HomeMy WebLinkAboutCT 13-03; ROBERTSON RANCH- RANCHO COSTERA; GEOTECHNICAL REVIEW OF REC CENTER; 2015-03-30Cl-F 13-1)3
LGC Valley, Inc.
Geotechnical Consulting
March 30, 2015
Mr. Greg Deacon
Toll Brothers
725 Town and Country Road, Suite 500
Orange, California 92868
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77 NCNEERIIè
Project No. 133023-06
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A-4, Ro)iertsor'Ranch, Subject: Geotechnical Review of the Proposed Recreation Center, I
Carlsbad Tract No. 13-03, Carlsbad, California, California
Introduction
In accordance with your request, LGC Valley, Inc., (LGC) has prepared this letter to provide a geotechnical
evaluation of the proposed Recreation Center located within Planning Area 4 of the Robertson Ranch project
located at 4980 El Camino Real, in Carlsbad, California. The purpose of this letter is to provide the necessary
geotechnical recommendations for development of the proposed recreation building, pool and spa, permeable
pavement, and associated improvements in accordance with the latest adopted building code (i.e. the 2013
California Building Code, which is based on the 2012 International Building Code).
Our study included a review of the existing as-graded geotechnical conditions and previous preliminary
geotechnical documents relative to the site; review of the preliminary site development plans, analysis of the
collected data; and preparation of our findings, conclusions, and recommendations relative to the fine grading
and construction of the recreation center improvements.
Based on our evaluation, it is our professional opinion that the site design is suitable from a geotechnical
perspective provided the findings, conclusions, opinions, and recommendations contained within this report are
implemented during site development.
Site and Project Description
The subject site, previously known as Robertson Ranch West Village or Rancho Costera, is approximately
211 acres in size and is located east of the intersection of El Camino Real and Tamarack Avenue in the
northeastern portion of the City of Carlsbad. The irregular-shaped site is bounded by El Camino Real on the
south, Tamarack Avenue on the northest, existing residential developments on the north and east, and by
Cannon Road on the southeast.
Specifically, the recreation center is located in the south-central portion of Robertson Ranch on the western
side of the main north-south trending canyon in the middle of the site. Pre-graded elevations on PA-4 range
from approximately 144 feet msl at the northwest corner to an approximate elevation of 116 feet msl at the
southeast corner of the site. Based on the rough grading plans (O'Day, 2013), PA-4 will be sheet-graded with
elevations ranging from approximately 132 feet msl at the northwest corner to 129 feet msl at the southeast
corner of the site.
2420 Grand Avenue, Suite F2 • Vista • CA 92081 (760) 599-7000 • Fax (760) 599-7007
Based on review of the recreation center site plans, it is our understanding that the proposed recreation center
site will consist of a recreation building structure, resort style pool, spa, children's pool, outdoor shower
facility, outdoor fireplace, cabanas, concrete deck and flatwork, fencing, landscaping and parking lot with a
permeable pavement. The recreation building will consist of a lounge, kitchen, outdoor kitchen, bathrooms,
equipment and utility rooms and a covered loggia. The recreational building will be located in the central
portion of the site while the pool and associated facilities will be located in the eastern portion and the parking
lot in the western portion of the site. The final fine-grading plans are not available at this time; however, we
anticipate that the final grades will be at or near the existing sheet-graded elevations currently present on the
site.
Previous Site Grading and Site Work
Rough grading operations for the recreation center were performed as a part of grading operations for the
entire Robertson Ranch Development which began in September of 2014; however, rough grading in the
vicinity of the recreation center was performed mainly between early October and late November 2014, while
fine grading of the sheet-graded pad was performed in middle to late part of February 2015. A temporary
retention basin was excavated in early March 2015 in the northeast portion of the recreation center. The
retention basin was approximately 175 feet by 75 feet and is on the order of 6 to 8 feet in depth below the
existing site grades.
The grading operations were performed under the observation and testing services of LGC. Our field technician
was onsite on a full-time basis during the rough grading operations while our field geologist was onsite on a
periodic basis. The rough grading operations included: 1) removal and off-site disposal of vegetation; 2)
removal of topsoil and colluvium to competent formational material; 3) excavation of the formational material
to design grades; 4) placement of compacted fill soils to near-design finish pad grades; and 5) trimming the
sheet-graded pad to the finish grades. Cuts on the order of approximately 13 feet and fills on the order of
approximately 17 feet are present on site.
Since the location of proposed improvements for the recreation center were not known at the time of the
previous rough grading operations, the existing cut/fill transition condition was not mitigated where it transects
settlement-sensitive improvements. Overexcavation of improvements such as the proposed recreation building,
pool, cabanas, etc. will need to be performed prior to the construction of these improvements.
