View from tunnel 1 at launching chamber of New Delhi Station…
Tag: The Job
TBM cutterhead
2nd TBM cutterhead lowering at Launching Shaft New Delhi Station for tunnel-496.
Later it will be mounted to cutterhead support this giant which will crush anything from soil to rock weight about 65 tonnes and excavation diameter will be 6.55-meter, manufactured by Herrenknecht.
The finished diameter of the tunnel after precast segment lining will be 5.8m.
Shotcrete
This days Shotcrete at Launching Chamber is in progress as hard rock was encounter during the excavation of it has been terminated 3m to 4m above formation level, so here comes wire mesh, shotcrete & rock bolting to secure the excavated face.
We don’t have much scope of Shotcrete in, our project we will be doing dry Shotcrete.
The sequence of the work as follows.
- All material including water will be thoroughly mixed and will be placed on the shotcrete equipment.
- Compressed air will convey material at high velocity to the nozzle where the water and accelerators will be added.
- Finally, the material will be consolidated on the excavated surface by high impact velocity.
Rock Bolting
Rock Bolting at launching chamber of New Delhi metro station.
Rock bolts are used for the support of underground and surface excavations.
Rock bolts generally consist of deformed steel rods with an end anchorage and a face-plate and nut at the rock surface, For short-term applications, the bolts are generally left un-grouted with end anchorage. For more permanent applications or the rock in which corrosive groundwater is present, the space between the bolt and the rock can be filled with cement or resin grout.
Anchor bars generally consist of deformed steel bars, which are grouted into the rock.
Steps of work will be as followed.
- Drill hole to be done as per approved design and drawing.
- After drilling of holes for end anchorage required no of fast setting resign capsules shall be inserted inside the holes.
- Rock bolts shall be inserted inside the hole in a rotary manner so that it can puncture the capsules for proper mixing with resin capsule.
- Rock bolts pull out test to be conducted as per design requirement.
- After satisfactory testing remaining drill holes to be grouted.
- At the face of the rock MS plate shall be used as washer & fixed at the face of the excavated rock.
TBM II
TBM 2 erection started at Launching chamber of New Delhi Metro, TBM-2 will start excavation on New Delhi to Shivaji Stadium tunnel by end of December while TBM-1 is on his way to Shivaji stadium. Back up gantries will be lowered next week and connection work for the initial drive will start.
Cutter head arrived at the site too, welding work is ongoing, I don’t want to miss the view when it will be lifted for lowering.
Temporary Decking
Temporary Decking ready for operating at Station Area.
This temporary decking really comes in handy in cut & cover construction this decking will be used for temporary road diversion we will be having three more temporary decking one will be above launching chamber for the segment and material stacking, two more are in cut and cover area for crane movement and concreting.
We will do a load test for the decking after a successful result it will open for traffic and we will break and excavate the existing road.
TBM Launching
Finally, the day arrived Mr. E.Sreedharan switching on the TBM. Feeling awesome to be a part of the celebration.
In our scope, we have Twin bored tunnel 495 & 496 from (New Delhi Station to Shivaji Stadium)
2.2 Km long and finished internal dia of the tunnel is 5.6m. Shivaji Stadium will be the receiving station. Well, it will take few more days, in reality, to start digging the tunnel muck disposal area not yet functional the open area above the launching chamber decking to complete for stacking of segments. I hope by the mid of November segment shifting will be in full fledge more inspections for us.
Soil Anchor Locking…
Drilling of ground anchor completed, HT tendon installation checked.
Grouting strength checked.
Now its time for stressing and locking of tendons, we will insert the HT strands
on to the anchor head & place bearing plate to water and weld than a hydraulic jack
will be connected to a pump with pressure gauge indicator above the anchor head.
Stressing will be done in two cycles with a max load of 125% of required load and will
be checked for 15 minutes for load reduction meantime we will note the elongations in stressing formats if the load reduction between two cycles is in the range of 5% anchor will be passed. Upon the completion of the second load, cycle anchor will be reloaded to 110% of working load and will be locked.
Shotcrete Trial
Today we did a trial for Shotcrete, we will be doing shotcrete in launching chamber, in cut and cover areas & in cross passages.
Shotcrete is concrete (or sometimes mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique.
Shotcrete is usually an all-inclusive term that can be used for both wet-mix and dry-mix versions.
Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. It can be impacted by any type or shape of the surface, including vertical or overhead areas.
Grouting Plant for Soil Anchor
Soil Anchor grouting plant arrived today at the site, grout plant consists of mixer, agitator, water measurement tank, storage water tank, water pump, and control panel.
We will be using a cement grout admixture will be added as per requirement.
For the quality control of grout mix, we will do the following tests.
1. Flowability check.
2. Shrinkage and bleeding test.
3. Compressive strength.
The grout will be injected into the tendon through the grout pipe extending up to the bottom of the hole in a continuous manner without any interruption until grout overflows from the top of the borehole. We will do the grouting at 2-5 bar pressure to fill the hole from bottom to top & displacing any water therein.
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