903 Wild Rose Ct - Engineering Review LetterLand Surveying
Civil Engineering
Geotechnical Engineering
Construction Material Testing
Environmental Services
1604 Riverview Lane
Northfield, MN 55057
Tel. 507.645.0964
Fax. 507.645.2842
e -mail. mlc@mbi- nf.com
Established 1995
Equal Opporlunity Employer
January 29, 2009
Mr. Dave Westermayer
Engineering Technician
City of Eagan
Northfield 3830 Pilot Knob Road
Minnesota Eagan, Minnesota 55112
Re: 903 Wild Rose Court
Eagan, Minnesota
MBI #N5423/N9032
Dear Mr. Westermayer;
It is our understanding that the City of Eagan is requesting an engineering review
of an excavation for a new residence at the above mentioned address. The
excavation is near a watermain utility and therefore frost heaving and
undermining of the pipe were issues that needed to be addressed before
construction would be allowed to occur. This letter is intended to discuss these
issues and recommend construction methods that could be implemented in the
field to prevent damage from occurring to the existing watermain.
Background
Based upon information provided to us by Brian Smith that he received from
Dave Westermayer with the City of Eagan, Delmar Schwanz Land Surveyors, and
Bruce Lehrer, the architect, it appears that the building is located such as the west
corner of the proposed structure is next to a 20 -foot easement for the watermain.
Construction of the building foundation will involve excavating into the easement
for sloping to the bottom of footing. Based on conversations we had with the City
of Eagan it is our understanding that the watermain should be expected to be in
the center of the easement, placing it 10 feet away from the building corner.
903 Wild Rose Court, Eagan, Minnesota
MBI #N5423/N9032 Page 2
Sheet 6, Section 2/6 of the Architectural Drawings indicated that the lowest
bottom of footings were at a depth of 3'8" below the upper footings at 884.67,
putting the lowest footings at 881.00. We used this bottom of footing elevation
for our review.
Frost
Damage could occur to the watermain where frost heaving of the soil causes
movement or where the water in the pipe freezes. Typically a minimum of 7%s
feet of ground cover is placed over the pipe to protect it from frost. This depth of
soil protection is based upon a full season of cold weather that would allow frost
to penetrate deeply into the ground. Short term excavations such as those planned
at this site are typically not open long enough for deep frost penetration to occur.
The expected excavations at the site will reduce the protective soil cover over the
watermain to 5.9 feet, as can be seen in the attached drawing. It is highly unlikely
that the frost could penetrate this depth in the 1 -2 weeks that the excavation is
expected to be open. If the excavation stays open longer than 2 weeks, the
contractor should place warming blankets at the building corner to protect the soil
from freezing.
If the bottom of footing elevation reveals poor soils and the excavation is required
to continue to deeper elevations, than frost could become a concern. Below is a
chart of the activity required to protect the pipe from frost based on excavations
below the bottom of footing elevation of 881.00
Excavation below Bottom
of Footing Elevation 881.00
Ground Cover
over Watermain
Frost Protection
Method
0'
5.9'
Warming Blankets
(optional)
1'
4.5'
Warming Blankets
2'
3.1'
Double - Layered
Warming Blankets
3'
1.7'
Warming Blankets and
Heat Source. *
3'/2' or more
Sheet Piling
Required — expect
1' cover
Warming Blankets and
Heat Source. *
903 Wild Rose Court, Eagan. Minnesota
MBI #N5423/N9032
Frost Protection Chart
* Monitoring of temperatures recommended with max/min thermometer.
Page 3
Undermining
Excavation of the building area is expected to require a 1:1 slope away from the
building for a temporarily stable bank. Excavation to bottom of footing elevation
of 881.00 will not present any undermining issues as illustrated in the attached
drawing. Excavations below the bottom of footing elevation to correct poor soil
conditions will require a 1:1 over excavation to support the footing. Since the
watermain location is not exact, we have been conservative in our
recommendations and provided a 2' oversize pad from the center of the expected
watermain location. Using a 1:1 slope to support the watermain allows us to
determine at what elevation the excavation will undermine the watermain. As can
be seen on the attached drawing, at an elevation of 877.5, which is a 3.5 foot
additional excavation below the bottom of footing, the excavation could
undermine the pipe support area. If additional excavations are required to deeper
903 Wild Rose Court. Eagan, Minnesota
MBI #N5423/N9032 Page 4
depths, then driving sheet piles into the slope is recommended to support the soils.
