A new subway line is being built in Rio de Janeiro, Brasil. The line includes the Gávea station where the formation consists of sand and stone layers combined with layers of large boulders and finally granite/quartz rock. Use of Wassara´s Jet Grouting hammer made it possible to significantly increase the grout column production rate which was stalling due to a time-consuming drilling operation.
The metro system is being extended in Rio de Janeiro, Brazil. The new part, named Line 4, is under construction in the West Zone of the city of Rio de Janeiro and will open in 2016. It is expected to carry over 300 000 people per day and to decrease the amount of cars on the road during rush hours by almost 2 000 cars.
The newest construction site is the Gávea station, located close to the middle of Line 4. This station will have two entrances at each end of the platform going up through a Ø 40 m shaft.
Challenge - Drilling and building in sandy formation
A decision was made to build two shafts for the entrances by jet-grouting 200 columns placed in two rings for each shaft. The columns will reach down to 15-20 m and 20-25 m depth, respectively. After completing the jet-grouting, excavation of the shafts will complete the entrances.
The formation presented a drilling challenge as it had layers of sand and stone combined with layers of large boulders and finally hard rock. That is why the contractor decided to test the Wassara Jet Grouting hammer and compare with a common technology where a roller bit is placed after the grouting monitor.
Drilling and jet grouting with Wassara
Where stones, boulders and other obstacles have made the drilling sequence complicated, Wassara´s patented W100JG-hammer makes it easier. The water-powered DTH hammer makes its way through any stone or boulder present in the formation and is a powerful tool for drilling a socket in solid rock.
Since the drill string is complete with all necessary tools, no changing of equipment is required between the drilling sequence and the jet-grouting sequence or vice-versa.
The hammer and jet grouting monitor are powered by separate pumps and can be controlled independent of one other.
The whole jet grouting operation is completed in two steps:
1. Drilling down to the desired depth
2. Jet Grouting on the way up
Saving valuable time
A comparison between the roller bit drilling and drilling with Wassara W100JG at the same site gave a very clear indication of the differences between them: