HomeMy WebLinkAboutPD 2020-0034; HARBOR POINTE SLOPE REPAIR; FINAL SOILS REPORT; 2021-06-24
As-Built Soils/Compaction Report
Harbor Pointe HOA
Slope Restoration below 6887 and 6899 Watercourse Drive
Project No. PD 2020-0034, Drawing No. 526-9A
Carlsbad, California
prepared for:
Harbor Pointe HOA
c/o Ms. Joanne Diaz
Curtis Management Company
5050 Avenida Encinas, Suite 160
Carlsbad, CA 92008
by:
TerraPacific Consultants, Inc.
4010 Morena Boulevard, Suite 108
San Diego, CA 92117
June 24, 2021
File No. 20-065.1
4010 Morena Boulevard, Suite 108 • San Diego, CA 92117 • (858) 521-1190 • (858) 521-1199 fax • terrapac.net
Harbor Pointe HOA June 24, 2021
c/o Ms. Joanne Diaz File No. 20-065.1
Curtis Management Company
5050 Avenida Encinas, Suite 160
Carlsbad, CA 92008
Subject: As-Built Soils/Compaction Report
Harbor Pointe HOA
Slope Restoration below 6887 and 6899 Watercourse Drive
Project No. PD 2020-0034, Drawing No. 526-9A
Carlsbad, California
Dear Ms. Diaz:
TerraPacific Consultants, Inc. (TCI) has completed field observation and testing services for
the subject slope restoration. These services included inspection of the keyway and back
cuts, observation of geogrid reinforcing layers, compaction testing of engineered fill, and
review of the subsurface drainage facilities within the restoration area.
Based on our observations and testing, it is our opinion that the geotechnical aspects of the
slope restoration have been completed in general conformance with the recommendations
provided in our referenced report and the approved plans. Further discussion regarding our
site observations, compaction test results, and recommendations are presented in the
accompanying report.
We appreciate the opportunity to be of service. If you should have any questions, please
do not hesitate to contact the undersigned.
Sincerely,
TerraPacific Consultants, Inc.
Dylan J. Thomas, PG 9857 Matthew H. Marquez, PE 70072
Associate Geologist Senior Engineer
Distribution: Ms. Joanne Diaz – Curtis Management Co.
Mr. Mike Bailey – City of Carlsbad
Mr. Brian Saltzman – TSAC Engineering
TABLE OF CONTENTS
1.0 INTRODUCTION ............................................................................................................. 1
1.1 Purpose and Scope ............................................................................................ 1
1.2 Site Description .................................................................................................. 1
2.0 GRADING AND COMPACTION ..................................................................................... 2
2.1 General Procedure ............................................................................................. 2
2.2 Site Preparation.................................................................................................. 2
2.3 Slope Keyway ..................................................................................................... 2
2.4 Keyway Drain System ........................................................................................ 3
2.5 Slope Reconstruction ......................................................................................... 3
2.6 Compaction Tests .............................................................................................. 4
2.7 Laboratory Testing ............................................................................................. 4
3.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................... 4
3.1 Conclusions ........................................................................................................ 4
3.2 Planting and Maintenance ................................................................................. 4
4.0 CLOSURE ....................................................................................................................... 5
4.1 Limitations .......................................................................................................... 5
APPENDICES:
Appendix A – Figures
Appendix B – Results of Field Density Tests
Appendix C – Laboratory Testing Results
Harbor Pointe Slope Restoration • 6887 & 6899 Watercourse Drive • File No. 20-065.1 • June 24, 2021
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1.0 INTRODUCTION
1.1 Purpose and Scope
The purpose of this report is to describe our site observations and present the results of
compaction testing during the restoration/earthwork activities for the subject slope, which
experienced a surficial failure in April 2020. The restoration, as described in this report, was
conducted to reconstruct the slope to the pre-failure configuration approved by the City of
Carlsbad.
