HomeMy WebLinkAboutMS 2020-0003; HEMLOCK COAST HOMES; FINAL SOILS REPORT; 2023-03-28
21 March 2023
(Revised 28 March 2023)
Mr. John Norum Job No. 20-12842
KMJ REAL ESTATE
1446 Front Street, Suite 300
San Diego, CA 92101
Subject: Report of Final Observations and Soil Testing
Hemlock Coastal Home Residential Project
320 Hemlock Avenue
Carlsbad, California
Dear Mr. Norum:
Per your request and as required by the City of Carlsbad, Geotechnical Exploration,
Inc. hereby presents this report of our final observations and soil testing performed
for the subject site. For the project location, refer to the Vicinity Map, Figure No. I.
The work reported herein was performed between January 24, 2022, and February
15, 2023. Our firm previously performed a geotechnical investigation of the property,
the results of which were presented in our Report of Preliminary Geotechnical
Investigation dated August 24, 2020.
We also issued a Report of Rough Grading Observation and Testing dated December
22, 2021 (revised on January 4, 2022), which presented earthwork observed and
tested between November 10 and December 20, 2021, and included the 4-foot
overexcavation removal in building pad areas and the remediation observations for
an unearthed septic tank and a deep vertical seepage pit that was located north of
Unit 4 building pad.
-~&i1 Geotechnical Exploration, Inc.
SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY
7420 TRADE STREET• SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 2
For the septic tank pit, the grading contractor removed all soft and loose soils in the
pit and placed recompacted backfill on top of the suitable bottom soils. The suitable
bottom was encountered at about 7 feet below the finished ground floor elevation of
Unit 4.
For the deep vertical seepage pit, a suitable bottom was encountered by the
compaction grouting contractor, Geotechnical Stabilization Inc. (GSI), at a depth of
15 feet below pad elevation. The grouting was extended to the top of the pit, which
was approximately 8 feet below the ground surface. A concrete slab was placed on
top of the remaining circular pit at about 7 feet below finish building pad grade and
extended at least 1 foot outside the 4-foot-diameter of the pit. The concrete slab
was at least 8 inches thick and reinforced with No. 5 steel grid reinforcing.
Compacted fill soils were placed on top of the concrete slab to the finish pad grade
elevation. The vertical seepage pit was backfilled in accordance to the recommenda-
tions presented in our November 12, 2021, Vertical Seepage Pit Backfill
Recommendations letter.
FIELD OBSERVATIONS
1. Our representative was requested by the contractor to observe the bearing soils
for the footing excavations of Building A (Units 1 and 2), which were found to
be founded in suitable recompacted fill soils on top of dense formational soils.
The bearing soils for the footing excavations of Building B (Units 3 and 4) were
also observed to be founded in recompacted fill soils and a footing memo was
issued to the contractor/contractors representative for the observed and
approved footing excavations.
2. Utility trench backfill placement for the sewer trench between the middle of
the building under the driveway area was observed on February 25, 2022.
i
i
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 3
Backfill placement for the for the electrical trenches located on the northeast
side of each building was also observed and both were tested for compaction.
3. Utility trench backfill placement for a joint trench located perpendicular to
Hemlock Avenue was observed and tested on March 7, 2022.
4. Utility trench backfill for the gas line was observed at the northeast corner area
of the site. Pipe bedding sand was used to backfill the utility trench on March
24, 2022. The backfill material probed dense.
5. Finished subgrade tests for the paver driveway located in the middle of both
residential buildings as well as the subgrade for the curb adjacent to Hemlock
Avenue were observed and tested on December 21, 2022.
6. Observation and compaction of the paver base was done between January 16
and January 31, 2023. The contractor placed ¾-inch-diameter rock
underneath the paver section followed by No. 57 rock and then No. 8 sand per
the paver details in the project plans. The material probed suitable and dense.
7. The base for the curb and sidewalk was observed and tested on February 6
and 9, 2023.
8. The finished base for the right-of-way apron and the street improvements were
observed and tested between February 10 and 15, 2023.
SOIL TESTING
Representative soil and base layer samples were collected during the grading to
determine laboratory maximum dry density of the soils per ASTM D1557-12e1. Field
density tests were performed at approximate locations shown on Figure No. II, Plot
i
i
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 4
Plan in accordance with ASTM D6938-17a. The complete list of field density tests
results is shown as Table A on Figure No. IIIa, and laboratory soil compaction test
results are shown as Table B on Figure No. IIIb. Grain size analysis tests were
performed for the base layer, for the No. 57 gravel material, and for the No. 8 sand
layer. The base, gravel, and sand sieve tests yielded results that complied with the
specifications.
