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HomeMy WebLinkAboutDRB140312_114189A (06-17-14) Rockfall Risk signed_1408486140.pdf F1...h\+oirh-Puulak Geotechnical, Inc. • i g 50:110 County Road 1 54 . eiC (nenw,,oJ Shrine's,et lura 6 51601 F hone:c)7O-945-7988 HEPWORTH-PAWLAK GEOTECHNICAL Rix:1)f0-945- 454 retail•I eo'4hhgri.rech.c in ROCKFALL RISK AND MITIGATION FEASIBILITY ASSESSMENT LOT 2, BIGHORN ESTATES 4288 NUGGET LANE VAIL, COLORADO JOB NO. 114 189A JUNE 17, 2014 PREPARED FOR: DESMOND HOME BUILDERS ATTN: BRYAN DESMOND P.O. BOX 3518 EAGLE, COLORADO 81631 brvan a desmondhomc builders.com Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - SUMMARY OF FINDINGS - 1 - PROPOSED DEVELOPMENT - 2 - SITE CONDITIONS - 2 - GEOLOGIC SETTING - 2 - FIELD OBSERVATIONS - 3 - ROCKFALL START ZONES - 3 - ROCKFALL BLOCK SIZE - 4 - CRSP MODELING - 4 - CRSP MODEL INPUT INFORMATION - 5 - RESULTS OF CRSP MODELING - 5 - ROCKFALL LIKELYHOOD AND SEVERITY - 5 - ROCKFALL MITIGATION INFORMATION - 6 - OTHER GEOLOGIC HAZARDS - 6 - LIMITATIONS - 7 - REFERENCES - $ - FIGURE 1 -PROJECT SITE LOCATION FIGURE 2 - POTENTIAL ROCKFALL START ZONES FIGURE 3 -ROCKFALL BARRIER LOCATION ANALYZED FIGURE 4 - POTENTIAL ROCKFALL START ZONE CLIFFS FIGURE 5 - CRSP PROFILE lA UPPER START ZONE FIGURE 6 - CRSP PROFILE 1B MIDDLE START ZONE FIGURE 7 - CRSP PROFILE 1C LOWER START ZONE TABLE I - SUMMARY OF CRSP ANALYSIS PROFILE 1A UPPER START ZONE TABLE 2 - SUMMARY OF CRSP ANALYSIS PROFILE IB MIDDLE START ZONE TABLE 3 - SUMMARY OF CRSP ANALYSIS PROFILE 1C LOWER START ZONE Job No. 114 189A Gtech PURPOSE AND SCOPE OF STUDY This report presents the findings of a rockfall risk and mitigation feasibility study at Lot 2, Bighorn Estates, 4288 Nugget Lane, Vail, Colorado. The lot is located in the eastern Vail area as shown on Figure 1. The purpose of our study was to: (1) assess the potential for rockfall at Lot 2, (2) assess of the potential severity of rockfall and(3) develop rockfall dynamic information that may be used by your designer to assess the feasibility of rockfall mitigation if the potential risk is unacceptable. Our study was preformed generally as described in our May 14, 2014 proposal to Desmond Home Builders. A field reconnaissance of the properly was made on June 5, 2014 to observe the site and potential rockfall conditions. In addition, we have reviewed published regional rockfall studies for the Town of Vail (Schmueser and Associates, 1984 and Town of Vail, 2000) and looked at aerial photographs. Rockfall dynamics for Lot 2 was developed using the Colorado Rockfall Simulation Program (CRSP version 4.0). Based on the above information an analysis of the rockfall potential and severity was made. This report summarizes the information developed by this study, describes our evaluations and presents our findings. SUMMARY OF FINDINGS Rockfall appears to be an active geologic process at Lot 2 and should be expected in the future. However, without long term observations, it is not possible to develop a statistical recurrence probability of future rockfall at Lot 2 with a high level of confidence. Recent rockfall has not occurred at Lot 2 and rockfall is likely statistically infrequent and may have recurrence times greater than 100 years. Although the probability a rockfall will hit the duplex during a reasonable exposure time for the building is likely low, a rockfall has the potential to cause major damage to the building with a high risk of severe harm to the building occupants. If this risk is not acceptable to the duplex owners and governmental regulatory agencies then the feasibility of risk mitigation should be evaluated. The Job No. 114 189A Ge Ptech - 2 - rockfall dynamic information in this report maybe used by your designer to assess the feasibility of rockfall mitigation. PROPOSED DEVELOPMENT A residential duplex structure is planned on Lot 2. The duplex will be located in the northern part of the lot where the hillside slope is around 6 percent, see Figure 3. We expect that the building will be a two or three story, wood frame structure similar to the existing buildings on the adjacent lots in the subdivision. SITE CONDITIONS The project site is located in the eastern Vail area on the lower northeast-facing Gore Creek valley side about 180 feet to the southwest of the creek as shown on Figures land 2. The proposed building site on Lot 2 lies at an elevation about 20 feet above the creek. Lot 2 was vacant at the time of this study but existing residential buildings are located on all of the nearby lots in the subdivision. The valley side profile in the area is shown on Figure 4. The ground surface at the proposed building site on Lot 2 is moderate with an average slope of 6 percent but just upslope to the southwest of the proposed building site the valley side abruptly transitions to steep grades that vary from 35 to 85 percent. The proposed building site is an open meadow. Small diameter(less than 1-foot) aspen trees with an occasional small conifer tree grow on the valley side between the meadow and the lower cliff shown on Figure 4. A mature conifer forest is present on much of the lower cliff band between some rock outcrops. More extensive rock outcrops are present on the middle and upper cliff bands directly upslope of Lot 2. The bench between the lower and upper cliff bands is an aspen forest with only a few conifer frees. GEOLOGIC SETTING A valley glacier occupied the Gore Creek valley during the "last global glacial maximum" that corresponds with the Pinedale glacial period in the Rocky Mountains. The terminal Job No. 114 189A GecPtech - 3 - moraine for the Pinedale-age, Gore Creek valley glacier is located about 6.5 miles downstream of Lot 2 (Scott and Others, 2003). The Pinedale-age valley glaciers in the southern and middle Rocky Mountains began to retreat from their terminal moraines starting about 16,800 years ago and it took about 7,200 years for cirques to become ice free around 9,600 years ago (Benson and Others. 2005; Price, 2004; and Porter and Others,1983). In the Gore Creek valley the average glacial retreat rate was about 0.18 miles per 100 years. This indicates that the Gore Creek valley glacier should have retreated past Lot 2 around 13,000 years ago and post-glacial surficial soil deposits and geologic processes near Lot 2 are younger than about 13,000 years old. The post-glacial deposits in the vicinity of Lot 2 are hillside colluvium and debris fan deposits that have formed at the base of the cliffs along the valley side. Rockfall from the cliffs has probably been an active geologic processes throughout post-glacial time. The cliff above Lot 2 and elsewhere along the northeast-facing valley side are formed by resistant beds in the middle Pennsylvanian-age, Minturn Formation (Kellogg and Others, 2003). The Minturn Formation is made up of interstratified arkosic sandstone, siltstone, pebbly