High-spiral core barrel tested in granite.

A barrel designed around the customer’s problem.

The site had small-diameter piles with substantial rock drilling. Existing guides were heavily worn, and the review found periods of thick or insufficient slurry and material accumulating around the cutting system. The customer needed a practical response to short roller-bit life, rather than another replacement supplied without investigating its use.

Our trial design combined a higher spiral with revised spacing around the roller bits. The purpose was to help move cuttings away from the cutting face and improve slurry movement, with better penetration and service life as the goals to test.

What the team found on the existing site tools

These are older conventional barrels inspected during the wider visit, not the new high-spiral trial barrel. Worn guides and replacement work helped explain why the review covered the steelwork, slurry and operating practice together.

Understand the rock before judging the tool.

The site account describes dense granite, with boulders, inclined rock faces and soil or sand interlayers. Conditions changed between nearby piles. The team examined recovered material alongside the pile log, because vibration, cutting response and core recovery depended on what each hole encountered.

Two tested site samples

These are individual results for two tested samples. Sampling depths were not entered, so the values are not assigned to every photograph or to the full drilling interval.

Follow the barrel from first entry into drilling.

Record the operating response with the crew

The follow-up tracked lowering, cutting, lifting and re-entry. For example, the 5–6 June overnight entry recorded 5.83 m of advance, with head speed measured at 14–15 r/min. On 6 June another rig drilled under assembly weight without additional crowd. These observations helped the discussion move from a general wear complaint to the actual use of the barrel.

The site summary reports that combined feed and rotary-speed adjustments raised the observed pure-cutting rate from the earlier 0.2–0.3 m/h to about 0.35 m/h. It was an encouraging field response, though below the team’s target. The readings below show the different rigs and stages; they are not a single operating recipe.

From the recovery attempt to the rock brought up.

On the morning of 7 June, machine 10 advanced from 16.46 to 17.03 m in the recorded pile entry. The crew reported high cutter temperature and strong vibration near the end of the run. The following recovery sequence shows the actual material brought to the surface.

The second attempt produced a visible rock recovery result. The first-attempt video below shows the preceding mud discharge. Together, the two attempts show why recovery performance needed to be assessed separately from cutting.

What the recovery sequence told us

The roller-bit barrel cut the rock; a separate recovery tool was used to grip and remove it. An earlier overnight entry had already brought the operator’s feedback that cuttings discharge was good but that recovering a core after a short advance was difficult. This showed why the next improvement needed to include core gripping and unloading, alongside the high-spiral cutting barrel.

The team proposed reviewing the recovery tool’s internal gripping arrangement and discharge geometry. That was a follow-up design recommendation; this trial does not record a completed recovery-tool redesign.

View this pile’s original time and depth record →

Keep the roller-bit checks with the drilling record.

Follow-up continued beyond the first run. The team photographed the cutters on 7 June at 17:00, then recorded hand checks of cone rotation at 09:30 on 8 June. These inspections formed part of the trial, alongside the running depth record and conversations with the operators.

The longest detailed pile entry ran from 6.85 to 20.93 m between 7 and 9 June: 14.08 m of recorded advance, including core-recovery events. It demonstrates continued field use and follow-up. It is a single-pile record, not a measured lifetime for an unchanged set of roller bits.

Follow the 14.08 m pile entry →

What did the trial deliver for the customer?

A purpose-built barrel, encouraging discharge feedback and a practical improvement plan grounded in site use. The customer’s wear problem was investigated through the complete cycle: tool geometry, rig operation, cuttings, core recovery and cutter condition.

Good cuttings discharge was reported

During the 6–7 June overnight entry, the operator described the new barrel’s discharge as good. That feedback supports the high-spiral design direction for this site. The same conversation identified core recovery after a short advance as a remaining constraint.

Operating adjustments produced a positive response

The site summary reports about 0.35 m/h after feed and speed adjustments, compared with the earlier 0.2–0.3 m/h described in the review. Several settings changed together, so this is a reported operating response, not a controlled comparison proving the high spiral alone increased penetration.

The next work was defined with the field evidence

The review identified three priorities: maintain the cuttings guides and slurry, improve core gripping and unloading, and keep each barrel’s usage and cutter-change record together. The dated inspections and eight pile entries provide a basis for that next trial. A verified service-life increase remains to be established.

For another contractor facing the same symptoms, the value is a tool and support plan matched to the site: review the existing assembly, choose the design changes, discuss operation with the crew and follow the results through drilling and inspection.

Discuss a similar problem on your site →