Grading equipment used for compaction consisted of pneumatic hand tampers, and
vibratory plates; ride on roller, a Bobcat and a backhoe. Water was added, when
needed to increase the soil moisture. Field density tests yielded a relative compaction
of at least 90 percent (95 percent at recommended locations) of the maximum dry
density at the tested locations with the soils properly moisture conditioned. On-site
soils were used during the observed backfill and field density testing. In general, the
on-site soils consisted of brown to reddish brown, silty sand and the import consisted
of gray decomposed granite sand material. The compacted imported soils were
visually observed to have an expansion index (E.I) less than 50 based on our
experience with similar soils consisting of a low fines content.
Proper finish drainage for the site is to be implemented by the general contractor
prior to completing construction. The graded areas are shown on the attached Plot
Plan, Figure No. II.
Any pending grading and earthwork should be observed by our field representative
prior to form, steel reinforcing placement, and just prior to concrete placement. Any
future utility or drainage trench backfill, or retaining wall backfill should also be
performed under the observation and testing of our firm as should any finished
subgrade testing for pending exterior flatwork or driveway. A report of additional
observations will be provided issued after additional soil-related work is performed
under our observation and testing
i
i
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 5
SITE SUITABILITY AND COMPLIANCE
The observed and tested areas of the project site are, in our professional opinion,
suitable for their intended use. The underlying formational soils are, in our
professional opinion, suitable to support the recompacted fill, building structures, and
new exterior improvements.
We certify that the geotechnical engineering aspects of the grading are in compliance
with the approved geotechnical reports and grading plans, current standards, and
the city grading ordinance.
LIMITATIONS
The findings and opinions presented herein have been made in accordance with
currently accepted principles and practice in the field of geotechnical engineering in
the City of Carlsbad. No warranty, either expressed or implied, is made.
All statements in this grading report are applicable only for the grading operation
observed and tested by our firm. The firm Geotechnical Exploration, Inc. shall
not be held responsible for fill soils placed without our observations and testing at
any other time, or subsequent changes to the site by others, which directly or
indirectly cause poor surface or subsurface drainage, water erosion, and/or alteration
of the strength of the compacted fill soils.
It is not within the scope of our services to provide quality control oversight for
surface or subsurface drainage construction or retaining wall sealing and base of wall
drain construction. It is the responsibility of the contractor to verify proper wall
i
i
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 6
sealing, geofabric installation, protection board installation (if needed), drain depth
below interior floor or yard surfaces, pipe percent slope to the outlet, etc.
In the event that any changes in the nature, design, or location of the building or
improvements are planned, the conclusions and recommendations contained in this
report should not be considered valid unless the changes are reviewed and the
conclusions of this report modified or verified in writing.
This opportunity to be of service is sincerely appreciated. If you have any questions
regarding this letter, please contact our office. Reference to our Job No. 20-12842
will help expedite a response to your inquiry.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________
Jaime A. Cerros, P.E.
R.C.E. 34422/G.E. 2007
Senior Geotechnical Engineer
_______________________________
Richard A. Cerros, P.E.
R.C.E. 94223
ichard A. Cerros, P. E.
R.C.E. 94223
D
VICINITY MAP
Hemlock Coast Homes
320 Hemlock Avenue
Carlsbad, CA.
Figure No. I
Job No. 20-12842
SITE
Thomas Guide San Diego County Edition pg 1106-E7
I
'9
tr}e~L "~ RTSCENTER
Carlsbad Hs
AQUA HEDIONDA
LAGOON
Geotechnical Exploration, Inc.
Approximate Limits ofObserved Grading and
Testing.Areas to Be Over-Excavated
Area of 5 A/C Placement
Gas Trench Location
Joint Trench Location
Electrical Trench Location
Sewer Trench Location
Water Trench Location
44 Approximate Location of
Field Density Test
1
3
4
5
7
6
8
9
10
13
12
11
2
14
15 1617
18
19
20
21
22
23
24
25
2636
34
27 28 29
30
31
32
333537
38
39
40
41
42
43
44 45
46
4748
49
50
51
52
53
54
55
56
57
58
60
59
61
62
63
64
65
66
67
80 69
70
71
72
Bottom of Excavation Elevation (feet)55
53
55
53
55
54
53.5
53.5
53
53
53
53
52
54
53
20-12842-p3.ai
Hemlock Coast Homes
320 Hemlock Avenue
Carlsbad, CA.
Figure No. II
Job No. 20-12842
PLOT PLAN
LegendREFERENCE: This Plot Plan was prepared from an existing undated GRADING PLAN by PASCO LARET SUITER & ASSOCIATES and from on-site field reconnaissance performed by GEI.