sandstone and conglomerate with some marine limestone beds. The resistant beds that form the cliffs shown on Figure 4 are predominantly limestone which is also the predominant rock type in the rockfall blocks on the lower valley side. FIELD OBSERVATIONS Our field observations supplemented by aerial photograph interpretations focused on identifying past and potential future rockfall start zones and evaluation of the size of past and potential future rockfall blocks. ROCKFALL START ZONES Our field observations show that past rockfalls have started on three cliff bands up slope of Lot 2 and elsewhere on the northeast facing valley side in the vicinity of the lot. The location of the cliffs that are potential start zones for future rockfall that could reach Lot 2 is shown on Figure 2 and a topographic profile of the valley side at Lot 2 is presented on Figure 4. The base of the lower cliff lies about 250 feet in elevation above the proposed building site on Lot 2, the base of the middle cliff is about 600 feet above the proposed Job No. 114 189A GEtPtech -4- building site and the base of the upper cliff is about 1,400 feet above the proposed building site. The potential of future rockfall appears to be greater on the upper and middle cliff bands than the potential on the lower cliff band. The valley side between the three cliffs has slopes between 35 and 65 percent and vegetation is mostly aspen trees. A mature conifer forest has become established between rock outcrops on the lower cliff. ROCKFALL BLOCK SIZE Numerous limestone and occasional sandstone blocks were observed at the ground surface on Lot 2 and elsewhere along the lower, northeast-facing valley side to the northwest and southeast of the lot. These rock blocks are most likely post-glacial rockfall from the three cliff bands upslope of Lot 2 and other lots in the subdivision. On Lot 2 most of the blocks are partially to completely embedded in the soil which indicates that recent rockfall has not occurred on the lot. Fifty-one of the larger rock blocks were measured in the field along the lower valley side on Lot 2 and for a distance of about 1,200 feet to the northwest and southeast of Lot 2. Twenty-six, about one-half, of the measured blocks were on Lot 2. The largest dimension of the fifty-one blocks surveyed ranged from 1.8 to 30 feet with an average of 7.6 feet. Rock blocks with a maximum dimension greater than 8 feet comprise 30 percent of the field sample set. The estimated weight of the fifty-one rock blocks ranged from 300 pounds to 330 tons with an average weight of 20 tons. For our rockfall simulation modeling we considered a sphere-shaped rock with a diameter of 12 feet and a weight of 83 tons. This is the mean value of 7.9 feet plus one standard deviation of the field sample set. CRSP MODELING The Colorado Rockfall Simulation Program(CRSP version 4.0) was used to assist in our assessment of the likelihood of future rockfall at Lot 2, the potential severity of future rockfall and to develop preliminary rockfall dynamic information that may be used to assess the feasibility of rockfall mitigation at Lot 2. CRSP is a computer program that simulates rockfall tumbling down a slope and predicts the probability distribution of Job No. 114 189A Gegtech - 5 - velocity, bounce height and kinetic energy. The program takes into account slope profile, rebound and frictional characteristics of the slope and rotational