Subgrade Exploration 3-24-08
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SUBGRADE EXPLORATION
FOR
DOH ENTERPRISES SITE
Chanhassen, Minnesota
CITV OF CHArJHASSEt-J
RECEIVED
Allied Project No. 08008
APR 1 [) 2008
March 24, 2008
CHl\NHASSF.N PLANNING Dr=P
INTRODUCTION
This report presents the results of subgrade exploration performed by our firm for the DOH
Enterprises site. This work was requested by Mr. Dave Hansen on March 13, 2008 and authorized
by the same also on March 13, 2008. Our work was performed as described in our proposal for
subgrade exploration dated March 13,2008. -
Four Standard Penetration Test (SPT) borings were put down on the site in order to obtain
information regarding the in-place sub grade materials.
PROJECT INFORMATION
As shown on the site plan which was provided by James R. Hill, Inc, the project site is located on
82nd Street and Peavey Road on the north side of 82nd Street, Chanhassen, Carver County,
Minnesota. The site is just south of a water tower and just east of a Holiday Service Station located
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at the intersection of 82nd Street and State Highway 41. It is approximately 3 acres in size and is
currently vacant land. A commercial dog kennel facility is proposed for the site.
BORING LOCATIONS AND ELEVATIONS
The borings were located and staked in the field by James R. Hill, Inc and they also provided
elevations of the ground surface for each boring location. We were unable to drill boring 1 at the
staked location because the slope was too steep to set up the drill rig. An alternate location 75 feet to
the east and 35 feet south of the staked location was selected. The site plan in the Appendix shows
the boring locations. The ground elevation for boring 1 was determined by shooting the original
location and the new location and adjusting the elevation written on the stake.
FIELD EXPLORATION
A total of 4 Standard Penetration Test (SPT) borings were each put down to a depth of 20 feet.
The borings were put down in accordance with ASTM 1586-84: "Standard Method for
penetration Test and Split-Barrel Sampling of Soils". Using this procedure, a 2" O.D. split barrel
sampler is driven into the soil by a 140-lb weight falling a distance of 30 inches. After an initial
set of6", the number of blows required to drive the sampler an additional 12 inches is known as
the standard penetration resistance or N-value. The N-value provides an indication of the relative
density of cohesionless (coarse grained) soils or of the consistency of cohesive (fine-grained)
soils.
As the samples were obtained in the field, they were visually and manually classified.
Representative portions of the samples were then sealed in clean glass soil jars and returned to
the laboratory for further examination and verification of the field classification. The recovered
soil samples were classified in accordance with the Unified Soil Classification System, ASTM D:
2488-84. A chart illustrating this classification method is included in the appendix to this report.
Logs of the test borings indicating the depth and identification of the various strata, measured
penetration resistances, soil classifications and the results of water level checks are included in
the appendix to this report
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SUBSURFACE CONDITIONS
Boring 1
Boring 1 consisted of 16 inches of clayey topsoil, underlaid by sandy clay to a depth of 21.5
feet. Two 6-inch sand lenses were present between 20 and 21.5 feet of depth.
Boring 2
Boring 2 consisted of 6 inches of clayey topsoil, underlaid by sandy clay to a depth of 21.5
feet.
Boring 3
Boring 3 consisted of 12 inches of clayey topsoil, underlaid by sandy clay to 21.5 feet of
depth. A soft wet clay was present at approximately 17.5 feet of depth and was most likely
due to a sand seam. Since no sample is taken between 16.5 feet and 20 feet, a grab sample of
this material was taken from the auger flight.
Boring 4
Boring 4 consisted of 12 inches of clayey topsoil, underlaid by slightly organic sandy clay to
at least 4 feet of depth, and sandy clay to a depth of21.5 feet. No sample was obtained at 15
feet because a rock was present below the sampler.
N-values ranged from 10 to 38, which indicates that the soil ranged from firm to hard. The N-value
of 56 in boring 4 is considered inaccurate because it was obtained while the sampler was on a rock.