The scope of our work included research of geologic/geo-hazard maps pertinent to the site,
review of original development documents available from the City of Carlsbad, on- and off-
site meetings, field observations and compaction testing, laboratory analysis of the fill
materials, engineering/geologic evaluation, and preparation of this report.
1.2 Site Description
The surficial failure area is located behind 6887 to 6899 Watercourse Drive on a west-facing,
descending slope situated north of Harbor Point Road. The approximate location of the site
is presented on the attached Site Location Map, Figure 1 in Appendix A. From the top, along
the rear property lines of Lots 49 through 52, the slope descends a maximum of
approximately 35 feet at 2:1 (horizontal: vertical) inclination to the rear property lines of the
homes along the toe of slope on Shearwaters Drive (Lots 53 through 55).
The surficial failure consisted of two well-defined scarps generally located between the
midpoint and top of the slope with associated debris and tension cracks. The larger of the
two scarps was located below 6895 Watercourse Drive and roughly measured 30 feet wide
by 16 feet long by 1.5-to 2.5 feet deep. The smaller scarp was below 6899 Watercourse Drive
and was approximately 10 feet wide by 6 feet wide by 1.5 feet deep. Soil/debris from the
failure flowed into the backyards of 6892 and 6896 Shearwaters Drive. The restored failure
area also included tension cracks that developed north of the scarps on the slope below the
southern portion of 6887 Watercourse Drive and most of 6891 Watercourse Drive. The
tension cracks were indicators of impending surficial failure and were generally aligned with
the defined head scarps located to the south.
Development documents related to the earthwork indicate the lots were graded in the mid-
1980s. Based on the grading plans and the subsurface investigation described in our
referenced report dated May 29, 2020, the subject slope is entirely composed of engineered
fill. The originally planned grading configuration of the slope was to be engineered fill over
cut soil/native bedrock. However, due to seepage conditions reportedly occurring at the
bedrock contact during grading, the lower portion of the slope was over-excavated. It
replaced as stability fill equipped with a subdrain system, which reportedly discharges near
Shearwaters Drive and Bluewater Road.
Harbor Pointe Slope Restoration • 6887 & 6899 Watercourse Drive • File No. 20-065.1 • June 24, 2021
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2.0 GRADING AND COMPACTION
2.1 General Procedure
In general, the slope restoration earthwork consisted of removing vegetation, failure debris,
and loose soil, followed by the placement of compacted fill to reconstruct the slope. Removals
were made to expose and bench into competent engineered fill with a keyway at the base of
the restoration area. Reinforcing geogrid was placed within the engineered fill mass to
provide additional stability for the restored slope area. Drainage facilities consisting of a
subdrain located at the heel of the keyway and a series of vertical chimney drains along the
back cut of the engineered fill mass were also constructed.
Groundforce performed earthwork activities and related soil compaction for the slope
restoration. Observation and testing during grading operations, as described in this report,
were conducted between April 20, 2021, and May 21, 2021. A representative from our office
observed removals benching and fill placement operations, including performing field density
tests, observation of the drainage facilities constructed, review placement of the geo-grid
reinforcement, and inspection of the keyway. Descriptions of the soil materials encountered,
grading procedures, and compaction test results are further described in the following
sections.
2.2 Site Preparation
Prior to placement of the new engineered fill, removals into competent fill soils were
performed at the surficial failure area. The removals were conducted near the mid-slope at
the base of the failure area. Removal operations continued as the restoration progressed up
the slope, which included benching into competent engineered fill. The engineered fill
encountered and primarily utilized for fill consisted of reddish-brown clayey sand. The
approximate limits of the slope restoration area are presented on the attached Geotechnical
Plan, Figure 2 in Appendix A.
2.3 Slope Keyway
A keyway for the new engineered fill was excavated into competent existing fill material at
the base of the restoration area. The dimensions of the keyway are approximately 8.5 feet
wide by 120 feet long. The keyway bottom was inclined at a minimum of 2 percent into the
slope. Prior to placement of compacted fill, the exposed surface was scarified, moisture-
conditioned to optimum moisture content or slightly above, and compacted in-place to a
minimum of 90 percent of the laboratory maximum dry density (ASTM D-1557). The
approximate keyway location is shown in Figure 2 in Appendix A.
