HomeMy WebLinkAboutPD 2023-0021; THE BLUFFS SLOPE REPAIR; PRELIMARY GEOTECHNICAL INVESTIGATION SURFICIAL WASHOUT EROSION ON NORTHERN SLOPE; 2023-05-21GeoSite Engineering, Inc.
27068 La Paz Road, #571, Aliso Viejo, CA 92656
949-940-6828
May 21, 2023
Triumph Property Management Project No: 23004
9454 Wilshire Blvd., Suite 800 Report No: 23-002
Beverly Hills, California 90212
Attention: Mr. David M. Page
Subject: Preliminary Geotechnical Investigation
Surficial Washout Erosion on Northern Slope
2701 Avenida de Anita Along Marron Road
Carlsbad, California
References: See Appendix A
Dear Mr. Page:
Geosite Engineering Inc. is presenting herein the results of our geotechnical investigation of the
surficial washout erosion on the north facing slope located above Marron Road at the subject
site. The slope washouts happened in two areas on the northern slope on January 1, 2023. The
cause of the washouts were surface drainage waters that overflowed a slope v-ditch that drains
east to west at the upper to mid-portion of the northern slope. The purpose of this study was to
obtain surface and subsurface information within the area of the surficial washout erosion to
determine soil and geologic conditions and to provide recommendations pertaining to
remediation of the slope.
SCOPE OF SERVICES
The scope of our investigation consisted of the following;
1. A site reconnaissance and geologic mapping of the slope areas.
2. Research and review of reports and literature concerning soil and geologic conditions
within and adjacent to the site.
3. Collection of representative bulk soil samples for laboratory identification.
4. Assessing the probable cause of the washout.
5. Performing an engineering evaluation of all information obtained.
6. Preparation of this report presenting the results of our investigation and providing
recommendations for remediation of the surficial slope erosion.
May 21, 2023 Project No: 23004
Report No: 23-002
Page No: 2
ILLUSTRATIONS AND APPENDICES
Figure 1, Site Map
Figure 2, Geologic Map
Figure 3, Geotechnical Map
Figure 4, Cross Section A-A’
Figure 5, Cross Section B-B’
Figure 6, Grading Details
Appendix A, List of References
Appendix B, Site Photographs
Plate 1, Topographic Survey Map
LOCATION AND SITE DESCRIPTION
The subject site is located on the northern slope of The Bluffs at Carlsbad apartment complex.
The general location of the site is shown on Figure 1. The northern slope area in the vicinity of
the washouts has a total relief of 30 to 50 feet and has an existing slope ratio ranging from 1.7 to
1.8 to 1 (horizontal to vertical) as shown in Figure 3. The base map for Figure 3 is a portion of a
topographic survey prepared in 2012 during remodeling of the property. Figure 3 shows the
approximate locations of the slope washouts defined in a west area and east area. The overall
slope is covered by a moderate to heavy growth of grass materials.
BACKGROUND lNFORMATION
The following background information was obtained during our review of letters, reports and
literature available to us at the time of our evaluation (see Appendix A).
The apartment site was developed during the late 1980’s to early 1990’s based on our review of
property records and aerial photography. The site is reported to be underlain at depth by bedrock
of the Santiago Formation (see Reference 3 and Reference 4). The Santiago Formation (map
symbol Tsa) is predominantly described as sandstone materials. The geologic map indicates
bedding strikes northwest to northeast and dips 5 degrees east and west, respectively. Vertically
and laterally throughout the formation there exists greenish-brown, claystone interbeds, and
tongues and lenses of often fossiliferous, lagoonal claystone and siltstone.
A comparison of ground elevation from the 2012 Site Topography Map (see Plate 1) and a
historical topographic map (Reference 5) shown in Figure 1, indicates that the property was
developed by site grading that included placement of various depths of fill soil above the original
grade contours. Original ground elevations in the vicinity of the northern slope ranged from
about 50 to 80 feet above mean sea level. Current site topography shows elevations in the
vicinity of the washout ranges from about 60 to 100 feet above mean sea level.
May 21, 2023 Project No: 23004
Report No: 23-002
Page No: 3
A brief review of the 2012 Site Topographic Map indicates that a significant portion of the
stormwater drainage from the site is directed to the northern slope where it drains into a v-ditch
on the northern slope. This v-ditch carries surface water to the west and then south into a
drainage structure located on the western slope. Stormwater drainage from areas located
adjacent buildings 8 through 13 in the western portion of the site appears to be collected in an
area drain system that drains to the western slope and the northern slope (western portion only).