Wood or steel sheet could be used as long as they are driven sufficiently deep
enough to be stable and support the soils.
Protection of the slope is important if rain occurs which could erode the slope and
cause potential undermining. If a rainfall event occurs then the slope shall be
protected with warming blankets or plastic sheeting to prevent erosion. A
snowfall event should not cause erosion concerns.
Field Observations
McGhie & Betts, Inc. has been retained to be onsite during the excavation at the
west corner of the building to observe the slope and determine if additional
methods are required to prevent damage to the watermain. Our scope of work is
limited to the west corner of the residence and the slope along the easement.
McGhie & Betts, Inc. will be onsite to observe blanket placement, monitor
max/min thermometers if necessary, and to observe the placement of any sheet
piling. After the excavation is completed and fill has been replaced, we will
provide a final letter detailing our observations and the methods used by the
contractor to prevent frost heaving or undermining of the watermain.
Comments
Additional testing related to fill placement and site observations below the bottom
of footing should be addressed with the contractor, our scope of services is limited
to the observation and protection of the watermain pipe.
903 Wild Rose Court, Eagan, Minnesota
MBI #N5423/N9032 Page 5
If you have any questions feel free to call me at (507)- 645 -0964. FYI, I will be
out of the office on Friday, January 30 and Monday, February 2.
Mark W. Osborn, P.E.
Geotechnical Engineer
MW /mwo
��y
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 CO 0 0 0 0 0 0 0 0 0 0 0 0 0
o O� o in - C7 (U o Or. CO N-
o N o 0 0 o o o o o r- n n n
CO CO m CO CO CO CO CO o CO CO CO CO CO 0
0
In
CD
0
0
N
z
O
Q
ce
0.
W
0
o 0 0 _ _ _
0 0
n qO 117 r co N o ON CO N
m m OD CO 0 CO CO CO 03 CO CO n n n N-
CO CO CO CO CO CO CO CO o CO CO CO CO OO CO
0 0 0 0 0 0
o 0 0 0 0 0
0 0 0 0 0 0 0 0
3
w
z
J
0
3
w
z
!—f
z
c H c
CZ
LJ
z
z
z
W
0 ce
4
• 1_
H
0
CY
tJ'.
X 0
D <
CY
4. 0
Z z
Y
F
• Q
Z 0
o o
Q W
N
W 0
J D
W 0
9 0. y
2 . 8
Na
d
O
W
z
z
a
1
7
o�
f
I
�
n
II
�
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 CO 0 0 0 0 0 0 0 0 0 0 0 0 0
o O� o in - C7 (U o Or. CO N-
o N o 0 0 o o o o o r- n n n
CO CO m CO CO CO CO CO o CO CO CO CO CO 0
0
In
CD
0
0
N
z
O
Q
ce
0.
W
0
o 0 0 _ _ _
0 0
n qO 117 r co N o ON CO N
m m OD CO 0 CO CO CO 03 CO CO n n n N-
CO CO CO CO CO CO CO CO o CO CO CO CO OO CO
0 0 0 0 0 0
o 0 0 0 0 0
0 0 0 0 0 0 0 0
3
w
z
J
0
3
w
z
!—f
z
c H c
CZ
LJ
z
z
z
W
0 ce
4
• 1_
H
0
CY
tJ'.
X 0
D <
CY
4. 0
Z z
Y
F
• Q
Z 0
o o
Q W
N
W 0
J D
W 0
9 0. y
2 . 8
Na
d
O
W
z
z
a
1
f
n
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 CO 0 0 0 0 0 0 0 0 0 0 0 0 0
o O� o in - C7 (U o Or. CO N-
o N o 0 0 o o o o o r- n n n
CO CO m CO CO CO CO CO o CO CO CO CO CO 0
0
In
CD
0
0
N
z
O
Q
ce
0.
W
0
o 0 0 _ _ _
0 0
n qO 117 r co N o ON CO N
m m OD CO 0 CO CO CO 03 CO CO n n n N-
CO CO CO CO CO CO CO CO o CO CO CO CO OO CO
0 0 0 0 0 0
o 0 0 0 0 0
0 0 0 0 0 0 0 0
3
w
z
J
0
3
w
z
!—f
z
c H c
CZ
LJ
z
z
z
W
0 ce
4
• 1_
H
0
CY
tJ'.
X 0
D <
CY
4. 0
Z z
Y
F
• Q
Z 0
o o
Q W
N
W 0
J D
W 0
9 0. y
2 . 8
Na
d
O
W
z
z
a
1