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GROUND ANCHORS

VSL ground anchors are used to mobilise dead loads deep in the ground in order to stabilise excavations, slopes and structures against forces including those induced by wind or suspension cables

  • Seelisberg Tunnel strengthening
    Revisiting a successful installation 20 years later to install additional rock anchors as part of an upgrade to a twin-bore tunnel.
    Switzerland - 2000 read more

    Seelisberg Tunnel strengthening

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  • Caselertobel Brücke
    VSL sicherte die Stabilität der Brückenpfeiler mit 57 elektrisch isolierten Ankern.
    Switzerland - 2003 read more

    Caselertobel Brücke

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  • A9 Lake Geneva Highway (wall 57)
    Using VSL permanent anchors to stabilise a highway retaining wall.
    Switzerland - 2011 read more

    A9 Lake Geneva Highway (wall 57)

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  • Rorbach Bridge
    A unique avalanche-proof tunnel-bridge that relies on VSL Anchors.
    Switzerland - 2007 read more

    Rorbach Bridge

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From basic unstressed temporary bar nails to sophisticated post-tensioned electrically isolated strand anchors

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Caselertobel, Switzerland: permanent anchors up to 60m-long and with a working load of 1,310kN prevent the slope from sliding.

VSL’s ground anchors are in use worldwide, securing famous structures, large dams and retain-ing walls, holding down underpasses and underground structures, stabilising wind turbine towers and preventing landslides. VSL has been designing, fabricating and installing post-tensioned ground anchors since 1957 and using bar anchors since the early 1970s.

Applications include bridges, cable cars and cable railways, as well as maintaining excavations against ground instability. The anchors provide an effective alternative to large gravity or stabilisation structures.

VSL’s products and services

VSL can supply and install a range of ground anchors:

  • Soil nails and rock bolts (generally short and unstressed)
  • Strand and bar anchors (generally longer, stressed or unstressed)
  • Bars for micropiles - foundation members working either in tension or compression

Advantages of VSL’s solutions

  • A wide range of solutions to suit the client’s needs while complying with all applicable international standards
  • A full range of services tailored to meet site constraints and procedures
  • Very reliable and sustainable ground anchor solutions, based on extensive
  • Support from a world leader in specialist construction engineering and associated tech-nologies and services
  • Access to a wealth of experience and expertise through VSL’s technical centres, from pre-liminary design to construction engineering
  • A strong local partner that belongs to an international group

VSL’s project experience represents an immense wealth of engineering and practi-cal know-how.

Today’s increased emphasis on safety, durability, the environment and sustainabil-ity means that engineers are faced with the challenge of complying with more stringent requirements while meeting the growing demands of urban congestion and other site conditions.

VSL has experience in dealing with these issues and can assist clients in achieving all their project requirements.

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Contributing to sustainable solutions

Saving material
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Ground anchors provide an efficient way of mobilising dead loads deep in the ground to stabilise slopes and excavations or to resist forces that would otherwise require large gravity foundations. Uses include resisting forces induced by wind and water pressure or tension forces such as those of suspension cables for bridges or cable cars.

Durability

VSL ground anchors comply with the most stringent international specifications with regards to corrosion protection.

Ease of removal

Temporary VSL ground anchors can be designed for removal when they are no longer required in order to mitigate the impact on the adjacent ground.

The choice of ground anchors depends on whether they are to be tensioned or not, used for rock or soil and whether they are for temporary or permanent use. Three main technologies are available:

1. VSL temporary strand anchors – economical for up to a two-year service life

Main components

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VSL temporary strand anchors

How it works

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Alpine Transit Tunnel, Switzerland – 2003: hundreds of ground anchors were installed.

The strands are of uncoated steel along the bond length. Spacers hold them apart from one an-other in order to obtain an optimal load transfer. External spacers may also be used if required to centre the anchor in the drill hole.

The strands in the free length are normally greased and individually sheathed. Alternatively, strands can be left uncoated and then assembled in a smooth sleeve, which is sealed at its lower end to prevent grout penetration.

Post-grouting

Ultimate external anchor resistance can be considerably improved by the use of post-grouting around the fixed length of the anchor. VSL can provide the following post-grouting systems:

  • Simple post-grouting
  • Repeated post-grouting with a return line
  • Repeated and targeted post-grouting using double packers

Removable anchors

VSL temporary anchors can be made so that they can be removed.

Removable anchors are often needed where it is undesirable or unacceptable to leave temporary anchors in the ground, particularly in urban areas where they often extend under adjacent properties.

The methods used by VSL for extracting the free lengths - and even the bond lengths - are based on specially designed mechanisms.

VSL has a long tradition in the use of these special techniques, with thousands of anchors suc-cessfully installed and subsequently removed.

VSL Temporary Strand Anchors have a limited service life – generally speaking less than two years – as they have limited or no corrosion protection.

Surveillance anchors with the VSL Load Cell

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Ground anchors can be monitored with load cells, which are installed together with the anchor. They may be included as part of VSL’s scope of services.

Ground anchors may be monitored during their service life. VSL Load cells are installed with the anchors, either as a permanent or temporary feature.

2.VSL Permanent strand anchors

Main components

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VSL Permanent strand anchors

VSL’s permanent anchors may be used as:

  • Standard working anchors, where the load is normally not modified after stressing
  • Adjustable anchors for regulating the load
  • Control anchors, which allow occasional monitoring with a removable load cell
  • Surveillance anchors, where the anchor load is monitored using a permanent load cell
  • Electrically isolated anchors

How it works

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Wind Turbine Tower - Aland Archipelago, Finland – 2007: ground anchors stabilise the tower, avoiding the requirement for a gravity foundation

Permanent ground anchors fulfil their function throughout the working life of the structure and require comprehensive corrosion protection. They are equipped with tightly fitting, thick-walled polyethylene (PE) encapsulation, which acts as a protective barrier against corrosion.