Expansion potential, soluble sulfate content, and corrosion testing of representative finish grade soils have not
been performed on any of the soils within the recreation center. Based on our observations during the site
grading operations and test results of similar soils in other portions of the Robertson Ranch project, we
anticipate that the soils within PA-4 will have a very low to low expansion potential, a negligible sulfate
content and are moderately corrosive to corrosive to buried metals. These test result will be confirmed after
the completion of the fine grade operations of the recreation center.
While we have not performed any infiltration testing at Robertson Ranch project as of this date, we did review
the prior geotechnical investigation reports for the site. Based on our review of GeoSoils report dated June 6,
2011 (GeoSoils, 2011), they performed three infiltration tests within the project: one of the infiltration tests was
performed in existing fills on the site; while the other two tests were performed in bedrock materials. The test
results indicated infiltrations ranging from 0.06 to 0.18 inches per hour (i.e. relatively low infiltration rates).
Project No. 133023-06 Page 2 March 30, 2015
Conclusions
Based on the results of our geotechnical review, it is our opinion that the proposed recreation center
development is feasible from a geotechnical standpoint, provided the following recommendations included in
this report are incorporated into the project plans and specifications, and followed during site fine grading
and construction.
Recommendations
The recommendations provided in the referenced report (LGC, 2014) are considered applicable and remain
valid, unless otherwise stated below, in which case the recommendations included in the referenced reports
are superseded by those included in this report.
We anticipate that earthwork during the fine grading and construction operations at the site will consist of
minor cuts and fills to achieve the design grades; overexcavation of the cut/fill transition condition beneath
settlement-sensitive improvements; infilling the temporary retention basin with compacted fill; and backfilling
of underground utility trenches. We recommend that earthwork on-site be performed in accordance with the
project geotechnical report recommendations (LGC, 2014), the following recommendations, and the City of
Carlsbad grading requirements.
Cut/Fill Transition Conditions
In order to reduce the potential for differential settlement in areas of cut/fill transitions, we recommend that
the entire cut portion of the transition building pad and the pool be overexcavated and replaced with properly
compacted fill to mitigate the transition condition beneath the proposed structures. Based on the as-graded
geotechnical conditions, the recreation building pad should be overexcavated a minimum of 5 feet below the
planned finish grade elevation of the building pad while the pool should be overexcavated a minimum of 8
feet below the planned finish grade elevation. The overexcavations should extend laterally at least 10 feet
beyond the building or pool perimeter or footprint.
Based on the as-graded conditions after the rough grading operations created the sheet-graded pad, the
cut/fill transition condition runs in a northeast/southwest direction through the cabana on the north side of the
pool, the northwest edge of the pool and the center of the recreation building. However, after the site was
sheet-graded, excavation of a temporary storm water retention basin (on the order of 6 to 8 feet in depth
below the existing sheet-graded pad) was made in the northeast portion of the recreation center (as indicated
on Figure 1). As a result, the cut/fill transition condition has already been mitigated beneath the cabana on
the north side of the pool and the majority of the pool has been partially overexcavated.
We recommend that the overexcavation of the recreation building be performed prior to the in-filling of the
retention basin and that the bottom of the current retention basin (or after any loose and/or overly wet
material is removed to competent material) be evaluated to ensure the pool is overexcavated to a depth of at
least 8 feet below the planning finish grade elevation.
Project No. 133023-06 Page 3 March 30, 2015
Fill Placement and Compaction
The on-site soils are generally suitable for use as compacted fill provided they are free of organic material,
trash or debris, and rock fragments larger than 8 inches in maximum dimension. All fill soils should be
brought to above-optimum moisture conditions and compacted in uniform lifts to at least 90 percent relative
compaction based on the laboratory maximum dry density (ASTM D1557). The optimum lift thickness
required to produce a uniformly compacted fill will depend on the type and size of compaction equipment
used. In general, fill should be placed in lifts not exceeding 8 inches in compacted thickness. Placement and
compaction of fill should be performed in general accordance with the current City of Carlsbad grading
ordinances, sound construction practices, and the recommendations presented in the project geotechnical
report.
Trench Backfill and Compaction
The onsite soils may generally be suitable as trench backfill provided they are screened of rocks and other
material over 6 inches in diameter and organic matter. Trench backfill underlying site improvements and
structures should be compacted in uniform lifts (generally not exceeding 8 inches in compacted thickness) by
mechanical means to at least 90 percent relative compaction (per ASTM Test Method D1557).
