December 10, 2013
Terra Nova Engineering, Inc
815 South 25th Street
Colorado Springs, Colorado 80904
Attention: Ms. Luanne Ducett, P.E
Subject:
UCCS Greenhouse Temporary Parking Lot
University of Colorado – Colorado Springs
Cragmor Village Road
Colorado Springs, Colorado
CTL|T Project No. CS18197.000-135
As requested, we conducted a subgrade investigation for the design and
construction of a temporary parking lot to the south of the UCCS Greenhouses in
Colorado Springs, Colorado. This letter summarizes our alternative sections and
recommendations for construction of the driveway.
INVESTIGATION
The site is bordered by newly-built Regent Circle on the south and Cragmor
Village Road on the north. There are several abandoned homes in the area, one of
which is in the parking lot area. The overall site slopes to the southeast at grades
of less than 10 percent. There is about 20 feet of elevation change across the site.
The near-surface subgrade soils were evaluated by drilling three (3) borings to
depths of 4 feet below the existing grade using a continuous flight auger and a
CME 55 truck mounted drill rig on November 26, 2013. Figure 1 shows the
approximate location of subgrade samples. The samples were returned to the
laboratory where index property testing (gradation and Atterberg Limits) were
performed.
Materials encountered consisted of silty to clayey sands. The soils
encountered in boring S-3 consist of a clayey sand fill. The materials classify
under the AASHTO system as A-1-b and A-2-4. Our experience with these types
of soils indicates Hveem stabilometer values (“R” values) typically range from 30
to 50. We have used a design “R” value of 30 in our design. Laboratory data is
presented in Fig. Nos. 1 and 2 and summarized in Table I.
5170 Mark Dabling Blvd | Colorado Springs, Colorado 80918 | Telephone: 719-528-8300 Fax: 719-528-5362
DESIGN
We understand the parking lot will service mainly passenger vehicle traffic
and once a week trash trucks over its expected life span. We based our design on
a Daily Traffic Number (DTN) of 2 for a projected life span of 10 years. These
values equate to an 18-kip, single-axle load (ESAL) of 7,300 We have provided
surfacing options consisting of asphalt concrete placed directly on a prepared
subgrade, 2) asphalt over aggregate base course and 3) a gravel surface
consisting of base course or a re-cycled material of either asphalt or concrete
meeting CDOT classifications for Class 5 or 6. Surfacing options are presented
below in Table I.
TABLE I
OPTION
SURFACING THICKNESS
Asphalt (AC) placed directly on a prepared
subgrade
Asphalt (AC) over Aggregate Base Course
(ABC)
Granular Surface
3.5 inches AC
3 inches AC+ 4 inches ABC
12 inches
ROADWAY CONSTRUCTION
There is the possibility of settlement of the fill material over the long term.
Since this is a temporary parking lot, and the extent of the fill is unknown, the
owner may wish to leave these soils in place. We can provide observations during
excavation on the extent of the fill and recommendations for replacement if it is
determined the fill will be removed.
Imported fill, if needed, should be of a classification equal to or better than
the on-site soils. The subgrade should be scarified to a depth of at least 8 inches,
moisture conditioned to within 2 percent of optimum moisture, and compacted to
95 percent of maximum modified Proctor dry density (ASTM D 1557).
Our design considers that roadway construction is completed in accordance
with the City of Colorado Springs standard specifications. The specifications
contain requirements for the quality of materials and the construction practices
used. Of particular importance are those recommendations directed towards
subgrade and base course compaction and proofrolling.
TERRA NOVA ENGINEERING, INC.
UCCS GREENHOUSE TEMPORARY PARKING LOT
CTL|T PROJECT NO. CS18197-135
S:\CS18000-18499\CS18197.000\135\2. Reports\CS18197-135-L1.doc
2
HYDROMETER ANALYSIS
4 MIN.
1 MIN.
*200
*100
*50 *40 *30
*16
CLEAR SQUARE OPENINGS
*10 *8
*4
3/8"
3/4"
1½"
3"
5" 6" 8"
0
90
10
80
20
70
30
60
40
50
50
40
60
30
70
20
80
10
90
0
.001
0.002
.005
.009
.019
.037
.074
.149
.297
.590
1.19 2.0 2.38
0.42
DIAMETER OF PARTICLE IN MILLIMETERS
FINE
COARSE
PERCENT PASSING
FINE
36.1
COARSE
GRAVEL
0%
SILT & CLAY
18 %
PLASTICITY INDEX
76.2
100
127 200
152
COBBLES
82 %
21 %
4%
SAND
LIQUID LIMIT
SIEVE ANALYSIS
HYDROMETER ANALYSIS
TIME READINGS
4 MIN.
19.1
GRAVEL
MEDIUM
SAND, CLAYEY, SILTY (SC-SM) (A-1-b)
S - 1 AT 0-4 FEET
60 MIN. 19 MIN.
9.52
SANDS
CLAY (PLASTIC) TO SILT (NON-PLASTIC)
25 HR. 7 HR.
45 MIN. 15 MIN.
100
4.76
U.S. STANDARD SERIES
1 MIN.
*200
*100
*50 *40 *30
*16
CLEAR SQUARE OPENINGS
*10 *8
*4
3/8"
3/4"
1½"
3"
5" 6" 8"
0
90
10
80
20
70
30
60
40
50
50
40
60
30
70
20
80
10
90
0
.001
0.002
.005
.009
.019
PERCENT RETAINED
60 MIN. 19 MIN.
U.S. STANDARD SERIES
.037
.074
CLAY (PLASTIC) TO SILT (NON-PLASTIC)
.149
.297
.590
1.19 2.0 2.38
0.42
DIAMETER OF PARTICLE IN MILLIMETERS
4.76
9.52
SANDS
FINE
SAND, SILTY (SM) (A-1-b)
S - 2 AT 0-4 FEET
TERRA NOVA ENGINEERING, INC.
