What are the differences between rock dowels and rock bolts?

Rock dowels are passive reinforcing elements which need some ground displacement for activation. In installation of rock dowels, a hole is drilled and untensioned steel bars are inserted into the hole. When displacements along joints occur, rock dowels are subject to both shear and tensile stresses. The level and ratio of shear and tensile stress depends on the properties of the surrounding ground, the grout material filling the annular gap between the dowel and the ground and the strength and ductility parameters of the rock dowel itself. Moreover, the degree of dilation during shear displacement affects the level of stress acting within the dowel.

Rock bolts are tensioned once the anchorage is attained to actively set up a compressive force into the surrounding rock. This axial force increases the shear capacity and is generated by pre-tensioning of the bolt. The system requires a bond length to enable the bolt to be tensioned. In essence, rock bolts start to support the rock as soon as they are tensioned and the rock does not have time to start to move before the rock bolt becomes effective.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.