Keller Ground Engineering have completed the first phase of anchor works at Gainsborough. 132 SBMAs with 700 kN working loads in Mercia Mudstone have been installed for river wall retention. A further contract with 350 SBMAs of similar load capacity are about to commence.

Prior to the first phase of working 6 trial SBMAs were loaded to 2400 kN without failure. This confirms that the capacities attained by SBMAs in particularly variable and weak rock are of much greater magnitude than that attainable by conventional anchors.

The use of high capacity Single Bore Multiple Anchors by Keller Ground Engineering allowed a reduction of 50% in the optimum conventional 600 kN working load anchors. SBMA's mobilised working loads of 720 to 1015 kN using shallow inclined anchors founded in the 3 to 4m thick band of gravelly sand with only limited overburden. Almost 200 permanent anchors were successfully installed with differing orientation and inclinations to avoid anchor interference.

SBMA Ltd will be presenting six technical papers at the forthcoming International Conference on Ground Anchorages and Anchored Structures in Service, November 2007 at Institution of Civil Engineers, London.

Two of these papers can be downloaded from our companion website, The Anchorman, and further papers will be added shortly.

Anchored Sheet Piles are being installed by Volker Steven to allow realignment of the Prescott Channel.

Boston Clay has long been considered a problem anchor founding strata, such that conventional anchors with fixed length of up to 60' (19m) have been utilised in the past. SBMA Ltd offered the design of increased capacity temporary anchors to anchor specialist Moretrench in order to retain a Trevi deep basement wall. Trials on four SBMAs were carried out over a 3 week period and these substantiated SBMAs design consideration and identified the most appropriate post grouting methodology. Testing of unit fixed lengths of between 10 and 20' (3 to 6m) achieved loads ranging from 90 kips to 186 kips (400 to 830 kN) some without failure. Anchor production works with design loads up to 210 kips (950 kN) start early in 2008. It is also intended to investigate the performance of the removal SBMAs in the contract works. On completion of the contract SBMA are confident that working SBMA anchors will achieve twice the load capacity (400 kips) of conventional anchors in Boston Clays and a removable anchor system will be available.

A prestigious anchor contract has been awarded to Keller Austria for motorway stabilisation between Graz and Vienna. In lieu of the 400 No 150T working load anchors Keller's alternative bid to install 200 No 360T working load SBMA's was accepted. Preliminary trials on the short high capacity encapsulation system will be initially required. However having previously achieved over 460T in gunbarrel tests on a single 2.3m long SBMA encapsulation no problems are anticipated. Each production anchor will consist of three unit anchors and the overall anchor lengths are 100m!

The new multi-million pound penthouses at 1 Hyde Park required temporary high capacity removable anchors in London Clay for basement support.

Over 100 anchors were installed by Keller and are currently being removed using a 10T winch. No problems are being encountered in removing all the looped strands from the patented SBMA anchors.

Extensive riverside developments at Rochester, Kent required anchors to 8 new quay walls. 250 SBMA's were founded with individual units in mixed strata of sandy gravels (upper units) and underlying chalk (lower units) (see Case History details and "The quay to success")

Seven rows of SBMA's retained a sheet pile and lower bored pile wall to provide retention of an 18m high vertical wall face topped by existing apartments. Lower row anchors were founded in the difficult 'lake silt deposits' and still provided safe working loads of 690 kN for seismic load conditions. Anchor loading and wall movement were kept under strict control to prevent any damage to the apartments and to stabilise the mountain slopes behind and below the site development.

Five rows of high capacity temporary anchors were recently completed by Keller Terra for "El Corte Ingles" Superstore - a deep basement in Albacete, Spain. Working Loads as high as 1800 kN were utilised in the stiff clays which in turn allowed a gross reduction in the number of anchors. Successful trials on removable SBMA's were also carried out (see "Anchors Away" in Case Histories).

High Capacity SBMA's could have restrained all of Hannibal's elephants at his point of departure for his alpine crossing! Hannibal left the ancient Spanish port of Cartagena and led his army and his elephants through the Alps and on to Rome. He never defeated the Romans nor did he apparently leave any elephants in what is now a huge marina resort.

Current developments in Cartagena lie in front of his fortifications in a mixture of fill and underlying sands and clays. Keller Terra are installing anchors to retain diaphragm walls for construction of the new quay side "Palace of Congress" in Cartagena. Furthermore the new Auditorium Building requires a deep basement extending well below the sea level. Diaphragm walls and anchors provided the solution. After successful preliminary trials SBMA's with loads as high as 2000 kN were installed steeply in the unusual seaward direction. Initial observations may suggest that the drill rigs were attempting to penetrate the hulls of the moored ocean yachts!

2100 kN was achieved without failure on two post grouted clay anchors each with only two 4m unit lengths at differing depths. This establishes a mobilised bond stress at maximum load of 666 kPa when corrected using the length efficiency factor. Totalling the unit capacities , this indicates that four unit SBMA's with 4m unit lengths in clay (16m fixed length) has a capacity in excess of 8400 kN! Anyone want 5000 kN working load soil anchors??