If trenches are shallow and the use of conventional equipment may result in damage to the utilities; clean
sand, having sand equivalent (SE) of 30 or greater, should be used to bed and shade the utilities. Sand
backfill should be densified. The densification may be accomplished by jetting or flooding and then tamping
to ensure adequate compaction. A representative from LGC should observe, probe, and test the backfill to
verify compliance with the project specifications.
Foundation Selection
Recommendations for foundation design and construction are presented herein. Based on the results of
expansion potential laboratory testing of similar soils within the adjacent lots, the proposed recreation
building and other improvements should be designed for a very low to low expansion potential (i.e. a 0-50
Expansion Index).
The following foundation recommendations are provided. The three foundations recommended for the
proposed structure(s) are: (1) conventional foundation for very low expansion potential and shallow fills; (2)
post-tension foundations; or (3) mat slabs.
Based on the site geotechnical conditions after the rough grading operations, the site is considered suitable
for the support of the anticipated structures using a conventional, post-tensioned, or mat slab-on-grade
foundation system for very low to low expansion potentials (0-50 Expansion Index).
The information and recommendations presented in this section are not meant to supersede design by the
project structural engineer or civil engineer specializing in the structural design nor impede those
recommendations by a corrosion consultant. Should conflict arise, modifications to the foundation design
provided herein can be provided.
Project No. 133023-06 Page 4 March 30, 2015
Bearing Capacity
Shallow foundations may be designed for a maximum allowable bearing capacity of 2,000 lb/ft2 (gross), for
continuous footings a minimum of 12 inches wide and 18 inches deep, and spread footings 24 inches wide
and 18 inches deep, that are excavated into certified compacted fill or competent bedrock. A factor of safety
greater than 3 was used in evaluating the above bearing capacity value. This value maybe increased by 250
pounds per square foot (psf) for each additional foot in depth and 100 psf for each additional foot of width to
a maximum value of 3,000 psf.
Lateral forces on footings may be resisted by passive earth resistance and friction at the bottom of the
footing. Foundations may be designed for a coefficient of friction of 0.35, and a passive earth pressure of
250 lb/ft2/ft. The passive earth pressure incorporates a factor of safety of greater than 1.5. All footing
excavations should be cut square and level as much as possible, and should be free of sloughed materials
including sand, rocks and gravel, and trash debris. Subgrade soils should be pre-moistened for the assumed
very low to low expansion potential (to be confirmed at the end of grading). These allowable bearing pressures
are applicable for level (ground slope equal to or flatter than 5H: 1V) conditions only. Bearing values
indicated above are for total dead loads and frequently applied live loads. The above vertical bearing may be
increased by one-third for short durations of loading which will include the effect of wind or seismic forces.
Conventional Foundations
Conventional foundations may be used to support proposed structures underlain by very low expansive soils
(i.e. Expansion Index less that 20 and Plasticity Index less than 15) and with less than 30 feet of fills.
Continuous footings should have minimum widths of 12 inches, 15 inches or 18 inches for one-story, two-
story or three-story structures, respectively. Individual column footings should have a minimum width of 24
inches.
Footings for the proposed structure should have minimum depths (below lowest adjacent finish grade) of 18
inches and 12 inches for exterior and interior footings, respectively for assumed very low expansion potential
(0-20 Expansion Index). The subgrade should be moisture-conditioned and proof-rolled just prior to
construction to provide a firm, relatively unyielding surface, especially if the surface has been loosened by the
passage of construction traffic.
The undersiab vapor/moisture retarder (i.e. an equivalent capillary break method) may consist of a minimum
15-mil thick, vapor barrier in conformance with ASTM E 1745 Class A material, placed in general
conformance with ASTM E1643, underlain by a minimum 1-inch of sand. The sand layer requirements
above the vapor barrier are the purview of the foundation engineer/structural engineer, and should be
provided in accordance with ACI Publication 302 "Guide for Concrete Floor and Slab Construction". These
recommendations must be confirmed (and/or altered) by the foundation engineer, based upon the
performance expectations of the foundation. Ultimately, the design of the moisture retarder system and
recommendations for concrete placement and concrete mix design, which will address bleeding, shrinkage,
and curling are the purview of the foundation engineer, in consideration of the project requirements provided
by the architect and developer. The undersiab vapor/moisture retarder described above is considered a
suitable alternative in accordance with the Capillary Break Section 4.505.2.1 of the CALGreen code.
Project No. 133023-06 Page 5 March 30, 2015
Subgrade soils should be pre-saturated to optimum moisture content to a depth of 12 inches for a very low
expansion potential. Expansion index testing should be performed at the end of grading for confirmation.
