60H_ThomasRd_Refraction Testing_2018

July 5, 2018

Mr. Cedric Combo
Century Communities
7400 Carmel Executive Park Drive, Suite 205
Charlotte, North Carolina 28226 Email: [e-mail]

Subject: Summary of Refraction Microtremor Testing
Thomas Road Site Southwest of the Intersection of Thomas Road and Zoar Road Charlotte, North Carolina
SUMMIT Project No. 4319.514

Dear Mr. Combo:
SUMMIT Engineering, Laboratory & Testing, Inc. (SUMMIT) is pleased to submit this
summary data-report for the Thomas Road Site located southwest of the intersection of Thomas
Road and Zoar Road in Charlotte, North Carolina. Refraction Microtremor (ReMi) analysis
of surface wave testing was performed in general accordance with ASTM D-5777 to aid in
determining the estimate depth of rock and determination of the potential for excavation
difficulties along the proposed sewer easement.
SEISMIC SITE CLASSIFICATION
We have evaluated the depth of rock and potential excavation difficulties for this site in general
accordance with the soil profile names and associated shear wave velocities as defined in Table
1615.1.1 of the International Building Code.
A graphical representation of the ReMi test results is attached to this letter.
DIFFICULT EXCAVATION
Based on the results of our ReMi analysis, it appears that the majority of general excavation
Summary of Refraction Microtremor Testing SUMMIT Project No. 4319.514
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for utilities will be possible with conventional excavating techniques. We anticipate that the
residual soils can be excavated using pans, scrapers, backhoes, and front end loaders.
Depending on the location, excavations deeper than approximately 25 to 30 feet may require
specialized equipment and procedures.
The depth and thickness of partially weathered rock, boulders, and rock lenses or seams can
vary dramatically in short distances and between the boring locations; therefore, soft/hard
weathered rock, boulders or bedrock may be encountered during construction at locations or
depths, between the boring locations, not encountered during this exploration. Our experience
in this geologic region is that materials with Shear Wave Velocities less than 1,200 feet per
second (fps) can generally be excavated with heavy-duty equipment such as a Caterpillar D-8
with a single-shank ripper. The actual rippability of these in-place materials is however,
dependent on many factors such as the operator’s skill level, the techniques used during
excavation, degree of weathering within the formation, rock hardness, rock structure (i.e.,
foliations or bedding), jointing and fracture spacing and necessary size or width of excavation.
Blasting and/or removal with impact hammers is typically required for materials with shear
wave velocities greater than 2,500 fps. Materials with shear wave velocities greater than 1,200
fps and less than 2,500 fps are considered marginally excavatable.
The table below may be used as a quick reference for rippability of in-place materials.
Summary of Rippability Based on Shear Wave Velocities
Shear Wave Velocities Soil Profile Anticipated Rippability
600-1,200 fps
Stiff Soil Profile
Array #1 (0-25’) Array #2 (0-29’)
These materials may generally be excavated
with heavy-duty equipment such as a Caterpillar D-8 with a single-shank ripper
1,200-2,500 fps Very Dense Soil and Soft Rock Array #2 (29-33’)
These materials are considered marginally
excavatable, even with heavy-duty equipment.
>2,500 fps
Rock (2,500-5,000 fps)
Array #1 (25-30’) Array #2 (33-35’)
Hard Rock (>5,000 fps)
Array #1 (30-100’) Array #2 (35-100’)
Blasting and/or removal with impact
hammers is typically required to excavate these materials.
*This table is for general information only. Actual rippability is dependent upon many other factors as stated
above.

Summary of Refraction Microtremor Testing SUMMIT Project No. 4319.514
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Care should be exercised during excavations for footings on rock to reduce disturbance to the
foundation elevation. The bottom of each footing should be approximately level. When
blasting is utilized for foundation excavation in rock, charges should be held above design
grades. Actual grades for setting charges should be selected by the contractor and he should
be responsible for any damage caused by the blasting. All loose rock should be carefully
cleaned from the bottom of the excavation prior to pouring concrete. Footing excavations in
which the rock subgrade has been loosened due to blasting should be deepened to an acceptable
bearing elevation.
In our professional opinion, a clear and appropriate definition of rock should be included in
the project specifications to reduce the potential for misunderstandings. A sample definition
of rock for excavation specifications is provided below:
Rock is defined as any material that cannot be dislodged by a Caterpillar D-8
tractor, or equivalent, equipped with a hydraulically operated power ripper (or
by a Cat 325 hydraulic backhoe, or equivalent) without the use of drilling and
blasting. Boulders or masses of rock exceeding ½ cubic yard in volume shall
also be considered rock excavation. This classification does not include
materials such as loose rock, concrete, or other materials that can be removed
by means other than drilling and blasting, but which for any reason, such as
economic reasons, the Contractor chooses to remove by drilling and blasting.

Summary of Refraction Microtremor Testing SUMMIT Project No. 4319.514
Thomas Road Site, Charlotte, North Carolina Error! Reference source not found.
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CLOSURE
We appreciate the opportunity to be of continued service to you on this project. If you have
any questions concerning the information presented herein, or if we can be of further
assistance, please feel free to call us at [phone].
Sincerely yours, SUMMIT Engineering, Laboratory & Testing, Inc.
Robert L. Price, PE
Geotechnical Department Manager
Attachments: Figure 1 – ReMi Profile Run Location Plan
Refraction Microtremor Shear Wave Velocity Test Results
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000
Depth, ftShear-Wave Velocity, ft/s
Vs100' = 2098 ft/s
Thomas Road Property #1, Charlotte, NC:Vs Model
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
4000.00
4500.00
5000.00
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4Rayleigh Wave Phase Velocity,ft/sPeriod, s
Dispersion Curve Showing Picks and Fit
Calculated Dispersion
Picked Dispersion
Thomas Road Property #1, Charlotte, NC: Supportive Illustration
p-f Image with Dispersion Modeling Picks
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000
Depth, ftShear-Wave Velocity, ft/s
Vs100' = 1787 ft/s
Thomas Road Property #2, Charlotte, NC:Vs Model
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4Rayleigh Wave Phase Velocity,ft/sPeriod, s
Dispersion Curve Showing Picks and Fit
Calculated Dispersion
Picked Dispersion
Thomas Road Property #2, Charlotte, NC: Supportive Illustration
p-f Image with Dispersion Modeling Picks