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GRo<·s RESIDENCE
1 Colli s Island
February 24, 2021
Project No. RS276.1
Newp rt Beach, CA 92625
c/o: Robert Sinclair, AIA, Sinclair Associates Architects
Subje t: PROPOSED POOL/SPA and CAISSONS at the
PROPOSED GROSS RESIDENCE
LOCATED AT 1 COLLINS ISLAND
NEWPORT BEACH, CALIFORNIA
Refere e: "Geotechnical Investigation for Proposed Single Family Dwelling located at 1 Collins Island,
Newport Beach , California," by EGA Consultants, Inc., dated December 14, 2020.
Dear earn ,
In ace rdance with your request, this addendum report is submitted to provide
geote hnical recommendations for the proposed infinity edge pool/spa to be located in
the re r (southeast) yard at the subject site.
Base on the preliminary plans, the proposed 3-to 5-feet deep pool/spa shall be built in
the re ative flat, graded, area in the southeast portion of the lot, setback approximately
2 feet from the existing sea wall bulkhead.
All po I/spa bottoms, and associated infinity edge elements shall be founded in
comp tent materials via a pier and grade beam system.
This r port shall be considered an Addendum to the soils report referenced above.
This a portunity to be of service is appreciated . If you have any questions, please call.
Very l ru ly Yours,
EGA on~~nc. ~--... ·---
cc:
A. WORTHINGTON CEG 2124
al Engineering Geologist
Gross Residence
Sinclair Associates Architects -Attn: Robert Sinclair, A/A
/amen Petrov, SE
375-' Mon te Vista Avenue • Cos t a Mesa, CA 92627 • (949) 642-9309 • FAX (949) 642 -1290
PA2021-055
PROPOSED POOL/SPA & CAISSONS
at the PROPOSED GROSS RESIDENCE
LOCATED at
1 COLLINS ISLAND
NEWPORT BEACH, CALIFORNIA
February 24, 2021
Project No. RS276.1
Associa ed References:
1.
2.
3.
4.
"Geotechnical Investigation for Proposed Single Family Dwelling located at 1 Collins Island, Newport
Beach, California," by EGA Consultants, Inc., dated December 14, 2020.
"Architectural Plans, Private Residence, 1 Collins Island, Newport Beach, CA 92662," by Sinclair
Associates Architects, dated January 20, 2021 .
"Precise Grading Plan, Sheet C2, 1 Collins Island, Newport Beach, California," by Forkert Engineering &
Surveying, Inc., undated.
"Project Memorandum -Proposed Sea Wall/Bulkhead Soil Parameters, Residential Dockside Lot: 1 Collins
Island, Newport Beach, California," by EGA Consultants, Inc., dated December 1, 2020.
INTRC DUCTION
The pt rpose of this memorandum is to provide recommendations and geotechnical
para eters for the underpinning of the proposed infinity edge pool/spa structure.
Base on the preliminary plans, the proposed 3 to 5-feet deep pool/spa shall be built in
the rel tive flat area within the southeast back yard of the subject property. The limits
of the reposed building footprint and the proposed pool/spa are shown in the attached Plot
Plan, igure "A"
The so I cond itions, soils values and applicable construction specifications outlined in the
refere ced soils report remain valid. Per the laboratory results in the above-referenced Soils
Report made available by G3SoiIWorks, Inc., of Cost Mesa, California, the confirmed soils
param ters utilized for the current pool design are as follows :
Very Low Expansion Index (El = 0),
17 ppm water soluble sulfate in soil [SO],
100.8 pct dry density in situ ,
phi angle of 29.0 degrees, and;
cohesion of 94 psf.
The sit soils consist of poorly graded sand with shell fragments . The on site soils exhibit low
to mod rate cohesion ; in accordance with the above referenced soils report, during grading
cemen treatment of the on site soils shall increase the cohesion of the on site soils , aiding in
the po I shaping process.
Note: ontractors should ensure that the nearby seawall and tiebacks are protected in-place
during onstruction. The design engineers should clearly locate and/or specify protection and
layouts of the proposed construction in relation to the existing tiebacks and deadman footings .