Harbor Pointe Slope Restoration • 6887 & 6899 Watercourse Drive • File No. 20-065.1 • June 24, 2021
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2.4 Keyway Drain System
A heel drain that consists of a 4-inch diameter perforated pipe surrounded by 3/4-inch gravel
and wrapped in filter fabric was installed at the back of the keyway. The heel drain was
constructed with high points at the north and south ends with flow toward the center at a
minimum 1 percent gradient. The subdrain outlet is located near the toe of the slope and
consists of a perforated spreader pipe.
In addition to the heel drain, a series of geo-composite chimney drains were installed vertically
up the back of the restoration area to help collect potential groundwater seepage that may
develop and migrate toward the back of the recompacted fill mass during periods of
prolonged rainfall/saturated conditions. The approximate heel drain, outlet pipe, and chimney
drains locations are shown on the Geotechnical Plan, Figure 2 in Appendix A.
2.5 Slope Reconstruction
Once the slope keyway was constructed, and the heel drain was installed, fill was placed and
compacted from the bottom up. The earth materials utilized for compacted fill generally
consisted of the existing fill materials encountered during excavation of the site. Processed
existing fill material utilized for the slope restoration was previously tested to verify the
minimum shear strength requirements specified.
Prior to fill placement and compaction, the soil material was moisture-conditioned and
blended as needed, placed in loose lifts approximately 6 to 8 inches in thickness, and
mechanically compacted with the remote-controlled vibratory sheep foot compactor, ride-
along vibratory sheep foot compactor, and/or mechanical tamper to at least 90 percent relative
compaction per the maximum dry density value determined in accordance with the ASTM D-
1557 test method (see Section 2.6 of this report). Each succeeding fill lift was treated similarly.
As the fill was brought up, the slope backcut was benched into competent fill, and geogrid
reinforcement layers were placed within the fill mass at an approximate vertical spacing of 24
inches. The type of geogrid reinforcement used was Tencate Miragrid 3XT.
Upon completion of fill placement, the slope face within the repair area was trimmed back
with a Komatsu excavator, wheeled with the compaction wheel, and further compacted by
track walking.
Harbor Pointe Slope Restoration • 6887 & 6899 Watercourse Drive • File No. 20-065.1 • June 24, 2021
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2.6 Compaction Tests
Based upon our testing and observations, the fill placed for the subject repair was compacted
to a minimum of 90 percent of the laboratory maximum dry density (ASTM D-1557), as
required. Compaction testing was conducted utilizing the sand cone test method (ASTM D-
1556) and Campbell Pacific Nuclear Test Gauges (ASTM D-2922 and D-3017). The compacted
fill was tested periodically as construction progressed. Testing was conducted at
approximately 12-inch to 24-inch vertical intervals. In general, the testing indicates the fill
construction met the minimum compaction standards required for the project.
The results of our field density tests are tabulated in Table 1 in Appendix B. Approximate
locations of the tests are indicated on the Geotechnical Plan, Figure 2 in Appendix A. The test
locations and elevations are approximate, based on our interpretation of the available plans.
It should be mentioned that the compaction test results are considered to be representative
of the conditions where the test was performed. Compaction levels beyond the locations
tested may vary.
2.7 Laboratory Testing
Supplemental laboratory tests were performed to support the construction monitoring and
provide a basis for our evaluation of compacted fill. The laboratory program included
determining the maximum dry density and optimum moisture content of soils utilized as fill.
The testing was performed in accordance with the ASTM D-1557 test procedure (modified
Proctor). All testing phases were conducted in general accordance with applicable ASTM
specifications and/or other accepted test methods. A summary of the laboratory test results
are available in Appendix C.
