HomeMy WebLinkAboutPD 2019-0029; 3559 CORTE ESPERANZA ADDITION; PROPOSED RETAINING WALL SITE; 2019-08-08P.O. Box 1195
Lakeside, California
August 8, 2019 92040
-- (619)443-0060
Britt Styr & Allen Chalepas
3559 Corte Esperanza
Carlsbad, California 92009
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SUBJECT: File No. 1148A4-19
SITE INSPECTION
Proposed Retaining Wall Site
3559 Corte Esperanza
City of Carlsbad
Dear Ms. Styr & Mr. Chalepas:
SCOPE
RECEIVED
AUG 23 2019
LAND DEVELOPMENT
ENGINEERING
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 cabana, garage, and retaining walls.
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 a test
excavation approximately 5 feet in height and tested for density, shear strength and expansive
characteristics.
SITE CONDITIONS
The subject site is located on the southeast side at the end of the cul-de-sac. The site is
relatively level and approximately 2 feet above street level with a 2:1 slope at the rear of the
property. The property is occupied by a single family residence, swimming pool and a
covered patio. Neighboring properties are occupied by residential structures. Fill materials
for landscaping were approximately 12 inches in depth; loose native soils were encountered
to a depth of 5 feet during the course of this inspection.
1
ME
Britt Styr & Allen Chalepas File No. 1148A4-19 August 8, 2019
SOIL CONDITIONS
Soils encountered in the test exploration fill soils consisting of loose, dark brown, sandy loam
to approximately 1 foot in depth. These surface soils were underlain with loose, grey to tan,
silty sandy clays sands to the bottom of the excavation approximately 5 feet in depth. See
Plate II for more detail.
Some of the soils we encountered were considered to be critically expansive with respect to
change in volume with change in moisture content.
CONCLUSIONS AND RECOMMENDATIONS
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 1500 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 109.5 pcf
Optimum Moisture 19.2%
Angle of internal friction 20°
Cohesion 318 psf
Unit weight 97.9 pcf
Expansion Index 133
2. The critically expansive soils encountered during this inspection should not be used
to support the proposed structure. It is our recommendation that these soils in the
proposed building areas be removed to a minimum depth of 5 feet and the critically
expansive soils exported. The excavation should extend at least 5 feet outside the
proposed building footprints and a minimum of 3 feet on the side where the open
space limits space. Prior to placing fill, Tencate Mirafi RS280i should be installed
on the native soils per manufacturer's instructions. Import soils that are not
detrimentally expansive (El <30) should be placed and compacted to 90 percent
compaction in accordance with the Grading Specifications in this report. The
import soils should used for the proposed retaining wall backfill. Any organic or
other deleterious material that may be encountered should be removed prior to
recompaction. During the grading operation, the critically expansive soils
encountered should not be placed within 3 feet of finish grade. Any critically
expansive soils within the top 3 feet must be removed from the building area to
achieve uniformly non-expansive soils for the building foundation.
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Britt Styr & Allen Chalepas File No. I l48A4-19 August 8, 2019
Once the critically expansive soils are capped with nonexpansive soils the following
recommendations may be used for the proposed structures. Conventional spread
footings founded a minimum of 24 inches below lowest adjacent grade and having a
width determined by the allowable soil bearing value as detailed above are
recommended for foundation support. Footing widths should be at least 12 inches for
continuous footings and 24 inches for square footings due to practical considerations
as well as Building Code requirements. These recommendations are based upon the
soil type encountered and do not take into consideration the proposed bearing load.
Reinforcing in footings should consist of at least one #4 steel bar placed continuously
in the top and bottom of continuous footings regardless of structural requirements.
Reinforcing for isolated footings is dictated by the structural requirements. These
recommendations are based upon on the soil type encountered and do not take into
consideration the proposed bearing load. Footings deeper than 24 inches should have
an additional #4 steel bar for each additional foot of depth.
Footings for the retaining wall will be founded in the critically expansive onsite soils,
the area under the footing should be lined with 3 inch minus angular crushed rock to a
depth of 6 inches and compacted in. We should be present to observe the placement
and compaction of the rock.
The native soils encountered during the site inspection should not be used to backfill
the retaining wall. The wall should not be backfllled until the masonry has reached an
adequate strength.
If a Concrete Slab-On-Grade, SOG is proposed, it 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 6 inches of Class II Virgin Aggregate Base (with approximately 2% +1- 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
fmal 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.
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Britt Styr & Allen Chalepas File No. 1 148A4-19 August 8, 2019
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 150
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.
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 45 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
dcsigned for the additional equivalent fluid of 36 pcf applied triangularly for
cohesionless type soils and trapezoidally for cohesive type soils.
The above design values and foundation design assume that the retaining walls are located in
soils similar to those we tested during our site inspection.
SEISMIC LOADING FOR RETAINING WALLS
The seismic event induced dynamic load should be added to the lateral static
pressures on basement, foundation and retaining walls for projects located in seismic
design categories D, E or F.
The following is the calculation for the dynamic load, which should be applied in
addition to the static loads.
References: USGS and IBC 2012/2016
Site Address: 3559 Corte Esperanza, Carlsbad
Site Soil Classification: Site Class "D"
S = 1.029 g Sms = 1.120 g Sd,= 0.747 g
S1 = 0.398 g Sm1 = 0.639 g SdL = 0.426 g
Kh =Peak Ground Acceleration= S& 12.5 = 0.747 12.5 = 0.30
BackFill Density (Assumed 90% compaction) = 109.5 * (0.90) = 98.6 PCF
4
FINISH GRADE
Th IQthVAI.ENT PI.UIDPRF.SSRE(psQI))
Th FORCE PER UNIT WJDTII OF WALL (1k/t)
10.3 H
k— P.)-4
Britt Styr & Allen Chalepas File-No. 1148A4-19 August 8, 2019
H =The height of the level backfill behind the wall in FT
Dynamic Load, for Yielding Wall= (.375) (0.30) (98.6 PCF) (H2) =
11.1 lbs/ft 2)
Dynamic Load, for Non-Yielding Wall= (0.30) (98.6 PCF) (H2) =
29.6 lbs/ft (H2)
The resultant dynamic load acts at a height of 0.6H above the base of the wall.
