HomeMy WebLinkAbout1988-08-02 Support Documentation Town Council Work Session~`
VAIL TOWN COUNCIL
WORK SESSION
TUESDAY, AUGUST 2, 1988
2:00 p.m.
AGENDA
1. Discussion of Spring Cleanup Day Proposal
2. Discussion of Booth Creek Rockfall Mitigation
3. Discussion of 1988 Second Quarter Financial Report
4. Discussion of Service Levei Analysis
5. Discussion of Bed and Breakfast Amendment
6. Discussion of Forest Service Proposal to Expand Gore Creek Campground
7. Information Update
8. Other
9. Executive Session - Legal Negotiations
VAIL TOWN COUNCIL
WORK SESSION
TUESDAY, AUGUST 2, 1988
2:00 p.m.
EXPANDED AGENDA
2:00 1. Discussion of Spring Cleanup Day Proposal
Erik Steinberg
Action Requested of Council: Hear proposal and give any
comments/suggestions you may havE~.
Background Rationale: Erik is proposing the Ski Club Vail
and Vail Junior Hockey Club take over the responsibility for
the Spring Cleanup in town. (See enclosed letter.)
2:15 2. Discussion of Booth Creek Rockfa1l Mitigation
Bill Cheney
Stan Berryman Action Requested of Council: Direction to staff on
proceeding with the project and formation of a special
improvement district.
Background Rationale: Banner Associates (Engineers) has
completed preliminary engineering designs and cost estimates
for construction of a trench-bean complex to mitigate
rockfall hazards in the Booth Creek neighborhood. Banner
retained the services of the Colorado Geologic Survey and
CTL/Thompson, Inc., Soils Engineers (reports enclosed) in
developing their designs.
Bill Cheney of Banner will make ~a presentation describing
the status of the project at the Work Session.
A preliminary budget for a special district is enclosed as
well as a letter from Banner describing the design
parameters for the project.
2:45 3. Discussion of 1988 Second Quarter Financial Report
Steve Barwick
Charlie Wick Action Requested of Council: Receive the report and make
comments or ask questions as desired.
Background Rationale: The results of the second quarter.
financial report will be summarized including estimates to
year end and projected fund balances.
3:00 4. Discussion of Service Level Analysis
Steve Barwick
Charlie Wick Action Requested of Council: Give additional input to staff
on priority issues to be addressed in preparation of the
1989 budget.
Background Rationale: The results of the Service Level
Analysis recently completed by Council members will be
presented.
3:20 5. Discussion of Bed and Breakfast Amendment
Kristan Pritz
Action Requested of Council: Camment on staff's approach to
reviewing bed and breakfast operations in Vail.
Background Rationale: The staff has outlined issues that
should be addressed before a bed and breakfast is approved.
Staff Recommendation: Proceed with an amendment to the
zoning code to allow bed and breakfast operations in .single
family, duplex, and primary/secondary zone districts.
3:45 6. Discussion of Forest Service Proposal to Expand Gore Creek
Peter Patten Campground
Action Requested of Council: Review the proposal and give
comments.
Background Rationale: See enclosed letter.
4:00 7. Information Update
4:05 8. Other
4:15 9. Executive Session - Legal Negotiations
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~EC'D J U L 1 9 1988
SKI CLUB
July 18, 1988
Mr. Ron Phillips,
Town of Vail
P.O. Box 518 • Vall, Colorado 81858.303/476-5119
Town Manager
75 N. Frontage Road W.
Vail, CO 81658
Dear Ron,
Representatives from the Boards of Trustees of Ski Club Vail and the Vail
Junior Hockey Club would like to meet with the trustees of the Town of Vail
at a Tuesday work session in the near future to discuss the possibility of
these two groups taking over the responsibility for 'the Spring Cleanup in
the town.
It has become apparent in recent years that the enthusiasm for this project
has dwindled. It is the feeling of both youth organizations that this would
be an ideal project - one that would give the kids and their-families a feeling
of contributing to the town and at the same time earn money to of set the cost
of their respective athletic interests. The cleanup also could occur at an
optimum time during the year, early May, when the kids are still in school and
yet ski races and hockey games are not scheduled. These two organizations are
also well-respected in the town, and perhaps could re-kindle the enthusiasm
of the community to support the clean up and our fund-raising effort.
Please advise as to when this topic could be put on the agenda. Both P~1erv
Lapin, representing Vail Junior Hockey Club, and I are anxious to discuss
this matter with the trustees.
Since ely,
SKI UB V IL
Eri Stei berg
Director
ES:gc
cc: Merv Lapin
Vail Junior Hockey Club
Preliminary Budget - June 27, 1988
Booth Creek Rockfall Mitigation
Special Improvement District
Engineering 48,637
Construction 367,500
Contingency 50,000
Finance 15,000*
Capitalized Interest 15,000*
TOTAL $496,137
Less TOV Contribution -20,000
Less Eagle County
Contribution -20,000
$456,137
«.
