**6.3. Grout behaviour**

### *6.3.1. Stress in grout*

It is known that grout bonds the shanks to the ground making the bolt an integral part of the rock mass itself. Its efficiency depends on the shear strength of the bolt - grout, and grout rock interface. Figure 32 shows the contours of induced stress through the resin layer surrounded by 20 MPa concrete, without pre-tension. It was revealed that the induced stress exceeded the uniaxial compressive strength of the grout near the bolt - joint intersection which crushed the grout in this zone. It shows that the value of induced stress in the grout near the shear joint is much higher than the uniaxial strength, and grout in this location can be crushed. The broken sample showed that the grout was crushed around this zone. The damaged area on the upper side of the grout was approximately 60 mm from the shear joint. Figures 33 and 34 show the gap formation after bending in the numerical and laboratory methods respectively. It is noted that the induced stresses were slightly reduced as the pretension increased (nearly 10 %). However, it shows they are slightly expanded.

**Figure 32.** Maximum induced stress contours in grout layer without pre-tension and 20 MPa

kN pre-tension

**6.3. Grout behaviour** 

Strain in bolt and concrete

*6.3.1. Stress in grout* 

A comparison of induced strain along the joint interface with and without pre-tension found that the strain in the shear direction is reduced (around 15%) with increasing pre-tension. In

Figure 31 shows the deformation behaviour of both concrete medium and bolt. Plastic deformation of concrete occurs nearly 15 % of the maximum shear load while the deformation of the bolt occurs at 33% of the loading steps. From the graphs it can be inferred that in very low values of bolt deflection and time steps, fractures happen in the concrete, which is in the elastic range of the bolt. Any further increase in shearing does not influence the stress at the hinge points, however induced stress in the concrete blocks causes

**Figure 31.** Induced strain in concrete and bolt as a function of loading steps in 20 MPa concrete with 80

Loading steps

Strain in bolt

Strain in concrete

It is known that grout bonds the shanks to the ground making the bolt an integral part of the rock mass itself. Its efficiency depends on the shear strength of the bolt - grout, and grout rock interface. Figure 32 shows the contours of induced stress through the resin layer surrounded by 20 MPa concrete, without pre-tension. It was revealed that the induced stress exceeded the uniaxial compressive strength of the grout near the bolt - joint intersection which crushed the grout in this zone. It shows that the value of induced stress in the grout near the shear joint is much higher than the uniaxial strength, and grout in this location can be crushed. The broken sample showed that the grout was crushed around this zone. The damaged area on the upper side of the grout was approximately 60 mm from the shear joint. Figures 33 and 34 show the gap formation after bending in the numerical and laboratory methods respectively. It is noted that the induced stresses were slightly reduced as the pre-

tension increased (nearly 10 %). However, it shows they are slightly expanded.

the axial and shear direction strain was concentrated near the shear joint.

extensively fractures and eventually leads to failure.

**Figure 33.** Gap formation in post failure region in 20 MPa concrete in the Numerical simulation

**Figure 34.** Gap formation in post failure region in 20 MPa concrete in the laboratory test
