Phi Group is the largest retaining solution specialist in the UK, manufacturing, supplying and building retaining structures including timber crib and concrete crib retaining walls, soil nailing, soil panels, modular block reinforced earth systems,
concrete panel faced reinforced soil and planted / grassed reinforced soil slopes.
The company is at the forefront of retaining structure technology, balancing engineering demands with environmental consideration. A complete service is offered including design, supply and construction and this service is backed up by full indemnity
insurance.
Phi Group is Constructionline approved, qualified to work within the public sector and UVDB approved to supply the electricity (including nuclear), water, gas and telecom sectors. Full Link Up accreditation enables Phi Group to provide engineering
solutions to the railway sector and many products have full BBA technical approval.
Permacrib timber retaining walls
Permacrib is a structurally engineered, timber retaining wall system, utilising the long established gravity wall concept. It is the world’s leading timber crib retaining wall system. Permacrib is simple and quick to build and it is immediately
serviceable. It is sourced from managed sustainable forests and BBA approved.
Phi Group utilized Permacrib for recent work on the Sunderland Metro line. Acoustic barriers had to be designed, supplied and built to reduce the noise of the trains and retaining structures were also required to support the sides of the railway
cutting.
In total, over 4,000m² of timber crib retaining walls were constructed at an average rate of 100m²/week. The Permacrib walls were designed to incorporate fencing at the top of the wall and this was constructed with a
high level of accuracy in both horizontal and vertical alignment due to its close proximity to live wires, which in most cases were less than 3m away.
Retaining wall systems
Phi Group also utilised Permacrib timber retaining walls for the Channel Tunnel Rail Link. The East Thames to Medway Valley and Waterloo section rail embankments needed a retaining wall solution. In order to minimise electrical and magnetic interference from the trains, timber was selected and the wall had to be built to a very high specification due to the close proximity of live rails.
Alfred McAlpine and Amec, working as a joint venture, contracted Phi Group to design, supply and build Permacrib timber retaining walls. 2,000m² of Permacrib was constructed in four months. In addition, over 15,000m³ of reclaimed stone from the existing cutting area was utilized as backfill to the Permacrib wall.
Phi Group’s Permacrib retaining wall system provided a quick cost effective solution. The product carries a BBA certificate, offering a 60-year guarantee against insect and fungal attack.
Permacrib soil nailed system
Permacrib’s soil nailed system was used for a retaining wall at Danescourt railway station in Cardiff. The soil nailing provided a stable temporary earthworks profile, preventing future movement of soils in the embankment. To achieve this, Phi Group
used a small, specialized soil nail rig together with a grout pump and inserted 275 soil nails with a maximum nail length of 3.6m.
The finish then given to the soil nailing was a timber crib retaining wall and for this Phi Group designed, supplied and built a Permacrib wall 116m long with an average height of 2.5m.
The soil nails were installed from the top downwards and the Permacrib facing from the bottom upwards. The nails extended to interlock with the Permacrib and formed a long term retaining solution.
Soil nailing, Permacrib and gabion retaining walls
In order to improve rail capacity to serve the new Wembley stadium, a new rail depot building and a new access bridge over the mainline had to be built. For construction of these to take place a critical part was the design, supply and building of
major retaining walls.
Phi Group was awarded the contract due to their ability to design, supply and build all of the retaining systems required within budget and tight delivery times.
The scope of work included 2,150m² of soil nailing with attached stone filled panels, 210m² of Permacrib timber crib walling and 200m² of gabions with a total length of over 450m. The products also had to meet a
120-year design life, as specified by the client.