HomeMy WebLinkAboutPD 2019-0032; GOERTZEN RESIDENCE; GEOTECHNICAL SITE INSPECTION - REVISED; 2020-02-25, .. '11!11'n!D,_
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February 25, 2020
Greg Goertzen
3466 Camino Michelle
Carlsbad, California 92009
SUBJECT:
Dear Mr. Goertzen:
SCOPE
File No. 1127H6-19
SITE INSPECTION -Revised
Proposed Residential Building Site
El Fuerte Street and Acuna Court
City of Carlsbad
P.O. Box 1195
Lakeside, California
92040
(619) 443-0060
In accordance with your request, a Site Inspection has been performed at the subject site. The
purpose of this investigation was to examine existing site conditions and provide engineering
recommendations for the proposed single family residence.
FIELD INSPECTION
In order to accomplish this purpose, a representative of this firm visited the site, reviewed the
topography and site conditions and visually and textually classified the surface and near
surface soils. Representative samples of the on-site soils were obtained from 2 test
explorations approximately 4 feet in depth and tested for density, shear strength and
expansive characteristics.
SITE CONDITIONS
The subject site is located on the northwest comer of El Fuerte Street and Acuna Court. The
property is a moderately sloped lot descending from the northeast to the southwest of the
vacant site. Neighboring properties are occupied by residential structures. Fill materials were
not encountered during the course of this inspection.
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Greg Goertzen File No. 1127H6-19 February 25, 2020
SOIL CONDITIONS
Soils encountered in the test explorations are topsoils consisting of loose, dark orange brown,
silty sands with organic materials to approximately 6 to 12 inches in depth. These surface
soils were underlain by native soils consisting of medium dense to dense, tan to red brown,
silty sands with light clay to the bottom of the explorations, approximately 4 feet in depth.
We did not encountered bedrock during our onsite visit.
There is an area of possible undocumented fill at the southwest portion of the site along El
Fuerte Street. This area will be inspected during the grading and removed during the keying
process. As indicated, the limits of the fill are approximate and should be confirmed during
grading.
The soils we encountered were considered to be moderately expansive with respect to change
in volume with change in moisture content.
CONCLUSIONS AND RECOMMENDATIONS
1. A representative sample of the foundation soil was remolded to 90% of maximum
dry density. Based on the following test results, a safe allowable bearing value of
at least 2000 pounds per square foot for 12 inch deep footings may be used in
designing the foundations and slab for the proposed structures. This value may be
increased by one third for wind and/or seismic loading. This value may be
increased by 20 percent for each additional foot of depth and or width to a
maximum of 3 times the designated value.
Maximum Dry Density
Optimum Moisture
Angle of internal friction
Cohesion
Unit weight
Expansion Index65
121.5 pcf
12.1%
29°
391 psf
109.5 pcf
2. Lateral resistance to horizontal movement may be provided by the soil passive
pressure and friction of concrete to soil. An allowable passive pressure of 250
pounds per square foot per foot of depth may be used. A coefficient of friction of
0.35 is recommended. The soils passive pressure may be increased by 1/3 for wind
and seismic loading.
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Greg Goertzen File No. 1127H6-19 February 25, 2020
3. The seismic parameters for the site coordinates 33.09791 °N, 117.247985°W for
assumed Site Class D, Risk Category II are as follows:
• Ss = 1.035 g
• s, =0.401 g
GRADING
Sms = 1.124 g
Sm1 = 0.641 g
Scts = 0.749 g
Sct1 = 0.427 g
2. The loose native soils encountered during this inspection should not be used to
support proposed structures. It is our recommendation that these soils in proposed
building areas be removed to competent natural ground prior to placement of
import soils and recompacted to 90 percent compaction to an anticipated depth of 2
feet in accordance with the Grading Specifications in this report. The recompaction
should extend at least 5 feet outside the proposed building footprints. Any organic
or other deleterious material that may be encountered should be removed prior to
recompaction.
3. The keyway should be a minimum of 3 feet in depth and 12 feet wide and will
follow the fill slope.
4. The cut portion of the cut/fill transition shall be undercut and over-excavated to a
minimum of 3 feet in depth from finish grade.
5. There should be a minimum of 12 inches of uniformly compacted fill under the
proposed footings. A representative of our company should observe the footing
excavations prior to the forms and reinforcing steel being placed.
6. Utility trench backfill beneath structures, pavements and hardscape should be a SE 30
soil or less and compacted to a minimum of 90% relative compaction. The upper 12
inches of subgrade beneath slabs and paved areas should be compacted to al least 95%
relative compaction. Any organic or other deleterious material that may be
encountered should be removed prior to recompaction. We should be present for
the trench backfill.
