DELMAG Low Head Room Rig Soil Mixing Under Power Lines
Hammer & Steel recently provided a DELMAG RH 12 drill rig, capable of low headroom applications, on a jobsite close to the airport in San Francisco. Performing the work was JAFEC USA, a leading ground improvement specialty contractor. Soil mixing was used to improve the poor, soft, plastic clays of the area for lane additions for a local highway.
The area surrounding the jobsite has power lines that limited the operating headroom to 25 ft. at the lowest point, up to 35 ft. The RH 12, using its low headroom capabilities, was supplied with a 5’ diameter soil mix auger, which was 18.5’ in length, to drill between 25 and 30’. The mixing tool was also equipped with a stabilizing bar that was just over 5’ in diameter to help keep the hole straight and to offer resistance to the mixing process, and also to break up the clays.
The target production rate was 6 holes per day, which was achieved within three days. A tight schedule required two daily shifts was also carried out to meet a deadline set by Caltrans (California’s Department of Transportation), so the highway can reopen quickly. A second Delmag drill rig, the RH 24 in short mast version, was also shipped to further speed up production.
In addition to the rigs, tooling was also supplied by Hammer & Steel, including drill rods with 150 mm hex connectors (with 84,000 ft. lbs. torque capacity) along with two 5 ft. diameter mixing tools. Moreover, a special holding bracket was installed at the base of the mast to hold the drill rods while the tool was extracted from the hole.
All soil mixing data was recorded by a G&H monitoring system mounted in the cab of the rig. The monitoring system was connected to a RPM sensor, a grout flowmeter, and a depth sensor and that records grout flow, grout volume, drill depth and drill head RPM. This allowed JAFEC’s operator to observe the construction of the soil mix column in real time, and for Caltrans to verify soil mix quality control by looking at reports generated by this system.
JAFEC also requested a radio remote grout pump to allow the operator to adjust grout volumes based on the penetration of the soil mix auger. The pump capacity needed on this site was a minimum of 45 gpm.
Hammer and Steel provided a Scheltzke grout pump model HDPC 400, which fulfilled this radio remote request, and was set up with 80 mm pistons, delivering 85 gpm at low pressures. The HDPC 400 pump is capable of also delivering 184 gal/min at 2500 PSI with 120 mm pistons, or 65 gal/min at 7500 PSI with 70 mm pistons for jet grouting applications. The high pressure pump was driven by a Tier4i diesel engine with 400 HP.