3.0 CONCLUSIONS AND RECOMMENDATIONS
3.1 Conclusions
Based on our observation and testing results, it is our opinion that the described earthwork
has been completed in general conformance with the recommendations contained in our
May 29, 2020 report, the referenced plans, and the intentions of this office. If required, a
formal survey of the repair area may be completed by others to prepare the as-built grading
plan.
3.2 Planting and Maintenance
The subject slope area is considered surficially and grossly stable and anticipated to remain
so under normal conditions, provided that erosion control measures are implemented as
soon as possible, i.e., erosion control mat, planting, etc. It is recommended that deep-
rooting, drought-tolerant trees, shrubs, and ground cover be used.
Harbor Pointe Slope Restoration • 6887 & 6899 Watercourse Drive • File No. 20-065.1 • June 24, 2021
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Some routine maintenance should be anticipated during the life of this project. This should
include maintaining grades, particularly along the top of the slope, so that water runoff is not
directed toward the slope. The responsible party should consider improving the surface
drainage conditions along the rear property line of Lot 53 (6896 Shearwaters Drive), e.g.,
install additional surface drainage facilities and/or a short retaining wall with a freeboard to
direct water around the lot as the original design of the project intended. Disturbed grades
due to burrowing animal activity or the uncontrolled action of water should be restored as
soon as possible to avoid channeling concentrated water into the slope. Additionally, regular
maintenance of the site drainage and irrigation systems for the slope should be conducted
to avoid any leakage due to disrepair. Adjust irrigation schedules as needed seasonally with
climatic conditions to prevent excessive drying or wetting of slope.
4.0 CLOSURE
4.1 Limitations
It is our opinion, within the scope of work defined for us by our client, that we have exercised
a degree of care which equals or exceeds that presently maintained by other professionals
in the field of geotechnical engineering and engineering geology; and, to the best of our
ability, have performed sufficient observations and testing to provide a rational basis for our
opinion that grading at this site was performed in general accordance with the
recommendations and provisions of the project specifications. No warranties are expressed
nor implied.
In reviewing the data, opinions, conclusions, and recommendations presented in this report,
it should be recognized that our services do not constitute a guarantee that the grading
contractor has performed his work in strict accordance with the recommendations and/or
specifications. In addition, no representations are made as to the quality or extent of
materials not observed by us, for any subsequent change to this site, or the failure of others
to properly repair damages by the uncontrolled actions of water.
* * * TerraPacific Consultants, Inc. * * *
APPENDIX A
Figures
SITE LOCATION
SITE LOCATION
5
5
5
78
Paseo Del NortePaseo Del NorteCarlsba
rd
B
lvd
Poinsettia Lane
Carlsbad
REFERENCE: Google Maps
NSite Location Plan Figure 1
LOCATION:6887-6899 Watercourse Drive
Carlsbad, CA
4010 Morena BoulevardSuite 108San Diego CA 92117858-521-1190
Harbor Pointe
File No. 20-065.1
June 2021
WATERCOURSE DRIVESHEARWATERS DRIVET-3
T-4
T-1
T-2
P-104.2
P-104.0
P-136.2
P-137.8
6895
(LOT 52)
6891
(LOT 51)
6887
(LOT 50)
6892
(LOT 55)
6888
(LOT 56)
A '
(Qop2-4)Qcf
(Td)Qls/Qcf Approximate location of slope restoration.
Approximate location of keyway for slope restoration
Tightline subdrain to spreader pipe discharge
Approximate location of subdrain system for slope restoration
Approximate location of drainage panels along back cut
Approximate location of compaction test
LEGEND
0 2010
APPROX. SCALE IN FEET
KEYWAY N27
REFERENCE:Grading Plan for Harbor Pointe Slope Repair,Sheet 2, prepared by TSAC Engineering
Geotechnical Plan4010 Morena BoulevardSuite 108San Diego CA 92117858-521-1190 Figure 2Harbor Pointe Construction
File No. 20-065.1June 2021
28
18 3131R
2323R
32
29
5
7
82
4
1
6
35
21
30
20
3
13
15
10
11
17
19
27
33
12
149
34
24
26
25
22
32R
APPENDIX B
Table
Field
Density
(PCF)
Field
Moisture
(%)
Max. Dry
Density
(lbs/cu. ft.)
