Next, Guildford

LocationNext, Guildford City Centre
RequirementBearing Piles to support new mezzanine
Techniques ,
Main ContractorSKS Construction Limited

Project Overview

TechnikGS (TGS) tendered and was then awarded the contract for the design and installation of the bearing piles for a new mezzanine floor, lift and escalator pit inside an existing retail unit.

Access was from an operational retail car park into the store through sliding glazed doors in the newly constructed, glazed curtain walling.

The works included the installation of 82 piles to a depth of approximately 6 metres below ground level in order to carry working loads of up to 130kN.

Project Challenges

  • Restricted access requiring compact minipiling rig and ancillary equipment with low emissions.
  • Material deliveries could only be taken it to the store in small lots during off peak times via pallet trucks.
  • The solution required being low noise, no vibration so as not to disturb adjacent and adjoining operational shop units and party wall.
  • Ground conditions comprised fill with occasional concrete obstructions over water bearing gravels.

Solution Delivered

As a result of the waterlogged granular bearing strata, TGS opted to install a hollow bar micropile. This solution is particularly effective in open matrix granular materials, achieving enhanced pile diameters and geotechnical capacity when using a continuous grout flush.

A 3 tonne Mini Sonic rig was deployed to install these piles using its high frequency rota-­‐sonic head. This enabled the hollow bar micropiles to be efficiently installed with minimal vibration, overcoming potential obstructions in the fill, before founding in the gravel. Achieving successful installation at the designated pile positions was crucial when working through discrete openings in the existing floor slab. Installing the micropiles using rota sonic techniques was the only way to ensure this was achievable.

The rig also has a small footprint which allowed it to pass easily through the double doors in to the building. With the combination of this rig and an electric grout mixer and pump the working area was easily ventilated using a simple in-­‐line fan extraction unit.

Design verification test was carried out to prove the load carrying capacity and performance of these micropiles.

The project was completed successfully within programme and budget.