BANNER
June 30, 1988
Mr. Larry Eskwith - Town Attorney
Town of Vail
75 S. Frontage Road
Vail, CO 81657
Re: Booth Creek RockFall Mitigation
Dear Larry,
This letter is in response to the meeting which took place
Monday, June 27. At that time you requested that Banner
Associates submit a short narrative pertaining to design
parameters and Engineer recommendations.
As you are aware the funding for this project is very limited.
It was therefore necessary to develop a design that does not
provide the normally accepted factor of safety from a engineering
standpoint in terms of slope stability.
The factor of safety of the existing hillside is approximately
1.5 with 1.0 being the point of failure and 2.0 being fairly
stable. Most slope structures are designed for factors exceeding
1.5 and slopes are generally considered suspect for failure when
factors lower than about 1.2 are calculated. The factors of
safety for the design as now developed range from 1.0 in non-
critical areas to 1.3 and 1.4 across the cut and fill slopes
respectively. If for some reason the hillside became saturated
the factors'of safety could be reduced to 1.0 or less resulting
in a surface failure, the magnitude of which is difficult to
predict. This scenario is unlikely, however the possibility does
exist and should be noted.
The berm configuration was developed utilizing information
supplied by the Colorado Geological Survey. The berm as designed
will theoretically stop 91~ of rocks weighing ten tons and 1000
of rocks weighing 2.4 tons or less. Based on a report prepared
by the Colorado Geological Survey in 1983, the rockfall
recurrence interval for rocks weighing from two to six tons is
every one to three years. As the rocks become larger in size the
recurrence interval increases in years to the point where a large
slab failure is estimated to occur once every 40 to 100 years.
BANNER ASSOCIATES. INC.
CONSULTING ENGINEERS & ARCHITECTS
2777 CROSSROADS BOULEVARD
GRAND JUNCTION, CO 81506 • (303) 243-2242
BANNED
Mr. Larry Eskwith - Town Attorney
June 29, 1988
Page Two
With this in mind it is necessary to weigh the risks of
construction (falling rocks, etc.) and the resulting berm
configuration with a risk of landslide, against the rock fall
hazard currently present. After reviewing the various reports
and analyzing the data mow available we feel the risks of serious
injury and property damage would be reduced considerably with the
construction of the (proposed berm complex even though other
pcssible hazards may be created. There will be maintenance
problems associated with the design; i.e. erosion and spalling;
however these problems are easily remedied :in comparison to the
rock fall hazard which 'now exists.
Additional information can be found in the CTL/Thompson, Inc.
report on slope stability prepared for Banner Associates in
conjunction with this study and design. If :further clarification
or explanation is required we are available at your request.
Sincerely,
BANNER ASSOCIATES, INC.'
i~~
Bill Cheney, P. .
BC/rg
cc: Stan Barryman
AN ANALYSIS OF THE BOOTH CREEK ROCKFALL AREA
USING A OOMPUTER MODEL OF ROCKFALL BEHAVIOR
~y
Susan H. Cannon and Bruce K. Stover
PREPAREll BY THE OOLORADO GEOLOGICAL SURVEY
FOR THE TOWN OF VAIL
JUNE, 1988
TABLE OF CONTENTS
Introduction
The Model
Model Variables
Slope materials
Rock material properties
Source area locations
Results
Preliminary Structure Design Evaluation
Conclusions and Recommendations
Figures
1. Slope profile of Booth Creek rockfall area showing cell delineation,
locations of two source areas, and location of analysis point.
2. Potential travel distances of rocks of varying dimensions.
3. Average velocities in each cell for rocks of varying dimensions.
~, 4. Maximum velocities in each cell for rocks of varying dimensions.
5. Average bounce heights in each cell for rocks of varying dimensions.
6. Maximum bounce heights in each cell for rocks of varying dimensions.
Tables
1. Data used in analyses showing high and low Rn and Rt coefficients, slope
roughness factor, and cell coordinates.
2. Velocity, bounce-height, and impact-force data at analysis point.
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AN ANALYSIS OF THE BOOTH CREEK ROCKFALL AREA
USING A OOMPUTER MODEL OF ROCKFALL BEHAVIOR
INTRODUCTION
Rockfall activity in the vicinity of Booth Creek in the town of Vail,
Colorado, has been a recurring problem for many years (Colorado Geological
Survey, 1983). Development in the rockfall acceleration and runout zones has
lead to increased damage by these events and interest in mitigating the hazard
has increased concurrently. In order to design an appropriate protective
structure, it is necessary to understand the behavior of rockfalls at the
site. CRSP, a computer model of rockfall behavior developed by Tim Pfeiffer
and Tim Bowen for the Colorado Department of Highways, provides an objective
tool for predicting the travel distances, velocities, and bounce heights of
rockfall events at Booth Creek.