Opt.
Moisture
(%)
Relative
Compaction
(%)
Pass/Fail
1 4/21/2021 118.0 117.2 9.4 A 127.5 9.5 92%Pass
2 4/21/2021 118.0 115.0 9.8 A 127.5 9.5 90%Pass
3 4/22/2021 120.0 116.8 9.6 A 127.5 9.5 92%Pass
4 4/22/2021 120.0 115.5 10.4 A 127.5 9.5 91%Pass
5 4/26/2021 122.0 114.6 9.8 A 127.5 9.5 90%Pass
6 4/26/2021 122.0 115.1 10.7 A 127.5 9.5 90%Pass
7 4/27/2021 124.0 115.0 9.9 A 127.5 9.5 90%Pass
8 4/27/2021 124.0 115.6 10.5 A 127.5 9.5 91%Pass
9 4/29/2021 118.0 116.4 9.7 A 127.5 9.5 91%Pass
10 4/29/2021 118.0 115.8 9.6 A 127.5 9.5 91%Pass
11 5/3/2021 120.0 118.6 9.7 A 127.5 9.5 93%Pass
12 5/3/2021 120.0 119.3 10.2 A 127.5 9.5 94%Pass
13 5/3/2021 120.0 115.2 9.6 A 127.5 9.5 90%Pass
14 5/4/2021 122.0 114.8 9.5 A 127.5 9.5 90%Pass
15 5/4/2021 122.0 115.4 9.7 A 127.5 9.5 91%Pass
16 5/4/2021 122.0 114.5 9.9 A 127.5 9.5 90%Pass
17 5/5/2021 124.0 117.0 10.3 A 127.5 9.5 92%Pass
18 5/5/2021 124.0 114.9 9.8 A 127.5 9.5 90%Pass
19 5/10/2021 126.0 114.7 9.2 A 127.5 9.5 90%Pass
20 5/10/2021 126.0 115.6 9.5 A 127.5 9.5 91%Pass
21 5/10/2021 126.0 115.1 9.8 A 127.5 9.5 90%Pass
22 5/10/2021 110.0 115.2 10.2 A 127.5 9.5 90%Pass
23 5/10/2021 112.0 113.4 10.1 A 127.5 9.5 89%Fail
23R 5/10/2021 112.0 114.8 9.7 A 127.5 9.5 90%Pass
24 5/11/2021 114.0 115.5 10.3 A 127.5 9.5 91%Pass
25 5/11/2021 113.0 114.9 10.6 A 127.5 9.5 90%Pass
26 5/12/2021 116.0 115.2 10.2 A 127.5 9.5 90%Pass
27 5/12/2021 128.0 111.8 11.0 Import A 122.0 10.5 92%Pass
28 5/12/2021 128.0 112.3 11.6 Import A 122.0 10.5 92%Pass
29 5/12/2021 128.0 110.4 11.2 Import A 122.0 10.5 90%Pass
30 5/12/2021 128.0 110.1 10.5 Import A 122.0 10.5 90%Pass
31 5/19/2021 130.0 109.0 11.3 Import A 122.0 10.5 89%Fail
31R 5/21/2021 130.0 110.3 10.7 Import A 122.0 10.5 90%Pass
32 5/19/2021 130.0 104.7 11.5 Import A 122.0 10.5 86%Fail
32R 5/21/2021 130.0 110.7 11.2 Import A 122.0 10.5 91%Pass
33SL 5/21/2021 124.0 117.8 9.6 A 127.5 9.5 92%Pass
34SL 5/21/2021 122.0 119.0 9.3 A 127.5 9.5 93%Pass
35SL 5/21/2021 128.0 120.2 9.0 A 127.5 9.5 94%Pass
I.D.
