Artificial Pitches – Subsurface Investigation, London

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Project summary:

The client, a sports construction and estate infrastructure specialist who provides end-to-end solutions for new build and refurbishment projects. As part of its Sports Construction Division, the client will undertake the installation, maintenance, and repair of artificial turf sports pitches across independent schools, sports clubs, contractors, and leisure operators nationwide.

The artificial pitches are typically constructed with 250mm of MOT type 3 sub-base, a 40mm porous Macadam base, and a 15-25mm rubber shock pad covered in artificial turf. When removing and replacing the artificial turf, the client would often find deterioration of the sub-base, or other layers underneath, mainly due to the general wear and tear of the pitch. The team wanted to find a non-intrusive way to understand the level of deterioration before the new turf was laid so they could effectively estimate and schedule the work without damaging or digging up the pitch or affecting the daily operation of the pitches.


The brief:

The client turned to Murphy Geospatial to determine the best non-intrusive method to investigate and determine the deterioration of the pitch below the top layers.

Following a full review of the project, Murphy Geospatial recommended the use of Ground Penetrating Radar (GPR) as the best method to determine the details and conditions of the construction layers of the pitches. GPR technology uses radar pulses to quickly and non-intrusively image through the artificial grass and top layers, preventing any damage to the pitch in the process.

The length of grass, the shock pads, and other construction features that would affect the GPR signal were theorised, however, were not exactly known thus a trial survey was conducted to prove the theory.


The challenges:

The trial was undertaken using two different GSSI GPR systems to determine the most effective system. As a general rule of thumb, the higher the antenna frequency the higher the resolution of data collected, although with a loss of depth penetration.

The systems used included:

  • A GSSI StructureScan MiniXT all in one GPR system with a pulsed antenna with a central frequency of 2.7 GHz.
  • A GSSI SIR-4000 control unit with a pulsed antenna with a central frequency of 1.6 GHz.


Our work:

Two different pitches were scanned for the trial in less than a day. These consisted of a 3G and sand-dressed pitch. A number of single scans were collected across the length and breadth of both pitches using both GPR systems. All of the captured site data was sent to our in-house geophysics team for processing and analysis using Radan 7, a state-of-the-art post-processing tool. The data was subject to a number of post-processing methods, including background removal, deconvolution, and stacking and was delivered back to the client within a few days.


Results:

The GPR subsurface investigation survey was successful in determining a number of layer interfaces and features across both pitches.


Figure 1: A scan showing typical a 3G pitch construction, scan taken from 1.6GHz data. Note that the vertical scale is only correct for the top ~30mm


Figure 2: A scan showing a typical sand-dressed pitch construction, scan taken from 1.6GHz data. Note that the vertical scale is only correct for the top ~60mm


Layer Thickness and Variation

For both pitches, GPR was able to resolve three construction layers, thought to be the FieldTurf and rubber shock pad layer, the macadam base, and the MOT type 3 stone sub-base. It was also possible to determine the thickness of these layers as well as determine variations of the layers and their interfaces, helping the team at S&C Slatter determine the level of deterioration of the different layers.

For this trial, the data was collected on random single scans and no previous knowledge of deterioration was known about the site. The trial was undertaken during wet weather and it’s thought that this caused an increase in the moisture content of the sub-base, resulting in high attenuation; these details were factored in during the post-processing of the data.

The trial concluded successfully with GPR chosen as the best method to conduct the subsurface investigation to map variations and possible deteriorations.


Contact:

For more information on this project, please contact Andy Kitson at akitson@murphygs.com or +44 203 598 3775


  • Client

    Artificial Pitch Construction

  • Sector/Market

    Infrastructure

  • Services

    InspectionSubsurface Investigation

  • Location

    London, UK

Services Used

Service Image

Inspection

Service Image

Subsurface Investigation

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