NOTE: This Plot Plan is not to be used for legalpurposes. Locations and dimensions are approximate.Actual property dimensions and locations of utilitiesmay be obtained from the Approved Building Plansor the As-Built Grading Plans.
March 2023
HEMLOCK AVENUE
GRAPHIC SCALE( feet)
SeepagePit
SepticPit
53
EXJSTINGJ
STRUCTURE TO
REMAIN
~~x
PORLOT2
BLOCKR
PALISADES#2
MAP 1803
' .~----,<'-----,
'
"AS BUILT'
PADr 57.1
I
I
b .------.---
I •
I I
~T~
-urJir3
FFi 57.8
PADf 57.1
I
I I e
PORLOT3 ~~~~: BLOCK R
•
•
EX/SnNG
RETAININGWAU
TOBE REMOVED
--:.~-:--1
-;----------t-• i'
I I
UNIT2
FF=57.8
PAD=57.1
U'llU.1 • ~
I I
I OHEJ EX~ I RESl~E
I ~ffPE I FOOFN<l
I I
I ------~~-'.---'-~=--
UNIT1
FF=57.8 •
PAD=57.1
------
.., 4.0
. I
I
: ,i
'1• I.
: . I , .
15' •
I , I. .
I -,·
--
. , ~-w -w-,-'\;-w
w-w-w-• 11)-w-~ 11
PERSDRSDG-1« N I
I
~m i
disT1HGPOIWl I
POLE TO REMAIN
EXISTING 12" RCP
STORM DR.'.IN PER 3:
D00139-l I
EXISTING~ ACP J:
RW\INPER
I ~
I (54.8RIMJ ,
41.3 IE IN NOR1H
(47.1/EIN~ST)
h (47.0IEOUT),:: 1
e,rrorc
----___ J ~
l/MfTOFFUI.L•WIOTHT
2" AC GRIND AND
OYE'RLAY(TYP.)
TABLE A
SUMMARY OF FIELD DENSITY TEST RESULTS (ASTM D1556 and/or ASTM D6938)
Approximate Water Dry Degree of
Test Elevation Content Density Compaction Compaction
~ Dit!il QfTHt T!illt LQ~ltiQ[! (Fggt} (0/g} (R!;f} (0/g} tYrv!il NQ. Rgm1rk1
1 11/10/21 GRADING 54 5.3 117.7 91 2
2 11/10/21 GRADING (PCC PATIO) 55 7.5 116.8 90 2
3 11/12/21 GRADING (UNIT 3) 54 7.2 117.0 90 2
4 11/12/21 GRADING (UNIT 3) 55 8.1 117.6 91 2
5 11/15/21 GRADING (PAVER AREA) 53 8.0 118.4 91 2
6 11/15/21 GRADING (PAVER AREA) 55 7.4 117.6 91 2
7 11/15/21 GRADING (UNIT 3) 56 7.0 118.1 91 2
8 11/15/21 GRADING (UNIT 3) 57 6.5 119.8 92 2
9 11/15/21 GRADING (UNIT 1) 55 10.0 117.5 91 2
10 11/15/21 GRADING (UNIT 2) 57 7.9 117.9 91 2
11 11/15/21 GRADING (PAVER AREA) 55 8.2 120.6 93 2
12 11/15/21 GRADING (UNIT 2) 57 8.7 118.5 91 2
13 11/16/21 BOTTOM OF OVERX 53.5 4.3 120.0 92 2
14 11/16/21 BOTTOM OF OVERX 53.5 3.1 116.8 90 2
15 11/16/21 SEPTIC TANK (UNIT 4) 52 6.6 120.2 93 2
16 11/16/21 GRADING (UNIT 2) 55 6.0 122.7 95 2
17 11/16/21 SEPTIC TANK (UNIT 4) 54 8.1 120.3 93 2
18 11/16/21 SEPTIC TANK (UNIT 4) 56 6.1 117.3 90 2
19 11/16/21 GRADING (UNIT 1) FSG 6.4 122.2 94 2
20 11/16/21 GRADING (UNIT 2) FSG 6.1 122.4 94 2
21 11/23/21 HEMLOCK AV FG-20 4.9 130.5 100 3 @95%. Water Trench Backfill
22 11/23/21 HEMLOCK AV FBG 9.8 120.3 96 4 @95%. Sewer Trench Backfill
23 11/24/21 HEMLOCK AV -SEWER FSG-4 10.5 120.7 97 4 @90%. Water Trench Backfill
24 11/24/21 HEMLOCK AV -H2O TRENCH FG-2 5.3 130.5 100 3 @95%. Water Drain Backfill
25 11/24/21 HEMLOCK AV -SEWER FG 9.0 119.9 96 4 @95%. Sewer Backfill
26 11/24/21 HEMLOCK AV -H2O TRENCH FG 11.8 123.4 99 4 @95%. Water Trench Backfill
27 11/30/21 NORTHEAST SEWER CAP FSG-5' 7.6 118.5 90 1
Job No. 20-12842
Figure No. Illa
Notes: 1) Curve number refers to Table B :• 2) FSG denotes finish subgrade elevation
3) FBG denotes finish base grade elevation
4) FPG denotes finish pavement grade ~
TABLE A
SUMMARY OF FIELD DENSITY TEST RESULTS (ASTM D1556 and/or ASTM D6938)
Approximate Water Dry Degree of
Test Elevation Content Density Compaction Compaction
~ Dit!il QfTHt T!illt LQ~ltiQ[! (Fggt} (0/g} (R!;f} (0/g} tYrv!il NQ. Rgm1rk1
28 11/30/21 NORTHEAST SEWER CAP FSG-3' 8.2 126.5 97 2
29 11/30/21 NORTHEAST SEWER CAP FSG-1.5' 10.9 122.1 98 4 @95%.
