Running sand is a well-known challenge in groundworks, particularly when it comes to mini piling (which is our specialism here at Vxcel Piling). Now, with around 15 years of experience behind us, we’re no strangers to running sand, and its potential to create significant complications during installation. If it’s not properly accounted for, it can end up affecting both the structural integrity of the piles and the overall progress of a project. Happily though, it’s not an issue that we’ll encounter on every project, and it can often be mitigated with enough preparation in advance.
In case you need a quick primer, here’s what you need to know.
What is running sand?
Running sand is a condition where sand behaves like a fluid due to water saturation or mechanical disturbance. It occurs in loose, granular soil that contains a high percentage of fine to medium sand particles. When groundwater levels are high or when external pressure disturbs the soil (such as excavation), the sand can lose its ability to support weight and begins to flow. This makes it incredibly unstable, leading to issues such as ground subsidence, loss of bearing capacity, and difficulties in construction.
As we’ve touched upon above, it’s not an issue that you’re guaranteed to face on your own project. It’s typically found in coastal areas, riverbanks, and locations with a high water table. However, one of the main reasons that it can cause problems is that it can appear solid until disturbed. Once movement begins, the sand effectively turns into a liquid-like state, making it challenging to work with – and potentially even hazardous for construction projects that require stable ground conditions.
Why can it cause problems for mini piling?
So, we’ve covered it in broad strokes so far – now let’s go into a little more detail. Mini piling relies on stable ground to support the piles and ensure they can bear the required loads. Running sand can introduce several problems that can severely impact the installation process and the long-term performance of the piles.
One of the main issues is borehole instability. As mini piles are installed, the surrounding soil needs to remain intact to provide lateral support. However, with running sand, the walls of the bore can collapse or shift, leading to deviations in pile placement or even complete failure of the bore. This can make it difficult to achieve the required depth and alignment for the piles.
Running sand can also affect load-bearing capacity. Since it behaves like a liquid when disturbed, it does not provide the firm resistance that piles need to transfer loads effectively. If not properly stabilised, piles installed in running sand may experience excessive settlement or even structural failure over time.
Then there’s the potential issue of dewatering. Given that running sand is associated with high groundwater levels, any attempt to excavate or drill into it can cause water ingress, making the working conditions even more difficult. This can slow down installation, increase costs, and require additional reinforcement to prevent collapse.
So, those are the three main challenges. A couple of other ones include:
- Difficulty maintaining vertical alignment. When the borehole is unstable, piles may shift or deviate from their intended position, compromising the accuracy of installation.
- Risk of over-excavation. As sand flows into the borehole, more material than necessary may be removed, leading to increased material use and difficulty achieving proper pile embedment.
- Issues with concrete placement. Unstable sand can cause concrete to mix with soil particles or become diluted with excess water, affecting its integrity and curing process.
- Increased wear on equipment. Constant movement of sand and water can put additional strain on drilling tools and pumps, which can sometimes cause delays.
Are there any effective ways to deal with it?
Happily, yes. Despite the challenges posed by running sand, there are several techniques that we can use to manage its effects and ensure successful installation – and we’ve got plenty of practice in doing so!
One common approach is the use of temporary casings. A steel or plastic casing inserted into the borehole as drilling progresses prevents the surrounding sand from collapsing. This provides stability throughout the installation process and ensures the pile remains in place. Once the pile is installed, the casing can either be removed or left in place depending on the design requirements.
Another effective method is the introduction of drilling fluids. Specialised polymer-based or bentonite slurry can create a stabilising pressure within the borehole, reducing the risk of collapse and keeping the sand in place while the pile is installed. These fluids also help to control water ingress and improve the overall drilling process.
Dewatering techniques, such as well-point systems or deep wells, can also be employed to lower the groundwater level before work begins. Reducing the water pressure in the surrounding soil minimises running sand conditions, allowing for easier and more controlled pile installation.
In cases where running sand is particularly problematic, ground stabilisation techniques like grouting may be used. This involves injecting cementitious or chemical grouts into the sand that helps bind the particles together, creating a firmer, more stable base for piling work. This approach is especially useful in situations where deep excavations or heavy loads are involved.
Careful planning and site investigation are also key factors in dealing with running sand effectively. Conducting thorough ground surveys before starting a project helps identify potential problem areas, which can help us to implement the right mitigation strategies from the outset.
That’s all the essentials covered! We should end by reiterating – in most projects, running sand isn’t something to worry too much about, as it’s fairly uncommon, and we have a whole range of options at our disposal for resolving its challenges here at Vxcel Piling. However, if you do still have any doubts or queries, don’t hesitate to let us know.
On the other hand, if you’re all set to start your project, we’re ready when you are. With well over a decade of experience, we’re here to make every aspect of the project go smoothly, and we’ve got all the in-house expertise and equipment we need to get it done. You can give us a call on 01254 314010 or to find out what we’ve achieved for previous customers, feel free to take a look through our case studies!
