HomeMy WebLinkAboutEngineer Evaluation of Rockfall Fence.pdf~tech HEPWORTH · PAWLAI( GEOTECHNICAL March 15, 2013 Rocky Gabossi 44523 Highway 6 Glenwood Springs, Colorado 81601 rocky@pilkiniron,com II I ii, I .\·1,1 \ !. " I I 11\11 I' I I \ I
,11\\, I '"I 1111 ~ , I, 01 " I I j.", 1\ 'i ." .. F; I ,,~ 'i' I I \11.,11 Iq ",f! Iq I I" 1\, Job No, 112 1448 Subject: Evaluation of Proposed Rockfall Fence, Vezzoso Property, Red
Mountain Road, County Road 115, Garfield County, Colorado Dear Mr. Gabossi: As requested, we have evaluated the rockfall fence proposed by ROTEC International, LLC for use at the subject
site. We previously provided a study for design ofrockfall mitigation at the site and presented our findings in a repOit dated January 15,2013, Job No. 112 144B. ROTEC proposes a 1500
kiloJoule Rockfall and Debris Flow Fence System, proposal dated March 3, 2013, The fence will be 12 feet high and be 504 feet long, located above the building area and about 20 teet
horizontally and downhill of County Road 115. We did not perform any structural analysis of the proposed fence but are commenting only on the fence rated capacity and height, relative
to the design parameters provided in our previous repolt for the lower fence location. The proposed energy absorption is 1500 kiloJoules which is about 553 It-tons. Table I of our previous
report shows an exceedence probability for the design boulder falling fi'OlTI the top of the potential rockfall start zone and striking the fence at the lower fence designated location
with an energy of553 It-tons is about 25%. That is, in our analysis, 25% of the trial rockfalls exceeded the 553 It-ton value, The fence meets the criteria for the 25% exceedence probability
based on energy and about 10% exceedence probability based on bounce height. As stated in our previous repolt, the risk of rockfall at the site is uncertain due to lack 0 f long-term
data. While it may be likely that rockfall striking the rockfall fence will occur over the life of the project, the likelihood of the design boulder (7,8 tons) falling from the top of
the rockfall start zone is more remote. Considering the proposed use of the
Rocky Gabossi March 15,20 13 Page 2 propelty (storage units), a higher exceedence probability for rockfall may be acceptable than if the use were residential, for example. The conclusions
submitted in this letter are based on our observation of the conditions at the site and our understanding of the proposed development. We should be advised of any changes in the proposed
development design which could result in possible changes to the conclusions contained in this letter. If you have any questions or need fillther assistance, please call our office.
Sincerely, HEPWORTH -PA WLAK GEOTCHNICAL, INC. Daniel E. Hardin, P. Rev. by: SLP DEHlksw Job No. 112 144B ~tech