Holdfast Training Services Trial Blog

As Project Engineer I have been overseeing the pile installation, pile breakback and enabling works prior to the FRP (form, reo, pour) contract on the two abutments and central pier for the Canal Bridge, sharing the work load with my partner from the Royal Australian Engineers (RAE).

Abutment A is situated between a high pressure gas main & sewer to its east, and 6 lane carriageway to its west, excavation has therefore been relatively complex to say the least.

After taking an academic day, I returned to site to quality assure the on going excavation.  A temporary works designer had supplied details on the installation of a UC shoring system to support the gas main while excavation took place for Abutment A (the gas main is marked by white vertical conduits in the photo).  Emanon (sheet driving subcontractor) had driven UC’s into the ground, ready for sleepers to be inserted between them as the excavation progressed. While away though the Site Foreman and Site Superintendent had decided the shoring needed to be extended (see photo below).

Figure 1 – Abutment A Excavation, Canal Bridge

Rather than reactivating Emanon to install further UC’s, they used a discarded railway line and used an excavator to drive it into the ground.  There were a number of issues with this;

• The railway line did not have the same local geometry as the UC’s;
• The correct toe depth was not achieved;
• Previous impact or damage to the railway line was not known;
• A verification of the revised temporary design was not signed off;
• A Senior Project Engineer had not signed off on the approved installation method of the temporary works.

I therefore closed the excavation and had it backfilled until the design could be approved or verification rectified the design.  This was to the annoyance of the foreman and superintendent with the usual retort of, “but we’ve always done it this way”.

I took measurements of the local geometry of the railway line and instructed our temporary works designer to calculate the suitability.  The soil properties were extracted from the GI and assumptions had to be made on the yield strength of the railway line (200 MPa). Brom’s method for laterally loaded piles was used and considered both short and long pile failure modes. A FOS of 2 was implemented in the verification. The design was then verified by a second temporary works designer, once complete the excavation could be reopened.

If you were wondering, the state of the reo cage in the pile in the foreground has had an NCR raised against it as the piling subcontractor forced it into the CFA pile using an excavator bucket rather than vibrating it into place.