In this report we briefly describe the computer model and the selection of
input parameters used to simulate the Booth Creek rockfalls. We present the
results as potential velocities, bounce heights and impact forces at the
proposed berm location, as well as velocities and bounce heights over the
length of the rockfall path. We also use the model to analyze the
effectiveness of containment structures of three different heights in stopping
a range of rock sizes.
THE MODEL
CRSP is a computer program that models rockfall behavior and provides a
statistical analysis of rockfall behavior at a given site. The model applies
equations of gravitational acceleration and conservation of energy to describe
the motion of a single rock traveling down a slope. Empirically derived
functions relating velocities, friction, and material coefficients are used to
model the dynamic interaction of the rock and slope. The statistical
variation among rockfalls is modeled by randomly varying the angle at which a
rock impacts the slope within limits set by rock size and the slope
characteristics. The program provides a site-specific analysis of rockfall
with output velocity and bounce height statistics at various locations on the
slope.
Pfeiffer and Bowen (1988) describe the assumptions made in developing the
model, and thus its limitations.
MODEL VARIABLES
The behavior of rockfalls is influenced by slope geometry, slope materials
properties, rock geometry, and material properties of the moving rocks
(Ritchie, 1963). How these variables were quantified for use in the model for
the Booth Creek area are discussed below.
Slope Geometry
In the CRSP model, the influence of slope geometry is quantified by dividing a
slope transect into a number of cells of equal gradient. A slope profile of
the Booth Creek rockfall area was generated by surveying the locations of 31
points in a line down the slope. (Two additional shorter transects 100 and
200 feet to the west were surveyed for comparison purposes.) Figure 1 shows
the inclination and length of the cells used in this analysis. A surface
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roughness coefficient that quantifies the perpendicular variation in a slope
segment is also assigned for each cell. These coefficients were assigned
based on field observations. The data used for each cell in the analysis is
shown in Table 1.
..
Table 1. Data used in analyses. Both the high and low slope material
coefficients (Rt and Ru) are shown.
Rn
Rt Normal
Tangential Coefficent
Surface Coefficient Restitution Beginning Ending
Cell #i Roughness Low High Low High X Y X Y
1 .2 .8 .83 .28 .32 0 844 136 741
2 .2 .8 .83 .28 .32 136 741 219 685
3 1 .83 .87 .28 .33 219 685 234 616
4 .2 .8 .83 .28 .33 234 616 604 317
5 .2 .8 .83 .28 .32 604 317 838 163
6 .75 .78 .82 .28 .32 838 163 986 96
7 .1 .8 .83 .28 .32 986 96 994 82
8 .1 .87 .92 .37 .42 994 82 1019 88
9 .1 .87 .92 .37 .42 1019 88 1028 87
10 1 .8 .83 .28 .32 1028 87 1053 74
11 1.5 .78 .83 .28 .33 1053 74 1187 34
12 1.5 .78 .83 .28 .33 1187 34 1273 22
13 .2 .78 .82 .28 .33 1273 22 1419 2
14 .1 .87 .92 .37 .42 1419 2 1504 2
Slope Materials
The properties of slope materials are quantified in the model by assigning
additional coefficients to each cell. Numerical representations of these
properties are termed the normal coefficient of restitution (Rn) and the
tangential coefficient of frictional resistance (Rt). Rn is a measure of the
degree of elasticity in a collision normal to the slope, while Rt is a measure
of the resistance to movement parallel to the slope. Specifically, Rn is
applied to the normal component of a rock's velocity at impact, and Rt is
applied to the tangential component of a rock's kinetic energy at impact.
Pfeiffer and Bowen (1988) define a range for these coefficients for the
materials present at Booth Creek. For example, Rn for talus with little
vegetation varies between 0.30 and 0.33. To insure that the modeling effort
is representative of the range of conditions possible, the program was run
with two data sets which included the upper and lower limits of the
coefficients, as shown in Table 1.
Rock Material Properties
Field observations and measurements were used to characterize the dimensions
and form of rocks involved in rockf alls at Booth Creek. To define the range
of variation in rockfall behavior, we evaluated the behavior of rocks of the
following dimensions:
Weight Form Dimensions
20,000 lbs equant radius = 3.1 t
10,000 lbs disk radius = 3 ft, thickness = 2 ft
5,000 lbs disk radius = 2.5 ft, thickness = 1.5 ft
800 lbs disk radius = 1.25 ft, thickness = 1.0 ft
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The 800 lb rock is thought to be representative of the average rock dimension
observed on the Booth Creek slopes, and the 20,000 lb rock represents a
typical largest rockfall boulder observed in the field.
Source Area Locations
An additional variable in the model is the locations of source areas. In the
Booth Creek area, both an upper and lower potential sources were identified,
as shown in Figure 1 (Stover, 1983).
