HomeMy WebLinkAboutDRB150434_DRB150434 Design_1442525580.pdf Hcpworth•Paul.ik Geo echnical, IncGeSt" .
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020 Count), Road 154
eCh X5020 Cou Springs,Colorado 81601
Phone.970-945.7988
HEPWORTH-PAWLAK GEOTECHNICAL Fax 970.945-8454
email:hpgco@hpgeotech Com
September 11, 2015
Michael Barney
5074 Main Gore Drive, Unit A
Vail, Colorado 81657
(tandmbarneyr @ comcast.ne t)
Job No. 115 168A
Subject: Wetland Evaluation and Ditch Bank Armoring Recommendations, Existing
Residence, Lot 5, Filing 1, Vail Meadows, 5074 Main Gore Drive, Vail,
Colorado.
Dear Mr. Barney:
As requested, Hepworth-Pawlak Geotechnical has performed a wetland impact evaluation
and provided recommendations for armoring for the ditch bank that flows near the
northern property boundary of the subject site. Our findings and recommendations are
presented in this report. The services were performed as part of our proposal to you dated
April 2, 2015.
We previously prepared a subsoil study for foundation design for the site dated May 15,
2015, Job No 115 168A. We also observed the foundation excavation and helical pier
installation for the building additions submitting our findings in a report dated June 15,
2015,Job No. 115 168A.
Site Conditions: The lot is located on the northeast, down-slope side of Main Gore
Drive as shown on Figure 1. The existing building is a two story duplex residence with
the additions on the northwest and northeast sides of the residence currently under
construction. The northwest wall line of that addition area is founded on helical piers and
the remainder of the addition areas are founded on shallow spread footings. The terrain
slopes moderately down toward the northwest, becoming steeper to the north of the
building.
There is a shallow ephemeral drainage ditch along the northwest side of the lot that is
about 4 to 6 feet deep with relatively steep channel side slopes. The ditch flows into the
neighborhood down Snowshoe Lane, across Main Gore Drive then along the east side of
Main Gore Drive underneath the subject property driveway then northeast through a
drainage easement between 5074 Main Gore and 5064 Black Gore Drive.
Parker 303-841-7119 • Colorado Springs 759-633-5562 • Silverthorne 970-468-1989
Michael Barney
September 11, 2015
Page 2
Scope of Study: There is a 20 feet wide drainage easement split evenly between the
subject lot and the property to the northwest at 5064 Black Gore Drive. Currently the
ditch is located entirely in the 10 feet of the easement located on the subject Lot 5 and at
some points slightly outside of the easement encroaching towards the existing Lot 5
residence. The addition on the northwest side of the residence extends to adjacent the
ditch. To reduce the potential for erosion of the foundation bearing soils for the addition
in this area, it is desired to armor the channel slope between the addition and ditch. This
report provides design for the ditch armoring as discussed below.
Wetland Evaluation: We performed an evaluation of the ditch and immediate vicinity
for potential wetlands on June 17, 2015. The ordinary high water mark was also flagged
and subsequently surveyed. Procedures outlined in the 1987 Army Corps of Engineers
Wetland Delineation Manual and 2010 Mountain West, Valleys and Coast Regional
Supplement were utilized for the evaluation. The ditch was flowing strongly from spring
snow-melt runoff during our site visit.
The channel flows northwest through a culvert underneath the driveway for the residence
then turns northeast and flows relatively straight along the northwest property boundary
of the lot within the 20 feet wide drainage easement. The high water mark of the channel
is generally about 4 to 5 feet in width across and the side slopes are on the order of
1.5H:I V to 2H:1 V. Due to the slope of the bank, and slope of the base of the channel
which is at about a 10%, the hydrology of the drainage cannot support a wetland
environment. Vegetation on the northern side of the channel consists of a grass lawn.
The south side of the channel consists primarily of a mix of upland grasses. Some
scattered wetland vegetation was observed on the south side of the channel, such as cow
parsnip and horsetail; however, wetland soil characteristics were not present and wetland
hydrology was not present outside of the ditch ordinary high water mark. Based on our
evaluation, wetlands are not present within the proposed disturbance area at the site.
Ditch Bank Armoring: An approximate 40 feet long section of the southeastern side
ditch bank is proposed to be armored to protect the northwestern addition foundation
from potential erosion during a high water event. The location of the armoring should
extend upstream and downstream at least 5 feet from the corners of the building addition
footings as shown on Figure 1. Per our conversations with Vail Town Engineer,Tom
Kassmel, the slope of the armoring must match the existing slope and an as-built survey
will be required following construction to ensure final grading meets the existing
conditions. We have provided two cross sections of the proposed armoring on Figure 2
Job No, 115 168A
C L'7tech
Michael Barney
September 11, 2015
Page 3
with location of the lines of cross-sections shown on Figure 1. Details for the proposed
armoring are provided below and on the attached figures.
• Boulders shall consist of hard, durable igneous or metamorphic rock. The
boulders shall be angular or subangular in shape. Rounded boulders should be
avoided.
• It is imperative that the boulders be placed in a manner which locks them together
and minimizes void space between the boulders.
• No soil, gravel, debris or other deleterious material should exist between the
boulder contact points. Rock-on-rock contact should be established between each
boulder. The contact points should be sloped against the uphill direction to
prevent sliding.
