Trial Pit Excavation UK | Ground Investigation Services

Understanding the shallow ground conditions beneath a site is essential for safe and cost-effective construction. At Phase Ground Investigations, we provide professional trial pit excavation services designed to give a clear visual assessment of sub-surface conditions. Trial pits are one of the simplest yet most informative methods for examining soil layers, identifying potential hazards, and collecting samples for testing.

Whether you are developing a new building, extending an existing structure, or assessing site feasibility, our trial pits provide the reliable data needed for informed decision-making.

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What Are Trial Pits?

Trial pits are shallow excavations—usually between 1 and 4 metres deep—dug to expose and visually inspect soil, rock and groundwater conditions. They allow engineers to directly observe the subsurface without relying solely on mechanical drilling or inferred data.

They can be excavated:

By machine for fast and efficient site coverage
By hand in restricted-access or sensitive locations

Because they combine practicality with high-quality information, trial pits are widely used in both early-stage and detailed site assessments.

What Trial Pits Can Identify

Trial pits help uncover a wide range of site conditions that can affect design, foundations and construction costs. They are particularly useful for confirming shallow ground conditions where deeper drilling may not be required.

Trial pits help identify:

Soil composition and bearing capacity
Made ground, fill materials and buried obstructions
Shallow groundwater levels and seepage
Changes in soil strata
Voids, soft spots or unstable ground
Evidence of shallow contamination
Suitability for soakaways or drainage features

This makes trial pits ideal for residential developments, small commercial projects, extensions, and early feasibility assessments.

Our Trial Pit Investigation Process

At Phase Ground Investigations, we follow a structured and safe investigation process to ensure consistent, high-quality results.

1. Pre-Excavation Preparation

Before any excavation, we undertake a detailed site review and safety checks to ensure everything can be carried out safely. This includes:

Utility drawings review
CAT & Genny scanning
Site walkover inspection
Risk assessments and method statements

This stage is essential for preventing service strikes and ensuring compliance.

2. Trial Pit Excavation

Trial pits are excavated using a mechanical excavator or hand tools depending on site constraints. During excavation, our engineers examine and record the soil profile layer by layer.

We document:

Soil types and consistency
Changes in strata
Depth of each material layer
Presence of groundwater
Buried structures or obstructions
Root systems or organic deposits

Photographs and logs are taken throughout excavation, providing a clear record for the final report.

3. Sample Collection & Infiltration Testing

If required, we take samples for laboratory analysis to better understand the geotechnical and environmental properties of the ground.

We can also carry out:

Soakaway (percolation) testing
Contamination sampling
Moisture content testing
Compaction and classification tests

These results help guide foundation design, drainage strategy and risk assessments.

4. Backfilling & Site Restoration

Once the inspection and sampling are complete, the trial pit is backfilled and the ground is compacted safely. We ensure the site is left clean and tidy with minimal disruption.

5. Reporting and Recommendations

You receive a clear, planning-ready report containing:

Full trial pit logs and descriptions
Soil layer analysis
Groundwater observations
Photographic records
Laboratory test results (if taken)
Foundation advice
Drainage and SuDS recommendations
Any further investigation requirements

Our reports are written in a practical, easy-to-understand format suitable for developers, architects, structural engineers and planners.

Why Choose Trial Pits?

Trial pits are highly valued because they offer an unmatched level of visual clarity compared to drilling methods. They are also fast, cost-effective and ideal for projects where shallow ground understanding is sufficien

Key advantages include:

Direct visual inspection of ground conditions
Fast results
Lower cost compared to deeper drilling
Minimal equipment required
Ideal for shallow foundations and extensions
Supports SuDS and soakaway design
Suitable for small or constrained sites

For many typical developments, trial pits provide exactly the information needed without the expense of deeper intrusive works.

Why Choose Phase Ground Investigations?

When carrying out trial pit investigations, choosing the right team ensures accuracy, safety and compliance. At Phase Ground Investigations, we deliver high-quality site data backed by technical expertise and modern equipment.

We provide:

Experienced engineering geologists and site technicians
Safe and compliant excavation methods
High-quality logging and sampling
Clear, reliable and planning-ready reports
Competitive pricing and fast turnaround
A tailored approach to each development site

We work on projects of all sizes—from single-plot extensions to large commercial developments.

Ready to Arrange a Trial Pit Excavation Services

If you’re planning a development, assessing a brownfield site, or concerned about radon levels in an existing property, we’re here to help.

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