Case Study: Carbide Core Bits in Middle East Construction

In 2023, Dubai's Roads and Transport Authority (RTA) launched the Green Line Extension, a 15-kilometer metro expansion designed to connect the growing residential districts of Dubai South to the existing rail network. The project, valued at $2.1 billion, included 10 new stations and a 7-kilometer underground tunnel—critical for avoiding disruption to surface traffic and preserving the city's iconic skyline.

But beneath Dubai's glittering surface lies a geological puzzle: layers of sedimentary rock, including abrasive limestone and dolomite, interspersed with pockets of gypsum and loose sand. For the tunnel's foundation design, engineers needed precise geological data—specifically, intact core samples from depths ranging from 20 to 80 meters. These samples would determine soil stability, water table levels, and the risk of karst formations (underground cavities) that could compromise tunnel integrity.

"We knew the drilling phase would make or break the project timeline," says Maria Al-Mansoori, the RTA's chief geotechnical engineer for the Green Line Extension. "The desert heat, which often exceeds 45°C (113°F) at ground level, and the hard, abrasive rock meant we needed drilling tools that could withstand extreme conditions while delivering consistent, high-quality cores."

Initially, the project's drilling contractor, Gulf Drilling Services (GDS), used conventional high-speed steel core bits—a common choice for softer formations. But within weeks, the team hit roadblocks:

• Low Durability: Steel bits wore down quickly in limestone, with an average lifespan of just 15–20 meters drilled. This meant frequent bit changes, halting progress and increasing labor costs.
• Inconsistent Core Quality: The soft steel tips deformed under pressure, leading to (broken) or incomplete core samples. In one section of dolomite, core recovery rates dropped to 65%—well below the 90% threshold required for accurate geological analysis.
• Heat-Related Failures: High ambient temperatures caused steel bits to overheat, reducing their hardness and accelerating wear. "We'd pull bits out after 30 minutes of drilling, and they'd be too hot to touch," recalls Khalid Omar, GDS's site drilling supervisor. "The metal would warp, making them useless for further drilling."

By month three, the project was already two weeks behind schedule. The RTA's deadline loomed: the tunnel needed to be structurally sound by Q1 2024 to align with Dubai's Expo 2025 preparations. GDS knew a new approach was needed.

After consulting with drilling tool specialists, GDS turned to carbide core bits—specifically, surface set carbide core bits with tungsten carbide buttons. Tungsten carbide, a composite of tungsten and carbon, is renowned for its hardness (9 on the Mohs scale, just below diamond) and heat resistance (melting point of 2,870°C). These properties made it ideal for Dubai's harsh conditions.

"We tested three types of carbide core bits: surface set (carbide buttons brazed to the bit face), impregnated (carbide particles mixed into the matrix), and matrix body (a dense carbide matrix for extra strength)," explains Omar. "The surface set design stood out—it offered the best balance of penetration speed and durability for our mix of limestone and dolomite."

The selected bits, 76mm in diameter (3 inches), featured 9 tungsten carbide buttons arranged in a spiral pattern to optimize chip evacuation and reduce heat buildup. They were paired with high-strength drill rods—critical for maintaining stability at depth and transferring torque efficiently from the drill rig to the bit.

"The drill rods were just as important as the bits," notes Al-Mansoori. "A flexible or poorly fitting rod can cause the bit to wobble, leading to uneven wear and broken cores. We chose heat-treated alloy steel rods with threaded connections to ensure a tight, stable fit—even when drilling at an angle for the tunnel's sloped entry points."

In April 2023, GDS began a two-week field test of the carbide core bits at three trial drill sites, each representing a different geological zone: limestone (Site A), dolomite (Site B), and gypsum-sand mix (Site C). The goal was to measure penetration rate, bit life, core recovery, and heat resistance.

At Site A (limestone), the results were immediate. The carbide bit drilled 45 meters in a single shift—more than double the 20 meters achieved with the steel bit. "The penetration rate jumped from 0.8 meters per hour to 2.1 meters per hour," Omar says. "We didn't need to stop for bit changes, so we completed the 45-meter hole in 21 hours instead of the usual 56."

At Site B (dolomite), known for its high silica content, the carbide bit's heat resistance shined. "Even after 30 meters of drilling, the bit temperature stayed below 120°C—cool enough to handle without gloves," Omar recalls. "The steel bits would have hit 180°C by that point, warping the tips and ruining the core sample." Core recovery at Site B rose to 94%, up from 65% with steel bits.

Encouraged by the trials, GDS scaled up to 12 drill rigs, each equipped with carbide core bits and matching drill rods. The team also adjusted drilling parameters: reducing rotational speed (RPM) from 800 to 600 to minimize heat, while increasing axial pressure to 12 kN to maximize carbide button penetration into the rock.

By the end of the drilling phase in October 2023, the impact of the carbide core bits was clear. The table below compares key performance metrics between the initial steel bits and the carbide core bits used for the majority of the project:

"The cost savings alone were staggering," says Al-Mansoori. "By reducing bit changes and drilling time, we cut the drilling phase budget from $2.4 million to $1.1 million—a 54% savings. That freed up funds for other critical areas, like tunnel reinforcement materials."

Beyond numbers, the human impact was equally significant. With fewer bit changes, the drilling team reduced exposure to heat and heavy lifting, lowering the risk of fatigue-related accidents. "Our crew used to spend 2–3 hours a day swapping bits," Omar notes. "Now, they focus on monitoring drill parameters and ensuring core samples are properly labeled—work that adds real value to the project."

Perhaps most importantly, the high core recovery rate gave engineers the data they needed to design the tunnel's foundation with confidence. "In one section, we discovered a 2-meter-wide karst cavity 65 meters down—something we might have missed with lower core recovery," Al-Mansoori says. "We adjusted the tunnel path by 10 meters, avoiding a potential collapse and saving millions in repair costs."

In December 2023, the Green Line Extension's drilling phase wrapped up—two weeks ahead of schedule. Today, the tunnel boring machines are advancing smoothly, and the project remains on track for its 2025 opening. For Al-Mansoori and the RTA team, the success underscores a broader truth: in the Middle East's unforgiving construction landscape, the right tools are not just accessories—they're project-critical.

"Carbide core bits weren't just a better option; they were the only option," she says. "Their durability, heat resistance, and ability to deliver consistent cores made them indispensable. We're now specifying them for all future metro projects, and we're seeing adoption across other sectors—from oil and gas exploration in Abu Dhabi to mining in Oman."

As the Middle East continues to build for the future—with mega-projects like NEOM in Saudi Arabia and Qatar's Lusail City—carbide core bits and advanced drilling tools will play an increasingly vital role. For contractors and engineers, the lesson is clear: investing in high-quality, application-specific tools isn't an expense. It's the key to turning desert challenges into construction triumphs.