Our modeling effort thus consisted of evaluating the behavior of four
different rock masses, originating from two possible source areas, and
traveling over slopes with a range (low and high) of slope-materials
characteristics. Combining all these variables gives a total of 16 runs of
the program to define the range of behavior of rockfalls at Booth Creek.
RESULTS
The output from C1tSP consists of velocity, bounce-height, and impact-force
data at one user-defined point (the analysis point) as well as velocity and
bounce height data for each cell. The range of potential travel distances of
rocks of varying dimensions are shown in Figure 2 as histograms of the number
of rocks stopped for a given slope position. The model predicts that a few of
the largest eyuant rocks are able to travel at least to I-70, while most stop
well before. The rocks of average dimensions (disks with radius = 1.25 ft)
generally stop below the small road cut, and most of the larger disk-shaped
rocks stop beyond the smaller rocks. These predictions are consistent with
field observations and thus impart a note of confidence in the range values
assigned to the coefficients used in the model.
We located the analysis point at the upslope edge of the proposed location of
the containment structure (Figure 1). The range of potential velocities and
bounce heights for rocks of varying dimensions at the analysis point are shown
in Table 2. The range in each parameter is a result of defining a range of
possible slope materials coefficients and the varying source area locations.
Table 2. Velocity, bounce-height and impact-force data at the analysis point.
Average Maximum Maximum
Maximum Average Minimum Bounce Bounce Kinetic
Velocity Velocity Velocity Height Height Energy
Rock (ft/sec) (ft/sec) (ft/sec) (f t) (ft) ft/lbs
2 0 1 sp ere 7~- ~ S~ ~- 4-~ 1, ,00 - ,3 ,U U
10,000 lb disk 66-80 58-73 45-66 4-5 5-6 630,000-1,000,000
5,000 lb disk 69-80 62-75 54-67 4-5 5-6 360,000-480,000
800 lb disk 74-83 66-72 58-64 5-6 7-9 69,000-87,000
We suggest that the maximum value of each parameter be used in developing
design criteria for the containment structure.
Maximum and average velocities as well as maximum and average bounce heights
are also predicted by the model for each cell. The maximum value predicted
for each of these parameters are shown for rocks of varying dimensions on
Figures 3, 4, 5, and 6. A range in these parameters was generated by .using a
range in slope materials coefficients and the two source area locations.
However, the maximum value generated from the analyses is depicted on the
figures as a worst case evaluation.
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PRELL~fINA1tY STRUCTURE DESIGN EVALUATION
The preceding analyses provide velocity, bounce-height, and impact-force data
that can be used in the preliminary design of a containment structure for the
Booth Creek area. However, the addition of a structure on a slope will alter
the behavior of rocks as they travel downslope. Of particular concern is the
possibility that if a rock impacts a structure at mid-bounce, the energy of
the impact may be sufficient to skip the rock over the top of the. structure.
Thus it is necessary to evaluate the effect of structures of various
configurations to insure that the desired effectiveness of catchment by the
barrier is attained.
To evaluate the effect of structures of varying heights on the rockfall
behavior at Booth Creek, CRSP was run with varying structure heights
incorporated into the model and both 20,.000 lb (maximum size) and 800 lb
(average size) rocks. The configuration of the structures consisted of a
1.3:1 (H:V) slope cut into the existing 1.6:1 slope over a distance of 72 ft
extending up to the proposed structure location; a 15-ft-high, 1:4 wall; and
then a 1:1 slope continuing from the existing ground surface to give the
remainder of height to the bean. The model was run with berm heights of 10,
15 and 20 ft to determine the effectiveness of the varying berm heights on
stopping both 20,000 and 800 lb rocks.
The analyses show that the 15-f t-high wall coupled with a 20-ft-high berm
stops 100 of both rock masses. The 15-ft-high wall and 10-ft-high berm
stopped 1000 of the 800 lb rocks, but only 40~ of the 20,000 lb rocks. The
rocks that were not stopped by the structure traveled the length of the runout
slope. The 15-ft wall coupled with the 15-f t-high berm stopped 1000 of the
800 lb rocks and 97~ of the 20,000 lb rocks. The remaining 3$ of the rocks in
the sample stopped on the top of the berm. A maximum kinetic energy of 2895
ft-lbs was exerted on the top of the berm by the 20,000 lb rocks that topped
the been.
We now know that the present 1.6:1 slope cannot be increased and still
maintain a 1.5 factor of safety, and so the 1.3:1 cut modeled is not possible
(B. Cheney, personal comrn., June 14, 1988). However, by eliminating the cut,
rock velocities and bounce heights will decrease slightly, and thus increase
the effectiveness of the 15-ft wall and 15 ft berm configuration on the ground
surface. The effectiveness of the structure will change with a change in the
form of the structure, so further simulations should be done for other
configurations under consideration.
