Trees on a plot of land

Author: Michael Willoughby

Site Investigation and Piling for UK Construction: Standards and Common Pitfalls

A site investigation is crucial for construction in the UK to ensure planning permission and successful project completion. Without performing one properly, you may run into weak soil types, a poorly calculated water table or buried obstructions, which can delay a project or make it non-viable. 

Ahead of the 2026 Geotechnical Engineering & Operations (GEO) Expo, we discuss the major stages of site investigation, piling machines and techniques that create stable site foundations, and the standards governing this work. We also highlight common mistakes contractors make that can cost time and money. 

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What Is a Site Investigation? 

Construction teams often begin a project by carrying out a site investigation. This stage assesses the land's viability, identifies risks and formulates a plan to remediate them, making it a critical part of project planning. Its success equally depends on two other types of land examination.

While a site investigation covers the proposed site — everything from environmental, archaeological and legal factors to ground conditions — a ground investigation focuses on the soil, rock, groundwater and contamination. 

Meanwhile, in a geotechnical survey, experts examine the structural strength and behaviour of the ground, measuring soil-bearing capacity, slope stability and shear strength. 

What site investigations seek to uncover

  • Soil conditions must be robust enough to support structures without them collapsing or the soil suffering from subsidence. If they aren't sufficiently strong, the structure must be piled: a process that drives or drills long, thin elements (piles) below the structure.
  • Rock strata can either act as a reliable foundation layer or impede excavation and piling. Weak rock can interfere with otherwise dependable foundations. 
  • Groundwater levels must be taken into account before building. A high water table makes excavation harder, interferes with foundation design and increases the risk of flooding and rising damp in the completed project. 
  • Contamination from previous industrial activities can cause sickness or even death of people and animals who later occupy the site — the most concerning risk for regulators.
  • Existing structures and obstructions need to be logged and potentially dismantled so the new project can be completed within time and cost constraints. Projects must also account for legal and heritage restrictions such as archaeological finds, protected habitats and rights of way. 
  • Geotechnical hazards such as disused mine shafts, sinkholes, unstable slopes or running sand can undermine buildings.

Why early investigation saves money

Reduces uncertainty 

The earlier contractors become aware of site constraints and composition, the fewer surprises they encounter on the project, reducing the chance of long delays.  

Prevents costly redesigns

Discovering something halfway through a project — for example, finding that the piling method no longer works due to over-shallow bedrock — requires engineers to go back to the drawing board and rescope the entire project, which can significantly increase costs.  

Improves procurement accuracy 

When a team understands the lay of the land, it has an accurate picture of the project scope and price, including machinery and materials. 

Supports regulatory compliance

A timely investigation helps the project stay aligned with planning permissions and standards from the outset, avoiding unexpected delays. 

The Stages of a Site Investigation 

A properly phased and scoped site investigation with clear objectives is necessary to get the critical data on which foundation design depends. 

Phase 1: Desk study and preliminary assessment

A desk-based study uses maps, geo-environmental data, any mining data, borehole logs and the site's planning history to reveal what the site might be hiding — for example, a history of landfill suggesting contamination or old mines. The goal is to make sure the right risks are targeted in the next stages. 

Phase 2: Site reconnaissance

During site reconnaissance or walkover survey, engineers test the findings of the desk study against actual ground conditions. They note signs of instability, surface water, drainage, vegetation, existing structures and services, and evidence of prior use or contamination. They assess where plants can access. The findings shape the drilling plan: the borehole positions, which risks from the desk study need sampling first, and whether access constraints affect the rig type. 

Phase 3: Intrusive investigation

Deep and thorough borehole investigations are essential for economic and appropriate piled foundations. The rule of thumb is to bore at least three to five metres below the projected pile toe. It's far cheaper to bore deep enough the first time than to discover mid-construction that piles extend below your target. In that case, you might be forced to run another ground investigation while the piling machine and crew stand idle.

In softer soils, cable percussive rigs can be the most economical; harder grounds might require rotary coring. 

Phase 4: Testing and reporting

In-situ and laboratory testing generate the data needed for optimal foundation design and risk mitigation. 

Some of the most common and important tests engineers carry out include: 

  • Standard penetration testing (SPT) counts the blows needed to drive the sampler a set depth — an index of the soil's density and strength.
  • Unconfined compressive strength (UCS) tests how much stress rock or clay soil can take before they fail. Stronger rock allows for shallower or fewer foundations. 
  • Sulphate testing examines how damaging soil is to concrete over time. Tests need to be conducted at every stratum. 
  • The Atterberg limit test gauges the moisture content at which ground changes between solid, plastic and liquid states. 
  • Particle size distribution (PSD) test classifies soil by grain size and sand, silt or clay make-up, which affects permeability, frost susceptibility and shear strength — key factors that affect how suitable soil is for foundations. 

