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Borros Anchors Subsurface Settlement Heave SSB0003C
Settlement points with Borros type anchors are mechanical, single point devices used to monitor subsurface settlement or heave of ground. The system consists of a three pronged anchor, a 6 mm (¼ in.) steel inner pipe and a 25 mm (1 in.) steel outer pipe. Pipes are assembled using standard couplings. After installation, the outer pipe serves as a friction reducer, allowing the inner pipe to move freely. Measurement of the elevation of the top of the inner pipe is conducted using standard optical survey methods. Changes in surveyed elevation are equal to the movement of the anchor. Anchors are most commonly deployed by pushing on the inner rod to extend the anchor prongs. Hydraulically actuated anchors are also available. Care must be taken in soft clays as the loss in strength caused by the pore pressures generated by extending the prongs may cause settlement due
to the weight of the riser pipe. Both installation-related settlement, and long term settlement of the anchor in soft clays due to riser weight may be mitigated by counterweighting the riser. Standard Borros anchor systems are prone to binding of the rods, or downdrag on the anchors caused by the rods binding where the riser pipe exits the friction reducer pipe at the anchor. RST Borros systems avoid this problem by incorporating a bearing/bushing at this critical location. In a surcharge or embankment application, as the fill rises, sections of inner and outer pipe are added to maintain the top at a manageable elevation. The top of the inner pipe should be surveyed before and after the addition of any pipe section. Fill around the installation should be placed by hand and care taken that installation is not damaged. In an excavation, pipe sections are removed, as necessary. Again, we recommend survey before and after pipe removal to ensure good high quality data.
RST Instruments Ltd.
11545 Kingston St.,
Maple Ridge, BC
Canada V2X 0Z5
Telephone: 604 540 1100
Facsimile: 604 540 1005