Need to do a deep excavation? We take a closer look at when a deep excavation is needed, why an engineer’s solution is required and how excavation brace systems are used to keep your team safe.
Posted 8 June 2024 by The SEL Team.
Deep excavations are a critical aspect of modern construction and plays a pivotal role in large-scale urban development, the building of underground infrastructure and ambitious architectural projects.
In this article we will explore and share our insights on this type of groundwork, the key considerations for a deep excavation and the best equipment to ensure the health and safety of those working within a deep excavation.
The benefits of deep excavations in modern construction
An excavation ‘above head height’ is considered a deep excavation and our ability to dig deep has some real benefits for the modern built environment, especially in the UK where land and space need to be maximised.
Planning is the very first step when it comes to deep excavation works and contractors will do well to instruct an engineer to complete a Temporary Works Design (TWD)
Taller Structures Maximise Land Use
By digging deeper, buildings can have more floors, which is essential for urban construction where taller structures are needed to maximise land use. Deep excavations also allow for the construction of basements, which is useful for multi-level underground parking facilities and/or the provision of basement storage for high-rise residential apartments, or for the installation of infrastructure for utilities and services.
Flood prevention
Flood prevention is also a key benefit of our ability to excavate deep. Most new development sites will require a storm attenuation strategy to control the amount of storm water landing on site and this requires the installation of huge tanks underground, made possible with deep excavations.
Tunnel construction
Tunnel construction also rely on deep excavation. Defined as “civil engineering structures that create an underground passage that may pass through a hill, under buildings or roads, under water or under entire cities”, tunnelling is used to traverse a mass obstacle, create mass urban transit systems, accommodate pipelines, provide underground sewage systems or provide connections beneath the sea.
Groundwork Planning
Key considerations when planning a deep excavation
Planning is the very first step when it comes to deep excavation works and contractors will do well to instruct an engineer to complete a Temporary Works Design (TWD). The engineer will put much focus on the anticipated pressure from the soil and/or groundwater and how to ensure the proposed earthworks support system can resist the pressure.
Nearby structures or other surcharges such as roads, the installation method and the extraction method for the equipment will also form part of the Temporary Works Design. The engineer will also consider the following:
Ground conditions
The engineer will look at the type of soil, how easy or difficult it is to excavate and the level of temporary support required. For example, whilst stiff clay exerts less pressure on the equipment, it can be harder to excavate and bigger sheet piles may be required.
Groundwater control
Basement construction, underground infrastructure works and tunnelling will most likely encounter the presence of groundwater. Without effective control measures, excavations and tunnels can be flooded, groundwater can cause instability in rock and soil, which in turn can cause an excavation to collapse. It is therefore prudent that an engineer doing Temporary Works Design advise on the appropriate measures to control or reduce groundwater.
A plan for pumping out groundwater may be put in place to mitigate these serious risks. Further risks include water and saturated soil ‘bubbling up’ from the bottom of the excavation, and ground settlement due to fines (really small particles) in the soil being washed out.
Excavation size and depth
Factors already mentioned, such as ground conditions and the presence of groundwater could impact the size and depth of the excavation. The scope of the project, the physical workspace available, the site access and the reach of the plant or machinery you plan to use, will also be factored into the size and depth of excavation needed.
The importance of RAMS and Training
An important part of planning groundworks is for project managers and site managers to write the Risk Assessment Method Statement (RAMS). The purpose is to identify hazards and risks related to the job and provide suitable control measures for a safe method. This can often include step-by-step instructions for carrying out the planned tasks, which is where instructing an engineer for Temporary Works Design makes lighter work of producing RAMS.
Project Managers should provide a full briefing session and potential training on the relevant plant needed for the job to ensure that the process and safety measures are fully communicated to everyone and that all are competent to perform their assigned tasks.
Groundwork Solutions
Excavation Bracing Systems
Site Equipment Ltd (SEL) has a range of Excavation Bracing Systems that will support a deep excavation with bracing struts. The Double Acting Brace System and H-Series Frame are effective for keeping workers safe during deep excavation works.
The Double Acting Brace System
The Double Acting Brace System is a robust and adaptable solution that can be used for the installation of an earthwork support system to maintain safe working environment for the construction of pumping chambers and manholes.
This bracing system features legs which can be interchanged to form the correct brace dimensions. For example, Type A legs (2m to 3m) and Type E legs (6m – 7m) form a brace which is 7m x 3m.
A range of sizes are available with sheet-to-sheet ranges from 2m – 7m and permissible loads up to 65 kN/m to suit your requirements.
The H-Series Double Acting Manhole Frame
Designed for larger excavations, the H-Frame Series Double Acting Manhole Frame is a tried and tested bracing system with interchangeable brace leg sizes.
This high-capacity shoring system is an extremely robust and adaptable system that can be used alongside trench sheets to create manholes or larger tank excavations at depth.
When digging excavations, always remember to take into account the measurements for the Trench Sheet pan depth as well as the Manhole Frame section and horizontal deflection of the brace system.
Cofferdam Safety Ladder Access Systems
This access system with a walk-on platform is built with complete safety in mind. With a spring shut and lock gate, this fully adjustable platform fits all Trench Sheeting from KD6 up to Larssen piles. It comes with a 2m hooped top section so no chance of falling back into the shaft excavation. Ladder sections come in 1m and 2m sizes, with a brace strut to stop sagging on to the ladder.
Davit Safety System
The Davit Safety System was designed for the safe entry and exit of an excavation or trench.
It comes in five sections, the base or clamp, the Davit crane, a winch, a fall arrest block and a harness.
This system can be fitted on to the SEL Trench Box System and Trench Sheet by simple way of changing the base. Also available is a counterbalance base, so that free standing over a manhole can be achieved.
All Davit arms are fully compatible with the Trench Box and Cofferdam Safety Panel System.
How to hire Bracing Systems for Groundwork or instruct an Engineer for Temporary Works Design
To hire our range of Bracing Systems for deep excavations and to get advice about an engineered solution for your next construction project, contact the nearest SEL depot or call us on 0117 982 8236.