Keller (UK) completed their preliminary trial anchor program at Scunthorpe with the installation of a 3660 kN capacity test anchor that could not be failed. Investigatory anchors were installed into very stiff clays where the presence of weathered Mudstone could not easily be detected. Based on 14 values of ultimate bond stress results from the multiple anchor system investigation, work on a full scale test anchor was designed to substantiate the proposed 1300 kN working load on production anchors. Generally agreement was reached that conventional anchors could not have achieved this capacity.

Keller (UK) has been awarded a particularly difficult anchor contract by Laing O'Rourke. This work demands the use of the SBMA "environmentally friendly" totally removable anchor system.

Anchors will be founded in the complex Hythe Beds. The variability of the strata can be accommodated in the SBMA design which makes allowance for soil unit anchor failures without any additional drilling or stressing work.

New technical paper "Enhancement of Ground Anchor Design based on Tests of Multiple Anchors" by A.D. Barley & M.E. Bruce. The International Association of Foundation Drilling - GEO Quality Assurance & Control - Dallas, USA, Nov 2005. (See www.theanchorman.com )

Directors from Keller Grundbau GmbH, Portugal inspect Keller Terra SBMA works in Madrid and discuss the benefits of high capacity and removable anchors.

Keller Terra successfully complete 2000 kN working load SBMA contract anchors in Murcia and Madrid.

Foundation Drilling, USA published "Ultra High Capacity and Totally Removable Tiebacks" in their August issue. (See paper in www.theanchorman.com )

Two trial anchors were installed into highly weathered gypsum and encountered relatively high grout takes. These anchors demonstrate that safe temporary capacities up to 2000 kN were available using a four unit anchor. Use of working loads as high as 3000 kN (6 units) were possible but anchor spacing was considered too large to utilise such enormous capacities

On completion of soil nail trials SBMA Ltd in conjunction with GMG Ltd (South Korea) demonstrated the performance of GMG's Real Time Monitoring system to Hong Kong Engineers. The monitor was moved and tilted and these movements were transmitted by the internet to GMG's website. Connection to GMG's website allowed observation on a laptop in the site cabin. A number of parties showed considerable interest and a license for the systems usage in Hong Kong is about to be awarded.

A trial anchor was successfully installed into difficult clay bound sands and gravels. Tests demonstrated the performance of the proposed temporary anchors with working loads up to 2000 kN incorporating a factor of safety of 2.0 at the grout/ground interface.

Actively stressed nails have been installed and tested during the stabilisation of an existing slope on Hong Kong Island. Three types of permanent, non-corrodible ASN nails were investigated. The actively stressed component was sheathed and transferred load deep into the ground

• 25 dia. steel bar plus an actively stressed strand isolated in plastic corrugated ducting.
• Two 24 dia. FT 500 composite tendons, one of which was stressed.
• A carbon fibre flat bar plus a stressed 24 dia. FT 500 tendon.

SBMA Ltd extend their thanks to the five parties involved in authorising and co-ordinating the demonstration test works:

• Hong Kong Geotechnical Engineering Office
• Landslip Preventative Measures Division
• Ove Arup and Partners (HK) Ltd
• Hong Kong Construction Company Ltd
• Weldgrip Co UK

Tested SBMA's in fine grained glacial till demonstrated the effect of the increase in load capacity resulting from the attainment of higher end of casing grout pressures. SBMA's in underlying weathered Schist could not be failed at 1600 kN test load applied to two 3m unit lengths.

Permanent anchor works for a deep basement are now proceeding with Anchor works carried out by SBMA Licensee, Austress Menard, in conjunction with local contractor March Construction.(Photo)

Published comment by Tony Barley regarding corrosion protection of prestressing anchor heads.

SBMA have secured a patent on a completely new tendon system. For permanent works the new non-corrodible tendon weighs only 13% of a conventional anchor less than 2kg.metre! for a 2500 kN capacity tendon.

Watch this space.......for anchors of the future!

All 190 permanent SBMAs with 1250 to 1500 kN working load in highly weathered dolerite have been completed successfully by Austress Menard at Greystanes.

Conventional anchors installed in the stiff clays at Hodenpyl Dam exhibited load losses due to creep that resulted in unacceptable wall movement. They were replaced by post grouted SBMA's which have exhibited small load change over the two year period. The majority of unit anchors maintained load of between 100% and 92% of lock-off load. Of the remaining 10% the lowest maintained load was 88%. It should be noted that the wall and anchor head movement was not monitored and the small load changes could have resulted from nominal wall movement.

The creep losses experienced during the 24 hour preliminary testing of SBMA's rarely exceed half of the tolerable amount. This is due to the benefit in uniformity of load distribution in SBMA anchors.

The patented system utilises optical fibre and other movement monitoring sensors in a wide variety of applications where real time monitoring of geotechnical structures is required. Instrumentation accuracy can accomodate changes in microstrain (optical fibre tehnology) or as little as 0.5mm for TRS Sensors used for slope monitoring.

Take advantage of this innovative and cost-effective technology to solve your real time monitoring needs.