The minimum thickness of the floor slabs should be at least 4.5 inches, and joints should be provided per usual
practice.
Post-Tension Foundations
Based on the site geotechnical conditions and provided the remedial grading recommendations provided
herein are implemented, the site may be considered suitable for the support of the anticipated structures using
a post-tensioned slab-on-grade foundation system, for the anticipated very low to low expansive soils. The
following section summaries our recommendations for the foundation system.
The following table contains the geotechnical recommendations for the construction of PT slab on grade
foundations. The structural engineer should design the foundation system based on these parameters
including the foundation settlement as indicated in the following section to the allowable deflection criteria
determined by the structural engineer/architect.
Project No. 133023-06 Page 6 March 30, 2015
Preliminary Geotechnical Parameters for Post-Tensioned Foundation Design
Parameter Value
Expansion Classification (Assumed to be confirmed at the Very Low to Low Expansion completion of grading):
Thornthwaite Moisture Index (From Figure 3.3): -20
Constant Soil Suction (From Figure 3.4): PF 3.6
Center Lift:
Edge moisture variation distance (from Figure 3.6), em: 9.0 feet
Center lift, Ym: 0.3 inches
Edge Lift:
Edge moisture variation distance (from Figure 3.6), em: 5.2 feet
Edge lift, ym: 0.7 inches
Soluble Sulfate Content for Design of Concrete Mix in Contact
with Site Soils in Accordance with American Concrete Institute Negligible Exposure
standard 318, Section 4.3:
Corrosivity of Earth Materials to Ferrous Metals: Moderately Corrosive to Corrosive
Modulus of Subgrade Reaction, k (assuming presaturation as 100 ci p indicated below):
Additional Recommendations:
Presaturate slab subgrade to at least optimum-moisture content or to 1.2 times optimum moisture, to
minimum depths of 12 inches below ground surface for very low to low expansion potential.
Install a 15-mil moisture/vapor barrier in direct contact with the concrete (unless superseded by the
Structural/Post-tension engineer*) with minimum 1 inches of sand below the vapor barrier.
Minimum perimeter foundation embedment below finish grade for moisture cut off should be 12
inches for low expansion potential.
Minimum slab thickness should be 5 inches.
* The above sand and Visqueen recommendations are traditionally included with geotechnical
foundation recommendations although they are generally not a major factor influencing the
geotechnical performance of the foundation. The sand and Visqueen requirements are the purview of
the foundation engineer/corrosion engineer (in accordance with ACI Publication 302 "Guide for
Concrete Floor and Slab Construction") and the homebuilder to ensure that the concrete cures more
evenly than it would otherwise, is protected from corrosive environments, and moisture penetration of
through the floor is acceptable to future homeowners. Therefore, the above recommendations may be
superseded by the requirements of the previously mentioned parties.
Project No. 133023-06 Page 7 March 30, 2015
- Mat Foundations
Mat foundations can be used for support of proposed structure. An allowable soil bearing pressure of 1,000
psf may be used for the design of the mat at the surface under the slab area. The allowable bearing value is
for total dead loads and frequently applied live loads and may be increased by one-third for short durations of
loading which will include the effect of wind or seismic forces. A coefficient of vertical subgrade reaction, k,
of 100 pounds per cubic inch (pci) may be used to evaluate the pressure distribution beneath the mat
foundation. The magnitude of total and differential settlements of the mat foundation will be a function of
the structural design and stiffness of the mat.
Resistance to lateral loads can be provided by friction acting at the base of foundations and by passive earth
pressure. Foundations may be designed for a coefficient of friction of 0.35. Minimum perimeter footing
embedment provided in the previous sections maybe reduced for the mat slab design.
Coordination with the structural engineer will be required in order to ensure structural loads are adequately
distributed throughout the mat foundation to avoid localized stress concentrations resulting in potential
settlement. The foundation plan should be reviewed by LGC to confirm preliminary estimated total and
differential static settlements.
Foundation Settlement
Based on our evaluation, the static post-construction settlements are estimated to be up to 2-inch with a
differential settlement of approximately of 1-inch in 30 feet for shallow foundations with shallow compacted
fills.
Foundation Setback
All foundation located close to slopes should have a minimum setback per Figure 1805.3.1 of the 2013
CBC. The setback distances should be measured from competent materials on the outer slope face,
excluding any weathered and loose materials. -
Project No. 133023-06 Page 8 March 30, 2015
Seismic Desikn Criteria
The site seismic characteristics were evaluated per the guidelines set forth in Chapter 16, Section 1613 of the
2013 California Building Code (CBC). The maximum considered earthquake (MCE) spectral response
accelerations (SMS and SM1) and adjusted design spectral response acceleration parameters (SDS and SDI) for
Site Class D are provided in the following table.
