The Use Of Self-Drilling Anchors
Self-drilling anchors can be used as reinforcing elements for most applications for Ground Engineering and Civil/Construction.
Basically, self-drilling anchors can be used as reinforcing elements for most applications for Ground Engineering and Civil/Construction as well as Mining principals in various ground conditions. Particularly considering the economic point of view the system is used in a variety of loose/unconsolidated soils and ground conditions ranging from clay, sand and gravel to inconsistent fills, boulders, rubble and weathered rock. Use of the self-drilling anchor system in these conditions makes evident all the benefits and advantages of the system.
Soil nailing and Rock nailing is a construction method used to maintain or enhance the stability of the Soil or Rock by installing reinforcing elements (nails) in accordance with principles for the execution of geotechnical works. Nailing forms a retaining structure of reinforced Soil or Rock mass with which the nail is predominantly subjected to tensile stress. In addition, it may also be subjected to bending and shear stresses.
The design of soil/ rock nailing solutions for slopes generally favour installation angles from 0° – 30° downwards from the horizontal and depending of the stress situation a standard nail drilling pattern of 1 to 3 m c/c in longitudinal and vertical direction for the extent of the slope. Soil nail lengths can normally vary from 4 to 15 meters.
The conventional method of installation involves drilling the self-drilling anchor with air or water flush to the design depth and then in a second phase, independent of drilling, a grout adapter is added and a cement based grout mix is injected through the hollow core to exit at the bottom of the borehole and then return upwards to fill the annulus, thus providing once cured for the transfer of tension load from the soil/ rock formation to the self-drilling anchor.
Anyhow, using a swivel injection adaptor makes it possible to perform both drilling and grouting simultaneously. Thus is increasing productivity and quality of grouting.
Ever since the ATM tunnelling principals have found industrial acceptance, in particular for unconsolidated/ fractured ground conditions, also self-drilling anchors have become an irreplaceable product.
The self-drilling anchors are part of the excavation process and serve as primary soil/rock support for:
- Radial consolidation of the tunnel circumference supports the rock, forming a load bearing ring thus enabling the rock supporting itself (together with shotcrete and other facing elements).
- Umbrellas and Fore poling as Pre-support in poor rock formation, shallow overburden and critical stress conditions.
- Face stabilisation to sustain rock pressure for excavation with large cross sections.
- Root piles to divert stress.
The conventional method of installation involves drilling the self-drilling anchor with water flush to the design layout and depth and in a second phase, independent of drilling, a grout adapter is added and a dense cement based grout mix is injected through the hollow core to exit through the flush holes at the drill bit filling the borehole annulus until the grout mix appears at the borehole mouth, once cured, enabling the transfer of stress from the rock/soil formation.
A Micro pile is small diameter pile which is used in various applications within Ground engineering. Generally, Pile foundations serves to transfer structural loads to the underlying formations of construction ground and/ or to limit deformations according to the principles of the execution of geotechnical and civil works. The Micro pile may thereby only be subjected to axial tensile, compressive or alternating loads. Self-drilling micro piles are featured products for Micro piling and preferred method of installation in these applications is simultaneous drilling and grouting.
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