Large construction and other big infrastructure often require boring deep holes for foundation installation. Although there are numerous boring options, it is a challenge to drill through a tough and compact surface. This is where percussion boring comes in. This is one of the inevitable methods and is used for various applications. Let’s take an in-depth look at this unique boring process.
What is Percussion Boring?
Percussion boring is a manual drilling method or cable tool method to drill through hard materials. This method uses a hammering or cutting bit attached to a cable and is repeatedly lifted and dropped into the borehole. This powerful impact creates a fracture in the earth’s surface, making it easier to extract and penetrate deeper into the ground.
Applications of Percussion Boring in Construction
Foundation Installation
This boring method is typically used for sinking deep pile foundations. Piles serve to stabilise and support tall structures or heavy construction, mainly in regions with weak soil. The technique aids in driving piles through harder strata of rock or dense soil where traditional excavation techniques fail.
Geotechnical Investigations
One of the main purposes for percussion boring is geotechnical investigations to collect soil and rock samples from various depths. This helps in determining the composition, strength, and stability of the ground, which is crucial in planning and designing the foundation and structures.
It can also be used to identify the geological characteristics of the structure, like identifying the water table, rock formations, and soil exploration, to plan the right construction approach.
Utility Installation
It is generally used for underground installations of water pipelines, gas lines, and electric and telecommunication conduits. It helps significantly in putting utilities in inaccessible terrain by making tunnels and corridors for pipes and cables.
Tunneling
This boring method is used for tunneling projects in rocks or dense ground materials. It helps in breaking the hard rocks to create tunnels for various infrastructure projects such as subways, road tunnels, or underground storage units
Equipment Used in Percussion Boring
Percussion Drill Rig
This is the main equipment of the percussion boring process, housing the hammer, drill rods, and other components. This machine is typically powered by hydraulic or pneumatic systems. They come in various sizes and configurations based on the project requirements.
Drill Bit
A drill bit is a tool that directly contacts and fragments the material being drilled. It is subject to repeated blows from the hammer that allow the earthy materials to break and crush through the materials. It features sharp edges or teeth, which help in effective penetration.
Drill Rods/Cables
Drilling rods are long, solid tubes that connect the drill bit to the rig’s hammer system and transfer the force onto the drill bit. In the cable percussion drilling method, the bits are connected to the cables. These rods or cables can withstand the repeated hammering blows and come in various lengths depending on the depth of the borehole.
Hammer
The hammer is vital for percussion boring as it gives rapid blows to the drill bit, breaking tough materials such as rock and hard soil. Hammers include pneumatic, hydraulic, and mechanical ones, which are employed based on the type of job and material. They also vary in size and strength: smaller hammers are for shallow drilling, while larger and more powerful ones are for drilling much deeper into hard rock.
Casing
The casing is a pipe-like structure fitted into the drilled hole to prevent its collapse and to maintain the integrity of the wellbore. Generally, as the hole is being drilled, casing is inserted and is often advanced with the drilling bit to keep the borehole open. It helps to stabilize the walls of the borehole, prevent groundwater contamination, and protect drilling tools against damage.
Bailer
A bailer is a hollow tube for the raising of liquids such as water, slurry, and mud from the borehole while drilling or afterward. It is lowered into the borehole, whereby debris or fluid enters the hollow body of the bailer and is then lifted back up to the surface to empty the collected material.
Steps Involved in Percussion Boring
Site Preparation
Clear the area of the drilling rig. Safety must be ensured by making the site accessible for the equipment. Then, the position of the drilling site is marked and checked for alignment.
Drilling/Boring
Percussion drilling is initiated, whereby the drill bit is repeatedly hammered into the ground. The drilling action serves to crush and break up the soil or rock at the bottom of the hole.
Casing Installation
Casing must be inserted into the drill hole as it gets deeper to prevent the collapsing of the hole. The casing is forced into the ground with the progress of drilling.
Sample Retrieval
From time to time, a bailer is lowered into the hole to remove debris, water, or mud. It can also be used to retrieve soil or rock samples for testing and analysis.
Finishing
When the bore reaches the desired depth, the boring is finished; the casing is installed, and the hole is ready for its intended purpose, such as well installation or geotechnical testing purposes.
Percussion Boring vs Rotary Drilling
| Feature | Percussion Boring | Rotary Drilling |
| Method | Repeatedly lifts and drops a heavy drill bit | Uses a rotating drill bit to grind through materials |
| Speed | Slower | Faster |
| Cost | Less expensive | More expensive |
| Effectiveness | Excellent in hard rock | Versatile across various ground conditions |
| Equipment Complexity | Simpler equipment | More sophisticated equipment |
Conclusion
In summary, percussion boring is an effective and dependable method of drilling through the toughest of grounds. Given its ability to cope with hard soil as well as rock, its economy and simplicity have made it a preferred method for various applications. Be it well drilling or geotechnical borehole drilling, percussion boring remains a trusted answer to keeping the task done.
Apoorva H P Achar