Bolts

Stability bolts, the specialty
cement for rock excavations

At Cimentaterra, we specialize in the installation of bolts, a fundamental technique for stabilizing excavations in rock masses. Bolts, also known as anchor bolts, consist of the introduction of bars of different materials into the rocky terrain to improve its stability and tensile strength.

This technique, which had its origins in the mining industry, has quickly spread to the field of civil engineering due to its effectiveness and ease of execution. Bolts are made of various materials, the most common being steel and fiberglass bars.

At Cimentaterra, we are proud to offer specialized services in the installation of bolts, providing effective solutions for the stabilization of slopes and tunnels. Our team of highly trained experts takes care of every aspect of the process, from initial planning to execution and subsequent follow-up.

Advantages of bolts

  • Simplicity
  • Functionality
  • Relative economy compared to other types of support
  • It can be used as a temporary or permanent support, and depending on this, the characteristics of the bolt to be used are very different.
  • Allows reducing the cross section in excavations
  • Supports total mechanization 

What are bolts?

A bolt is a metal component designed to reinforce and support fractured or unstable rocks, preventing their collapse. It acts as a support mechanism that, when inserted into the ground, increases its rigidity or its resistance to traction and shear. When the ground attempts to deform, the bolt introduces additional stresses into the rock mass, contributing to its overall stability. It could be said that the bolts "unite" the discontinuities of the rocky terrain, preventing slips and falls of wedges and blocks, in addition to providing a confinement effect.

The length of a bolt, for construction reasons, generally varies between 1.5 and 10 meters. They are installed inside the ground through a drill from an exposed surface. However, the load capacity of each bolt is relatively low, requiring a high application density. It is common to use steel bars with a diameter of 20 to 40 mm, capable of supporting loads of approximately 10 to 25 tons.

What types of bolts exist?

A bolt can be a punctual anchor or a distributed anchor. The former are practically not used in civil engineering while, in the latter, their use is widespread.

However, bolts are frequently classified based on the stress transmission system between the bolt and the rock.

Know the different types of bolts

Adhesion anchor bolts are independent of normal tension.
You can distinguish between bar, self-drilling, fiberglass, etc. They are characterized because the annular space between the hole in the bolt drilling and the bolt itself is filled with some adhesive element such as cement slurry or resins.

In the case of tunnels, cement grouts are uncommon due to the time it takes for the grout to set, except in long bolts or self-drilling bolts.

The bar bolts are made of corrugated steel bars whose most common diameters are 25 and 32 mm and with type B 500 steel that support loads of 14 to 25 t. However, they also come in other diameters and types of steel. The lengths are usually between 4, 5 or 6 m.

They are those bolts that have a single-use drill bit at their tip that allows them to drill into the ground. They also consist of threaded joints to increase their length and are usually hollow to facilitate the injection of grout or resin inside.

They are used in poor quality terrain where the drilling walls are not stable and therefore do not allow a rebar to be introduced into the hole after drilling. Like bar bolts, the most common diameters are 25 and 32.

Fiber bolts are made of polyester, vinyl and fiberglass resins. Its main characteristic is a tensile strength similar to the rest of the bolts, a lower elasticity modulus, a much lower weight and, above all, a lower resistance to cutting, which makes it especially advantageous in areas that will be excavated later. This type of bolt is removed more easily than steel bolts.

In this case, adhesion is achieved through the bolt-rock contact pressure, which gives it a pressure-dependent frictional component.