Seismic Design Parameters
Seismic Selected Parameters from 2013 CBC, Section 1613 - Earthquake Loads Design Values
Site Class per Chapter 20 of ASCE 7 D
Risk-Targeted Spectral Acceleration for Short Periods (Ss)* 1.083g
Risk-Targeted Spectral Accelerations for 1-Second Periods (5)* 0.417g
Site Coefficient Fa per Table 1613.3.3(l) 1.067
Site Coefficient F per Table 1613.3.3(2) 1.583
Site Modified Spectral Acceleration for Short Periods (SMs) for Site Class D 1155 . g [Note: S = FaSs]
Site Modified Spectral Acceleration for 1-Second Periods (SM1) for Site Class D 0.66g . g [Note: SM1 = FS1]
Design Spectral Acceleration for Short Periods (SDs) for Site Class D 0.77g g [Note: SDS = (213)SMs1 .
Design Spectral Acceleration for 1-Second Periods (SDI) for Site Class D 0.44g g [Note: SDI = (2/3)SM1} .
Mapped Risk Coefficient at 0.2 sec Spectral Response Period, CRS (per ASCE 7) 0.968
Mapped Risk Coefficient at 1 sec Spectral Response Period, CR1 (per ASCE 7) 1.02
* From USGS, 2013
Section 1803.5.12 of the 2013 CBC (per Section 11.8.3 of ASCE 7) states that the maximum considered
earthquake geometric mean (MCEG) Peak Ground Acceleration (PGA) should be used for geotechnical
evaluations. The PGAM for the site is equal to 0.453g (USGS, 2013).
A deaggregation of the PGA based on a 2,475-year average return period indicates that an earthquake
magnitude of 6.79 at a distance of approximately 11.4 km (7.1 mile) from the site would contribute the most
to this ground motion (USGS, 2008).
Project No. 133023-06 Page 9 March 30, 2015
Corrosivitp to Concrete and Metal
The National Association of Corrosion Engineers (NACE) defines corrosion as "a deterioration of a
substance or its properties because of a reaction with its environment." From a geotechnical viewpoint, the
"environment" is the prevailing foundation soils and the "substances" are the reinforced concrete foundations
or various buried metallic elements such as rebar, piles, pipes, etc., which are in direct contact with or within
close vicinity of the foundation soil.
In general, soil environments that are detrimental to concrete have high concentrations of soluble sulfates
and/or pH values of less than 5.5. ACT Criteria (ACI 318R-08 Table 4.3.1), provides specific guidelines for
the concrete mix design when the soluble sulfate content of the soils exceeds 0.1 percent by weight or 1,000
ppm. The minimum amount of chloride ions in the soil environment that are corrosive to steel, either in the
form of reinforcement protected by concrete cover, or plain steel substructures such as steel pipes or piles, is
500 ppm per California Test 532.
Based on finish grade soil testing, the onsite soils are classified as having a negligible sulfate exposure
condition in accordance with ACT 318R-08 Table 4.3.1. Concrete in contact with onsite soils should be
designed in accordance with ACT 318R-08 Table 4.3.1 for the negligible category. It is also our opinion that
onsite soils should be considered moderately corrosive to corrosive to buried metals.
Asphaltic Concrete Pavement
Based on a preliminary assumed minimum R-value of 10, and an assumed Traffic Index (TI) of 5, we
recommend the following minimum pavement section. The R-value should be determined during the
concluding stages of grading, and the final pavement section should be designed accordingly. TI's for the
recreation center driveway and parking lot should be obtained from the appropriate regulatory agency. Final
pavement sections should be confirmed by the project civil engineer based upon the project traffic index and
the City of Carlsbad minimum requirements.
Recommended Minimum Pavement Section
Traffic Index 5
Asphalt Concrete (inches) 4
Aggregate Base (inches) 8
The aggregate base material should conform to the specifications for Class 2 Aggregate Base (Caltrans) or
Crushed Aggregate Base (Standard Specifications for Public Works Construction). The base material should
be compacted to achieve a minimum relative compaction of 95 percent. The subgrade should achieve a
minimum relative compaction of 90 percent through the upper 12 inches. Base and subgrade materials
should be moisture-conditioned to relatively uniform moisture content at or slightly over optimum.