These test results inform a two-part ground investigation report. The factual part includes the borehole logs, test results and groundwater readings. The interpretive part creates a ground model and details founding recommendations and risks. 

This ground investigation report forms the basis of the wider geotechnical design report. Both these reports are covered by Eurocode 7 (see below).  

What Is Piling, and When Does it Become Necessary?

Piles are typically made of steel or reinforced concrete. Driven or drilled beneath a structure, they transfer its vertical load past weak surface soils into deeper, more dependable soil or rock.  

Piling may be needed in several cases, such as: 

  • Weak or compressible soils, which are unsuitable for shallow foundations. Loose or saturated sands and gravels settle or erode; soft clays shrink and swell with moisture, causing heave; silts are weak when wet; and peat is highly compressible. 
  • Sites with a history of mining, tunnelling or subsidence, which usually don't have sufficient structural integrity due to cavities or cracks in the ground. 
  • Large buildings such as skyscrapers, which naturally demand more bearing from the ground. 
  • Urban development sites where buildings are close together, and sites have obstructions from prior development, limiting foundation options. 
  • Infrastructure projects such as bridges or railway embankments, which impose a heavy load on the ground that shallow foundations won't carry.

Common Piling Methods Used in UK Construction 

Piling can be of two types: displacement piling, which pushes soil aside, and replacement (or bored) piling, which removes soil before the space is filled with concrete. Displacement piling includes driven or screw augers. Mini-piling and sheet piling are variants used in specific situations; these can be either driven or bored. 

Each method uses a different type of piling machine. The one you choose will depend on ground conditions, load and site constraints.  

Driven piling

Driven piles are normally precast concrete or steel, pressed or hammered into the soil to push it sideways, creating a compact zone. Though fast and economical, the noise and vibration make the method unsuitable for urban sites or construction work close to nearby foundations. 

Screw auger piling

Screw auger piling compacts soil through rotational pressure. As the tool withdraws, concrete is injected into the soil. The lower spoil makes the method ideal for contaminated sites where removing arisings is expensive.

Bored piling

This type of piling involves drilling large holes into the ground and filling them with concrete. The load is transferred through a steel reinforcement cage set in the mix. These methods produce a lot of spoil, but are low on vibration and favoured in inner-city sites. 

  • Rotary bored piles are drilled in a temporary casing to hold the bore open while earth and rock are removed. A steel cage is then installed to the full length of the open bore before concreting. Often used in big infrastructure schemes, rotary boring can push through obstructions, go deeper and handle larger diameters than CFA. 
  • Continuous flight auger (CFA) is bored piling without a temporary casing; the auger itself supports the bore. It's extremely common in the UK due to its versatility and speed, and suits soft, wet and granular ground. Concrete is pumped through the auger stem as it’s withdrawn, and a steel reinforcement cage is plunged into this wet concrete.

Mini-piling

These piles are between 100 and 300 mm and can be bored or driven. Fitted with smaller, more manoeuvrable piling machines, they're ideal where access or headroom is low. Despite their size, they can carry substantial loads down to a suitable stratum. 

Sheet piling

Sheet piles are interlocking sections pushed down to form a continuous wall to retain soil or water or to support excavations. 

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Piling Methods: A Comparison 

Method

Ground suitability

Key advantage

Key limitation

Driven

Variable; needs a firm bearing stratum

Fast and affordable with no spoilage

Can't be used easily in sensitive urban sites or near existing structures due to noise and vibration

Screw auger 

Softer, granular soils; ideal for contaminated sites

Low spoil reduces the cost of arisings

Not suitable in very hard ground or where obstructions exist

Rotary bored 

Any, including hard and obstructed rock

Large diameters and depth with full-length reinforcement cage

Creates significant spoil to be removed and is slower, requiring more coordination 

CFA

Soft, wet and granular, even below the water table

Default in the UK due to versatility and low vibration

The plunged cage limits potential depth; not suited to extremely hard ground 

Mini-piling

Most ground types down to a stable stratum

Good for sites with narrow access and low headroom

Limited load per pile

UK Standards for Site Investigation and Piling 

A framework of British and European standards governs ground investigation and piling in the UK. These standards: 

  • Define competent practice.
  • Give all parties (clients, designers and contractors) a common technical language.
  • Standardise the basis of planning permission or building regulations approval.

