called gravity systems. More information on this subject can be found at HERE.

Finally, we present our experience when working with a mole in various types of soil:

It is worth mentioning that with the participation of our MAX K130S, we won 1st place in the First Official International Pressing Competition, the so-called RODEO KRETÓW (details HERE). It was this accuracy that was decisive for our success.