In August 2007, the trenchless technology for laying sewers with small diameters by pilot pipe drillings had successfully found its way into Colombia’s capital city of Bogotá in the quarter of Fontibón in the context of the project “Construccion del Allcantarillado Pluvial des Fontibón Oriental Fase II.”
In June 2010, almost exactly three years later, again a BM 500 pilot drilling machine from the company Bohrtec was used for a new project in Bogotá.
The company Microtunel S.A de C.V received the order to renew the sewer in the street Calle 94 from Empresa de Acueducto y Alcantarillado de Bogota E.S.P. The project with an estimated total budget of $3.5 million USD includes the new construction of 1,955 m of sewers ID 300 and ID 400. The hydraulic performance of the existing sewer in the Calle 94, which is located in a residential and commercial quarter with very high traffic volume, is so much affected by root penetration that the laying of a new sewer is inevitable. The new sewer will be laid in the area of the outer lane, close to the walkway.
In total, 1,485 m of steel concrete jacking pipes ID 300 and 470 m of steel concrete jacking pipes ID 400 will be laid in a depth between 3 and 4 m; 14 starting shafts and 16 target shafts have to be built..
Since the drilling lengths, with a maximum of 100 m, are relatively short and the ground onsite is comparatively soft, the project is ideal for pilot tube microtunnelling. Furthermore, the pilot pipe technology is characterized by short set-up times and low efforts fort he preparations onsite. Like this, a minimum effect on the traffic in the residential and commercial quarter of the Colombian metropolis around Calle 94 could be guaranteed.
In order to assure optimal preparation and a smooth course of action onsite from the beginning on, a complete drilling was performed before starting the jacking works. This took place on an industrial area in Bogota together with the operating crew of Microtunel S.A. and the training crew from Bohrtec. Certainly this kind of procedure is not an every day occurrence, but later during preparations and performance of the first drillings, it proved to be absolutely right. From the beginning, the crew was totally aware of the important points regarding pilot pipe jacking and how to achieve a maximum performance by optimal preparation onsite.
The company Microtunel S.A., an experienced user of microtunnelling slurry machines, used a BM 500 from Bohrtec for the project in Bogotá. Regarding the pipe diameters of ID 300 and ID 400, a BM 400 would have been sufficient. Nevertheless, Antonio Torres, owner of Microtunel S.A., decided to buy a BM 500, because he plans to jack pipes with ODs of up to 1,000 mm in the future with this machine, which is designed for a 3.2 m standard jacking shaft.
Due to the soil conditions onsite, which were soft clay, the contractor and machine manufacturer decided together for the so-called three-phase procedure. First, the guided pilot drilling is performed followed by the first extension step with steel casings Ø 279 mm. In the third step, the drilling is reamed up to the OD of the jacking pipes. The excavated soil is transported to the reception shaft. This process technology allows for covering different jacking pipe diameters with only one set of steel casings.
After the so-called “training drilling,“ the first two jackings on “Calle 94“ were in cooperation with the Bohrtec training crew. Subsequently, the operational team of Microtunel S.A. was prepared at best to complete the other drillings without any problem.
As in the year 2007, when pilot tube microtunnelling was successfully used in Bogotá in the quarter of Fontibón for the first time, this project on Calle 94 has proved that sewers with small diameters can be laid extremely economically even in short drilling lengths due to the simple machine and process technology.
Dr.-Ing. Gregor Nieder is with Bohrtec GmbH.