Their challenge:

To determine the contents of two redundant storage silos scheduled for demolition at an operational cement production facility with an assessment of the contents for potential reuse or waste disposal.

The contents of the silos were unclear and as such the client asked that we undertake an investigation to ascertain the volume and type of material within. One silo was assumed to contain a quantity of PFA, with the other likely to be waste processing materials. An intrusive inspection from the sides and roof was requested with analysis of the material complete with assumed volumes.

Our solution:

From an initial inspection of the site and working area, the investigation was designed to enable representative sampling throughout the two silos to fully characterise the material within each, including if discrete layers of material were present, whilst not hindering the operational status of the surrounding plant.

Drilling from the top down was ruled out due to structural uncertainties of loading the silo roof, although access could be facilitated to the top of the structures, some 21m in height. Therefore, the approach taken was to externally core the silo walls at varying heights and orientations to enable sampling of interior materials using hand held auger or percussive drilling, whilst considering the potential for encountering free flowing powder or potential liquids due to rainwater ingress. Varying sizes of height access vehicles, with full safety precautions for working at height were utilised.

Scope of works included:

The investigation was carried out on the basis of the following scope of works:

• Site inspection with removal of feeder pipe headers
• Small diameter probe drilling to determine the presence of free flowing material
• Concrete coring at varying heights up to 18m in height over pipework and a warehouse canopy
• Horizontal sampling using augers and percussive sampling methods
• Geotechnical and geochemical analysis
• Interpretive reporting with guidance on reuse of material and waste classification

The results:

The initial probing exercise, carried out in advance, confirmed that whilst one silo contained dry material, water ingress had occurred in the other silo, associated with external cracking, leading to cementing of material inside the silo walls. No free flowing material was encountered and progression to sampling of material was made ahead of schedule.

The follow up works were completed safely and on time, with no delay contingency required due to the initial findings. Through both visual and laboratory analysis, the material was characterised and confirmed to be different in each silo, with the results indicating the reasons for more structural decay on the silo containing the known materials.

Following completion, the results of the investigation have allowed the project to progress to the demolition tender stage, with the uncertainties associated with the disposal of the unconfirmed materials reduced, allowing for a more competitive tender process.

Testimonial:

“This project provided a challenge to the team in terms of an unusual, above ground investigation, compared to our standard soil and rock investigations. The working at height requirement added an additional complication in terms of the safety aspects which were overcome with close liaison and dialogue between the team, client and site operators. Meticulous planning which included several inspections and contingencies in terms of time and emergency procedures culminated in delivering the required results safely and within budget” – Project Manager