Additionally, when the right standards are specified in a brief, contractors can accurately price their tenders. We've listed below the most important standards to follow throughout a project's development. 

Investigating the ground

  • BS 5930:2015+A1:2020: The Code of Practice for Ground Investigations, the overarching UK guide to desk study, boring, sampling and reporting.
  • BS 10175: The standard for investigating potentially contaminated land and assessing and managing risk. 
  • BS EN ISO 22476: A series specifying how geotechnical investigation and field testing should be carried out.

Designing the foundation 

  • Eurocode 7 (BS EN 1997): The geotechnical design code. It's currently transitioning to a second generation. The new parts (BS EN 1997-1:2024 and -3:2025) have been published, while -2:2024 is under review. The first-generation code will stay in force until March 2028. 

Building the piles

Specification and industry guidance

Common Procurement and Specification Mistakes 

  • Under-scoping the ground investigation: Inadequate scoping can leave gaps in crucial data that need to be filled in later, usually at greater expense. A thorough desk study should scope the work to cover all build aspects, from foundation requirements to contamination.
  • Procuring on price alone: It's tempting to go with the most affordable option when hiring a specialist. However, a low-quality ground investigation is a false economy; it might produce design data, but won't reduce risk.
  • Separating investigation from design decisions: Ground investigations are meant to provide data for pile selection and design. If the two aren't connected, the investigation can probe the wrong location and depths, gathering data that design doesn't need while missing what's crucial.  Sometimes, the data doesn't reach the right people, so the foundation design and choice of piling are uninformed, causing various types of failures. 
  • Not accounting for contamination or obstructions: In addition to testing the strength and integrity of the ground, site investigations need to locate contamination or buried obstructions so that planners can account for the time and costs of any remediation or removal at a project's start.
  • Choosing a piling method too early: A site investigation aims to establish the ground conditions before foundation design. The piling method should be chosen after these have been determined, so the design team doesn't incorrectly commit to, say, CFA where there are buried rocks, or to driven piles before a vibration-sensitive site rules them out. Switching to another method midway can be costly. 
  • Getting procurement wrong: A leading industry survey identified the biggest barriers linked to procurement as poor engagement with specialists, late procurement, non-ground specialists managing investigations, inappropriate contracts, poor risk allocation and inadequate budgets.

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Where to Stay Current on Geotechnical Practice and Standards 

Follow these standout sources to stay current on geotechnical practices.

The GEO Expo, part of the 2026 Environmental Services & Solutions (ESS) Expo, will bring together geotechnical engineers, piling contractors, ground investigation specialists and equipment suppliers. Learn about the latest rigs and techniques and hear from the people shaping best practices and standards to stay ahead of the industry. 

Don't miss out on the UK's leading geotechnical event. Get your free tickets today. 

FAQs: Site Investigation and Piling for UK Construction 

What ground investigation is required before piling?

A staged ground investigation consisting of a desk study and a walkover. This should be followed by intrusive investigation, boreholes that extend below the proposed pile depth, then in-situ and lab testing. Results of these investigations are written up into a ground investigation report, which drives pile selection and foundation design. 

What is the difference between displacement and replacement piling? 

Displacement piles (driven and screw auger) compact soil as they are installed, without creating spoil. Replacement piles or bored piles, including rotary bored and CFA, remove the soil and then fill the gap with concrete around a steel reinforcement cage. 

What standards apply to piling in the UK?

Eurocode 7 (BS EN 1997) covers geotechnical design. It's currently transitioning to a second generation, with the first remaining in force until March 2028. Execution is guided by BS EN 1536 for bored piles, BS EN 12699 for displacement piles and BS EN 14199 for micropiles. Ground investigation is covered by BS 5930. 

Author bio: Michael Willoughby is a British content writer and journalist based in Kosovo. He has more than 20 years' experience in B2B communications, starting as a dot-com PR practitioner in New York City. He later retrained as a journalist and became a staff writer on OnOffice and Building magazines, covering sustainability, construction, architecture, engineering and the built environment. He was communications manager for Willmott Dixon's Re-Thinking (sustainability) department.

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About ESS Expo: Environmental Services & Solutions Expo (ESS Expo) is the UK's largest cross-sector environmental event, taking place annually at the NEC Birmingham. ESS Expo 2026 runs 16-17 September and unites seven co-located industry shows spanning resource, waste management, recycling, water management, air quality, sustainable engineering, decarbonisation, land remediation, circular economy,  net zero, energy from waste, and geotechnical engineering. Register free at ess-expo.co.uk.

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