• The largest boulders shall be placed in the bottom row with a minimum diameter
of 2 feet and a minimum embedment of 6 inches. Smaller boulders shall be
placed in the top row of the upper wall with a minimum diameter of 1 foot. Void
spaces should be filled with smaller angular cobble sized material.
• The batter of the bank armor should match the existing slope.
• The slope between the top boulders and foundation wall should be protected from
erosion with 4 to 6 inch size cobbles.
• Exterior footings and footings and grade beams for helical pier supported
foundations beneath unheated areas should be provided with adequate soil cover
above their bearing elevation for frost protection. A minimum of 42 inches of
vertical soil cover is considered adequate for this condition.
• We should observe the ditch armoring construction to evaluate compliance with
our design. Some field modifications to the design may be needed.
Limitations: This report has been prepared in accordance with generally accepted
geotechnical engineering principles and practices in this area at this time. We make no
warranty either express or implied. The conclusions and recommendations submitted in
this report are based upon the site plan elevations, existing ditch channel alignment, the
proposed type of construction, information provided to us and our experience in the area.
If conditions encountered during construction appear different from those described in
this report, we should be notified so that revaluation of the recommendations may be
made.
This report has been prepared for the exclusive use by our client for design purposes. We
are not responsible for technical interpretations by others of our information. As the
Job No. 115 168A
Michael Barney
September 11, 2015
Page 4
project evolves, we should provide continued consultation and field services during
construction to review and monitor the implementation of our recommendations, and to
verify that the recommendations have been appropriately interpreted. Significant design
changes may require additional analysis or modifications to the recommendations
presented herein.
Please feel free to contact us if you have any questions or require further information.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Jason A. Deem
Project Geologist
Reviewed by:
ton
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David A. Young, P.EE �r q?�
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74. 2-216 I.
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attachments Figure 1 -Site Fl"ai
Figure 2- Ditch Cross Sections
cc: Piper Architects—Duane Piper(dpiper@vail.net)
Haskins Construction—Wayne Haskins (wavne@waynehatikinsconstructian.com)
Job No, 115 I68A
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EXISTING HIGH
WATER MARK -
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, ASPHALT DRIVE t°
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Iii\L\2... 8os.a 4.. 11\/rt?. SCALE:1" = 10'
ptech 5074 MAIN GORE DRIVE '
115 1613A ( ��"� FIGURE 1
HEPWORTH-PAWLAK GEOTECHNICAL SITE PLAN
8610 4 TO 6 INCH ANGULAR COBBLE - - -
FROM TOP OF ARMORING TO
8609 FOUNDATION WALL -'--- ------ - -PROVIDE ARMORING 12'
8608MIN ABOVE TOP OF
'
+�� FOOTING ELEVATION II
8607 �
+ -.- ------- ------ �l
Elis
8608X40
`! +ft► EXISTING GROUND SURFACE
8605 ; --
8604
' HIGH WATER LIRE
• TONMESOF
8603
8602 PROPOSED BANK ARMORING
8601 2'MIN DIAMETER AND
6'MIN EMBEDMENT ON
8600 LOWER ROW
8598 APPROXIMATE SCALE
1 INCH-4 FEET
A
86101
8609
8608' •
' 4 TO 6INCH ANGULAR COBBLE
FROM TOP OF ARMORING TO
8607 FOUNDATION WALL
PROVIDE ARMORING 12'
8606 ' II/6466 MIN ABOVE TOP OF
FOOTING ELEVATION
860 �T Of
8604 •� _.4Ge9.r
•
860,Tr x
SCF HIGH WATER LAZE
8602
PROPOSED BANK ARMORING
8601 •
8600
8599 2 MIN DIAMETER AND
APPROXIMATE SCALE 6'MIN EMBEDMENT ON
1 INCH 4 FEET LOWER ROW
B B,
Bank Armoring Notes:
General:
1. The contractor is responsible for site safety. HP Geotech is not responsible for means or methods of construction or for safety of the
workers or public.
2. HP Geotech should provide construction observation and testing services during construction. The subsurface conditions must be
observed to verify that our recommendations are appropriate. All soft,wet and/or disturbed soil shall be removed prior to placement of
bank armoring.
3. No alteration of the width of depth of the existing channel is allowed. Armoring should mimic the existing slope.
4. Construction should be completed when the ditch is dry.
Boulders:
1. Boulders shall consist of hard,durable igneous or metamorphic rock. The boulders shall be angular or subangular in shape. Round
boulders should be avoided.
2. It is imperative that the boulders be placed in a manner which locks them together and minimizes void space between the boulders
Smaller angular cobbles may be used to fill void spaces.
3. No soil,gravel,debris or other deleterious material should exist between the boulder contact points. Rock-on-rock contact should be
established between each boulder. The contact points should be sloped against the uphill direction to prevent sliding. The largest
boulders shall be placed in the bottom row with a minimum diameter of 2 feet. The smallest boulders shall be placed in the top row of the
upper wall with a minimum diameter of 1 foot. The embedment of the lower row of boulders shall be at least 6 inches.
4. The batter of the bank armor should match the existing slope.
5. The slope between the top of the boulder armoring and the existing foundation should be protected from erosion with 4 to 6 inch angular
cobbles.
I"IPtec�..� 5074 MAIN GORE DRIVE FIGURE 2
1151 B8A
HEPWORTH—PA1kLAK GEOTECHNICAL DITCH CROSS SECTIONS AND NOTES