Waterview - Geotech Pg6 &10 - SBI Response 080824
10
Another alternative for reducing frost heave is to support the slabs on frost depth footings. A
void space of at least 4 inches should be provided between the slab and the underlying soil to
allow the soil to heave without affecting the slabs.
4.8 Site Grading and Drainage
We recommend the site be graded to provide positive run-off away from the proposed
buildings. We recommend landscaped areas be sloped a minimum of 6 inches within 10 feet
of the building and slabs be sloped a minimum of 2 inches. In addition, we recommend
downspouts with long splash blocks or extensions.
We recommend the lowest floor grades be constructed to meet City of Chanhassen
requirements with respect to groundwater separation distances.
4.9 Utilities
We anticipate that new utilities will be installed as part of this project. We further anticipate
that new utilities will bear at depths ranging from about 7 to 10 feet below the ground surface.
At these depths, we anticipate that the pipes will bear on compacted engineered fill or native
glacial till soils, which in our opinion are suitable for pipe support. We recommend removing
all vegetation, topsoil and any soft or otherwise unsuitable soils, if any, beneath utilities prior
to placement.
We recommend bedding material be thoroughly compacted around the pipes. We recommend
trench backfill above the pipes be compacted to a minimum of 95 percent beneath slabs and
pavements, the exception being within 3 feet of the proposed pavement subgrade, where 100
percent of standard Proctor density is required. In landscaped areas, we recommend a
minimum compaction of 90 percent.
Groundwater was encountered in the borings at depths ranging from about 5 to 20 feet below
the ground surface. See Section 4.4 for dewatering considerations.
4.10 Estimated Infiltration Rates
We anticipate that stormwater management areas, such as ponds or rain gardens, could be
constructed as part of the project. Information regarding the locations or depths of any ponds
or rain gardens was not provided. Below the topsoil the soils encountered in the borings
consisted of clayey sand and sandy lean clay that correspond to the ASTM Classifications of
SC and CL, respectively. It is our opinion that the infiltration rates presented in Table 5, which
were obtained from the Minnesota Storm Water Manual, can be used for infiltration basin
design.
Table 5. Estimated Design Infiltration Rates
Soil Description & ASTM
Classification
Hydrologic Soil
Group
Estimated Design
Infiltration Rate (in/hr.)
Clayey Sand (SC) D 0.06
Sandy Lean Clay (CL) D 0.06
6
The underlying stiffer/denser glacial till soils, in our opinion are suitable for foundation
support.
Soil moisture contents ranged from about 20 to 49 ½ percent indicating that the soils were
likely above their assumed optimum moisture content based on the standard Proctor test.
Soils that will be excavated and reused as fill or backfill will likely require some moisture
conditioning (drying) to meet the recommended compaction levels. Summer months are
typically more favorable for drying wet soils.
Groundwater was encountered in four of the soil borings while drilling and sampling at
depths of about 5 to 20 feet below the ground surface, corresponding to elevations ranging
from about 963 to 973 feet above mean sea level. Based on the Grading & Erosion Control Plan
the lowest floor slabs for the proposed homes will bear at elevation ranging from 975.1 to 981.4
which are above the water levels observed in the boring. We do not anticipate that
groundwater will be encountered during foundation construction.
Soil corrections are anticipated to extend about 7 feet below the ground surface at boring SB-
3. With perched water encountered in boring SB-3 at about 5 feet below the ground surface,
groundwater could be encountered during soil corrections and dewatering could be required.
If groundwater is encountered then the successful contractor may need to develop and submit
a dewatering plan.
The following sections provide recommendations for foundation design and construction.
4.3 Site Grading Recommendations
Excavation We recommend that all vegetation, topsoil and any soft or otherwise unsuitable
soils, if encountered, be removed from below the proposed building, utility and oversize areas.
We recommend that all remnants of the structures including footings, floor slabs, foundation
walls, exterior flatwork and underground utilities be removed from within the proposed
building, utility and oversize areas. Table 3 summarizes the anticipated excavation depths at
the soil boring locations. Excavation depths may vary and could be deeper.
Table 3. Anticipated Excavation Depths
Boring
Number
Measured
Surface
Elevation
(feet)
Anticipated
Excavation
Depth (feet)*
Anticipated
Excavation
Elevation (feet)*
Approximate
Groundwater
Elevation
(feet)*
SB-1 977.1 7 970 NE
SB-2 977.8 4 ½ 973 ½ 963
SB-3 972.2 7 965 967
SB-4 984.4 7 977 ½ 964 ½
SB-5 984.2 4 ½ 979 ½ NE
SB-6 980 4 ½ 975 ½ NE
SB-7 987.5 7 985 ½ 973
* = Excavation depths and elevations were rounded to nearest ½ foot.