CR112 - The beginning of CRL excavation (Hougang Q2 2023)

 

2 June 2023 - Excavation at the northern end of the site with completed diaphragm walls.

Contract CR112 was one of the first civil contracts awarded for the Cross Island Line (CRL) phase 1. As such, it is also one of the first contracts to have commenced excavation works with a portion at the northern end of the station site having soil removed within an area where diaphragm wall works have completed. Join us as we bring to you an update on work progress as of the second quarter of 2023 at Hougang station.

7 May 2023 - Casting of the safety parapet wall on top of the diaphragm wall is under way.

7 May 2023 - A close up view of the ongoing work.

7 May 2023 - A hyperlapse of ongoing work.

2 June 2023 - Excavation done and a slab cast at the northern end of the site.

2 June 2023 - Excavation ongoing towards the southern end of this area.

2 June 2023 - Rebar for diaphragm wall panel installation still ongoing.

7 May 2023 - Parapet wall being cast around the completed diaphragm wall panels.

2 June 2023 - Another view of the area where excavation has started.

2 June 2023 - A close up view of the king posts installed.

Northern site
The northern site is where most of the activity had taken place prior, beginning with the closure of Hougang Central (Minor) and followed by diaphragm wall works commencement. The site is still a hive of activity with remaining diaphragm wall works ongoing, in addition to the commencement of excavation works.

We understand that originally, the launch shaft to facilitate tunneling works had been planned to be located mid-way along the tunnel alignment between Hougang and Serangoon North stations. Typically, when bidding for the contracts, the tenderees are allowed to make proposals on how construction can be carried out and adjust the Land Transport Authority (LTA)-proposed plans should the result be increased efficiency or cost savings. As such, this is likely the case, as we now understand that the mid-way tunneling launch shaft is no longer on the boards and the launch shaft will be integrated at the station site instead.

It is highly likely that due to the integration of the launch shaft with the station structure, the northern site saw the most activity since construction began. Within the completed area of diaphragm wall works, where excavation has begun, a parapet wall has been cast to help keep any workers from falling into the cavity. There exist some temporary openings in the side of the parapet which may be used to provide rails for gantry cranes to operate over the opening once completed.

As of 7th May 2023, there were 2 hydrofraise machines and 1 clam shell grabbing machine operating within the northern site. By 2nd June 2023, only 2 hydrofraise machines were left here, with the other clam shell grabber having been relocated.

7 May 2023 - The beginning of works at the southern site.

2 June 2023 - Works at the southern site in full swing.

2 June 2023 - Diaphragm wall works for the transfer linkway ongoing. One end is where the
hydrofraise machine is located and the other where the workers are standing.

7 May 2023 - Beginning of work at the site next to the bus interchange.

2 June 2023 - A recent view of the area with more equipment on site.

2 June 2023 - Workers on site where the diaphragm wall for the transfer
linkway will be built.

2 June 2023 - A view of the southern site along Hougang Central (Major).

2 June 2023

2 June 2023 - Hydrofraise machine excavating a diaphragm wall panel
for the transfer linkway.

2 June 2023 - A view of the southern worksite, seen from Hougang Central (Major).

Southern site
In recent days, the southern site has come alive with equipment beginning to move it. Initially, it started with a crawler crane and 1 hydrofraise machine. Subsequently, these were joined by several other cranes and a clam shall grabber, moved from the northern site following the largely completed diaphragm wall works there.

The southern site will see the construction of diaphragm walls that will intersect with the existing North East Line (NEL) station at two locations - the transfer linkway between the NEL & CRL and also at the existing NEL station Exit A. Work here is still in the early stages of diaphragm wall construction and will take some time to complete. Similarly to the northern site, once completed, excavation works can begin. It is likely that as tunneling works were to have commenced from the northern end, diaphragm wall construction was focused on that end first.

Tunneling from neighbouring contract CR111 at Defu will see tunnel boring machines dock at this end of the station. However, as contract CR111 was awarded much later, it is not anticipated that this will happen so soon.

7 May 2023

7 May 2023

2 June 2023

2 June 2023

Staging site
Along Hougang Avenue 4 is a big site that has been allocated as a staging site for the contract. Here, rebar panels for the diaphragm walls are woven together and stored till either the northern or southern sites requires their use, upon which the rebar panels are transported over. The site also serves to store other construction equipment and hoarding which may not be required at that exact moment.

Additionally, abutting the staging site, is the site for a new exit for the upcoming station that will provide easier access to the Hougang Polyclinic located nearby. Diaphragm wall works have been completed for this exit for some time and the outline of the area where the exit will be constructed.

Overall, progress is looking great for contract CR112. With excavation works underway, it will be a matter of time before the launch shaft is prepared for tunneling works to commence - likely in 2024. We can look forward to spotting the tunnel boring machines in the lead up to the commencement of tunneling works, but before then, more excavation will need to take place. Due to the built-up environment, it is highly likely that the station box itself will use the top-down approach where the station is built level by level as excavation progresses downwards. Very little can be seen of the progress internally with this method.

However, the launch shaft itself should be built using the bottom-up method where excavation progresses all the way down to the base layer. Launch shafts require open space for the lifting and lowering of excavated soil and tunnel segments, hence there should not be any obstructions to the gantry crane's operations. Do stay tuned as we bring you more updates in time to come.

This post will also be available on Instagram & Facebook later in the afternoon on 3 June 2023.