energy of the rocks. The program is a tool commonly used in analysis and mitigation of rockfall hazards. CRSP MODEL INPUT INFORMATION CRSP models were developed to simulate rockfall from the three cliff bands up slope of Lot 2. The profile for the upper cliff is shown on Figure 5, the profile for the middle cliff is shown on Figure 6 and the profile for the lower cliff is shown on Figure 7. The size of the rockfall block analyzed was a sphere-shaped rock with a diameter of 12 feet and a weight of 83 tons. This is the mean plus one standard deviation of the field sample set of past rockfall blocks on Lot 2 and in the vicinity. Model tangential (Rt) and normal (R„) coefficients were adjusted to produce model rockfall runout similar to those observed in the field. RESULTS OF CRSP MODELING Rockfall dynamic parameters which include the probability distribution for rockfall velocity, kinetic energy and bounce height were calculated at the location of a possible rockfall mitigation barrier on Lot 2 uphill of the proposed building site as shown on Figure 3. The calculated probability distribution for rockfall from the upper start zone is presented on Table 1, the probability distribution from the middle start zone is presented on Table 2 and the probability distribution for the lower start zone is presented on Table 3. The probability distributions for the three start zones molded were based on one hundred independent rockfall trials. The probability distributions for the three start zones modeled do not vary substantially for the dynamic parameters analyzed. All three start zones produce rockfall with very high kinetic energy at the barrier location analyzed. ROCKFALL LIKELYHOOD AND SEVERITY • Rock blocks at the ground surface indicate that rockfall has occurred on Lot 2 during about the past 13,000 years and rockfall appears to still be an active geologic process and should be expected in the future. Our field observations and CRSP modeling show that the rockfall runout near Lot 2 is in general agreement with runout estimated in previous Job No. 114 189A GE Ptech - 6 - regional studies for the Town of Vail (Schmueser and Associates, 1984 and Town of Vail, 2000). Without long term observations, it is not possible to develop a statistical recurrence probability of future rockfall at Lot 2 with a high level of confidence. Recent rockfall has not occurred at Lot 2 and rockfall is likely statistically infrequent and may have recurrence times greater than 100 years. Future rockfall will likely occur with no advanced warning and once a rockfall starts it will reach the proposed building site in less than one minute. Although the probability a rockfall will hit the duplex during a reasonable exposure time for the building is likely low, a rockfall has the potential to cause major damage to the building and there is a high risk of severe harm to the building occupants. If this risk is not acceptable to the duplex owners and governmental regulatory agencies then the feasibility of risk mitigation should be evaluated. ROCKFALL MITIGATION INFORMATION Rockfall risk in western Colorado has been mitigated with rockfall catching barriers which may or may not be feasible at Lot 2. These barriers have included commercially available ring net arresting systems, mechanically stabilized earth(MSE)walls and compacted earth embankments and ditch systems. The rockfall dynamic information shown on Tables 1, 2 and 3 maybe