HomeMy WebLinkAboutCT 04-09; LA COSTA GREENS NEIGHBORHOOD 1.17; UPDATE GEOTECHNICAL REPORT; 2006-03-10L-rc)+'01
UPDATE
GEOTECHNICAL REPORT
VILLAGES OF LA COSTA
THE. GREENS - PHASE 2
NEIGHBORHOOD 1.17
CARLSBAD, CALIFORNIA
PREPARED FOR
WARMINGTON HOMES -
CARLSBAD, CALIFORNIA
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MARCH 10, 2006
PROJECT NO. 06403-52-26
I GE000N
INCORPORATED
I GEOTECHNICAL CONSULTANTS
(low)
Project No. 06403-52-26
March 10, 2006
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I Warmington Homes
701 Palomar Airport Road, Suite 280
Carlsbad, California 92009
1 Attention: Mr. Neal Keating
Subject: VILLAGES OF LA COSTA - THE GREENS, PHASE 2
I NEIGHBORHOOD 1.17
CARLSBAD, CALIFORNIA
UPDATE GEOTECHN1CAL REPORT
I Gentlemen:
I In accordance with your authorization of our Proposal No. LG-06079 dated February 27, 2006, we
have prepared this update geotechnical report for the subject project. The accompanying report
presents the results of our study and contains conclusions and recommendations pertaining to the
I
geotechnical aspects of the proposed development of the site. Provided that the recommendations
contained in this update report are followed, the site is considered suitable for construction and
support of the proposed structures and improvements as presently planned.
Should you have any questions regarding this report, or if we may be of further service, please
contact the undersigned at your convenience.
I . Very truly yours,
GEOCON INCORPORATED
1
7Y (),
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Michael C. Ertwine
Senior Staff Geologist
Z4- Sadr Shane Rodacker
CEG 1778 RCE 63291
1
MCE:AS:SR:dmc
(6/del) Addressee
(2) Real Estate Collateral Management
c/0 Morrow Development
Attention: Mr. Tim O'Grady
r *l PRO .r7. r\A.
I .I SMINEERING
'1!
6960 Flanders Drive I San Diego, California 92121.2974 0 Telephone (858) 558-6900 I Fox (858) 558.6159
I.
UPDATE GEOTECHNICAL REPORT
1. PURPOSE AND SCOPE
This report presents the results of the update geotechnical study for the proposed residential
development of Neighborhood 1.17, Lots 1 through 107 and associated improvements located in
Phase 2 of the Villages of La Costa -The Greens development. The site is situated south of
Poinsettia Lane, north of Dove Lane and west of the existing La Costa Resort and Spa golf course
(see Vicinity Map, Figure 1). The purpose of this update report is to provide foundation and retaining
wall design recommendations.
The scope of the study included a review of the following: ' 1. Update Soil and Geological Investigation, Volume I and II, Villages of La Costa - The
Greens, Carlsbad, California, prepared by Geocon Incorporated, dated June 25, 2001
(Project No. 06403-12-03).
Final Report of Testing and Observation Services Performed During Site Grading, Villages
of La Costa - The Greens, Neighborhoods 1.17— Lots I through 107 and Lot]]] (Park Site),
p Carlsbad, California, prepared by Geocon Incorporated, dated February 24, 2006 (Project
No. 06403-52-19A).
Grading and Erosion Control Plans for: La Costa Greens Neighborhood 1.16 & 1.17,
- prepared by Hunsaker and Associates, City of Carlsbad approval dated May 10, 2005.
2. PREVIOUS SITE DEVELOPMENT
Neighborhood 1. 17, Lots 1 through 107, was graded to finish-pad configuration during mass grading
P operations for Phase 2 of The Greens development. Grading was performed in conjunction with the
observation and testing services of Geocon Incorporated. A summary of the observations, compaction
test results, and professional opinions pertaining to the grading are presented in the above-referenced
final report of grading. Mass grading for the subject area has been completed and consisted of
developing 107 single-family residential lots and associated streets. Fill and cut slopes were created
with design inclinations of 2:1 (horizontal: vertical) or flatter, with a maximum height of
approximately 40 feet. The maximum thickness of the compacted fill soil is approximately 62 feet.
p An "As-Graded" Geologic Map is provided in the above-referenced report and depicts the existing
geologic conditions and topography.