UCCS GREENHOUSE TEMPORARY PARKING LOT
CTL|T PROJECT NO. CS18197-135
S:\CS18000-18499\CS18197.000\135\2. REPORTS\CS18197-135_GRADATION.XLS
MEDIUM
19.1
36.1
76.2
PERCENT RETAINED
PERCENT PASSING
SIEVE ANALYSIS
TIME READINGS
25 HR. 7 HR.
45 MIN. 15 MIN.
100
100
127 200
152
GRAVEL
COARSE
FINE
GRAVEL
0%
SILT & CLAY
14 %
PLASTICITY INDEX
COARSE
COBBLES
SAND
LIQUID LIMIT
Gradation
Test Results
86 %
21 %
3%
FIG. 2
HYDROMETER ANALYSIS
4 MIN.
1 MIN.
*200
*100
*50 *40 *30
*16
CLEAR SQUARE OPENINGS
*10 *8
*4
3/8"
3/4"
1½"
3"
5" 6" 8"
0
90
10
80
20
70
30
60
40
50
50
40
60
30
70
20
80
10
90
0
.001
0.002
.005
.009
.019
.037
.074
.149
.297
.590
1.19 2.0 2.38
0.42
DIAMETER OF PARTICLE IN MILLIMETERS
FINE
COARSE
PERCENT PASSING
FINE
36.1
COARSE
GRAVEL
8%
SILT & CLAY
28 %
PLASTICITY INDEX
76.2
100
127 200
152
COBBLES
64 %
26 %
9%
SAND
LIQUID LIMIT
SIEVE ANALYSIS
HYDROMETER ANALYSIS
TIME READINGS
4 MIN.
19.1
GRAVEL
MEDIUM
SAND, CLAYEY, SL. GRAVELLY (SC) (A-2-4)
S - 3 AT 0-4 FEET
60 MIN. 19 MIN.
9.52
SANDS
CLAY (PLASTIC) TO SILT (NON-PLASTIC)
25 HR. 7 HR.
45 MIN. 15 MIN.
100
4.76
U.S. STANDARD SERIES
1 MIN.
*200
*100
*50 *40 *30
*16
CLEAR SQUARE OPENINGS
*10 *8
*4
3/8"
3/4"
1½"
3"
5" 6" 8"
0
90
10
80
20
70
30
60
40
50
50
40
60
30
70
20
80
10
90
0
.001
0.002
.005
.009
.019
PERCENT RETAINED
60 MIN. 19 MIN.
U.S. STANDARD SERIES
.037
.074
CLAY (PLASTIC) TO SILT (NON-PLASTIC)
.149
.297
.590
1.19 2.0 2.38
0.42
DIAMETER OF PARTICLE IN MILLIMETERS
4.76
9.52
SANDS
FINE
MEDIUM
S:\CS18000-18499\CS18197.000\135\2. REPORTS\CS18197-135_GRADATION.XLS
36.1
76.2
100
127 200
152
GRAVEL
COARSE
FINE
GRAVEL
SILT & CLAY
PLASTICITY INDEX
TERRA NOVA ENGINEERING, INC.
UCCS GREENHOUSE TEMPORARY PARKING LOT
CTL|T PROJECT NO. CS18197-135
19.1
PERCENT RETAINED
PERCENT PASSING
SIEVE ANALYSIS
TIME READINGS
25 HR. 7 HR.
45 MIN. 15 MIN.
100
COARSE
%
%
COBBLES
SAND
LIQUID LIMIT
Gradation
Test Results
%
%
%
FIG. 3
TABLE A-I
SUMMARY OF LABORATORY TESTING
CTL|T PROJECT NO. CS
ATTERBERG LIMITS PASSING WATER
MOISTURE LIQUID PLASTICITY NO. 200 SOLUBLE
SUBGRADE DEPTH GROUP CONTENT LIMIT
INDEX
SIEVE SULFATES
SAMPLE (FEET) NAME
(%)
(%)
(%)
(%)
(%)
S-1
0-4
A
4.1
21
4
18
S-2
0-4
A
4.7
21
2
14
<0.1
S-3
0-4
B
7.8
26
9
28
* SWELL MEASURED WITH 200 PSF APPLIED PRESSURE.
CLASSIFICATION
GROUP
INDEX
AASHTO
UNIFIED
0
0
0
A-1-b
A-1-b
A-2-4
SC-SM
SM
SC
DESCRIPTION
SAND, CLAYEY, SILTY
SAND, SILTY
SAND, CLAYEY, SLIGHTLY GRAVELLY
Page 1 of 1