The City of Carlsbad indicates that the northern slope washouts occurred during heavy rains on
January 1, 2023. The slope washouts are indicated to have occurred due to high water drainage
volumes in conjunction with sediment and debris build-up in the v-ditch. A review of the site
(see photographs in Appendix B) shows that the eastern slope washout occurred right after the
curved transition from the north flowing drainage swale to the western flowing v-ditch (see
Appendix B, Figures B-3 and B-4). The downslope splash block on the v-ditch was sufficient to
contain the stormwater flow at the transition. The washout at the western area was located at a
location where an area drain outlet was directing stormwater in a northerly direction (see
Appendix B, Figure B-7) across the width of the v-ditch.
FlELD EXPLORATION
Our field exploration was performed on April 7, 2023 and consisted of mapping the slope
washout areas and the collection of surface and subsurface soil samples from the washout areas.
Soil materials predominantly consisted of silty fine sand, but also included soil materials
comprised of a varied mixture of silt, lean clays, and sand.
FINDINGS AND CONCLUSIONS
The findings and conclusions presented below are based on our site reconnaissance, mapping of
the subject slope, previous subsurface investigation and laboratory testing, and review of the
2012 topographic map and the referenced reports.
The approximate gross limits of the slope washout areas are shown on our Geotechnical Map
(Figure 3). The width of the erosion areas ranges from 3 to 6 feet (east area) and 3 to 9 feet (west
area). The depth of the washout areas is estimated to range from 2 to 3 feet in depth. Cross
section views of the washout areas showing the approximate subsurface geologic conditions are
presented on our Cross Section A-A’ and B-B’ (Figures 4 and 5).
Based on the overall good performance of other areas of the northern slope, it is concluded that
the overall slope is grossly and surficially stable and needs no overall remedial action. It is our
opinion that the slope erosion that occurred was solely caused by storm waters that overflowed
the northern v-ditch. Drainage improvements should as a minimum include placement of a 6-
inch concrete splash block (curb) along the outer edge (downslope side) of the northern v-ditch
and a 90-degree elbow on the end of all drainage pipes that direct stormwaters along the flow
line of the v-ditch.
May 21, 2023 Project No: 23004
Report No: 23-002
Page No: 4
Locally eroded areas in the west and east areas will require remedial surficial grading to replace
the slope to near the original conditions. This will include soil removal and replacement for a
typical width of 10 feet in the eroded areas, exposure of competent fill soil beneath the eroded
areas, and standard keying and benching into the slope to establish competent support prior to
placement of compacted fill (see Figure 6). Re-landscaping of the eroded and covered areas of
the slope will be needed to provide for long-term good performance. Landscaping of slope areas
should include placement of grasses and deep-rooted, drought-resistant plants. A landscape
architect could be consulted if desired to determine the most suitable groundcover for the slope.
Jute netting or equal materials should be placed over the repaired slope areas to protect the slope
until vegetation is re-established.
RECOMMENDATIONS
Based on our understanding of site conditions and the recent washouts, we propose the following
scope of repair for restoration of the slope as follows:
1. Remove all irrigation lines, vegetation and other debris from the planned work area.
2. Implement measures to enhance the future performance of the northern v-ditch. Drainage
improvements should as a minimum include placement of a 6-inch concrete splash block
(curb) along the outer edge (downslope side) of the northern v-ditch and a 90-degree
elbow on the end of all drainage pipes that direct stormwaters along the flow line of the
v-ditch. Corrective measures should be recommended by the project Civil Engineer.
3. Construct a stabilization fill in the western and eastern repair areas. A key should be
established at the toe of the erosion surface (see Figure 4 and 5) that is at least five feet wide
and two feet deep and founded in competent fill soil material (see Figure 6). Removal
benches should be at least 4-feet wide. All grading should be reviewed, tested and
approved by the geotechnical consultant during grading.
4. Removal bottoms will be scarified and recompacted to achieve at least 90 percent relative
compaction at a moisture content of 110 percent of optimum moisture content per ASTM
D1557. Engineered fill soil is to be placed in 4 to 6-inch loose lifts and be compacted to at
least 90 percent relative compaction at a moisture content of 110 percent of optimum
moisture content per ASTM D 1557.