In the bond length, the strands are uncoated steel and encased in a corrugated duct. Spacers hold them apart from one another in order to obtain an optimal load transfer. The corrugated duct is then bonded to the ground with grout. External spacers are used for overall centring of the tendon and corrugated duct in the drill hole while grouting the assembly.

Today’s state-of-the-art permanent anchors are electrically isolated, a technology that has been fully mastered by VSL.

Alternatively, VSL ground anchors can be provided with two protective barriers against corrosion attacks. These are DCP (Double Corrosion Protection) anchors, which comply with EN 1537 and feature two concentric corrugated ducts in the bond length, where they are pre-grouted prior to installation.

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Hotel Pestana Promenade – Ocean Resort Hotel, Madeira, Portugal - 2007
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Valanche tunnel, Switzerland – 2007: anchors provide security against the effect of avalanches
Load monitoring
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VSL produces a special load cell for ad-hoc load checks

Permanent anchors can be inspected throughout their service life. In addition to visual checks of the anchorage, anchor loads can be measured by lift-off procedures using either a special load cell in combination with a threaded anchor head, or by pulling on the protruding strand bundle. Carrying out these tests as part of a defined inspection schedule provides an invaluable check on the behaviour of the anchors.

Special lift-off jacks

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VSL’s lift-off jack for special applications

Where anchors have neither threaded heads nor protruding strands, VSL can provide special jacks that allow the anchor head to be lifted off. These are available in capacities of up to 1,670kN.

3. VSL Bar anchors

Main components

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VSL bar anchors

How it works

A full range
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Central Hidroélectrica Porce III, Columbia - 2005

VSL has marketed bars for the construction industry since the early 1970s and offers an extensive range of hot-rolled and cold-rolled products. VSL’s product line complies with international standards including Eurocodes, ASTM, Australian and British Standards and SIA. Diameters range from 16mm to 75mm, depending on the steel grade, to allow fine-tuning to suit the required loads.

Soil nails, rock bolts, micropiles

The VSL Bar System, which is available in B500 and S670-grade steel and diameters of up to 75mm, is used for soil nails, rock bolts, micropiles and similar applications. VSL offers a variety of protection options to meet international regulations, ranging from no special measures for bars for short-term use through to pre-grouted bars with a high level of corrosion protection.

Bars for mining and tunnelling
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Maladière Football Stadium, Switzerland - 2007: preparation of the micropiles

VSL’s B450 and S600-grade bars are used in mining applications while B500 and S670 are used in tunnelling. Different anchoring methods are available and include fully cement and resin-grouted bonded anchors, as well as expansion-shell anchors. The bars can be provided with saw-tip, chisel-tip or point-tip end finishes.

Bars for prestressed anchor applications
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Sunshine Motorway Duplication, Australia - 2008

VSL Post-Tensioned Anchors consist of a high-strength Y950/1050-grade steel tendon, which is fitted with a stressing anchorage at one end and a means of permitting force transfer to the grout and rock or soil at the other end. Anchors are usually shop-fabricated and fitted with the required corrosion protection for delivery to site with either double or single corrosion protection.

VSL Anchoring systems - a versatile solution provider

Securing slopes

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Nisigaya Factory, Japan – 2006: Stabilisation of slope during excavation for site preparation

The use of post-tensioned soil and rock anchors provides an economical solution for securing slopes where excavation for new roads, railways or similar projects means that the stability would not otherwise be guaranteed. The load is usually transmitted to the underlying ground through foundations against which the anchorages of the ground anchors are stressed. Nor-mally, the inclination of the slope is chosen to avoid slippage and hence is equal to the angle of friction of the soil or rock.

Securing retaining walls

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A10 Highway from Bucelas to Carregado, Portugal - 2003

In general, retaining walls are more or less vertical to avoid excessive removal of rock or soil. Their stability is assured by post-tensioned anchors. An anchored retaining wall can also be a sustainable solution for stable rock faces, as it provides effective and durable protection against erosion and crumbling of the rock due to weathering by rain, snow or frost.

Securing excavations

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Neufeld Tunnel, Switzerland - 2007

The vertical walls of excavations are anchored simply and economically by post-tensioned an-chors. This method provides an obstruction-free excavation face that allows the use of mechanical equipment. Various methods are available for the construction of excavation walls, depending on the requirements of each particular site.

Clients increasingly demand the removal of temporary anchors, particularly to suit local authority and neighbours’ requirements in urban areas. VSL can supply two types of removable anchors - one where the total length is pulled out and another where just the free length is removed.

Stabilisation against overturning

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Bank of China, Hong Kong – 1987: ground anchors at the base of the tower stabilise it against typhoons

The need to prevent overturning arises when a structure may be subjected to horizontal forces from water, earth or ice pressure, wind, waves or earthquakes. To avoid costly increases in weight or dimensions, the structure’s stability can be ensured by means of anchors, which save both construction time and materials. This solution is appropriate for towers, masts, pylons, dams and spillways as well as lightweight high-rise buildings.

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Wind Turbine Tower - Aland Archipelago, Finland – 2007

Other applications

Other economical uses of ground anchors include:

  • Anchoring against hydrostatic uplift
  • Securing caverns
  • Anchoring concentrated forces

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