Time-critical issues

Following a conference call with Karla Dakin and Lisa Benjamin, several time-critical engineering design issues came up. We would like to resolve these with Winters-Schram and Belzberg Architects before the concrete is cast.

To aid the discussion an annotated site plan is posted below based on A2.1a 10-22-09: ADA walls, 42” or higher (red), planted areas are numbered (orange), low curbs/parapets surrounding planted areas (blue), proposed curbs surrounding planted areas (green), and walls/beams where anchors must be installed are shown as broad blue lines. The highlighted areas show the decomposed granite walkways.

Our comments are as follows:

1. Slope stabilization: With the wall layout, the only viable approach to support the steep slopes would appear to be by suspending cellular confinement webs or high-strength geogrid from the top of the slopes. Since the pitched areas are transected by walls, this will mean that attachments will be required along at least 5 different wall segments and also at the structural bean on the far west of the project. These attachments could take the form of stainless steel anchors that are either cast into the walls or installed by drilling into the finished walls. In our opinion, the spacing between anchors should not be more than 18”. Once the thickness of the soil layers in planted zones 3, 4, and 5 are established, Roofscapes, Inc. can compute the static pull-out forces for the anchors. The height of the anchors above the slab will depend on the final design for the landscape. Moment forces associated with these anchors will have to be taken into account for the design of the walls.

2. Border edging: In transitions between decomposed granite and planted areas (associated with planted zones 1 and 10, some sort of structural edge will be needed to stabilize the decomposed granite walkways. While this could be custom fabricated stainless steel, we believe it would be considerably cheaper to cast curbs at these locations (green lines on the layout).

3. Walkway transition: We would like to receive a definitive cross-section showing the transition between the decomposed walkway the planted zone 10. We believe that the most practical solution for this transition will be to install the decomposed granite (and curb) over a high-strength sheet drain. This will allow percolated rainfall and excess irrigation water to flow underneath the walkways. Effective uniform drainage of the planted zones is essential. Alternatively --- the walkways could be constructed as barriers to flow. In this case an efficient subsurface drainage network will be required to collect underflow and convey it to an area drain located within zone 10.

4. Barriers to flow: Many of the walls, unless modified, will provide barriers to water drainage. There are two possibilities: a) install these walls over high-strength sheet drains that will allow free flow of water under the length of these walls, or b) provide substantial scupper openings at all low points. We recommend building rectangular scuppers into the walls, each several inches high and a foot, or more, in length. We can work with the design team to determine how best to design and position scuppers.

5. Flow patterns: Based on Drawing A2.1e and P-2, it appears like the rows of drains located on the north and south perimeters of the building as well as the row immediately south of the ramp will serve only the narrow planters in these areas. In particular it appears like the southern row cannot be effective in capturing runoff from the adjacent and up-gradient planted areas and walkways. Is there a plan to connect the areas north of the high parapet wall with these drains? We can be of assistance in suggesting some solutions.

6. Waterproofing flashings: We understand that most, or all, of the walls will be constructed using shot-crete. Will this concrete be hydrophobic? We are concerned that if this concrete can absorb water, it will become necessary to flash the walls at least 6 inches above the soil layer. This will have aesthetic and cost implications. There are many possible solutions for flashing the walls. We would be happy to discuss these with the team.

7. Irrigation: Unless 2” diameter sleeves are installed across and under the various walls, curbs, and walkways, stub-ups for irrigation will be needed in every planted zone. Also, the irrigation valves and controls can be either centralized inside the building (e.g., in a closet or utility space) or they can be placed on the roof. The downside of placing them on the roof will be that each irrigation zone will require its own valve chamber (typically 8”-12” high, 15” wide and 24” long. These will be visible.