Trial Pit Excavation Services
Detailed Ground Assessment Through Controlled Excavation
Trial pits are a widely used and highly effective method of investigating near-surface ground conditions. Chelmer provide a comprehensive trial pit service as part of their site investigation and subsidence offering, allowing direct visual inspection of the ground, foundations and any buried features. This method provides valuable information that supports both geotechnical design and the assessment of existing structures.
Trial pits can be undertaken using a range of excavation techniques, depending on site conditions, access restrictions and the objectives of the investigation. Both hand excavation and mechanical excavation methods are available, ensuring that each trial pit is carried out safely and efficiently while obtaining the required level of detail.
Excavation Methods
Chelmer utilise two primary approaches when carrying out trial pits, selecting the most appropriate method based on the specific requirements of the project.
Hand Dug Trial Pits are typically used in areas where access is restricted or where a more controlled excavation is required. This method is commonly adopted for domestic properties, internal investigations or sensitive locations where existing structures must be carefully exposed. Hand excavation is particularly useful for exposing existing foundations in subsidence investigations, as well as for retrieving samples for contamination testing or CBR assessment.
Machine Dug Trial Pits are used where access allows and where deeper or more extensive excavation is required. Mechanical excavation is suitable for new build developments, soakage testing, contamination assessments and the exposure of deeper foundations or underground services such as drainage runs and sewers. This method allows larger areas to be investigated quickly while still maintaining control over the excavation process.
Health and Safety Considerations
All trial pit excavations are carried out in accordance with current health and safety regulations. Where excavations exceed depths of approximately 1.5 metres, appropriate shoring or support systems are implemented to ensure the safety of operatives and the stability of the excavation. Chelmer’s teams are fully trained and equipped to manage these requirements, ensuring that all works are completed safely and in compliance with industry standards.
Careful planning is undertaken prior to excavation to identify any potential risks, including the presence of underground services or unstable ground conditions. This approach minimises disruption and ensures that investigations can proceed without unnecessary delays.
Sampling and In-Situ Testing
Trial pits provide an excellent opportunity to retrieve soil samples directly from the ground for further analysis. Both disturbed samples and bulk samples can be collected during excavation and submitted to Chelmer’s in-house laboratory for geotechnical or contamination testing as required.
In addition to sampling, trial pits allow for a range of in-situ testing methods to be carried out. Depending on ground conditions, tests such as shear vane testing or Mackintosh probing may be undertaken to assess soil strength and consistency. These tests are particularly useful in situations where rapid assessment is required to support design or investigation objectives.
Trial Pits in Subsidence Investigations
Trial pits play a critical role in subsidence investigations, where they are primarily used to expose and inspect existing foundations. By excavating adjacent to a structure, Chelmer are able to determine foundation depth, type and condition, as well as identify any signs of movement or deterioration.
Detailed records are taken during the excavation process, including photographs and measured sections, which are incorporated into the final report. Where required, extended trial pits can be undertaken to expose structural elements such as underpinning, ground beams, pads or pile caps, providing a more complete understanding of the construction.
Trial pits are often used in conjunction with boreholes and other investigation methods to build a comprehensive picture of ground conditions. This combined approach ensures that all relevant factors contributing to subsidence can be identified and assessed accurately.
Locating Services and Supporting Investigations
In addition to foundation exposure, trial pits are frequently used to locate underground services such as drainage systems, sewers and utility runs. This is particularly useful on sites where existing records are incomplete or unreliable, allowing services to be identified and confirmed prior to further works being carried out.
Trial pits may also be used to support soakage testing and other site-specific investigations, providing direct access to the ground and enabling accurate assessment of soil conditions. Their versatility makes them an essential tool across a wide range of investigation scenarios.
Integrated Reporting and Service Delivery
All findings from trial pit investigations are carefully recorded and incorporated into Chelmer’s reporting process. By combining excavation data with laboratory testing and consultancy input, a clear and comprehensive understanding of site conditions can be achieved.
Chelmer’s integrated approach ensures that trial pit investigations form part of a coordinated service, supporting efficient project delivery and informed decision-making. Whether used for new developments, structural assessments or subsidence investigations, trial pits provide reliable and practical insight into ground conditions at shallow depths.