3. SITE AND PROJECT DESCRIPTION
The development of The Greens - Neighborhood 1.07 consists of 107 single-family residential homes
and associated improvements. Compacted fill soil is exposed at grade and underlain by compacted
. It fills placed during the grading of Bressi Ranch, the Santiago Formation, and alluvium. The Santiago
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7.1 General
7. CONCLUSIONS AND RECOMMENDATIONS
7.1.1 No soil or geologic conditions were encountered during previous geotechnical
investigations or grading operations that, in our opinion, would preclude the continued
development of the property as presently planned, provided that the recommendations of
this report are followed.
7.1:2 The site is considered suitable for the use of conventional foundations and slab-on-grade,
and/or a post-tensioned foundation system. We understand that a post-tensioned foundation
system will be used throughout the project. Therefore, conventional footing
recommendations are not included in this report but can be provided upon request. Design
criteria for post-tensioned slabs are provided in Section 7.5.
7.2 Seismic Design
7.2.1 The site is located within Seismic Zone 4 according to UBC Figure 16-J. Compacted fill
soil and formational materials underline the proposed buildings. For seismic design, the site
is characterized as soil types Sc and SD. Table 7.2.1 summarizes site design criteria. The
values listed in Table 7.2.1 are for the Rose Canyon Fault, which is identified as a Type B
fault. The Rose Canyon Fault is located approximately 7 miles west of the site. Table 7.2.2
presents a summary of soil profile type for each building and the corresponding values
from Table 7.2.1 should be used for seismic design.
TABLE 7.2.1
SITE SEISMIC DESIGN CRITERIA
Parameter
Soil Profile Type UBC Reference
SD Sc
Seismic Zone Factor 0.40 0.40 Table 16-I
Soil Profile Sc Table 16-J
Seismic Coefficient, Ca 0.40 0.44 Table 16-Q
Seismic Coefficient, C 0.56 0.64 Table 16-R
Near-Source Factor, Na 1.0 1.0 Table 16-S
Near-Source Factor, N 1.0 1.0 Table 16-T
Seismic Source B B Table 16-U
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7.2.2 Based on a review of the as-graded conditions presented in the as-graded report referenced
below, as well as the seismic setting, the lots are assigned the seismic design parameters as
indicated in the following table.
TABLE 7.2.2 4 SUMMARY OF SOIL PROFILE TYPE
Lot Nos. UBC Classification
1 SD
2 through 4 Sc
5 through 9 SD
10 SC
11 through 16 SD
l7 and l8 Sc
19 through 21 SD
22 and 23 SC
24 through 29 SD
30 through 33 Sc
34 through 38 SD
39 and 40 Sc
41 through 44 SD
45 through 51 SC
52 and 53 SD
54 through 56 SC
57 through SD _59
60 through 71 SC
72 through SD _78
79 through 97 - Sc
98 through 107 5D
7.3 Finish Grade Soil Conditions
7.3.1 Observations and laboratory test results indicate that the prevailing soil conditions within
the upper approximately 3 feet of finish grade have an expansion potential of "very low" to
"medium" (Expansion Index of 90 or less) as defined by Uniform Building Code (UBC)
Table 18-I-B. Expansion Index test results for each lot are included on Table I.
Project No. 06403-52-26 .-6 - March 10, 2006
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7.3.2 It should be noted that although rocks larger than 6-inch-diameter were n
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placed within the upper 3 feet of pad grades, some larger rocks
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locations. In addition, concretionary lenses or layers may exist within the
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cause difficult excavation.
