Rock, slopes and mines
Rock bolting and self-drilling anchors
Jointed rock fails along its joints. Bolts and anchors pin the loose block to the sound rock behind it. In broken ground, where a drilled hole will not stay open, a self-drilling anchor drills its own hole, stays in it, and is grouted through its own hollow bar.
When to call us
The signs
- Tunnel crowns and walls in jointed or blocky rock.
- Portals and cuttings with blocks that can slide or topple.
- Caverns, shafts and declines.
- Slopes above roads and railways.
- Ground that collapses before a conventional bolt can be put in.
- 1Note 1: A joint dipping out of the face: the block above it can slide.
- 2Note 2: Hollow self-drilling bar with a sacrificial bit. It drills the hole and stays in it.
- 3Note 3: Grout pumped through the bar fills the hole and the joints it crosses.
- 4Note 4: Couplers extend the bar to the length the design needs.
- 5Note 5: Plate and nut lock the face once the grout has set.
- 6Note 6: A set share of bolts is pull-out tested.
How we do it
Method, step by step
Map the joints
Orientation and spacing of the joints, and the blocks they form.
Design
Bolt type, length, spacing, angle and capacity.
Drill and install
Conventional bolts where the hole stands; self-drilling anchors where it does not.
Grout
Through the hollow bar, filling the hole and the joints it crosses.
Lock and test
Plate and nut once the grout has set; pull-out tests on a set share of bolts.
What we use
Made at our plant in Alwar
Quality
Checks and proof
- Drilled length and angle recorded per bolt.
- Grout take and return recorded.
- Pull-out tests on a set share, to the load the design calls for.
On record
Where we have done it
Rampur Hydro Electric Project
Rock bolting in loose, fissured strata on a 412 MW hydro project in the Sutlej valley.
Parsik tunnel, Thane–Kalyan
Seepage controlled in a brick-lined railway tunnel built in 1916, on a busy main line, without stopping the trains.
Micro-tunnel pit, Pipavav
Seawater pouring into a micro-tunnel pit through a crack, after repeated attempts to seal it had failed. Sealed up to 85 per cent by grouting.
Balia Nala landslide, Nainital
A failing slope over 300 m long and 240 m high, crossed by faults, above the town’s lake outlet. Anchored, grouted and protected.
Questions
What clients ask
What is a self-drilling anchor?
A hollow threaded bar with a sacrificial drill bit. It drills its own hole, stays in it and is grouted through the bar. In ground where a hole collapses, it saves the separate steps of casing, drilling and inserting.
Are the bolts tested?
Yes. A set share of the bolts is pull-out tested to the load the design calls for.
Related services
Often used together
Slope stabilisation
Soil nails, anchors, mesh, drainage and rockfall barriers for slopes above roads, railways and towns.
Pre- and post-excavation grouting
Water cut off and weak ground consolidated ahead of the face; voids closed behind it.
Tunnel rehabilitation
Old and operating tunnels: seepage stopped, ground consolidated and lining repaired, under traffic.
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