Anchor type and anchoring force

The anchor is a rod-like structure anchored in the rock body to maintain the stability of the surrounding rock. For the surrounding rock of the underground engineering, the anchor rod is used as the main component of the support system, and the bolt support system is formed. The single anchor rod is mainly composed of an anchor head (anchor section), a rod body, an anchor tail (outer anchor head), a tray and the like.

1. Classification of anchors

1 Mechanical anchoring anchors include expansion shell anchors, inverted wedge anchors, and wedge-stitch anchors.

2 Bonded anchor bolts include resin anchors, fast hard cement coil anchors, and cement mortar anchors.

3 Friction anchored anchors include seamed anchors, water-swellable tubular anchors, etc.

According to the length of the anchoring section of the shaft, it can be divided into end anchoring, full-length anchoring and lengthening anchoring.

According to the working characteristics of the anchor rod body, it is divided into rigid anchor rod, limited stretchable and stretchable anchor rod.

According to the characteristics of the bolt, it can be divided into active anchor and passive anchor.

Anchor rod according to material of the bolt can be divided into wood, bamboo anchor, anchor metal, (reinforced) concrete anchor bolt and the like, and polyester.

2. Anchoring force of anchor

The bolt support changes the mechanical state of the surrounding rock by anchoring the rod inside the surrounding rock. Its stress condition and its effect on the surrounding rock is much more complicated than the shed bracket. The national standard GBJ86-85 defines the anchoring force as the binding force of the anchor to the surrounding rock.

(1) Defining the anchoring force according to the way the anchor rods restrain the surrounding rock

1 Anchoring force: The anchoring force includes the pre-tightening force of the bolt plate generated by tightening the nut to the surrounding rock when the bolt is installed, and the longitudinal expansion of the tubular tubular bolt body causes the pallet to pre-tighten the surrounding rock. And the radial support force applied to the surrounding rock when the anchor pallet prevents the displacement of the surrounding rock into the tunnel.

2 Adhesive anchoring force: The binder binds the surrounding rock and the anchor rod into a whole. Due to the difference between the deep and shallow deformation of the surrounding rock, the anchor exerts a cohesive force on the surrounding rock through the binder to suppress the deformation of the surrounding rock. The anchoring force is the axial force of the anchor rod body. The friction anchor bolt exerts anchoring force on the surrounding rock through the friction between the rod body and the surrounding rock to suppress the deformation of the surrounding rock.

3 Tangential anchoring force: The deformation of the surrounding rock mass mostly starts from the weak surface of the rock mass, and the surrounding rock slides or opens along the weak surface under the action of confining pressure. The anchor body penetrates the weak surface to restrict the surrounding rock from sliding or opening along the weak surface. This restraining force is called the tangential anchoring force.

(2) Defining the anchoring force according to the anchoring stage of the anchor

1 Initial anchoring force: When the anchor is installed, the anchor is artificially stretched so that the force of the anchor that acts on the surrounding rock is called the initial anchoring force.

2 Working anchoring force: After the anchor is installed, the surrounding rock deforms and the anchoring agent acts as a bonding; or the friction between the shaft and the surrounding rock restricts the deformation of the surrounding rock. At this time, the force of the anchor to the surrounding rock is the working anchoring force. .

3 Residual anchoring force: When the relative deformation of the surface and deep part of the surrounding rock exceeds the ultimate deformation of the anchoring agent, the anchoring agent destroys the working anchoring force. However, since the damaged anchoring agent still has residual bond strength, there is friction between the surrounding rock, the damaged anchoring agent and the anchor rod body, and the anchor rod still has binding force on the surrounding rock, which is called residual anchoring force.

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