OONCLUSIONS AND RECOIrA4ENDATIONS
The rockfall model provides a valuable tool for quantitatively evaluating
rockfall behavior in the Booth Creek area. The extent of travel of rocks of
varying dimensions predicted by the model fits well with field observations,
suggesting that the values assigned for the various slope and rock materials
coefficients were reasonable for the area. The rockfall model provides
information on predicted velocities, bounce heights, and impact forces for a
range of rock sizes at the proposed location of the containment structure.
These analyses suggest that velocities of 84 ft/sec, bounce heights of 9 ft,
and impact forces up to 2,300,000 ft lbs should be used in developing
preliminary design criteria for the containment structure.
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The model also provides information on predicted velocities and bounce heights
for each cell that should be considered if the location of the structure is
moved from that considered here.
The effect of the addition of a structure to a slope on the rockfall behavior
and the structure's rock-stopping effectiveness was also evaluated briefly in
this study. A preliminary analysis demonstrated that a 15-ft-high, nearly
vertical wall cut into the slope, in conjunction with a 15-ft-high berm on the
existing ground surface, would stop 97$ of all 20,000 lb rocks that travel
down the slope. The effectiveness of a structure of this configuration would
increase if the entire structure (wall and berm) were at ground level.
The CEiSP model should be used for evaluating the effectiveness of other design
possibilities.
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REFERENCES
Pfeiffer, T.J., and Bowen, T.D., 1988, Computer Simulation of Rockfalls:
Bulletin of the Association of Engineering Geologists.
Ritchie, A.M., 1963, The evaluation of rockfall and its control: Highway
Research Record, National Academy of Sciences-National Research Council,
Washington D. C., No. 17, pp. 13-28.
Stover, B.K., 1983, Preliminary evaluation of rockfall hazard in
the Booth Creek area: Report prepared for the Town of Vail, Colorado,
Colorado Geological Survey, 17 p.
3808
-6-
CTL/THOMPSON, INC.
CONSULTING GEOTECHNICAL AND MATERIALS ENGINEERS
PRELIMINARY SLOPE STABILITY EVALUATION
PROPOSED BOOTH CREEK ROCKFALL MITIGATION
KATOS RANCH ROAD ""
VAIL, COLORADO
Prepared For:
Banner Associates
Consulting Engineers and Architects
2777 Crossroads Boulevard
Grand Junction, Colorado 81 S01
Attention: Mr. Bill Cheney
Job No. 15, 194 June 16, 1988
1971 WEST 12TH AVENUE DENVER, COLORADO 80204 (303) 825-0777
'e
TABLE OF CONTENTS
SCOPE
SITE CONDITIONS
PROPOSED CONSTRUCTION 2
INVESTIGATIONS 2
Subsurface Conditions 3
Laboratory Testing 4
PRELIMINARY STABILITY ANALYSIS ~ 4
DISCUSSION 5
LIMITATIONS 6
FIG. I -LOCATION OF EXPLORATORY TEST PITS
FIG. 2 -LOGS OF EXPLORATORY TEST PITS
FIG. 3 - SUMMARY OF STABILITY ANALYSES
(CONCEPTUAL BERM CONFIGURATION -STA. 6+00)
FIG. 4 - SUMMARY OF STABILITY ANALYSES
(1.6: I CUT SLOPE)
FIG. S - SUMMARY OF STABILITY ANALYSES
(1.3: I CUT SLOPE)
FIG. 6 - SUMMARY OF STABILITY ANALYSES
(I :I CUT SLOPE)
APPENDIX A -LABORATORY TEST RESULTS
SCOPE
This report presents the results of our preliminary slope stability evaluation
for the proposed Booth Creek Rockfall mitigation program. The purpose of our
investigation was to sample subsoils at the site, perform laboratory tests and
preliminary stability calculations, and provide our opinions of the stability of the
proposed construction. The report contains results of field and laboratory
investigations, summaries of stability calculations, our opinions and
recommendations.
This report was prepared based upon conceptual designs for the project. If
final design is accomplished, we recommend further analyses be performed to
assess the slope stability of the proposed configuration.
SITE CONDITIONS
The Booth Creek Rockfall area investigated as part of this investigation is
located north of Interstate 70 and Katos Ranch Road in East Vail, Colorado
(Fig. I). The site was identified as a rockfall hazard area in studies completed for
the Town of Vail. The hazard exists due to cliffs of Permian-age bedrock which
occur above the site, to the north. Periodically, rocks from these cliffs fall and
roll down the slope. We understand rocks have impacted one or more of the homes
along Katos Ranch Road and Booth Creek Road since (980. The homeowners wish
to consider construction of a rockfall mitigation structure to reduce the risk of
further damage.