7.3.3 Random samples obtained throughout the subject neighborhoo
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water-soluble sulfate testing to evaluate the amount of water-soluble s
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finish-grade soil. These test results are used to determine the potentia
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normal Portland Cement concrete. The test results indicate sulfate conte
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to "negligible" to "severe" sulfate exposure ratings as defined by LJBC Table 19-A-4. The
results of the soluble-sulfate tests are summarized on Table ifi. Tab
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summary of concrete requirements set forth by UBC Table 19-A-4.
TABLE 7.3
REQUIREMENTS FOR CONCRETE EXPOSED TO
SULFATE-CONTAINING SOLUTIONS
Sulfate
Exposure
Water-Soluble
Sulfate Percent
by Weight
Cement
Type
Maximum Water
to Cement Ratio
by Weight
Minimum
Compressive
Strength (psi)
Negligible 0.00-0.10 -- -- --
Moderate 0.10-0.20 II 0.50 - 4000
Severe 0.20-2.00 V 0.45 4500
Very Severe >2.00 V 0.45 4500
7.3.4 Geocon Incorporated does not practice in the field of corrosion eng
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improvements that could be susceptible to corrosion are planned, it is r
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further evaluation by a corrosion engineer be performed.
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7.4 Future Grading
7.4.1 Any additional grading performed at the site should be accomplished in
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our observation and compaction testing services. Grading plans fo
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should be reviewed by Geocon Incorporated prior to finalizing. All trenc
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should be compacted to a dry density of at least 90 percent of the la
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density at or slightly above optimum moisture content. This office
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least 48 hours prior to commencing additional grading or backfill operation
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March 10, 2006
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TABLE 7.5
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PT!)
Design Parameters
Foundation Category
i ii 111
Thornthwaite Index -20 -20 -20
Clay Type - Montmorillonite Yes Yes Yes
Clay Portion (Maximum) 30% 50% 70%
Depth to Constant Soil Suction 7.0 ft. 7.0 ft. 7.0 ft.
Soil Suction 3.6 ft. 3.6 ft. 3.6 ft.
Moisture Velocity 0.7 in/mo. 0.7 in/mo. 0.7 in/mo.
Edge Lift Moisture Variation Distance 2.6 ft. 2.6 ft. 2.6 ft.
Edge Lift 0.41 in. 0.78 in. 1.15 in.
Center Lift Moisture Variation Distance 5.3 ft. 5.3 ft.
Center Lift 2.12 in. 3.21 in. 4.74in.
7.5.3 UBC Chapter 18, Div. III, §1816 uses interior stiffener beams in its structural design
procedures. If the structural engineer proposes a post-tensioned foundation design method
other than UBC Chapter 18, Div. III, §1816, the following recommendations apply:
The deflection criteria presented in Table 7.5 are still applicable.
. Interior stiffener beams be used for Foundation Categories II and ifi.
The depth of the perimeter foundation should be at least 12 inches for Foundation
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Category I, 18 inches for Foundation Category II, and 24 inches for Foundation
Category III.
- Geocon Incorporated should be consulted to provide additional design parameters as
required by the structural engineer.
7.5.4 Our experience indicates post-tensioned slabs are susceptible to excessive edge lift,
regardless of the underlying soil conditions, unless reinforcing steel is placed at the bottom
of the perimeter footings and the interior stiffener beams. Current PTI design procedures
primarily address the potential center lift of slabs but, because of the placement of the
reinforcing tendons in the top of the slab, the resulting eccentricity after tensioning reduces
the ability of the system to mitigate edge lift. The structural engineer should design the
foundation system to reduce the potential of edge lift occurring for the proposed structures.
