Permanent VENIS© Shoring Wall

SPINNER BUILDING
BELLEVUE, WA


The Spinner Building is located Southeast of the I-405 and SR-520 interchange in Bellevue, Washington. The project required excavation into an adjacent hillside for construction of the proposed office building. The excavation was up to 24-ft high, with several interior and exterior corners, a 3.5H:1V hillside backslope, and included a total of 6,500 SF of shoring wall area.

The subsurface materials in the adjacent hillside consisted of 6 to 8 feet of dense silty sand overlying hard silt and clay. During the geotechnical investigation, significant perched groundwater was encountered on top of the hard silt and clay. Therefore, the geotechnical engineer for the project recommended that a shoring system be used that was capable of handling groundwater and potentially unstable face conditions.

When the Architect for the proposed Spinner Building approached Malcolm Drilling for a bid for an Owner-Designed permanent anchored soldier pile wall, Malcolm Drilling asked Ground Support PLLC to develop a more cost-effective Design-Build Alternate shoring system. We therefore developed a VENIS© shoring wall design to meet the project requirements.

The shoring wall was to be offset from the back of the building roughly 1 or 2 feet, and would therefore not be very visible to the public once the building was completed. The main purpose of the shoring wall to provide permanent earth retention for the adjacent hillside. Therefore, as with the Owner-Design, a final concrete or shotcrete facing was not included in the Design-Build alternate VENIS© shoring wall.

VENIS© stands for Vertical Element and Nail Integrated Support system. The shoring system combines a modified facing system with standard soil nails in order to deal with adverse face stability conditions that would normally require a conventional shoring wall. For this project, an 8-ft horizontal by 7-ft vertical soil nail pattern was adopted. The facing system was comprised of vertical elements, timber lagging, and horizontal walers. The vertical elements consisted of small wide-flange beam elements placed in 10-inch diameter boreholes on a 4-ft spacing along the wall. The soil nails were connected to the vertical elements with horizontal tube steel walers. Finally, 2-inch timber lagging provided local support to the cut face. The soil nails were epoxy-coated, the walers were painted, and the timber was pressure-treated, providing a completely permanent earth retention system for 15% less cost than the conventional anchored soldier pile wall system.The shoring wall was to be offset from the back of the building roughly 1 or 2 feet, and would therefore not be very visible to the public once the building was completed. The main purpose of the shoring wall to provide permanent earth retention for the adjacent hillside. Therefore, as with the Owner-Design, a final concrete or shotcrete facing was not included in the Design-Build alternate VENIS© shoring wall.



Overall view of wall near completion.


Close-up view of interior corner.


Wall face excavation and lagging placement.


Detailed view of soil nail head connection system.