Proposed ol/Spa + Caissons -Gross Residence
I Collins I land, Newport Beach, CA
Project No RS276. I
February 2 , 2021 2
PA2021-055
Due t site conditions and infinity edge tolerances, all pool/spa structures will be support by
cast-i -place concrete caissons extending a minimum 7 feet into competent materials (caisson
botto s should target 10 feet below existing grade).
The proposed swimming pool/spa shall be designed in accordance with the City of Newport
Beach building requirements and the 2019 CBC and the 2021 ISPSC (International Swimming
Pool d Spa Code).
mmendations outlined in the referenced soils reports, should be followed during the
desig , earthworks, and construction phases.
ommend all pool/spa and infinity edge elements be founded in competent materials via
a pier nd grade beam system as follows:
Underpinning of Pool/Spa and Elements (Deck and Landscape Walls)
The infinity edge pool/spa should be a freestanding design, supported entirely by piles
deriving support from competent soils . Pool/spa walls should be designed to support
the water, having a density of 62.4 pounds per cubic foot without bearing from the
adjacent soil. The walls should be able to support the adjacent soil when the pool is
empty. The earth pressure may be calculated as an equivalent fluid pressure of 62.4
pcf, plus the lateral pressure due to superimposed surcharge when the pool is empty.
Expansion joints should be place between the deck and the pool.
All excavation sidewalls and bottoms should be inspected/approved by the geotechnical
consultant.
Additional pier and grade beam soil parameters are outlined below.
GEOT CHNICAL PARAMETERS
The fo owing Geotechnical Parameters may be used in the design of the underpinning
constr ction:
Deepened Foundations-Swimming Pool/Spa Caissons
The estuarine sand deposits beneath the site are considered suitable for the support of
the proposed swimming pool/spa using a deep foundation system. The rear and side
yard foundation elements may be extended into deeper sands through the use of
drilled , cast-in-place caissons extending a minimum of 10 feet into competent material.
We estimate the caisson depths to be on the order of 15 feet below existing grade.
Caisson depths should be verified in the field by the geologist.
Cast-in-place concrete caissons may be designed for both end bearing and friction .
Proposed ol/Spa + Caissons -Gross Residence
I Collins I land, ewport Beach, CA
Project No RS276. I
February , 2021 3
PA2021-055
Caissons may be designed for and allowable bearing capacity of 3,000 pounds per
square foot for caissons seated at least 10 feet below existing grade. This bearing
value is considered to be a net value and as a result the weight of the caissons may be
ignored in calculating the footing loads. The caissons may be designed for a skin
friction of 250 pounds per square foot for that portion of the caisson in contact with the
competent materials (neglect the upper 3 feet of fill). The caissons should be
connected by grade beams (in two horizontal directions) and the structure loads
transferred to the caissons as required by the structural engineer. Caisson spacing and
dimensions should also be determined by the structural engineer.
The fo lowing design parameters may be used in for underpinning construction:
Design Item
Foundations:
Footing Bearing Pressure
Passive Lateral Resistence
Passive Lateral (submerged )
Coefficient of Friction
Allowable Skin Friction
Uplift Forces
Recommendations
3,000 psf for bedrock
300 psf per foot
200 psf per foot
0.30
300 psf between concrete and bedrock
75 percent of the allowable capacity
For design purposes the upper 3 feet of soils shall not be considered for skin friction
values.
Caisson fixity may be taken at 3 feet below grade. No lateral or downdrag loads need to
be considered.
In general, ca isson shafts should be spaced no closer than 2.5 diameters, with a
minimum 3.0 diameters preferred. The holes drilled for the installation of the caissons
should be clean, dry, and free of debris or loose soil. The caisson shaft shall not deviate
more than 1 % from vertical.
From a construction standpoint, any excavations advanced down to within the
tidal zones should be expected to experience severe caving.
For caisson depths in excess of 10 feet, concrete should be placed via a tremie. The
end of the tremie tube must remain embedded a minimum of 4 feet into the concrete at
all times.
Concrete shall have a minimum compressive strength of 3,500 psi with a water to
cement ratio not greater than 0.50, or, as specified by the project structural engineer. A
higher compressive strength may be required for structural considerations.
he caisson shafts should contain steel reinforcement as determined by the project
structural engineer in accordance with the applicable CBC or ACI Standards. All
caisson shaft construction should be observed and approved by the geotechnical
consultant.
