Understanding ground conditions and soil classification for excavation projects

Did you know, an estimated 4 million digging projects take place in the UK each year, according to the British Safety Council? It’s crucial to understand your site’s ground conditions and soil classification before starting your excavation project, as this will put you in a better position to reduce the risk of trench collapses and ensure you complete your project safely and on-time.

In this guide, we’ll explain the different soil types, as well as the impact of groundwater on excavation and what you can do to mitigate these issues.

Soil classification and types

The main soil types are clay, sand, gravel and loam, and rock and hardpan.

Clay 

• Characteristics: Cohesive, sticky, dense, holds moisture well, can become slippery when wet.
• Excavation considerations: Clay requires equipment that can handle dense material, such as Vermeer trenchers or directional drills (HDD)
• Challenges with clay: Excessive moisture can cause the soil to become unstable, potentially leading to slumping or collapse in deeper excavations.

Sand

• Characteristics: Loose, granular soil that allows water to pass through easily.
• Excavation considerations: Sand needs equipment that can operate in loose, shifting conditions. Vermeer horizontal direction drills can excavate in sandy or loose soil, as they offer precision and minimise surface disruption.
• Challenges with sand: The main issue with sand is its instability, especially in deep excavations. Shoring systems or trench boxes are typically used to support excavation walls and avoid cave-ins.

Gravel and loam

• Characteristics: Gravel is made up of larger particles, while loam is a mixture of sand, silt and clay. Loam is well-draining.
• Excavation considerations: For gravel and loam, Vermeer trenchers and HDDs work well, especially for utility installations or when working in areas where precision and speed are critical.
• Challenges with gravel and loam: Gravel may be loose and challenging to compact, which could affect the stability of trenches. The presence of large rocks in gravel may require more specialised equipment, such as a rock trencher.

Rock and hardpan

• Characteristics: Very dense, compact soil or solid rock layers.
• Excavation considerations: Vermeer rock trenchers or HDD machines with high-torque capabilities are ideal for cutting through solid rock or compacted layers.
• Challenges with rock and hardpan: Rock excavation often requires more time, effort and expense. Blasting or other specialised techniques might also be needed to reduce the size of the rocks.

Excavation and utility installation project methods can depend on the type of soil present on site. You can read more about the different methods in our guide here.

What is the impact of groundwater on excavation?

We all know that the presence of water in the soil can weaken the ground and make excavation more challenging. Let’s take a closer look at groundwater, its effects on excavation and how to deal with it.

Groundwater refers to the water that naturally exists beneath the surface of the earth. It fills the soil and rock layers below the ground. The water table is the upper boundary of groundwater and this fluctuates based on the season, weather and local conditions, e.g. heavy rainfall or drought. Carrying out an excavation project in areas with high groundwater levels or near bodies of water like rivers and lakes can introduce complications like soil erosion, instability or flooding during the project.

Dealing with groundwater during excavation

There are a few different techniques and solutions that your excavation teams can implement to manage the challenges that groundwater poses to excavation projects:

1. Dewatering systems – these lower the water table around the excavation site and pump excess water away.
2. Waterproofing and shoring – shoring systems help stabilise excavation walls and prevent collapse, and waterproofing barriers may be applied to the trench walls to prevent water from infiltrating the excavation site.
3. Specialised equipment – some excavation machines are specifically designed to handle wet or waterlogged ground, and our directional drills, like the D24X40 S3 and the D100X140 S3  can bore through saturated soil with minimal disruption to the surrounding ground.
4. Chemical stabilisers – these can be used to solidify loose, water-logged soil, reducing the risk of shifting or collapse.
5. Compaction techniques – these can densify the soil, especially sandy or loamy soils that are prone to instability when wet.

How does soil stability affect excavation safety?

A site’s soil stability is a major safety factor to consider for excavation projects, especially when working at greater depths. Unstable soil can lead to dangerous situations, such as trench collapses.

Proper trenching methods and shoring methods can help prevent cave-ins, particularly in unstable or granular soils like sand. Vermeer directional drills and trenchers can help minimise the depth and width of trenches, reducing the need for extensive shoring.

Depending on the depth and conditions of your site’s soil, shoring may include trench boxes or hydraulic shores to ensure excavation walls stay stable and secure.

Learn more about the hazards involved in HDD projects here.

Geotechnical surveys and soil testing

Before starting an excavation project, conducting a geotechnical survey is crucial. This survey will involve drilling boreholes and performing tests to accurately determine the soil’s composition, strength and moisture content. We recommend working with geotechnical engineers to understand the specific soil conditions of your site and ensure that the right equipment and safety measures are in place.

If you’re looking for more advice on the best machinery to choose for your ground conditions, you can contact our team of experts on 01933 274400 or email us at sales@vermeeruk.co.uk. Alternatively, fill out an enquiry form with details of your request and we’ll get back to you. 

Vermeer Corporation delivers a real impact on the way important work gets done through the design, manufacture and support of high-quality industrial and agricultural equipment that helps connect people to the necessities of life, manage natural resources and feed and fuel communities. With a reputation for being built tough and built a better way, that equipment is backed by localized customer service and support provided by independent dealers around the world. To learn about Vermeer Corporation, products, the dealer network, financing options and careers, visit vermeer.com.