The dynamic load is represented as an inverted triangular pressure distribution. These
lateral earth pressures assume the walls are totally drained with no water behind
them and assume there is no surcharge applied. If there is any surcharge applied, it
should be considered accordingly.
See Figure below:
XINDrnON
UC11EQUWALENT FLUID PRESSURE (p011)
ITH FORCE P1I( UNIT W3DTH Of Wf,LL (lb/il)
27.5 W
. iO PVUROSTATIC BUILDUP REHI1D THE RETAIXThiC WALLS.
21 l H ?tET.
As(!M?:s LP 1v M., (lRAUL.AR BACK FILL COMPACTED MINIMUM 90
rUkC.F1 A?;DWITHIN ' PLRCL'(rOFOflLMU-NI.
I ' 1ACifl.C).\S HAVE NOT IUFnNCLUDED.
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Britt Styr & Allen Chalepas File No. 1148A4-19 August 8,2019
RETAINING WALL DRAINAGE
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 cmu 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-
mirafi N-140, nonwoven (or equal) in a burrito wrap around the 3A inch washed crushed
rock. The contractor shall vibrate every 2 feet of lift to interlock the rock.
The lower cmu wall along Churchward Street, the contractor can either 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 with
3/4 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 backfihling.
SURFACE DRAINAGE
It is with the understanding that no surface drainage system ties together with the retaining
wall drainage system.
The minimum slope for the surface drainage system shall be 2 percent fall and for self
cleaning slope shall be 3 percent fall. When you go below 2 percent fall slope than you will
need to increase the pipe size one size larger and if you go below 1 percent fall than the pipe
size will be the minimum of 6 inch pipe.
Connecting catch basins, down spots, landscape area drains to the main drainage system tie
into the pipe using street ells or large sweeps. This will permit the use of snakes, and
cameras for maintaining the drainage lines. Contractor shall place a clean out at the property
line on all drainage pipes prior to discharge.
The design of all drainage systems shall be shown and labeled/identified on the plan. All
drainage pipes shall have either a headwall or projecting out from a retaining wall, face of
curb, and be shown as a detail on the plans if a discharge at grade.
All pipes shall have the labels up and glued and inspected prior to backfihling.
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Britt Styr & Allen Chalepas File No. 1148A4-19 August 8, 2019
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
cave 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.
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.
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Britt Styr & Allen Chalepas File No. 1148A4-19 August 8, 2019
The following grading specifications should be utilized.
RECOMMENDED GRADING SPECIFICATIONS
For
Proposed Residential Building Site
3559 Corte Esperanza
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 shalt 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.
SOIL TEST METHODS:
Maximum Density & Opt Moisture
Density of Soil In-Place
Soil Expansion
Shear Strength
Gradation & Grain Size
Capillary Moisture Tension
Organic Content
-- ASTMD1557-70
- ASTM D1556, D2922 and D3017
-- UBC STANDARD 29-2
-- ASTM D3080-72
-- ASTM Dl 140-71
-- ASTM D2325-68
-- % Weight loss after heating for 24 hoths.
at 300° F and after deducting soil moisture.
LIMITING SOIL CONDITIONS:
Minimum Compaction 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.
Expansive Soils Expansion index exceeding 20
Insufficient fines Less than 40% passing the #4 sieve.
Britt Styr & Allen Chalepas File No. 1 148A4-19 August 8,2019
Oversized Particles Rocks over 10" 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 10' or greater in width. Scarify area to receive fill to 6" depth and
compact.
FILL MATERIAL shall not contain insufficient fines, oversized particles, or excessive
organics. On-site 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: 3/4" #4 #30 #200
%Passing: 90-100 25.50 5-20 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.
CAPPING EXPANSIVE SOILS: If capping expansive soils with non-exj,ansive soil to
mitigate the expansive potential is used, the cap should be compacted, non-expansive, select
soil placed for a minimum thickness Y Over the expansive soil and fbr 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 90%
Maximum Expansion Index 30
Minimum Angle of Internal Friction 33 Deg
Cohesion Intercept 100 psf
Britt Styr & Allen Chalepas File No. 1148A4-19 August 8, 2019
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 H are parts of this report.
Respectfully submitted,
&/t.,-. eel--
Chin C. Chen, RPE C34442
CCC/mlj
10
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PRO ED
t' R 'V
ARAC
EXPLORATION TRENCH
upO 4AiE'
LOCATION OF I iI4'àA-1°I I
SOIL EXPLORATION TRENCHES
PLi+r& t
11421 Woodside Ave., Suite C
Santee, California 92071
(619) 562-0500
.Britt Styr & Allen Chalepas File No. 1148A4-19 August 8, 2019
Plate No. 11
EXPLORATION NUMBER 1
Date Logged: 07/01/19 Equipment Used: Hand dug
Date Reported: 08/08/19 Groundwater: Not Encountered
Depth Unified Classifications Soil Descrintion Soil Tvoe
0 to 1' SC Dark brown, moist, loose, SILTY CLAYEY SANDS
with roots and organic materials (Landscape Fill)
1 to 4' SC Layered grey to tan, moist, loose, SILTY SANDY CLAYS
with roots (Native)
4 to 5' SC Grey, moist, loose, SILTY SANDY CLAYS
with clay (Native)
bottom of excavation _____