30 11/30/21 NORTHEAST SEWER CAP FSG 8.8 121.1 97 4 @95%.
31 12/1/21 E-W WATER LINE (S END OF STREET) FSG-1' 10.4 118.2 95 4
32 12/1/21 E-W WATER LINE (S END OF STREET) FSG-1' 9.2 124.2 99 4
33 12/1/21 E-W WATER LINE (S END OF STREET) FSG 9.1 118.6 95 4
34 12/2/21 AC PLACEMENT HEMLOCK AV FG 0.0 143.7 96 5
35 12/2/21 AC PLACEMENT HEMLOCK AV FG 0.0 144.2 96 5
36 12/3/21 AC PLACEMENT HEMLOCK AV FG 0.0 145.7 97 5
37 12/3/21 AC PLACEMENT HEMLOCK AV FG 0.0 144.8 97 5
38 12/17/21 UNIT 2 -PAD FG 9.1 121.7 94 2
39 12/17/21 SEEPAGE PIT (UNIT 4) 50' (FG-5') 7.4 126.2 96 3
40 12/17/21 SEEPAGE PIT (UNIT 4) 52' (FG-3') 4.3 106.3 82 2 test failed, see #41
41 12/17/21 SEEPAGE PIT (UNIT 4) 52' (FG-3') 6.1 118.8 92 2 retest of #40
42 12/17/21 SEEPAGE PIT (UNIT 4) 54 (FG-1') 7.2 126.4 97 2
43 12/17/21 UNIT 1 56' (FG-1') 8.2 116.5 90 2
44 12/17/21 UNIT 1 57' (FSG) 7.0 125.1 95 1
45 12/20/21 UNIT 2 -PAD 56.5-57' 6.0 116.4 90 2
46 12/20/21 UNIT 2 -PAD 56.5-57' 6.0 125.0 96 2
47 2/25/22 SEWER TRENCH 53 7.8 113.6 88 2 test failed, see #48
48 2/25/22 SEWER TRENCH 53 8.6 119.3 92 2 retest of #47
49 2/25/22 SEWER TRENCH 54 9.6 117.1 90 2
50 2/25/22 SEWER TRENCH 53 8.4 116.3 90 2
51 2/25/22 SEWER TRENCH 55.5 9.1 116.8 90 2
52 2/25/22 WATER AND ELECTRICAL TRENCH 56 8.0 118.4 91 2
53 2/25/22 ELECTRICAL TRENCH 56 7.4 116.8 90 2
54 2/25/22 ELECTRICAL TRENCH 56 7.1 116.3 90 2
Job No. 20-12842
Figure No. Illb
Notes: 1) Curve number refers to Table B :• 2) FSG denotes finish subgrade elevation
3) FBG denotes finish base grade elevation
4) FPG denotes finish pavement grade ~
Job No. 20-12842
Figure No. IIId
TABLE B
LABORATORY COMPACTION TEST RESULTS (ASTM D1557)
Compaction Maximum Optimum
Test Source of Dry Density Water Content
Curve No. Description of Material Material (pcf) %
C-1 SILTY SAND (SM) Brn to Red Brn On-Site 131.5 8.6
C-2 SILTY SAND (SM) Red Brn On-Site 129.8 8.6
C-3 GREY DG-SAND (Shade H2O) Import 131.0 7.7
C-4 CLASS II RECYCLED BASE Import 125.0 8.2
C-5 TYPE III B2 1/2 AC Import (SRM) 150.0 +2.9 N.A.
C-6 CLASS II BASE Import 137.9 5.2