Down the hole hammers: a guide for drillers and engineers

As urban redevelopment projects continue to rise, geotechnical engineers face greater challenges—how can these works be done without damaging surrounding buildings? To meet increasingly specific requirements for foundation works and drilling operations, specialized solutions have become ever more important. One of the most commonly used tools in the drilling industry to meet such challenging scenarios is the Down the Hole Hammer (DTH hammer).

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The Impact of DTH Hammers

DTH hammers are predominantly utilized in hard rock formations and are specifically designed to handle complex tasks such as drilling in populated areas without jeopardizing existing structures. They are ideal for creating large diameter boreholes, typically ranging from 3 inches (85mm) to 48 inches (1219mm) or greater, in hard rock formations.

Furthermore, DTH hammers can achieve greater depths when drilling in hard rock compared to other methods. Depending on the size of the hammer and the specific rock formation being drilled, these hammers can reach depths of up to 1,000 feet (305 meters) or more.

They offer drilling efficiencies with a high rate of penetration (ROP). This is due to the air-powered hammer consistently minimizing energy loss to the drill bit, enabling efficient rock breakdown. Additionally, compressed air flushes out the cuttings, reducing the likelihood of clogging or binding the drill bit.

While high-pressure air is often necessary for efficient bit flushing, caution is advised when working with overburden ground as it may compromise existing foundation stability.

Drilling in Sensitive Areas

Urban redevelopment projects present unique challenges, particularly when drilling in sensitive areas. Minimizing disturbance to the surrounding environment during drilling is a key challenge faced by drillers, and this is where low pressure Down the Hole (DTH) hammers prove advantageous.

In such projects, it is crucial to minimize noise and vibration to avoid disturbing nearby residents, buildings, and infrastructure. Low pressure DTH hammers operate within an air pressure range of around 12 to 18 bar, significantly lower than conventional high-pressure DTH hammers. As a result, they produce less noise and vibration, causing minimal ground disturbance during drilling.

Using low pressure DTH hammers allows for effective operation in areas unsuitable for conventional drilling techniques. This makes them an excellent option for densely populated areas or regions with sensitive infrastructure, such as hospitals, schools, or historic buildings.

Another benefit of low pressure DTH hammers is their ability to drill through a variety of soil types, whether it's hard rock or soft soil, without causing significant ground disturbance. This enables the use of a single drilling method across various soil conditions, reducing the need to switch between techniques and minimizing drilling time.

Low-pressure DTH hammers have grown in popularity due to their ‘gentler’ impact on ring bit sets compared to high-pressure hammers. Operating at a lower frequency with less impact energy reduces wear and tear on the ring bit sets, making them more efficient, cost-effective, and environmentally friendly. Engineers should consider integrating low-pressure DTH hammers into their operations to improve drilling performance and reduce maintenance costs.

Additionally, low pressure DTH hammers can be used to drill deeper and wider holes, advantageous for foundation and pile construction in urban developments. With better penetration rates, they ensure faster and more efficient drilling, which is particularly important in urban areas with tight construction schedules where delays can be costly.