Holdfast Training Services Trial Blog

 

Concrete Placement.  32Mpa, 100mm slump concrete poured into 6m slabs with 2m c/c dummy joints and 20mm rigid joints.  Originally specified to be 2.5m slabs with 10mm joints for the full 310m walkway.  It is assessed that the small slab size was specified to allow for movement found within embankment dams and RE Walls.  However, an RFI was raised to increase the slab size from 2.5m to 6m lengths.  As the risk of cracking was therefore increased, dummy joints at 2m c/c were specified in order to control the crack locations.  It was also advised by the superintendent that I snip every other steel bar within the steel mesh to promote the crack induction.  This advice was not taken but in hind sight it may have been a reasonable suggestion.  Increasing the bay size served two purposes: 1) Buildability  2)  To align the joints of the walkway with those found in the vertical RE Wall panels.

Piezometers. At various locations within the dam, piezometers are permanently set deep within the earth and rock-fill dam in order to monitor internal pore pressures. It falls to JH to relocate the piezometer conduit vertically to the new walkway surface level and across to the bridge linking the dam and the morning glory spillway.

Piezo Realignment.  With 7 x piezometer cables, it was critical to monitor which cable corresponded to which piezometer.  A simple coloured tape marking method was adopted as shown above.  Each piezometer cable was approximately 500m in length and had to be unwound, threaded through the electrical pit and 310m of white comms conduit before being and re-spooled.  Fortunately, as the electrical pits were simply formed using toughened plastic casing, I decided to attempt slicing one part-way open to allow it to slide it around the piezometer cable rather than threading it.  This trial paid off and saved the JH labour force a considerable amount of time and messing around in a congested working space.  Importantly, it prevent JH from delaying the Fusion team who were constructing the walkway. (Unfortunately, snipping and rejoining the cables was not an option according to our PM..)

Due to the lack of fixing points, I was required to design a fall restraint system.  M16 5.8 bolt was used with a small steel plate to provide an anchor point for harnesses.  The simple anchor design required external verification before it could be signed off.  A couple of hours later and the design was approved for immediate use.

Securing the L-Units. As part of the RECO L-Unit system, hot dip gal sheer keys are provided which meaure 1m in length.  These slot vertically in between each concrete unit and ensure that the individual units operate as a continuous structure, whilst allowing a certain degree of movement.  However, due to the subsequent placement and compaction of the cobble fill material between the RE Wall and the L-Units, I decided to pin them in place using 4 x steel rods as shown below.  This was to prevent the units moving laterally away from the RE Wall as compaction occurred.

ISSUES

Piezometer Alignment. When initially setting out for the installation of the walkway, it soon became apparent that the piezometer alignment would conflict with the position of the precast concrete L-Units.  Consequently, 100mm holes had to be drilled through the precast units to allow the piezometer conduit to pass through.  As JH were also responsible for the location at which the piezometers rose vertically during prior groundworks (and before my arrival!) it was a simple matter that could have been avoided.

Missing Materials.  Despite being fully assured by my predecessor that all components were correct and present I was a little under the moon to find out that approx. 10m of handrail fixings were not accounted for but an additional 30 vertical post were present… A swift call to the manufacturer and all was well.

5 x P’s!! – Poor planning lead to several avoidable issues during construction. ie. Precast L-Units requiring core drilling (5 x 100mm Ø holes) to allow for the Piezometers to pass up vertically to the surface of the walkway.

Precast Unit QA – Do not rely on consistent geometry of precast unit in planning.

Each of the precast L-Units has 2 x preinstalled ferrules.  These provided a metric thread fixing point in precast concrete panels to which the permanent handrail will be installed.  Due to the lack of conformity in the geometry of the precast units, the horizontal alignment of all the ferrules once all of the L-units was far from straight (even by Aussy standards).  The final handrail would have looked terrible.  As such the decision was made to drill and install new ferrules in order to achieve an aesthetically pleasing handrail alignment.  See final alignment above.

Check and Double Check material quantities!!

Reo Bar Chairs – Ordered 1000 x 45mm plastic bar chairs to sit on the uneven 4B material.  Thought to be too many but required more 75% way through bay construction.  Underestimated spacing required due to uneven 4B material…

Bolts and Ferrules. To determine the bolt length that was required for a pre-installed ferrule which is not detailed on the drawings, do not simply measure the ferrule depth using a steel rod (who would do that?..).  As the base of the ferrule is rounded, the depth that a bolt can actually penetrate is approx. 5-10mm less than the full ferrule depth.  If a bolt then protrudes greater than required the handrail baseplate will be loose (apparently..).