What made this project one that stands out is the nature of the site itself. The location for the job was a small plot of land sandwiched between retail units on either side. The plot faced onto a busy main road in the outskirts of Manchester, and access was restricted to a narrow service road along the back of the high street shops.
The work was part of the first phase of a two-phase redevelopment, which once completed will see a brand new superstore outlet, almost double the size of the existing store. Manchester Superstores operates its Longsight branch from premises on the busy A6 Stockport Road and has acquired land adjacent to this in order to extend its current store.
This first phase of works encompasses the clearing, excavation and construction works on the newly acquired site - and once completed the existing store will move into the new premises. The second phase of works will then see the current store demolished and a new building constructed in its place. The two new structures will then be joined to form one new superstore. The new three-storey building will also have basement storage.
While the ground conditions were relatively straight forward there were other important factors to consider when planning to undertake sheet piling works at this site location: site access in a bustling commercial area; noise restrictions, and the potential for transmitted ground vibrations to nearby structures.
The previous building on the site had been demolished some time previously, and the ABI rig was required to pre-auger the ground, and then install the steel sheet piles around the plot boundary, prior to the start of the excavation of the basement itself. Installation was done using both pressing and vibration techniques - and ABI was able to provide all the necessary equipment for this stage of the project, interchangeable on the one rig.
DWM selected one of ABI's TM 14/17 V Mobilrams due to its high manoeuvrability, compact size and piling versatility. Initially, the rig was coupled with an MDBA 4500 auger drive for pre-drilling the ground ahead of sheet piling works. The sheet piles were then installed using a combination of MRZV20V vibrator (in locations away from structures) and ABI's HPU 600 Hydropress pile press to press the piles to their final depth without the use of vibration (in locations close to boundary walls or sensitive structures).
The combination of equipment ensured that guidelines and restrictions regarding noise and vibration could be met, without compromising the speed or efficiency of the works. It is on projects such as this that the Mobilram system excels, with a range of piling attachments and techniques which can be rapidly interchanged as the soils or site circumstances vary around a jobsite. Changing attachments and tooling is a fast and efficient process.
This phase of the project saw the installation of L604 U-shaped sheet piles in a range of lengths between 6m and 9m around the perimeter of the acquired site. Following the completion of piling works, DWM was able to install temporary internal props, and then the basement excavation could begin.
Scott Raftry, operations director, DWM Civil Engineering commented: "The piling package is generally the first item of work we carry out for our clients', it is important that we demonstrate our professionalism from the outset. We have to ensure the kit specified and used is correct for the project first time. We find using the Hydropress method over other forms of pressing system on certain projects can provide a better overall solution as the rig's versatility to accept the auger and press allow for a single item of plant to carry out the works."