5. Consult a landscape architect as-desired to design plantings consistent with the soil
conditions, climate, and that are similar and equivalent to the previous conditions.
6. Place jute netting or equal over the graded slope areas and other slope areas scheduled for
new vegetation. Jute netting should be stapled or otherwise affixed to the slope so that it will
remain in-place during the rainy season.
May 21, 2023 Project No: 23004
Report No: 23-002
Page No: 5
LIMITATIONS
Our work was performed in accordance with generally accepted practice in the engineering
geologic and soils engineering field. No further warranty is offered or implied. Conclusions
presented are based on visual observation, review of investigations by others, and information
collected from others.
The opportunity to be of service is appreciated. If there are any questions, please call.
Respectfully submitted,
GEOSITE ENGINEERING, INC.
Russell C. Lamb, G.E. 2207
Chief Geotechnical Engineer
Date Signed: 5/21/2023
RCL/rcl
Distribution: Addressee
Aldrich Consulting Engineers
SITE
SITE MAP - FIGURE 1
78 78
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L
C
A
M
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O
R
E
A
L
EL
C
A
M
I
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O
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A
L
REFERENCE: USGS - SAN LUIS REY, CA 1997
SITE
PACIFIC OCEAN
78 78
EL
C
A
M
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EA
L
Tsa
GEOLOGIC MAP - FIGURE 2
SITE
__
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L
C
A
M
I
N
O
R
E
A
L
A
A'B
B'
0'30'60'
N
WEST
AREA
EAST
AREA
GEOTECHNICAL MAP - FIGURE 3
Af/Tsa
Af/Tsa
Af/Tsa
Af/Tsa
Af/Tsa
A A'
110
80
50
110
80
50
WEST AREA
EROSION
SURFACE
CROSS SECTION A-A' - FIGURE 4
-
V-DITCH
PRE-EROSION GRADE
ORIGINAL GRADE
Af FILL
1 .........---•• .... . ···-~ --------• - - -.J ' , .----J
1----r----...-----·r---
------1
POSSIBLE BENCHING Tsa BEDROCK
SCALE 1 INCH= 20 FEET HORIZONTAL AND VERTICAL
B B'
EROSION
SURFACE
110
80
50
110
80
50
EAST AREA
CROSS SECTION B-B' - FIGURE 5
z 0 -~ < Gj
...:i i:I.:l
V-DITCH
PRE-EROSION GRADE
ORIGINAL GRADE
~ r
i:I.:l Cl -r./)
• ~
Af FILL
--~ .,, '(,
• ,,,,, " . -· • • . -
___.____, --------1 J----·
' .-------r - - -
. -----------·,---_,
I -------POSSIBLE BENCHING Tsa BEDROCK
SCALE 1 INCH = 20 FEET HORIZONTAL AND VERTICAL
5 feet
GRADING DETAILS - FIGURE 6
TOP OF FILL
-5 FT. (1.5 m) OR
GREATER
----------KEY
--------11
------s s 14 .. I
2 FT. (0.6 m)
MINIMUM
NATURAL SLOPE
--------------------
REMOVE UNSUITABLE
MATERIAL
----
APPENDIX A
LIST OF REFERENCES
1. City of Carlsbad, Watershed Protection Division, 2023, “Courtesy Notice – 2701Avenida de
Anita – Slope on north side of property adjacent to Marron Road,” Watershed Protection
Investigation SWC2023-0001, dated January 23.
2. Don Barrie and Associates, 2012, “Topographic Survey Map, Villa Real Apartments,” dated
November 22.
3. Kennedy, M.P., Tan, S.S., Bovard, K.R., Alvarez, R.M., Watson, M.J., and Gutierrez, C.I.,
2007, “Geologic Map of the Oceanside 30’ x 60’ Quadrangle and adjacent Areas,
California,” California Geological Survey, Regional Geologic Map RGM-2, 1:100,000.
4. Stoney-Miller Consultants, Inc., 2012, “Limited Geotechnical Investigation, Conclusions
and Recommendations, Residential Multi-Family Apartment Buildings, Villa Real
Apartments, 2601-2723 Avenida de Anita, Carlsbad, California,” dated October 25, Project
No: 13667-00, Report No: 12-13580.
