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EMBANKMENT TECHNOLOGIES


Clancy Docwra explains its work to improve the stability of embankments on the London Underground network. F


ollowing concerns regarding the sta- bility of embankments at a number of locations on the eastbound District Line adjacent to Acton Depot, LUL produced a design solution which was competitively tendered and subsequently awarded to Clancy Docwra Rail.


Phase 1 (EM2-3-4) was undertaken dur- ing an extended possession with site teams working at the three locations simultane- ously, utilising road/rail units to install a king post and plank solution requiring the installation of 161no 5m steel piles and 1,100 concrete planks to form new high- level embankment retaining walls.


The void between the wall and existing sleeper level was in-filled with 250 tonnes of 20/40 gravel wrapped in geotextile and compacted in layers, topped by a new walk- way created with 84 tonnes of Type 1.


All planned works were completed com- fortably within the possession, with finish- ing works such as safety handrails under- taken during traffic hours.


The base of embankment EM4 also re-


quired the construction of a stepped toe re- taining wall, which was constructed using the Redi-Rock proprietary system incorpo- rating interlocking concrete sections.


Phase 2 (EM5-6) required a different solu- tion due to the confined nature of the sites, which were located between the rear of the cable run and residential property at low level, with some properties within touching distance of the works.


Each of these sites had a single access point and required a controlled reduced dig, with the installation of temporary support works to ensure the integrity of the rail- way above. Full-length access scaffold was erected at the foot of both sites adjacent to the existing retaining walls.


The dig was carried out by a single small excavator working into the site with 1,250 tonnes of spoil removed by a small convey- or system on EM5, and a motorised barrow on EM6; all arisings were delivered directly to a skip at low level for removal to a recy- cling facility.


The design solution at these sites required


the installation of Ram Wall, another pro- prietary system, which comprises steel grid layers installed in sections to an agreed overlapping and fixing pattern, and stag- gered as it rises to accommodate the slope of the embankment. The single entry point dictated that Ram Wall installation was carried out in reverse to the excavation method, starting at the far end and work- ing back to the entry; a distance of 200m on EM5 and 80m on EM6.


As the Ram Wall installation progressed, a lightweight Maxit Aggregate fill was intro- duced into the matrix. This serves to sup- port the embankment whilst reducing the loads placed onto the existing retaining walls. To contain the Maxit as the struc- ture was built, the existing retaining wall was raised by up to 1.7m using a galvanized mesh cage in-filled with track ballast, and tied in to the Ram Wall matrix.


Approximately 1,400m3 of Ram Wall and 1,900m3 of Maxit were installed to com- plete the operation, making it the largest scheme yet undertaken using this system.


On completion, the Ram Wall formed a gentle slope from the newly-formed walk- way directly behind the cable run down to the top of the raised retaining wall, and was capped with 150mm of seeded top soil. This serves to both retain the Maxit fill and promote vegetation to enhance the aspect from adjoining properties.


The finish point of EM6 was adjacent to the end of the platform at Chiswick Park Sta- tion, which had been identified as an area where track ballast was being lost beneath the platform. As a variation to the existing scheme, Clancy Docwra were instructed to clear 30m3 of litter, debris and vegeta- tion from beneath the platform, re-profile the slope and install a NeoWeb retaining membrane. This was in-filled with new bal- last and secured at sleeper level to form a retaining barrier, preventing further loss to the ballast shoulder.


FOR MORE INFORMATION


T: 01895 823711 E: enquiries@theclancygroup.co.uk W: www.theclancygroup.co.uk


94 | rail technology magazine Jun/Jul 11


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