used by your designer to assess the feasibility of using a rockfall barrier to protect the proposed duplex and its occupants. The appropriate exceedance probability to be used in feasibility evaluations will depend on the risk level acceptable to the duplex owners and governmental regulatory agencies. As shown on Figure 3, it will not be possible to protect the duplex on Lot 2 from all potential rockfall paths unless the barrier is extended onto Lot 3 to the west. OTHER GEOLOGIC HAZARDS In addition to rockfall the proposed duplex on Lot 2 is also exposed to potential snow avalanche, debris flow and debris avalanche hazards. The evaluation of these conditions is beyond the scope of this study. Your designer should evaluate if a barrier capable of mitigating the potential rockfall hazard can also be used to mitigate the snow avalanche, debris flow and debris avalanche hazards. Job No. 114 189A GecPteCh - 7 - LIMITATIONS This study was conducted according to generally accepted geotechnical engineering principles-and practices in this area, at this time. We make no warranty either express or implied. The information presented in this report is based on our field observations, aerial photograph interpretations, CRSP modeling and our experience. This report has been prepared exclusively for our client to assess the likelihood and severity of future rockfall and to provide rockfall dynamic information for rockfall feasibility evaluations if the rockfall risk described in this report is unacceptable to the building owners. We should review proposed mitigation designs when available to evaluate if the design is consistent with the information presented in this report. We are not responsible for technical interpretations by others of our information presented in this report. Respectfully Submitted, HEPWORTH -PAWLAK GEOTECHNICAL, INC. ,/(74 1AP Ralph G. Mock Senior Geologist And by: '441erf. 4i° 4or Steven L. Pawlak, P.E. `*►'..ts 15'222 ` 01'71€7�).,L�,: ths) RGM/ksw ,�dlq�.;�oti& �' .�Q©r" £of I;QLQ.= Job No. 114 189A C- -tech - 8 - REFERENCES Benson, L. and Others, 2005,New Data for Late Pleistocene Pinedale Alpine Glaciations from Southwestern Colorado: Quaternary Science Review V. 25, p. 49-65. Kellogg, K. S. and Others, 2003, Geology Map of the Vail East Quadrangle, Eagle County, Colorado: U. S. Geological Survey, Map MF-2375, Version 1.0. Pierce K. L, 2004,Pleistocene Glaciations in the Rocky Mountains in The Quaternary Period in the United States, Gillespie A. R., Porter, S. C and Atwater Editors: Elsevier,New York, p. 63-78. Porter S. C. and Others, 1983,Late Wisconsin Mountain Glaciers in the Western United States in Late-Quaternary Environments of the United States, Wright, H. E. Jr., and Porter, S. C. editors: University of Minnesota Press, Minneapolis. Schmueser and Associates, 1984,Rockfall Study- Town of Vail: Prepared for the Town of Vail (November, 29, 1984). Scott R. B. and Others, 2002, Geology Map of the Vail West Quadrangle, Eagle County, Colorado: U. S. Geological Survey, Miscellaneous Field Studies Map 2369, Version 1.0. Job No. 114 189A Gtech ..ePr..'".".. 'Sr'''''""..e 'N:\ '1 r>,:::*::::,.',;'"..1i...7) F.i.r/41,.\,\ \ \‘I:4,1/ .',I\ '' ',, ''..-..'•,'',..."`,.:**,-,..,,.....". /2:,...// .-. .• N. -••,.-1--�' `t ,',,� �w..4 ' '' y"'4 \ '• \ '.,-. ,, \....../A..,...." �/�• I, Si� ��'i.w• ' '''':,..0 �' `` ` 4 t .1 'J(It�, �...�''... ✓..` ,r cam- <� \` 'N.:::.1:1,' ` .