Groundwater was found in boring 2 at 20 feet of depth and in boring 3 at 17.5 feet of depth. It
was at 18'9" at the time of backfill. It should be noted that sufficient time may not have elapsed
for equilibrium conditions to have been achieved in the hollow-stem auger cased bore holes.
Groundwater conditions may vary both seasonally and annually, based on precipitation amounts,
patterns and both surface and subsurface drainage in the local area. Included in the appendix to
this report are logs of the test borings, which describe the conditions, encountered at each drilling
location. The depth of the individual strata of soil may vary at and between the drilling locations
due to unsampled intervals, the occurrence of transitions between soil layers and the natural
variability of the subsurface conditions.
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CONCLUSIONS AND RECOMMENDATIONS
Organic topsoil, peat, organic soils, and any soft soil layers, which may be encountered, should
not be relied upon for support of the proposed commercial footings, slabs or controlled fills that
will support these elements. The soft wet clay layer found at 17.5 feet of depth in boring 3 is
sufficiently deep and limited in thickness that the load from commercial spread footings would
be spread out enough so as not to exceed the bearing capacity, in our opinion.
It should be possible to provide support for the planned structure with conventional spread
footing foundation systems by using excavation and controlled refilling procedures together with
an observational approach. This should require excavation at the boring locations in order to
prepare for the placement of controlled fill to make grade for concrete for footings or slabs.
The non-root infested and inorganic on-site soils would generally be suitable for reuse as
controlled and compacted fill material. The topsoil or other materials, which would not be
suitable for use as controlled fill, may be able to be used as surface fill in the lawn and
landscaping areas. Additional recommendations are presented in the following sections:
1. EXCAVATION
In general, grubbing and stripping operations should remove all significantly organic or root
infested soils from the areas to be worked. Frozen material, soft consistency clays or otherwise
unsuitable soil and debris should be removed. Where undocumented fill or otherwise unsuitable
soils are exposed in the base of excavations which will support slabs, pavements or footings,
these materials should also be removed. Frozen soils resulting from frost penetration may turn
soft upon thawing and would need to be removed
For the support of fill sequences, slabs or footings it will be important to remove unsuitable soils
prior to the placement of the controlled and compacted fill to make grade for concrete for
foundations.
Once the organic topsoil layers and otherwise unsuitable materials have been removed, the
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completed excavations should be observed by an experienced soil engineer or technician and the
conditions judged suitable prior to the placement of controlled and compacted fill to make grade
for concrete for footings or slabs.
2. FOUNDATIONS
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It should be possible to provide support for commercial spread footing foundations systems
using excavation and controlled filling procedures. As mentioned previously, the topsoil and any
uncontrolled fill deposits encountered during the excavation work should not be relied upon for
support of footings, slabs or controlled fills which will support these elements. It will be
important to monitor the conditions exposed in the excavations during the grading work prior to
the placement of fill to make grade for concrete for footings or slabs. Hand auger borings should
be put down in the completed excavations and the exposed conditions judged suitable by an
experienced soil engineer or technician prior to the placement of footings or fill. ITCO Allied
Engineering Co. is capable and available to do this work.
Once the recommendations presented in this report have been implemented, a net allowable
bearing pressure of 2500 pounds per square foot may be utilized for the proportioning of
individual footings. In designing the footings, it is recommended that they be designed to exert
approximately equal pressures to the bearing strata. This should limit total and differential
settlements to 111 and WI respectively.
For frost protection, we recommend that footings in unheated areas be placed at a depth of 48
inches below finished grade. For decks and porches it is recommended that this be increased to
60 inches if the soil is frost susceptible. In heated portions of the buildings where frost
susceptible materials are absent, a depth of 42 inches would be adequate. Where full or partial
basements are utilized, frost depths for garage areas and porch structures should be maintained as
outlined above
3. FILL PLACEMENT
Fill material should be mineral soil, preferably granular, and free of debris, boulders and organic
material. The on-site soils would be suitable for reuse as controlled fill material, with the
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exception of unsuitable soils identified previously.