Project No. 133023-06 Page 10 March 30, 2015
Portland Cement Concrete (FCC) Pavement Section
Portland Cement Concrete Pavement (PCCP) may be designed using a minimum of 6-inches of Portland
cement concrete over 6-inches of base. The modulus of rupture of the concrete should be a minimum of 500
pounds per square inch (psi) at 28 days. Contraction/control joints should be placed per usual practice, as
necessary. Where the outer edge of a concrete pavement connects to an asphalt pavement, the concrete slab
should be thickened by 50 percent at a taper not to exceed a slope of 1 in 10. This following section is only
applicable for passenger car driveway/parking areas and should be thickened and reinforced if heavy truck
loading is anticipated.
Preliminary Permeable Paver Recommendations
While we have not performed any infiltration testing at Robertson Ranch project as of this date, we did review
the prior geotechnical investigation reports for the site. Based on our review of GeoSoils report dated June 6,
201 1(GeoSoils, 2011), they performed three infiltration tests within the project: one of the infiltration tests was
performed in existing fills on the site; while the other two tests were performed in bedrock materials. The test
results indicated infiltrations ranging from 0.06 to 0.18 inches per hour (i.e. relatively low infiltration rates).
The concrete payers should have a minimum thickness of 3 1/8-inches and be underlain by a sand bedding
course. Base course should consist of a minimum of 8-inches of an open-graded base such as a No.57 stone (or
equivalent). Additional thickness of the open-graded base such as the No. 57 or No. 2 Stone may be needed as
a reservoir layer based on the design infiltration rate and amount of storm water flow as designed by the site
civil engineer.
Base should be compacted to a minimum of 95 percent relative compaction over subgrade compacted to a
minimum of 90 percent relative compaction per ASTM- D1557. Track equipment with low ground pressure
should be used within the pervious pavement area to limit over-compacting the subgrade. A filter fabric
should be installed on the bottom and sides of the trench between the subgrade and reservoir/base course.
Pervious pavement area of infiltration should be setback a minimum of 10 feet from any adjacent building or
foundations.
Concrete Flatwork
Concrete flatwork (such as trash enclosure, walkways, pool deck etc.) have a high potential for cracking due
to changes in soil volume related to soil-moisture fluctuations because these slabs are typically much thinner
than foundation slabs and are not reinforced with the same dynamic as foundation elements. To reduce the
potential for excessive cracking and lifting, concrete should be designed in accordance with the minimum
guidelines outlined in the following table. These guidelines will reduce the potential for irregular cracking
and promote cracking along construction joints, but will not eliminate all cracking or lifting. Thickening the
concrete and/or adding additional reinforcement will further reduce cosmetic distress.
Project No. 133023-06 Page 11 March 30, 2015
Concrete Flatwork
Pool Deck Concrete PCC Paving @ Trash
Flatwork/Pedestrian Use Enclosure
Minimum 4 4 6-inches concrete over 6-
Thickness (inches) inches of base
Presaturation Presoak to 12 inches Presoak to 12 inches Presoak to 12 inches
Reinforcement No. 3 at 18 inches on Welded Wire Mesh 6x6 No. 3 at 18 inches on
centers 6/6 (or equivalent) centers
Saw cut or deep tool joint Saw cut or deep tool joint Saw cut or deep tool joint
Crack Control to a minimum of 1/3 the to a minimum of 1/4 the to a minimum of 1/4 the
concrete thickness concrete thickness concrete thickness
Subgrade 90% relative compaction 90% relative compaction 95% relative compaction
Compaction in upper 12 inches in upper 12 inches in upper 12 inches
Swimmin-e Pool and Spa Recommendations
The proposed pool, spa, pool decking and associated improvements should be constructed in accordance with
the attached Figure 2, Geotechnical Guidelines for Swimming Pool Construction. The pool area should be
overexcavated and replaced with uniform compacted fills (as indicated herein) and is anticipated to be
relatively uniform consisting of the sandy soils. Consideration should be given to the low expansive potential
of onsite soils in design of the pool, and associated decking. Also concrete in contact with the onsite soils
should be designed in accordance with the negligible category per ACT 318R-08 Table 4.3.1. The proposed
pool, spa should be designed for a minimum lateral equivalent fluid pressure of 60 pounds per cubic foot
(pcf).
Excavation and subsequent fill placement for the pool, and spa including the placement of drains, outlets,
water-proofing, etc. should be performed under the observation and testing of a geotechnical consultant.
Observation and testing should be performed by the geotechnical consultant during pool excavation to verify
that the exposed soil conditions are consistent with the design assumptions.
