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The Tower of Pisa is indeed a famous monument. Yet, it is also a monumental error of civil engineering. Built in 1173 with no foundations on a flood plain, the white marble tower started tipping on its southern side even before it was completed. Its peculiar inclination is like a spectacular warning to all builders around the world.


Yet, people have studied the ground under their feet, way before the 12th century. They have done so ever since they started extracting rock, building houses and bridges and digging irrigation systems. At first purely empirical, soil investigation has been rationalised since the 17th century and has given rise to geotechnics, a technoscience combining geology and geomechanics.   

Today, the most frequently used measurement instrument in geotechnics is the penetrometer. “Imagine it as a giant hydraulic press that digs a measurement cone in the ground…” explains Paolo Bruzzi, Pagani Geotechnical’s sales manager. The Italian company, whose factory is based in Piacenza, near Milan, has become a global leader in the field of geotechnical equipment.

Penetrometers render high-fidelity images: “Our equipment detects layers - sand, clay or other - as thin as 10-15 cm.” Enough to make reliable estimates on soil behaviour when building a road or a bridge, digging foundations or simply setting up the pillar of a ski lift.

As for all measurement instruments, the quality of penetrometers depends on their reliability. “The system verifies itself its accuracy after every measurement”, explains Paolo Bruzzi. “Incoherent data would immediately signal that the cone had been damaged. So, we can be sure that our measurements are always absolutely precise.” Furthermore, the cones require mandatory calibration every year, a further warranty of correct measurement. Material and processes are standardised defacto on an international level. The cone sizes, the forces applied, the penetration speed … everything is defined to enable traceability, repeatability and data sharing.

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Penetrometer tests can be used for other types of measurements as well. In particular, for seismic measurements.  “In such cases, we stop penetrating after every meter and create a seismic wave from the surface” explains Bruzzi. “Its amplitude and propagation speed is measured by a sensor on the cone, which makes it possible to evaluate the soil’s behaviour in case of earthquakes.”

Anecdotally, the “elastic” soil, isolating the structure from earthquakes, which provoked the tipping of the Tower of Pisa, also protected it from several earthquakes.

The instant results obtained by the penetrometers have greatly contributed to the popularity of these instruments. Carried out in situ, the tests do not require any soil sampling, nor waiting for laboratory analysis results. “They disturb the soil much less than core drilling, so they are less likely to influence the results,” says Paolo Bruzzi.

Whether disturbed or not, ground is not easy to deal with. The equipment must possess huge power to drive in a cone. “In the past, the only solution was using heavy duty trucks, up to 20 tons” recalls Bruzzi. “Such trucks are still used in certain cases and they usually cost in excess of 400,000 euros, require a heavy vehicle driver, an entire team and, since the measurements need to be carried out vertically, a flat, large enough piece of land …”

In a nutshell, a costly and constraining solution. The idea of developing an alternative is how the story of Pagani Geotechnical began.

It all started back in the seventies in Italy. As building requirements were being strengthened, Ermanno Pagani created his geotechnical consulting company. Tests became widely used and the entrepreneur realised that engineers were increasingly using heavy trucks for projects that were much smaller than building bridges or blocks of flats, such as family homes. He wanted to carry out tests with equipment that would be much less disproportionate. Wouldn’t it be possible to have a penetrometer capable of analysing with precision the first 20-25m of soil (deep enough for a large number of projects), but that would be more compact, easy to use and much less costly than geotechnical trucks? Since he couldn’t find anything to meet such needs, he developed his own equipment. As it attracted his customers’ attention, he could foresee the potential market and launched his business. Since then, Pagani Geotechnical stopped being a consultant, and became a manufacturer. His first penetrometers were sold in 1983.

A year later, the company launched its TG 73-200 model, a modular and mobile device. Its mast can be tilted forward and backward enabling measurement even on sloping terrain. It anchors automatically into the ground so that it can exert the necessary thrust, in spite of its modest 3 tons. Handling, anchoring and measurements are automated to such an extent that only a single operator is needed to carry out the tests.

Pagani has put a particular accent on the robustness of the product. “The TG 73-200 was built to be indestructible” laughs Bruzzi. “It withstands all types of “abuse” – very difficult terrain or heavy-handed, clumsy operators!”

Thanks to these “over the top” characteristics, the 73-200 remained Pagani’s high-end model, selling five of them a year. “Its customers are large companies that require no-compromise performance for some highly demanding applications.”  As for other applications, Pagani Geotechnical has taken another step forward.

The TG 63-150, even easier to use, was launched in 1989. It is slightly bigger than 1m by 2m and weighs only a ton. The engineer can transport it himself in a van (no longer a need for a truck and a truck driver) and carry out the measurement on his own. It is a first in its field which simplified the tests and cut the costs considerably. The price (44,000 euros, which is half the price of a 73-200 and close to one tenth of a truck) contributes to broadening the client base – medium-sized companies, consultancy firms, universities, laboratories...

The 63-150 was the first of its kind”, says Paolo Bruzzi. “It had immediate success. With 800 units sold in over 70 countries, it has even become the best-selling compact penetrometer in the world.” It is still Pagani’s best-seller, who sell over sixty of them every year.

The TG 30-20 and 63-100 completed Pagani’s range of penetrometers. The Italian company, still managed by its founder, employs 25 people. Its factory produces between 70 and 80 machines a year and its 800 customers come from almost 90 countries.

Apart from the engines and hydraulic systems, everything is developed and produced “in-house”: accessories, electronic cones, seismic modules, power units… Even its data acquisition systems, including the new CPT AS, launched this spring, fully fitted with LEMO connectors. “This watertight system needs to operate on all terrain, from snow-covered northern countries to the Amazonian rainforest” explains Bruzzi. “We have chosen IP65 certified LEMO connectors for their resistance and compactness, as well as for aesthetic reasons – the excellence of our solutions also derives from design!”

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Pagani’s material is robust (its penetrometers are used for “an average of more than 20 years”). Technical components remain stable (“there hasn’t been found anything better for exploring the soil!”). Improvements are made essentially in the electronics system and the accessories. Two or three annual upgrades optimise measurement precision and ease of use. Safety is reinforced to follow the continuous evolution of regulations. Applications have become mobile.

“Many innovations arise from our partnerships with universities and research centres in Italy, Brazil, England or other countries, and, obviously, from feedback from our 800 customers from almost 90 countries, who use our technologies regularly in all possible conditions: in jungles, frozen soil, deserts …”

Pagani, proudly claiming “Made in Italy”, is happy to be associated with high quality. The durability of its machines hasn’t hindered regular sales progress for the last few years. For what reason? There’s been a growing demand for geotechnical tests. “The quality of infrastructures has been improving, requirements have become stricter and additional countries, in particular in emerging economies, have started performing tests.” In short, everything is done to ensure that the Tower of Pisa stays unrivalled.

This article originally appeared in IEEE Spectrum on 5 August 2020.