14 Nov, 2023

Site investigations are crucial in determining ground conditions and subsurface, assessing the suitability of a site for development, and identifying any potential contamination risks. They provide valuable insights to assist in construction and environmental projects. 

Borehole drilling and coring is one of the most popular methods of site investigation consultancy services. Two of the most efficient techniques within this include windowless/window sampling and cable percussion drilling. 

Both techniques provide effective and reliable intelligence and can be undertaken on a wide range of sites. These services can also be tailored to meet specific development or investigation needs.

In this article, we are going to take a deeper look into the power and efficiency of both techniques and their effectiveness in gathering reliable data.

What Is the Purpose of Windowless/Window Sampling & Cable Percussion Drilling?

Windowless Sampling (often just called window sampling) allows geotechnical experts to collect soil samples to assess soil properties, determine contamination levels, evaluate soil structure, and provide support in engineering design and the environmental impact of developments. Windowless/window sampling is typically used to a depth of up to 10m below ground level.

Where greater depths are required, cable percussion drilling is often used to investigate soil profiles for geotechnical sites or ground investigations and allows deeper boreholes to be sunk to depths beyond 40m below ground level. This technique generally offers greater depth of sampling than window sampling. Cable percussion drilling is the most commonly used technique for drilling and sampling.

Both techniques provide valuable data and insights, allowing engineers and environmental experts to make informed decisions about project safety and the development of potential sites. 

Understanding Windowless/Window Sampling

Windowless, or window sampling, is particularly useful for retrieving relatively shallow undisturbed soil samples for geotechnical and environmental site investigations. 

The process involves the insertion of a thin-walled, transparent tube (made from semi-clear materials such as acrylic or PVC) within a steel sampler into the ground using a percussion hammer or direct push technology. The tube supports the retrieved soil samples which can be observed visually and allows for accurate assessments of the layering and presence of any contamination or other issues. 

There are lots of advantages to window/windowless sampling. This technique provides undisturbed samples and preserves the natural structure and properties of the soil. This can be vital when assessing the composition, stratigraphy, and contamination of soils. Windowless sampling minimises cross-contamination between soil layers which is unavoidable with other drilling techniques.

Windowless sampling provides vital geotechnical investigations to determine soil properties that are essential for foundation design before the progression of construction projects. 

This is a valuable technique that provides quick and efficient data for assessment, making it a cost-effective option for many industries. 

When to Use This Method?

Windowless, or window sampling, is often used in a range of geotechnical and environmental situations where the collection of relatively undisturbed soil or sediment samples is necessary, such as:

  • Environmental site assessments
  • Geotechnical site investigations
  • Contaminated land remediation schemes
  • Groundwater monitoring wells
  • Ground gas monitoring wells
  • Sampling for laboratory testing
  • Foundation design
  • Land development and due diligence
  • Mineral exploration

This technique of borehole drilling is usually used due to its small footprint and versatile access capabilities allowing it to traverse site quickly where other rigs would be unable to access. Its visual inspection and non-disruptive nature make it a valuable environmental, geotechnical, and geological tool to aid in investigations. 

Window sampling also allows core and bulk samples to be taken for laboratory testing, and contamination testing in line with regulations such as BS EN ISO 14688-1 and BS EN ISO 14689-1.

Understanding Cable Percussion Drilling

Cable percussion drilling requires a more open site with access for a 4x4 vehicle, this vehicle is used to tow the rig and carry extra equipment. Cable drilling requires an area of approximately 5x5m to enable the setup of the rig and safe working. 

The tools used in cable percussion drilling include augers, shells, and sampling tubes which are all suited to different subsurface conditions.

Once set up is complete, the tool is lowered into the ground and drilling is actioned by repeatedly lifting and dropping a heavy weight. The repetition of the lifting and dropping of the weight impacts the tool which breaks up soil/rock, following which, cuttings can be removed from the surface. 

There are lots of advantages in cable percussion drilling. It provides reliable and high-quality samples making it ideal for geotechnical assessment. Cable drilling is also very versatile and is suitable for soils and moderately hard rocks. It can penetrate various layers allowing samples to be taken from each layer. 

This method of borehole drilling is a robust and reliable technique that offers quicker sampling compared to some other drilling techniques. It is also cost-effective for projects with budget constraints. 

When to Use This Method?

Cable percussion drilling is often used in a range of geotechnical and environmental situations to provide accurate soil and rock samples, such as:

  • Geotechnical Site Investigations
  • Environmental Assessments
  • Mineral Exploration
  • Contaminated land remediation schemes
  • Water well Installation
  • Groundwater monitoring wells
  • Ground gas monitoring wells
  • Sampling for laboratory testing
  • Foundation design
  • Land development and due diligence
  • Geological studies

This type of site investigation method can help in collating interpretative reports to provide advice on foundation design solutions, contamination levels, and any necessary remediation measures required for specific developments.

Cable percussion drilling is a powerful method more commonly used to gather geotechnical data for designing piled foundations at depths beyond window sampling limits. 

Our Borehole Drilling Services

At ACS, we have been providing quality testing and material consultancy to the construction industry since 1987. 

We provide a full range of drilling and coring services, including:

  • Windowless sampling
  • Cable percussion sampling
  • Rotary sampling, Rotary Sonic sampling
  • Limited access cut-down and modular drilling rigs

We have extensive equipment held and operated by ourselves and available through our trusted subcontractors, including all the latest borehole drilling equipment. 

Our expert experience and equipment allow us to undertake a wide range of investigation services across the whole of the South of England, Midlands, London, Wales, and the Isle of Wight to British and European Standards. Our services can be tailored to suit every individual project or development.

We provide our clients with UKAS-accredited sampling of materials including aggregates, bituminous, concrete, soils, and water monitoring. We understand the needs of our clients and offer both day and night work, whatever the weather, to meet deadlines where appropriate to ensure projects are not delayed.