Prep work for RCC - a ShotCrete inner sidewall l- Drilling, Hammering, + Adhesive --> Anchor Bars into RCC
Workers preparing reinforcement steel mesh and anchor bars to emplace a layer of a structural Shotcrete inner section for the temporary* RCC spillway sidewalls. Holes are first drilled into the RCC, then the Anchor bars are hammered into the RCC. Other images reveal a blue color type of adhesive used around the anchor bars placed using a caulking gun. It is likely the adhesive is placed in the drilled hole before hammering the "L" shaped anchor bars into the RCC (inferred by a bulging circular extrusion of the adhesive at the protruding bar opening when the anchor bar is fully seated to depth).
An inner layer and outer layer of steel mesh provide reinforcement to the next step of placement of the structural concrete. DWR notes that this step will be done as ShotCrete. This process eliminates the need for a wooden form, but adds a complexity of keeping the "flow line surface" of the inner wall to be constructed using guide "jigs" (or lasers?) and skilled hand surfacing work. Future images will reveal what their planned process will be to accomplish this important wall surface alignment. Any ripples in the wall could induce turbulence or even undesirable damaging cavitation effects in high speed flows.
The choice of Shotcrete gives an advantage of speed of construction to meet the tight schedule demands.
*All of this wall is temporary for the 2017/2018 rainy season. The sidewall will all be demolished and replaced with the final structural design as observed in the upper and lower spillway sections in the 2018 construction phase.
Scaffolding along the thick RCC sidewall - workers doing final prep work before a Shotcrete wall is applied to the inner section of the thick RCC temporary sidewalls.
Close up view of the drilling and emplacement of Anchor bars. Outer wire mesh layer is wire tied to the anchor bars. Adhesive (epoxy?) observed as part of the anchor bar emplacement (including hammering the bars into the holes). Inner wire mesh already partially imbedded in the RCC.
Shotcrete Inner Sidewall finishing - Worker using a "guide cable" - Simple pre-alignment with board & anchor for taut cable
A simple, but effective, tightly pulled guide wire (small cable) is being used to assure the proper finish of the shotcrete wall that lines the RCC. Layers of steel mesh and individual vertical reinforcement bars with separate anchor bars were placed prior to this shotcrete wall layer. Earlier images of the "stay in place" fine metal mesh revealed anchors that extend into the wide layer of RCC that was being placed during construction. This adds an additional contribution to a tie-in to the anchorage of the steel mesh, vertical reinforcement bars, and the "drilled then hammered in" anchor bars.
See: Prior post 4250
Prep work with rebar for Inner Shotcrete Sidewall (post 4250)
Fig. 1 Reveals how the upslope alignment of this sidewall layer is carefully maintained by the "guide cable/wire" reference in the finish work. What looks to be a colored wood stud (or a denser material) is being used to hold the guide cable/wire and keep its tension. This approach is effective and can be easily adjusted, repositioned, and aligned. Most likely there is a survey "shoot laser" that is being used to keep this placement of the guide wire accurate to the upslope alignment of the sidewall surface. Another clue to the "laser" is that the board does not have an optical survey "target". Overspray of the shotcrete on the board infers that the board is positioned, and thus the cable, before the shotcrete layer was placed. This would serve as a depth to completion reference in the process of applying the shotcrete..
Fig. 2 Reveals the skill of the concrete workers as the wall is very well finished and clean. There is a significant amount of this work to be done as both sides of the RCC temporary spillway will require this shotcrete surfacing process. The "meet up" date to the upper construction concrete spillway section by the RCC is stated to be the last week of October. This would mean that these workers would be scurrying to finish the inner walls as this happens after the main RCC is emplaced. The other "race" will be the chemically treated 10 to 12 inch hardened RCC layer that still needs to be applied to the RCC spillway horizontal surface. This is also noted to be started when the RCC meets up with the upper construction concrete spillway section.
Note to KC Burke: I'm up late - not early. So you, Abb, and others can be the "early birds"… :)
Fig. 1 Worker carefully finishing shotcrete surface of concrete wall to a guide wire/cable. Simple arrangement allows wire to be repositioned as construction work progresses. No sign of a survey target - indicates wire placed by a laser "shoot" (from a survey position).
Fig 2. Professional finish, including the vertical continuity, of the wall reveals the skill of the concrete workers. Notice the "excess" shotcrete on the plastic. Likely from the finish process of a careful removal of shotcrete to arrive at the final aligned vertical surface.
