OWNER:
Royal London Asset Management Property
ENGINEER:
Curtins
GENERAL CONTRACTOR:
Winvic Construction Limited
MAIN FIGURES:
c.7,500 VSCs
Project Details
Winvic Construction appointed Menard for ground improvement works at the second phase of Atlantic Park in Bootle. Having successfully completed ground improvement on Phase 1 ( four large industrial units), Menard brought this valuable experience to bear in Phase 2. Our prior involvement gave us insight into the variability of made ground, the presence of compressible Alluvium, and the widespread Glacial Till across the area. This knowledge allowed us to consider a number of ground improvement techniques, tailored to the site’s geotechnical profile. This then allowed us to offer a technically sound and cost-effective solution for Phase 2. Our previous experience also helped us to provide continuity and efficiency in the design and construction process, which was of great benefit to the client.
Ground Conditions
The site comprises made ground to depths of up to 3.7 m, consisting of sandy gravel with occasional construction debris. Underlying deposits include Shirdley Hill Sand (very loose to medium dense fine to coarse sand) which varies in depth across the site. Underlying Alluvium is present as soft to firm sandy clays or organic silts, which were unsuitable for traditional shallow foundations due to their low bearing capacity and potential for differential settlement. Beneath this, Glacial Till is widespread, comprising stiff to very stiff sandy gravelly clay with interbedded granular layers. The bedrock at depth consists of weathered, competent Sandstone (Sellafield Member/Wilmslow Formation), ranging in strength from very weak to moderately strong.
Solution
Based on the ground conditions encountered, Vibro Stone Columns (VSCs) offered a practical and effective ground improvement solution. VSCs were installed using a vibrating probe that displaces the in-situ soil and introduces compacted stone into the ground, forming vertical columns. These columns reinforce the soil matrix, improving load-bearing capacity and reducing settlement. At this site a total of 7,500 VSCs were installed across 3 industrial units. Columns were approximately 400 mm in diameter and installed to depths of up to 7.0 m. This method is particularly beneficial as it produces no spoil and can be easily adapted to varying soil profiles. Following installation, bearing capacities of up to 150 kPa beneath the foundations & 90 kPa on the floor slab were achieved, limiting residual settlements to less than 25 mm and differential settlements to less that 1/500.
Sustainable Development
The VSC solution produces no spoil and provides a much lower carbon-intensive solution in comparison to trench fill or piled foundations.
