Land Reclamation without Exposure

Soil exchange drillings are a popular practice within reclamation of contaminated soil. Within this the burdened ground is drawn out by drilling & overlapping large holes and afterwards backfilled. German based company DEMLER Spezialtiefbau GmbH + Co. KG is using a Prolec pcX3D GPS with ascos-correction datas (reference network), to automatically position the drilling rod via satellite signals. Thereby the exposure of employees on jobsite is minimized and efficiency improved.

Tar oil is a spin off product within power generation and therefore is seen very often in grounds of older power station areas and brownfields. The oily and water insoluble substance is highly toxic and represents a danger for ground water. Decontamintion and disposal of this environmental poison therefore is strictly regulated by law. In addition to conventional excavation, 3D machine control has introduced a more efficient and accurate method for drilling overlapping holes vial a design grid. This provides an exact position using an existing coordinate system. Overlapping of drilling holes is used as a safety margin and guarantees the residue-free change of earth volumes. Drilling itself is executed by a big drilling machine, which lays out the points, then as-builts (stores existing) the points with a receipt report before finally boring out the soil

Work under inherent protection
Within this precise positioning of drilling rod is basic requirement for a safe and complete disposal of harmful substances. Positioning via total station fails in most of the cases due to regulatory requirements. These make arrangements that work in the pit only can be carried out under inherent protection, to avoid contact with the cancer-causing substance. This includes gloves, protective suits and breathing masks, which almost eliminates working with a total station. Additionally work hours in the pit are restricted. Surveyor, operator and assistant are only allowed to remain in the contaminated zone for two hours before mandating a break ? too short for efficient work.


Complex Sensor System
On the area of a former tar oil and ammonia cistern in 2009 the reclamation was pending. As a first step a cut off trench was set in order for breaking off the old cistern. For disposal, company DEMLER executed exchange drillings on an area of 600 sqm. Exactly 400 drilling holes, each one with a depth of 7.60m and a diameter of 1.5 meters were planned in the design. ?Within given circumstances a very high personal effort, which would have been reflected in the costs,? states project manager Jan Wiegand. From there the company invested in a high precise machine guidance system, which allows satellite real time positioning of drilling machine. Javad GNSS receivers were mounted on top of the drilling rod, to ensure sufficient satellite visibility. Due to prior excavation, the work began in a pit 6m deep, therefore standard installation on the upper carriage of machine would not have offered proper results. ?Despite it?s immense size, the machine is working with highest precision, we barely do not have any inaccuracy by oscillation of machine?s drilling rod?. This at least towers 20m out of pit. It?s slope is permanently monitored by Prolec CANBUS sensors and adjusted if needed. Balance between inaccuracy of GPS and GLONASS signals is carried out by ascos reference network signal from AXIO-NET. To connect to GSM/GPRS and for transmission of ascos data, the come2ascos modem was used instead of standard radio modem when using a base station. All collected data are flowing into Prolec?s machine guidance system pcX-3D, and it?s special version for drilling and piling. This is an affordable solution, resulting in high precision and a safer environment. The total system achieves a proven accuracy of 2cm.

High reduction of costs
Within a period of seven months, the complete reclamation on the area was completed. More than 4.500 m? of ground have been exchanged, more than 1.000 sqm of cut off trenches were built. Savings realized by using the GPS positioning, even on that smallish area were substantial. Working time of crew on working field was reduced by one hour per day. Additionally one skilled worker was saved. In summation, this approach resulted in a saving of more than 1.000,00 Euro per day over the entire period. On the other hand an investment of 20.000,00 ? for renting and installation of system components as well as supply of reference correction datas via GSM.

Further applications
As well in not contaminated areas, automated positioning of drilling machines makes good business sense. Within urban jobsites, the required view of the sky can be limited. During the construction of drilled pile walls for example, the previous ground markers very often are not clearly identifiable after very few passes. Using GNSS technology every drilling place can be re-located at any time.

Read more articles by Jurgen Reineke