The Beginner’s Guide to Piling

This beginner’s guide to piling aims to equip you with a comprehensive understanding of piling fundamentals. We’ll explore the various piling techniques, outline key stages like site investigation and pile testing, and delve into critical aspects such as equipment, safety protocols and contractor selection. By the end, you’ll be well-versed in the essential knowledge required to navigate piling works on any construction project with confidence.

What is Piling and Why is it Important?

Piling is a construction process where deep foundations are created by driving slender columns (called piles) into the ground to transfer structural loads through weak or unstable soil layers onto stronger, more compact soil or rock layers below. Piling is essential in many construction projects to provide a stable and secure base that can support the weight of the structure above.

Without proper piling, buildings constructed on poor soil conditions are at risk of uneven settlement or even catastrophic foundation failure. Piling allows structures to be safely built on sites with loose, soft, or water-saturated soils that would otherwise be unable to bear the loads imposed by the construction. Common applications where piling is necessary include high-rise buildings, bridges, offshore platforms, and other major infrastructure projects.

Main Types of Piling Systems

There are several main types of piling systems used in construction, categorised primarily by the materials used and installation methods:

Driven Piles

Precast concrete, steel, or timber piles that are driven into the ground using a piling rig with a heavy hammer or vibratory driver. Common driven pile types include precast reinforced concrete, steel H-piles, and timber piles.

Bored Piles

Also called cast-in-place or drilled shafts. These are formed by drilling a hole in the ground and filling it with concrete, sometimes with steel reinforcement added. The two main bored pile types are:

  • Continuous Flight Auger (CFA) piles formed by drilling with a hollow-stem auger and pumping concrete through it as the auger is extracted.
  • Drilled shafts where a hole is bored using buckets or drilling tools, a steel reinforcing cage is inserted, and then filled with concrete.

Other Piling Types

  • Driven and jacked piles – Precast concrete piles driven part way and then jacked deeper
  • Helical piles/screw piles – Steel shafts with helical plates screwed into the ground
  • Micropiles – Small diameter bored piles typically less than 300mm

The choice of piling system depends on factors like soil conditions, load requirements, groundwater levels, site access constraints, and project budget. In the next section, we’ll cover how to evaluate these factors when selecting a piling solution.

Factors to Consider When Choosing a Piling System

Several key factors need evaluation to determine the most suitable and cost-effective piling solution for a project:

Soil Conditions

Construction firms must investigate the soil type on site and its bearing capacity. Soil reports detailing the strata, strength parameters like SPT or CPT values, and groundwater levels are crucial. For example, contractors should prefer driven piles for dense granular soils, while bored piles are better for clays and loose sands.

Load Requirements

Companies need to anticipate the loads that the piles must resist, including compression, tension, and lateral loads from the superstructure and wind. This determines the required pile depth, diameter, and layout/spacing. Higher loads generally necessitate larger diameter or deeper piling solutions.

Site Access and Headroom

The available space and access routes on site impact what size of piling rig and equipment can be used. Restricted access urban sites may only accommodate smaller rigs for micropiles or CFA piles rather than large rigs for driven precast piles. Headroom limitations from overhead obstacles are also a factor.

Environmental Factors

Noise, vibration, and potential disruption caused by different piling methods need to be considered, especially in built-up areas near existing structures, utilities or sensitive receptors like hospitals. This may rule out impact-driven piling in some cases.

Project Timeline and Budget

The construction program and overall budget can influence pile type selection as different methods have varying production rates and costs associated with materials, labor and plant.

Piling Process Overview

Once the appropriate piling system is selected based on the above factors, the overall piling process generally involves the following key stages:

1. Site Investigation and Testing

Boreholes, trial pits and in-situ testing like CPTs are carried out to assess the ground conditions and determine the required pile depths and capacities. This data informs the piling design.

2. Piling Rig Selection and Setup

Contractors need to select the correct piling rig(s) and attachments based on the pile types, diameters, and anticipated lengths. They must properly set up the rig and make it operational with due consideration for working platforms, health and safety requirements, etc.

3. Pile Installation

Contractors perform the actual installation process, whether driving precast piles, continuous auger boring, or drilling/concreting bored piles. This stage is iterative across the required pile locations on site.

4. Testing and Quality Control

Companies must implement procedures like pile integrity testing, load testing on working piles, and monitoring of pile positions/verticality to validate the installed piling works meet the design specifications.

5. Addressing Challenges

Contractors need to promptly deal with potential challenges like obstructions, excessive pile drift or deflection, groundwater control issues, etc. on site through redesigns or mitigation measures to ensure project progress.

With the key factors considered and overall piling process outlined, we’ll next look at the specific equipment involved in pile installation works.

Piling Equipment and Accessories

A variety of specialised equipment and accessories are utilised for the installation of different piling systems:

Piling Rigs

These are the large machines that provide the power and guidance for driving precast piles or drilling/boring holes for cast-in-place piles. Common piling rig types include:

  • Impact Hammers: For driving precast concrete, steel or timber piles using a heavy ram that delivers vertical impact blows. Examples are drop hammers and hydraulic hammers.
  • Vibratory Hammers: Use a vibrating mechanism instead of blows to drive precast piles. Generates less noise/vibration than impact hammers.
  • Rotary Bored Piling Rigs: Used for drilling shafts for bored concrete piles. Can be crane-suspended, truck-mounted or self-erecting rigs with rotary Kelly bars and drilling tools.
  • Continuous Flight Auger (CFA) Rigs: Specialized piling rigs with hollow-stem continuous augers for boring holes and simultaneously pumping concrete to form CFA piles.

