Single Bore Multiple Anchor Systems (SBMAs) in Challenging and Variable Ground Conditions-Paper

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Single Bore Multiple Anchor Systems (SBMAS) place several independently designed tendon units of different bond lengths in one borehole. Unlike conventional anchors, which transfer load progressively along a long bond zone and may underuse ground strength, SBMAS distribute load across short unit anchors. This can improve bond efficiency and, in suitable soils and weak rocks, provide up to twice the capacity of conventional anchors.<br /><br />Each unit’s bond length can be tailored to local ground strength, including variable layers and weak zones. Designers can also allow for the possible failure of one or more units while maintaining the required overall capacity. SBMAS are used as temporary, permanent, or removable anchors; permanent systems have double corrosion protection, while removable systems allow tendons to be extracted after their service life.<br /><br />Installation broadly follows conventional grouted-anchor methods. Testing applies equal loads simultaneously to each unit, usually with synchronized hydraulic jacks, though a single-jack method is also possible. Tablet-based software can support real-time analysis, acceptance checks, and data management.<br /><br />Case histories demonstrate the system’s performance in diverse conditions. In Boston clay, three-unit anchors sustained test loads up to 1,200 kN, exceeding conventional-anchor capacity by as much as 50%. In Moscow, SBMAS more than doubled capacities achieved previously in similar ground and helped limit wall movement. In Izmir, testing enabled a redesign that reduced total anchor length by about 64%, construction time by up to 60%, and anchoring costs by 35%. Permanent systems in Austria replaced 400 corroded conventional anchors with 200 higher-capacity SBMAS. Removable anchors were also used on a deep excavation project in Abu Dhabi.<br /><br />By reducing the number of anchors, drilling operations, and stressing tasks, SBMAS can shorten construction schedules and lower costs, while offering adaptable support in heterogeneous ground.

Keywords

Single Bore Multiple Anchor Systems

SBMAS

anchor capacity

bond efficiency

grouted anchors

tendon units

temporary anchors

permanent anchors

removable anchors

ground support