The M25/J28 Interchange Project is an upgrade to the existing J28, reducing congestion experienced on the junction at peak times. The project consists of a new loop road connection from the M25 Northbound to the A12 Northbound along with a new slip road from J28 onto the M25 Anti Clockwise.
PJE were contracted to complete piling works on 8no. structures across the site using both CFA and Rotary techniques of varying diameters. First to be installed were 50no 750mm/880mm cased rotary piles to depths up to 40m. These piles were for a protection slab over a newly installed gas main running under the line of the new road. Piling began in Jan 23 and was completed in 3 weeks. Dynamic tests were undertaken on 6no of the piles with all exceeding capacity requirements.
Piling work then moved on to install 2no contiguous piled walls to form abutments and wingwalls for a new underpass called Alderwood Bridge. Here PJE mobilised a Llamada P150 CFA Rig to install 133no 1050dia piles to a depths in excess of 20m. The CFA method was offered here to allow for a reduction in installation time and hence benefit the overall program whilst also offering cost reductions to the client. Installation tolerances were very critical for the two walls which were achieved without the need for a guide wall. Two number piles were dynamically tested, with a further pile also statically tested. All tests exceeded design values for loading. Works began in early Feb 23 and were completed in 6 weeks.
The second phase of piling work started in July 23 which incorporated a further 3no. structures, all piled using large diameter rotary piles.
Work initially started on the west abutment at Duckwood Bridge where PJE installed 12no 1050dia/1180mm cased piles to circa 40m deep. These piles were installed over 2 weeks and were subject to two dynamic tests which again exceeded design requirements. The east abutment piles for this bridge were installed at the end of the visit after the mainline works had been completed.
From Duckwood west abutment PJE moved over onto the mainline Mayland and Grove Bridges which incorporated 1200mm/1300mm cased piles and 1050mm/1180mm cased piles respectively.
Mayland Bridge consisted of two abutments and two piers, each with 5no. piles. These piles were installed with our Mait HR260 with drilled depths up to circa 36m. Two piles on this structure were load tested, both exceeding design requirements for loading.
The final Structure of the mainline works, Grove Bridge, consisted of 18no piles over two abutments and one pier. The western abutment and pier were installed by our Mait HR260 while the eastern abutment was installed as "Low Headroom Piles" as they were situated directly under a line of overhead power lines. For the "LHR" piles PJE utilised a TesCar CF8 in rotary mode to drill piles to circa 28mBGL while also constructing a static test which again exceeded design parameters.
The final section of the works, carried out in late 2023 and early 2024, was to install 16no 900dia Rotary cased piles to 28.0mBGL. These piles were distributed over 5no bases on the verge of the live M25 for foundations of new sign gantries spanning the motorway. Thes piles were installed using a Solimec SR45 rig in order to cope with limited space constrains while working next to live traffic in lane closures provided by the main contractor. These piles were also dynamically tested, all passing the tests as expected.
This contract demonstrates PJE's ability to mobilise multiple rigs and techniques across a multi-phase contract to install piles using the best technique for the ground conditions and structure, saving on both installation costs and programme.