The URL can be used to link to this page

Home My WebLink AboutGSA Map Change Request - Buffehr Creek Lot 1 - ROCKFALL MITIGATION REPORT Received TOWN DF�Q��." ByLynneCampbellat11:48am,May0J,7013 Arthur I. Mears, P.E., Inc. Natural Hazards Consultants 555 County Road 16 Gunnison, CO 81230 Tel/Fax: (970)641-3236 November 15, 2007 Mr. Brennen Scott Fitzgerald, AIA Turnipseed Architects ��?-�� P.O. Box 3388 Eagle, CO 81631 RE: Site visit, The Valley Phase IV" rockfall mitigation, Lots 1 — 3. Dear Brennen: This letter, as requPsted, evaluates the rockfall hazard potential at building sites 1, 2 and 3, recommends mitigation, and discusses the feasibility of mitigation. My conclusions are based on a site visit last Friday, evaluation of detailed topographic maps and my experience with rockfall hazard evaluation and mitigation at various Colorado locations. 1= Rockfall �4�?ar� � :w � �` - �. :�� r � ��' � �� t ti �, .� �f ��`.�;_ � ', �-� All of Lots 1, 2, and 3 appear to be ��r ��: � �.:_. � � s. _ �'�.: . .� > :. a � V}*,.,. f Y � �recluded in a "high severity" rockfall �� ;,��,< ,� �'' �.', . „� �rea on Town of Vail maps produced w �". �i�, , L.�': , ��».� . m 1984. My site ins ection last .��,� '�� :�� p , �_ �.�� J`'' ,��*�, , � , �� vv�ek a�d �xp�rier�ce wi�n � rockrall- �, '�+�� - �'�!=�i '` �� ' hazard evaluation completed by me e i ,��='':s�i1"'�� -r \ ��! '� ��r�•, 1 � � ,,i� �� • �j{� '.�;�y�,��' in 1990 suggests that rockfall ��y�� T.� 91 �� 7 7 : ° a� �f � a ��, ,�: � �-�� hazard is not severe by Colorado ;,f,�r .�,� :� �r :� ;� t 3 �r general mountain standards; it y ��wr` ��„�`,; ��;��, _- y�,� should be classified instead as L' ...�� ' ' ••'�a'�;,''.�� v, ,, �� "moderate.,, --1'��Y.y�� _. ..`l.. .,:��...3a�.•.�s , .•rc. Rockfall hazard originates in sandstone outcroppings of the Minturn formation. This formation crops out roughly 150-300 feet vertically above the building sites staked on the ground. The outcrops are small in aerial extent and have produced some rockfall in the past. Figure 1 shows a typical example roughly 2 feet in length found on the slope. Judging from the intersection ofjoints and bedding plains in the rock and isolated rocks that have stopped on the slope, this is 'A.I. Mears, P.E., Inc., "Rockfall Hazard Analysis, The Valley, Phase IV, Vail, Colorado", prepared for Ed Zneimer, June 25, 1990. typical of the size of rock to be considered in mitigation design. According to the A.I. Mears (1990) report, rockfall has occurred in the past several decades (prior to 1990) and has reached the valley bottom. Because of the limited rockfall source area, rockfall events will probably be relatively infrequent (one event per decade or less) and will probably consist of only one or two boulders. Most will stop on the slope above the building sites. Because moderate rockfall hazard does exist, structural mitigation for rockfall is recommended, as discussed below. 2. Rockfall Mitiqation Two mitigation techniques are feasible at these sites: (a) construction of barriers at or directly above the proposed buildings, and (b) construction of small rockfall energy-absorbing fences on private property below the source areas. Building sites on lots 1, 2 and 3 should all be protected because rockfall paths rnay be somewhat unpredictable. Rockfall barriers at the buildings, while feasible from a technical perspective, are probably not desirable. Building walls lined on the uphill sides with deformable gabions or planter boxes could be made to absorb rockfall energy and distribute impact forces over a large area, thus avoiding point loads from rock impact and structural darnage. The heights of the required structures at the building have not been determined but should be based on the newly-available Town of Vail GIS topography and updated rockfall modeling. Previous work suggests the wall heights might be up to 6 feet at the proposed houses. While this technique could be effective it may not protect the entire house because of the locations of doors, and it may have an undesirable appearance. The second feasible mitigation technia,ue would be c:�nstr►action c�f�rru�ll r�ckf�ll energy-absorbing fences on the slope, a short distance below the source areas. The design heights and strengths of the fences would be modest because energy and bounce heights will also be modest. They would probably be fairly short at each of the two rock outcroppings2. As discussed at the start of this report, one objective has been to discuss the feasibility of rockfall mitigation. Rockfall mitigation does appear to be feasible at these sites, and should, in my opinion be assumed as such during the permitting process. Sincerely, Arthur I. Mears, P.E. 2 As a rough estimate (not based on detailed analysis)fences may need to be no more than 50 feet in length at possibly two locations between the trail switchbacks but on private properry. JUN-26-200g 11 :0° AM NEWY.IRK. ENGINEERING 830 249 0925 P. 01 . � N�WKIRK ENGINEERING Consulting Struatura�$ngi�$eri�ng 407 ICandall�arkway �oerne,7"X 78Q13 June 26, 20D8 p�./�a�a7S5�81b4 Mr, 9rennen Fitzgerald, Praject Manager Scott S, Turnipgeed, AIA 1143 Capital St., �uitc 2l l Eagle,CQ�1631 R�a: New R��idence 168?But�ehr Creek Vail, Colorado 81657 l�ear Srenn�r�� I have revi�vved the"Rockfall Mitigation" requir�ments for th�e reference�prp�ect a� proso�cd in tho repnrt prepared b� Arthur I, Mear�, P,E., �nc. The concreto fc►�a��ta�n w�11a indsc,aetad o� �h��t �1.1 and detailed an subaequend detail ahctts in the Conatruction Documen# dr�wing set that I have pr�parad moet the requirement noted in the Mear�raport. Fladsa I�t me know if you have any questione or if I may be c�f further esaistanco, Sinc,�rely; F!E°,lV;Cl��f�IW�IRiEEF�iPIG �\��1151U111 1111f1 , ..�� aul H.Newkirk, . � :,� j��y�"`�`'�'� �'rincipal =�'t�*� '��'�� :� 3 :�,�� _�; ��, �,�` .�,��