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civil Engineering

Innovation under the ground

Mantle applied on top of water or sewage pipes guarantees savings in installation

Since the times of the ancient Romans, the first people to used buried structures, engineering has always invested in the development of materials for underground use. Today, beneath our feet, there are a series of services at work, such as water, sewage, telephones and electricity, amongst others. There are thousands of kilometers of pipes, the degree of the economic and social importance of whose functions can easily be imagined. However, the technique employed for carrying out the installation of these works has seen few advances in the course of history.

If one takes into consideration what there still is to be implanted in underground infrastructure in telecommunications, and even with the elimination of posts and the consequent burying of wires in the ground, the news of a new kind of installation of pipes that is cheaper and shallower is welcome. It was developed at the Geosynthetics Laboratory of the Geotechny Department of the São Carlos Engineering School, of the University of São Paulo (EESC/USP). The objective of the group of researchers, under the coordination of Professor Benedito de Souza Bueno, was to reduce as much as possible the load over pipes, allowing installations closer to the surface, without the danger of excessive weight, and with the possibility of using more flexible conduits.

Resistant and durable
The project is called Geovala, and its technique uses geosynthetic materials – products manufactured on the basis of polyester or polypropylene, forming highly resistant and durable mantles or grilles – on top of the underground trenches, creating an empty space where the pipes are laid. Accordingly, the whole weight is distributed away from the area of the trench, which is free from any excess load.

The proposal is not to develop new kinds of pipes, but to modify the way they are installed, with the use of the same geosynthetics used in building reinforced earth retaining structures, waste treatment lagoons, waterproofing and drainage. Benedito Bueno, who is a civil engineer, believes in the technique as an important and innovative solution for the installation of underground conduits. He is the supervisor for the thesis for a doctorate Trench to Accommodate Buried Structures and Process of Accommodation of Buried Structures, carried out at the EESC/USP by researcher Paulo Márcio Viana, with a FAPESP scholarship.

The technique is appropriate both to be used in pipes made with more specific metals, as in the case of those applied in oil pipelines and gas pipelines, and in pipes of polyvinyl chloride (PVC) and high density polyethylene (HDPE), suitable for general use. The material used in the pipes can be of any nature, because the innovation, in this case, sets out to reduce or even eliminate the vertical loads in the region of the trench, which is covered by the geosynthetic material before being buried. The weight of the earth on the mantle, which absorbs the vertical loads as if it were a membrane under traction but allows liquid elements to pass through, makes the product create a span over the empty space in the trench, freeing the pipes from excess weight. Free of these excesses, the pipes can be larger, less thick, and, as a consequence, more flexible.

If on the one hand wider pipes gain in flexibility, on the other they also increase the risks of the deterioration of the material. However, the lower the load on the pipes, the safer the system is, since with greater resistance to the pressure of loads on the pipes, the trench can be shallower – going from 1.5 meters to a mere 0.5 meter in depth -, which makes installation less costly, by between from 30% to 40%, according to calculations by Bueno. There is also the environmental benefit to be seen, because the technique helps to diminish the possibility of leaks and contamination of the soil.

Refined technique
The high capacity of geosyntehtic materials to bear traction loads was what inspired the researchers from the São Carlos Engineering School to use the product, which has been used increasingly in retaining works by civil and geotechnical companies. It has an excellent performance, coupled with a cost-benefit ratio that is regarded as extremely favorable, above all when applied on a large scale. The possibility of increasing the useful life of the trenches, with greater speed in carrying out the works in burying conduits at a lower cost is a combination that Bueno hopes to be sufficient to awaken the interest of companies in Geovala.

Over four years, all the possibilities of soil pressure were tested and recorded by the researchers, with a variation in the kinds of pipes employed, the types of soil and loads, in a physical modeling of true greatness. The results were compiled by means of a computer simulation, with numerical modeling software. Tests were also carried out on large dimensions, on a reaction beam, in a steel box 2 meters high and 1.8 meters wide, in which a tube 400 millimeters in diameter and 2 meters in length was buried, reproducing a series of situations that simulated real conditions of use. After the trench is grounded in and the geosynthetic product installed, an overload was also applied, simulating extra weights, representing vehicles or works on the surface.

After dimensioning the loads and the variation of the weight of the soil itself, itwas possible to choose the kind of geosynthetic material most suitable to each case.

Geovala is applicable any kind of use, such as sewage, gas, oil or wiring for electricity or telephony, and the depths can be applied according to the environmental conditions and the capacity of the geosynthetic material used, which may vary, depending on the type of soil and material employed in the pipes. Another advantage pointed out by the researchers from Geovala, in the cases of pipes monitored internally to detect leaks or problems with corrosion, is the possibility of carrying out this monitoring externally, which would also increase the safety of the buried structures. As the process makes it possible to create an empty space where the pipe lies, remote control sensors can be installed in this space to measure the mechanical characteristics of the pipe.

Industrial scale
The technique for this new kind of burying of pipes had a patent lodged with the National Institute of Industrial Property (INPI), financed by FAPESP’s Nucleus for Patenting and Licensing Technology (Nuplitec). According to Bueno, the technique without precedent in the world, and it has now awakened the interest of companies from the public and private sectors, which are at the moment negotiating the right to apply the technique. As the products employed are already produced on an industrial scale and are available commercially, the inventors’ expectation is that the use of these materials with Geovala technology will bring down the price of geosynthetic products and of pipes.

The projects
1. Buried Conduits: Reduction of Forces on the Structure (nº 98/07444-0); Modality Regular line of research grants; Coordinator Benedito de Souza Bueno – EESC/USP; Investment R$ 151,218.97
2. Geovala – A Technical Solution for Reducing Vertical Tensions on Pipes (nº 01/13245-4); Modality Intellectual Property Support Program; Coordinator Benedito de Souza Bueno – EESC/USP; Investment R$ 6,000.00

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