Proposed ol/Spa + Caissons -Gros Residence
l Collins I land, Newport Beach, CA
Project No RS276. I
February , 2021 4
PA2021-055
Pool/Spa Excavation
Over-excavation of the swimming pool/spa is not necessary since the pool/spa shell will
be supported by a pier and grade beam system. The pool shell excavations may be
subject to caving in dry sandy zones and/or groundwater.
Pile Drilling and Potential Caving
Based on the results of our field explorations, severe caving is expected to occur within
the tidal zones at or below the depth of 5 feet during caisson drilling operations. If
significant caving is encountered, casing, drilling slurry, or similar measures will be
required in order to mitigate caving.
All pile installation should be observed by the project geotechnical consultant to verify
that they are cast against the anticipated geotechnical conditions, that pile excavations
are properly prepared, that proper dimensions are achieved, and that proper installation
procedures are followed.
The a tual design of the foundation and pool shell should be completed by the swimming pool
and/or structural engineer.
To ver fy compliance with guidelines provided in the soils reports , the geotechnical consultant
should review the proposed pool/spa underpinning plans prior to the onset of construction.
If appr ved , the geotechnical consultant shall sign/stamp the applicable Plans from a
geoteo nical standpoint.
GEOT CHNICAL OBSERVATION AND TESTING DURING CONSTRUCTION
Geote hnical observation/testing, during the construction phase of the project is required by the
City of Newport Beach. This is to verify the compliance with the design, specifications and or
endations, and to allow design changes in the event that subsurface conditions differ
se anticipated.
r/pile hole excavations should be cleaned of all slough and debris and should be
by the geotechnical consultant prior to the concrete pour.
!Additionally, geotechnical observations/testing should be performed at the following
stages:
During ANY grading operations, including excavation, removal, filling,
compaction , and backfilling , etc.
After excavations for footings/grade beams and/or drilling for piles/caissons to
verify the adequacy of underlying materials.
After excavations for footings (or thickened edges) and/or grade beams verify
the adequacy of underlying materials.
After pre-soaking of new slab sub-grade earth materials and placemen plastic
Proposed ol/Spa + Caissons -Gross Residence
I Coll ins I land. Newport Beach, CA
Project No RS276. I
February 2 , 202 1 5
PA2021-055
membrane, prior to pouring concrete (if applicable).
• During backfill of drainage and utility line trenches, to verify proper compaction.
• When/if any unusual geotechnical conditions are encountered.
• Prior to interior and exterior slab pours to ensure proper subgrade compaction
and moisture barriers.
• During installation of drainage devices.
CLOS NG STATEMENT
Based on the findings of our geotechnical investigation, the proposed swimming pool/spa,
associ ted improvements, drainage devices, minor earthworks, and construction will not impact
the ge logic stability/safety of the subject or surrounding sites.
The ti dings and recommendations contained in this report are based upon the specific
tions, observations, laboratory tests and project plans, as noted. The materials
imme ately adjacent to or beneath those observed may have different characteristics and no
repres ntations are made as to the quality or extent of materials not observed.
This report is subject to review by the controlling authorities.
Constr ction described herein should be performed by a qualified, licensed subcontractor in
compli nee with governing regulations and appropriate construction materials.
Propo ed I ol/Spa + Caissons -Gross Residence
I Collins I and, Newport Beach, CA
Project No RS276. I
February 2 , 2021 6
PA2021-055
-I ~
I
CPT-1
-0-
EXISTING SEA WALL
------~B-1
LEGEND
1 COLLINS ISLAND
PROPOSED RESIDENTIAL
FOOTPRINT
~ 8-2
2 COLLINS ISLAND
-$-1 GEOTECHNICAL BORINGS
BY EGA CONSULTANTS
-0-CONE PENETRATION TEST
BY KEHOE TESTING AND ENGi NEERING
NEWPORT BAY
73'
Reference: INSET MAP OF COLLINS ISLAND
BALBOA
ISLAND
p .L.
ate Residence,! Collins Island, Newport Beach, CA 92662," by Sinclair Associates Architects, A.IA, dated August 24, 2020. -----EGA
onsultants
PLOT PLAN
1 COLLI NS ISLAND
NEWPORT BEACH, CALIFORNIA
Project No:
Date:
Figure No:
RS276.1
FEB 2021
A
PA2021-055
PA2021-055