Excavation of side phase

Drilling with casagrande

king post pile

final view of shoring system

Location: Terminal 1D, New Delhi

Brief of the Problem: Slope Protection work having Variable Strata for Construction of Metro Station and Interchange Section of Train

Metro Station was proposed near Domestic Airport Terminal 1D, and the station has to pass under the main road leading to the airport. For the construction of the station, the cut and cover technique was adapted. The cut and cover method need to be executed with precision so as not to affect the adjoining structures and necessitate proper support for the stability of the slope.

Engineered Solution: Supporting System for Safe Deep Excavation Works

To complete the station with minimum impact on adjoining facilities and structures and to not cause much hindrance to the moving traffic, the excavation work was proposed and executed.

Slope protection work was a temporary solution, and later on, permanent retaining walls were constructed. The protection systems used included soldier piles, timber lagging with cable anchors in soil strata, and rock bolts with shotcrete in rocky strata.

The retaining structure using a row of soldier pile was installed at the first stage as the soldier piles are vertical elements for the temporary protection wall. Soldier piles were made of H-shaped steel beams that are drilled deep into the strata before excavation commences.

The excavation started from the ground level to reach up to the bottom slab of the station box. Support to the soldier piles was given using timber lagging in between the soldier piles and by installing tie back cable anchors at different elevations with Waller Beam on the soldier piles. In some areas strut with king posts were also installed to support the soldier pile wall, which in turn supported the soil at the sides.

Rock bolts with shotcrete were used for supporting the sides of the rock surface. The choice of installation of places with anchor and rock bolt was made according to active earth pressure through earth pressure analysis. The anchors were used for temporary support, which was retrieved after the construction of concrete retaining walls. The anchor of capacity 68 and 45 tons were installed.

King post piles were installed beneath the steel platform. The steel platform was placed to keep traffic moving since the road is the main access road.

Difficulties Faced during Execution:

The geological strata in the area were of mixed geology. It included soil and rock. It created many difficulties to adhere to the H design of the work as the length of the pile, cable anchors, and king posts varied because of strata at different locations. Also, coordination was required between the excavation agency and us.

Achievements:

We are proud to have completed the work within the time frame despite many difficulties. The metro has started working on that Magenta line, and we are happy to be a part of making that possible.