Project No. 133023-06 Page 12 March 30, 2015
Control of Surface Water and Drainage Control
Positive drainage of surface water away from structures is very important. No water should be allowed to pond
adjacent to buildings. Positive drainage may be accomplished by providing drainage away from buildings at a
gradient of at least 2 percent for a distance of at least 5 feet, and further maintained by a swale or drainage path
at a gradient of at least 1 percent. Where necessary, drainage paths may be shortened by use of area drains and
collector pipes.
Planters with open bottoms adjacent to buildings should be avoided. Planters should not be designed adjacent
to buildings unless provisions for drainage, such as catch basins, liners, and/or area drains, are made.
Overwatering must be avoided.
Slope Maintenance
To reduce the potential for erosion and slumping of graded slopes, all slopes should be planted with ground
cover and deep-rooted vegetation as soon as practical upon completion of grading. Surface water runoff and
standing water at the top-of-slopes should be avoided. Oversteepening of slopes should be avoided during
construction activities and landscaping. Maintenance of proper lot drainage, undertaking of property
improvements in accordance with sound engineering practice, and proper maintenance of vegetation,
including regular pad and slope irrigation, should be performed. Trenches excavated on a slope face for
utility of irrigation lines and/or for any purpose should be properly backfilled and compacted by a vibratory
plate, or equivalent, in order to obtain a minimum 90 percent relative compaction, in accordance with ASTM
Test Method D1557, to the slope face. Observation/testing and acceptance by the geotechnical consultant
during trench backfill is recommended. A rodent control program should be established and maintained.
Limitations
Our services were performed using the degree of care and skill ordinarily exercised, under similar
circumstances, by reputable engineers and geologists practicing in this or similar localities. No other
warranty, expressed or implied, is made as to the conclusions and professional advice included in this report.
Changes in conditions must be evaluated by the project soils engineer and geologist and design(s) adjusted as
required or alternate design(s) recommended.
This report is issued with the understanding that it is the responsibility of the owner, or of his/her
representative, to ensure that the information and recommendations contained herein are brought to the
attention of the architect and/or project engineer and incorporated into the plans, and the necessary steps are
taken to see that the contractor and/or subcontractor properly implements the recommendations in the field.
The contractor and/or subcontractor should notify the owner if they consider any of the recommendations
presented herein to be unsafe.
Project No. 133023-06 Page 13 March 30, 2015
Closure
This letter is issued with the understanding that it is the responsibility of the owner, or of his/her
representative, to ensure that the information and recommendations contained herein are brought to the
attention of the structural/foundation engineer and the necessary steps are taken to see that the information is
implement in the structural/foundation design, as necessary.
If you should have any questions, please do not hesitate to contact us. The undersigned can be reached at
(661) 702-8474.
Respectfully submitted,
LGC Valley, Inc.
Randall Wagner, CEG 1612
Senior Project Geologist
RKW/BIH
a Ao#-.
Basil Hattar, GE 2734
Principal Engineer
No. 2734
Exp.W3w1
Distribution: (6) Addressee
Attachments: References
Figure 1: PA-4 Recreation Center As-Graded Geotechnical Map
Figure 2: Geotechnical Guidelines for Swimming Pool Construction
Project No. 133023-06 Page 14 March 30, 2015
References
American Society of Civil Engineers (ASCE), 2013, Minimum design loads for buildings and other structures,
ASCE/SEI 7-10, Third Printing, 2013.
California Building Standards Commission (CBSC), 2013a, California Building Code, California Code of
Regulations, Title 24, Part 2, Volume 1 and 2 of 2 (based on the 2012 International Building Code).
CBSC, 2013b, California Residential Building Code, California Code of Regulations, Title 24, Part 2.5,(based on
the 2012 International Residential Code).
CBSC, 2013c, California Green Building Standard Code, California Code of Regulations, Title 24, Part 11.
Dahlin Group, 2015, Site plan and perspectives, PA-4 recreation building @ Robertson Ranch, Sheet Al-i
through A 1-5, dated January 8.
GeoSoils, Inc., 2002, Geotechnical evaluation of the Robertson Ranch property, City of Carlsbad, San Diego
County, California, W.O. 3098-Al-SC, dated January 29.
GeoSoils, Inc., 2004, Updated geotechnical evaluation of the Robertson Ranch property, Carlsbad, San Diego
County, California, W.O. 3098-A2-SC, dated September 20.
GeoSoils, Inc., 2010, Updated geotechnical investigation for Robertson Ranch West Village, Carlsbad, San Diego
County, California, W.O. 6145-A-SC, dated October 10.