The slopes below the cliffs are relatively steep and gradually flatten to the
south. The upper areas slope down at about 1.5:1 (horizontal to vertical) and
-2-
flatten to about 1.7:1 and about 2:1 about 100 feet north of Katos Ranch Road.
Our understanding of site geology indicates the slopes were created as glaciers
retreated through the Vail Valley. The present conditions were established by
subsequent erosion by Gore Creek and deposition of slope wash from the north. At
the time of this investigation, slopes above Katos Ranch Road were covered with
native grass and scrub vegetation with very few trees, except near the road. The
slopes to the west were vegetated with aspen, pine and native grasses.
PROPOSED CONSTRUCTION
We understand the proposed rockfall mitigation scheme will include a trench
and berm structure constructed on the hillside, to the north of the existing
residences; Fig. 3 shows the conceptual berm configuration. Construction of the
proposed berm will involve excavating a trench to a depth of 8 feet below existing
site grades. This trench will be about 12 feet wide. The cut slope above the
trench will match existing grade approximately 200 feet north of the berm. You
indicated the cut slope may range from I :1 (horizontal to vertical) to 1.6:1.
The berm will be constructed with the soils generated from the trench and
cut slope excavations. The top of the berm will be about 10 feet above existing
site grades and the downhill face will slope at 1.5:1 to a catch point on the slopes
below. The uphill face of the berm will be constructed at a I:I slope.
INVESTIGATIONS
' The investigations completed as part of this study included sampling of soils
from two exploratory test pits and laboratory testing of soils obtained from the
pits. The test pits were excavated at the approximate locations shown on Fig. I
-3-
with atrack-mounted backhoe. Our representative was on site during excavation
to observe soil conditions exposed in the pits, perform field density tests and
obtain samples. Test pit locations were somewhat limited by backhoe access and
the available time.
Subsurface Conditions
The subsoils exposed in the test pits can generally be described as a '"
matrix of silty to clayey sands surrounding gravels, scattered cobbles and
boulders. Samples were obtained by driving athin-walled metal tube (or
liner) into the soil matrix and with bulk methods. In test pit TP-I, we found
about 4 feet of dark brown, moist soils at the ground surface. These soils
were generally more clayey and silty than the underlying materials. Cobbles
and boulders up to about 4 feet in diameter were found at various depths
within the soil profile. In test pit TP-2, the moist, silty and clayey soils
extended to a depth of about S feet where drier, sand and gravel type soils
were exposed. From about 13 feet to 18 feet, a tense of cleaner, sands and
gravels was found. Cobbles and boulders up to about 4 feet in diameter were
also excavated in TP-2.
We performed field density tests using a Troxler nuclear gage during the
test pit excavations. The results of these tests are summarized on
Table A-I. In general, we found the existing soils to be of comparatively low
density; dry densities ranged from 100 to I I I pcf. The average wet density
from the six field tests was 114 pcf. The tests were performed in soil matrix
and results may not reflect the large rock contribution to the soil mass
density. In our opinion, wet densities of about 120 pcf should be appropriate
for the materials found in the test pits.
-4-
Laboratory Testing
Samples of the soils found in the exploratory test pits were returned to
our laboratory for testing. We performed grain size analyses, direct shear
tests and a modified Proctor (ASTM D 1557) compaction test. The results of
laboratory testing are presented in Appendix A. Direct shear tests on liner
samples of the near-surface silty to clayey sands and sandy silt were run at
natural moisture content. We measured sample cohesion from 350 to 500 psf
with an angle of internal friction of 34 degrees. Bulk samples from each test
pit were combined and remolded to approximate field densities for additional
direct shear tests. These tests were performed by immersing the sample in
water prior to shearing. A friction angles of 38 to 39 degrees was measured
with no apparent cohesion. In our opinion, the test results are consistent with
our experience with the soils in the Vail Valley. We believe these soils exhibit
some cohesion in a dry condition, but upon wetting the cohesion is lost and
the soils become purely frictional materials.
PRELIMINARY STABILITY ANALYSES
The analyses of slope stability focus upon determination of a "factor of
safety" which is commonly defined as the ratio of the available shear strength of
the soil to the shear strength required to bring the slope to incipient failure.
When forces are considered, "factor of safety" is defined as the sum of forces
resisting failure divided by the sum of forces tending to cause failure. These
definitions imply that slopes with a factor of safety greater than one are "safe".
The actual safety of a slope is influenced by many variables and it is .virtually
-5-
impossible to fully evaluate the variables. Thus, "factor of safety" must be
viewed as a qualitative measure of mass stability. Most slope structures are
designed for factors exceeding 1.5 and slopes are generally considered suspect
when factors lower than about 1.2 are calculated.
Our stability analyses were limited to preliminary evaluations of a
conceptual berm configuration and analyses of cut slopes of 1.6:1, 1.3:1 and I:I.
