Corrosion protection

SBMA Ltd

PO Box 342, Harrogate LDO, HG3 1YR, UK. +44 (0) 7961 134 943

Company Registration No: 4026709, VAT registration: VRN 788 994 822

Understanding SBMA Technology / Information Hub

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An anchor tendon with a 8m fixed length in soil or rock will, at test load, need to extend some 25mm at the proximal end of the fixed length before any load will be transferred to the distal end of the tendon.

It is unusual for the elastic behaviour of the grouted soil around the anchor tendon to be compatible with the elasticity of the tendon and allow a uniform distribution of load along the fixed length.

Thus, it is widely acknowledged that, in the majority of circumstances where conventional anchors are used, debonding at the tendon/grout or the grout/ground interface must occur as anchor load increases and prior to any load being transferred to the distal end of the fixed length.

This phenomenon is commonly known as progressive debonding and is associated with grossly non-uniform distribution of bond stress along the fixed length at all stages of loading.

Information has been published by a multitude of researchers on this topic.

Progressive debonding generally results in a highly inefficient use of the existing ground strength. In circumstances where the ground strength far down the fixed length is being utilised, the ground strength above this has been exceeded and only some residual strength is available. This reduces the overall efficiency of the fixed length (Fig.1).

Stronger by design

However, a system that can transfer the load simultaneously to a number of shorter lengths in the fixed anchor bore without the occurrence of Progressive Debonding, will mobilise the in-situ ground strength more efficiently and result in a considerable increase in anchor capacity (Fig 1).

This is the principle of the single bore multiple anchor (SBMA).

For more technical background information on progressive debonding, or for answers to any of your questions, Please - Contact Us

SBMA systems offer technology that completely isolates the tensile steel tendon from the surrounding environment.

In the fixed length this is achieved by employing double corrosion protection via two impermeable corrugated HDPE ducts in accordance with:

• BS8081: 1989 (British code of practice for Ground Anchorages); and

• EN1537: 2011 (Euronorm: Execution of special geotechnical work – ground anchors).

In the free length two plastic sheaths are used to create a suitable barrier from the environment, again providing double corrosion protection.

NOTE: Total anchor load equates to shaded area under the curves

Fig. 1

Anchor Load Distribution For Normal Anchor

Single Tendon Fixed Length

Bond Stress

Initial Loading

Ultimate Loading

Load Distribution Along Fixed Anchor

0

Fixed anchor length generally 10m max

Loading

Proximal End

Distal End

Grout

S

Ground

SBMA Load Distribution

Bond Stress

Load Distribution Along Fixed Multiple Anchors

0

Fixed anchor length can be increased to 25m+

Loading

Multiple Anchor Units

Grout

Ground