5. United States Geological Survey, 1997, “San Luis Rey, California Quadrangle,” HTMC
2000 Edition, Scale 1:24000.
APPENDIX B
SITE PHOTOGRAPHS
EAST WASHOUT FROM TOE - FIGURE B-1
EAST WASHOUT FROM TOP - FIGURE B-2
DRAINAGE SWALE TO NORTH V-DITCH
ABOVE EAST WASHOUT- FIGURE B-3
DRAINAGE SWALE TRANSITION TO
NORTH V-DITCH - FIGURE B-4
WEST WASHOUT FROM TOE - FIGURE B-5
WEST WASHOUT FROM TOP - FIGURE B-6
OUTLET PIPE ABOVE WEST WASHOUT - FIGURE B-7
OUTLET PIPE
PLATE 1 - TOPOGRAPHIC SURVEY MAP
o' 30' 60'
SCALE" 1 '=30'
NET AREA:
415268 SQ. FT.
9.53 ACRES
90'
Toe
•
Toe
137
OJ'-..
"'
''-.1
N 45 53"22"" E 403.09 ---+----
'17
"6'
0
------------------------------------------
---
BENCH MARK:
CITY OF CARLSBAD BENCH MARK CLSB-087
FOUND 2.5" DISK IN WEST CURB OPPOSITE
2906 AVENI DA DE ANITA. 190FT. NORTH OF
CALLE SUSANA.
El.=165.36
LEGAL DESCRIPTION:
A PORTION OF LOTS 3, 4, AND 5 IN SECTION 32,
TOWNSHIP 11 SOUTH, RANGE 4 WEST, SAN BERNARDINO
MERIDIAN, IN THE CITY OF CARLSBAD, COUNTY OF SAN
DIEGO, STATE OF CALIFORNIA, ACCORDING TO OFFICIAL
PLAT THEREOF
PREPARED BY:
DON BARRIE & ASSOCIATES
LAND SURVEYORS
12408 N. JEFFERSON STREET
ANAHEIM, CA 92807
-
CURVE DATA:
CURVE DELTA < RADIUS ARC LENGTH
Cl 04"15'09" 1042.00' 77.34'
C2 04"36'26" 958.00' 77.03'
C3 90·00·00" 25.00' 39.27'
C4 41"49'46" 120.00' 87.61'
cs 12·57•1 o" 440.00' 99.47'
C6 79"31 12B" 280.00' 388.63'
C7 41·49'45" 150.00' 109.51'
CB 12"57'1 O" 470.00' 106.25'
C9 79"31 '28" 250.00' 346.99'
--------'-' '--,
~"' "-.
_______ , "'-
'
-
STATEMENT OF ACCURACY:
CHORD LENGTH TANGENT
77.32' 38.69'
77.01' 38.54'
35.36' 25.00'
85.67' 45.86'
99.26' 49.95'
358.18' 232.97'
107.09' 57.32'
106.03' 53.35'
319.80' 208.01'
APARTMENT BUILDING SCHEDULE
& BUILDING ELEVATIONS:
(Ground Floor -Finish Floor)
♦ Indicates Finish Floor Elevation Location
BLDG•
1
2
3
4
5
6
7
8
9
10
11
12
13
14
REC
' ""' ' '
ADDRESS
2701
2703
2705
2709
2603
2601
2605
2719
2723
2721
2717
2715
2713
2711
2707
' ' '
F.F. EL
EL=110.33
EL=108.74
EL=107.39
EL=111.69
EL=108.37
EL=107.25
EL=107.26
EL=107.44
EL=107.50
EL=109.81
EL=110.91
EL=112.78
EL=114.46
EL=115.05
EL=110.80
' ""' ' ""' ' ' '¾ ' ________ ,
""' '
""' ' ""' '-.. ---
""' ' '' ' ,,, ' '-.. "'--'-.. ''
"-~
THE RELATIVE POSITIONIONAL ACCURACY OF THIS TOPOGRAPHIC SURVEY
(VERTICAL RELIEF) IS 0.1ft/3cm., 1/10 OF 1ft. CONTOUR INTERVAL REVISION: DATE:
PREPARED FOR:
TRIUMPH MANAGEMENT COMPANY
9601 WILSHIRE BLVD. #560
BEVERLY HILLS, CA 90210
ADDED ADDITIONAL DATA
& ELEVATIONS
11-22-12
TOPOGRAPHIC SURVEY
DRAWN DATE VIA REAL APARTMENTS
11/06/12 CARLSBAD, CA
APPROVED DATE
SCALE SHEET PROJECT NO.
, .. = 30'