GeoSoils, Inc., 2011, Supplement to the updated geotechnical investigation for Rancho Costera (formerly
Robertson Ranch West Village), Carlsbad, San Diego County, California, W.O. 6145-Al-SC, dated June 6.
LGC Valley, Inc., LGC Valley, Inc., 2014, Geoteclmical and environmental recommendations for Robertson
Ranch West, Carlsbad Tract No. 13-03, Carlsbad, California, Project Number 133023-03, dated 4/29/14.
O'Day Consultants, 2013, Grading plans for Rancho Costera, Robertson Ranch West Village, Carlsbad Tract No.
13-03, Drawing No. 480-3A, 26 sheets, dated November 25.
O'Day Consultants, 2014, Vesting tentative map for Carlsbad Tract No. 13-03-2, 23 sheets, dated 1/16/2014.
Post-Tensioning Institute, 2006, Design of post tensioned slabs-on-ground, Third Addition, Addendum 1 dated
May 2007, and Addendum 2 dated May 2008, with errata February 4, 2010.
Summer/Murphy & Partners, 2015, Robertson Ranch recreation center plot plan, 1 sheet, dated January 5.
United States Geological Survey (USGS), 2008a, "2008 National Seismic Hazard Maps - Fault Parameters"
retrieved from: http://geohazards.usgs.gov/cfusion/hazfaults search/hf search main.cfm
USGS, 2008b, "2008 Interactive Deaggregations (Beta)," retrieved from:
https://geohazards.usgs.gov/deaggint/2008/
USGS, 2013, U.S. Seismic Design Maps, retrieved from:
http://geohazards.usgs.gov/designmaDs/us/batch.php#csv
Project No. 133023-06 Page 15 March 30, 2015
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Recreation
I
Center
As-Graded Geotechnical Map
Robertson Ranch
L'flI Inc.Carlsbad, Base Map: Summer/Murphy 2015,___________________
Recreation Center Plot Plan '
SCHEDULE
Depth of I Lateral
Expansion moisture cut-off I Slope creep Equivalent
Index I footing zone distance I Fluid Pressure
distance "B" "" A I I (pcf)
low-very low 8 inches 7 feet 60
Portion of pad most susceptible to slope creep.
Concrete deck, minimum of 4 inches thick with
#3 bar 18 inch on center each way with
construction joints 1.5 inches deep (minimum)
with maximum spacing of 5 feet.
Flexible sealant between pool .. . .
coping and concrete decklrfg ..
Clean sand backfill . .
......
4.
(2' minimum)
N lope creep / Pool shell to be
designed for any added
s
load of adjacent
o zone
Pool Shell structures.
Pressure relief valve
For pools adjacent to descending slopes, the pool shell should be designed assuming total loss of soil support for the portion of the
pool located within the assumed "creep zone". For design purposes, the creep zone should be considered to extend a distance "A"
from the top of slope (see schedule "A" above). The creep zone should be considered as parallel to the slope face.
Concrete flatwork adjacent to the pool should be a minimum of 4 inches thick reinforced with No. 3 rebar at 18-inches on center each
way with a perimeter cut-off footing per the above schedule. Construction joints or weakened plane joints should be provided in all
flatwork to a minimum depth of 1.5 inches at frequent internals (5 feet or less). The presoaking should saturate the subgrade to a
minimum depth of 12 inches. The subgrade below the concrete flatwork should be inclined so that any moisture that seeps through
cracks in the concrete due to irrigation, rain, or pool splash will be directed away from the pool.
All pool design should be performed by a qualified designer, using the equivalent fluid pressures shown in the schedule.
A geotechnical consultant should be contacted to review the final design which is based on the recommendations of this detail. This
is not a design document and has been provided for INFORMATIONAL PURPOSES ONLY unless stamped and signed by LGC and
pertaining to a specific pool.
To reduce the potential of lifting and cracking of the pool decking, landscape planters should not be located in islands within the
decking unless they are lined with a waterproof membrane and provided with a subdrainage system to prevent moisture variations
below the decking.
The pool shell should be designed to account for any additional loading due to improvements (building, raised planters, etc.)
Raised planters should not be located at the top of slopes unless specially designed by the geotechnical consultant.
The recommendations above will not eliminate all movement of the pool and associated improvements, however they should reduce
the degree of movement, and promote cracking along construction joints, not flatwork.
2
Geotechnical
Guidelines for
Swimming Pool
Construction
Project Name Rec Pool (PA-4)
Project No. 133023-03
Eng. / Geol. BIH/RKW
Scale Not to Scale
Date 1 03/30/15