Fill should be placed and compacted in a manner that will allow complete compaction of the
entire fill layer to a minimum of 95% of the Standard Proctor Density according to ASTM D:
698 in the building pad area. Required compaction should be increased to 98% for fill areas 4
feet and deeper below [mal grade and below all footings. A minimum of one representative field
density test should be performed for each two feet of fill placed at a time in a given work area.
Density tests in mass fill areas should be performed at a rate judged sufficient to represent the fill
sequence as a whole. Where sand fills are to be compacted, smooth "drum" type vibratory
equipment would be preferred, however, a sheepsfoot roller with short wide pads may provide
adequate compaction.
Fill areas should be properly oversized to provide for adequate distribution of the imposed loads.
The fill supporting structural elements should extend at least one foot horizontally beyond the
structure, slab or edge of the footing. Fill surfaces should extend downward and outward on a 1:1
slope to competent soil. If the fill slope is unconfined by other soils, the downward and outward
slope should be flattened and stabilized. Also, no unremedied excavations should be carried out
within the fill oversize areas.
4. FOUNDATION DRAINAGE
Although groundwater was only found in two of the borings at fairly deep levels, backfill zone
drainage should be considered because groundwater levels can fluctuate. Additionally, many
cities require drain tiles regardless of the presence of groundwater. Local building codes should
be checked. Backfill zone drainage, if provided, should be planned and the installation monitored
at the time of construction by an experienced individual who fully understands the intent of these
drainage recommendations.
In planning backfill zone drain tile installation, the invert elevation should be below the level of
the lowest floor slab and the line should be adequately protected from blockage prior to
backfilling by a suitable encapsulation of gravel, (such as MnlDot spec 3149.2 H; "coarse filter
aggregate"), and geotextile separation fabric. In the backfill zones above the drain tile the use of
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granular material is recommended. Sand for this purpose should contain less than 12% passing
the number 200 sieve, (Mn/Dot "select granular borrow"; spec 3149.2 B). Care should be taken
during the backfilling operations to ensure that the drainage materials are not crushed or
deformed. Fill installation in these areas should be initiated with a two-foot lift of the granular
backfill. A two to three foot thick compacted clay cap, with a positive slope away from the
structure, may be placed at the top of the backfill zone to aid in reducing the infiltration of
moisture into this area which would need to be carried by the drain tile system. It should be
noted that the construction of the backfill zone drainage system should be performed with the
same level of care as the foundation wall itself.
5. PAVEMENTS
The results of our work indicate that conditions are suitable for the construction of flexible
bituminous pavements if the design of the pavement section and preparation of the sub grade take
into account the nature of the subsurface soils present. Once the topsoil layers are removed, the
material type most influencing the pavement design would be the sandy clay found in the borings
below the topsoil. A gradation test and P.r. test were done on samples of this soil from borings 1
and 2. Test results indicate it is an AASHTO A-6 soil. A copy of the results is in the appendix.
An R-value of 12 would be suitable for a sub grade constructed of an AASHTO A-6 soil. The
MnDOT Road Design Manual indicates that the minimum granular equivalent for a 7 -ton design
is a minimum of 11.5 inches of G.E. One possible pavement section for a 7 ton design would be
1.5 inches of bituminous plant mixed wear course, (Mn/DOT 2360), 1.5 inches of plant mixed
base course, (Mn/DOT 2360), and 5.5 inches of class 5 aggregate base, (Mn/DOT 3138). This
section would meet a G.E. of 11.5 inches.