The results of the stability analyses are summarized on Figs. 3 through 6. The
analyses were completed using the computer program Stabl. This program uses a
Modified Bishop solution procedure and circular failure surfaces. For our
analyses, we assumed the existing materials and the proposed berm fill would have
similar shear strength properties. This assumption is somewhat conservative in
that we believe the berm materials will most likely have slightly higher strength.
We varied cohesion from 0 to 250 and 500 psf and angle of internal friction from
33 to 35 and 37 degrees for each configuration. Our experience and the laboratory
test results indicate the natural soils under dry conditions could exhibit an
apparent cohesion and friction in the lower portion of the range. When the soils
are wetted, the apparent cohesion is lost and the soils behave as "friction only"
materials.
Our preliminary analyses of the conceptual berm configuration was based
upon topography at Sta. 6+00 and our interpretation of the conceptual berm based
upon verbal communications with Banner Associates. The critical failure surface
for cohesion of 250 psf and a friction angle of 37 degrees is shown on Fig. 3
(calculated factor of safety 1.59). A Table on the figure summarizes the critical
safety factors for paired combinations of friction and cohesion. The safety
factors reported represent. the minimum value obtained from 16 different failure
surfaces through the slope configuration.
-6-
The results of cut slope analyses are presented on Figs. 4 through 6. Since
the precise horizontal extent of cut slopes was not provided, we limited the
horizontal extent of the failure surface to 160 feet. The critical failure surface
for cohesion of 250 psf and friction angle of 35 degrees is shown on these figures.
A table on each figure also summarizes additional analyses for the cut
configurations.
DISCUSSION
The results of our preliminary stability analyses indicate marginally stable
conditions for strength parameters in the lower range of those evaluated. The
calculations generally showed that slopes should be relatively stable, as long as
the soils maintain their cohesive, characteristics. If the soils become wetted, it is
likely some failures could occur. The proposed cut slope of I:I (horizontal to
vertical) does not produce a reliably safe slope regardless of soil strength
parameters considered.
We believe it is possible to construct the berm as conceived, provided the
fill is properly benched into the existing slope and adequate drainage measures are
provided to limit infiltraton of surface runoff into the soils below the berm.
The cut slope analyses generally indicated slopes steeper than about 1.6:1
become marginally safe when no cohesion is assumed. We believe the cut slopes
planned involve higher comparative risk than the berm fill. It may be possible to
compact the surface of the cut slopes while limiting their steepness to improve
performance. Revegation or artificial reinforcement of the cut slopes and use of
man-made retaining structures above the trench and berm may also be possible.
-7-
Summary
I. Analyses and our experience indicate the berm fill of 10 feet is
comparatively safe. The fill should be benched into the existing
slopes. Surface drainage from slopes to the north must be
positively controlled to minimize infiltration of water into the
berm and underying soils.
2. We believe the cut slopes planned involve risk of slope failures. If
possible, they should be eliminated and an import fill used. Cut
slopes steeper than 1.6:1 involve comparatively high risk of
failures.
LIMITATIONS
This report was prepared based upon preliminary concepts of the proposed
construction and limited stability analyses. The slope stability of alternative
construction should be checked during final preparation of drawings.
We appreciate the opportunity to work with Banner and Associates on this
project. Please call if we can answer any questions or be of further service.
CTL/THOMPSON INC. '~` °•'°`•~
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Ronald M. McOmber, P.E. ~ ~,o
Reviewed by: <~.<~".~
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/// Robert W. Thorri'p""s'bh', .E.
President
RMM:RWT:gI
(3 copies sent)
TO: Town Council
FROM: Community Development Department
DATE: August 2, 1988
RE: Bed & Breakfast Amendment
In mid-May, the Council discussed whether or not it would be
appropriate to allow Bed & Breakfast operations in single
family, duplex and primary/secondary zone districts. In
general, the Council concurred that it was appropriate to allow
for the Bed & Breakfast use. The Council comments included:
1. The conditional use approach seems like a reasonable
way to handle this type of use.
2. The residence for the Bed & Breakfast operation must
be used as a primary residence for the proprietor of
the B&B.
3. The approval of an adjacent duplex owner should be
required.
4. Council members were concerned about parking.
5. It was felt that the covenants should be checked so
that there was not a conflict with the use and
restrictions within the subdivision.
The staff is recommending a review process that would allow for
B&B operations while maintaining the residential character of
single family, duplex, and primary/secondary zone districts.
The following outline identifies how the staff would like to
review Bed & Breakfast operations (B&Bs).
I. B&B QUALIFICATIONS
A. The proprietor of the B&B operation must live on the
premises.
B. The proprietor of the B&B operation may short term
rent separately up to three bedrooms or a maximum
square footage of 900 square feet per dwelling unit.
