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Soil subsidence, also known as settlement and ground slumping, is a significant issue on a lot of industrial sites. Usually it happens because there’s a void underneath the surface, and then over time material moves into it, changing the structure of the land on top. This is harmless if the property isn’t being used, but if there is industrial machinery or buildings present, then it can lead to serious shifting and structural damage. 

Fortunately, though, engineers are able to manage ground slumping on industrial properties. They use a combination of mitigation, ongoing monitoring, prevention, and assessments to develop strategies that help companies thrive. They also tailor multiple techniques from different disciplines to ensure the best possible outcomes. 

Site assessment

The first step is to conduct a thorough site assessment. This is where engineers carry out various investigations to determine the nature of the soil, the slumping, and the surrounding geology. The main method is soil boring, followed by lab testing. This is where the soil is bored with a large drill. 

Engineers also conduct slope analysis using software. The idea here is to characterize the nature of the slope, whether it is unstable. If it isn’t, then it often means that engineers can continue with business as usual, but if there are factors involved, then they’ll need to change their construction schedule. 

The most common sign is tension cracks at the top of the slope. Usually this is bulging and shows a desire to want to fall downhill. 

Prevention during construction

Engineers also prevent ground slumping during construction. They do this with proper grading, compaction, and concrete lifting. 

Dynamic compaction is one of the best tools because it drops heavy weights and helps to densify loose soils over time. It’s also possible to conduct soil replacement and improvement. When this happens, it can be useful to excavate and replace weak soils and replace them with engineered mixes that have the characteristics that business premises owners want. This could include sub-grade enhancement as well. Before pouring concrete slabs or foundations, it is useful to add aggregates and ballasts to the under layers of the property so they remain more stable over time. 

They could also be the installation of new drainage design instead of conventional run-off or allowing nature to take its course. Adding surface grading directs water channels towards subsurface drains and interceptor ditches. These can then carry storm water to the main drainage system, where it can be processed and let out into the environment at the rate that the premises owner requires. 

Mitigation and stabilization techniques

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Sometimes active slumping requires mitigation and stabilization techniques. This is essential in locations where soil subsidence is both detected or anticipated. Mitigation and stabilization techniques take place at the surface as well as deep into the ground.

The most cost-effective first step for subsidence mitigation is to improve drainage. This means adding surface drainage to enable water to flow across the property in ways that won’t cause erosion. For example, engineers will sometimes seal up cracks and install berms while changing the grading of specific areas to reduce ponding. It’s also possible for them to add subsurface drainage in areas where above-ground drainage is not possible using things like wicker or horizontal drains. These improve the capacity of the land to weather storms without requiring major excavations

Even so, sometimes excavation and regrading are necessary. This often involves removing the top layer of unstable material from a slope to reduce the driving forces that are present on it. This also means using benched or terraced set-ups to contain slopes so that they are less likely to slump over time because of drainage issues. Finally, engineers will often flatten slumps and replace material with a lighter fill. The goal of this method is to prevent gravity from causing additional slumps and subsidence.

There are, of course, various reinforcement and structural support methods:

  • Retaining walls made of concrete or rock-filled baskets can mechanically stabilize earth.
  • Crib bin walls can be installed to hold back soil.
  • Soil nailing involves drilling and grouting steel bars into the slope to create a synthetic reinforced soil mass.
  • Toe buttresses and berms for additional weighted material to prevent slumping from occurring and to provide a counterweight.
  • Piles or anchors to hold sections of soil in the ground, preventing load transfer.

There are also ground improvement techniques that some engineers will use. For example, it’s possible now to use chemical stabilization on soils. This might involve injecting them with polyurethane, lime, or other chemicals that make it more likely for the soil to remain in place. This is particularly useful for keeping soil in place under cement floors or other ground coverage.

Deep soil mixing is another option. Sometimes the top of soil can be too loose and require denser soils to hold them in place. Proper mixing with various binders can keep the mass of soil together so that it doesn’t slump over time. 

Implementation considerations for industrial premises

Of course, industrial premises are a little different from regular premises. To prevent subsidence here may require special techniques. For example, a lot of businesses operating industrial plants and factories require minimal disruption. This is where trenchless methods for injecting grouting or using soil nailing are a good idea. These don’t require massive excavation that disrupts site activities. It’s also a good idea to repair soil slumping with load-specific designs. Companies that can think carefully about the machinery that’s going to be using the soil subsurface can benefit over time. 

Of course, even newly landscaped and engineered slopes still require maintenance over time. They need you to perform drain cleaning and vegetation trimmed back. 

For example, take warehouses with settling slabs. These often require chemical injection under the floor to strengthen the subgrade to keep them in place long term. Embankments and cut slopes around plants can also be challenging. These need a combination of drainage, soil nailing, and retaining walls to hold them in place effectively long term. Large open areas of ground can also be prone to slumping and may require lime treatment.