Testing a new equipment only through final acceptance tests at the factory or by drilling some metres at our test site sometimes is not enough, as an accurate feedback is needed on the solutions and techniques adopted. This becomes absolutely necessary when it comes to the hydromill that has been designed to reach a 150 m depth.
The first challenge is to identify the right site for testing. We were looking for an area in which the soil stratigraphy is predominantly characterized by rocks, due to the major strengths of the hydromill: minimum deviation from verticality and rapid crossing of rocky layers. We carried out a geological investigation and identified the suitable site a few kilometres from the Soilmec headquarters, along the Savio river valley, on the slopes of the Apennines.
A continuous core boring down to a depth of 160 m allowed to detail the site stratigraphy which is made up as follows: under the first metres of sandy and gravel silts there are marly clays down to 50 m, a bank of bituminous clays characterized by high fragmentation and, within it, fibrous gypsum down to a depth of 100 m; an underwater clay landslide with sandstone and limestone down to 125 m and an alternation of medium-tocoarse grained compact and sandstone marls, weakly cemented.
We tested the Tiger SC-135 c/w P450, powered by two C18 diesel engines – total power 900 kW – mounted on a SC-135 carrier, and fitted with the hydromill module SH-50 – 3,200 mm x 1,500 mm size –, tested with three different cutting units HH-10/12/14. A real challenge in the challenge, as the panels drilled using this technique usually measure 2,800 mm with a thickness of 1,000/1,200 mm.
The mud processing plant is integral part of every jobsite with hydromill where drilling with bentonite slurry is carried out. In our case, we adopted the new SMT-500 system characterized by a double stage of cyclones, where the first stage cyclones are two, with cut point D50 = 60 μm, whereas the second stage cyclones are 15 with cut point D50 = 20 μm. The system is perfectly integrated with the debris elimination system SDM-35 and the innovative centrifuge SDM-90s for fine components separation. The latter has been specially patented by Soilmec and is able to collect the mud directly treated by the SMT-500 system, in order to ensure an operation system in series with drilling and obtain the best performances in terms of bentonite slurry treatment.
The results are very satisfactory, and even more so if you consider the size of the panel and drilling rig, and the plastic nature of some soil layers, which are not beneficial to the hydromill performances.