C. The proprietor of the B&B operation shall ensure that
the operation of the B&B meets the occupancy
standards identified in Section 18.04.110 Family of
the Town of Vail Zoning Code.
18.04.110 Family - Family shall be deemed to be
either A or B:
A. An individual, or two or more persons related
by blood, marriage, or adoption, excluding
domestic servants, living together in a dwelling
unit used as a single housekeeping unit. B. A
group of unrelated persons not to exceed two
persons per bedroom plus an additional two
persons per dwelling unit used as a single
housekeeping unit.
D. The parking requirement for a B&B operation shall be
one space for the proprietor plus one space per short
term bedroom. All parking must be located on site.
The removal of landscaping to provide additional
parking for a B&B is strongly discouraged.
E. The adjacent duplex or primary/secondary owner must
also approve the B&B operation if the property is a
primary/secondary or duplex lot.
F. The dwelling unit housing the B&B operation shall be
allowed two square feet for a wall sign to identify
the use. Subtle spot lighting is allowed for the
signage.
G. The proprietor of the B&B shall provide adequate
enclosed trash facilities and regular trash pick up
service.
II. REVIEW PROCESS
The staff recommends that the conditional use review process be
used to allow for a Bed & Breakfast. The conditional use
criteria are:
Section 18.60.060 Criteria-Findings
A. Before acting on a conditional use permit
application, the planning commission shall consider
the following factors with respect to proposed use:
1. Relationship and impact of the use on
development objectives of the town;
2. Effect of the use on light and air, distribution
of population, transportation facilities,
utilities, schools, parks and recreation
facilities, and other public facilities and
public facilities needs;
3. Effect upon traffic, with particular reference
to congestion, automotive and pedestrian safety
and convenience, traffic flow and control,
access, maneuverability, and removal of snow
from the streets and parking areas;
.9 w
4. Effect upon the character of the area in which
the proposed use is to be located, including the
scale and bulk of the proposed use in relation
to surrounding uses;
5. Such other factors and criteria as the
commission deems applicable to the proposed
use (i.e., Vail Comprehensive Plan);
Staff believes that the conditional use process is appropriate
as it 1) allows for the notification of adjacent property
owners 2) addresses the potential impact of B&Bs in respect to
parking and 3) addresses the effect of this type of use on the
residential character of the area. The conditional use process
is probably the most streamlined way to handle the review of a
B&B. The proprietor would also be required to get a business
license.
Staff considered reviewing this use under the Home Occupation
Permit process or creating a special Bed & Breakfast review
process. The problem with the Home Occupation Review is that
there is no notification procedure and the criteria are not
very specific to a Bed & Breakfast operation. A special Bed &
Breakfast review process could allow for a specific criteria
related to B&Bs. However, even if adjacent property owners
were informed of the use, it would be difficult for the staff
to weigh adjacent property owners' concerns and determine if it
really is appropriate to approve or deny a Bed & Breakfast
request.
III. ZONING CODE CHANGES
The following sections of the Town of Vail Zoning Code would
need to be amended to allow for Bed & Breakfast operations:
A. 18.58.310 Short Term Rental
"Short Term Accommodation Unit. No rooms in any
structure or building located in any single family,
two family, or primary/secondary zone district within
the Town shall be short term rented, separately as
accommodation units."
This section of the Code would need to be
removed.
B. 18.04 Definitions
A Bed & Breakfast would need to be defined.
C. 18.10
The single family zone district will need to be
amended to allow for Bed & Breakfast operations as a
conditional use.
D. 18.12
The primary/secondary zone district will need to be
amended to allow for Bed & Breakfast operations as a
conditional use.
E. 18.13
The duplex zone district will need to be amended to
allow for Bed & Breakfast operations as a conditional
use.
__ f ~~
RECD J U L 1 8 'i988
United States Forest White River Holy Cross Ranger District
Department of Service National P.O. Box 190
A riculture Forest _ Minturn Colorado 81645
Reply to: 2300
Date: July 13, 1988
Town of Vail
75 So. Frontage Road
Vail, CO. 81657
Dear Interseted Public:
The Holy Cross Ranger District is proposing to expand Gore Creek campground
located east of Vail during the summer of 1989. The expansion would occur east
of the existing facility and would involve the construction of 1,200 ft. of low
standard roadway, 400 ft. of walkways, 8 tentpad sites (with firegrates and
picnic tables), a 12 car parking lot and toilet. A site map is attached for
your information. In 1987 the existing campground sites were enlarged to
accomodate recreational vehicles. The new planned expansion will provide sites
for tent campers without utilizing sites more suitable for RV's. The expansion
will serve a broader mix of recreational campers in addition to increasing the
capacity of the campground. I would appreciate any comments (pros or cons) you
may have with regards to this proposal by August 5, 198.
Thank you for your review time.
Sincerely,
,rte--~~-
WILLIAPf A.WOOD
District Ranger
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