Project No. 06403-52-26 - 9 - March 10, 2006
Approximate Approximate
Lot Maximum Maximum Depth Expansion Foundation
No. Pad Condition Depth of Fill of Differential Fill Index Category
(feet) (feet)
21 Undercut due to 23 20 16 III cut-fill transition
22 Cut N/A N/A 33 I
23 Cut N/A N/A 33 I
24 Undercut due to 23 20 54 III cut-fill transition
25 Fill 32 7 63 II
26 Fill 39 21 63 III
27 Undercut due to 38 35 63 III cut-fill transition
28 Undercut due to 35 32 63 III cut-fill transition
29 Undercut due to 25 21 58 III cut-fill transition
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30 Undercut due to 18 15 58 II cut-fill transition
31 Undercut due to 14 11 58 II cut-fill transition
32 Undercut due to 19 16 58 II cut-fill transition
33 Undercut due to 17 14 58 II cut-fill transition
34 Undercut due to 21 18 61 II cut-fill transition
35 Fill 22 17 61 II
36 Fill 26 15 61 II
37 Fill 46 28 61 III
38 Fill 44 23 61 III
39 Cut N/A N/A 51 II
40
Undercut due to 10 7 51 II cut-fill transition
41 Undercut due to 32 28 51 III cut-fill transition
Project No. 06403-52-26 March 10, 2006
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY ;Z0, FOR NEIGHBORHOOD 1.17, LOT NOS. 1 THROUGH 107
TABLE II
SUMMARY OF FINISH GRADE EXPANSION INDEX TEST RESULTS
VILLAGES OF LA COSTA; THE GREENS
NEIGHBORHOOD 1.17, LOTS 1 THROUGH 107
Lot Numbers Sample at
Finish Grade
Expansion
Index
IJBC
Classification
1 through 5 EI-Q 65 Medium
6 through 10 El-R . 78 Medium
11 through 14 El-S 76 Medium
15 and 16 EI-T 86 Medium
17 El-AG 16 Very Low
18 El-AR 33 Low
19 through 21 El-AG 16 Very Low
22 and .23 El-AR .33 Low
24 El-Al 54 Medium
25 through 28 EI-Y 63 Medium
29 through 33 . EI-X 58 Medium
34 through 38 EI-Z 61 Medium
39 through 44 EI-AF 51 Medium
45 El-AD 89 Medium
46 through 50 El-AB 16 Very Low
51 through 53 EI-AA 82 Medium
54 through 59 EI-W 66 Medium
60 through 64 El-V 54 Medium
65 through 68 El-U 71 Medium
69 through 71 El-AC 28 Low
72 through 74 El-K 61 - Medium
75 through 79 EI-J 47 Low
80 El-AE 42 Low
81 El-lb 52 Medium
82 El-Ic 82 Medium
83 El-Id 60 Medium
84 EI-Ie 38 Low
85 through 88 El-P 47 Low
89 through 92 EI-O 58 Medium
93 through 97 . El-N 44 Low
98 through 102 ELL 53 Medium
103 through 107 EI-M 66 Medium
Project No. 06403-52-26 . - - March 10, 2006
to TABLE III
SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS
CALIFORNIA TEST 417
Sample No. Water-Soluble Sulfate (%) Sulfate Exposure
UBC Table 19-A-4
El-lb 0.092 Negligible
El-1c 0.240 Severe
El-Id 0.225 Severe
El-le 0.132 Moderate
EI-J 0.495 Severe
El-K 0.156 Moderate
EI-L 0.138 Moderate
EI-M 0.380 Severe
El-N 0.520 Severe
EI-O 0.720 Severe
El-P 0.540 Severe
EI-Q 0.675 Severe
El-R 0.555 Severe
El-S 0.585 Severe
EI-T 0.585 Severe
El-U 0.690 Severe
El-V 0.675 Severe
EI-W 0.270 Severe
EI-X 0.375 Severe
El-Y 0.195 Moderate
EI-Z 0.720 Severe
EI-AA 0.765 Severe
El-AB 0.100 Moderate
El-AC 0.720 Severe
El-AD 0.765 Severe
El-AB 0.435 Severe
El-AF 0.051 Negligible
El-AG 0.255 Severe
EI-AH 0.345 Severe
El-Al 0.255 Severe
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Project No. 06403-52-26 March 10, 2006