7. All graded fill slopes should be graded to a maximum of a 2:1 gradient. Graded cut
slopes will be stable at a 2:1 gradient. The graded slopes in compliance with current
grading ordinances will be considered surficially stable.
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Greg Goertzen File No. 1127H6-19 February 25, 2020
FOUNDATIONS
4. The foundation soils are moderately expansive. The following foundation depth is a
minimum due to the expansive nature of the soil and must be used in order to prevent
possible damage to the proposed structures from adverse effects of expansive soils.
These recommendations for footings and slabs are based upon the soil type only and
do not take into consideration the structural requirements.
■ Use continuous exterior perimeter foundations (including door openings).
They should be founded a minimum of 18 inches below lowest adjacent
grade.
■ Interior footing depth should exceed 12 inches below top of slab or 12 inches
for raised floor construction.
■ Reinforce continuous concrete foundations as a beam with at least one #4
bar positioned 3 inches above the bottom of footing and one #4 bar
positioned 1 inch below top of foundation or top of finish floor.
5. Concrete Slab-On-Grade, SOG, should be designed by the project's structural
engineer based on anticipated loading conditions. We recommend that
conventional reinforced concrete SOG for this project be founded on 4 inches of
Class II Virgin Aggregate Base (with approximately 2% +/-over optimum moisture
content and 90% compaction, relative to the lab maximum dry density, ASTM D
1557), overlying a 12 inch thick zone of adequately placed and compacted
structural fill. We recommend that a moisture barrier be provided by a membrane,
visqueen 10 mils in minimum thickness or equivalent, be placed at top of well
compacted Class II Aggregate Base, then covered with 2 inches of moist clean sand
having a minimum sand equivalent of 30 when tested in accordance with the
American Society of Testing and Materials test method 'ASTM D1555.
Floor slabs, as a minimum, should be 5 inches thick with #4 reinforcing steel at 16"
on-center each way. Reinforcement should be placed at mid-height of the slab. The
final slab thickness and reinforcement should be determined by the structural
design engineer. Control joints should be provided in accordance with the
recommendations of the structural design engineer.
6. The structural engineer should design all concrete flatwork and structural concrete to
meet the sulfate exposure category ACI 318 unless corrosion testing is provided.
Sulfate testing should be done in the import material during the grading operation.
The sample should be located at a depth of 12 to 18 inches subgrade.
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Greg Goertzen File No. 1127H6-19 February 25, 2020
7. We should be consulted to review the structural and architectural plans to detennine if
they comply with our geotechnical recommendations.
RETAINING WALLS
8. It is our understanding the proposed retaining wall is Regional Standard C-04 from
the San Diego County Regional Standard Drawings.
9. Resistance to horizontal movement may be provided by allowable soil passive
pressure and/or coefficient of friction of concrete to soil. The allowable passive
pressure may be assumed to be 250 psf at the surface and increasing at the rate of 200
psf per foot of depth. These pressures assume a frictionless vertical element, no
surcharge and level adjacent grade. If these assumptions are incorrect, we should be
contacted for values that reflect the true conditions. The values are for static
conditions and may be increased 1/3 for wind and/or seismic loading. The coefficient
of friction of concrete to soil may be safely assumed to be 0.3.
10. Active pressures for the design of unrestrained, cantilevered, individually supported
retaining walls, capable of slight movement away from load may be considered to be
equivalent to the pressures developed by a fluid with a density of 40 pcf. This value
assumes a vertical, smooth wall and level drained backfill. We should be contacted
for new pressures if these assumptions are incorrect. Restrained walls, incapable of
movement away from load without damage such as basement walls, should be
designed for the additional equivalent fluid of 32 pcf applied triangularly for
cohesionless type soils and trapezoidally for cohesive type soils.
11. If the back fill is 2: 1 slope behind the top of the wall, the wall should be designed as
the additional wall height for the actual wall height divided by 2. e.g.: If the actual
retaining wall is 6 feet from the top of footing to the top of the wall, then the wall
height design load should be 6 feet plus 6'/2 = 3 feet. The wall should be designed for
9 feet in height.
RETAINING WALL DRAINAGE
For the restraining walls, the waterproofing: BG 2000 by Multicoat Corporation, being a
water base coating, follows the manufacture for their recommendation. Place coating on top
of footing and up on the inside of emu wall to the top below the proposed slab ( or equal).
All wall drains shall be of 4 inch slotted drain pipe by (SDR-35-4") with a sock coverage
throughout. The pipe shall have a minimum of 1 percent fall. Place Tencate geosynthectics-
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Greg Goertzen File No. 1127H6-19 February 25, 2020
mirafi N-140, nonwoven ( or equal) in a burrito wrap around the ¾ inch washed crushed
rock. The minimum thickness of crushed rock around the pipe is 4 inches on all sides. The
contractor shall vibrate every 2 feet oflift to interlock the rock.
