Rock Bolts for Granary Island

At the junction of Motława River and Dead Vistula River lies a block of land known as Granary Island, located in the heart of the famous Amber district in downtown Gdansk. Until 1945, Granary Island was an important part of the city’s industry with wharves and warehouses. In the course of time, the island was slowly being lost to the two rivers, which caused both landslides and increasing damage to the quayside.

Due to the city’s growing economy and tourist industry, it became more and more important to stabilize both quaysides and deepen the waterway along the Motława River in the Gdańsk area. To stabilize the quaysides, 1,036 T76 self drilling rock bolts with a total length of 23,930m were chosen as the tie back solution for the new sheet piles. In the Granary Island, sheet piles were installed 15-17m deep into the ground.

The rock bolts were installed in maximum lengths of 3m. Initial flush to depth was carried out with a 0.9 w/c grout ratio, followed by a 0.5 w/c grout ratio with flush back to the surface. The cement grout was injected using a grout pump through a H90/T76 rotary injection adapter.

Ground conditions consisted of silts with sand and gravels overlying clay. To drill into this ground, T76/200 and T76/280 drill bits were used. In the deep end of the boreholes, full reaming was employed to clean the boreholes and enhance the bond at the grout/ground interface.