Rock Anchor
Rock anchors are frequently used in stabilising structures, improving stability and increasing strength of structures exposed to dynamic loads, such as wind and wave load. Rock anchors also accommodate tensions which result from differential movement between two neighbouring structures.
Rock anchors are capable of transferring load in both tension and shear. To allow for this dual effect, two types of anchors are used - straight and curved. Straight anchors are used when the load is in tension, while curved anchors are used when the load is in shear. Generally, the rock anchors consist of a steel rod (bar) and a tendon. The tendon is then typically strapped to the steel bar or it may be grouted into a borehole.
In certain applications, such as shallow depth in rock, a steel bar alone may serve as an anchor. The steel bar, also known as a deadman, is installed into a hole in the rock and typically has an expansion plate near the end to help the anchor grip the rock and hold the load. Generally, when load is applied to an anchor, it will cause an increase in stresses around the anchor and the surrounding rock. This can be used to measure the performance of the anchor.
The installation of rock anchors is essentially a simple process - first the anchor is placed in the rock, then the anchor is secured in place, and finally the load is applied. Various techniques can be used for installation, such as drilling, grouting, or expansion. Generally, it is important to ensure that there is enough room for the anchor to be fully seated and for the anchor to be able to effectively develop the required holding capacity.
Grouted rock anchors are commonly used in applications where a reliable bond is required, such as in water retaining or dam structures. Grouting refers to the process of filling a void space with a material – usually a cement-based slurry. Grouted anchors consist of a pre-tensioned bar with a grout section at the end. The grout is injected into the rock mass around the anchor, effectively forming an adjustable steel-rock composite that provides the necessary load transfer and gripping power to the anchor.
Generally, grouted rock anchors can provide high holding strength, far greater than that of soil anchors. Soil anchors are generally used in soils where the strength of the soil is insufficient to support the load without additional reinforcement. An anchor system consists of a tendon that is buried in the soil and attachment plates to transfer the load to the ground.
In conclusion, rock anchors provide an economical and effective way to reinforce structures. The straight and curved designs ensure that the anchors are able to withstand both tension and shear forces, while grouted anchors provide a reliable bond and additional reinforcement.