� .,, -.;,;�, `[ , _ 1 ` ,� ...\------------.-7-..17-.:•..e;;;.-7//11./6 • j �,j_le t t �'['i t I �\ 1 .> w $ k4} f (f' J (I. t/ / / I// 'J./ S\ 4� �'` ` I' ;.R `ti d rs \1 '''' , 11' \\ 1\,, i i;__.,� ''.. \,1,_ \ 1/4 -. ,BM 410 ;' °roi P• . _.� i / fill ( iii ; "�} 1?..!--,-- .-`. 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O `.\ \,, ,,,. ... ,.. ,_.....„...„,,,....„,...� 1,I K `r Explanation: 4:1 Lot 2 Bighorn Estates L 1 1 CRSP Profile 1: 0 1000 ft. See Figures 4 through 7. I Scale: 1 in.=1000 ft. Contour Interval=40 ft. June 2014 114 189A E--- —"-----1,_ .._ C}i Bighorn Estates Lot 2, 4288 Nugget Lane, Vail, Colorado Fig LI 1 HEPNiORTH-PAVJIAi<GEOTECHNICAI I Project Site Location \,,,,N, NkNKb 4, s\) 0„. it, 04 ....„. ... , ._...44 ._ 1***&* .„., 0.. * p....-..., 4t, \----N lett Go ,, .0, -...4 Gore Vie* 11W4111. 2p0 _.,...„.. 94o, NI Cree 0-11N.0l-40 44,01/4_41, <N, Lower #4.40. `�� %c ls000,tart Zone iii;421t4r 41 iir \ \ V r „I\ �___.___----10000 �� Middle \ • Start Zone ,� \h' �. 11,' hi( tart Zone Qe�of G. 4 4114111 ,9 a 0 ---) _.... Ns, 00 O S60 9F� \ \\N"\\ \\\ Explanation: ip • Lot 2 Bighorn Estates Potential Rockfall Start Zones: Cliff bands that are potential start zones for rockfalls. I I CRSP Profile 1 0 600 ft. 1_1_1 Scale:1 in.=600 ft. Contour Interval: 40 ft. Topography from:Peak Land Consultants and USGS June 2014 114 189A 1 Gilt-11)6d, I Bighorn Estates Lot 2,4288 Nugget Lane, Vail, Colorado I Figure 2 HEFWORTH-PAWLAK GEOTECHNICAL Potential Rockfall Start Zones 44 of 5 iopt 'VP %get Max.CRSP Runout Cage / `° ' II 111111b0.. r Lot 3 -41111111111111111 1111"111114%r 11111, Lot 2Lot 1 rillir / c�Q Qcoe G � fr :,; /,,/ ,,� /,• esoo I i Rockfall Barrier Location 4 414114tors\ Analyzed o, cp so �Q ..co ��e` �e Oil* Explanation: gProposed Duplex Lot 2 Direction of Rockfall CExisting Buildings iiimmilimi Rockfall Barrier: Location of rockfall barrier 0 60 ft. analyzed by the CRSP. I 1 I Scale: 1 in.=60 ft. Contour Interval: 2 ft. Topography from:Peak Land Consultants and Town of Vail GIS June 2014 114 189A I GEITIKEteChI Bighorn Estates Lot 2,4288 Nugget Lane, Vail, Colorado Figure 3 HEPWORTH-PAWLAK GEOTECHNICAL Rockfall Barrier Location Analyzed (.4)uolienal3 0) m ' 0 0 o 0 0 0 0 0 0 O o 0 r O O o 0 o O O o O O O O N O 0 (O V N O CO W V N Z O 0 CI w 0) 0) m m CO CO CO O ..i 1 I I I I I I 1 I 1 2' U O o r O. _0 p LO OV ,,_O 8U M 11. Cu)uoi3ena13 Vi oo 0 CD 0 0 0 0 0 0 0 O .�OWO0NOWOO a) N O d' CD "t O O O 0) O d) 0) CO CO COV' W O O Z a) D 1 1 1 1 1 1 1 1 I I V N O a. 7i Ocu o C• _0 M ?N ,O R, O N M N CO R rUU _ C 7 C R' N O o(NJ CO.E.: N U -a UU N !n N e' O NDN p 2 O U gay; OQJ ,- p _o N °. o v-C Co it; I.i F- N N 0 IV a)'E O Q (1) fn 40 . _O Z . 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("g)uoilena13 H Bighorn Estates Lot 2,4288 Nugget Lane, Vail, Colorado 114 189A Figure 5 HEPWOPTH-PAWLAK GE�NICAL CRSP Profile 1A Upper Start Zone (11)ual;enal3 C u o as - C) 0 0 0 0 0 0 0 0 0 0 0 0 'C N 0 CO CO V 0 0 0 co 0 O N o 0 0 0) 0) 0) O) 0) CO CO 00 O N t6 I 1 I I I I I I 1 , 1 U ` 0 O'C Q T O �; (1j)uoivenae N C =(6 0 0 0 0 o 0 0 0 0 o 0 0 0 oo -c N 0 O (9 d' N O CO o O O c0 O o O 0 0 0 o co co co co Z N To 1 1 1 1 1 1 I I I 1 tK U (q 1 0 ' O co O co N,t Q -0O 0 `o U _O M 11 N l6 m 0 C— (`7 a 0 r _ oO 0 CN MI N N U U co -oo t+) co .