Chris Knight, Regional Director, Target Structural Chiltern

The Root of the Problem: Heli Pile Foundation near Tree Roots

In the world of UK Construction, few challenges are as persistent, or as frustrating, as designing a new structure’s foundation near mature trees. For Structural Engineers, Building Surveyors, and Architects, the goal is simple: ensure stability. For Property Developers en Huiseigenaren, the objective is to build without destroying a valuable landscape asset. When a new garage, extension, or garden room is planned, the traditional approach dictates a concrete trench foundation. But what happens when that trench inevitably intersects with a mature tree’s root system?

Digging trenches near trees, especially those protected by a Tree Preservation Order (TPO), is fraught with risk. Deep excavations can sever major structural roots, destabilizing the tree and potentially leading to its demise. Furthermore, roots extract moisture from the soil, causing volumetric changes that lead to soil shrinkage and settlement, or, conversely, soil heave if the roots are removed. This dynamic environment is a nightmare for rigid concrete foundations. The conflict between the need for a stable foundation and the necessity of root conservation requires a non-traditional, non-invasive solution.

Foundation for a New Garage

We, at Target Structural Chiltern, a licensed installer of the innovative Doelbevestigingen product range, were recently approached with just such a dilemma. The main contractor working on a residential project had raised serious concerns to their client’s Structural Engineer regarding a significant tree located in the immediate vicinity of a proposed new garage. The concern was clear: traditional foundations would almost certainly have a negative, perhaps catastrophic, impact on the tree, and the tree’s roots would inevitably pose a threat to the foundation’s long-term stability.

Following careful deliberation and review of the soil conditions and tree proximity, a piled raft solution was meticulously designed. This design specified the utilisation of our Doelbevestigingen Helipalen to provide the essential structural support for the new building, while also offering crucial resistance against potential soil heave—a key advantage when building on soil prone to moisture fluctuation near large vegetation.

Heli Pile Foundation Near Tree Roots: The Non-Invasive Solution

The reason the Target Fixings Heli Pile system was the favoured solution in this sensitive environment lies in its unique engineering. Unlike traditional piles, Helipalen work effectively in both tension and compression due to their distinctive helical shape. The shape acts as a permanent anchor in the ground, providing exceptional uplift resistance, which is vital for counteracting the expansive force of soil heave that can occur when tree roots are disturbed or removed.

Critically, the installation process for a Heli Pile foundation near tree roots is fundamentally different from traditional methods, making it the ideal non-invasive foundation for tree roots. To ensure we avoid damaging major root structures, we employ a highly sensitive, low-impact process of establishing a passage through the ground before the Heli Pile itself is installed.

This involves what we call ‘spiking’ the ground: driving a sacrificial, 40mm diameter nylon cone into the soil. This cone creates a precisely sized pilot hole that the Heli Pile can then follow. This method allows us to gently push past and around the tree roots without causing the deep, wide-scale disruption associated with trenching or boring. This is a game-changer for working near trees, offering a genuine TPO Alternative to standard disruptive foundations.

Low Impact Installation and Structural Integration

The installation equipment itself is also deliberately lightweight. Our machines and Heli Piles are carried to the site by hand, meaning the load exerted upon the ground during the entire installation process is limited to simple foot traffic. This dramatically reduces the risk of root compression or surface damage, demonstrating our commitment to conservation alongside construction excellence.

The installation on the garage project proceeded smoothly and exactly as scheduled. Once installed, the piles were rigorously tested in tension to ensure they achieved the required load specifications—a necessary step for guaranteeing the long-term integrity of the structure above.

The specification required the piles to be perfectly embedded within the proposed concrete slab for a robust connection. To enhance the connection and increase punching shear resistance, a steel plate was fixed to the top of each pile. Our team meticulously levelled all the piles to a datum provided by the main contractor, ensuring an equal and consistent embedment across the entire footprint of the proposed raft slab. This precision is key to ensuring the load is distributed evenly across the new structure.

Once our work was complete, we removed all our lightweight equipment, leaving the site tidy and ready for the next phase. The slab reinforcement can now be installed, and the concrete will be cast, encasing both the pile heads and the steel mesh. This harmonious combination provides a robust and ‘neat’ solution, ready to bear the weight of the new garage, safe in the knowledge that both the structure and the surrounding natural environment have been respected.

If you are a Structural Engineer facing a complex foundation challenge, a Property Developer looking for an efficient alternative to concrete foundations near tree roots, or a Homeowner hoping to build without felling a cherished tree, the Target Fixings Heli Pile system, installed by Target Structural Chiltern, is the advanced, non-disruptive solution you need. Contact us today to discuss how our Heli Piles technology can secure your next build.