Substructure Logistics

Constructing the substructure requires the use of a lot of machinery, equipment and vehicles

It is under the main contractors remit to assess site and produce a logistics plan for where the required plant and equipment will be situated. This is often done with input from the specialist Groundworks Subcontractors.

I recommend finding the latest logistics plan drawing for your project and understanding it. This can usually be found within the Construction Phase Plan (CPP), which is a requirement in the Construction Design and Management Regulations (CDM).

The plant, equipment and vehicles needed for Substructure works can be split into categories as follows:

Excavation Plant

Excavation is the process of removing soil or other forms of ground to create a hole, trench, or cavity, often for a purpose such as casting foundations.

The images within each section are a guide, all machines come in various sizes, shapes and colours dependant on the size of the task.

1. Excavators - commonly known as a digger or shortened from 360 excavator to a '360'. These machines are mainly for excavating ground but at times use their buckets for lifting materials or placing concrete.

Sizes of excavators are defined by roughly how much they weigh i.e. a 16 ton excavator will generally be bigger and have more capacity than a 3 ton excavator.

How much space is there on site for an excavator to drive around and swing it's bucket?

A big excavator would do the job quicker but can this be accommodated?

2. Dumper Trucks - used to move excavated ground or 'muck' around site. An excavator would load a dumper and the muck may be transported to a stockpile on site until a collection wagon arrives.

Is there a clear route for the dumpers required to manoeuvre to where they need to go?

3. Muck Away Lorry - the vehicle which is loaded with the excavated ground. These take the muck to licensed facilities for recycling, re-use or disposal off site.

A variation of these are called grab lorries which have a hydraulic arm inbuilt. This eliminates the need for an excavator to load the muck into it.

Is there suitable access to where muck is stockpiled?

4. Rollers - used to compact the ground. Sit does this by exerting pressure and vibration which reduces air voids and increases the grounds density and stability.

What size roller can be accommodated on the site footprint?

Is one required at all? It may not be for a smaller site

5. Plate Compactors - do the same job as a roller but cover less area. Likely to be used in areas where a roller cannot be driven due to space restrictions.

Concrete Equipment:

1. Concrete wagons/mixers - vehicle in which concrete is delivered onto site to be poured into the substructure elements. They are equipped with rotating drums or agitators that continuously mix the concrete during transit to maintain its consistency and quality.

Is there a clear route to the pump or excavation where concrete is required?

2. Concrete pumps - concrete is deposited from the concrete wagon into the hopper incorporated in the concrete pump. This then pumps concrete through a large concrete line - think of this as a large diameter garden hose which pumps concrete instead of water.

What's the longest the concrete line can be? Will it need to be relocated?

The above is an example of a static concrete pump. These are common if they can be situated in one area and won't constantly require moving.

The alternative is the below - a mobile concrete pump which can be driven to site when it's needed. It serves the same purpose but is usually driven away once concrete pour is complete.

Is the ground under where the mobile pump is planned to be situated suitable?

3. Concrete vibrators - commonly referred to as a 'poker'. Placed into wet concrete whilst it's freshly poured to compact it and reduce any air voids.

4. Curing tank - a water storage tank with a maintained temperature. Used to store concrete cubes (shown below) which are to be taken away to be tested for their compressive strength.

Is there a power supply in close proximity?

Reinforcement Material/Equipment:

1. Reinforcement bars (rebar) - the inclusion of materials like steel bars (rebar) or mesh within concrete structures.

These materials provide additional tensile strength to the concrete, helping it withstand tension forces that it might otherwise crack or fail under.

Is there a suitably sized lay down area for reinforcement steel to be dropped into?

Do the excavators planned on site have the capacity to lift the reinforcement?

2. Rebar cutters and benders - used to cut or bend reinforcement bars or mesh to size required. Sometimes an angle grinder isn't sufficient as the bars are too strong.

Note: in theory there should be no cutting of reinforcement required as what is shown on the Structural Engineers bending schedules is ordered. However, this often isn't the case and modifications are required to solve issues which arise in practice.

Temporary Works Equipment:

1. Formwork systems (for creating foundation shapes) - also known as shuttering, refers to the temporary structure or mould used to shape and support freshly poured concrete until it sets and gains sufficient strength to support itself.

Commonly constructed using timber as image below with pins in the ground to hold it in place.

If the concrete is to be poured in the ground a twin wall polypropylene sheet system can be used to hold the concrete - this is referred to as Cordek on site after the brand that produces these.

What formwork system will we use?