R
SL
Max A
Import A 122.0 pcf @ 10.5
Re-test
127.5 pcf @ 9.5
Legend
Slope Test
ASTMD-1557 Results
Table 1
Results of Field Compaction Tests
Harbor Pointe Slope Repair
FN 20-065.1
Test No.Date Tested Elevation
(ft.)
ASTM D-6938 /
D-1556
Soil Type
APPENDIX C
Laboratory Test Results
Project Name:Harbor Pointe
Project No. :20-065.1
Boring No.:Import
Technician:JMS
Date:5/11/2021
Visual Sample Description: Light Brown Silty Sand
X Manual Ram
Ram Weight 10 LBS Drop 18 inches
TEST NO.1 2 3 4 5 6
A Wt. Comp. Soil + Mold (gm.)3736.00 3821.00 3857.00 3810.00
B Wt. of Mold (gm.)1794.00 1794.00 1794.00 1794.00
C Net Wt. of Soil (gm.)A - B 1942.00 2027.00 2063.00 2016.00
D Wet Wt. of Soil + Cont. (gm.)1848.5 1760.9 1804.8 1774.5
E Dry Wt. of Soil + Cont. (gm.)1724.7 1626.4 1643.9 1603.5
F Wt. of Container (gm.)302.7 241.8 298.9 301.2
G Moisture Content (%)[(D-F)-(E-F)]/(E-
F)8.7 9.7 12.0 13.1
H Wet Density (pcf)C*29.76
/453.6 127.4 133.0 135.4 132.3
I Dry Density (pcf)H/(1+G/100)117.2 121.2 120.9 116.9
Maximum Dry Density (pcf)122.0 10.5
PROCEDURE USED
Procedure
COMPACTION TEST
ASTM D 1557
Modified Proctor
TerraPacific Consultants, Inc. 4010 Morena Boulevard, Suite 108, San Diego, CA 92117 / Phone: (858) 521-1190 Fax: (858) 521-1199
95.0
100.0
105.0
110.0
115.0
120.0
125.0
130.0
135.0
140.0
145.0
150.0
0.0 5.0 10.0 15.0 20.0Dry Density (pcf)Moisture Content (%)
SP. GR. = 2.65
SP. GR. = 2.70
SP. GR. = 2.75
Project Name:Harbor Pointe
Project No. :20-065
Boring No.:T-1 @ 0-2'
Technician:JS
Date:5/7/20
Visual Sample Description: Light Brown Silty Sand
X Manual Ram
Ram Weight 10 LBS Drop 18 inches
TEST NO.1 2 3 4 5 6
A Wt. Comp. Soil + Mold (gm.)3659.00 3783.00 3902.00 3928.00
B Wt. of Mold (gm.)1794.00 1794.00 1794.00 1794.00
C Net Wt. of Soil (gm.)A - B 1865.00 1989.00 2108.00 2134.00
D Wet Wt. of Soil + Cont. (gm.)1486.8 1733.9 1649.3 906.5
E Dry Wt. of Soil + Cont. (gm.)1425.1 1636.7 1543.1 835.1
F Wt. of Container (gm.)193.1 187.6 302.3 187.7
G Moisture Content (%)[(D-F)-(E-F)]/(E-
F)5.0 6.7 8.6 11.0
H Wet Density (pcf)C*29.76
/453.6 122.4 130.5 138.3 140.0
I Dry Density (pcf)H/(1+G/100)116.5 122.3 127.4 126.1
Maximum Dry Density (pcf)127.8 9.5
PROCEDURE USED
Procedure
COMPACTION TEST
ASTM D 1557
Modified Proctor
TerraPacific Consultants, Inc. 4010 Morena Boulevard, Suite 108, San Diego, CA 92117 / Phone: (858) 521-1190 Fax: (858) 521-1199
95.0
100.0
105.0
110.0
115.0
120.0
125.0
130.0
135.0
140.0
145.0
150.0
0.0 5.0 10.0 15.0 20.0Dry Density (pcf)Moisture Content (%)
SP. GR. = 2.65
SP. GR. = 2.70
SP. GR. = 2.75