In using the R-value method for pavement design, it is essential that the sub grade be constructed
of uniform soil across the pavement section and compacted at a moisture content and to a density
in accordance with MN/DOT spec. 2105 and be capable of passing test rolling, in accordance
with MN/DOT Spec. 2111. The completed sub grade should be observed and judged suitable by
an experienced individual prior to the placement ofthe aggregate base or paving. Compaction of
the upper 3 feet of the sub grade to a minimum of 100% of the standard proctor density within
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appropriate moisture limits, (65 to 102% of optimum), should provide the necessary stability
required for proof rolling.
6. FINAL SITE TOPOGRAPHY
The final soil surfaces should be graded to provide adequate drainage away from structures and
pavements in order to minimize deleterious effects associated with water infiltration. The areas
adjacent to footing walls should be adequately compacted, (not loosely placed), and provided
with drainage outlets to avoid this zone acting as a "sump" and creating nuisance water
conditions.
Compliance with the building code provision for positive surface drainage away from the
structure should also aid in reducing the quantity of infiltration into the backfill zones adjacent to
foundation walls.
STANDARD OF CARE
The recommendations contained in this report are professional opinions. These opinions were
arrived at in accordance with generally accepted engineering practices currently in use at this
time, location and for projects of this type. Other than this, no warranty is implied or intended.
Soil samples recovered from the test borings will be retained in our offices for a period of thirty
days from the date of this report. After that time they will be discarded unless prior written
instructions to the contrary are received.
I hereby certify that this report and/or specification has been prepared by me or under my direct
supervision and that I am a duly registered Professional Engineer under the laws of the State of
Minnesota. If you have any further questions or we can be of any further assistance, please do
not hesitate to phone or write.
ITCO ALLIED ENGINEERING COMPANY
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Robert Sullentrop, P.E.
Project Engineer
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AlliED TEST DRilliNG COMPANY
PROJECT: DOH Enterprises Site NUMBER: 08008
82nd Street & Peavey Road PAGE 1 OF 1
SURFACE ELEVATION LOG OF BORING
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22.0 ------------ - - _ _ _ _ _ _ _ .1 _ _ _1_ _ _ L _ L J ..J J 1.1
WATER-LEVEL CHECKS METHOD
DATE TIME SAMPLED TO CASING CAVE-IN WATER SPT
03/20/2008 1:15 21.5' 20' 17' 7" None
03120/2008 ~~,... ~~. ~~
03/20/2008
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Craig CME-55
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ALLIED TEST DRILLING COMPANY
PROJECT: DOH Enterprises Site NUMBER: 08008
82nd Street & Peavey Road PAGE 1 OF 1
SURFACE ELEVATION LOG OF BORING
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------------ - - _______~__~___L_L .J ~I
WATER-LEVEL CHECKS METHOD
DATE TIME SAMPLED TO CASING CAVE-IN WATER SPT
03120/2008 11:40 21.5' 20' 17' 4" 20'
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03120/2008 03/2012008
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AlliED TEST DRilliNG COMPANY
PROJECT: DOH Enterprises Site NUMBER: 08008
82nd Street & Peavey Road PAGE 1 OF 1
SURFACE ELEVATION LOG OF BORING
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22.0 ------ - -------------------------------- ------------ - - ------- ___'___L_L..l 1.1
WATER-LEVEL CHECKS METHOD
DATE TIME SAMPLED TO CASING CAVE-IN WATER SPT
03/20/2008 9:15 21.5' 20' 19' 0" 17.5'
10:10 18' 9" -- II::U
03/20/2008 0312012008
Craig KIl;; CME-55
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AlliED TEST DRilliNG COMPANY
'PROJECT: DOH Enterprises Site NUMBER: 08008
82nd Street & Peavey Road PAGE 1 OF 1
SURFACE ELEVATION LOG OF BORING
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-------------------------------- ------------ - - ------- ___1__- - JJ l.1
WATER-LEVEL CHECKS METHOD
DATE TIME SAMPLED TO CASING CAVE-IN WATER SPT
03/20/2008 3:10 21.5' 20' 17' 8" None
~ 03/2012008 "'.... ..............~
03/2012008
Craig RIG
CME-55
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