For the retaining wall, the contractor can either follow the recommendations above or install
a slotted pipe design or every six feet have a block turned on its side at 6-foot intervals and
place half-inch galvanize wire between two layers of Tencate geosynthectics-mirafi N-140,
nonwoven with¾ inch crushed rock behind for the full width and length of the block.
All pipes shall have the labels up and glued and inspected prior to backfilling.
A representative of our company should be contacted to observe the placement of the
waterproofing and the wall drains.
SITE EROSION CONTROL
During the construction, surface water should be controlled via berms, gravel bags and/or
sandbags, silt fence, straw wattles, siltation basins, while maintaining positive surface
grades or other methods to avoid damage to the finish work or adjoining properties. All
site entrances and exits must have coarse gravel or steel shaker plates to minimize offsite
sediment tracking. Best management Practices (BMP's) must be used to protect storm
drains and minimize pollution. The contractor should take measures to prevent erosion of
graded areas until such time as permanent drainage and erosion control measures have
been installed. After completion of grading, all excavated surfaces should exhibit
positive drainage and eliminate areas where water might pond.
SITE AND SURFACE DRAINAGE
Drainage at the site should be directed away from foundations, collected and tight lined to
appropriate discharge points. Consideration may be given to collecting roof drainage by
eave gutters and directing it away from foundations via non-erosive devices. Water, either
natural or from irrigation, should not be permitted to pond, saturate the surface soils or
flow towards the foundation. Landscaping requiring a heavy irrigation schedule should not
be planted adjacent to foundations or paved areas. The type of drainage issues found within
the project and materials specified and used should be determined by the Engineer of
Record.
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Greg Goertzen File No. 112786-19 February 25, 2020
GROUNDWATER AND SURFACE WATERS
There was no indication of a near-surface groundwater table within our exploratory trench
or perched groundwater. Although groundwater is not expected to be a significant
constraint to the proposed development, our experience indicates that near-surface
groundwater conditions can develop in areas where no such groundwater conditions
previously existed, especially in areas where a substantial increase in surface water
infiltration results from landscape irrigation or unusually heavy precipitation. It is
anticipated that site development will include appropriate drainage provisions for control
and discharge of surface water runoff. The type of drainage issues found within the project
and materials specified and used should be determined by the Civil Engineer. The type of
plants and soil specified along with proper irrigation used should be determined by the
Landscape Architect.
The following grading specifications should be utilized if grading is proposed.
RECOMMENDED GRADING SPECIFICATIONS
For
Proposed Residential Building Site
El Fuerte Street and Acuna Court
City of Carlsbad
GENERAL: Soil Testers and 'Engineer' are synonymous hereinafter and shall be employed
to inspect and test earthwork in accordance with these specifications, the accepted plans, and
the requirements of any jurisdictive governmental agencies. They are to be allowed adequate
access so that the inspections and tests may be performed. The Engineer shall be apprised of
schedules and any unforeseen soil conditions.
Substandard conditions or workmanship, inadequate compaction, adverse weather, or
deviation from the lines and grades shown on the plans, etc., shall be cause for the engineer to
either stop construction until the conditions are corrected or recommend rejection of the work.
Refusal to comply with these specifications or the recommendations and/or interpretations of
the engineer will be cause for the engineer and/or his representative to immediately terminate
his services.
Deviations from the recommendations of the Soil Report, from the plans, or from these
Specifications must be approved in writing by the owner and the contractor and endorsed by
the engineer.
7
Greg Goertzen
SOIL TEST METHODS:
Maximum Density & Opt Moisture
Density of Soil In-Place
Soil Expansion
Shear Strength
Gradation & Grain Size
File No. 1127H6-19 February 25, 2020
--ASTM D1557-70
--ASTM D 1556, D2922 and D3017
--UBC ST AND ARD 29-2
--ASTM D3080-72
--ASTM D1140-71
--ASTM D2325-68 Capillary Moisture Tension
Organic Content --% Weight loss after heating for 24 hours
at 300° F and after deducting soil moisture.
LIMITING SOIL CONDITIONS:
Minimum Compaction
Expansive Soils
Insufficient fines
Oversized Particles
90% for 'disturbed' soils. (Existing fill,
newly placed fill, plowed ground, etc.)
84% for natural, undisturbed soils.
95% for pavement subgrade within 2' of
finish grade and pavement base course.
Expansion index exceeding 20
Less than 40% passing the #4 sieve.
Rocks over 1 O" in diameter.
PREPARATION OF AREAS TO RECEIVE FILL:
Brush, trash, debris and detrimental soils shall be cleared from the areas to receive fill.
Detrimental soils shall be removed to firm competent soil. Slopes exceeding 20% should be
stepped uphill with benches 1 O' or greater in width. Scarify area to receive fill to 611 depth and
compact.
