We’ve been providing mini piling solutions for around 15 years here at Vxcel, delivering success for customers across the domestic and commercial sectors alike. Now, while we do have lots of commercial customers who come to us already knowing most or all of what they need, we also know that not everyone knows everything about mini piling. So, if you’re not sure about exactly which method is best for you, our team is always on hand to provide a useful bit of advice.
If you need a quick starter guide on the basics, here are some of the essentials on what you need to know about the three main types of mini piling services we provide.
Method #1 – Bottom-driven mini piles
Sometimes known as driven piles or simply as mini piles, bottom-driven mini piles are slender structural elements used in foundation construction to transfer loads from the structure to deeper, load-bearing soil or rock layers.
We use steel-cased mini piles here at Vxcel Piling, but they can also be made of concrete. Whatever the material, they’re installed the same way: by driving them into the ground using hydraulic hammers, or vibratory drivers (sometimes referred to as ‘moles’). These piles are ideal for projects where access is limited, or the soil conditions are challenging.
Key advantages
With their relatively small diameter, bottom-driven mini piles are specifically designed to excel in scenarios where traditional deep foundations are impractical. (As we’ve touched on above, this is generally because of restricted access or poor ground conditions.)
Their efficient installation is complemented by a compact rig size (at Vxcel, we use a Cobra D500 or D1000), which makes them well suited to urban environments, or in and around other buildings and structures, or other heavy machinery. In short, anywhere with limited manoeuvrability!
Bottom driven mini piles are also noted for their versatility, and can be installed in a variety of soil conditions, including cohesive soils, granular soils, and even rock formations. The installation process is less disruptive compared to some other types of piles, making them suitable for projects in urban areas or sensitive environments.
Bottom-driven mini piles provide high load-bearing capacity, so they’re often used to support a wide range of structures, from residential buildings to industrial facilities. That’s a big part of the reason why they’re often used for new builds. It’s easy to see why so many people consider bottom-driven mini piles to be a dependable and cost-effective solution for such a wide variety of projects!
Installation process
Firstly, the site is prepared by clearing any obstructions and ensuring proper access for the piling equipment. The piles are then positioned at predetermined locations based on the design specifications, before being driven into the ground using hydraulic hammers (like the Cobra D500 rig) or vibratory drivers / “moles” until they reach the required depth or a load-bearing stratum. We use Grundomat-style moles here at Vxcel, which are renowned for their efficiency and reliability.
During the installation process, the piles are continuously monitored to ensure they are driven to the correct depth and alignment. Once installed, the piles are tested to verify their load-bearing capacity and integrity. Finally, the tops of the piles are trimmed to the required level, and pile caps or other structural elements are attached to transfer the load from the superstructure to the piles.
Method #2 – Open bored auger piles
Open bored auger piles are a type of deep foundation element used to transfer structural loads to solid ground; effectively stable soil, or rock strata. These piles are formed by drilling into the ground with an auger – essentially, an industrial-sized screw.
Now, it’s worth clarifying at this stage that an open bored auger differs in a small but significant way from Continuous Flight Auger. When the piles are drilled, CFA involves filling them with concrete simultaneously, whereas open bored augers are not connected to a concrete pump, so the voids are concreted after they’ve been drilled.
Open bored auger piles are commonly used in construction projects where noise, vibration, or groundwater control is a concern, as they produce minimal disturbance to the surrounding soil, and require no casing during installation.
Key advantages
Open bored auger piles are suitable for a wide range of soil conditions, including cohesive soils, granular soils, and even weak rock formations. (Although DTH piling is better for the latter – we’ll go into that in just a moment.) They can be installed quickly and efficiently, making them especially cost-effective for large-scale projects.
The installation process generates minimal noise and vibration, so they can be an excellent option for use in urban areas or near existing structures. The absence of casing during installation reduces material costs and simplifies the construction process. Crucially, open bored auger piles provide high load-bearing capacity, and can be designed to accommodate various structural loads, making them suitable for supporting a wide range of building types.
Installation process
Firstly, the site is prepared by clearing any obstructions and ensuring proper access for the drilling equipment. The auger is then positioned at the designated pile location, and drilling begins. As the auger rotates, it advances into the ground, creating a void in the soil or rock.
Once the design depth is achieved, the auger is removed from the pile. That leaves an “open bore” – in other words, a borehole that’s been created in the ground without casing or lining, which means the ground needs to be stable enough to hold that shape (at least temporarily). That borehole then serves as the channel for driving the steel reinforcement into the ground, followed by concrete, which completes the pile.
Finally, just as with bottom driven piles, the top of the pile is typically trimmed to the required level, and pile caps or other structural elements are attached to transfer the load from the superstructure to the piles.
Method #3 – Down the hole hammer piles (DTH)
Down the hole hammer (DTH) piles are a type of deep foundation element used to transfer structural loads to stable soil or rock strata. Unlike traditional pile driving methods, which mainly rely on external force to install piles, DTH piles are installed by hammering a drill bit into the ground using compressed air or hydraulic pressure.
As the drill bit penetrates the ground, it creates a borehole into which concrete or grout is eventually pumped, forming the pile shaft. DTH piles are commonly used in construction projects where rapid installation and high load-bearing capacity are required, such as building foundations, bridges, and retaining walls.
Key advantages
DTH piles are especially versatile, since they can be installed in a variety of soil and rock conditions, including hard rock formations – which may prevent the use of other mini-piling methods. What’s more, they can be installed particularly quickly and efficiently, making them excellent for projects with tight schedules or limited access.
Like other mini-piling methods we’ve detailed above, the installation process is less disruptive than traditional pile driving methods, as it generates minimal noise and vibration, reducing the impact on the surrounding environment and nearby structures.
Installation process
The first step of any installation process with DTH piles involves clearing the site of any obstructions, ensuring proper access for the drilling equipment. A drill rig equipped with a down-the-hole-hammer and drill bit is then positioned at the designated pile location.
The drill bit is lowered into the ground, and compressed air or hydraulic pressure is applied to the hammer, causing it to strike the drill bit repeatedly. (It’s much like a hand-held hammer-drill in this regard.)
As the drill bit penetrates the ground, it creates a borehole of the desired diameter and depth. Simultaneously, concrete is then pumped through the hollow stem of the drill bit to fill the void, forming the pile shaft.
Once the desired depth is reached, the drill bit is withdrawn, and reinforcement may be inserted into the fresh concrete to enhance the pile’s load-bearing capacity if required.
Finally – well, you know the drill (pun very much intended). The top of the pile will be trimmed to the required level, and pile caps or other structural elements are attached, so the load can be transferred from the superstructure to the piles.
These are just the essentials for each method – if you have any questions or need any more detailed advice about their suitability for your own project, don’t hesitate to get in touch with our team on 01254 314010, and we’ll be happy to see how we can help!
As highly experienced mini piling contractors here at Vxcel, we have well over a decade of delivering exceptional results – encompassing domestic projects, commercial properties, and industrial warehouses. To find out what we’ve achieved for previous customers, feel free to take a look through our case studies!