-- O O O 2 N ,,x N N N coM O.O -O co N O aoJ � 0 0 • I.L F c� o o_O M N o N N co'i w co a) co o p u) <n.o -o Z N o co c "g V-V N O N N m m U_ 0 O (o E _O N 2 N -i5 N m U 0 N o -q- -g _O N 0 N a 1- U _oo 0 N _O N CO 0 N 0 �— _ 0 o N Nm o N _o CL (n _o coO - N Cl.. L c Cl) (I) m o - U O o -coo 0 J _N C 0 N O •E: 0 - 0 rd' 0 _0 r I O 0 _0 O N -O O 0 O O -O CO U N Y Oi V 00 N O _ ` 0 co c -ON d' U V N 0 .0 0_ - co ma.-CI 0 0a` CC 0 O 02 CVy _0d- z= N—_ I 1 I 1 I I I 0 ce3 -6 0 0 0 0 0 0 0 0 o a N a 'Cr .N- 0 O coo d- 0 0 co 2 o o 0 U Q d I3 dSI0 N 0 (11)uoi�ena C tto /-°,._ I 1 I 1 I 1 I I 0 0 0 0 0 0 0 0 0 0 0 0 4) 0 0 0 0 0 0 0 0 0 0 0 �- -C (N 0 CO rn dr' o 0 COm co coo co X LU o cii (j;)uogena 3 114 189Ajtech Bighorn Estates Lot 2,4288 Nugget Lane, Vail, Colorado I CRSP Profile 1 C Lower Start Zone I Figure 7 HEPVJORTH-PAW LAK GEOTECHNICAL I Job No.114 189A June 2014 HEPWORTH-PAWLAK GEOTECHNICAL, INC. Table 1 Lot 2 Bighorn Estates Summary of CRSP Analysis Profile 1A Upper Start Zone Excedance Analyzed Point Velocity Kinetic Energy Bounce Height Min. Barrier Probability Height 50% Barrier(see Fig. 5) 42 fps 3,300 ft-tons 2 ft. 8 ft. 25% Barrier(see Fig. 5) 49 fps 4,300 ft-tons 5 ft. 11 ft. 10% Barrier(see Fig. 5) 55 fps 5,300 ft-tons 8 ft. 14 ft. 5% Barrier(see Fig. 5) 58 fps 5,800 ft-tons 10 ft. 16 ft. 2% Barrier(see Fig. 5) 62 fps 6,400 ft-tons 12 ft. 18 ft. Notes: 1. CRSP Profile 1A is shown on Figure 5. 2. Rockfall analyzed was a 12-foot, sphere-shaped rock weighing 83 tons and starting at the top of the potential rockfall start zone shown on Figure 5. 3. Minimum barrier height is the bounce height plus the radius of the sphere-shaped rock. 4. Excedance probabilities are based on statistical analysis of 100 independent rockfall trials Job No. 114 189A June 2014 HEPWORTH-PAWLAKGEOTECHNICAL, INC. Table 2 Lot 2 Bighorn Estates Summary of CRSP Analysis Profile 1B Middle Start Zone Excedance Analyzed Point Velocity Kinetic Energy Bounce Height Min. Barrier Probability Height 50% Barrier(see Fig. 6) 44 fps 3,500 ft-tons 1 ft. 7 ft. 25% Barrier(see Fig. 6) 51 fps 4,400 ft-tons 4 ft. 10 ft. 10% Barrier(see Fig. 6) 56 fps 5,500 ft-tons 6 ft. 12 ft. 5% Barrier(see Fig. 6) 60 fps 5,700 ft-tons 7 ft. 13 ft. 2% Barrier(see Fig. 6) 64 fps 6,300 ft-tons 9 ft. 15 ft. Notes: 1. CRSP Profile 1B is shown on Figure 6. 2. Rockfall analyzed was a 12-foot, sphere-shaped rock weighing 83 tons and starting at the top of the potential rockfall start zone shown on Figure 6. 3. Minimum barrier height is the bounce height plus the radius of the sphere-shaped rock. 4. Excedance probabilities are based on statistical analysis of 100 independent rockfall trials Job No.114 189A June 2014 HEPWORTH-PAWLAK GEOTECHNICAL, INC. Table 3 Lott Bighorn Estates Summary of CRSP Analysis Profile 1C Lower Start Zone Excedance Analyzed Point Velocity Kinetic Energy Bounce Height Min. Barrier Probability Height 50% Barrier(see Fig. 7) 43 fps 3,300 ft-tons 2 ft. 8 ft. 25% Barrier(see Fig. 7) 49 fps 4,300 ft-tons 4 ft. 10 ft. 10% Barrier(see Fig. 7) 55 fps 5,100 ft-tons 7 ft. 13 ft. 5% Barrier(see Fig. 7) 58 fps 5,600 ft-tons 8 ft. 14 ft. 2% Barrier(see Fig. 7) 62 fps 6,200 ft-tons 9 ft. 15 ft. Notes: 1. CRSP Profile 1C is shown on Figure 7. 2. Rockfall analyzed was a 12-foot, sphere-shaped rock weighing 83 tons and starting at the top of the potential rockfall start zone shown on Figure 7. 3. Minimum barrier height is the bounce height plus the radius of the sphere-shaped rock. • 4. Excedance probabilities are based on statistical analysis of 100 independent rockfall trials