On a recent project, Lockhart Enterprises in Los Angeles was able to use an ABI Mobilram that it purchased from Hammer & Steel Inc. to complete a project 60 days ahead of schedule and $1 million under budget.
Lockhart was asked to provide shoring for a washed-out road in Tunjunga, Calif. The road sits next to a river bed with boulders, gravel and sand underlain by bedrock. Instead of using a traditional down-the-hole hammer (DTH) system with casing, the company went with an ABI Mobilram rig with the quick-coupling docking system.
“Switching out attachments quickly is the key to saving time and coming in under budget in projects like this one,” says Daraius Tata, territory manager for Hammer & Steel. “However, oftentimes projects utilize many types of equipment in order to perform similar functions within drilling and pile driving. The Mobilram features many different attachments, such as vibratory driver/extractors, vertical boring heads for pre-drilling, auger-cast piles, diesel hammers, double-head auger drives for installation of secant piles and silent piling/hydro-press system to press sheet pile, that all can be used with the main rig to complete a variety of tasks.”
For this particular project, the ABI rig pre-drilled the holes with a small 8-inch DTH hammer with casing, stitch drilling a five-hole pattern for a heavy-duty, 40-foot-long I-beam. An MDBA 6000 drill was used with a 150-hex connector and a side-entry flushing swivel that was mounted below a knuckle device, which meant the entire drill string could be mounted on the ground, and was easy to install and remove. In addition, a breakout tong for the DTH hammer bit was provided to make bit changes easy. Each hole took roughly 15 minutes to 30 minutes to drill, depending on the amount of bedrock and the size of the boulders.
Once the holes were predrilled, the ABI rig vibrated in the 125 beams approximately 20 feet deep. Each beam took only a few minutes to drive. The beams were driven to grade into the predrilled bedrock with a Delmag D30 diesel hammer. At the end of the project, only two beams needed to be pulled and re-driven because the computerized, automatic alignment feature of the Mobilram helped facilitate verticality of the beams.
The entire project was completed on an extremely narrow and long jobsite, with a temporary road running parallel to the site. And to complicate the project, the jobsite was shut down for three weeks due to wildfires, which got as close as 300 feet from the job site.
“Working in a confined space can be a challenge for this type of project,” explains Tata. “Having to switch equipment types for any project can be expensive, due to the time needed to move equipment in and out of a space. However, when a space is this narrow and long, multiple pieces of equipment complicate this matter even further. With the low set-up time for the Mobilram, and the ability to use one piece of equipment for many aspects of the job, it helped the project keep moving. The Mobilram by ABI is one of the most sophisticated pile drivers on the market right now, and it enabled Lockhart to come in under budget on this complicated project.”