FILL MATERIAL shall not contain insufficient fines, oversized particles, or excessive
organics. On-sit.e disposition of oversized rock or expansive soils is to be at the written
direction of the Engineer. Select fill shall be as specified by the engineer. All fills shall be
compacted and tested.
SUBDRAINS shall be installed if required by and as directed by and detailed by the engineer
and shall be left operable and unobstructed. They shall consist of 3" plastic perforated pipe set
in a minimum cover of 4" of filter rock in a 'vee' ditch to intercept and drain free ground from
the mass fills. Perforated pipe shall be schedule 40, Poly-Vinyl-Chloride or Acrylonitrile
Butadienne Styrene plastic. Rock filter material shall conform to the following gradation:
Sieve size:
¾Passing:
3/4"
90-100
#4
25-50
#30
5-20
#200
0-7
Subdrains shall be set at a minimum gradient of 0.2% to drain by gravity and shall be tested
by dye flushing before acceptance. Drains found inoperable shall be excavated and replaced.
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Greg Goertzen File No. 1127H6-19 February 25, 2020
CAPPING EXPANSIVE SOILS: If capping expansive soils with non-expansive soil to
mitigate the expansive potential is used, the cap should be compacted, non-expansive, select
soil placed for a minimum thickness 3' over the expansive soil and for a minimum distance of
8' beyond the exterior perimeter of the structure. Special precautions should be taken to
ensure that the non-expansive soil remains uncontaminated and the minimum thickness and
dimensions around the structure are maintained. The expansive soils underlying the cap of
non-expansive cap should be pre-saturated to a depth of 3' to obtain a degree saturation
exceeding 90% before any construction supported by the compacted cap.
The non-expansive soil comprising the cap should conform to the following:
Minimum Compaction
Maximum Expansion Index
Minimum Angle of Internal Friction
Cohesion Intercept
90%
30
33 Deg
100 psf
UNFORESEEN CONDITIONS: Soil Testers assume no responsibility for conditions,
which differ from those, described in the applicable current reports and documents for this
property. Upon termination of the engineer's services for any reason, his fees up to the time of
termination become due and payable. If it is necessary for the engineer to issue an
unfavorable report concerning the work that he has been hired to test and inspect, the engineer
shall not be held liable for any damages that might result from his 'unfavorable report'.
If we can be of any further assistance, please do not hesitate to contact our office. This
opportunity to be of service is sincerely appreciated.
Plates I through V are parts of this report.
Respectfully submitted,
Chin C. Chen, RPE C34442
CCC/mlj
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EL FUERTE STREET
[.;iii EXPLORATION TRENCH -=-RETAINING WALL
"7I._ PROPOSED TOP OF SLOPE
PROPOSED TOE OF SLOPE
rv--... EXISTING TOPOGRAPHY
LOCATION OF
EXPLORATION TRENCHES
PLATE I
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12-31-19
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P.O. Box 1195
Lakeside, CA 92040
619-443-0060
Greg Goertzen
Plate No. II
EXPLORATION NUMBER 1
Date Logged:
Date Reported:
05/02/19
11/29/19
D th U "fi d Cl "fi f ieo Ill le ass1 1ca ions
0 to 6" SM Red brown,
lawn roots
6 to 30" SC Red brown,
File No. 1127H6-19 February 25, 2020
Equipment Used: Hand dug
Groundwater: Not Encountered
S ·1 D 01 'f escnp 10n S ·1 T 01 ype
dry, loose, SILTY SANDS
(Topsoils)
dry, dense, SIL TY CLAYEY SANDS 1
with some decomposed granite (Native)
30 to 48" SM Yellow tan, dry, dense, SILTY SANDS
(Native)
bottom of excavation -Bedrock was not encountered
Greg Goertzen
Plate No. III
EXPLORATION NUMBER 2
Date Logged:
Date Reported:
05/02/19
11/29/19
D h U . fi d Cl . fi ept Ill e ass1 cations
0 to 5" SM Dark brown,
lawn roots
5 to 16" SM Light brown,
with some clay
16 to 48" SM Orange brown,
with some clay
File No. 1127H6-19 February 25, 2020
Equipment Used: Hand dug
Groundwater: Not Encountered
S 'ID 01 escnptlon S ·1 T 01 ype
dry, loose, SILTY SANDS
(Topsoils)
dry, firm to dense, SILTY SANDS
(Native)
dry, dense, SILTY SANDS
(Native)
bottom of excavation -Bedrock was not encountered
...
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GEOLOGIC SECTION A -A
GOERTZEN RESIDENCE
LOT -84, EL FUERTE STREET
CARLSBAD, CALIFORNIA
Approximate limits of possible undocumented fill (af)
during street improvements
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