RYZUK GEOTECHNICAL Geotechnical Field Review / Site Instruction (November 24, 2020)
A follow-up slope stability assessment for Lot 1 at 221 Atkins Road, summarizing results of additional analyses regarding building setbacks.
GEOTECHNICAL FIELD REVIEW / SITE INSTRUCTION
Project No: 7439-1
Client: David McAllister
Project: Proposed Subdivision
Contact: As above
Project Address: 221 Atkins Road – View Royal, BC
Email: davmca@yahoo.com
Date: November 24, 2020
Distribution:
- Stantec – Keith Provan – keith.provan@stantec.com
- Gye and Assocaites – Jermey Gye – jgye@gyeandassociates.ca
Lot 1 Stability Assessment
As requested, we have carried out additional slope stability analyses to determine safe building setbacks within Lot 1 given new excavation constraints directed by the project arborist. The following summarizes the results of our analyses.
We understand that in order to maintain tree health for the protected trees within the Streamside Protection and Enhancement Area (SPEA), is it not permissible to disturb any soil beyond the "Limit of disturbance" line as shown on the draft drawing "Tree Management Plan for Sub-division & Site Servicing" from Gye & Associates, dated October 13 2020. As such, unloading along the slope crest would be limited to approximately 2.0 m below existing lot grades as opposed to the previously considered 3.5 m.
In order to assess the slope stability condition given 2.0 m of unloading, a stability analysis was conducted using the Software Slide 2 Modeler by Rocscience (version 9.005). Our analysis was carried out in conformance with Engineers and Geoscientists British Columbia (EGBC) guidelines for Legislated Landslide Assessments. The results of our analyses indicate that a setback of 6 m can be maintained from the crest of the unloaded slope (i.e. 6 m setback from the SPEA/Limit of disturbance line). The geotechnical setback can follow the Limit of disturbance line where parallel with the north property boundary. The attached Setback Sketch drawing shows the approximate delineation of the recommended geotechnical setback within Lot 1. We note that the above setback considers a residential structure utilizing conventional shallow spread foundations. It may be possible to construct the residence within the 6 m setback if an alternative foundation approach is considered (i.e. deep foundations). Details for such can be made available upon request.
Excavation works associated with slope unloading and site preparations should be carried out with care in accordance with recommendations from a Qualified Professional. Excavation cutslopes should be prepared in a stable configuration to ensure stability over the short to medium term in the event that the lots are not be developed immediately following excavation. We expect that temporary cutslopes configured at 1 Horizontal to 1 Vertical would be stable, although such should be confirmed at the time of excavation.
If there are any questions or comments with respect to the above, please contact us.
Regards,
Ryzuk Geotechnical
Colden Van Ommen, EIT
Advanced Junior Engineer
Andrew Jackson, P.Geo./Eng.L.
Project Geoscientist / Engineering Licensee
Attachments – Sheet 1: Setback Sketch
The above does not constitute approval to proceed with the noted work if the work is perceived to be an extra to the Contract. Such can only be authorized by the Contract Manager.