Appendix D
Geotechnical Hazard Assessment
Cascade Geotechnical Ltd.
Geotechnical Addendum
Rockfall Hazard Remedial Measures
Cascade
201 – 1889 Spall Road
Kelowna, BC, V1Y 4R2
Phone: 250-878-6446
Fax: 250-762-8073
Geotechnical Ltd.
CGL File No: J06-0154
October 30, 2008
By email: [email protected]
New Town Planning & Architectural Services
1450 Pandosy Street
Kelowna, BC
V1Y 1P3
Attention:
Mr. Keith Funk
Dear Sir,
Subject:
Rockfall Hazard Remedial Measures
Proposed Pincushion/Ponderosa Ridge Area Sector Plan
Peachland, BC
Cascade Geotechnical Ltd. (Cascade) conducted an assessment of the proposed
Pincushion/Ponderosa Ridge Area Sector Plan during September of 2006. A geotechnical
report (dated November 6, 2006) was prepared and presented recommendations for
development of the area.
The assessment had identified areas which had a rock fall hazard due to some bedrock cliffs
and outcrops located in the upper and mid slopes of the site. The outer zone of potential hazard
area is termed the “rock fall shadow zone”. The rock fall shadow zone is defined by an angle of
27.5° (52%) measured to the top of the talus slope, as shown on the attached Figure 1. This
angle is independent of the height of the rock faces above the talus.
We had recommended that development below the bedrock cliffs and outcrops, in the rock fall
shadow zone, should include some form of remediation to reduce the hazard of rock fall from
impacting the proposed development. Some of the possible rock fall remedial measures for this
site are presented below. The required remedial work may include one or more of the
measures described below and would be evaluated on a case by case basis at the zoning
phase of the development.
Scaling
Bedrock cliffs with loose rocks can be scaled prior to development of the area located
downslope of the cliffs. The scaling would remove loose rocks which have an imminent hazard
of dislodging. A qualified and experienced bedrock scaler should be retained to conduct the
scaling of the bedrock. Periodic scaling may be required.
Installation of Mesh
A possible remedial measure includes covering bedrock faces in hazard areas with wire mesh.
The application of mesh could consist of draping the bedrock face with a chain link fence
product so that the momentum of rocks dislodged from the rock face are minimized and
prevented from rolling down the talus or rock slope. The top of the fencing would be pinned to
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J06-0154
October 30, 2008
the top of the bedrock bluff and any rock fall that occurs would collect at the bottom of the rock
face. Alternatively, chain link fencing could be bolted to the bedrock surface to prevent the rock
from dislodging. A qualified and experienced contractor should be retained for installation of
mesh products.
Construction of a Berm
In order to prevent any dislodged rock from reaching development, a soil berm and/or ditch can
be constructed to provide a catchment area for rock fall. The required size and height of a
berm, or depth of a ditch, would need to be evaluated on a case by case basis. An example of
a typical rock fall protection berm is provided as the attached Figure 2. In addition, concrete
Lock Blocks or large boulders can be used to construct the protective structure.
Protective Fencing
Protection from rock fall can also be provided by the installation of a suitable type of fencing. An
example of a typical fence product designed to accommodate impact loading from rock fall is
presented in Figure 2. The type and height of the fencing would need be evaluated on a case
by case basis, and would be based on the size of rocks expected and the configuration of the
slope at that location.
Based on our understanding of the proposed development and the site conditions, CGL
considers that, from a geotechnical perspective, areas identified in our November 6, 2006
geotechnical report as being “Developable with Remedial Work” can be constructed to be
geotechnically safe, with respect to rock fall hazards, after the construction of rock fall hazard
remedial measures as discussed above. For the purposes of this project, safe is defined as
having less than a 10% chance in 50 years of experiencing a geotechnical hazard which would
affect the proposed building sites.
We trust the information provided above meets with your present requirements. Should you
require any additional information or elaboration please feel free to contact the undersigned at
your convenience.
Yours truly,
Cascade Geotechnical Ltd.
Ron Campbell, P.Eng.
Geotechnical Engineer
Attachments:
Figure 1 – Rock Fall Shadow Zone
Figure 2 – Rock Fall Protection Structures
Cascade Geotechnical Ltd.
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LEGEND
CASCADE GEOTECHNICAL LTD.
Ponderosa/Pincushion Ridge
Rock Fall Shadow Zone
Project No: J06-0154
Scale: NTS
Drawn By: RC
Date: Oct, 2008
Figure: 1
Typical Protective Berm Configuration
Typical Rock Fall Protective Fencing
LEGEND
CASCADE GEOTECHNICAL LTD.
Ponderosa/Pincushion Ridge
Rock Fall Protection Structures
Project No: J06-0154
Scale: NTS
Drawn By: RC
Date: Oct, 2008
Figure: 2