Though years of development Williams has produced and patented the Pre-stressable, Hollow-Core, Groutable Spin-Lock Rock Bolting Systems. The hollow-core allows the bolt to always be grouted from the lowest gravitational point. In an up-bolting situation, the grout is pumped in through the plastic grout tube and begins to fill the drill hole from the plate. The grout rises until the entire hole is filled and the grout returns through the hollow bar. In down grouting situations, the grout is pumped through the hollow bar and starts at the bottom of the hole. It rises and returns through the de-air tube when the hole is filled. Improperly or incomplete grouted bolts are subjected to relaxation and corrosion. Pre-measured capsule systems cannot properly account for unknown fissures and voids and often leave the bolt vulnerable to deterioration. The Williams Hollow-Core Grouting System spreads grout through the rock fissures creating a completely protected monolithic section including rock, grout and bolt.
Because the Spin-Lock head assembly provides 300º perimeter expansion anchorage and develops the full strength of the rod, the hollow-core rock bolt may be pre-stressed to the desired load and tested prior to grouting.