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GRUNDODRILL and GRUNDOBURST enable steerable steel pipe installation

08.04.19 - The civil engineering firm Aples s.a., based in the city of Burgos in northern Spain, was established in 1984 with the aim of supplying and implementing effective, tailor-made concepts for pipeline construction. Through continuous innovation, the family-run company has since made a name for itself throughout the country as a specialist for custom solutions. These include the trenchless solutions that the company has specialised in from the outset, and as a founding member of IbSTT, the Spanish association for trenchless technology, Aples is among the pioneers of this technology in Spain.
One of these custom trenchless solutions – which could only be implemented with the appropriate expertise – was the installation of a steel pipe 800 mm in diameter through non-cohesive soil below the ground-water table of Zaragoza. At first glance, this appeared to be the perfect job for dynamic steel pipe installation with GRUNDORAM, since this comparably simple, non-steerable method is perfectly suited for use in such conditions: The borehole cannot collapse, no blowouts can occur and there is no danger of contaminating the groundwater or destabilising the roads and railways that pass over the bore path.

The difficulty with such a procedure in this instance, however, was that the steel pipe was intended to serve as a protection pipe for a drain, requiring a gradient of precisely 0.7 % to be maintained all along the 70 m line. Since dynamic steel pipe rammin is a non-steerable method – unlike HDD (horizontal directional drilling) method, for instance – this need for precise positioning presented a particular issue. This is because, although the pipe string is indeed aimed directly at the target and constantly pushed forward during the ramming procedure, it is entirely possible for small deviations to occur in longer driving operations. These are usually of no consequence for large pipe diameters – however, in this case a solution needed to be found that would ensure the stipulated gradient of the line was consistently adhered to.
 
In order to solve this problem, the experienced engineers at Aples drew upon a clever concept that they had come up with years ago. This involved combining the dynamic strength of the rammer with the accuracy of the HDD procedure and the static pulling force of a GRUNDOBURST to be able to lay the steel pipe with the necessary precision. More specifically, the bore bath was pre-drilled with an HDD unit with a PE pipe inserted afterwards in the reverse phase as a guide for the bursting rods; this was then combined with the rammer and subsequently pulled back during the steel pipe installation process.
 
The necessary equipment was sourced from Aples' well organised pool of machinery. In addition to a GRUNDORAM type "Koloss", a GRUNDODRILL 18ACS and a GRUNDOBURST 800G were used. This made for a truly clever combination, since the "all-conditions" HDD device was able to operate reliably even in difficult terrain. At 800 kN, the bursting device had enough static tensile force to guide the steel pipe dynamically driven by the Koloss along the entire length with extreme precision. The details of the procedure were as follows:
 
1. Using the GRUNDODRILL 18ACS, a pilot bore with an gradient of 0.7 % was made along the specified line, which was to have a PE pipe of 110 mm in diameter as a guide for the bursting rods during the reverse upsizing. This was necessary as the gravelly and rocky ground allowed no stable bore channel to be made through which the rods could have been pushed without getting stuck.
 
2. Afterwards, the GRUNDOBURST 800G was installed in the target pit and the bursting rods pushed through into the launch pit. At the same time, the GRUNDORAM Koloss was installed in the launch pit and the steel pipes lowered down.
 
3. Once the rod string had arrived in the launch pit, it was combined with the steel pipe by means of a hammer head specially designed by Aples. This special construction, which was attached to the front of the steel pipe, was the one thing that made combining the procedures possible in the first place without damaging the bursting rods. Subsequently, the steel pipe was precisely installed through simultaneous pile driving and retraction of the rods. The PE pipes that were no longer needed were retracted with the rods and retrieved in the target pit. Shortly before the steel pipe arrived in the target pit, the GRUNDOBURST 800G was disassembled to create space for the steel pipe and the emptying.
 
Using this method, the steel pipe for the drain was able to be successfully installed with precision over the entire length of 70 m with the required incline of 0.7 %. Carlos Gomez, Managing Director of Aples, was evidently pleased with the success of the procedure: "We still have plenty to learn about combining tractive and propulsive power, but one thing is certain: We can achieve double the length that we would usually accomplish with a defined ram. If you are able to achieve a drilling length of 40 metres with a ram in certain soil conditions, for example, you can use a tractive system to drill a 80 m borehole with a guarantee of achieving your target, without any issues."
 
With this tailor-made solution, the specialists from Aples have not only proven their technical expertise and innovative capabilities, but have also demonstrated the impressive versatility and flexibility that trenchless technology allows.
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