Everything You Need to Know About Ground Investigations

There are so many benefits to procuring a ground investigation of your site. Our team of experts can discuss your project to ensure we understand the purpose and the specific details which are important to report on.

In this guide, we provide all the information you need to know about ground investigations, and answer some of the frequently asked questions we receive from our clients regarding ground investigation works.

What is a Ground Investigation?

A ground investigation is used to assess the ground conditions and sub surface structure of a site. Ideally, a ground investigation should be deployed before the construction on the site starts. Ground investigations are a vitally important aspect of any development project, as having a detailed understanding of what you are building on is vital to the success of the construction process.

It is imperative to gain an accurate understanding of ground conditions when undertaking a development project. This will determine whether a proposed building design is feasible and safe from a geotechnical perspective.

When is a Ground Investigation Survey Needed?

A ground investigation is essential for gathering factual data for the underlying geology and groundwater levels, that can be interpreted for geotechnical and geo-environmental purposes across a wide range of projects, including residential and commercial developments, as well as infrastructure like highways and bridges.

Ground Investigation is required by but not limited to:

• Architects and Engineers.
• Construction Contractors.
• Environmental Consultants.
• Geotechnical and Civil Engineers.
• Property Developers.

The Steps Involved in Ground Investigations

To ensure that the outcome of a ground investigation fulfils the objectives of your project, we will follow the steps below and keep you informed throughout the project:

• Evaluate the Project specification
• Produce Phase 1 Desk Study which includes historical maps, published geology and environmental data
• Identify the methodology that fits to purpose and produce a scope of work
• Produce Method Statements and Risk Assessments
• Undertake Site Works
• Undertake Laboratory Testing
• Ground Investigation Report

What is the Difference Between a Geotechnical and a Geoenvironmental Survey?

Both surveys use similar site techniques, but the data obtained and how we manage the data make the difference. The difference comes in the type of samples obtained, the scheduled laboratory tests and data interpretation.

More specifically:

• Geotechnical surveys primarily focus on engineering properties of the soil and rock. The main objective is to assess the soil and rock conditions to determine their suitability for construction projects, including foundations, retaining walls, and other structures. Geotechnical surveys provide information about factors such as soil composition, bearing capacity, compaction, and shear strength.
• Geoenvironmental surveys are conducted to assess the environmental quality of a site. These surveys aim to identify potential environmental hazards, contamination, and risks associated with soil and groundwater. The focus is on investigating the presence of contaminants, such as hazardous chemicals, heavy metals, and pollutants, as well as their potential impact on the environment and human health.

How Do You Manage and Report the Risks of a Site?

Depending on the site, a range of risks can be recognised, including the potential for unsuitable ground conditions for the intended use of land. Technics goal is to determine the most appropriate ground investigation techniques that align with the site’s characteristics and its current or future land use and deliver results that fit the purpose of the project. All results are provided to the client as a Factual or Interpretative Report according to the project requirements.

Here are a few examples.

• In some instances, the ground conditions may not be suitable for the intended development, necessitating adjustments to the initial foundation design. A Ground Investigation Report plays a crucial role by offering the civil engineer design values and soil-bearing capacities. This information assists the engineer in making necessary modifications to ensure the project’s structural integrity.
• During a ground investigation, it’s possible to come across unforeseen contamination resulting from historical land use, which will necessitate remediation to ensure the safety of the area for future users. This remediation process may involve actions such as implementing capping layers for soft landscapes or installing gas membranes and suitable ventilation systems in buildings to cut the pathway of contamination.
• Intrusive site investigation methods, like coring, are effective in uncovering potential weaknesses in structures, and this technique can be applied across a diverse range of projects, including buildings, retaining walls, bridges, and highways. Coring provides valuable insights into the composition of these structures, and it allows us to collect samples for laboratory testing, which, in turn, informs us about the strength of the materials used.

Does a Ground Investigation Mitigate the Risks?

Ground investigation doesn’t directly mitigate risks, but rather, it aims to identify the underlying hazards responsible for those risks (if any). The investigation process helps identify these hazards, allowing for the development of solutions or additional actions to reduce the likelihood of these hazards occurring. These hazards can be either poor ground conditions for future site development or ground and groundwater contamination.

Are There Any Limiting Factors With Ground Investigation Works?

Like any survey, ground investigation has its limitations. When we investigate the ground we can never achieve complete certainty about the challenges we may encounter on a site, even in simple projects, and that’s why we need to treat each project uniquely.

Limiting factors can be irrelevant to the ground conditions, such as limited access, safety hazards, buried services, overhead cables, working on highways or near rails, or in some cases there is the need for temporary works design to be undertaken to enable ground investigation works such as the building of a platform to allow access to the drilling locations.

Our work is to identify these limiting factors, evaluate them, and devise a detailed plan to overcome them.

What Methods and Techniques Will Be Used On-site for the Survey?

Depending on site requirements we can use a variety of ground investigation techniques, which are explained below.

Rotary Drilling

This method involves the use of a rotating drilling which is capable of core through and sampling various types of rock and soil and giving us Class A samples. We can get disturbed, bulk, SPT’s samples and core samples.

Percussion Drilling

This is a dynamic sampling technique where a drill bit is repeatedly lifted and dropped to sample any type of soil. This technique is relatively cheap and gives us samples to great depths. We can get disturbed, bulk, SPT’s and undisturbed samples.

Window Sampling

Small flexible dynamic sampling technique. The principle is the same as cable percussion but on a smaller scale. It reaches shallower depths and is cheap and ideal for areas with limited access. We can get disturbed, bulk, SPT samples.

Trial Pits

For shallow investigations, excavations or hand-dug trial pits are employed to visually inspect and sample soil up to a maximum depth of 1.20 meters below ground level. In cases requiring deeper investigations, machine-excavated trial pits are the preferred choice. We can get disturbed and bulk samples.

Insitu Testing

Hand Shear Vane – measures the shear strength in cohesive soils and informs us on Cu value.

TRL-DCP – a good way to get the bearing capacity of the soil and CBR% for shallow depths. This technique gives us essential information on flexible pavement and roadwork design.

Groundwater Monitoring – falling head test, rising head test: helps to measure the groundwater levels and calculate the permeability of the ground.

Soakaway Test – an infiltration test is a method used to determine the rate at which water can infiltrate through the ground. This information is crucial when designing drainage systems, particularly for soakaways.

What Standards Do You Adhere to for the Site Works and Reporting?

Technics are always keeping the highest standards in both on-site work and reporting. We work under the requirements of the CDM Regulations 2015. All our works are according to the standards below:

• BSI (2018) BS 1377-3:2018+A1:2021 – Methods of test for Soils for Civil Engineering Purposes – Chemical and electro-chemical testing – British Standard Institution
• BSI (2015) BS 5930:2015+A1:2020 – Code of Practice for Ground Investigation – British Standard Institution
• BSI (2017) BS 10175:2011+A2:2017 – Investigation of Potentially Contaminated Sites- Code of Practice – British Standard Institution
• BSI (2007) BS EN1997-2:2007 – Geotechnical Design: Part 2 Ground Investigation and Testing – British Standard Institution
• BS 8004:2015+A1:2020 – Code of practice for foundations

You may wish to read about our ground investigation work with Surrey County Council.

To discuss your project with our expert Michail Kamperis, please call 01483 230 080 or email enquiries@technicsgroup.com to discuss your ground investigation survey requirements. Alternatively, please use our contact form to get in touch.