Pile Driving Accessories

  • Pile Caps/Helmets: Fitted on pile heads to protect them from damage during driving.
  • Pile Shoes: Reinforced conical tips attached to pile toes to aid penetration.
  • Splices: For joining precast pile segments during driving of longer piles.

Augers and Drilling Tools

  • Continuous flight hollow-stem augers for CFA piling
  • Bucket augers, core barrels, down-hole hammers for drilling bored pile shafts

Pile Accessories

  • Pile Casings: Temporary or permanent steel casings used to stabilise bored pile shafts
  • Pile Reinforcement: Rebar cages or steel reinforcement installed in bored piles

Monitoring and Testing Equipment

  • Inclinometers and Shape Arrays: Measure pile deviation/verticality
  • Strain Gauges: Embedded for testing pile integrity and load capacity
  • Pile Driving Analyzers: Attached sensors to monitor stresses during driving

Safety Considerations for Piling Works

Piling operations involve heavy construction machinery, deep excavations, and potentially hazardous procedures if not executed properly. Strict safety protocols need to be followed in line with regulations and industry best practices:

Regulations and Guidance

Key Risks and Hazards

  • Ground movement/collapse risks from excavations and pile drilling
  • Struck-by risks from pile driving rigs, suspended loads, moving plant
  • Noise and vibration hazards, especially for impact driving
  • Buried utility strike risks during piling works
  • Working at height risks for piling rigs and cranes

Control Measures

  • Mandatory Personal Protective Equipment (PPE) – hard hats, hi-vis, safety boots, etc.
  • Establishing and maintaining exclusion zones around piling rigs
  • Implementing traffic management plans and designated haul routes
  • Careful planning to avoid underground service strikes
  • Use of safety monitoring systems like RASCI for piling rigs
  • Employment of qualified and trained piling operatives and supervisors

Embedding a strong safety culture through comprehensive risk assessments, method statements, regular briefings and strict enforcement of rules is paramount for ensuring piling works are carried out in a safe and controlled manner on construction sites.

Sustainability and Environmental Impact

While piling is essential, contractors must proactively manage and mitigate its environmental impacts:

Minimising Noise and Vibration

Certain piling techniques like impact driving of precast piles generate high levels of noise and ground-borne vibrations which can disturb local residents and businesses, damage nearby structures, and negatively impact wildlife. Using alternatives like:

  • Auger boring or vibratory pile driving methods
  • Enclosing impact driving rigs with noise shrouds
  • Scheduling noisy works at approved times

…can help reduce these disturbances.

Reducing Waste and Reusing Materials

Companies must adopt sustainable practices to minimise virgin material consumption and reduce piling waste:

  • Using recycled concrete and steel in precast piled elements
  • Recycling of drilling spoils and water from bored piling operations
  • Reusing temporary casings across multiple bored pile locations

Protecting the Environment

Contractors need to implement proper controls to avoid pollution and habitat destruction:

  • Containment of drilling fluids/slurries and treatment before disposal
  • Dust suppression and cleaning of public roads
  • Fencing off sensitive ecological areas and avoiding vegetation removal
  • Monitoring and protecting existing watercourses from contamination

Carbon Footprint Reduction

Companies should reduce the carbon footprint through measures like:

  • Employing efficient piling rigs and plant with low emissions
  • Locally sourcing materials to minimize transportation
  • Utilising energy from renewable sources on site where possible
  • Offsetting remaining emissions through carbon credits

Choosing the Right Piling Contractor

With a multitude of piling contractors operating in the UK market, it’s crucial to carefully evaluate and select an experienced and capable specialist for your project’s piling requirements. Key factors to consider include:

Experience and Qualifications

  • Number of years the contractor has been operational
  • Portfolio of completed projects of similar scope and complexity
  • Accreditations held (e.g. CHAS, ISO certifications, trade body memberships)
  • Qualified and skilled personnel (supervisors, rig operators, engineers)

Services Offered

  • Full design and consultancy services for temporary/permanent works designs
  • Wide range of piling techniques and equipment to suit different scenarios
  • In-house testing and quality control capabilities
  • Design of working platforms, groundwater control, obstructions removal etc.

Equipment Capabilities and Fleet

  • Size, age and condition of the contractor’s piling rig fleet
  • Range of rig types and attachments for different pile installation methods
  • Availability of support plant and accessories
  • Ability to self-deliver or hire-in specialist equipment as required

Safety and Quality Commitment

  • Robust safety management systems with a proven track record
  • Commitment to quality through accredited procedures and testing
  • Ability to implement inspection test plans and provide full traceability
  • Membership and adherence to industry bodies’ health and safety codes

Quotes and Budgeting

  • Transparency in pricing structure and cost components
  • Ability to work within project budgets and cash flow requirements
  • Flexibility to value engineer cost-effective piling solutions
  • Availability of warranties and insurance-backed guarantees

By thoroughly evaluating prospective piling contractors against these criteria, construction firms can make an informed choice and engage a reliable specialist to ensure their piling works are completed safely, on time, within budget and to the highest quality standards.

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