Is there enough working area around where formwork is to be installed for operatives?

2. Sheet Piles - long, interlocking structural sections made of steel that are driven into the ground to create a retaining wall.

When doing deep excavations for foundation works it may not be possible to dig a battered excavation, especially when in close proximity to neighbouring properties.

Where may we require sheet piles?

Do we have the area for a rig to install these? A design and consultation with sheet pilign specialist contractors may be required

Surveying and Measurement Equipment:

1. Total stations - Surveying instruments and tools are necessary for accurate setting out and positioning of substructure elements to the construction plans.

Initially, if no site control has been established a GPS version may be used.

Is the ground suitable for someone to operate surveying equipment on?

Have site control points been set out? Are they visible?

2. Laser levels - spins a beam of light fast enough to create a complete 360 degree horizontal plane. Can be used in tandem with a surveying staff set up off a datum to indicate if dig or foundations are at the correct level as per drawings.

Is there a datum visible where required to set up laser level on?

Temporary Services

1. Temporary Water Supply - usually in the form of a bib tap. This provides water to site for cleaning and other activities.

Note: temporary services are usually down for the main contractor to provide

2. Temporary Electric Supply - ideally before the Groundworks subcontractor start on site there is an established temporary building electric supply in the form of a substation of some description.

If there isn't all plant and equipment will need to be powered with fuel or portable generators.

Have a temporary electrical supply been established?

If so, where is it in relation to the substructure works?

Others

1. Dewatering Pumps - required in cases where excavations are at risk of water ingress. They pump water out to a designated point where it can be safely discharged, a license for the company who own the asset being discharged into may be required.

What does the site investigation report mention about water levels in the ground?

Is there a drain run manhole ground water can be pumped into?

2. Personal protective equipment (PPE) - besides the standard hard hat, hi-visibility vest, gloves, glasses and safety boots required on sites there may be a requirement for hearing protection or specialist goggles for higher risk activities.

For example, when using an angle grinder to cut steel reinforcement, higher impact safety goggles will be required to reduce chances of damage to operatives eyes.

Is there a safe space to store PPE?

3. Safety barriers and signs - To protect workers, the public, and adjacent areas from construction hazards, temporary safety barriers, and fencing may be installed around the substructure works.

In particular, around any excavations to avoid anyone falling in or injury due to an excavation collapse. These should ideally be clearly labelled.

Are the barriers installed fit for purpose?

4. Hand tools - may be required where it is not possible to use mechanical methods due to space constraints. These include; shovels which should ideally insulated to reduce injury to operatives in the event of striking services in the ground and pneumatic breakers.

5. Wheel washing facilities - to clean the wheels of any vehicles exiting site to reduce mud onto roads outside of site boundary.

The image below shows a full size wheel wash which vehicles can driven onto. There may not be space on site for this in which case a jet wash can be used.

6. Cable Avoidance Tool (CAT) and Signal Generator (Genny) - used to locate underground cables and pipes; the Signal Generator tool emits a specific signal that is detected by the CAT.

To be used by trained operatives only to identify any services that may be in the ground before starting excavation works.

Definitions

Construction Phase Plan (CPP) - according to the Health and Safety Executive (HSE): A CPP must be prepared by the principal contractor before the construction phase of a project begins. It must outline the health and safety arrangements, site rules and specific measures concerning any work involving the risks listed in the CDM Regulations

Health and Safety Execuite (HSE) - Britain's national regulator for workplace health and safety

Construction Design and Management Regulations (CDM) - Regulations which aim to ensure health, safety, and risk management in UK construction projects, involving all stakeholders

Plant - Construction plant refers to machinery and equipment used in projects for tasks like excavation, lifting, and material handling

Compressive Strength - the ability of a material to withstand compressive or crushing forces without collapsing or undergoing significant deformation. Measured in kN/m squared

Tensile strength - the ability of a material to withstand stretching or pulling forces without breaking or undergoing permanent deformation. Measured in kN/m squared

Setting out - process of establishing position and level of an element of a project physically on site, references usually taken from drawings.

Battered excavation - when the sides of the excavation are inclined at an angle away from the vertical axis. Enhances stability of the ground whilst digging to prevent cave-ins and control any soil erosion.

Site Control - is established by setting control points. These are points on the ground or any permanent structure whose horizontal and vertical position is known.

Posts to Follow

We plan to go into more details on Substructure and add sections on:

·       Temporary Works

·       Build Sequence

·       Health, Safety & Environment

·       Quality

·       Programme

·       Commercial

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